Effect of internal heat leakage on the performance of a high pressure ratio centrifugal compressor

Centrifugal compressors are widely used in compact gas turbines in industrial and military applications where a high pressure ratio in small size is needed. The trend in centrifugal compressor is high pressure ratios and high efficiencies. However, higher pressure ratio increases the temperature difference between upstream flow and downstream flow which leads to a heat leakage from downstream to upstream through the solid parts. This heat leakage negatively affects the performance as well as the reliability of the compressor. In this study the effect of heat leakage through solid impeller and casing on the compressor performance has been studied for different pressure ratios. The compressor performance has been calculated using a three dimensional numerical model. Conjugate Heat Transfer (CHT) method has been used to calculate the temperature in the solid parts. The results show that the internal heat leakage through both the impeller and casing reduces the efficiency by 2.5% and the total pressure ratio by about 0.83 at pressure ratio up to 11. The effect of the internal heat transfer on the compressor performance is more noticeable at pressure ratios higher than 5. Meanwhile, heat transfer inside the solid impeller alone from the hot region to the cool region reduces the maximum impeller temperature while this heat leakage has a small effect on the compressor performance. However, heat leakage inside the casing alone slightly increases the impeller temperature while it strongly affects the compressor performance.