Helically coiled solar cavity receiver for micro-scale direct steam generation. (25th February 2021)

• Record Type: Journal Article
• Authors: Swanepoel, Jonathan K.; le Roux, Willem G.; Lexmond, Axel S.; Meyer, Josua P.
• Is Part Of: Applied thermal engineering. Volume 185(2021)
• Publication Date: 2021-02-25
• Subjects: Steam generation -- Solar thermal -- Dish concentrator -- Cavity receiver -- Rankine; Heat engineering -- Periodicals; Heating -- Equipment and supplies -- Periodicals; Periodicals; 621.40205
• DOI: 10.1016/j.applthermaleng.2020.116427
• Languages: English
• ISSNs: 1359-4311

Abstract

Highlights: Naturalistic, micro-scale direct steam generation using a solar dish is considered. A helically coiled cavity receiver and a novel multifaceted solar dish are used. Energy and exergy analysis of the helically coiled cavity receiver is presented. Collector and receiver efficiencies of 42% and 50% were found, respectively. Flow patterns inside the receiver coil were investigated. Abstract: Concentrated solar systems have a large potential for power generation and water pumping in rural off-grid settlements with a high solar irradiance resource. With the use of a solar dish concentrator, superheated steam can be directly generated in a solar cavity receiver. Volumetric expanders show promise for micro-scale power production (below 1 kW). However, naturalistic experimental investigations of micro-scale direct steam generation using a solar dish is limited. In this work, a low-cost helically coiled cavity receiver and a novel solar concentrator manufactured from off-the-shelf components are experimentally investigated for steam generation at water pressures of above 3 bar. Working fluid temperatures were measured throughout the coil length and pressures were measured at the inlet and outlet of the receiver coil. Using a concentrator with a total incident area of 2.70 m 2 and a water flow rate of 0.294 g/s, the working fluid captured 861 W of heat with an outlet temperature of 343 °C at an average solar irradiance of 757 W/m 2 . The average thermal efficiencies of the collector and receiver were determined to be 42% and 50%, respectively, for the testing period. Furthermore, the average second-law efficiency was 12%. Flow patterns within the coil were investigated by considering the temperature differences between the coil surface and the working fluid. A heat loss model was developed that could predict the steady-state heat loss rate with an accuracy of 97%. The observations made during the study and the results obtained highlight important design aspects that need to be considered in future work.