Experimental study of a bubble mode absorption with an inner vapor distributor in a plate heat exchanger-type absorber with NH3-LiNO3

Abstract

Absorption systems are a sustainable solution as solar driven air conditioning devices in places with warm climatic conditions, however, the reliability of these systems must be improved. The absorbing component has a significant effect on the cycle performance, as this process is complex and needs efficient heat exchangers. This paper presents an experimental study of a bubble mode absorption in a plate heat exchanger (PHE)-type absorber with NH3-LiNO3 using a vapor distributor in order to increase the mass transfer at solar cooling operating conditions. The vapor distributor had a diameter of 0.005 m with five perforations distributed uniformly along the tube. Experiments were carried out using a corrugated plate heat exchanger model NB51, with three channels, where the ammonia vapor was injected in a bubble mode into the solution in the central channel. The range of solution concentrations and mass flow rates of the dilute solution were from 35 to 50% weight and 11.69 to 35.46 × 10-3 kg·s-1, respectively. The mass flow rate of ammonia vapor was from 0.79 to 4.92 × 10-3 kg·s-1 and the mass flow rate of cooling water was fixed at 0.31 kg·s-1. The results achieved for the absorbed flux was 0.015 to 0.024 kg m-2·s-1 and the values obtained for the mass transfer coefficient were in the order of 0.036 to 0.059 m·s-1. The solution heat transfer coefficient values were obtained from 0.9 to 1.8 kW·m-2·K-1 under transition conditions and from 0.96 to 3.16 kW·m-2·K-1 at turbulent conditions. Nusselt number correlations were obtained based on experimental data during the absorption process with the NH3-LiNO3 working pair.