Adaptable control approach on a new HFO-R1234yf heat driven jet cooling system

Abstract

The ejector heat driven refrigeration systems are extensively under study nowadays. The current major challenge with such system is how to keep the ultimate ejector performance with the expected variations in the operating conditions. This work takes one step forward towards a full control technique on the single phase ejector cooling cycle using the promising refrigerant HFO-R1234yf utilizing the nozzle exit position (NXP). This is to accommodate all the operating scenarios seeking a continuous ejector critical operation. A prototype of a nominal cooling load of 20 kW was utilized to formulate the control correlations. The impact of the entrained and the motive streams conditions on the ejector performance were investigated and justified based on validated CFD simulations. NXP was found a practical and significant optimization parameter. In addition, a dimensionless form of the NXP was introduced for the sake of extending its effect over a wide range of cooling loads for future studies. Generally, it is recommended to operate at the optimum NXP. The only obstacle is that the condenser pressure has to be equal to the critical backpressure , or less, in order for the critical mode to be guaranteed. Correlations of the entrainment ratio , dimensionless NXP, and the optimum dimensionless NXP as a function of condenser and boiler pressures were derived using regression analysis to keep the required ultimate performance. Moreover, a control and throttling valve with temperature sensor were introduced to bypass some fraction of the ejector outlet flow to the evaporator inlet for the capacity control purposes.