This study aims to provide an experimental investigation and comparison of the condensation heat transfer characteristics in a plate–fin heat exchanger (PFHE). The heat flux, mass flux, and saturation pressure were adjusted as experimental parameters to verify the effects on the condensation heat transfer. In addition, condensation heat transfer correlation of two-stream PFHEs was provided based on the experimental data for utilization as a design reference for the heat exchanger. The turbulence is the most influential in heat transfer. One of the ways to foster turbulence is to increase shear stress. The higher flow velocity results in the higher shear stress. That was why increasing mass flux or the flow with higher vapor quality showed the higher heat transfer coefficient (HTC). Refrigerant properties such as viscosity and specific volume of vapor changed according to the saturation pressure. It is expected they affect the degree of turbulence too in similar manners. The mass flux was more influential than the heat flux and saturation pressure. Thus, the equivalent mass flux of the refrigerant is dominant in the derived correlation model. The average difference between experimental and calculated HTC from correlations was about 6.5%. Multi-stream PFHE comprises an additional heat transfer surface, which implies a more active droplet formation. The average pressure drop in the multi-stream is 15% larger than that of the two-stream.

In this research, a device for injecting condensate-water generated from the evaporator into the distributor on the top of the condenser was fabricated as a method for improving the efficiency of the portable air conditioner. To compare the efficiency, the condensation temperature, blowout air temperature, power consumption, cooling capacity, and COP of the system were measured. As a result of the experiment, the condensation temperature dropped by about 6.2 °C. Also, the power consumption of the compressor was reduced by about 0.16 kW and the cooling capacity increased by 0.2 kW. As a result, it was confirmed that the COP increased by about 16 % when the condensate-water was sprayed on the condenser.

As the use of semiconductors in industrial site increases, research on ultra-low refrigerators is required to increase the life and quality of the semiconductors. While various types of refrigerators exist, Joule–Thomson refrigeration with the mixed refrigerant is preferred because of its compactness and stability. The performance of Joule–Thomson refrigeration with mixed refrigerants is based on the mixing ratio of the refrigerants. Therefore, in this study, three kinds of refrigerant groups, namely high boiling point (R-600a), middle boiling point (R-23), and low boiling point (R-14), are used to examine the change in the system’s performance according to the composition ratio of each refrigerant. The results indicate that as the ratio of the high boiling point refrigerant increases, the discharge, and suction temperature decrease. As the ratio of the middle boiling point refrigerant increases, the condensation pressure decreases, and thus, the inlet temperature of the expansion valve also decreases. As the ratio of the low boiling point refrigerant increases, the cooling capacity tends to increase.