• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.4
• /
• pp.642-653
• /
• 1995

An analysis is made of the laminar fluid flow and heat transfer characteristics in a parallel-plate channel to whose walls are fitted with a series of equidistant staggered fins placed transversely to the flow direction. The governing equations are solved numerically by a finite-volume method for elliptic flows. Based on the obtained solutions of flow and temperature fields, the effects of Reynolds number and various geometric parameters on the heat transfer performance and pressure drop are evaluated. A comparson of the heat transfer characteristics between the channels with and without staggered fins is also made.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.3
• /
• pp.271-281
• /
• 1998

In this study, condensation heat transfer experiments were conducted with two small diameter(ø7.5, ø4.0) tubes. Comparison with existing in-tube condensation heat transfer correlations indicated that the correlations overpredict the present data. For example, Akers correlation overpredicts the data upto 104%. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300kg/$m^2$s, the difference was 12%. The pressure drop data of the small diameter tubes ware highly(two to six times) overpredicted by the Lockhart-Martinelli correlation. Subcooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.7
• /
• pp.592-598
• /
• 2002

The characteristics of a pulsating flow field from a heated block representing heat-dissipating electronic component in a channel have been numerically investigated. At the channel inlet a pulsating sinusoidal flow is imposed. The Reynolds number based on the channel height (H) is fixed at Re=500, and the forcing frequency is varied in the range of $0\leqSt\leq2$. Numerical results on the time-dependent flow field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters such as the Strouhal number is investigated in detail. The results indicate that the recirculating flow behind the block is substantially affected by the pulsation frequency. To characterize the periodic vortex shedding due to the inflow pulsation, numerical flow visualizations are carried out.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.7
• /
• pp.599-606
• /
• 2002

uniform temperature. The surfaces of the block are taken at a constant higher temperature. The channel walls are assumed to be adiabatic. Results on the time-dependent temperature field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters, such as the Strouhal number on the flow and the heat transfer is investigated in detail. The results indicate that the recirculating flow behind the block are substantially affected by the pulsation frequency. These, in turn, have a strong influence on the thermal transport from the heated element to the pulsating flow. The frequency at which the enhancement is maximum is determined.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.3 no.4
• /
• pp.215-221
• /
• 1991

Laminar film condensation of a saturated vapor in forced flow over a flat plate is analyzed by using integral method. Laminar condensate film is so thin that the inertia and thermal convection terms in liquid flow can be neglected. Approximate solutions for water are presented and well agreed with the similarity solutions over the wide range of physical parameter, Cp1(Ts-Tw)/Pr.hfg. For the strong condensation case, it is found that magnitude of the interfacial shear stress at the liquid-vapor interphase boundary is approximately equal to the momentum transferred by condensation, i.e., ${\tau}_i{\simeq}\dot{m}(U_O-U_i)$.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.11 no.2
• /
• pp.1-9
• /
• 1982

Friction losses and heat transfer characteristics were studied experimentally for fully developed tubulent flow in tubes with twisted tape swirl generators. Data were obtained for pitch- to-diameter ratios from 8.10 to 25.71 with water under forced convection cool ins conditions. The experimental results of this and that of previous swirl flow investigation by Smithberg and Landis were compared. Nusselt number and friction data are combined in a constant pumping power comparision for swirl and straight flow, which indicates that improvement of 2.0 times in the best performance can be obtained with twisted tape-insert tube. A twisted tape-insert tube is recommended in the case of low temperature difference in heat-exchanger.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.13 no.3
• /
• pp.141-147
• /
• 1984

2차원 채널 입구에서의 꿰떼 난류 유동하는 찬 물 위를, 같은 방향으로 빠르게 난류 유동하는 수증기의 응축은 액체필름 초기상태의 과냉 정도에 의하여서 응축능력이 정하여진다. 수증기와 액체의 채널 입구에서의 균일한 속도 및 온도, 그리고 채널 입구에서 액체와 증기가 차지하는 체적비, 즉 액체필름과 채널 높이를 알고 있을 때, 하류로 유동하면서 응축이 일어나는 현상을 예측하는 모델을 제안하고, 실험치와 비교한 것이다. 채널 입구에서 윗쪽으로는 더운 기체, 아래쪽으로는 찬 액체가 평행한 방향으로 유동하면서 접촉하고 평균적인 액체필름의 두께와 단열된 채널 벽체를 가정하여서, 기본방정식으로 연속방정식, 운동방정식을 세우고. 에너지와 운동량 전달 메카니즘 사이에 유사성이 존재한다고 가정하였으며, 전단응력의 크기는 필자의 모델을 적용하였다. 기본방정식을 기체 속도, 액체 속도, 필름의 두께, 압력에 대해서 수치해를 구하여서 동일조건 하에서 실험한 데이터와 비교하였다. 수증기와 액체 경계면에서의 전단응력은 매우 좋은 일치를 보여주고 있다.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.11 no.2
• /
• pp.10-15
• /
• 1982

An experimental study on the storage tank which uses sensible heat of water is done. The influence of inlet flow rate (Re), the difference between initial temperature and inlet water temperature(Gr) and the location of inlet and outlet on the performance of storage tank is studied. Development of stratification is examined by measuring the transient temperatures of 36 points inside the tank. Measured values are transformed to the dimensionless parameters in order to calculate the temperature efficiency of storage tank. In the presence of combined natural and forced convection, the development of stratification becomes clearer and thus the efficiency becomes higher, as $Gr/Re^2$ increases.

• Journal of computational fluids engineering
• /
• v.20 no.1
• /
• pp.65-76
• /
• 2015

In this study, the natural convection phenomenon of the air side and the forced convection phenomenon of the oil side were simulated in the radiator through a 3-D numerical analysis, and the total heat released by the oil side into the radiator heating plate and then to the air side was evaluated. Also, a quantitative analysis was carried out on the effect of each thermal resistance on the overall heat transfer coefficient through a 1-D thermal circuit analysis on the heat transfer mechanisms of the radiators considered in this study. In addition, for the diverse shapes of the heating plates considered in this study, the pressure drops of the oil side were quantitatively compared and evaluated. The temperatures at the air side and the oil side outlets of the radiators with 8 different fin shapes considered in this study had almost similar values showing a difference of +/-3% and, accordingly, the total heat transfer also showed similar heat dissipation performance in all the models. As a result of the 1-D thermal circuit analysis, in all the models considered in this study, while the thermal resistance of the air side accounted for 92% to 96% of the total, that of the oil side was 5 to 7%, and that of the heating plate showed a very small value of 0.02%.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.34 no.7
• /
• pp.715-720
• /
• 2010

We propose an electroosmosis-based air delivery scheme for polymer electrolyte fuel cells and experimentally investigate its feasibility. An electroosmotic pump under a low-frequency AC electric field is used to displace initially a volume of pump working liquids. This working liquid is then pumped into a space enclosed by a flexible membrane and the movement of the membrane delivers air to a fuel cell. We successfully demonstrated the operation of a forced-convection fuel cell using this technique. In this preliminary study, however, the power consumption of the pump exceeds the power generated by the fuel cell. We conclude this paper with a discussion of several ways to reduce the pump-to-fuel cell power ratio.