Experimental study of ammonia flow boiling in a vertical tube bundle: Part 4 – Comparative analysis

Abstract

This paper is the last leg of the previous three papers of the same series with experimental study carried on a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. Three different tube configurations were tested. (1) bare tube (2) with full length solid PVC nonconductive round rod insert (12.7 mm diameter) and (3) 33% cut insert. For the same flow, tubes with rods developed annular flow within the annular portion between the tube and the rod. Source of heat was hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20 °C ≤ Tsat ≤ -2 °C, heat flux range 5 kW m−2 ≤ q˙ ≤ 45 kW m−2 and mass flow rate of 0.008 and 0.015 kg s−1. Tests were conducted for each mass flow rate at four saturation temperature. Two-phase heat transfer coefficient increased with saturation temperature and heat flux for all cases with initial increase and then a drop at the onset of partial dry out. The tube with 33% cut rod exhibited better overall performance. Results were also compared with plate type evaporator data.