Numerical and experimental studies on plastic solar air-heaters for heating processes

الملخص EN

A theoretical study including the combined convective and radiative heat transfer analysis of a flexible cylindrical type solar air-heater for heating processes is presented.

The solar collector is manufactured from PVC films acting as a black absorber and a transparent cover sealed together along its edges.

The collector is to be blown with a flow of pressurized air.

A computer program is written for calculating the collector thermal and exergy efficiencies.

The contour (line) integral method is applied for predicting the diffuse radiation interchange between the absorber and the cover.

The analysis yields expressions for calculating the configuration factor in case of part-loaded and full-loaded collectors for different lengths and aspect ratios.

Outdoors experimental investigations are carried out on three types of flexible cylindrical solar air-heaters with a single cover as well as double covers with and without a back insulation.

The tests show that the solar air-heater having double covers and a back insulation has the highest efficiency while that of a single cover and without a back insulation has the lowest efficiency.

Moreover, the Nusselt number between the absorber and the heated air is determined experimentally in relation with the Reynolds number.

Comparisons between the experimental data and the theoretical methods for the collector efficiency and the configuration factor demonstrate a good agreement.

In addition of this, the present experimental results of Nusselt number are correlated and compared with a correlation of another authors.