Abstract
The impulse turbo expander (ITE) is employed to replace the throttling valve in the vapor compression refrigeration cycle to improve the system performance. An improved ITE and the corresponding cycle are presented. In the new cycle, the ITE not only acts as an expansion device with work extraction, but also serves as an economizer with vapor injection. An increase of 20% in the isentropic efficiency can be attained for the improved ITE compared with the conventional ITE owing to the reduction of the friction losses of the rotor. The performance of the novel cycle is investigated based on energy and exergy analysis. A correlation of the optimum intermediate pressure in terms of ITE efficiency is developed. The improved ITE cycle increases the exergy efficiency by 1.4%–6.1% over the conventional ITE cycle, 4.6%–8.3% over the economizer cycle and 7.2%–21.6% over the base cycle. Furthermore, the improved ITE cycle is also preferred due to its lower exergy loss.
Highlights
Compression refrigeration and heat pump systems consume a large amount of high-grade energy.On the other hand, hydrochlorofluorocarbons (HCFCs) that are widely used refrigerants at present are Entropy 2014, 16 subject to total phase-out in a scheduled time-frame due to their potential harm to the environment.the probable substitute refrigerants, such as carbon dioxide (CO2) or hydrofluorocarbons (HFCs), are often thermodynamically less efficient compared with the conventional HCFC-based systems
The results show that employments of the conventional impulse turbo expander (ITE), the improved ITE
The performance of the new cycle is investigated based on energy and exergy analysis, and is compared with that of the conventional ITE
Summary
Compression refrigeration and heat pump systems consume a large amount of high-grade energy. Various expander concepts and prototypes have been investigated and developed for the transcritical CO2 refrigeration cycles as well as subcritical refrigeration systems with traditional HCFCs/HFCs as refrigerants, e.g., piston [2,3], rolling/swing piston [4,5,6,7], vane [8,9,10], scroll [11,12,13], and screw [14,15], which have demonstrated the viability of this approach The economizer is another device used to decrease the throttling loss and improve the cycle efficiency.
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