Heat transfer coefficients in two-phase flow for mixtures used in solar absorption refrigeration systems

This paper describes the experimental results obtained on the heat transfer in saturated nucleate boiling of refrigerant mixtures used in solar absorption refrigeration systems flowing upward in a uniformly heated vertical tube. The mixtures analysed were water/ammonia, ammonia/lithium nitrate and water/lithium bromide. The concentration range for the water/ammonia was from 38 to 48 wt%, for the ammonia/lithium nitrate was from 38 to 48 wt% and for the water/lithium bromide was from 48 to 58 wt%. It was observed that the average heat transfer coefficients increased for the mixtures with an increase in the quality, the heat flux and the solution concentration. Comparing the values of the average heat transfer coefficients for the three mixtures, it was observed that the highest values were obtained for the ammonia/water mixture.