Modeling and Analysis

Shell and tube heat exchanger with segmental baffles is designed using Kern's method to cool the EGR gas. Mass flow rate of air, fuel and exhaust gas temperature are measured for different load conditions of single cylinder DI diesel engine. The shell and tube heat exchanger with segmental baffles and helical baffles are modeled using 3D modeling software. The surfaces near the wall are meshed with fine mesh. For volume mesh tetrahedral mesh type is used. Appropriate boundary conditions are given to the model by choosing mass flow inlet for water and Gas, pressure outlet for both water and gas in the EGR cooler and coupled heat transfer in wall boundaries. For each helical and segmental baffle the percentage of EGR flow rate is varied from 14% to 20% of the exhaust gas. Assumptions are made by considering it as steady state flow, fluids at mean temperature and neglecting the leakage due to the gap between the tube and baffles.

Figure showing the Temperature profile on the shell side for segment Baffles

Conclusion

CFD analysis was done to examine the flow as well as heat transfer for different cases of the EGR flow rate varying from 14% to 20% of the exhaust gas. For each case temperature at different planes was plotted and comparison was done to determine the deviation in the values of heat transfer coefficient and pressure drop from Kern's modeling to CFD analysis. The predicted shell side heat transfer coefficient and shell side pressure drop shows good agreement with analytical results for Shell and tube heat exchanger with segmental baffles. The predictions shows accurate trend for change in EGR flow rates. The shell side pressure drop for heat exchanger with helical baffle is lower than the heat exchanger with segmental baffles. The flow in the shell side of the heat exchanger with conventional segmental baffles has dead zones because the fluid impacts right onto the wall perpendicularly. The flow in the shell side of the heat exchanger with helical baffles is smooth, rotational and helical due to the shape of the baffle, which results in decrease in pressure drop.