Boiling heat transfer of carbon dioxide in small tubes and simulation of carbon dioxide evaporator

Boiling heat transfer of carbon dioxide flowing inside four horizontal stainless steel tubes (0.7, 1, 2, and 4mm I.D.) are investigated by experiment under the condition of refrigerant quality from 0.1 to 0.9, mass velocity from 360 to 1440kG/m(2)s, and heat flux from 9 to 36 kW/m(2) The heat transfer coefficient correlation is developed within the deviation of +/-30% and the correlation for pressure drop is within the deviation of +/-10%. The potential of using small tubes in carbon dioxide evaporator is further explored. The evaporator with given cooling capacity is numerically simulated and optimized for a series of small tubes. The simulation results demonstrate the striking superiority of reducing contour size by using small diameter tubes in carbon dioxide air coil evaporators.