INVESTIGATION OF SOME PARAMETERS OF A LOW CONCENTRATION EVACUATED TUBE SOLAR COLLECTOR

Resumo

This paper investigates the influence of essential parameters on a low concentration
evacuated tube solar collector in their efficiency. The conventional models of evacuated tube solar
collectors have an absorber tube covered by a glass tube with a vacuum between them. The studied
model collector has an absorbing tube eccentrically positioned inside a glass cover tube which has a
reflective film insert on its inner surface and vacuum in eccentric annular space. The proposed model
is based on the conservation equations of mass, momentum and energy and discretized by using the
finite volumes method. A home-built numerical code is developed to evaluate the desired parameters.
This code is validated against available experimental and numerical results. The influence on the
efficiency of parameters such as absorptivity of the absorber tube, reflectivity of the reflecting surface
and radius of the absorber tube will be evaluated. Effects of the tracking systems in the thermal
efficiency are also evaluated. The results showed that a 20% drop in the absorber’s absorptivity can
generate a 15% reduction in collector efficiency and a 10% drop in reflectivity of the reflecting surface
can lead to a drop of around 4% in the efficiency of the solar collector.