A Study on the Reduction of Throttling Losses in Automotive Air Conditioning Systems Through Expansion Work Recovery

Refrigerant flow control of the vapor compression refrigeration cycle has been largely relied upon throttling devices, such as capillary tubes, short tube orifices and expansion valves. The expansion process through these devices represents an obvious thermodynamic loss that can be mitigated by the application of different solutions such as intracycle evaporative cooling, economizer and ejector cycles or work producing expansion devices. The present paper concentrates on studying the latter, specifically applied for automotive air conditioning systems. A basic thermodynamic model was developed to simulate a vapor compression cycle for automotive air conditioning purposes employing expanders. Data and cycle conception from devices that were successfully tested and reported in the literature are briefly commented. A preliminary study was carried out taking into account some of the several characteristics that are inherent to mobile air conditioning systems, including high rejection temperature. This preliminary study concentrated in the subcritical vapor compression R134a cycle with an expander and a thermostatic expansion valve placed downstream the expander.