**CFD and Thermography Techniques Applied in Cooling Systems Designs**

Samuel Santos Borges and Cassiano Antunes Cezario *Research and Technological Innovation Department, WEG Brazil* 

### **1. Introduction**

134 Applied Computational Fluid Dynamics

Zubkov, V. A. & Golovko, Y. D. (1969). Flow of Liquid in Rotor Outlet of a Tubular

The focus of this work consists in optimizing the water flow inside a water cooled electric motor frame, aiming at the maximization of the power/frame size ratio, the minimization of pressure drop and the avoidance of hot spots. For the development of this work computational fluid dynamics (CFD) and thermography techniques were used.

For many years water cooled electric motors have been used by industry, especially in specific applications that require features that can not be provided by conventional fan cooled motors. Among theses features are a better power/frame size relation, low noise levels, enclose applications, among others.

Cooling by means of water circulation is frequently used in large motors, typically frame sizes above IEC 315. A justification for this practice not to be widely used in smaller motors is its higher cost compared to air cooling systems. However, provided that it presents some technical and/or economical viability, water cooling can also be used in smaller frame sizes. The technological progress have resulted in the development of new tools that facilitate the study of this motor type, such as the computational fluid dynamics and the thermography techniques, which consist, respectively, in the use of numeric models applied to fluid mechanics and the obtaining of the motor surface temperature distribution.

### **2. Benefits and drawbacks**

The following advantages and disadvantages of this kind of motor can be mentioned, in comparison with air cooled motors.

### **2.1 Advantages**


CFD and Thermography Techniques Applied in Cooling Systems Designs 137

The convection is the heat transfer between a solid surface and a moving fluid. This phenomenon can be natural, induced by density difference (low fluid velocity), or forced,

The thermal radiation is provided by electromagnetic waves emission. The classic example of this phenomenon is the heat transfer between sun and earth. It is given by Stefan-

It is boiling, condensation, freezing and melting. These processes are given by following

In the heat transfer in the fluid flowing in a conduit, the temperature is neither uniform in the fluid flow direction nor in the heat flux direction. Therefore, the bulk temperature is assumed as reference temperature. The use of a temperature reference allows to execute the heat balance in steady state. In this case, the transferred heat per time unit is a direct

measure of the bulk temperature difference between two conduit sections. That is,

4 4 1 2 ( ) *<sup>r</sup> q TT* 

( ) *h s q hA T T* (2)

(3)

*Q mH* . (4)

. . *<sup>p</sup> <sup>b</sup> q mc T* (5)

customarily supplied by fans or pumps (high fluid velocity).

**3.2.2 Convection** 

*qh*: Heat flux of convection; *h*: Convection coefficient; *A*: Heat transfer area; *Ts*: Surface temperature; *T∞*: Fluid temperature.

Where,

**3.2.3 Radiation** 

Boltzmann Law.

*qr*: Heat flux of radiation;

**3.2.4 Phase – Change** 

*Q*: Amount of heat;

*ΔH*: Specific latent heat.

**3.2.5 Heat transfer in conduits** 

*σ*: Stefan-Boltzmann constant; *T1, T2*: Surface temperatures.

Where,

*ε*: Emissivity;

equations.

Where,

*m*: Mass;

Better resistance to local impact.

#### **2.2 Disadvantages**


### **3. Fundamental concepts**

#### **3.1 Cooling system**

The cooling systems are apparatus usually comprised of several components that interact to keep the temperature of machines and systems in general controlled in order not to exceed the limits imposed by quality, safety, performance and/or efficiency. For instance, systems such as internal combustion engines, turbines, compressors, bearings, electric machines, electronic structures, electrical conductors, chemical and welding processes, among many others, can be mentioned as some examples of systems comprising thermal restrictions. Consequently, the cooling systems are very important to industries and should therefore be designed to keep a good performance and reliability.

The more commonly used coolants are gases and liquids. Among them, due to their wide occurrence, low cost and practicality, air and water are customarily employed. They can be used in many different ways: in direct or indirect contact with the systems, by means of one or more fluid combinations, separated or mixed. And they can be forcedly or naturally moved, by physical mechanisms respectively known as forced convection and natural convection.

#### **3.2 Heat transfer**

Heat transfer concerns the exchange of thermal energy from one region of higher temperature to another of lower temperature in one or more means. This exchange occurs by mechanisms as conduction, convection, radiation and phase-change.

#### **3.2.1 Conduction**

The conduction occurs due to interactions between the particles of fluids. Thermal insulation, tanks, plates and ducts walls, fins, and others are examples of devices that exchange heat by conduction. It is described by Fourier's Law and the following equation:

$$q\_k = -kA \frac{\partial T}{\partial n} \tag{1}$$

Where,

*qk*: Heat flux of conduction; *K*: Thermal conductivity; *A*: Heat transfer area; *T* : Temperature gradient; *n*: Direction.

#### **3.2.2 Convection**

The convection is the heat transfer between a solid surface and a moving fluid. This phenomenon can be natural, induced by density difference (low fluid velocity), or forced, customarily supplied by fans or pumps (high fluid velocity).

$$
\eta\_h = hA(T\_s - T\_\infty) \tag{2}
$$

Where,

136 Applied Computational Fluid Dynamics

The cooling systems are apparatus usually comprised of several components that interact to keep the temperature of machines and systems in general controlled in order not to exceed the limits imposed by quality, safety, performance and/or efficiency. For instance, systems such as internal combustion engines, turbines, compressors, bearings, electric machines, electronic structures, electrical conductors, chemical and welding processes, among many others, can be mentioned as some examples of systems comprising thermal restrictions. Consequently, the cooling systems are very important to industries and should therefore be

The more commonly used coolants are gases and liquids. Among them, due to their wide occurrence, low cost and practicality, air and water are customarily employed. They can be used in many different ways: in direct or indirect contact with the systems, by means of one or more fluid combinations, separated or mixed. And they can be forcedly or naturally moved, by physical mechanisms respectively known as forced convection and natural convection.

Heat transfer concerns the exchange of thermal energy from one region of higher temperature to another of lower temperature in one or more means. This exchange occurs

The conduction occurs due to interactions between the particles of fluids. Thermal insulation, tanks, plates and ducts walls, fins, and others are examples of devices that exchange heat by conduction. It is described by Fourier's Law and the following equation:

*n*

(1)

*k <sup>T</sup> q kA*

by mechanisms as conduction, convection, radiation and phase-change.

Better resistance to local impact.

Risk of fouling in the water circuit;

More precautions on maintenance.

**3. Fundamental concepts** 

 Need to control the water chemical composition; Risk of corrosion inside of the water circuit;

designed to keep a good performance and reliability.

 Higher manufacturing cost; Auxiliary system to provide water;

**2.2 Disadvantages** 

Risk of leaks;

**3.1 Cooling system** 

**3.2 Heat transfer** 

**3.2.1 Conduction** 

*qk*: Heat flux of conduction; *K*: Thermal conductivity; *A*: Heat transfer area; *T* : Temperature gradient;

Where,

*n*: Direction.

*qh*: Heat flux of convection; *h*: Convection coefficient; *A*: Heat transfer area; *Ts*: Surface temperature; *T∞*: Fluid temperature.

#### **3.2.3 Radiation**

The thermal radiation is provided by electromagnetic waves emission. The classic example of this phenomenon is the heat transfer between sun and earth. It is given by Stefan-Boltzmann Law.

$$q\_r = \varepsilon \sigma (T\_1^4 - T\_2^4) \tag{3}$$

Where,

*qr*: Heat flux of radiation; *ε*: Emissivity; *σ*: Stefan-Boltzmann constant; *T1, T2*: Surface temperatures.

#### **3.2.4 Phase – Change**

It is boiling, condensation, freezing and melting. These processes are given by following equations.

$$Q = m\,\Delta H\tag{4}$$

Where, *Q*: Amount of heat; *m*: Mass; *ΔH*: Specific latent heat.

#### **3.2.5 Heat transfer in conduits**

In the heat transfer in the fluid flowing in a conduit, the temperature is neither uniform in the fluid flow direction nor in the heat flux direction. Therefore, the bulk temperature is assumed as reference temperature. The use of a temperature reference allows to execute the heat balance in steady state. In this case, the transferred heat per time unit is a direct measure of the bulk temperature difference between two conduit sections. That is,

$$q = \dot{m} \mathcal{L}\_p \Delta T\_b \tag{5}$$

CFD and Thermography Techniques Applied in Cooling Systems Designs 139

(9)

(10)

<sup>1</sup> 2.51 2.log 3.7 Re. *e D f f*

Where,

Where,

*Δp:* Pressure drop; *f:* Friction factor; *L:* Length of pipe; *D:* Pipe diameter; *ρ:* Fluid density;

*v:* Mean velocity in the section.

is desired low fluid velocity.

**3.4 Turbulence models** 

**3.4.1 The** *κ* **-** *ε* **model** 

computational cost.

 

 

surfaces.

given by:

*f:* Friction factor; *Re:* Reynolds number; *e:* Absolute roughness; *D:* Pipe diameter.

And the pressure drop is determined by:

<sup>2</sup> . . . <sup>2</sup> *L v p f <sup>D</sup>* 

Therefore, to minimize the pressure drop and consequently reduce the energy loss of flow, it

Among several turbulence models known in the literature, will be discussed here only those

The simplest complete turbulence model has a wide range of applications in industrial and engineering problems. It can be applied to mass or heat transfer, combustion, multi-phase flows simulations, and others. The *κ* - *ε* model has been incorporated in most commercial CFD codes due to its stability and numerical robustness, good accuracy and low

This model should be avoided in complex flow applications, such as flows with boundary layer separation, sudden changes in the mean strain rate, rotating fluids, and over curved

The standard *κ* - *ε* model is based on model transport equations for the turbulence kinetic energy *κ* and its dissipation rate *ε*. Transport equations for the standard *κ* - *ε* model are

() ( )*<sup>i</sup> <sup>t</sup> kb Mk*

 

*k k <sup>k</sup> PP Y S*

   *C PCP C S*

1 32

(11)

(12)

2

 

 

 

*i j kj*

() ( ) . *<sup>i</sup> <sup>t</sup> k b*

*t xx x*

*ij j*

*t xx x*

ones involved in this work: *κ* - *ε* model, *κ* - *ω* model and Shear-Stress Transport (SST).

Where,

*q*: Amount of heat per time unit; *m* : Mass flow rate; *cp*: Specific heat of fluid; *ΔTb*: Bulk temperature difference of fluid among two conduit sections.

#### **3.3 Fluid dynamics 3.3.1 Mass flow rate**

The mass flow rate is given by the mass of fluid which passes through a surface per time unit and can be calculated from the following equation:

$$
\dot{m} = \rho \,\upsilon.A \tag{6}
$$

Where,

*m* : Mass flow rate; *ρ*: Fluid density; *v*: Mean velocity in the section; *A*: Area of conduit section.

#### **3.3.2 Pressure drop**

The pressure drop in pipes may be occasioned by means of:


The pressure drop is obtained as a function of Reynolds number, which depends on the fluid velocity, given by:

$$\text{Re} = \frac{\rho.v.D}{\mu} \tag{7}$$

Where,

*Re*: Reynolds number;

*ρ*: Fluid density;

*v*: Mean velocity in the section;

*D*: Diameter of pipe;

*μ*: Viscosity.

If the Reynolds number is smaller than 2300 the flow is laminar and friction factor is calculated by:

$$f = \frac{64}{\text{Re}}\tag{8}$$

Where,

*f*: Friction factor;

*Re*: Reynolds number.

But, if the Reynolds number is greater than 2300 the flow is turbulent and friction factor is calculated by:

$$\frac{1}{\sqrt{f}} = -2.\log\left(\frac{e\Big/2}{3.7} + \frac{2.51}{\text{Re}\sqrt{f}}\right) \tag{9}$$

Where,

138 Applied Computational Fluid Dynamics

The mass flow rate is given by the mass of fluid which passes through a surface per time

*m vA* 

The pressure drop is obtained as a function of Reynolds number, which depends on the

. . Re *v D* 

If the Reynolds number is smaller than 2300 the flow is laminar and friction factor is

64

But, if the Reynolds number is greater than 2300 the flow is turbulent and friction factor is

. . (6)

(7)

Re *<sup>f</sup>* (8)

*ΔTb*: Bulk temperature difference of fluid among two conduit sections.

unit and can be calculated from the following equation:

The pressure drop in pipes may be occasioned by means of:

Localized drops (valves, curves, and others);

Where,

Where,

*q*: Amount of heat per time unit;

*m* : Mass flow rate; *cp*: Specific heat of fluid;

**3.3 Fluid dynamics 3.3.1 Mass flow rate** 

*m* : Mass flow rate; *ρ*: Fluid density;

**3.3.2 Pressure drop** 

fluid velocity, given by:

*Re*: Reynolds number; *ρ*: Fluid density;

*D*: Diameter of pipe;

*μ*: Viscosity.

calculated by:

*f*: Friction factor; *Re*: Reynolds number.

calculated by:

Where,

*v*: Mean velocity in the section;

Friction;

Where,

*v*: Mean velocity in the section; *A*: Area of conduit section.

Difference of piping height.

*f:* Friction factor; *Re:* Reynolds number; *e:* Absolute roughness; *D:* Pipe diameter. And the pressure drop is determined by:

$$
\Delta p = f. \frac{L}{D}. \frac{\rho.v^2}{2} \tag{10}
$$

Where,

*Δp:* Pressure drop;

*f:* Friction factor;

*L:* Length of pipe;

*D:* Pipe diameter;

*ρ:* Fluid density;

*v:* Mean velocity in the section.

Therefore, to minimize the pressure drop and consequently reduce the energy loss of flow, it is desired low fluid velocity.

#### **3.4 Turbulence models**

Among several turbulence models known in the literature, will be discussed here only those ones involved in this work: *κ* - *ε* model, *κ* - *ω* model and Shear-Stress Transport (SST).

#### **3.4.1 The** *κ* **-** *ε* **model**

The simplest complete turbulence model has a wide range of applications in industrial and engineering problems. It can be applied to mass or heat transfer, combustion, multi-phase flows simulations, and others. The *κ* - *ε* model has been incorporated in most commercial CFD codes due to its stability and numerical robustness, good accuracy and low computational cost.

This model should be avoided in complex flow applications, such as flows with boundary layer separation, sudden changes in the mean strain rate, rotating fluids, and over curved surfaces.

The standard *κ* - *ε* model is based on model transport equations for the turbulence kinetic energy *κ* and its dissipation rate *ε*. Transport equations for the standard *κ* - *ε* model are given by:

$$\frac{\partial(\rho k)}{\partial t} + \frac{\partial(\rho k \,\mu)}{\partial \mathbf{x}\_i} = \frac{\partial}{\partial \mathbf{x}\_j} \left[ \left( \mu + \frac{\mu\_t}{\sigma\_k} \right) \frac{\partial \mathbf{k}}{\partial \mathbf{x}\_j} \right] + P\_k + P\_b - \rho \varepsilon - Y\_M + S\_k \tag{11}$$

$$\frac{\partial(\rho\boldsymbol{\varepsilon})}{\partial t} + \frac{\partial(\rho\boldsymbol{\varepsilon}\boldsymbol{\mu})}{\partial\boldsymbol{\alpha}\_{i}} = \frac{\partial}{\partial\boldsymbol{\alpha}\_{j}} \left[ \left( \mu + \frac{\mu\_{t}}{\sigma\_{\varepsilon}} \right) \frac{\partial\boldsymbol{\varepsilon}}{\partial\boldsymbol{\alpha}\_{j}} \right] + \mathbf{C}\_{1\varepsilon} \frac{\boldsymbol{\varepsilon}}{\kappa} \left( P\_{k} + \mathbf{C}\_{3\varepsilon}, P\_{b} \right) - \mathbf{C}\_{2\varepsilon} \rho \frac{\boldsymbol{\varepsilon}^{2}}{\kappa} + \mathbf{S}\_{\varepsilon} \tag{12}$$

CFD and Thermography Techniques Applied in Cooling Systems Designs 141

*i jj kk k GYS*

 *<sup>t</sup>* 

In the Figures 1 and 2 two simulations of temperature and velocity of the fluid are presented, with the same boundary conditions for SST and *κ* - *ε* model. Note that the results are similar for both models, however SST models capture more flow characteristics than *κ* - *ε* model.

*<sup>u</sup> GYDS*

*t xxx*

*i jj*

: Generation of turbulence kinetic energy due to the mean velocity gradients;

*k kkk*

 

 

(17)

(15)

(16)

() ( )*<sup>i</sup>*

 

*t xxx*

; *<sup>t</sup> <sup>k</sup> k* 

 

*Yk, Yω*: Dissipation of κ and ω due to turbulence;

Fig. 1. Fluid temperature using SST and *κ* - *ε* model

*Гk, Гω*: Effective diffusivity of κ and ω;

*σω*: Turbulent Prandtl number for ω;

**3.4.4 Comparing SST and κ - ε model** 

( ) ( )*<sup>i</sup>*

The base equations are:

Where, *Gk*

*Gω*: Generation of ω;

*Sω*: Source term.

*Gω*: Cross-diffusion term;

Where,

*μt:* Turbulent viscosity; *Pk:* Generation of turbulence kinetic energy due to the mean velocity gradients; *Pb*: Generation of turbulence kinetic energy due to buoyancy; *YM*: Fluctuating dilatation in compressible turbulence; *ρ*: Density; *μ*: Viscosity; *C1ε, C2ε, C3ε*: Model constants; *σk, σε*: Turbulent Prandtl number for κ and ε; *Sk, Sε*: Source term.

#### **3.4.2 The** *κ* **-** *ω* **model**

The *κ* - *ω* model is widely used and is superior for boundary-layer flows both in the viscous near-wall region treatment and in the streamwise pressure gradients application. However, it is not appropriate outside the shear layer that is a free-stream boundary. The standard *κ ω* model is an empirical model based on model transport equations for the turbulence kinetic energy *κ* and the specific dissipation rate *ω*, which is obtained by *ε* to *κ* ratio. Based on Wilcox, *κ* and *ω* are obtained from:

$$\frac{\partial(\rho k)}{\partial t} + \frac{\partial(\rho \mathbb{I} I\_j k)}{\partial \mathbf{x}\_j} = \frac{\partial}{\partial \mathbf{x}\_j} \left| \left( \mu + \frac{\mu\_t}{\sigma\_k} \right) \frac{\partial \mathbb{k}}{\partial \mathbf{x}\_j} \right| + P\_k - \beta' \rho \kappa \phi + P\_{kb} \tag{13}$$

$$\frac{\partial(\rho\alpha o)}{\partial t} + \frac{\partial(\rho\mathcal{U}\_{j}\alpha o)}{\partial \mathbf{x}\_{j}} = \frac{\partial}{\partial \mathbf{x}\_{j}} \left[ \left( \mu + \frac{\mu\_{t}}{\sigma\_{o}} \right) \frac{\partial \alpha o}{\partial \mathbf{x}\_{j}} \right] + \alpha \frac{\alpha o}{\kappa} \mathcal{P}\_{k} - \beta \rho \alpha o^{2} + \mathcal{P}\_{\alpha \flat} \tag{14}$$

*Pκb, Pωb*: Turbulence buoyancy term; *U*: Velocity vector; *σω*: Turbulent Prandtl number for ω; *β', β, α*: Model constant.

#### **3.4.3 The shear-stress transport model (SST)**

The shear-stress transport *κ* - *ω* model was developed by Menter to effectively blend the robust and accurate formulation of the *κ* - *ω* model in the near-wall region with the free-stream independence of the *κ* - *ε* model in the far field. To achieve this, the *κ* - *ε* model is converted into a *κ* - *ω* formulation. The SST *κ* - *ω* model is similar to the standard *κ* - *ω* model, but the modeling constants are different in one and another and the SST model includes some changes in the standard one, such as the multiplication of both transformed *κ* - *ε* and *κ* - *ω* models by a blending function, which activates standard *κ* - *ω* model in the near-wall region and activates transformed *κ* - *ε* model away from the surface, the incorporation of a damped cross-diffusion derivative term in the *ω* equation, and a modification in the definition of the turbulent viscosity to account for the transport of the turbulent shear stress.

These improvements provide more accuracy and reliability for a wide range of flow classes than the standard *κ* - *ω* model. For instance, adverse pressure gradient flows, airfoils, and transonic shock waves.

The base equations are:

$$\frac{\partial(\rho k)}{\partial t} + \frac{\partial(\rho k \mu)}{\partial \mathbf{x}\_i} = \frac{\partial}{\partial \mathbf{x}\_j} \left( \Gamma\_k \frac{\partial \mathbf{k}}{\partial \mathbf{x}\_j} \right) + \tilde{\mathbf{G}}\_k - \mathbf{Y}\_k + \mathbf{S}\_k \tag{15}$$

$$\frac{\partial(\rho oo)}{\partial t} + \frac{\partial(\rho oo u\_i)}{\partial \mathbf{x}\_i} = \frac{\partial}{\partial \mathbf{x}\_j} \left(\Gamma\_{oo} \frac{\partial oo}{\partial \mathbf{x}\_j}\right) + \mathbf{G}\_{oo} - \mathbf{Y}\_{oo} + \mathbf{D}\_{oo} + \mathbf{S}\_{oo} \tag{16}$$

$$
\Gamma\_k = \mu + \frac{\mu\_t}{\sigma\_k}; \qquad \Gamma\_{\alpha} = \mu + \frac{\mu\_t}{\sigma\_{\alpha}} \tag{17}
$$

Where,

140 Applied Computational Fluid Dynamics

The *κ* - *ω* model is widely used and is superior for boundary-layer flows both in the viscous near-wall region treatment and in the streamwise pressure gradients application. However, it is not appropriate outside the shear layer that is a free-stream boundary. The standard *κ ω* model is an empirical model based on model transport equations for the turbulence kinetic energy *κ* and the specific dissipation rate *ω*, which is obtained by *ε* to *κ* ratio. Based

( ) ( ) '

*k k U k*

*t xx x*

*t xx x*

*j j kj*

*jj j*

*<sup>j</sup> <sup>t</sup> <sup>k</sup> kb*

(13)

 

 

(14)

 

<sup>2</sup> ( ) ( ) *<sup>j</sup> <sup>t</sup> k b*

The shear-stress transport *κ* - *ω* model was developed by Menter to effectively blend the robust and accurate formulation of the *κ* - *ω* model in the near-wall region with the free-stream independence of the *κ* - *ε* model in the far field. To achieve this, the *κ* - *ε* model is converted into a *κ* - *ω* formulation. The SST *κ* - *ω* model is similar to the standard *κ* - *ω* model, but the modeling constants are different in one and another and the SST model includes some changes in the standard one, such as the multiplication of both transformed *κ* - *ε* and *κ* - *ω* models by a blending function, which activates standard *κ* - *ω* model in the near-wall region and activates transformed *κ* - *ε* model away from the surface, the incorporation of a damped cross-diffusion derivative term in the *ω* equation, and a modification in the definition of the turbulent

These improvements provide more accuracy and reliability for a wide range of flow classes than the standard *κ* - *ω* model. For instance, adverse pressure gradient flows, airfoils, and

*P P*

*P P*

 

 

*Pk:* Generation of turbulence kinetic energy due to the mean velocity gradients;

*Pb*: Generation of turbulence kinetic energy due to buoyancy; *YM*: Fluctuating dilatation in compressible turbulence;

Where,

*ρ*: Density; *μ*: Viscosity;

*μt:* Turbulent viscosity;

*C1ε, C2ε, C3ε*: Model constants;

*Sk, Sε*: Source term.

**3.4.2 The** *κ* **-** *ω* **model** 

*σk, σε*: Turbulent Prandtl number for κ and ε;

on Wilcox, *κ* and *ω* are obtained from:

*Pκb, Pωb*: Turbulence buoyancy term;

*σω*: Turbulent Prandtl number for ω;

**3.4.3 The shear-stress transport model (SST)** 

*U*: Velocity vector;

*β', β, α*: Model constant.

transonic shock waves.

*U*

viscosity to account for the transport of the turbulent shear stress.

 

*Gk* : Generation of turbulence kinetic energy due to the mean velocity gradients; *Gω*: Generation of ω;

*Yk, Yω*: Dissipation of κ and ω due to turbulence;

*Гk, Гω*: Effective diffusivity of κ and ω;

*Gω*: Cross-diffusion term;

*σω*: Turbulent Prandtl number for ω;

*Sω*: Source term.

#### **3.4.4 Comparing SST and κ - ε model**

In the Figures 1 and 2 two simulations of temperature and velocity of the fluid are presented, with the same boundary conditions for SST and *κ* - *ε* model. Note that the results are similar for both models, however SST models capture more flow characteristics than *κ* - *ε* model.

Fig. 1. Fluid temperature using SST and *κ* - *ε* model

CFD and Thermography Techniques Applied in Cooling Systems Designs 143

*R R*

If the heat exchanger is clean, then *Rfou* = 0. Table 1 presents typical values of fouling

Some variables must be taken into account in the design and operation of cooling systems,

Flow velocity: for water, it should be kept above 2 m/s to suppress fouling and above 1 m/s

Surface temperature: for cooling towers, the water temperature must be kept below 60 °C.

For liquid coolants, fouling inhibitors should be used, such as: corrosion inhibitors, antidispersants, stabilizers, biocides, softeners, acids, and polyphosphates. However, if such fouling controls are not effective, the exchanger must be cleaned either on-line or off-line.

Corrosion is electrochemical destructive attack of the base material with its environment. Water in direct contact with a metal surface causes oxidation, which is a process where

*U*

Where,

resistance.

*U*: Overall heat transfer coefficient; *Rhec*: Resistance of cleaned heat exchanger; *Rfou*: Resistance of fouled heat exchanger.

Table 1. Typical fouling resistance

to minimize fouling.

**3.6 Corrosion** 

in order to avoid fouling. The most important are:

Tube material: select materials to avoid corrosion, for instance.

1 *hec fou*

(19)

Fig. 2. Fluid velocity using SST and *κ* - *ε* model

#### **3.5 Fouling**

Fouling is a term employed to represent undesired accumulation of solid material on the surfaces of heat exchangers. This accumulation results in thermal resistance increment reducing exchanger performance. Fouling reduces the flow area and increases surface roughness, causing a reduction in the flow rate as a consequence of the pressure drop increase.

The fouling deposits may be loose particles or fix and hard layers, comprising sediments, polymers, inorganic salts, fuel or corrosion products, biological growth, and others. The maximum fouling layer can occur in few hours or may require many years to be formed. In any case, it should be avoided, because it increases capital costs, maintenance costs, production and energy losses, etc.

The main fouling mechanisms are crystallization, precipitation, sedimentation, chemical reaction, corrosion, biological and freezing fouling.

The amount of heat per time unit can be calculated by:

$$q = \mathcal{U}.A.\Delta T\tag{18}$$

Where,

*q*: Amount of heat per time unit;

*U*: Overall heat transfer coefficient;

*A*: Heat transfer area;

*ΔT*: Bulk temperature difference between two conduit sections.

And U is obtained by the following equation:

$$
\Delta U = \frac{1}{R\_{\text{hcc}} + R\_{\text{fou}}} \tag{19}
$$

Where,

142 Applied Computational Fluid Dynamics

Fouling is a term employed to represent undesired accumulation of solid material on the surfaces of heat exchangers. This accumulation results in thermal resistance increment reducing exchanger performance. Fouling reduces the flow area and increases surface roughness, causing a reduction in the flow rate as a consequence of the pressure drop

The fouling deposits may be loose particles or fix and hard layers, comprising sediments, polymers, inorganic salts, fuel or corrosion products, biological growth, and others. The maximum fouling layer can occur in few hours or may require many years to be formed. In any case, it should be avoided, because it increases capital costs, maintenance costs,

The main fouling mechanisms are crystallization, precipitation, sedimentation, chemical

*q UA T* . . (18)

Fig. 2. Fluid velocity using SST and *κ* - *ε* model

production and energy losses, etc.

*q*: Amount of heat per time unit; *U*: Overall heat transfer coefficient;

*A*: Heat transfer area;

reaction, corrosion, biological and freezing fouling. The amount of heat per time unit can be calculated by:

And U is obtained by the following equation:

*ΔT*: Bulk temperature difference between two conduit sections.

**3.5 Fouling** 

increase.

Where,

*U*: Overall heat transfer coefficient;

*Rhec*: Resistance of cleaned heat exchanger;

*Rfou*: Resistance of fouled heat exchanger.

If the heat exchanger is clean, then *Rfou* = 0. Table 1 presents typical values of fouling resistance.


Table 1. Typical fouling resistance

Some variables must be taken into account in the design and operation of cooling systems, in order to avoid fouling. The most important are:

Flow velocity: for water, it should be kept above 2 m/s to suppress fouling and above 1 m/s to minimize fouling.

Surface temperature: for cooling towers, the water temperature must be kept below 60 °C. Tube material: select materials to avoid corrosion, for instance.

For liquid coolants, fouling inhibitors should be used, such as: corrosion inhibitors, antidispersants, stabilizers, biocides, softeners, acids, and polyphosphates. However, if such fouling controls are not effective, the exchanger must be cleaned either on-line or off-line.

#### **3.6 Corrosion**

Corrosion is electrochemical destructive attack of the base material with its environment. Water in direct contact with a metal surface causes oxidation, which is a process where

CFD and Thermography Techniques Applied in Cooling Systems Designs 145

The value of *L* was considered as the total losses of the motor, that is, it is considered that all heat generated by the motor will be removed by water, which in practice does not happen, once that a portion of generated heat will be dissipated to environment through the endshields, the shaft and the terminal box. However, the heat portion removed by water is greater than by other means, so that it can be considered conservative, thereby simplifying

The next step consists in checking the circuit thermal saturation in relation to the water flow that is, quantifying how much an increase in the flow causes the coil temperature to reduce. Therefore, it is necessary to verify the behavior of the coil average temperature fluctuation, *ΔTw*, with the water flow. For this verification equations obtained by heat transfer laws will

The equations (21) and (22) relate *L* in W with *Tw*, *Tframe* and *Tfluid* in K and with *Req* and *Rh* in

 *<sup>w</sup> frame eq*

 *frame fluid h*

*R*

1

And to obtain *Rh* it is used (23), where the convection coefficient, *h*, is in W / (m2 . K) and

*T T*

(21)

(22)

. *Rh h A* (23)

*R*

*T T*

*L*

*L*

the thermal exchange surface between the frame and the fluid, *A*, is in m2.

Fig. 3. Simplified thermal circuit of the motor

the problem.

K/W.

be used, as described next.

metal dissolved in fluid; this phenomenon generates serious problems in the worldwide. Corrosion causes:


The many aspects of corrosion problems constrain it control, which is achieved by recognizing and understanding corrosion mechanisms. The control and prevention of corrosion damage can be obtained basically by following methods:


### **4. Water-cooled frame**

The objective of this work consists in optimizing the water flow inside a water cooled frame considering the boundary conditions intrinsic to both the manufacturing process and the electric motor itself.

One of the challenges of this development is the frame manufacturing, which consists in a single cast iron piece free of welds or seals, making it difficult to obtain the water circuit.

Due to the increasing demand for smaller water cooled motors, in this work an IEC 200 frame size – 75 kW – IV Poles – 60 Hz motor was used.

#### **5. Thermal circuit and equations**

The first step of the design is the definition of the motor simplified thermal circuit as represented in Figure 3. It can be observed that the produced heat, *L*, is transferred through the equivalent resistance, *Req*, and the convection resistance, *Rh*, thus causing an increase in the average temperatures of the coil, *Tw*, the frame, *Tframe* and the fluid, *Tfluid*.

The next step is calculating the water flow that is needed to remove the heat produced by the motor. This can be obtained by means of (20) and (5), where *L* is the heat amount to be removed in W, *m* is the mass flow in kg/s, *cp* is the specific heat of water in J/(kg . K), *To* is the outlet water temperature and *Ti* is the inlet water temperature both in K.

$$L = \dot{m} \mathcal{L}\_p.(T\_o - T\_i) \tag{20}$$

Using (20) and the values shown in Table 2, it is obtained a mass flow of 0.239 kg/s.


Table 2. Value and units for variables

metal dissolved in fluid; this phenomenon generates serious problems in the worldwide.

The many aspects of corrosion problems constrain it control, which is achieved by recognizing and understanding corrosion mechanisms. The control and prevention of

The objective of this work consists in optimizing the water flow inside a water cooled frame considering the boundary conditions intrinsic to both the manufacturing process and the

One of the challenges of this development is the frame manufacturing, which consists in a single cast iron piece free of welds or seals, making it difficult to obtain the water circuit. Due to the increasing demand for smaller water cooled motors, in this work an IEC 200

The first step of the design is the definition of the motor simplified thermal circuit as represented in Figure 3. It can be observed that the produced heat, *L*, is transferred through the equivalent resistance, *Req*, and the convection resistance, *Rh*, thus causing an increase in

The next step is calculating the water flow that is needed to remove the heat produced by the motor. This can be obtained by means of (20) and (5), where *L* is the heat amount to be removed in W, *m* is the mass flow in kg/s, *cp* is the specific heat of water in J/(kg . K), *To* is

. . *L mc T T <sup>p</sup> o i* (20)

the average temperatures of the coil, *Tw*, the frame, *Tframe* and the fluid, *Tfluid*.

the outlet water temperature and *Ti* is the inlet water temperature both in K.

Using (20) and the values shown in Table 2, it is obtained a mass flow of 0.239 kg/s.

Variable Value

*L* 5.000 (W) *cp* a 20 °C 4 184.3 (J / kg / K) *To - Ti* 5 (K)

Corrosion causes:

 Plants shutdowns; And others.

 Efficiency reduction of machines and plants; Increase costs of maintenance and overdesign;

corrosion damage can be obtained basically by following methods:

Application of cathodic or anodic protection and etc.

frame size – 75 kW – IV Poles – 60 Hz motor was used.

Losses or contaminations of products;

Employment of suitable materials;

**5. Thermal circuit and equations** 

Table 2. Value and units for variables

 Use of protective coatings; Change to the environment;

**4. Water-cooled frame** 

electric motor itself.

Fig. 3. Simplified thermal circuit of the motor

The value of *L* was considered as the total losses of the motor, that is, it is considered that all heat generated by the motor will be removed by water, which in practice does not happen, once that a portion of generated heat will be dissipated to environment through the endshields, the shaft and the terminal box. However, the heat portion removed by water is greater than by other means, so that it can be considered conservative, thereby simplifying the problem.

The next step consists in checking the circuit thermal saturation in relation to the water flow that is, quantifying how much an increase in the flow causes the coil temperature to reduce. Therefore, it is necessary to verify the behavior of the coil average temperature fluctuation, *ΔTw*, with the water flow. For this verification equations obtained by heat transfer laws will be used, as described next.

The equations (21) and (22) relate *L* in W with *Tw*, *Tframe* and *Tfluid* in K and with *Req* and *Rh* in K/W.

$$L = \frac{\left(T\_w - T\_{frame}\right)}{R\_{eq}}\tag{21}$$

$$L = \frac{\left(T\_{frame} - T\_{fluid}\right)}{R\_h} \tag{22}$$

And to obtain *Rh* it is used (23), where the convection coefficient, *h*, is in W / (m2 . K) and the thermal exchange surface between the frame and the fluid, *A*, is in m2.

$$R\_h = \frac{1}{hA} \tag{23}$$

CFD and Thermography Techniques Applied in Cooling Systems Designs 147

there will be no shortage. So the possible hot spots will be generated only by water flow recirculation, thus allowing the elimination of the heat transfer calculation on the numerical simulations, making possible to identify the hot spots by means of association with the recirculation. It is emphasized that with this consideration the hot spots can be only

The water circuit geometry has as basic shape a cylinder with an inlet and an outlet of water as presented in Figure 5, where the difference between the external radius, *re*, and the internal radius, *ri*, is 0.015 m and the length, *l*, is 0.400 m. These values are limited by both the manufacturing process and the motor geometry. Flow directional guides will be inserted

To make easy the study of the flow inside the frame, the cylinder was transformed into a planned shape with a separation guide between inlet and outlet (configuration I) as presented in Figures 6 and 7. In Figure 6 it can be observed the flow inside the cylinder and in Figure 7 the flow inside configuration I. It is possible to observe the similar behavior of the flow in both of them, allowing for the use of configuration I as the base for the circuit optimization. This similarity happened because the gravitational force is considered null and, as the channel average speed is approximately 0.04 m/s, the centrifugal force caused by

The frame inlet and outlet channels are the main responsible for the pressure drop; therefore, an optimization in these regions can significantly reduce the total pressure drop. In the analysis of the inlet and outlet channels it was used the planned cylinder technique and nine simulations were made. The three more significant ones from these simulations

identified, but not thermally quantified.

Fig. 5. Basic geometry of water circuit

the cylinder curvature can be despised.

**6.3 Inlet and outlet channels** 

will be presented.

if needed, after analyzing the simulation results.

**6.2 Geometry** 

Fig. 4. Mass flow saturation

Knowing that *h* is a variable dependent on the fluid properties, the channel geometry and the flow, then the fluctuation temperature, *ΔTw*, can be related to the mass flow *m* , according to (21), (22), (23), the fluid properties and the channel geometry, obtaining the curve presented in Figure 4. It can be observed that the motor operation point, *Po*, is located on the curve saturation region, what means that when increasing the water flow, the coil temperature reduction can be despised, because it is necessary a great increase the flow for the temperature to be slightly reduced. Therefore, this flow is correct for the design. For the obtainment of this curve the following considerations were made:


### **6. Numerical analyses**

Once analytically defined the flow value to be used in the design, the numerical analyses are initiated to check the water flow behavior inside the frame. For better use of the computational capacity, some considerations and simplifications were made concerning both the physical phenomenon and the geometry.

#### **6.1 Heat transfer**

The possible hot spots inside the water circuit can be generated basically by three causes, local heat generation, cooling fluid shortage in determined regions, and/or fluid recirculation. For simulation purposes local heat generation is neglected, because the heat flow from the stator to the frame is uniformly distributed throughout the surface. As for fluid shortage, it can be considered that the water circuit will be totally filled and therefore there will be no shortage. So the possible hot spots will be generated only by water flow recirculation, thus allowing the elimination of the heat transfer calculation on the numerical simulations, making possible to identify the hot spots by means of association with the recirculation. It is emphasized that with this consideration the hot spots can be only identified, but not thermally quantified.

### **6.2 Geometry**

146 Applied Computational Fluid Dynamics

Knowing that *h* is a variable dependent on the fluid properties, the channel geometry and the flow, then the fluctuation temperature, *ΔTw*, can be related to the mass flow *m* , according to (21), (22), (23), the fluid properties and the channel geometry, obtaining the curve presented in Figure 4. It can be observed that the motor operation point, *Po*, is located on the curve saturation region, what means that when increasing the water flow, the coil temperature reduction can be despised, because it is necessary a great increase the flow for

a. *Req* is constant and, due to the difficulty to theoretically calculate its value, it was

Once analytically defined the flow value to be used in the design, the numerical analyses are initiated to check the water flow behavior inside the frame. For better use of the computational capacity, some considerations and simplifications were made concerning

The possible hot spots inside the water circuit can be generated basically by three causes, local heat generation, cooling fluid shortage in determined regions, and/or fluid recirculation. For simulation purposes local heat generation is neglected, because the heat flow from the stator to the frame is uniformly distributed throughout the surface. As for fluid shortage, it can be considered that the water circuit will be totally filled and therefore

the temperature to be slightly reduced. Therefore, this flow is correct for the design.

obtained through (21) and (22) using experimental data of preliminary tests;

For the obtainment of this curve the following considerations were made:

Fig. 4. Mass flow saturation

b. Fluid properties are constant;

**6. Numerical analyses** 

**6.1 Heat transfer** 

c. Dimensions of channel: 0.400 x 0.015 m; d. Average diameter of the channel: 0,350 m.

both the physical phenomenon and the geometry.

The water circuit geometry has as basic shape a cylinder with an inlet and an outlet of water as presented in Figure 5, where the difference between the external radius, *re*, and the internal radius, *ri*, is 0.015 m and the length, *l*, is 0.400 m. These values are limited by both the manufacturing process and the motor geometry. Flow directional guides will be inserted if needed, after analyzing the simulation results.

Fig. 5. Basic geometry of water circuit

To make easy the study of the flow inside the frame, the cylinder was transformed into a planned shape with a separation guide between inlet and outlet (configuration I) as presented in Figures 6 and 7. In Figure 6 it can be observed the flow inside the cylinder and in Figure 7 the flow inside configuration I. It is possible to observe the similar behavior of the flow in both of them, allowing for the use of configuration I as the base for the circuit optimization. This similarity happened because the gravitational force is considered null and, as the channel average speed is approximately 0.04 m/s, the centrifugal force caused by the cylinder curvature can be despised.

### **6.3 Inlet and outlet channels**

The frame inlet and outlet channels are the main responsible for the pressure drop; therefore, an optimization in these regions can significantly reduce the total pressure drop. In the analysis of the inlet and outlet channels it was used the planned cylinder technique and nine simulations were made. The three more significant ones from these simulations will be presented.

CFD and Thermography Techniques Applied in Cooling Systems Designs 149

Fig. 8(a). Inlet and outlet channel

Fig. 8(b). Inlet and outlet channel

Fig. 8(c). Inlet and outlet channel

Fig. 6. Original cylinder

#### Fig. 7. Configuration I

The first simulation presented in Figure 8(a) consists in an inlet channel with circular pipe format located in the left side of the water main circuit. In this case, a water flow concentration is making tangent to the circuit walls occasioning a low flow in the middle of the circuit, which would cause an heterogeneous heat exchange.

In the second case, presented in Figure 8(b), the flow was improved if compared with the first case. In this case a diffuser on the inlet, instead of a pipe, was used. The flow further improved when the inlet diffuser was moved to the middle of the main circuit that can be seen in the Figure 8(c).

Fig. 8(a). Inlet and outlet channel

The first simulation presented in Figure 8(a) consists in an inlet channel with circular pipe format located in the left side of the water main circuit. In this case, a water flow concentration is making tangent to the circuit walls occasioning a low flow in the middle of

In the second case, presented in Figure 8(b), the flow was improved if compared with the first case. In this case a diffuser on the inlet, instead of a pipe, was used. The flow further improved when the inlet diffuser was moved to the middle of the main circuit that can be

the circuit, which would cause an heterogeneous heat exchange.

Fig. 6. Original cylinder

Fig. 7. Configuration I

seen in the Figure 8(c).

Fig. 8(b). Inlet and outlet channel

Fig. 8(c). Inlet and outlet channel

CFD and Thermography Techniques Applied in Cooling Systems Designs 151

The simulation meshes were made with the software *ICEM CFD 11.0.1*. The used elements were prisms on the walls and tetras inside the mesh, always respecting the quality criterion

The simulations were made with the software *CFX 11.0*, using the following simulation

As yet only one motor with water circuit similar to the configuration I was tested. Due to the manufacturing process the dividing guide had been interrupted, therefore, the water inlet and outlet were not separated. This fact was confirmed using thermography techniques.

To check the guide arrangement inside the channel the following procedure was accomplished: the motor was turned on and kept running for 30 minutes without water circulation. The water inlet valve was then opened, while keeping the motor working. The phenomenon of water filling in the frame channel was recorded by the thermographic camera. The sequence captured on the video can be visualized in Figure 11. In this case, the outlet is located on the top and not on the lateral of the frame, thus assuring the removal of

**6.5 Simulation data** 

 Heat transfer: *None*; Buoyance: Non buoyancy;

 Turbulence: Shear Stress Transport; Convergence criteria: *10-5 (RMS)*.

**7. Experiments and thermography** 

**7.1 Thermal visualization techniques** 

air from the frame inside, as presented in Figures 11(d) and 11(e).

Fig. 11(a). Water filling frame channel - Closed valve

parameters:

*Smooth Elements Globally – Quality* with value above 0.2.

Due to the similarities observed during the work between the flow behavior in the inlet and in the outlet channels, the improvement of the inlet channel also could be applied to the outlet channel.

### **6.4 Water circuit**

When the source of heat generation is constant in a surface, the cooling system needs to keep a constant fluid speed, keeping the heat transfer coefficient also constant in order to avoid undesired speed variation. Then, according to (24), where *Q* is the volumetric flow in m3/s, *V* the average speed in m/s and *S* the area of the transversal section of the flow in m2, in order to keep the speed constant, the ratio *Q / S* must be kept constant. In this case, as the flow is constant the area can also be kept constant throughout the circuit. Thus the whole design of the cooling circuit will be based on this premise.

$$Q = V.S\tag{24}$$

In accordance with the Figure 7 the configuration I presented a good flow, but without guides inside the circuit. The absence of these guides could compromise the frame stiffness; therefore, other configurations with guides inside the circuit were simulated. Among the 16 simulated configurations, it was initially expected that the configuration II would present a good result, what did not happen, because such configuration caused low speeds in the back of the guides, as shown in Figure 9.

Due to the result obtained with the configuration II, the configuration III, presented in Figure 10, is proposed. In this configuration it was obtained the double water speed of the initial configuration I, besides presenting a good flow and low pressure drop.

Fig. 9. Configuration II – intercalated opposite guides

Fig. 10. Configuration III – central guide with curved guide

### **6.5 Simulation data**

150 Applied Computational Fluid Dynamics

Due to the similarities observed during the work between the flow behavior in the inlet and in the outlet channels, the improvement of the inlet channel also could be applied to the

When the source of heat generation is constant in a surface, the cooling system needs to keep a constant fluid speed, keeping the heat transfer coefficient also constant in order to avoid undesired speed variation. Then, according to (24), where *Q* is the volumetric flow in m3/s, *V* the average speed in m/s and *S* the area of the transversal section of the flow in m2, in order to keep the speed constant, the ratio *Q / S* must be kept constant. In this case, as the flow is constant the area can also be kept constant throughout the circuit. Thus the whole

In accordance with the Figure 7 the configuration I presented a good flow, but without guides inside the circuit. The absence of these guides could compromise the frame stiffness; therefore, other configurations with guides inside the circuit were simulated. Among the 16 simulated configurations, it was initially expected that the configuration II would present a good result, what did not happen, because such configuration caused low speeds in the back

Due to the result obtained with the configuration II, the configuration III, presented in Figure 10, is proposed. In this configuration it was obtained the double water speed of the

initial configuration I, besides presenting a good flow and low pressure drop.

*Q VS* . (24)

design of the cooling circuit will be based on this premise.

Fig. 9. Configuration II – intercalated opposite guides

Fig. 10. Configuration III – central guide with curved guide

of the guides, as shown in Figure 9.

outlet channel.

**6.4 Water circuit** 

The simulation meshes were made with the software *ICEM CFD 11.0.1*. The used elements were prisms on the walls and tetras inside the mesh, always respecting the quality criterion *Smooth Elements Globally – Quality* with value above 0.2.

The simulations were made with the software *CFX 11.0*, using the following simulation parameters:


### **7. Experiments and thermography**

As yet only one motor with water circuit similar to the configuration I was tested. Due to the manufacturing process the dividing guide had been interrupted, therefore, the water inlet and outlet were not separated. This fact was confirmed using thermography techniques.

### **7.1 Thermal visualization techniques**

To check the guide arrangement inside the channel the following procedure was accomplished: the motor was turned on and kept running for 30 minutes without water circulation. The water inlet valve was then opened, while keeping the motor working. The phenomenon of water filling in the frame channel was recorded by the thermographic camera. The sequence captured on the video can be visualized in Figure 11. In this case, the outlet is located on the top and not on the lateral of the frame, thus assuring the removal of air from the frame inside, as presented in Figures 11(d) and 11(e).

Fig. 11(a). Water filling frame channel - Closed valve

CFD and Thermography Techniques Applied in Cooling Systems Designs 153

Through this test it can be observed that two dark bands appear between the inlet and the outlet, allowing to affirm that two openings exist on the dividing guide. Theses bands can be visualized in Figures. 11(d) and 11(e). Therefore, when the outlet is located on the frame lateral, as proposed in the configuration I, the flow passes directly from the inlet to the outlet.

Although the dividing guide between inlet and outlet to have been interrupted, thus causing recirculation, this motor presented a temperature rise of 73 °C on the windings,

The next steps of this work consist in testing motors of higher power rates in the same frame

When increasing the power in these frames, the bearing temperature can be a limiting factor for the motor integrity. Therefore, it is also intended to design motors with water cooled

Note that in this design step the fouling and corrosion were not considered, however, due to

With the support of the CFD technique it was possible to foresee the water flow behavior inside the frame channel without visualizing directly the water flow. Through the use of the CFD it was also possible to double the water speed inside the frame channel, thus reducing

Another advantages provided by CFD were the reduction obtained both in the development time and in the number of prototypes. These advantages have been proven in this work: in spite of the 22 frame configurations that have been initially proposed, after the simulation results were obtained only the three best prototypes have been actually manufactured. The use of thermography techniques in the field of electric motors helps to improve not only the development of products, but also the quality control and the maintenance of operating

Fig. 11(e). Water filling frame channel - time: 10 min

below the higher limit of its thermal class (80 °C).

size using the configuration III previously presented.

its meaning should be contemplated before product execution.

the pressure drop in 18 % when compared with the initial design.

**7.2 Results** 

bearings.

**8. Conclusions** 

**7.3 Final considerations** 

Fig. 11(b). Water filling frame channel - time: 10 s

Fig. 11(c). Water filling frame channel - time: 1 min and 10 s

Fig. 11(d). Water filling frame channel - time: 3 min and 10 s

Fig. 11(e). Water filling frame channel - time: 10 min

Through this test it can be observed that two dark bands appear between the inlet and the outlet, allowing to affirm that two openings exist on the dividing guide. Theses bands can be visualized in Figures. 11(d) and 11(e). Therefore, when the outlet is located on the frame lateral, as proposed in the configuration I, the flow passes directly from the inlet to the outlet.

### **7.2 Results**

152 Applied Computational Fluid Dynamics

Fig. 11(b). Water filling frame channel - time: 10 s

Fig. 11(c). Water filling frame channel - time: 1 min and 10 s

Fig. 11(d). Water filling frame channel - time: 3 min and 10 s

Although the dividing guide between inlet and outlet to have been interrupted, thus causing recirculation, this motor presented a temperature rise of 73 °C on the windings, below the higher limit of its thermal class (80 °C).

### **7.3 Final considerations**

The next steps of this work consist in testing motors of higher power rates in the same frame size using the configuration III previously presented.

When increasing the power in these frames, the bearing temperature can be a limiting factor for the motor integrity. Therefore, it is also intended to design motors with water cooled bearings.

Note that in this design step the fouling and corrosion were not considered, however, due to its meaning should be contemplated before product execution.

### **8. Conclusions**

With the support of the CFD technique it was possible to foresee the water flow behavior inside the frame channel without visualizing directly the water flow. Through the use of the CFD it was also possible to double the water speed inside the frame channel, thus reducing the pressure drop in 18 % when compared with the initial design.

Another advantages provided by CFD were the reduction obtained both in the development time and in the number of prototypes. These advantages have been proven in this work: in spite of the 22 frame configurations that have been initially proposed, after the simulation results were obtained only the three best prototypes have been actually manufactured.

The use of thermography techniques in the field of electric motors helps to improve not only the development of products, but also the quality control and the maintenance of operating

**8**

*Canada* 

**Computational Fluid Dynamics (CFD)**

**Modeling of Photochemical Reactors** 

Masroor Mohajerani, Mehrab Mehrvar and Farhad Ein-Mozaffari *Department of Chemical Engineering, Ryerson University, Toronto, Ontario* 

Advanced oxidation processes (AOPs) play an important role in the degradation or the production of a wide range of organic materials. Many organic compounds such as pharmaceuticals, dyes, herbicides, and pesticides have been subjected to degradation and remediation purposes in water and wastewater treatment systems using AOPs. Some of the organic compounds such as drugs, vitamins, or fragrances could be also produced by

As the standard of living increases, many chemicals such as pharmaceuticals, pesticides, herbicides, and dyes are extensively consumed. Each of these products may cause health issues by their accumulation in aquatic environment. Pharmaceuticals such as antibiotics are partially metabolized and excreted by humans and animals. Improper disposal, dumping, and accidental discharge of drugs lead to the increase of the concentration of compounds such as analgesics, antibiotics, steroids, and hormones in aquatic environment, which cause environmental and health problems. Residual pesticides and herbicides originate from the direct pollutant in production plant, disposal of empty containers, equipment washing, and surface runoff. High levels of these compounds are toxic, mutagenic, carcinogenic, and tumorigenic. Some other wastes such as landfill leachate are subjected to advanced treatment methods. Old landfill leachates (>10 years) are nonbiodegradable in nature due to the existence of organic compounds with high molecular weights. Although the composition of landfill leachates varies widely with respect to the age of the landfill, type of wastes, and climate conditions, they can be categorized into four groups of dissolved organic matter, inorganic macro components, heavy materials, and xenobiotic organic substances. Another type of toxic chemicals which cannot be removed using conventional treatment methods is endocrine disrupting compounds (EDCs). EDCs, especially the steroidal hormones, are well recognized exogenous agents that interfere with the synthesis, action, and/or elimination of natural hormones in the body. Conventional processes are not effective in destruction of these types of organic compounds; therefore, powerful advanced treatment processes are required in order to mineralize them. There are several options for choosing an oxidation

process: wet air oxidation, supercritical water oxidation, incineration, and AOPs.

AOPs have been promising in the treatment of contaminated soils and waters. The AOPs could be employed to fully or partially oxidize organic pollutants usually using a combination of different oxidants. In contrary to the conventional physical and chemical treatment processes, AOPs do not transfer pollutants from one phase to another, i.e., organic

**1. Introduction** 

oxidation processes.

machines in the field. In this case, specifically, it was possible to visualize the guides configuration and the water flow inside the frame channel preventing the need to destroy it.

#### **9. Acknowledgement**

The authors would like to thank all Weg colleagues that directly or indirectly participated in this project.

#### **10. References**

Fox, R. W. & Mcdonald, A. T., *Introdução à mecânica dos Fluidos*, fifth edition, 2001.

