A new calorimetric facility to investigate radiative-convective heat exchangers for concentrated solar power applications

Abstract

Summary A new calorimetric facility for the aerothermal assessment of radiative‐convective heat exchangers in concentrating solar power applications has been developed and is described in this paper. The configuration of volumetric solar receivers enables concentrated sunlight to be absorbed and conducted within their solid volume, from where it is gradually transferred by forced convection to a heat transfer fluid flowing through their structure. Current design trends towards higher thermal conversion efficiencies have led to the use of complex intricate geometries to maximise temperatures deep inside the structure. The work presented aims to aid these objectives by commissioning a new experimental facility for the fully integrated evaluation of such components. The facility is composed of a high‐flux solar simulator that provides 1.2 kW of radiative power, a radiation homogeniser, inlet and outlet collector modules, and a working section that can accommodate volumetric receivers up to 80 mm × 80 mm in aperture. Irradiance levels and flow field nondimensional governing parameters are highly representative of on‐sun experiments at larger scales. Results from experiments with a siliconised silicon carbide monolithic honeycomb are presented, conducted at realistic conditions of incident radiative power per unit mass flow rate to validate its design point operation. Measurements conducted include absorber solid temperature distributions, air inlet and outlet temperatures, pressure drop, incident heat flux, and overall thermal efficiency. The relative influence of different sources of thermal loss is analysed and discussed.

Homogeneous Flux Distribution in High-Flux Solar Furnaces

“…Experimental results such as those presented in the previous section show that even when the system is completely aligned, the flux distribution tends to decrease rapidly from the centre (in the radial direction), and from the focal point (in the axial direction), significantly decreasing the range of applications for this source of energy. A solution often used to overcome this problem [24][25][26] is to use a multi-mirror homogeniser (Figure 2), to try to obtain a more homogeneous distribution for the flux of energy, as a result of the many reflections that take place inside the homogeniser, that tend to mix the radiation beam.…”

Solar-Driven Thermochemical Water-Splitting by Cerium Oxide: Determination of Operational Conditions in a Directly Irradiated Fixed Bed Reactor

“…The experimental facility is presented in Figure 2 and is composed of a high flux solar simulator (HFSS), a solar reactor and several setup devices and sensors [21]. The HFSS radiation source consists of a 7 kW Xenon arc lamp and an truncated ellipsoidal reflector [22]. The Xenon arc lamp is located at one of the ellipsoid focal points, so that the reflected radiation is concentrated in the second focal point (Figure 3).…”

Computer Modelling of the Optical Behavior of Homogenizers in High-Flux Solar Furnaces

“…The so-called "radiation flux homogenizers" used by some researchers [4][5][6][7][8][9][10][11] are multi-reflective devices (with mirrored sides) designed to reshape the solar radiation flux coming from a concentrator so that, after passing through the homogenizer, the flux becomes as much evenly distributed as possible; i.e., homogenizers are optical devices aiming to increase the homogeneity of the distribution of flux, and they need to be studied in depth, together with other strategies for overcoming the problem of thermal inhomogeneity [12,13].…”