Low temperature convector made from polymeric material for heat-pump applications

With a view to reducing the operating temperature of air heaters, a convector consisting of a plate heat-transfer matrix, placed at the bottom of an enclosure acting as a chimney, was designed and tested. An inexpensive polymericmaterial (polypropylene) was selected for the heat-transfer plates to achieve a lightweight low-cost unit. An appropriate computer program was used to optimize the prototype convector and to evaluate the influence of the main geometric and operational parameters: plate spacing and height; chimney height; heat carrier temperature and rate. The performance of the unit subsequently fabricated, measured in a thermostatic test chamber, was in good agreement with the theoretical predictions. As an example, an output of 1.2 kW was obtained for a mean water temperature of 41°C with a convector volume of 0.22 m3, two-thirds of which was occupied by the chimney. The convector exhibited a good thermal output even when fed at very low water rates, thus achieving a thorough cooling of the incoming water. The convector performance could be enhanced by resorting either to higher chimneys or to a mechanical draught. In the latter case, it is shown theoretically that a small fan's power consumption (say 5 W) is sufficient to at least double the natural convection output, provided the heat-transfer matrix is re-optimized.geometric and operational parameters: plate spacing