Influence de la position et de l'orientation d'un système de brumisation sur l'efficacité d'un échangeur de chaleur

Abstract

4th International Conference on Contemporary Problems of Thermal Engineering (CPOTE), Katowice, POL, 14-/09/2016 - 16/09/2016International audienceSpraying water in the upstream air flow of a heat exchanger improves the heat transfer. Two effects are part of this phenomenon: the spray evaporation that decreases the air temperature by adiabatic cooling and the spray impingement on the heat exchanger surface that increases the heat exchanger coefficient. In general, those effects don't apply on the entire heat exchanger surface. So, an experimental study has been carried out in order to compare the influence of several positions and orientations of water spraying on the efficiency of heat transfer. A pilot has been built allowing moving easily the atomizer injecting droplets in air while controlling flow rates, temperatures and humidity. Among the experimental conditions, it has been chosen a low pressure atomizer that produces a hollow cone spray. This choice has been done to keep in the meantime a good atomization (Sauter mean diameter of 50 µm), a low pressure (5 bar) and low water consumption (1 L/h). For each configuration tested, a global and a local study of the system have been made. The global study consists in an overall energy balance. Until now, the best overall energy balance reveals an increase of the heat transfer of 10% for a water flow rate injected of 1 L/h with a heat exchanger power of 5 kW. The local study consists, on one hand, in an energy balance on a pass of the heat exchanger and, on another hand, on the characterization of the impacted surface. The energy balance is based on the microchannels temperatures of the heat exchanger pass. The impacted surface is characterized by the local cooling in the downstream flow of the heat exchanger and a qualitative measure with an infrared camera. With all these results, an optimization of the system has been done and gave the best position and orientation of the atomizer to obtain the maximal heat transfer