Development of Multi-Layered Type of Gas-to-Gas Heat Exchanger Provided with Self-Insulation Function

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In the academic year 2001, the multi-layered type of gas-to-gas heat exchanger was designed and fabricated, and fundamental data acquisition, development of simulation code, and investigation on effects of key parameters on the total and effective heat recovery rates and the outer wall temperature of the system were conducted. A series of experiments were performed under the conditions of the inlet gas temperature of the high temperature section T_<gho>=400〜600℃, the optical thickness of the porous metal plates τ_0=7.7, the thickness of the demister h=55mm, the walls with and without fins, and the mean working gas velocity u_m=0.15, 0.23m/s for two to five-layered heat exchanger structure. As a result, it has been clarified that, by adding the heat recovery section, the present heat exchanger is effectively insulated and at the same time good heat recovery rates are obtained, and even for T_<gho>=600℃, the total heat recovery rate of about 40% is attained by the five-layered structure. … More Further, a new calculation method for simulating the temperature distributions and 1he heat recovery rates of the system, which applies the spread sheet of Excel to the coupled equations of one-dimensional combined radiation and convection heat transfer, is proposed and is shown effective for practical calculation purposes.In the next academic year 2002, such important subjects as data acquisition under broader conditions, evaluations of heat transfer performance and unsteady state characteristics, and proposition of simple correlation equations were performed. The representative key parameters are T_<gho>= 300〜700℃, τ_0=0〜15.4, positions of the demister, and fin shape. From the experimental and theoretical studies, a lot of valuable findings have been obtained. Namely, the total heat recovery rate increases with the number of layer, the optical thickness of 8 is enough for obtaining sufficient heat recovery rates, fin design with high effective emissivity is required, walls with zigzag fins are effective for increasing heat recovery rates, position of the demister in the system needs to be decided by taking account of the flow conditions of working gas and emission and absorption of radiation energy, the porous metal plates exhibit good unsteady state characteristics and the transient response of the system is dominated by the main body and the walls of the heat exchanger, In addition, concerning the total heat recovery rate, simple correlation equations are proposed for the representative optical thickness of τ_0=0, 7.7. Less