| Summary: | Heat is the most essential form of energy for mankind lives. Steam is the most widely used as heat-carrying medium in the world. The boiler is the best system for the conversion of chemical energy contained in fuels into steam or hot fluid. According to the efficiency of all existing boilers, one of the most important factors that substantially affect this boiler performance index is the stack losses. This research proposed a novel direct-fired porous boiler (DPB). Because of it has no stack losses, this proposed boiler could outperforms all of the existing boilers. The purpose of this article is to discuss the potential of enhancing the suggested DPB performance by using different physical characteristics of packed-bed porous medium (PPM). The experimental results show that among the four most bed shapes available in the market and have a high heat transfer aspect, the hex-nut shape has been selected to use in the proposed DPB. At the heat input rate of about 14 kW, the steam generation rate of about 20 kg/h, (at 1.5 barg and 300 °C), is obtained. Because it has only surface heat loss, thermal efficiency of more than 98% can be achieved. It can be concluded that the possibility of using a hex-nut bed as a packed bed porous medium in a low-pressure porous boiler is confirmed with the proposed boiler.
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