HEAT EXCHANGE AND FLUID OF REFRIGERANT IN VERTICAL U-TUBE OF THE DIRECT EXPANSION GROUND-SOURCE HEAT PUMPS

摘要

With a vertical U-tube ground heat exchanger serving as a physical model, a mathematic model of distributed parameter is derived using R134a as refrigerants. It is possible to conduct the non-steady performance study of the condensation heat-exchange process, acquiring a time-dependent variation process, such as the liquid/vapor fluid temperature, pressure and heat exchange along the pipe length etc. Based on the modeling results, the conclusions below can be drawn: 1) The convective heat transfer coefficient of refrigerant along the pipe length increases nearly linearly; 2) Although the temperature change smaller, the phase transition is not a fixed temperature one, in which the refrigerant condense; and the higher the mass flow, the more influence the pressure drop is.