Experimental study on bubble group and the distribution uniformity of temperature difference field in direct contact heat transfer process

Continuous phase circulation flow and continuous heating in the direct contact heat exchanger to maintain a constant heat source inside the evaporator. A new metric, the bubble-averaged area, is proposed for evaluating the local bubble size in direct contact heat exchangers. The bubble average area is defined as the average area of the total number of bubbles in the instantaneous image. The characteristics of the bubble population and distribution uniformity in direct contact boiling heat exchange were compared for two scenarios: continuous phase stationary with an unconstant heat source in the evaporator and continuous phase circulating and flowing with a constant heat source in the evaporator. The results show that under the same experimental conditions, the continuous phase cyclic flow leads to an increase in the number of bubbles, a tendency for the average area of bubbles to increase and a significant increase in the uniformity of bubble distribution. Simultaneously, the disturbance caused by the two-phase mixing results in an increased uniformity in the temperature difference field, which is beneficial for enhancing the heat transfer performance of the heat exchanger. Among them, the initial temperature difference and the flow rate ratio have a greater influence on the temperature difference field uniformity. This study presents a method for investigating the bubble characteristics and temperature difference field uniformity in direct contact heat transfer with continuous phase circulation flow, which facilitates a comprehensive understanding of the synergistic relationship between two-phase mixing efficiency and heat transfer process.