• 한국전산유체공학회지
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• 제3권1호
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• pp.82-88
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• 1998

As a par of a project related to the development of the design algorithm of a compact heat exchanger for the application of the electronic home appliances, the effect of the discreteness of the airflow boundary generated on the cooling fin surface on the heat transfer and pressure drop characteristics of the heat exchanger was studied numerically. In general, there are two critical design parameters seriously considered in the design of the heat exchanger; heat transfer rate(Q) and pressure drop coefficient(C/sub p/). Even though the higher heat transfer rate with lower pressure drop characteristics is required in a design of the heat exchanger, it is not an easy job to satisfy both conditions at the same time because these two parameters are phenomenally inversely proportional. To control the boundary layer thickness and its length along the streamline, the surface of the flat fin was modified to accelerate the heat transfer rate on the fin surface. To understand the effect of the discreted fin size(S/sub w/) and its location(S/sub h/) on the performance of the heat exchanger in the airflow field, the flat fin was modified as shown in Fig. 1. From this study, it was found that the smaller and more number of slits on the fin surface showed the higher energy diffusion rate. It means that the discreteness of the boundary layer is quite important on the heat transfer rate of the heat exchanger. On the other hand, if the fin surface configuration is very complex than needed, higher static pressure drop occurs than required in a system and it may be a reason of the induced aerodynamic noise in the heat exchanger.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.19-24
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• 2003

This paper is to research the heat transfer characteristic in copper-water variable conductance heat pipes(VCHP) with a non-condensable gas and gas reservoir. The heat transfer characteristics in the VCHP have not yet been studied much researches. VCHP are used in many applications. These applications range from thermal control of components and systems on satellites, to precise temperature calibration duties, conventional electronics temperature control and thermal diodes. The practical use of VCHP is a simple way to control the temperature of satellites. As the quantity of NCG was increased, there was an increase in the saturation vapor temperatures. As the input heat has loaded from 90 W to 110 W, the difference of the evaporator surface is lower than $10^{\circ}C$.

• 설비공학논문집
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• 제24권4호
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• pp.323-329
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• 2012

In this study, a rational procedures for estimation of insulation thickness of a vertical wall for condensation control or personnel protection has been investigated. Design parameters are height of the wall, thermal conductivity, emissivity, and operating temperatures. The results indicated that the surface emissivity plays a very important role in the design of insulation for the purpose of surface temperature control, especially in natural convection situation. radiation heat transfer coefficients for some new insulation material surface, such as elastomers, estimated to be more than 90% of the total surface heat transfer coefficient.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 B
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• pp.1146-1148
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• 1996

In this paper, uncertain parameters of the heat transfer model of a Dynamically Tuned Gyroscope (DTG) are estimated by the Recursive Least Squares (RLS) method. Also, using this model, a temperature controller for a DTG is designed. As the temperature controller, a PI controller is used. It is presented that a controller can be easily designed when the heat transfer model of a DTG is used. By simulations and experiments, it is shown that the estimated heat transfer model is appropriate and the desired performance of the temperature controller is satisfied.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.294-299
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• 2005

In order to control indoor air quality and save energy. it is needed to install a suitable ventilation system equipped with heat exchanger for heat recovery. Paper heat exchanger can recover $50{\sim}70$ of the enthalpy difference between supply and exhaust air. The purpose of this research is to obtain the experimental correlations for the friction factor, heat transfer coefficient, mass transfer coefficient and permeance of paper heat exchanger, which can be used for the performance prediction of the paper heat exchanger. Pressure drop at various velocities and heat transfer rate at various dry-bulb temperatures, relative humidities, and specific humidities are measured to make experimental correlations. The results of prediction using correlations show fairly good agreement with experimental data.

• 대한기계학회논문집B
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• 제28권10호
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• pp.1139-1146
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• 2004

The effect of triangular tabs attached at the perimeter of jet nozzle on heat transfer enhancement was investigated experimentally. The modified flow structure was visualized using a smoke-wire method. Four different types of jet nozzle having 0, 4, 6 and 8 tabs were tested at jet Reynolds number Re=15,000 to investigate the effect of tabs on the variation of heat transfer rate. The local and average Nusselt numbers are increased with increasing the number of tabs. At nozzle-to-plate distance of L/D=4, the average Nusselt number was increased about 9.9% at Re=15,000 in the impingement region for the case of 8 tabs attachment. As the nozzle-to-plate distance increases, however, the heat transfer enhancement effect of triangular tabs is reduced. For the case of 4 tabs, the heat transfer enhancement is not so distinctive at L/D=8. As the protrusion depth of tabs into the jet flow increases, the heat transfer rate is also enhanced when the nozzle-to-plate distance is smaller than L/D=6.

• Journal of Advanced Marine Engineering and Technology
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• 제26권4호
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• pp.439-449
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• 2002

Experimental investigations of the flow structure and heat transfer enhancement in a channel with a built-in circular cylinder and a wing-let type vortex generator are presented. Without any vortex generators, relatively low heat transfer takes place in the downstream of the circular cylinder where is a recirculation region with low velocity fluid is formed. However with a wing-let type longitudinal vortex generator in the wake region behind the cylinder, heat transfer in the region can be enhanced. In order to control the strength of longitudinal vortices, the angle of attack of the vortex generators is varied from $20^{circ} to 45^{\circ}$, but spacings between the vortex generations are fixed to be 5 mm. The 3-dimensional mean velocity field downstream of the vortex generator is measured by a five-hole pressure probe, and the hue-capturing method using thermochromatic liquid crystals has been used to provide the local distribution of the heat transfer coefficient. The vorticity field and streamwise velocity contour are obtained from the velocity field. Streamwise distributions of averaged Stanton number on the measurement planes show very similar trends for all the experimental cases($\beta=20^{circ}, 30^{circ} and 45^{\circ}$). Circulation strength and heat transfer coefficient have the maximum values when the angle of attack($\beta$) is $30^{\circ}$.

• 대한기계학회논문집
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• 제18권10호
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• pp.2738-2750
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• 1994

The Effects of radiative heat transfer on turbulent flow in a partitioned enclosure is studied numerically. The enclosure is partially divided by a thin, poorly conducting vertical divider projecting from the ceiling of the enclosure. The low Reynolds number $k-{\epsilon}$ model is adopted to calculate the turbulent flow field. The solutions to the radiative transfer equations are obtained by the discrete ordinates method(DOM). This method is based on control volume method and is compatible with the SIMPLER algorithm used to solve the momentum and energy equations. The effects of optical thickness and Planck number on the flow, temperature fields and heat transfer rates are investigated for a moderate Rayleigh number($=10^9$). The changes in buoyant flow fields and temperature distributions due to the variation of baffle length are also analyzed. From the predictions, radiant heat exchange between the baffle and the sidewalls strongly influences the temperature distribution in the baffle and its vicinity and total heat transfer increases as the optical thickness and the baffle length decrease. It is possible to neglect the radiative heat transfer effect when Planck number is over one.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권4호
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• pp.196-205
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• 2005

In this paper, recent research trend on heat transfer in impinging jet is reviewed. We focused on submerged jet that air issued into air or liquid issued into liquid. To control and enhance the heat transfer in single jet, researchers have performed a lot of experiments by considering the nozzle geometry, impinging surface and active method such as jet vibration, secondary injection and suction flow. The studies on multiple jet have been mainly focused on finding out the optimum condition and on investigating many different factors concerned with application condition (crossflow, rotation and geometry etc.) and combined techniques (rib turbulator, pin fin, dimple and effusion hole etc.). All most experiments showed the detailed heat transfer data by using liquid crystal method, infrared camera technique and naphthalene sublimation method. Many numerical calculations have been performed to investigate the flow and heat transfer characteristics in laminar jet region. Various turbulence models such as $k-\varepsilon-\bar{\nu^2}$, modified $k-\varepsilon-f_{\mu}$ were applied to the calculation for turbulent jet and the predicted results showed a good agreement with the experimental data. Although a lot of studies on impinging jet have performed consistently up to recently, further studies are still required to understand the flow and heat transfer characteristics more accurately, and to give a guideline for optimum impinging jet design in various applications.

• 대한기계학회논문집B
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• 제22권8호
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• pp.1183-1194
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• 1998

This paper describes a theoretical model developed for analyzing the heat transfer of automotive cooling systems. From the model, heat transfer rate of automotive cooling systems can be predicted, providing useful information at the early stages of the design and development. The aim of the study is to develop a simulation program for automotive cooling system analysis and a performance analysis program for analyzing heat exchanger. Heat release rate from combustion gas to coolant through cylinder wall in engine cylinder was analyzed by using a two zone combustion model. This paper studied how cooling condition would affect engine heat release rate and measured temperature distribution of coolant in water jacket.