Abstract
Nanofluids have great potential in a wide range of fields including solar thermal applications, where molten salt nanofluids have shown great potential as a heat transfer fluid (HTF) for use in high temperature solar applications. However, no study has investigated the use of molten salt nanofluids as the HTF in direct absorption solar collector systems (DAC). In this study, a two dimensional CFD model of a direct absorption high temperature molten salt nanofluid concentrating solar receiver has been developed to investigate the effects design and operating variables on receiver performance. It has been found that the Carnot efficiency increases with increasing receiver length, solar concentration, increasing height and decreasing inlet velocity. When coupled to a power generation cycle, it is predicted that total system efficiency can exceed 40% when solar concentrations are greater than 100×. To impart more emphasis on the temperature rise of the receiver, an adjusted Carnot efficiency has been used in conjunction with the upper temperature limit of the nanofluid. The adjusted total efficiency also resulted in a peak efficiency for solar concentration, which decreased with decreasing volume fraction, implying that each receiver configuration has an optimal solar concentration.
Highlights
IntroductionThe overall efficiency of a concentrating solar power system depends on three main factors, the efficiency of the receiver, field efficiency (effective capacity to theoretical capacity) and the Carnot efficiency
The overall efficiency of a concentrating solar power system depends on three main factors, the efficiency of the receiver, field efficiency and the Carnot efficiency
This study aims to address this issue by developing a computational model of a receiver in order to determine an optimal receiver design for direct absorption solar collector systems (DAC) systems using molten solar salt (NaNO3 -KNO3 ) nanofluids as the heat transfer fluid (HTF)
Summary
The overall efficiency of a concentrating solar power system depends on three main factors, the efficiency of the receiver, field efficiency (effective capacity to theoretical capacity) and the Carnot efficiency. With the use of nanofluids both receiver and Carnot efficiencies can be improved [1,2]. Nanofluid heat transfer fluid will have significant impact of thermal storage performance [3,4]. In a conventional solar thermal receiver the solar radiation is directed onto a high-absorptive surface where it is converted to thermal energy [5,6,7,8,9]. The collected thermal energy is transferred to a heat transfer fluid (HTF) to be used in a thermodynamic cycle. These surface based receivers, while being efficient at converting solar to thermal energy, suffer from two major drawbacks at high temperatures.
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