Effect of an electrolyte (MgSO4) on the boiling flow regime and heat transfer for water at low heat flux and low pressure

The effect of doping distilled water with MgSO4 on the boiling flow regime and heat transfer on a vertical surface at low pressures was experimentally determined. The experiments were performed in a sealed 20 mm x 20 mm square cross section, 300 mm long vertical pipe. Two opposing walls were made of copper and the other two walls were made of polycarbonate for flow visualization. The tube was filled to 100 mm and heat was applied at the lower end of one copper wall and cooled at the upper end. The boiling dynamics on the heated copper vertical wall and the resulting two phase flow was visualized using a high speed camera for pure distilled water and 0.1 M, 0.2 M and 0.4 M concentrations of MgSO4. The presence of MgSO4 significantly changed the boiling dynamics, with a suppression of bubble coalescence and a promotion of nucleate boiling. The two phase flow exiting the heated section changed from slug to bubbly with the addition of the MgSO4. There was a significant increase in the heat transfer coefficient with the addition of the MgSO4.