Numerical design of a high-flux microchannel solar receiver

Graduation date: 2015This thesis discusses the design of several microchannel solar receiver devices for use in CSP (concentrated solar power) using CFD (computational fluid dynamics) simulations. The goal is to demonstrate that, by taking advantage of the higher heat transfer coefficienct of microchannels, solar receivers can achieve higher efficiency than current receiver technology, reducing the cost of solar thermal power. Design using CFD simulations is necessary in order to estimate the performance of different designs and identify potential issues before investing in a real device. The lack of previous research into such devices is most likely due to challenges concerning (a) the manufacturing of microchannels in materials that are suited to the high temperature and stress of the application and (b) the design of a headering system for a large scale implementation. Both supercritical carbon-dioxide and molten salt are used as heat-transfer fluids. The required inlet and outlet temperatures of the fluid are 773 K and 923 K for carbon-dioxide and 573 K and 873 K for molten salt. These values are determined by the CSP application and the properties of the fluids. Designs presented range in size from 1 cm² to 4 cm² and in heat transfer rates from 200 W to 400 W. These values are determined by the capacity of the solar simulator, which will be used for testing. For carbon-dioxide, three designs are developed with varying manufacturability. The high risk design features a circular micro-pin-fin array created using chemical etching and is constructed using diffusion bonding. The low risk design features machined and welded parts and parallel circular channels. The medium risk design features machined and diffusion bonded parts and parallel rectangular channels. For molten salt, two designs are developed: one using parallel rectangular channels and one using a circular pin-fin array. Conjugate CFD simulations of each design are used to evaluate pressure drop, receiver efficiency, and flow distribution. Two- and three-dimensional structural analyses are used to ensure that the devices will withstand the mechanical and thermal stress. An efficiency of 89.7%, pressure drop of 0.2 bar, and structural safety factor of 1.3 was achieved for carbon-dioxide. An efficiency of 92.1%, pressure drop of 0.5 bar, and structural safety factor of 2.5 was achieved for molten salt. The results demonstrate that microchannel devices can withstand the high flux, temperature, and stress of a CSP appliction and have high efficiency. However, additional work is needed before these designs can be implemented on a large scale