Experimental determination of the boiling heat transfer coefficients of R-134a and R-417a on a smooth copper tube

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Flooded evaporators are widely used as compact cooling units so as to cool liquids. They consist of a shell-and-tube heat exchanger, with the fluid to cool flowing inside the tube bundle and a refrigerant that evaporates over those tubes. Pool boiling on the external surface of the tubes is a very complex process and, therefore, an experimental analysis is required in order to determine the boiling heat transfer coefficients (HTCs). Copper and copper alloys tubes are commonly employed in such heat exchangers, due to their high thermal conductivity and low cost when compared to other materials. On the other hand, refrigeration and air conditioning sectors are undergoing significant changes caused mainly by the necessity of replacing existing refrigerants with more environmentally-friendly ones. This paper reports the work carried out to determine pool boiling HTCs of two HFCs refrigerants, R-134a and R-417A blend on a smooth copper tube with and outer diameter of 18.87 mm, at two saturation temperatures of 10 ºC and 7 ºC. This work has been done experimentally by means of a test rig specifically designed and prepared for the study of these processes. The experimental setup and data acquisition are described, the experimental procedure is explained, the data reduction methodology is detailed and the results are presented and discussed.dc201

Simulation and experimental validation of a helical coil used as condenser in a heat pump for domestic water heating in a tank

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Although the use of helical coils are widely used in engineering applications for heating and cooling production there is little information available about their thermal behavior. The purpose of this work was to simulate the behavior of a helical coil used as condenser in a heat pump for domestic hot water heating in a tank. The simulation was carried out by developing a mathematical model. The mathematical model was implemented in a computer program. The program results were validated against the experimental results obtained by using an experimental set-up. In the paper the mathematical model is detailed, the experimental setup and the experimental procedure are described and the results are presented and discussed.dc201