Thermal Management Of Turbocharging System With A High Pressure Ratio For IC Engines

Turbocharging is the main method for fuel consumption and emissions reduction and increasing the power density in IC engines.The development trend is toward high pressure ratio turbocharging systems.Compressor reliability,high power consumption and high gas temperature after the compression process are the main problems in developing a high pressure ratio compressor.This thesis focused on thermal management of high pressure ratio turbocharging system and charge air cooler used in an IC engine.In this thesis,a numerical model was employed to study the effects on the performance and impeller temperature by cooling on shroud,diffuser and backplate in a centrifugal compressor.Results showed that shroud cooling has the most significant performance improvement and increases the pressure ratio and efficiency by 4.6% and 1.49%,respectively with 2.4k W cooling power.Diffuser cooling has a minor effect on impeller temperature and compressor performance.Only backplate cooling reduces the impeller temperature.Internal heat leakage was also studied and a noticeable effect was found at pressure ratios higher than 5.Internal heat leakage through solid parts reduces the efficiency by 2.5% and total pressure ratio by 7.5% in high pressure ratios(up to 12).Heat leakage inside the impeller prevents excessive impeller temperature while internal heat transfer in casing significantly degrades the compressor performance.Large eddy simulations were carried out to study the characteristics and vortical motions in flow over different corrugation shapes.It was found that quasi-streamwise vortices initially form on the leeward face by the unification of unsteady and threedimensional recirculation regions.Burst happens through two different mechanisms.Two parallel vortices siphon the retarded flow near the trough to the main flow or two quasistreamwise vortices with different orientations intersect and cancel each other and absorb to the main flow.Burst significantly increases the turbulent energy of the flow and improves the heat transfer and mixing.In this thesis flow distribution by using corrugated channels was studied using a numerical model.Results showed that,employing corrugated channels even with identical friction factors can significantly improve the flow distribution in the header.Better flow distribution improves the total thermal performance in a heat exchanger.Flow distribution improves further using channels with higher friction factors in front of the inlet pipe and channels with smaller friction factors elsewhere.The maximum to minimum velocity ratio and maldistribution parameter reduced from 3.59 to 1.14 using corrugated channels.