Availability Analysis For Optimizing A Vehicle A/C System

Availability analysis is based on the combination of First and Second Laws of Thermodynamics. Availability is defined as the maximum amount of potential work in relation to the surrounding environment. In the present paper, availability loss method was applied to evaluate a dual-evaporator vehicle air conditioning (A/C) system in order to identify a critical component that had led to the poor system performance. Second Law Efficiency analysis was also used to evaluate a vehicle A/C system at different operating conditions. It was found that A/C systems always display better Second Law Efficiencies at highway running conditions than at other operating conditions. In the calculations provided in this paper, availability analysis identified that a new prototype slimline Thermal Expansion Valve (TXV) in a new A/C system had caused lower Second Law Efficiency as compared with the current block TXV A/C system. Consequently, it was concluded that revisions be made to the slimline TXV for optimal performance. NOMENCLATURE af: specific fluid flow availability A: fluid flow availability Af: flow availability transfer Aq: availability transfer due to heat flow AW: availability transfer due to work interaction ε: Second Law Efficiency h: specific enthalpy I: availability loss q: specific heat transfer rate Q : time average parameter o: dead state (environment ) s: specific entropy T: temperature t: time OSA: outside supply air mode REC: recirculated air mode R/D: receiver and dryer