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Characteristics of natural convective heat transfer in a vertical minichannel with two grooves
김은필 한국마린엔지니어링학회 2019 한국마린엔지니어링학회지 Vol.43 No.8
The heat transfer characteristics were investigated in a vertical minichannel with two grooves. The wall geometry of the minichannel possessed grooves with several modified groove ratios. To determine the effects of natural convective heat transfer, the finite volume numerical method was used. The results showed that when d/D = 0.1 and d/D = 0.25, there was no flow separation. When d/D = 0.4, however, there was flow separations at both walls. For the left wall, the local Nusselt number decreased dramatically starting at the leading edge. For the case of two grooves, there were four flow separations at d/D = 0.5. The heat transfer patterns were similar to the single-groove case. However, at the end-section of the first groove, the temperatures dispersed downstream. These heat transfer characteristics corresponded to the flow field. When there was a 1-mm distance between the grooves, the Nusselt number showed a larger variation compared to the other cases. When the channel pitch was 3 mm, the distance between the grooves was not a large factor after a 2-mm groove distance was reached.
김은필,정석권,민경현,김재돌,윤정인,Kim, Eun-Pi,Jeong, Seok-Kwon,Min, Kyung-Hyun,Kim, Jae-Dol,Yoon, Jung-In 한국마린엔지니어링학회 2004 한국마린엔지니어링학회지 Vol.28 No.7
The experiment of thermal performance about cross flow type cooling tower was conducted in this study. Generally the ambient air condition can affect the thermal performance of cooling tower to improve or not. However it is hard to control the cooling water temperature that we want under bad air condition or during rainy season. In this paper, the effect of variables, which the ambient air have. especially wet-bulb temperature, are experimentally investigated for controlling the cooling water temperature more successfully. The result is that there is appropriate air flow rate in respective air condition to preserve the cooling performance in the cooling tower and the maximum air flow rate can't overcome the approach under bad air condition.
김은필 한국마린엔지니어링학회 2000 한국마린엔지니어링학회지 Vol.24 No.5
A finite element method is applied to investigate the characteristics of the fluid flow and heat transfer performance in a channel in terms of the various effects of baffle cuts, baffle angles, and leakages. The results show that the decrease of a baffle cut gives a good heat transfer enhancement. However, it also increases pressure drop. In the case of an inclined baffle, the result shows that the pressure drop decreases with a reasonable heat transfer performance. But a steeply inclined baffle gives adverse effects on the performance of the channel. The clearances between baffle-to-shell and tube-to-baffle affect the overall performance. The effects of these parameters are discussed in details.
3차 B-spline 함수를 이용한 열전도 및 유체문제의 해석
김은필,Kim, Eun-Pil 한국전산유체공학회 1998 한국전산유체공학회지 Vol.3 No.2
We make use of cubic B-spline interpolation function in two cases: heat conduction and fluid flow problems. Cubic B-spline test function is employed because it is superior to approximation of linear and non-linear problems. We investigated the accuracy of the numerical formulation and focused on the position of the breakpoints within the computational domain. When the domain is divided by partitions of equal space, the results show poor accuracy. For the case of a heat conduction problem this partition can not reflect the temperature gradient which is rapidly changed near the wall. To correct the problem, we have more grid points near the wall or the region which has a rapid change of variables. When we applied the unequally spaced breakpoints, the results show high accuracy. Based on the comparison of the linear problem, we extended to the highly non-linear fluid flow problems.
김은필,Kim, Eun-Pil 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.2
It was demonstrated earlier that for laminar, isothermal flow of the lubricant in long journal bearings, inertia has negligible effect on the load carrying capacity and influences only the stability characteristics of the bearing. The question in the present paper is: 'will these conclusions of the isothermal theory remain valid in the presence of significant dissipation, or will lubricant inertia and dissipation interact non-linearly to bring about qualitative changes in bearing performance\ulcorner' The results obtained here assert that the effect of lubricant inertia on load carrying capacity remains negligible, irrespective of the rate of dissipation. The stability of the bearing is, however, affected by lubricant inertia. These results, although obtained here for long bearings with Sommerfeld and Gumbel boundary conditions, are believed to be applicable to practical bearing operations and affirm that bearing load may be calculated from classical, i. e., non-inertial theory.