Session: 19-02: Symposium to Honor Professor Jane Davidson II

Paper Number: 156619

156619 - Low-Cost Thermally Enhanced Board to Mitigate Hot Spots in Large Scale Concentrated Solar Receivers 

Abstract: 

Concentrated solar power (CSP) using gas or solid particle heat transfer media holds promise for meeting CSP cost targets set by the Department of Energy because it improves solar power plant efficiency at incremental cost. To support solid heat transfer media (e.g., sand or ceramics), falling particle receivers are under development. Falling particle receivers increase receiver efficiency because they directly irradiate the heat transfer media to enable operation at higher temperatures than in conventional designs. Obstructed flow falling particle receivers hold out particular promise because they heat particles in a single pass and reduce particle loss from convection currents.  One challenge facing falling particle receivers in particular but also other receiver archetypes is the formation of hot spots on receiver surfaces due to non-uniform solar fluxes or variability of the flux distribution during operation.  Hot spots can lead to immediate and catastrophic receiver failure.  They also increase thermal losses and accelerate material fatigue.

In this study, we evaluate heat pipes as an approach to distribute concentrated solar process heat in a solar receiver application.  Heat pipes operate using liquid-vapor phase transitions in which rapid heat transfer is possible.  Thermal energy enters the heat pipe via evaporation of a working fluid.  The energy is transported in the vapor phase of the working fluid and exits the heat pipe when the vapor condenses back to a liquid.  When the working fluid is pure sodium, the heat pipe can operate over a large temperature range from 400°C to 1,100°C . In this temperature range, traditional heat transport methods and materials are not suitable, whereas sodium heat pipes provide robust, high power transport over a relatively small temperature difference.  They have been employed commercially to provide temperature uniformity heat transfer at high-temperatures.

To evaluate the performance of the sodium heat pipes to mitigate hot spots on a receiver surface, temperature distributions on two stainless steel (304SS) boards were measured when exposed to concentrated solar thermal input in the solar furnace located on the campus of Valparaiso University.  On the back of one board, we welded heat pipes fabricated from square tube steel stock; we call this board a constant conductance heat pipe thermally enhanced board (CCHP TEB).  No modifications were made to the other steel board.  The temperatures of the two boards were measured by both K-type thermocouples and an Optris PI 1M thermal imaging camera.  At the same nominal power input, 0.93 kW, the CCHP TEB was shown to have lower, more uniform temperatures than the plain stainless steel board. The maximum temperature of the CCHP TEB was 590 °C, compared to 719°C for the plain board. To reach a comparable maximum temperature with the CCHP TEB, a much higher solar input of 1.57 kW was required.

Presenting Author: Luke Venstrom Valparaiso University

Presenting Author Biography: Dr. Luke Venstrom is an Associate Professor of Mechanical Engineering and the Paul H. Brandt Professor of Engineering at Valparaiso University where he co-directs the James S. Markiwiecz Solar Energy Research Facility, home to the only solar furnace at a primarily undergraduate engineering college. He is a graduate of Valparaiso University (B.S.M.E.) and the University of Minnesota—Twin Cities (M.S.M.E., Ph.D.). His research broadly encompasses the thermal fluid sciences, with a focus on renewable energy systems and, in particular, high-temperature solar thermal and electrothermal chemistry. He was the 2019-2020 Valparaiso University Research Professor and the 2021 recipient of the Award for Excellence in Research and Creative Work for his integration of undergraduate students into cutting-edge, high-temperature concentrated solar energy research.