Wang, D., Liu, C., and Chen, J., "Research on the Application of Micro-Channel Evaporator in R134a Roof-Top Bus Air Conditioner," SAE Technical Paper 2017-01-0161, 2017, doi:10.4271/2017-01-0161.
This study investigates the cycle performance and potential advantages of the replacement of fin-and-tube evaporator with parallel flow micro-channel evaporator, in R134a roof-top bus air conditioner (AC) system. The heat exchangers for bus AC system are featured by a stringent space height limitation. The configuration of inclined four piece or six piece micro-channel evaporators was proposed to satisfy this space requirement, instead of original two piece fin-and-tube evaporators. Additionally, the individual superheat control method with thermostatic expansive valve (TXV) in each evaporator was adopted to improve refrigerant distribution. Three kinds of micro-channel evaporators were designed and equipped in an 8-m roof-top bus AC system. Except the replacement of evaporators, TXV and connecting pipes, other cycle components were kept same. Comparison experiments were carried out to evaluate the cycle performance with micro-channel evaporator configuration in psychometric calorimeter test facility at rated cooling condition. Experiment results, including R134a refrigerant charge, superheat performance, cooling capacity and system coefficient of performance (COP) were compared between micro-channel evaporator system and fin-and-tube evaporator system. Results show that individual superheat control method improved the superheat distribution uniformity among multiple evaporators, and enhanced the system cooling capacity. Besides, the optimum micro-channel evaporator configuration achieved equal cooling capacity and COP with fin-and-tube evaporators. Furthermore, potential advantages including refrigerant charge reduction, cost saving, system mass reduction, and compact installation were also discussed for the application of micro-channel evaporator in roof-top bus AC system.