Numerical analysis of convective and radiative heat losses from trapezoidal cavity receiver in LFR systems

• Heat losses from trapezoidal cavity used in LFR system are considered.
• Both radiative and convective heat losses are analysed numerically.
• Comprehensive correlations are developed for different Nusselt numbers.
• Selection of parameters for the correlations and their form has been analysed.

Solar linear Fresnel reflector (LFR) system is a simple and cost effective technology for heat generation for medium temperature (<400 °C) applications. The system consists of a trapezoidal cavity receiver enclosing the flux absorbing surface. This study is aimed at understanding the coupled convective and radiative heat loss from the trapezoidal cavity receiver. The top wall of the cavity is isothermal, bottom wall is losing heat by convection and others two inclined vertical walls are insulated. Although several studies in heat transfer from such cavities are available, these have been limited emphasis on development of non-dimensional correlations. The development of correlations is important as it leads to wider applicability of the results for design of such cavities. A few correlations developed earlier for such cavities either do not consider all the parameters or have some limitations. In the present work a comprehensive correlation is developed with Grashof number, aspect ratio, geometrical parameter (cavity angle and aspect ratio), radiation-conduction number and external Nusselt number. Special emphasis is given on choosing the correct form of these correlations.