OCR Text |
Show Because the surface combustor-heater combines the combustor and the heat exchanger in a unit, the entire system can be compact and, therefore, low in cost. The overall energy conversion from fuel combustion to the working fluid can be accomplished in a very high density. Preliminary proof-of-concept tests conducted in the U.S.S.R and the U.S.A. demonstrated excellent performance, such as high combustion intensity, high heat-transfer rates, and low combustion emissions. 1-4 However, the fundamental heat-transfer processes and the interaction with combustion in the surface combustor-heater system are not fully understood. In addition, the potential for further reduction of emissions, enhancement of heat transfer, and design optimization of this device for applications have not been investigated yet. A thorough theoretical analysis and parametric experimental study are being conducted to explore the mechanism of combined convective-radiative heat transfer in conjunction with combustion in the porous matrix combustor-heater, and these will develop extensive data and a computer program for optimizing the design and unit scale-up. This paper presents the experimental approach and some results obtained from the parametric study. EXPERIMENTAL APPROACH The purpose of the experimental study is to evaluate the performance of a bench-scale surface combustor-heater and to explore the mechanism of the interactive combustion/heattransfer process within the porous matrix. The extensive data obtained from the parametric study will be used for verification and validation of the mathematical model as well as for optimizing the design of a commercial prototype. Surface Combustor-Heater Test Unit The firing capacity of the bench-scale surface combustor-heater test unit was determined to be 60 kW. The combustor-heater unit consists of six segments connected together by flanges: • Natural gas/combustion air mixture plenum • Water-cooled distribution grate • Combustor-heater section • Measuring section • Exhaust plenum • Exhaust stack. The mixture of natural gas and combustion air is brought into the unit by a 1-1/4 inch pipe and mixture plenum. The distribution of the mixture is provided by the water-cooled grate equipped with specially designed distribution nozzles. The cooling water is channeled through the double-wall grate in such a way that the body of each nozzle is evenly cooled. In addition, each nozzle contains a cooling rod that is attached to the cap of the nozzle on one side and exposed to the cooling water on the other side. This arrangement assures additional cooling of the caps of the nozzles. The grate assembly is attached to the support frame in a way so that the distance between the first row of cooling tubes and the top of the distribution nozzles can be adjusted. The cooled grate sustains the flame above the grate and prevents the risk of flashback. 3 |