| Summary: | 碩士 === 國立中山大學 === 機械工程學系 === 87 === R-134a is used as working fluid and air is used as a cooling medium in this study to simulate the heat transfer process in an air-cooling condenser. Plate, Lance and Louver types of externally finned exchangers are used as test sections. The effects of outside heat transfer coefficients, overall heat transfer coefficients and the pressure drop are studied with the experimental data of varing parameters, such as mass flux ,inlet condensation temperatures, inlet quality, cooling air velocity, and temperatures.
Three louvers、one lance and two plate fin condensers with identical tube diameters(DO) 、longitudinal and transverse tube pitches (Pl、Pt) are included in this thesis . Differential spiral angles of micro-fin tubes are tested and analyzed in the same heat transfer tubes and pressure drop characteristics .The results are presented by Colburn j factor and Fanning f factor following with the Reynolds numbers ( ReDc) which are based on the tube collar diameters(Dc ) in the range of 300 to 3000. Experimental data shows that j and f factors decrease when Reynolds numbers increase .
This study not only compares the performance of j and f factors but also the performance of area and volume . The results shows that the performance of louvers are 18o> louver 25o> louver > lance> plate 18o> plate 25o
According to the results of j and f factors , I get the corrections of j and f factors by using the multi-regression method. Besides , the micro-finned tubes are better than smooth tubes. The plate type condenser has the lowest overall heat transfer rate when its pressure drop is the highest . Also, the lance type has the lowest pressure drop. The micro-finned 18o tubes are better than micro-finned 25o tubes of heat transfer tubes . The micro-finned 25o tubes are better than micro-finned 18o tubes of pressure drop.
Heat transfer enhancement factors (EF)，pressure drop penalty factors (PF)，and a performance evaluation index ( PEI ) of micro-finned tubes are also proposed to be compared as fin tubes in this thesis.
Key words: heat transfer enhancement、 mico-fin、condensation
、R-134a、air-cooled condenser、heat exchange
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