Thermal And Physical Avior Of A Dish/Stirling System Analysis

A mathematical model which is investigated the thermal and physical behavior of a dish/Stirling system is presented, then the system was designed, analyzed and optimized. There are many types of heat losses in the dish/Stirling system, such as convection and conduction heat losses and radiation heat losses by emission in the cavity receiver and reflection heat loss of solar energy in the parabolic dish. There are also internal and external conduction heat losses, energy dissipation by pressure drops and energy losses by shuttle effect in displacer piston in the Stirling engine. All of these heat losses in the parabolic dish, cavity receiver and Stirling engine were calculated using mathematical modeling using MatlabTM software. For validation
This energy is transferred to a solar receiver which it absorbs and conveys this thermal energy to the Stirling engine. In this system, the parabolic dish uses a two-axis tracking system to maintain a zero incidence angle. The cavity receiver in dish/Stirling systems is responsible for absorbing solar radiation reflected by the concentrator and transferring this energy as heat to the working fluid. The most efficient receivers for this system are cavity receivers with a small aperture through which concentrates entered sunlight. The absorber is placed behind the aperture to reduce the intensity of concentrated solar flux. The isolated cavity between the aperture and absorber reduces the amount of heat loss. Increasing receiver aperture will increase the concentrated sunlight. On the other hand, it also increases radiation and convection losses. Consequently, there is a trade-off between the effect of input heat to the receiver and heat losses.
In a solar dish/Stirling systems, Stirling engine has an important contribution in the whole system. High efficiency, high power density, low maintenance operation and the potential for long-term use make the Stirling engines the most preferred engines for these solar systems. An elementary Stirling engine is comprised of a compression piston, an expansion piston, and three heat exchangers: a cooler, a heater and a
[9] proposed a new design of Stirling engine. Popescu et al. [10] worked on improving the non-adiabatic regenerator in order to increase the performance of the engine. Kongtragool and Wongwises [11] presented a literature review on the technology of low temperature differential Stirling engines and use of Stirling engines in solar power systems. Martini [12] has identified several heat losses, such as dissipation by pressure drop, conduction losses in the heat exchangers, and some other dissipation by gas spring hysteresis. Urieli and Berchowitz [13] have developed a quasi-steady model. In this model, they only focused on the pressure drop in the heat exchangers. Kongtragool and Wongwises [14] worked on the effect of regenerator efficiency on the input heat and engine efficiency. Tlili and Timoumi [15] have proposed a novel design of Stirling engine. Their design was very helpful for use of Stirling engine in solar systems. Tlili and Timoumi [16] have also presented an optimization based on a model which is used to determine all of heat losses which occurs in different parts of the