• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.3
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• pp.194-200
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• 2011

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of pure water are measured on horizontal 26 fpi low fin, Turbo-B and Thermoexcel-E square surfaces of 9.53 mm length. HTCs are taken from 10 $kW/m^2$ to critical heat flux for all surfaces. Test results show that critical heat fluxes(CHFs) of all enhanced surfaces are greatly improved as compared to that of a plain surface. CHFs of water on the 26 fpi low fin surface, Thermoexcel-E surface, and Turbo-B are increased up to 320%, 275%, and 150% as compared to that of the plain surface, respectively. CHF of the Turbo-B enhanced surface is lower than that of the 26 fpi low fin surface due to the surface geometry. The heat transfer enhancement ratios of the Thermoexcel-E surface, low fin surface and Turbo-B enhanced surface are 1.6~2.9, 1.6~2.1, 1.4~1.7 respectively in the range of heat fluxes tested. Judging from these results, it can be said that these types of enhanced surfaces can be used in heat transfer applications at high heat fluxes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.683-689
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• 2002

This paper is to present the results of a comprehensive study on heat transfer in annuli with spirally corrugated inner tubes in the turbulent regime. Tube surface-temperature measurements were used to explain the enhancement phenomena in the annuli with several different corrugated tubes. Nusselt numbers were between 1.1 and 2 times the smooth annulus values. These enhancement values can be used to determine the appropriate range of applicability for spirally corrugated annuli.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.3
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• pp.167-175
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• 2009

In this study, condensation heat transfer coefficients(HTCs) of R22, R123, R134a and R245fa are measured on both 26fpi low fin and Turbo-C tubes. All data are taken at the vapor temperature of $39^{\circ}C$ with a wall subcooling of $3{\sim}8^{\circ}C$. Test results show that HTCs of the newly developed low vapor pressure alternative refrigerant, R245fa, are $7.8{\sim}9.2%$ and $10.3{\sim}18.6%$ higher than those of R123 for 26fpi low fin tube and Turbo-C tube respectively. For all refrigerants tested, HTCs of Turbo-C enhanced tube are higher than those of 26fpi low fin tube. For the low fin tube, Beatty and Katz's prediction equation yielded 20% deviation for all fluids. The heat transfer enhancement ratio of R245fa on the Turbo-C tube is $5.9{\sim}6.4$ while that of R123 is $5.7{\sim}5.9$. From the view point of environmental safety and condensation heat transfer, R245fa is a long term candidate to replace R123 currently used in centrifugal chillers.

• Solar Energy
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• v.17 no.3
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• pp.67-73
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• 1997

In order to development of a new wall structure type thermal diode for energy saving, the numerical studies have been performed for natural convection across an rectangular enclosure with the various lengthes of the heat source and sink plate. The governing equations for the two-dimensional, laminar, natural convection process in an enclosure are discretized by the control volume approach which insures the conservative characteristics to be satisfied in the calculation domain, and solved by a elliptic SIMPLE algorithm. The momentum and energy equations are coupled through the buoyancy term.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.7
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• pp.315-321
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• 2014

In this study, external condensation heat transfer coefficients (HTCs) of two non-azeotropic refrigerant mixtures of HFC32/HFC152a at various compositions were measured on both 26 fpi low-fin and Turbo-C enhanced tubes, of 19.0 mm outside diameter. All data were taken at the vapor temperature of $39^{\circ}C$, with a wall subcooling of 3~8 K. Test results showed that the HTCs of the tested mixtures on the enhanced tubes were much lower than the ideal values calculated by mass fraction weighting of the pure component HTCs. Also, the reduction of HTCs due to the diffusion vapor film was much larger than that of a plain tube. Unlike HTCs of pure fluids, HTCs of the mixtures measured on enhanced tubes increased, as the wall subcooling increased, which was due to the sudden break-up of the vapor diffusion film with an increase in wall subcooling. Finally, the heat transfer enhancement ratios for mixtures were found to be much lower, than those of pure fluids.

• Journal of Energy Engineering
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• v.9 no.4
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• pp.334-341
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• 2000

회전 히트파이프의 열 전달 특성은 내부 관벽에 형성되는 응축 액막 두께와 증발부로 귀한되는 응축액의 유동율에 의해 결정된다. 본 연구는 축 방향으로 그루브(groove)를 갖는 회전 히트파이프의 열 전달 성능에 대한 실험 연구로써, 그루브에 의한 효과를 파악하기 위해 2종류의 히트파이프를 제작하고 작동성은 시험을 수행하였다. 회전 히트파이프가 작동시, 원심력에 의해 그루브로 응축액의 유동을 촉진시키며, 따라서 응축부 벽면에 형성되는 액막 두께가 얇게 된다. 응축부에 그루브를 갖는 히트파이프의 열전달 계수는 풀 유동에서 2000~4000W/$m^2$$^{0}$ C, 환상 유동 영역에서 1500~2500W/$m^2$$^{0}$ C로써, 전체 원형단면을 갖는 히트파이프와 비교하여 약 1.5배 정도의 열저달 향상을 볼 수 있었으며, 열전달 한계는 약 40% 정도 향상되는 것으로 나타났다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.981-989
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) are measured on a low fin tube and Turbo-C tubes at the saturated vapor temperature of $30^{\circ}C$, $39^{\circ}C$, and $50^{\circ}C$ for R22, R410A, R407C and R134a with the wall subcooled at $3{\~}8^{\circ}C$. The HTCs of all refrigerants decreased as increasing the saturation temperature from $30^{\circ}C$ to $50^{\circ}C$. This trend is due to better thermodynamic properties of the liquid phase at low temperature Beatty and Katz's prediction yielded a $20.0\%$ deviation for the low fin tube data. The heat transfer enhancement factors for the 26 fpi low fin tube and Turbo-C tubes are 4.0${\~}$5.5 and 3.0${\~}$8.1 respectively for the refrigerants tested. Finally the performance of Turbo-C tube is better than that of the low fin tube.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.25-33
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• 1998

The characteristics of evaporation heat transfer for the utilization of LNG cold energy was investigated experimentally using liquified nitrogen and a solution of ethylene-glycol and water under horizontal two-phase conditions in the small-scale equipment of a cryogenic heat exchange system. The inner tubes in the double pipe heat exchanger with 8 mm and 15 mm inner diameter and 6 m length were adopted as a smooth test tubes and enhanced tubes by means of wire-coil inserts. Heat transfer coefficients and Nusselt number for the test tube were calculated from measurements of temperatures, flowrates and pressures. The correlations in a power-law relationship of the Nusselt number, the Reynolds number and Prandtl number for heat transfer were proposed which can be available for design of cryogenic heat exchangers. The correlations showed heat transfer coefficients for the wire-coil inserts were much higher than those for the smooth tubes, increased by more than 2.5 ${\~}$ 5.5 times depending upon the equivalent Reynolds number. Form and length of cryogenic double pipe heat exchanger were proposed for applicable to the utilization of LNG cold energy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.71-80
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• 1985

The various sizes of wires are attached to the outside of the inner tube in a double pipe heat exchanger to enhance the thermal performance. The diameters of the wires range from 0.5mm to 1.6mm while the pitches are chosen between 5mm and 50mm. Experiments have been performed with the range of Reynolds numbers from 15000 to 30000 in annular space where air flows. The friction factors are increased by 1.5 to 4.5 times depending on the sizes and the pitches of the wires. However, the Nusselt numbers are increased by the factors of 1.8 to 2.8 within this experimental range. It is suggested that there should be an optimum configuration rendered when the weighting values of the heat transfer promotion and the pumping power are given.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.789-798
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• 1999

The evaporating heat transfer experiments with refrigerant HCFC 22 are performed for performance evaluation using 4 and 6 kinds of microfin tubes with outer diameter of 9.52mm and 7.0mm, respectively. Used microfin tubes have different shape and number of fins with each other, The experimental results are represented with effects of quality, mass flux and EPR. The evaporating heat transfer characteristics are represented by the existence of not only heat transfer area and turbulence promotion effect but also additional other enhancement mechanism, which are the overflow of the refrigerant over the microfin and microfin arrangement. Microfin tubes having a shape which can give much overflow over the microfin show large evaporating heat transfer coefficients. The effect of refrigerant overflow is much severe in evaporation than condensation. The effect of microfin arrangement is related to overflow effect of the refrigerant over the microfin.