Experimental study on forced convective boiling of ammonia-water mixtures in a vertical smooth tube

As part of our work on the absorption solar refrigeration cycle and with the objective of optimizing the efficiency of flat plate solar collectors in the generation phase, an experimental study has been conducted on the forced convective boiling heat transfer of NH₃-H₂O mixtures flowing inside a 6 mm inner diameter vertical smooth tube. Using a water-heated double pipe type generator, the local heat transfer coefficients are measured inside the inner tube for a range of heat flux (8.211-18.521 kW/m²), mass flux (707-2688 kg/m².s), mass flow rate (0.02-0.076 kg/s), and ammonia mass concentration (42%, 55%, and 61%). Three theoretical models are used to predict the boiling heat transfer coefficients. Experimental data were compared with the available correlations. The obtained results confirm the good performance of Mishra et al. and Bennett and Chen's models in predicting the convective boiling heat transfer coefficient of ammonia water mixtures. These models are able to predict the boiling heat transfer data within an accuracy of ±20 %.