A review on the thermodynamic optimisation and modelling of the solar thermal Brayton cycle

Abstract

Many studies have been published on the performance and optimisation of the Brayton cycle and solar thermal Brayton cycle showing the potential, merits and challenges of this technology. Solar thermal Brayton systems have potential to be used as power plants in many sun-drenched countries. It can be very competitive in terms of efficiency, cost and environmental impact. When designing a system such as a recuperative Brayton cycle there is always a compromise between allowing effective heat transfer and keeping pressure losses in components small. The high temperatures required in especially the receiver of the system presents a challenge in terms of irreversibilities due to heat loss. In this paper, the authors recommend the use of the total entropy generation minimisation method. This method can be applied for the modelling of a system and can serve as validation when compared with first-law modelling. The authors review various modelling perspectives required to develop an objective function for solar thermal power optimisation, including modelling of the sun as an exergy source, the Gouy-Stodola theorem and turbine modelling.With recommendations, the authors of this paper wish to clarify and simplify the optimisation and modelling of the solar thermal Brayton cycle for future work. The work is applicable to solar thermal studies in general but focuses on the small-scale recuperated solar thermal Brayton cycle.2

The efficiency of an open-cavity tubular solar receiver for a small-scale solar thermal Brayton cycle

“…For this specific open-cavity receiver design coupled with a solar thermal Brayton cycle, an optimum mass flow rate and receiver tube diameter must exist for the system to deliver maximum net power output. The benefit of the receiver investigated in this paper is that it will be a simple, low-cost receiver, since it operates at low pressure [2][3][4][5]. The authors wish to optimise this specific design of receiver.…”

“…The authors wish to optimise this specific design of receiver. The authors are well aware of other receiver designs available from the literature, for example, [11-13, 16, 18, 19, 21-30] and receivers referred to by [5]. However, these receivers often come with added costs and complexity.…”

“…A closed recuperative solar thermal Brayton cycle with helium as working fluid was also studied [10]. The small-scale solar thermal Brayton cycle with recuperator has been thermodynamically optimised in recent work [2][3][4][5].…”

“…The aim of the paper is to propose a method for determining the receiver surface temperatures and receiver efficiencies for various sizes of cavities with different tube diameters. With this method, the entropy generation rate due to such a receiver can be obtained and used to determine the net power output of a solar thermal Brayton cycle [5].…”

“…The recuperator also allows for lower operating pressures in the receiver. The receiver in this paper is a low-pressure receiver as it is to be operated with low-pressure turbomachinery operating between 1.3 and 2.5 times the ambient pressure [2][3][4][5]. According to [6], solarised Brayton microturbines are adapted from the small stationary gas turbine market, which allows for lower costs due to high production quantities in the stationary market.…”