**3.3 Optimizing the design of heat exchanger for earth to air**

The fluid flow analysis for a different design of earth to air heat exchanger has been evaluated by using the computational fluid dynamic fluent model for the cooling mode of the hot and dry climate of the Bikaner region, the ambient temperature of the Bikaner region is considered 47.6°C for the inlet temperature of optimizing the design of heat exchanger for the earth to air. In this analysis, the


**Table 3.**

**3. Result and discussion**

**Figure 9**.

**Table 2.**

**Figure 9.**

**272**

*Graph of temperature v/s number of grids [11].*

**Minimum size of element (mm)**

**3.1 Grid independence study**

The result of CFD analysis is based upon the number of grid elements or size of meshing. If the number of elements is increased, the computational result quality will be good at a certain limit and if the number of elements is decreased, the computational result quality will be poor. In the present study number of an element is depending on the size of the element, if the size of an element increases the number of an element is decreases and vice versa. For good quality of computational fluid dynamic result, we need to reduce the size of an element. Due to reduce in size the resulting quality will improve at a certain size of an element. After a certain size, the CFD result will be constant. Performance of computational fluid dynamic evaluation at the specific variety of detail is called grid independence. For the heat exchanger for the earth-to-air model, the grid independence study has been executed with an exceptional quantity of mesh elements is shown in **Table 2** and

The maximum and minimum detail size 0.15 and 0.011 is a stander heat exchanger for earth to air model. This size of an element is further utilized for the

0.11 1.5 93,750 31.36 0.0275 0.375 16,98,836 32.38 0.0157 0.214 49,54,034 32.17 0.0129 0.176 72,11,741 32.14 0.011 0.15 94,92,039 32.12 0.0095 0.13 1,22,92,650 32.12

**Number of element**

**Outlet temperature of EATHE (°C)**

earth air tunnel model optimization of the design.

*Heat Transfer - Design, Experimentation and Applications*

*Grid independence study with different number of mesh element.*

**Maximum size of element (mm)**

*Physical and thermal parameters used in validation [3].*

**Figure 10.** *Graph of temperature v/s length of EATHE [8].* simulation of optimizing the design heat exchanger for the earth to air has been carried out to for finding the temperature of air under the steady-state conditions by keeping the soil around the pipe of the heat exchanger for the earth to air at a constant temperature of 300°K. The fluid flow analysis of optimizing the design heat exchanger for the earth to air system has been considered the outer surface of the soil thickness with 200 mm which is fourth times the diameter of the heat exchanger for the earth to air pipe. The solution of the governing equation shows the temperature profile of fluid which is air with different pipe designs of heat exchanger for the earth to air. Different design of heat exchanger for the earth to air pipe like straight pipe, spiral pipe, and a helical pipe has been selected for analysis. This all types of heat exchanger for the earth to air has been carried out for finding the thermal performance of heat exchanger for the earth to air and find out the optimum design of heat exchanger for the earth to air. The analysis has been performed for hot and dry climate of Bikaner where maximum outdoor temperature was found as 47.6°C and was taken as inlet design temperature for heat exchanger. The various material properties like thermal conductivity, density, and specific heat capacity are used for different types of pipe material is used in simulation which is shown in **Table 4**.
