Internally grooved tubes generally used in heat exchangers of Room Air-Conditioner (RAC) andPackage Air-Conditioner (PAC), have been contributed to miniaturize the size and to enhance theperformance. Recently it is becoming hard to enhance heat exchanger performance by the tube shapeimprovements such as deepening the grooves and enlarging the bottom width of grooves. A point ofview in this work is the influence of tube shape changes between before and after tube-expanding atassembling of heat exchangers on heat transfer performance in internally grooved tube. This paperprovides heat transfer coefficient and pressure drop for HCFC-22 condensation and evaporation inplain tube and two kinds of internally grooved tubes with and without the tube-expanding. Heattransfer coefficient and pressure drop for evaporation in test tubes after tube-expanding are higherthan that before it, however those for condensation after tube-expanding are lower than that before it.The collapse of fin tip after tube-expanding is considered to decrease the heat transfer coefficient andthe pressure drop both for condensation and evaporation in internally grooved tubes. The microstructural surface and the axial undulation are taken place on the bottom of grooves. The microstructural surface and the axial undulation are suspected to enhance respectively nuclear boiling andturbulent flow under low refrigerant mass velocity.
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