A theoretical analysis of a solar/fuel-assisted Brayton cycle for cooling purposes

Abstract

This article demonstrates, through a thermodynamic analysis, the advantages of applying the Brayton cycle instead of the widely used Rankine cycle in a solar power generating unit. This is coupled to a vapour compression water chiller with a total cooling capacity of 65 ton refrigeration. Present work shows the benefits of combining solar, desalination, power and cooling disciplines to obtain a reasonably cheap solar cooling system. Hot water leaves a flat plate collector/storage loop at 95°C and is introduced into a flashing chamber. In the Brayton cycle, the generated vapour from the chamber is compressed, heated in a regenerator using turbine exhaust steam and passes to a fuel-fired superheater. The superheated steam at 120 kPa, 400°C expands in a steam turbine coupled directly to the vapour compressor. The net shaft power output drives a separate vapour compression cooling unit. In this theoretical cycle the nonsolar input energy represents 16% of the system total energy requirements with a basic power cycle efficiency of 15.7%. The overall coefficient of performance of this system is comparable to that of a sophisticated, pressurized solar cooling system with suntracking parabolic troughs. Comparison with the fuel-assisted solar steam Rankine power cycle shows that the present cycle requires 21% less fuel per unit power produced, with a 30% reduction in the superheater volume required, and requires 16% instead of 22% nonsolar energy.