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Purpose This paper aims to deal with characterisation of the thermal performance of a hybrid tubular and cavity solar thermal receiver. Design/methodology/approach The coupled optical-flow-thermal analysis is carried out on the proposed receiver design. Modelling is performed in two and three dimensions for estimating heat loss by natural convection for an upward-facing cavity. Heat loss obtained in two dimensions by solving coupled continuity, momentum and energy equation inside the cavity domain is compared with the loss obtained using an established Nusselt number correlation for realistic receiver performance prediction. Findings It is found that radiation emission from a heated cavity wall to the ambient is the dominant mode of heat loss from the receiver. The findings recommend that fluid flow path must be designed adjacent to the surface exposed to irradiation of concentrated flux to limit conduction heat loss. Research limitations/implications On-sun experimental tests need to be performed to validate the numerical study. Practical implications Numerical analysis of receivers provides guidelines for effective and efficient solar thermal receiver design. Social implications Pressurised air receivers designed from this method can be integrated with Brayton cycles using air or supercritical carbon-dioxide to run a turbine generating electricity using a solar heat source. Originality/value The present paper proposes a novel method for coupling the flux map from ray-tracing analysis and using it as a heat flux boundary condition for performing coupled flow and heat transfer analysis. This is achieved using affine transformation implemented using extrusion coupling tool from COMSOL Multiphysics software package. Cavity surface natural convection heat transfer coefficient is obtained locally based on the surface temperature distribution.

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