Performance of plate heat exchangers for evaporation of ammonia

Measurements on a semi-welded plate heat exchanger (PHE) and on various versions of the nickel-brazed PHE were performed in a large experimental refrigeration rig. Experiments were carried out with the refrigerant ammonia, which was completely evaporated in vertical upward flow in PHEs connected in a U-type manner. A multiple linear regression analysis produced three Nusselt number correlations for the different PHEs that can predict the measured Nusselt number decently. The values for the C-coefficient ( in the correlation of the two-phase multiplier) for the higher Reynolds number are somewhat higher than those reported in other investigations. An inlet flow distributor in the semi-welded heat exchanger made it possible to achieve a higher performance at low Delta T-out. The nickel-brazed heat exchanger with an integrated inlet flow distributor was found to have a better performance compared to a nickel-brazed heat exchanger without the flow distributor.