Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8954096 | Experimental Thermal and Fluid Science | 2019 | 40 Pages |
Abstract
This study experimentally investigates the heat transfer characteristics of R134a at supercritical pressures in a 10.3â¯mm horizontal tube to provide basic heat transfer data and heat transfer correlation. The experiments cover wide parameter ranges of pâ¯=â¯1.02-1.2 pc, Gâ¯=â¯400-1500â¯kg/m2â¯s, and qâ³â¯=â¯20-100â¯kW/m2. The influences of the heat flux, the mass flux and the pressure on the wall temperature and heat transfer coefficient are analyzed. The results show that in a horizontal tube, the buoyancy effect due to density variations causes non-uniformity of the wall temperatures in the circumferential direction. The heat transfer deteriorates along the top surface at high qâ³/G (heat flux to mass flux ratio), while the heat transfer along the bottom surface is enhanced at all operating conditions. The pressure mainly affects the heat transfer coefficient on the bottom surface at small qâ³/G because of the cp variation with pressure. Nine heat transfer correlations are evaluated with the results showing that the Dittus-Boelter type correlations with property modifications have acceptable accuracy for the bottom surface but all of the correlations fail to predict the heat transfer coefficients on the top surface. A new correlation using a buoyancy parameter to include the buoyancy effect is then developed to predict the top surface temperatures and a DB type correlation with property modifications is used to predict the bottom surface temperatures. Results show that the new correlations agree well with the data.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
Ran Tian, Dabiao Wang, Yue Zhang, Yuezheng Ma, Hui Li, Lin Shi,