Computational study of laminar free convection inside tilting irregular cavity of a batch-type solar collector

Abstract

Batch-type solar collector is a tilt-able water-heating solar-thermal system comprising an isosceles-trapezoidal enclosure housing a circular-cylinder absorber at the bottom wall, insulated side-walls, and flat-top glazing. Free convection of air inside such trapezoidal enclosure is studied numerically by varying the tilt angle of the whole enclosure from 0o-70o. The influence of tilt on the flow field has been demonstrated by plotting the streamlines and isotherms. The present study successfully identifies the importance of enclosure-tilt in quantifying heat-loss between absorber and glazing by developing a computational correlation between Nusselt and Rayleigh as a function of tilt. The correlation trend is non-monotonic over the range of angular Rayleigh numbers numerically experimented with having a peak around angular Rayleigh number 3?105 corresponding to the tilt-angle 30 degrees. The irregular-shaped cavity implies that the heat-transfer correlations already existing for regular-shaped cavities may not be used otherwise they will draw implausible conclusions and this argument identifies the novelty of the present study.