• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.855-860
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• 1999

An experimental study of jet impingement on the surface with linear temperature gradient is conducted with the presentation of the turbulent characteristics and the heat transfer rates measured when this jet impinges normally to a flat plate. The jet Reynolds number ranges from 30,000 to 90,000, the temperature gradient of the plate is 2~$4.2^{\circ}C$/cm and the dimensionless nozzle to plate distance(H/D) is from 6 to 10. The results show that the peak of heat transfer rate occurs at the stagnation point, and the heat transfer rate decreases as the radial distance from the stagnation point increases. A remarkable feature of the heat transfer rate is the existence of the second peak. This is due to the turbulent development of the wall jet. Maximum heat transfer rate occurs when the axial distance from the nozzle to nozzle diameter(H/D) is 8. The heat transfer rate can be correlated as a power function of Prandtl number, Reynolds number and the dimensionless nozzle to plate distance(H/D). It has been found that the heat transfer rate increases with increasing turbulent intensity.

• Transactions of Materials Processing
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• v.23 no.7
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• pp.419-424
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• 2014

In order to improve efficiency, an outdoor unit using a refrigerant cooling method is designed into many air conditioner systems. The heat exchanger is composed of a Cu tube and an plate. The optimal design for the cold plate is very important because the efficiency of the heat transfer depends on the contact area between the Cu tube and the cold plate. The current study focused on the design of the cold plate to obtain a uniform contact between the Cu tube and the cold plate. Both FE(finite element) analysis and optimization were used in the design. The contact area between the tube and plate was predicted and improved by 16% through the press forming simulations. The springback after press forming was also reduced when the optimized design parameters were used. To verify the validity of the optimal cold plate design, a verification test was conducted. As a result, the performance of the heat exchanger improved by 34% when compared to benchmarked products.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.522-528
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• 2004

Heat analysis of the plate type and wave type heat sink were carried out by using computational simulation. The heat resistance and air flow of two heat sink models were analysed according to natural and forced convection condition and positions of fan. When a fan was at the position of z-axis and y-axis in forced convection, the heat resistances of plate type heat sink were $0.17^{\circ}C/W$, and $0.28^{\circ}C/W$ respectively. In the case of wave type heat sink, they were $0.18^{\circ}C/W$ and $0.53^{\circ}C/W$. As the air flow velocities were averagely $0.386\;m/s\~3.269\;m/s$, air flow velocity of plate type heat sink was faster than that of wave type. In this experiment, it was observed that the plate type heat sink showed a good ability of heat radiation comparing with wave type one.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.1
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• pp.17-27
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• 2009

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.477-482
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• 2001

An experimental study on the performance evaluation of a brazed plate heat-exchanger with 10RT of normal cooling capacity has been carried out. In the present study, a brazed type plate heat exchanger was tested at a chevron angle $25^{\circ}$ with refrigerant R-22. Mass flux was ranged from $23\;to\;58kg/m^{2}s$ in condensation, and from $22\;to\;53kg/m^{2}s$ in evaporation. The heat transfer coefficient and pressure drop increased with the mass flux increases. The water side pressure drop increased with the cooling water flow rate and chilled water flow rate increases, while mass flux has little affect. It is also shown that the system performance can be improved by enlarging condensation heat transfer area.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.4
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• pp.301-307
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• 1982

The purpose of this investigation is to study heat transfer characteristics at a stagnation point on a flat plate caused by upward impinging water jet. At the stagnation point, heat transfer results by impinging water jet are being compared with the ones with supplementary water. Optimum supplementary water quantity are supplied in order to improve the effect of heat transfer for each nozzle-to-plate distance. As the nozzle outlet velocity increases, the heat transfer coefficient at stagnation point consequently increases. Changing the nozzle-to-plate distance, growth rate of heat transfer also varies accordingly. This optimum range of Reynolds number is obtained to improve heat transfer effect.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.511-518
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• 2000

The present experimental study investigates the impact of porous fins on the pressure drop and heat transfer characteristics in plate-fin heat exchangers. Systematic experiments have been carried out in a simplified model of a plate-porous fin heat exchanger at a controlled test environment. Comparison of performance between the porous fins and the conventional louvered fins has been made. The experimental results indicate that friction and heat transfer rate are significantly affected by permeability as well as porosity of the porous fin. The porous fins used in the present study show a similar air-side performance to the louvered fin. The correlations of friction and modified j-factor are also given for the design of the plate-porous fin heat exchanger.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.557-563
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• 2001

Small capacity gas absorption systems for cooling and heating have been favorably considered to reduce the seasonal imbalance of electrical loads and LNG consumption recently. A multifunctional plate-fin heat exchanger was adopted as an absorber and the performance was tested and analyzed to reduce the size and weight of the absorption heat pump. The test was performed using breadboard type ammonia absorption machine. The performance was compared with the plate type absorber and there was little difference in heat and mass transfer characteristics. The heat and mass transfer performance was a function of poor solution and vapor flow rates and the mass transfer was dependent on vapor flow rate more than heat transfer.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1447-1452
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• 2003

Vortex is very interesting flow phenomena on the heat transfer enhancement. In the present study, naphthalene sublimation technique is used to determine the average and local mass transfer coefficients on the flat plate with vortex generator. A parametric study with Reynolds number and angle of attack is carried out to investigate the heat transfer enhancement. The heat transfer coefficients on the flat plate with rectangular type and delta type vortex generator are compared with those of the flat plate without the vortex generator. Comparing heat transfer coefficients between rectangular type and delta type vortex generator, rectangular type vortex generator has much higher value than delta type vortex generator at the same condition.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.121-125
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• 2008

In this study, the characteristics of internal flow and the heat transfer performance of dimpled plate heat exchanger were numerically investigated. For the numerical analysis, conjugate heat transfer method between cold fluid - plate - hot fluid was studied with appropriate boundary conditions. Velocity magnitude, temperature and pressure distribution were obtained from the simulation. Correlations for fanning f-factor and Colburn j-factor were obtained from numerical results and compared to the experimented data.