**3. Computational fluid dynamics (CFD) in microchannels**

FLUENT, the most widely used Computational Fluid Dynamics (CFD) software package, based on the finite volume method, and was used to run the thermal simulations. Meshes were created, with 117353 elements, together in the fluid and solid domain. In order to simulate a fully developed flow, tubes at the inlet and outlet are selected with a length equals to 10 tube diameters.


**113**

**Figure 5.**

*Top view of heat sink geometry.*

**Figure 4.**

*Heat sink with mesh.*

*Analysis of Liquid Cooling in Microchannels Using Computational Fluid Dynamics (CFD)*

i.A constant inlet mass flow rate condition, ranging from 0.005 to

ii.A constant heat flux 134.839 kW/m2 [22] as the reference is set at the base

*DOI: http://dx.doi.org/10.5772/intechopen.96248*

0.013 kg/s.

wall of the heat sink.

The fluid flow BCs used in the CFD are as follows:

**Table 3.** *Generated grid values.* *Analysis of Liquid Cooling in Microchannels Using Computational Fluid Dynamics (CFD) DOI: http://dx.doi.org/10.5772/intechopen.96248*

The fluid flow BCs used in the CFD are as follows:


**Figure 4.** *Heat sink with mesh.*

*Heat Transfer - Design, Experimentation and Applications*

and outlet ports. The average temperature of the four thermocouples indicates the

FLUENT, the most widely used Computational Fluid Dynamics (CFD) software

package, based on the finite volume method, and was used to run the thermal simulations. Meshes were created, with 117353 elements, together in the fluid and solid domain. In order to simulate a fully developed flow, tubes at the inlet and

Total number of elements 117353 Elements in find domain 77408 Elements in the solid domain 39948

Interior fluid 0.099 Interior solid 0.1176 Minimum fluid 0.207 Minimum solid 0.164 Maximum fluid 0.990 Maximum solid 0.989

experimentally measured base temperature of the heat sink.

outlet are selected with a length equals to 10 tube diameters.

**Properties of cell mesh**

*Microchannel with inlet and exit ports.*

**Figure 3.**

**Orthogonal quality**

**3. Computational fluid dynamics (CFD) in microchannels**

**112**

**Table 3.**

*Generated grid values.*

**Figure 5.** *Top view of heat sink geometry.*

#### **Figure 6.**

*Top view of microchannel showing velocity vector.*

As a basic assumption, a fully developed flow (pressure outlet) is imposed. At all walls, a zero velocity (No-slip condition) boundary condition is applied and simulations are performed until the steady-state value of T base is attained. The generated grid values are tabulated in **Table 3**.

Mesh with three different sizes was generated for the grid independency test. With maximum mesh size of 2 mm (mesh-1), 1 mm (mesh-2) and 0.75 mm (mesh-3) respectively. The change in Average temperature values between (mesh-2) and (mesh-3) is only about 0.4%. So, mesh–2 with a size of 1 mm is used in further simulations. The typical microchannel with final meshing is shown in **Figure 4**. The top view of the heat sink without meshing is shown in **Figure 5**.

Simulations are performed for laminar flow in the channel path of the fabricated heat sink and examined for various conditions. **Figure 6** indicates the top view of the microchannel with the velocity vector showing the fluid flow directions. The direction of the velocity vector indicates the flow of the hybrid coolant from the inlet to the outlet port through the microchannels.

### **4. Various contours of graphene - iron oxide**

The temperature contours of graphene - iron oxide coolant are shown in **Figures 7**–**9** for 0.05 volume %, 0.075 volume %, and 0.1 volume % respectively. These contours represent the temperature distribution all along the length of the channel from inlet to exit port in the X direction. From these contours, it is implicit that the coolant temperature increases as it flows along the length of the channel. From **Figure 9**, it is inferred that more heat is absorbed for 0.1 vol % graphene iron oxide coolant and the base plate temperature of the heat sink was 310.81 K for 0.1 volume fraction of coolant for the flow rate of 0.75 LPM.

#### **4.1 Wall base temperature**

The processor operating temperature (heat sink base temperature) under various flow rates for different coolant concentration is represented in **Figure 10**. It is inferred

**115**

**Figure 9.**

**Figure 7.**

**Figure 8.**

*Analysis of Liquid Cooling in Microchannels Using Computational Fluid Dynamics (CFD)*

*DOI: http://dx.doi.org/10.5772/intechopen.96248*

*Temperature contours for 0.05 volume % graphene-iron oxide.*

*Temperature contours for 0.075 volume % graphene-iron oxide.*

*Temperature contours for 0.1 volume % - graphene-iron oxide.*

*Analysis of Liquid Cooling in Microchannels Using Computational Fluid Dynamics (CFD) DOI: http://dx.doi.org/10.5772/intechopen.96248*


#### **Figure 7.**

*Heat Transfer - Design, Experimentation and Applications*

**114**

**4.1 Wall base temperature**

**Figure 6.**

*Top view of microchannel showing velocity vector.*

generated grid values are tabulated in **Table 3**.

inlet to the outlet port through the microchannels.

**4. Various contours of graphene - iron oxide**

0.1 volume fraction of coolant for the flow rate of 0.75 LPM.

top view of the heat sink without meshing is shown in **Figure 5**.

As a basic assumption, a fully developed flow (pressure outlet) is imposed. At all walls, a zero velocity (No-slip condition) boundary condition is applied and simulations are performed until the steady-state value of T base is attained. The

Mesh with three different sizes was generated for the grid independency test. With maximum mesh size of 2 mm (mesh-1), 1 mm (mesh-2) and 0.75 mm (mesh-3) respectively. The change in Average temperature values between (mesh-2) and (mesh-3) is only about 0.4%. So, mesh–2 with a size of 1 mm is used in further simulations. The typical microchannel with final meshing is shown in **Figure 4**. The

Simulations are performed for laminar flow in the channel path of the fabricated heat sink and examined for various conditions. **Figure 6** indicates the top view of the microchannel with the velocity vector showing the fluid flow directions. The direction of the velocity vector indicates the flow of the hybrid coolant from the

The temperature contours of graphene - iron oxide coolant are shown in **Figures 7**–**9** for 0.05 volume %, 0.075 volume %, and 0.1 volume % respectively. These contours represent the temperature distribution all along the length of the channel from inlet to exit port in the X direction. From these contours, it is implicit that the coolant temperature increases as it flows along the length of the channel. From **Figure 9**, it is inferred that more heat is absorbed for 0.1 vol % graphene iron oxide coolant and the base plate temperature of the heat sink was 310.81 K for

The processor operating temperature (heat sink base temperature) under various flow rates for different coolant concentration is represented in **Figure 10**. It is inferred *Temperature contours for 0.05 volume % graphene-iron oxide.*

#### **Figure 8.**

*Temperature contours for 0.075 volume % graphene-iron oxide.*

#### **Figure 9.**

*Temperature contours for 0.1 volume % - graphene-iron oxide.*

**Figure 10.** *Simulated base temperature versus flow rate - graphene-iron oxide.*

from the graph representing the lowest temperature of 310.01 K for the concentration of 0.1 vol. % graphene-iron oxide system for 0.5 mm fin spacing while for water it is 317.05 K. These hybrid coolants because of their high thermal conductivity are capable of removing more heat when used in microchannels. The percentage reduction in base temperature when using graphene-iron oxide is 1.96%.
