Experimental investigation on the start-up behaviors of a Joule–Thomson refrigeration system with pressure control

• Start-up behaviors of the J-T refrigeration system with pressure control were explored. • Reducing the pressure control time could accelerate pull-down rate. • Increasing control pressure and expansion valve opening decreases pull-down time. • Reducing compressor speed and R1150 concentration could reduce pull-down time. The excessively high discharge pressure of mixture-based Joule–Thomson (J–T) refrigeration system for low-temperature freezers at the start-up process without active control leads to the reduction of operation reliability of compressors. Start-up characteristics of a J–T refrigeration system with an expansion tank for pressure control were investigated in this study. The binary mixture R1150/R600a was selected as the working fluid, and influences of the control pressure, compressor speed, throttle valve opening, and mixture concentration on the system’s dynamic performances were experimentally explored. Results demonstrated that the discharge pressure could be effectively limited below the compressor’s safety pressure with an expansion tank. Meanwhile, the close relationship between pull-down rate and time of the pressure control phase was associated with the control pressure, compressor speed, throttle valve opening, and mixture concentration. The pull-down rate can be accelerated by increasing the control pressure and throttle valve opening and reducing the compressor speed and the R1150 concentration at the start-up process. The excessively rich R1150 concentration caused the continuous action of the pressure switch and the malfunction of the low-temperature freezing at an acceptable time range. The build-up of the heat recuperation played a significant role in pressure control time and freezing temperature reduction rate.