鋳物砂の対向空気流による冷却

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With the increase of the production speed of castings, it becomes important to cool the foundry sand forcedly. In this paper we deal with the cooling effect when the naturally falling sand is cooled by counter air flow. First the following assumptions have been made in working out the theoretical equations for the estimation of the cooling effect. (1) Sand falls separately and at a uniform speed. (2) Each grain of sand is regarded as a sphere which has the same projection area as the sphere itself has. (3) The temperature distribution in the grain of sand may be neglected. (4) Sand consists of dry sand and uniformly wetted sand. (5) The heat of sand is taken away by evaporation of water and heat transfer. Especially when dry sand is cooled, the temperature of sand at the outlet of the cooling tower can be calculated from equation (1) [Written in non-displayable characters.]····(1) [Written in non-displayable characters.], [Written in non-displayable characters.]where c : specific heat (Kcal/Kg°C), ds : mean diameter of the sand (m), t0 : passing time of the sand from inlet to outlet of the cooler (hr), G : weight flow rate (kg/hr), α : coefficient of hea ttransfer (Kcal/m2hr°C), γ : specific weight (Kg/m3), η : cooling effectsubscripts 1, 2 : refers to inlet and outlet of the cooler, a : refers to air, s : refers to sand. If equation (2) which was obtained by Yuge for a sphere is used for fhe coefficient of heat transfer α, the theoretical curve almost coincides with the experimental results. [Written in non-displayable characters.]····(2)where λa : coefficient of heat conduction of air (Kcal/m•hr•°C) Re : Reynolds number for mean diameter of sandAs we can see from equation (1), cooling efficiency η becomes greater with the decrease of φ'. When φ' is greater than 1.0, the maximum value of η is 1/φ', so it is useless to make the length of cooler too long. When sand is wetted, it can be cooled in much shorter time than with dry sand. The cooling process has been solved numerically and analytically from heat transfer equation, heat and mass balance equations and evaporation equation in which the Lewis' law is used. The numerical results considerably coincide with experimental results. Especially on the following conditions, the temperature of the wetted sand at the outlet can be calculated from equation (3). (1) Water content of sand is greater than 0.7% at the outlet and sand is uniformly wetted. (2) The temperature of sand is between 80°C and 40°C. (3) The mean absolute humidity Xm of cooling air in the cooler is less than 2%. [Written in non-displayable characters.]····(3)Where a=0. 000433 b=0.0598 [Written in non-displayable characters.] Ls : heat of vaporization (Kcal/kg) In this case the cooling efficiency η becomes greater with the increase of the temperature Ts1 of sand at the inlet, and the value of φ'=CsGs/ (CaGa) does not affect η very much when the humidity of cooling air is lower than the saturated humidity. As the critical water content of silica sandis about 0.4, 0.7%, it is desirable for the water content at the outlet to be greater than 0.7%. It is practically difficult to separate sand into each grain and get it uniformly wet, therefore η decreases.
Japan Foundry Engineering Societyの論文

鋳物砂の対向空気流による冷却

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Japan Foundry Engineering Society | 論文

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