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This paper describes and presents the direct numerical simulation of a volumetric solar receiver under concentrated irradiation. The simulations systematically analyze the receiver performance and thermal loss mechanisms for operating conditions when outlet temperatures are in the 1000–1500 °C range. The implemented numerical method fully considers interactions between radiation, convection, and conduction using a discrete ordinates approach as a radiation model. The power over air mass (POM) and air mass flux were modified for six receiver channels with different cell sizes. The receiver efficiency decreased when the air mass flux increased beyond a certain criterion for constant POM. For a 3.8 mm cell, the receiver efficiency decreased to

This study analyzes the effect of cut-back inlets on the conjugate heat transfer of honeycomb-channel solar receivers. Two-way coupling simulations are reported for a plane-surface inlet, and five kinds of cut-back inlet receivers. The receivers are based on a 1.9-mm × 1.9-mm square cell with a 1.0-mm wall thickness. The cut-back inlet receivers have different amounts of material removed from the walls at the channel inlets. Numerical simulations demonstrate that receivers with a 2.4-mm cut from the channel inlet increased the exit temperature by 20.0 K or more, and decreased the pressure drop relative to the plane-surface receiver. Therefore, the results indicate that the cut-back inlet receiver’s thermal, and hydrodynamic performance is better for industrial use than is the plane-surface receiver. This performance is then explained with detailed examinations of the individual heat-transfer processes in the model. These detailed comparisons indicate that the top cuts reduce shadow effects as light irradiates the channel walls, allowing more direct irradiation to reach the wall surface, thus improving the overall performance.

A loop thermosiphon thermal collector was developed for the waste heat recovery power generation with electric capacity of 500 W. The heat collector with heat transfer area of 0.159 m2 (500 mm width and 300 mm depth) was connected to the condenser with a shrunken heat transfer area by a loop. The thermal performance of the apparatus was declined when increasing the water filling rate to 90% as the working fluid occupied the internal volume. In the range of water filling rate between 30% and 60%, the effective thermal conductivity was around100 times of the conductivity of copper.

This paper describes a volumetric solar receiver that is vertically integrated with beam-down optics for condensed light irradiation. The heat-transfer performance of a silicon carbide honeycomb receiver was investigated using a 30-kW th solar simulator and numerical simulation. The experiments achieved an air temperature of 840 K at the receiver outlet by varying the operational parameters. Numerical simulations were performed for a vertical honeycomb block with beam-down irradiation and a horizontal honeycomb block with tower-type irradiation to elucidate the effects of buoyancy. Three blocks with different sizes were simulated for a variety of operational parameters. When the block was oriented vertically, the flow and temperature fields remained nearly symmetric in and near the receiver. In contrast, when it was oriented horizontally, the flow and temperature became asymmetric, with the hot spot moving toward the receiver's side wall and the stream in the receiver being reversed. The vertical orientation's robustness to buoyancy effects prevented any reduction in the receiver efficiency or outlet temperature and suppressed the thermal leakage.

The point-concentration receiver evaluation system was developed using the world class 30 kWth light source of 19 arc xenon lamps. The system comprises of a receiver unit, heat exchanger, blower, chiller and light source. Precise measurement of the thermal power absorbed by air was performed by the enthalpy rise of the coolant water and that of the exhausted air. The experimental test was performed using silicon carbide honeycomb in order to achieve a high air temperature of 560 °C. The efficiency of the receiver, based on the power of the aperture, was 40% to 80%. A three-dimensional simulation based on the dual cell approach was made to reveal detailed information of the flow and temperature fields. This successfully reproduced the thermal nonequilibrium between the solid and fluid parts of the receiver. The air exit temperature and efficiency of the numerical simulation were consistent with that determined experimentally. Air was suctioned from the broad space above the receiver top surface. The adopted simulation model with the free stream was confirmed to be essential for evaluating an open loop receiver.

Numerical simulation was made for high-temperature solar and thermal receivers of pressurized air for solar micro gas turbine system. The solar / biomass hybrid gas turbine was considered to generate 30kW to 100kW power. The gas turbine system was provided with the concentrated solar light from the dish reflector at the solar receiver and the combustion heat from the biomass synthesis gas at the thermal receiver. Numerical model was developed to the solar receiver and the thermal receiver to reveal their thermal potential. The solar receiver was a close loop concentric annuli to receive highly condensed solar light of 1,000kW/m2. The inner cylinder was made of high-temperature resistance ceramic irradiated by the condensed light on the inner side. The liner was inserted between the inner cylinder and the outer shell. The pressurized air passes the many holes of the liner to impinge the outer surface of the irradiation wall. These impinging jets caused high heat transfer coefficient on the irradiation wall and alleviates the thermal distribution in the receiver aisle. The liner and the outer shell were made by the high temperature resistance INCONEL alloy. The thermal receiver was also a close loop annuli. This uses the same part as the solar receiver and the biomass gas combustor combined to it. The combustor comprises of the liner and the center tube, installed to the inside of the ceramic cylinder. The biomass gas was provided to the gap between liner and the center tube, and the oxidant air to the outer side of the liner. The biomass gas was spouted from the many holes of the liner and mixed with the oxidant air. The resulted hot combustion gas impinged directly to the inner side of the ceramic cylinder. The impingement of the hot combustion gas thinned the thermal boundary layer and enhanced the heat transfer on the ceramic wall. The thermal receiver was designed to attain the preferable heat transfer performance by the inner impinging jet of the hot combustion gas as well as the outer impinging jet of the pressurized air. Three dimensional numerical model was developed to the solar receiver and the thermal receiver considered in the present study using ANSYS FLUENT. Parameter study showed that the exit air from the solar receiver was heated above 1200K or higher presently, and was continued to search better condition and better configuration of the system to obtain higher temperature. The numerical simulation revealed that the distance from the jet nozzle (linear holes) and the heat transfer surface is critical to the thermal distribution. The concept of the new solar and thermal receivers was confirmed on their usefulness; the multiple impinging jet effectively enhanced the heat transfer on the ceramic wall of the solar receiver and the thermal receiver to reduce the thermal inhomogeneity near the heat transfer surface with pressure loss of order 800Pa.

The volumetric solar receiver is a promised technology for high-temperature solar absorption in the concentrated solar power, industrial solar thermal usage and solar fuel production. Existing numerical simulation separated computations of light and convective flow and two-way coupling was not perfectly integrated between radiation and convective transport. This paper describes conjugate analysis of radiation, convection and conduction heat transfer in the volumetric receiver for perfect three-way coupling between three mechanisms of heat transfer. The numerical scheme was used for the volumetric receiver with plane surface and that with cut-back inlets for optimization of the geometry. The simulation was made for single cell of honeycomb with 2.4 mm pitch and 0.5 mm wall thickness. Two cases of surface geometry was computed: plane surface; cut-back inlet with 10 mm depth. Basic equations are momentum and energy equations with radiation transport equation. The discrete ordinates method was applied for solving the radiation intensity to consider perfect interaction between radiation, convection and conduction. The material of the receivers are assumed as stainless steel. The numerical simulation demonstrated the superiority of the cut-back receiver which increased the exit temperature by 30 K and decreased 2 Pa for the smallest beam angle of 10°. The contour plot of total heat flux on the wall revealed that the shadow effect was attenuated by the cut-back inlet leading to heat transfer enhancement. The novelties of this work are to treat perfect interaction between radiation and convection in volumetric receiver and to demonstrate the excellence of cut-back inlet receivers.

In 2014, Niigata University and the Institute of Applied Energy developed a point-concentration receiver-evaluation system using a silicon carbide (SiC) honeycomb and a three-dimensional simulation method. The system includes several improvements over its forerunner, including the ability to increase/decrease the power-on aperture (POA), air-mass flow-rate (AMF) and the height of the focal surface. This paper will focus on the results of tests using an improved receiver evaluation system, at a focal height of 1600 mm. Maximum outlet air temperature reached as high as 800 K, but exerted no untoward effects on the system. Also, receiver efficiency rated between 45 % and 70 %, according to POA. A numerical, 3D method of analysis was created at the same time, in order to analyze temperature and flow-distribution, in detail. This simulation, based on the dual-cell approach, reproduced the thermal non-equilibrium between the solid and fluid domain of the receiver material. The most interesting feature of this s...