Experimental study of ammonia flow boiling in a vertical tube bundle: Part 1-Enhanced dimple tube

This paper presents the experimental results of saturated two-phase flow ammonia in a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. The tests were conducted for a wide range of parameters. The heat load was provided by hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20 degrees C < Tsat < 2 degrees C, heat flux range 5 kW m- 2 < q < 45 kW m- 2, exit vapor quality range 0.1 < x < 0.9 and a mass flux range of 34.99 kg m- 2 s- 1 < G < 66.32 kg m- 2 s-1. For each saturation temperature, the effects of heat flux and mass flux were studied for the saturated temperature range while the exit vapor quality at each mass flux was varied between 0.2 and 0.9. Two phase heat transfer coefficient increased with saturation temperature and heat flux. For all experimental conditions, performance showed initial increase and then a classic drop at the onset of dry out. The dimple tube showed better heat transfer coefficient compared to the previous studies performed on plain tubes with ammonia.