Thermodynamic studies on a solar assisted transcritical CO2 based tri-generation system with an ejector for dairy applications

Abstract

A simple thermodynamic analysis is carried out on a novel solar energy based trigeneration system suitable for dairy applications. CO2 is considered as the working fluid for the entire system, in which an ejector replaces the throttle valve. The effect of important design and operating parameters on system performance is obtained. The performance is indicated in terms of overall COP, specific net power output and specific milk flow rate. The ranges of operating parameters are constrained to always produces a net positive power output. Results show that the milk heat exchanger influences the performance strongly. The specific net power output increases as the gas cooler pressure decreases and ambient temperature increases. However, the specific milk flow rate and overall COP are high at higher gas cooler pressure and lower ambient temperature. This shows the need for controlling the gas cooler pressure depending upon requirement of milk flow rate or power output. For the ranges of operating parameters considered, the overall COP of the trigeneration system is found to be around 0.8. Use of work recovery expander in place of ejector increases the overall COP by about 12%. However, when the ejector is replaced with a conventional throttle valve, then the net power output from the system becomes negative. It is expected that this preliminary study is useful in assessing the feasibility of the novel solar energy based CO2 system for dairy plants where there is a simultaneous need for heating, refrigeration and electrical power.