• Proceedings of the KSME Conference
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• 2001.11b
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• pp.280-287
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside the rib-roughened cooling passage of the gas turbine blades. A square duct with rectangular ribs is used and $\wedge-$ and V-shape ribs with $60^{\circ}$ attack angle are installed on the test plate surfaces. Naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vortices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. A square duct with $\wedge$ and V-shape ribs has two pairs of secondary flow because of the rib arrangement. So, the duct has complex heat/mass transfer distribution. The average heat/mass transfer coefficient and pressure drop of $\wedge-$ and V-shape ribs are higher than those with $90^{\circ}$ and $60^{\circ}$ attack angles. The average heat/mass transfer coefficient on the $\wedge-shape$ ribs is higher than that on the V-shape ribs. Also, the uniformity of heat/mass transfer coefficient on discrete ribs is higher than that on continuous rib.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.6
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• pp.128-140
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• 1997

A new super compact condenser(SCC), which has been developed recently is especially suitable for an alternative refrigerant HFC-134a due to its high performance and compactness. The SCC is composed of two pipe headers, baffles, narrow multi-rectangular channels, and louvered fin arrays. Alternating inlet and outlet by the inserted baffles in pipe headers guide refrigerant to and from the narrow multi-rectangular channels. Since the flow rate and its lengh are changed depending on the number and location of baffles, the corresponding pressure drop and heat transfer rate are changed. The present study aims to theoretically and experimentally investigate the effects of baffle location and its number on the pressure drop and thermal performance of the SCC with 40 multi-rectangular channels. The results show that the present method provides an acceptable prediction of pressure drop and heat transfer rate for a 4 pass SCC. However, the model significantly under predicts the performance of a 3 pass SCC, which may be attributed to the phase separation of refrigerant flowing through header pipes. Pressure drop is more signifi- cantly influenced than heat transfer rate by the baffle location.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1888-1893
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• 2007

In this study, the microchannel plated heat exchanger were numerically studied for the enhancement of heat transfer in the channel configuration. Unit cold and hot fluid region with the microchannel were modeled and periodic boundary condition at the side wall was applied to continuously repeating geometry. The material of micro-structured plate is STS304 and working fluid is water. Triangular obstacles were placed in micro channel to enhance heat transfer. The performance of microchannel plated heat exchangers were numerically investigated with various obstacle configuration and Reynolds number under the parallel and counter flows. Heat transfer rate has increased about 18% compared with straight channel, but pressure drop also increased about 3.5 times. The main factor of increasing of pressure drop and heat transfer rate is considered that the momentum was lost to collide against obstacles, generation of secondary flow and boundary layer separation, wake and vortex forming phenomena.

• International Journal of Air-Conditioning and Refrigeration
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• v.14 no.3
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• pp.102-109
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• 2006

Experimental results for heat transfer characteristics and pressure gradients of HCs refrigerants R-290, R-600a, R-1270 and HCFC refrigerant R-22 during evaporating inside horizontal double pipe heat exchangers are presented. The test sections which has one tube diameter of 12.70 mm with 0.89 mm wall thickness, another tube diameter of 9.52 mm with 0.76 mm wall thickness are used for this investigation. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were higher than that of R-22. The average evaporating heat transfer coefficient increased with the increase of the mass flux, with the higher values in hydrocarbon refrigerants than R-22. Hydrocarbon refrigerants have higher pressure drop than R-22. Those results from the investigation can be used in the design of heat exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.143-147
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• 2008

Numerical analysis is performed to find flow and heat transfer characteristics for ring type heat exchanger. 3-D numerical predictions are carried out for the ring type heat exchanger system with Reynolds number varying in the range of 1,000 and 10,000. From the prediction, streamwise velocity, pressure drop, flow rate and heat transfer coefficient are analyzed. It is also found that characteristics of pressure drop and heat transfer generally follow well proportional variations of Re$m^$for the wide range of Reynolds number considered in this study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.3
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• pp.213-219
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• 2008

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. In this study, the performance evaluation of micro-channel plated heat exchangers with straight, V-shaped and Y-shaped channels has been experimentally carried out under the counterflow condition. It is found that the mixing effect in V-shaped and Y-shaped channels enhances the heat transfer but pressure drop does not increase seriously in the range of low Reynolds number.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.172-177
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• 2005

The object of this experiment is comparing heat transfer performance and pressure drop characteristics by baffle cut rate, fluid velocity and heating temperature. Experiments were carried out in cross flow heat exchanger with water as a working fluid. In this experiment, baffle cut rate is 30%, 40%, 50%, velocity is 0.5m/s, 1.0m/s, 1.5m/s, and heating temperature is $30^{\circ}C$, $40^{\circ}C$, $50^{\circ}C$. An experimental device to measure the heat transfer coefficient was constructed. The experimental result were obtained for the fully developed turbulent flow of water in tube on the condition of uniform heat flux.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.7
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• pp.623-629
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• 2004

Rapid development of electronic technology requires small size, high density packaging and high power of electronic devices, which result in more heat generation by the electronic system. Present cooling technology may not be adequate for the thermal management in the current state-of-the-art electronic equipment. Forced convective heat transfer in a channel filled with pin-fin array is studied experimentally in this paper as an alternative cool-ing scheme for a high heat-dissipating equipment. Various configurations of the pin-fin array are selected in order to find out the effect of spacing and diameter of the pin-fin on the heat transfer and pressure drop characteristics. In the low porosity region, interfacial heat transfer and pressure drop seem to show different trend compared to the conventional heat transfer process.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.11
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• pp.957-963
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• 2003

The present work was conducted to investigate the air-side thermal-hydraulic performance of the brazing fin-tube heat exchanger. Pressure drop and heat transfer coefficient for a plain and a louvered fin configuration were compared numerically and experimentally. It was found that the heat transfer characteristics for the plain fin were similar to the developing flow in the rectangular channel. The louver fin showed about twice better heat transfer coefficient than the plain fin. Previous empirical correlations presented by Davenport, Sunden and Svantesson, Sahnoun and Webb, Chang and Wang, Achaichia and Cowell, and Kang were compared with the present experimental data.

• 연구논문집
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• s.34
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• pp.29-38
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• 2004

The objective of this study is to investigate the pressure drop and heat transfer characteristics of the micro-fin tubes before and after the tube-expansion process. Test tubes are single-grooved micro-fin tubes made of copper with an outer diameter of 9.52 mm before the tube-expansion. The direct heating method is applied in order to make the refrigerant evaporated in the micro-fin tubes. The test ranges of the heat flux, mass flux, and the saturation pressure are 5 to 15kW/$m^2$, 100 to 200 kg/$m^2s$ and 540 to 790 kPa, respectively. The effects of the mass flux, heat flux, and the saturation pressure of the refrigerant on the pressure drop and the heat transfer are presented for the refrigerant R22. In the test conditions of this study, the heat transfer coefficient for the micro-fin tube after the tube-expansion is about 16.5% smaller than that before the tube-expansion because the fin height of micro-fin is reduced and the fin shape becomes flatter. The micro-fin tube after the tube-expansion has about 7.7% greater average pressure drop than that before the tube-expansion process.