HEAT TRANSFER MEASUREMENTS OF R134a AND PROPANE BOILING ON EVAPORATOR TUBES WITH PLAIN AND ENHANCED FINNED TUBES

摘要

The influence of micro- and macrostructures on the heat transfer coefficient is investigated with propane andrnR134a by boiling at low temperatures on surfaces of different roughnesses and on structured surfaces. First,rnmeasurements of propane boiling on structured steel-tube surfaces within a recently built up apparatus arernpresented and compared to the results of a literature survey on propane and R134a boiling with steel tubes.rnHeat transfer measurements and bubble formation of R134a and propane boiling on plain surfaces withrndifferent roughnesses show good correlations. This applies for a wide range of pressures and differentrnsurface materials, e.g. steel and copper. Therefore propane may be used as a replacement for the refrigerant,rnwhich has a large GWP.rnRecent measurements of both fluids at some enhanced tubes presented in this work, show differences in thernheat transfer. This may be affected by thermo-physical properties of both fluids which are negligible on plainrnsurfaces but are important for tubes that are optimized for special fluids.rnThe influence of the macrostructure on the heat transfer coefficients of R134a and propane boiling on steelrntest tubes using different structures at different regimes of boiling will be discussed for a wide pressurernrange. The heat transfer measurements of the test tubes are carried out in a standard apparatus usingrnelectrical heated mild steel test tubes with plain and enhanced structures. The results of the heat transferrnmeasurements are compared to the results of a literature survey. Also the bubble formation of both fluids willrnbe discussed.