Parabolic trough CSP modelling and its application to a domestic scale solar air Brayton engine

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2021

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Ross, Ryan

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Abstract

Linear focus concentrated solar power collectors such as parabolic troughs and linear Fresnel collectors are usually relegated to relatively low temperature operation. The large surface area of the receiver suggests a propensity for significant heat losses to occur. Conventional linear focus receivers operate at approximately 350 °C. At these temperatures, it is common to employ the use of Steam Turbines or Organic Rankine Cycles for electricity generation .In this work it is shown that a contemporary parabolic trough linear focus receiver is capable of operating with an outlet temperature of 700 °C –much greater than conventional operation at 350 °C –at a cumulative receiver efficiency of 57 to 62 %. A numerically intensive linear receiver model was successfully developed to model linear focus receivers for practically any combination of dimensions, materials of construction, Heat Transfer Fluids and atmospheric conditions. In this work it was applied to parabolic trough receivers, however, the model may be easily adapted to linear Fresnel reflector collectors or any other newer designs of linear focus collectors. Modifying vehicle turbochargers to operate as small, inexpensive and relatively efficient gas turbines have been discussed in a multitude of papers. Such engines produce power at a domestic or small commercial scale. In this work, a simulation of using a linear focus receiver together with such an engine was investigated. An apparatus was built as a first iteration proof of concept in hybrid operation of a modified turbocharger air gas turbine Brayton Cycle Engine. An off-the-shelf Garrett GT0632SZ turbocharger was used in conjunction with fabricated parabolic trough collectors to preheat air prior to combustion with LPG fuel. Maximum power extraction was 30 W at a calculated air flow rate of 2.63 kg/min, with a single uncovered bare copper receiver parabolic trough providing a temperature gain of up to 39 °C, at a maximum outlet temperature of 133 °C. Complications were experienced due to the diminutive size of the turbocharger and its implied low operating efficiencies, however, it was indeed shown to be possible to extract electricity from a modified vehicle turbocharger. This work challenges the heuristic that linear focus collectors be relegated to low temperature operation. The intensive linear receiver model predicts reasonably efficient operation of contemporary linear receivers at moderate to high temperatures. The cost benefit of linear focus receivers may be leveraged together with the use of more efficient engine designs, such as supercritical CO2, or alternate heat cycles such as gas turbines such that thermal and cost efficiencies, power production and profitability may be maximised

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A dissertation submitted to the Faculty of Engineering and the Built Environment, University of Witwatersrand, in fulfilment of the requirements for the degree of Masters of Science in Engineering, 2021

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