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고정형 Blade의 기계교반식 박막장치에서의 열전달 특성

Heat Transfer Characteristics in the Mechanically Agitated Thin Film Apparatus with Rigidly Fixed Blades

HWAHAK KONGHAK, February 1987, 25(1), 9-18(10), NONE
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Abstract

고정형 blade의 기계교반식 박막장치에서 미소 열전달 면적의 열류계를 사용하며 축방향의 질량 흐름속도, 회전축의 회전속도, blade의 수, clearance 및 유체의 점도에서의 변화에 대한 국부 열전달계수를 얻었다.
본 실험에서 blade의 회전에 의한 국부 열전달계수에서의 변화는 blade의 수와 회전축의 회전속도와의 곱의 0.5승에 비례함으로써 penetration model에 의하여 예측되는 변화율과 같은 결과를 보였다. 그러나, 질량흐름속도, blade의 수, clearance 및 유체의 점도의 변화에 기인되는 것으로 해석되는 액막에서의 난류의 정도에 차이가 있음으로써 penetration model 과 일치하지는 않았다.
본 실험 영역에서의 국부 열전달계수는 penetration model을 축방향의 Reynolds수, clearance 및 blade의 수의 항으로써 보정한 다음과 같은 상관식으로 잘 표현될 수 있었다.
rm N u=0.12(Rer·Pr)0.5it rm·Ref0.164 it·(rm delta over R)-0.124it rm·B-0.423
The local heat transfer coefficient was obtained from the experiment using the heat flux meter of infinitesimal heat transfer area in the mechanically agitated thin film apparatus with rigidly fixed blades. The experimental variables were axial mass flow rate, rotational speed of a shaft, number of blades and viscosity of liquid.
It was shown that the heat transfer coefficient was dependent on the product of the number of blade and the rotational speed of a shaft by 0.5th power. This dependence was same as that predicted by penetration model. However, the results did not coincide with the penetration model due to the different degree of turbulence in liquid film, which was affected by the changes in axial mass flow rate, number of blades, clearance and viscosity.
As a result, the heat transfer coefficient could be described as the penetration model in combination with correction factor including the above effects. The dimensionless correlation equation within the experimental range was represented by
rm N u=0.12(Rer·Pr)^0.5it rm·Ref^0.164 it·(rm delta over R)^-0.124it rm·B^-0.423

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