Experimental Investigation on Heat Transfer of CO₂ Solid-Gas Two Phase Flow With Dry Ice Sublimation

From the viewpoint of protecting the ozone layer and preventing global warming, there is now strong demand for science and technology based on ecologically safe ‘natural’ working fluids. A CO₂ refrigeration method has been proposed and developed several years ago, using CO₂ solid-gas two phase fluid as refrigerant. Heat transfer of the CO₂ solid-gas two phase flow in a horizontal tube is important to design of such a refrigeration system. In the present paper, an experiment work is conducted to measure its heat transfer characteristics in the horizontal tube. The results show an average value 310 W/(m²-K) of heat convective coefficient is experimentally obtained, which is much higher than that of gas flow. In the sublimation area, the Nusselt number is observed to increase slowly along the tube length, the phenomena may be physically explained that the sublimation process changes the thermal boundary layer thickness; makes the flow turbulence stronger; or changes the flow and the pressure fields.