ejector, COP, improvement, low GWP, regenerative heat exchanger
Recently the ejection system became more nad more interesting for investigators. The reason for this is, on the one hand, the necessity to apply new low-GWP working fluids, and on the other hand, the necessity to save electric energy required by classic compression refrigeration systems. Ejection system can utilize free renewable or low-grade waste heast as a motive source. Despite all advantages of the ejection systems, such as simple construction, no moving parts, no maintenance operation one of the main disadvantage of these systems is their low efficiency described by coefficient of performance (COP). Improvement of the COP of the system by simple and low-cost method seems to be the natural direction for the investigations. The internal heat transfer by means of the internal heat exchanger which is located at the ejector discharge line/ liquid line may be thought as the most simple and effective approach. In the internal heat exchanger heat taken from the superheated vapour is transferred to the liquid feeding the vapour generator. The vapour superheating at the ejector outlet may be thought as a waste heat so along with condensation heat is transported to the ambient. As an effect of the heat transfer the temperature of this liquid increases. In effect thermal load required by the vapour generator decreases. In the paper the results of calculation for low-GWP refrigerant will be presented. Experimental results obtained from the ejection system operating with low-GWP refrigerant R1234zeE driven by low-grade heat will used for validation. The basic parameters describing heat exchangers, e.g. temperature changes, thermal capacity, pressure losses, heat exchanger effectivenes will be presented and discussed. Finally, the improvement of the COP will be shown. The experiments show that for analysed operating parameters the heat exchanger is able to use the superheating and preheat the liquid for about 20 K. As an effect the COP increase up to 15%.