Air heating in a steady hemispherical concentrating system for various applications

This publication deals with the heating of air in a fixed hemispherical concentrating system. It differs from other systems that heat first a black plate with fins or not, and then the heat is recovered from the plate with a fluid by convection. The device that we propose uses the sunspot corresponding to the actual image of the sun formed in the focus of a hemispherical concentrator which by effect of concentration, generates a very hot zone. The heat from that zone can be directly transmitted to the circulating air. The recovery zone was gradually reduced to strips (or bands) by 4 mm mirrors to reduce the amount of air to be heated by the spot. There is no receiver to dispose, rather the assumption is made that recuperation of air directly from the sun-spot is more efficient than air-plate convection. The results obtained lead to the following observations: The more bands we have, the higher the temperature of the bands, allowing to suppose that the temperature can still rise with the increase of the number of bands. The bands take the maximum value in turn, indicating the position of the hot spot. The shape of the temperature curves follows the pace of the daily irradiation. By way of example, for a division of the 4-band concentration zone, temperatures in the hottest band are obtained which range from 44°C at 9h 36 min and rise to 102°C at 13 h 35 min, then go down to 60° C at 15h 36min. The maximum irradiation value of the day is 830 W/m2 for the day of March 16, 2016. The main advantage of such a system is that it produces warmer air, without any sun tracking system, and is even better than natural convection systems.