Flow boiling of ammonia in vertical small diameter tubes : Two phase frictional pressure drop results and assessment of prediction methods

Two phase pressure drops were measured for ammonia at a wide range of test conditions in two sizes of vertical mini channels. The test sections were made of stainless steel (AISI 316) tubes with internal diameter of 1.70 mm and 1.224 mm and a uniformly heated length of 245 mm. Experiments were conducted at three saturation temperatures of 23 °C, 33 °C and 43 °C, the heat flux ranging from 15 to 355 kW/m2 and the mass flux ranging from 100 to 500 kg/m2s. The effect of the heat flux, the mass flux, the vapour quality, the saturation temperature and the internal diameter on the two phase pressure drop are presented in this article. Some generalized two phase pressure drop correlations suggested for macro and micro scale channels are examined by comparing them with our experimental data. None of the examined correlations agreed well with the test data. A new correlation (modified form of Tran et al. correlation) is proposed which is able to predict the experimental data with MAD of 16% and 86% of the data is within ±30% range.QC 2012021