3. TiO2 nanofluids as coolant for radiator and electronic devices

Radiator (usually a cross flow heat exchanger) is an important component of automobile. It cools down the liquid which is carrying heat from engine block and protecting it from damage. For high heat transfer rate, if the size of radiator is increased then it will increase both the volume and weight, which is undesirable. Researchers are interested to increase the effectiveness and compactness of radiators by using coolants with additives such as nanoparticles to the base fluids.

Hussein et al. [11] used SiO2 and TiO2 nanofluids in automotive cooling system to check the effects of volumetric flow rate, inlet temperature and volumetric concentration on Nusselt number. Statistical models have been obtained by statistical softwares using multiple linear regression methods and factorial methodology. Nusselt number increases as the volume flow rate, inlet temperature and volume concentration is increased. Wadd et al. [12] performed experimentation on automobile radiator to check the performance of metal (copper/water) and non-metal (titania TiO2/water) nanofluids. Sodium lauryl sulphate was used as dispersant. Copper-based nanofluids showed more thermal conductivity than TiO2. The stability of metal nanoparticle was found to be less than non-metal nanoparticles. Friction factor and pressure drop was found to be nearly same for both.

Figure 1 shows the flow of nanofluid through radiator.

Figure 1. Flow diagram showing flow of nanofluid through radiator [11].

Researcher

and base fluid

Hamid

TiO2-water

50 nm 3000–

30, 50 and

–

0.5, 0.7, 1.0, 1.3

2–20 LPM

 A tube with length of 1.25

Maximum factor obtained is 1.29

times that of base fluid

performance

184 Application of Titanium Dioxide

m, inner diameter of 16

mm and outer diameter

of 19 mm

and 1.5% by

volume

24,000

70C

et al. [1]

and ethylene glycol (60:40)

Vakili

TiO2-Ethylene

25 nm 2030, 2960

–

Laminar and

0.5, 1.0 and 1.5

0.5–5.0 LPM

 A vertical copper tube

A maximum of more than

44% convective heat transfer

coefficient is achieved.

Maximum in heat transfer coefficient

is 24.2% for TiO2

nanofluids.

enhancement

enhancement

 in

with a length of 120 cm,

inner diameter of 6 mm

and outer diameter of

8 mm

Turbulent

% by volume

and 3960

et al. [2]

glycol and

water (60:40)

Azmi

TiO2-water

50 nm

–

30, 50 and

Turbulent

 0.5–1.0% by

2–20 LPM

 A tube with inner diameter of 16 mm and

outer diameter of 19 mm

volume

70C

13 nm

et al. [3]

and ethylene glycol (60:40)

Al

O2 and ethylene glycol (60:40)

Wang

TiO2 paraffin wax

(anatase)-

20 nm –

15–65C

–

0–7% by

–

 –

Considerable

latent heat is achieved by

addition of

at around 0.7% by weight

Maximum

in Nusselt number is

about 28.9%

enhancement

nanoparticles

 increase in

weight

et al. [4]

Azmi

TiO2-water

50 nm –

30–80C

 Turbulent

 0.5–1.5% by

3.9–21.15 LPM Copper tube with length

of 1.5 m, inner diameter

of 16 mm and outer

diameter of 19 mm

volume

et al. [5]

and ethylene glycol (60:40)

> Sajadi and

TiO2-water

 30 nm 5000– 30,000

–

Turbulent

 0.05, 0.1, 0.15,

–

Copper tube with inner

Enhancement

transfer coefficient was

about 22%

 in heat

> diameter of 5 mm, length

of 1800 mm and thickness

of 0.675 mm

0.20, and 0.25%

Kazemi [6]

Wei

TiO2 diathermic

 oil

(anatase)-

10 nm –

20–50C

–

0.1–1% by

–

Test tube

Thermal achieved at 50C and 1%

volume 0.136 W/mk

concentration

 is

conductivity

volume

et al. [7] Table 1. TiO2

nanofluids

 used to enhance thermal

performance.

3-water

Nanoparticle

Size

 Reynolds

Temperature

Flow type

Nanoparticle

Flow rates

Experimental

 setup

 Results

concentration

number

range

range

Sandhya et al. [13] used TiO2 water/ethylene glycol base nanofluid in car radiator to check the improvement in cooling performance. Nusselt number showed enhancement by increasing volume flow rate, volume concentration and Reynolds number. By increasing the volumetric flow rate, outlet temperature of the nanofluid also increased. The inlet temperature of nanofluid has slight effect on Nusselt number. Bhimani et al. [14] used TiO2/water nanofluid as a coolant in automobile radiator to study heat transfer enhancement. Chemical treatment is done to avoid agglomeration and sedimentation because of hydrophobic nature to TiO2. Heat transfer coefficient enhanced as the flow rate and volume concentration increased.

According to Newton's law of cooling, heat transfer can be calculated as given by Eq. (7)

$$Q = hA\_s \Delta T = hA\_s (T\_b - T\_s) \tag{7}$$

where h is heat transfer coefficient, As is surface area of tube, Tb is bulk temperature and Ts is tube wall temperature.

Heat transfer rate can be calculated as given by Eq. (8)

$$Q = m\mathbb{C}\Delta T\tag{8}$$

and heat transfer coefficient can be calculated as given by Eq. (9)

$$h\_{\rm exp} = \frac{m\mathbb{C}(T\_{\rm in} - T\_{\rm out})}{nA\_{\rm s}(T\_{\rm b} - T\_{\rm s})} \tag{9}$$

where n is number of tubes.

While Nusselt number can be calculated as given by Eq. (10)

$$N\mu = \frac{h\_{\text{exp}} \times D\_{\text{h}}}{k} \tag{10}$$

Chen and Jia [15] experimentally checked the enhancement in thermal conductivity and convective heat transfer coefficient by using TiO2 nanofluid in automobile radiator. Pump damage due to application of nanofluid is studied by using cavitation corrosion test. Nanofluid showed good corrosion impediment capability under circulation. Hamid et al. [16] did experimental work to find pressure drop by application of TiO2 nanofluid. Increase in pressure drop will lead to higher pump power requirement, which is not desired at all. Experimental findings showed no significant increase in pressure drop. Friction factor decreased at high Reynolds number.

Darcy equation to calculate pressure drop is given by Eq. (11), and to calculate friction factor Eq. (12) can be used as follows:

$$
\Delta P = \frac{f \rho v^2 L}{2D} \tag{11}
$$

$$f = \frac{0.3164}{R\epsilon^{0.25}}\tag{12}$$


Sandhya et al. [13] used TiO

186 Application of Titanium Dioxide

According to Newton

tube wall temperature.

h is heat transfer coefficient,

n is number of tubes.

Eq. (12) can be used as follows:

Heat transfer rate can be calculated as given by Eq. (8)

and heat transfer coefficient can be calculated as given by Eq. (9)

While Nusselt number can be calculated as given by Eq. (10)

where

where

number.

<sup>2</sup> water/ethylene glycol base nanofluid in car radiator to check the

Q ¼ hAsΔT ¼ hAsðTb � TsÞ (7)

Q ¼ mCΔT (8)

2/water nanofluid as a coolant in

Tb is bulk temperature and

<sup>Þ</sup> (9)

<sup>k</sup> (10)

<sup>D</sup> (11)

:<sup>25</sup> (12)

2. Heat transfer coeffi-

Ts is

improvement in cooling performance. Nusselt number showed enhancement by increasing volume flow rate, volume concentration and Reynolds number. By increasing the volumetric flow rate, outlet temperature of the nanofluid also increased. The inlet temperature of nanofluid

automobile radiator to study heat transfer enhancement. Chemical treatment is done to avoid

<sup>s</sup> is surface area of tube,

<sup>h</sup>exp <sup>¼</sup> mCðTin � <sup>T</sup>out<sup>Þ</sup> nA s ð Tb � T s

Chen and Jia [15] experimentally checked the enhancement in thermal conductivity and convective heat transfer coefficient by using TiO2 nanofluid in automobile radiator. Pump damage due to application of nanofluid is studied by using cavitation corrosion test. Nanofluid showed good corrosion impediment capability under circulation. Hamid et al. [16] did experimental work to find pressure drop by application of TiO2 nanofluid. Increase in pressure drop will lead to higher pump power requirement, which is not desired at all. Experimental findings showed no significant increase in pressure drop. Friction factor decreased at high Reynolds

Darcy equation to calculate pressure drop is given by Eq. (11), and to calculate friction factor

Δ P ¼ f ρ v 2 L 2

f ¼ 0 :3164 Re 0

Nu ¼ hexp � D h

's law of cooling, heat transfer can be calculated as given by Eq. (7)

has slight effect on Nusselt number. Bhimani et al. [14] used TiO

agglomeration and sedimentation because of hydrophobic nature to TiO

A

cient enhanced as the flow rate and volume concentration increased.

Heat Transfer Applications of TiO 2 Nanofluids http://dx.doi.org/10.5772/intechopen.68602 187



where ΔP is pressure drop, f is friction factor, ρ is density, v is velocity, L is length and D is diameter.

#### 3.1. Cooling of electronic devices

Researcher

and base

fluid

Rafati

Silica(SiO2)

SiO2

–

 –

Laminar

 0.5, 1.0 and

0.5, 0.75 and

Quadcore processor

(Phenom II X4 965)

1.5% for silica

1 LPM

> 0.1, 0.25 and

0.5% for

titania

0.5, 0.75 and

1.0% for

alumina

particle

size is 14 nm

Al

O2 3 particle

size is 40 nm

TiO2

particle

size is 21 nm

> Table 2. TiO2

nanofluids

 used in radiator and electronic devices.

Alumina

(Al

O2 3) Titania (TiO2)/

water (75%

vol.) and

ethylene glycol

(25%

et al. [17]

Nanoparticle

Size

 Reynolds

Temperature

Flow

Nanoparticle

Flow rates

 Design

Results

Enhancement

using SiC-water and TiO2-

water nanofluids velocity of 6 m/s was 12.43 and

12.77%, respectively.

Twice

convective heat transfer coefficient is found for alumina

with 0.5% volumetric

concentration

1 L/min.

 at flow rate of

enhancement

 in

 with inlet

 in heat flux by

188 Application of Titanium Dioxide

concentration

number

range

type

range

Nowadays cooling of electronic devices is a challenging task because of compactness and high heat dissipation. Different approaches are being used to increase the thermal performance of electronic systems. One of such way is to enhance the thermal performance of coolant being used in the system. Nanofluids have showed better thermal performance than base fluid.

Rafati et al. [17] used three different types of nanofluids as coolant for cooling of microchips. A high conductive thermal paste is used between block and processor's integrated heat spreader. For computer cooling, the selection of nanofluid is based on factors such as better thermal performance, economic aspect and having no chemical and corrosion impact. The highest decrease in temperature was observed for alumina nanofluid, which was about 5.5�C.

Ijam et al. [18] used SiC and TiO2 nanofluids as coolant in electronic devices. Enhancement in thermal conductivity and heat flux is achieved by increasing volume concentration. Pressure drop increases as flow rate is increased, which results in increase in pumping power. Pressure drop for SiC and TiO2 nanofluid increases from 2159.26 and 2170 Pa, respectively, at 0.8% volume fraction to 2319.58 and 2375.07 Pa, respectively, at 4% volume fraction with 2 m/s inlet velocity. Pumping power increased from 0.28 to 5.49 W for SiC and from 0.26 to 5.64 W and for TiO2 with 4% volume fraction when inlet velocity increased from 2 to 6 m/s. Table 2 provides information about different parameters and result obtained in cooling of radiators and electronic devices.
