Abstract
Two convectors for space heating, designed for low-temperature operation, were built and tested. Both convectors consisted of an extended surface heating element placed at the bottom of an enclosure acting as a chimney. The first one was intended for an almost isothermal operation while the second one allowed an important cooling of the heating medium. A computer program was employed to optimize the heaters' geometry. Fin efficiency was found not to be accurately predicted by ordinary relationships in the case of unusual fin geometries: a finite difference analysis was employed as a more satisfactory computation tool. Tests were performed in a thermostatic test chamber and gave results in good agreement with the theoretical predictions. Owing to the influence of air temperature around the heater on chimney draft, ambient air temperature distribution is to be taken into account in the theoretical model in order to obtain accurate results. Both heaters tested gave a considerably better output than ordinary heaters of similar dimensions and working at the same temperature. In order to increase the heat delivery, one of the heaters was modified to accommodate a small fan. Even for extremely low electric power input, assuring a totally noise-free operation, a sizeable improvement of thermal power output was observed.
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