Thermal improvement of solar hot water system using accelerated riser in flat plate collector

الملخص EN

This study includes a comparison between the performances of two locally fabricated similar flat plate solar collectors.

One of these collectors is a new design of accelerated absorber, its risers are of converging ducts (the exit area is half that at the entrance).

The other collector is of conventional absorber (its risers have the same cross sectional area along its length).

Each collector is the major part of an indirect thermosyphon circulation solar hot water system facing the south with a fixed tilt angle of 33.3 o from the horizontal.

A side by side experiments are conducted for three months 1,2, & 3 of 2009 for different water withdrawal profiles, continuous, interrupted and no load, also for horizontal and vertical storage tank orientations.

Two types of storage tanks are investigated (two concentric cylinders and helically coiled tube in cylinder).

Results show that a considerable enhancement of thermal performance approximately (60 %) of absorbed heat (useful gain) at solar noon is obtained for the new design in comparison with the conventional type.

The instantaneous efficiency was 31.5 % for the accelerated absorbed flat plate at solar noon, while that of conventional absorber was (16.5 %).

The longitudinal water temperature variations in the risers of accelerated absorber were larger than that belong to the conventional absorber.

The stratification in the storage tank is considerably improved for the solar hot water system with the new absorber design in which the maximum temperature indicated was 50 oC (vertical storage tank) while that for conventional absorber was 37 oC.

The stratification obtained for coiled tube in cylinder storage tank indicates a good thermal performance with less space requirements.

Also the circulation rate in the accelerated absorber was higher when it is connected to coiled tube than that when it is connected to the concentric cylinders.