On sun testing of a single spike of the spiky central receiver air preheater (SCRAP)
Date
2020-12
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Concentrating solar power (CSP) provides a significant advantage over other forms of renewable energy due to its high energy potential and low cost. When CSP central receiver technology is implemented in a combined Brayton-Rankine cycle with thermal energy storage (TES), the overall Bray-ton cycle efficiency can be increased, while allowing for dispatchable energy generation at night or during times of reduced solar radiation. The SUNSPOT cycle consists of a solarized Brayton cycle with a rock bed TES facility which powers a bottoming Rankine cycle. The Spiky Central Receiver Air Pre-heater(SCRAP) is the central receiver concept envisaged for implementation in the SUNSPOT cycle’s solarized Brayton cycle. The receiver would need to provide outlet air temperatures of above 800◦C with a total pressure drop of less than 30 kPa in order to satisfy the cumulative Brayton-Rankine cycle demands.This study sought to investigate the thermal characteristics associated with a single spike of the SCRAP receiver. To this end an experimental receiver approximating a full-scale receiver was designed based on suggestions from a previous study. The experimental receiver was installed at the Helio40 facility at the University of Stellenbosch and tested in on-sun conditions. An experimental setup was designed to capture the key variables required to analyze the spike performance. An investigation to characterize the performance of the heliostat field was also conducted.
Through experimental testing, it was found that the irradiation concentration on the spike surface increases exponentially from behind the tip, leading to low irradiation at the front of the spike. It was further found that the exponential growth would cause high heating of the receiver base due to flow separation in the air manifold, limiting the selection of construction materials for a full-scale SCRAP receiver implementation. With an open annulus spike configuration, the receiver was also found to be susceptible to convective losses.Finally, it was found that the coiled fins are effective in increasing the spike’s thermal efficiency by a great margin by virtue of increased heat transfer surface area as well as higher heat transfer coefficients, which result when
the coiled ducts impart a centrifugal force to the air flow, moving the flow closer to the spike wall. The coiled ducts would also be effective in equalizing surface temperature variations caused by uneven circumferential irradiation distributions, mitigating the effects of local hotspots.
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
Description
Thesis (MEng)--Stellenbosch University, 2020.
Keywords
UCTD, Solar energy, Pressurized air receiver, Tubular receiver, Concentrating solar power, Renewable energy