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