Heat transfer characteristics of ammonia during flow boiling in a horizontal small diameter tube.

The heat exchanger with small diameter tubes can always has a higher heat transfer coefficient. In order to characterize the heat transfer of ammonia in heat exchangers, an experimental apparatus was built up to investigate the heat transfer characteristics of ammonia during flow boiling in a horizontal small diameter tube. In this study, the test section is made of an AISI 316L stainless steel tube with internal diameter of 4 mm. The experiments were performed at the saturation temperatures of -5 oC, the mass flux range is from 50 to 100 kg m-2 s-1, and the heat flux range is from 7to 21 kW m-2. The results show that the heat transfer
coefficient increases withvapor quality. And the mass flux and heat flux all have positive effect on the heat transfer coefficient, that is, the heat transfer coefficient increases with the rises of mass flux and heat flux.

小直径管换热器（heat exchanger）通常具有更高的传热系数（heat transfer coefficient）。为表征氨在换热器中的传热特性，搭建了实验装置以研究氨在水平小直径管内流动沸腾（flow boiling）过程中的传热特性。本研究中，测试段采用内径为4 mm的AISI 316L不锈钢管制成。实验在饱和温度-5℃下进行，质量通量（mass flux）范围为50至100 kg m⁻² s⁻¹，热通量（heat flux）范围为7至21 kW m⁻²。结果表明，传热系数随蒸汽干度（vapor quality）增大而升高；质量通量和热通量均对传热系数具有积极影响，即传热系数随质量通量和热通量的增大而升高。