• 설비공학논문집
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• 제7권2호
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• pp.298-309
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• 1995

Low-fin tubes are widely used to enhance condensation heat transfer. In this study, condensation heat transfer experiment was conducted on the low-fin tube using R-11. Three different fin densities-787 fpm (fins per meter), 1102 fpm. 1378 fpm-were tested. The results show that low-fin tube enhances the condensation heat transfer considerablely. The enhancement increases as the fin density increases. It was also found that the fin shape and height have a significant effect on the condensation heat transfer coefficient. Slender or high fins showed a higher condensing heat transfer coefficient compared with fat, low fins. For the tube with 1378 fpm, however, excessive fin height decreased the condensing heat transfer coefficient. The reason may be attributed to the increasing condensate retention angle as the fin density increases. The experimental data are compared with existing prediction models. Results show that Webb's surface tension model predicted the data best (within ${\pm}20%$), which confirms that surface tension plays the major role in low-fin tube condensation.

• 대한기계학회논문집
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• 제19권9호
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• pp.2316-2327
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• 1995

Experimental results from nucleate pool boiling heat transfer with various finned tubes in CFC11, HCF123 and HCFC141b are reported. One plain tube and four low fin tubes of various fin densities were tested in an attempt to find out the optimum fin density in the heat flux range of 10-60 kW/m$^{[-992]}$ at near atmospheric pressure. The results indicated that CFC11 showed the highest heat transfer coefficients. Its alternatives, HCFC123 and HCFC141b, showed 3-5% lower heat transfer coefficients than those of CFC11 at the same heat flux. As the fin density increases, so does the heat transfer surface area. Measured heat transfer coefficients, however, do not necessarily always increase as the fin density increases. This unique phenomenon seems to be caused by the coalescence of the bubblers that prevent the cool liquid from entering into the fin valleys. For all the refrigerants tested, the optimum fin density yielding the highest performance was 28 fins per inch confirming the previous results by other researchers.

• 수산해양기술연구
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• 제32권1호
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• pp.67-77
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• 1996

The heat transfer performance of R - 11 vapor condensing on integral fin tubes has been studied using fin tubes having the fin density from 748 to 1654 fins per meter. Electric heater supplied heat energy to the boiler to generate R - 11 vapor over the range of 25-60W. Condensation rates of each tubes were tested under the condition of cooling water flow rate from 400l/h to 2500l/h. For the seven fin tubes tested, the best performance has been obtained with a tube having a fin density of 1417fpm and a fin height of 1.3mm. This tube has yielded a maximum value of the heat transfer coefficient of 16500W/$m_2$K, at a vapor to wall temperature difference of 3K. Experimental results of integral fin tubes have been compared with available predictive models such as Beatty - Katz's analysis, Webb's analysis, Sukhatme's analysis and Rudy's empirical relation. The experimental results were shown to be in good agreement with that of the Sukhatme's analysis.

• 수산해양기술연구
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• 제34권2호
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• pp.200-211
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• 1998

Heat transfer performance improvement by fin and groovs is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapczodially shaped integral-fins having fin density from 748 to 1654fpm(fin per meter) and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also used for comparison. R-11 condensates at saturation state of 32 $^{\circ}C$ on the outside tube surface coded by inside water flow. All of test data are taken at steady state. The heat transfer loop is used for testing singe long tubes and cooling is pumped from a storage tank through filters and folwmeters to the horizontal test section where it is heated by steam condensing on the outside of the tubes. The pressure drop across the test section is measured by menas pressure gauge and manometer. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, overall heat transfer coefficients of finned tube are enhanced up to 1.6 ~ 3.7 times that of a plain tube at a constant Reynolds number. 2. Friction factors are up to 1.6 ~ 2.1 times those of plain tubes. 3. The constant pumping power ratio for the low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio. 4. A tube having a fin density of 1299fpm and 30 grooves has the best heat transfer performance.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.31-41
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• 2016

본 연구에서는 발전소 응축기를 모사할 수 있는 프로그램을 개발하고 발전소 응축기에 전열 촉진관 적용시 얻을 수 있는 여러 효과에 대하여 검토하였다. 평활관을 촉진관으로 교체한다면, 전열량의 증가에 따른 수증기 응축 온도가 내려가게 되므로 발전소의 효율이 증가하게 된다. 따라서 촉진관을 사용하면 기존 설비를 그대로 두고서도 상당량의 전력 여유도를 확보할 수 있다. 고려된 전열 촉진관은 외경 22.2 mm 티타늄 재질의 코류게이트 관, 리브 조도 낮은 핀관, 삼차원 조도 낮은 핀관이다. 내측 조도의 경우 최적 조도 높이가 존재하였다. 또한 삼차원 조도 낮은 핀관이 다른 두 형상보다 우수하게 나타났다. 삼차원 조도의 경우 원주 방향으로 인접한 딤플 사이에서 흐름 방향으로 선회류가 유발되고 이 선회류에 의하여 열전달이 촉진되기 때문이다. 600 MW 발전소 응축기에 전열 촉진관을 적용하면 0.5 MW~1.3 MW 가량의 추가 전력을 생산할 수 있다. 또한 냉각수 온도가 올라가면 추가 전력도 증가한다. 실제로 발전소 응축기에 적용하기 위해서는 열 성능 외에도 화울링, 부식, 기계적 특성 등이 고려되어야 한다.

• 수산해양기술연구
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• 제34권2호
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• pp.212-222
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• 1998

Heat transfer performance improvement by fin and groovs is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapczodially shaped integral-fins having fin density from 748 to 1654fpm(fin per meter) and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also used for comparison. R-11 condensates at saturation state of 32 $^{\circ}C$ on the outside tube surface coded by inside water flow. All of test data are taken at steady state. The heat transfer loop is used for testing singe long tubes and cooling is pumped from a storage tank through filters and folwmeters to the horizontal test section where it is heated by steam condensing on the outside of the tubes. The pressure drop across the test section is measured by menas pressure gauge and manometer. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, overall heat transfer coefficients of finned tube are enhanced up to 1.6 ~ 3.7 times that of a plain tube at a constant Reynolds number. 2. Friction factors are up to 1.6 ~ 2.1 times those of plain tubes. 3. The constant pumping power ratio for the low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio. 4. A tube having a fin density of 1299fpm and 30 grooves has the best heat transfer performance.

• 한국산학기술학회논문지
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• 제16권3호
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• pp.1684-1691
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• 2015

흡수식 냉동기의 고효율화와 소형화를 위해서는 고성능 전열관의 연구가 필수적이다. 하지만 재생기용 전열관에 대한 연구는 많이 미흡한 실정이다. 본 연구에서는 만액식 재생기용 전열관의 성능을 파악하기 위한 기초연구로, 형상이 다른 7종의 전열관에 대해 풀비등 실험을 수행하고 비등열전달계수를 도출하였다. 실험은 압력 7.38~101.3 kPa, 열유속 $20{\sim}40kW/m^2$의 범위에서 수행되었다. 실험결과 모든 전열관에서 압력이 증가하고 열유속이 증가할수록 비등열전달계수 값은 증가하였다. 대기압 조건에서는 notched fin 관과 low fin 관이 높은 비등열전달계수를 나타내었고(열전달계수가 가장 낮은 19.0 mm O.D. 평활관의 225% 와 202%), 압력이 낮아질수록 low fin 관이 다른 전열관에 비해 현저히 높은 비등열전달계수를 나타내었다 (12.34와 7.38 kPa에서 19.0 mm O.D. 평활관의 290%와 288%).

• Journal of Mechanical Science and Technology
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• 제19권10호
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• pp.1957-1963
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) of six flammable refrigerants of propylene (RI270), propane (R290), isobutane (R600a), butane (R600), dimethylether (RE170), and HFC32 were measured at the vapor temperature of $39^{\circ}C$ on a 1023 fpm low fin and Turbo-C tubes. All data were taken under the heat flux of $32\~116\;and\;42\~142kW/m^2$ for the low fin and Turbo-C tubes respectively. Flammable refrigerants' data obtained on enhanced tubes showed a typical trend that external condensation HTCs decrease with increasing wall subcooling. HFC32 and DME showed up to $30\%$ higher HTCs than those of HCFC22 due to their excellent thermophysical properties. Propylene, propane, isobutane, and butane showed similar or lower HTCs than those of HCFC22. Beatty and Katz' correlation predicted the HTCs of the flammable refrigerants obtained on a low fin tube within a mean deviation of $7.3\%$. Turbo-C tube showed the best performance due to its 3 dimensional surface geometry for fast removal of condensate.

• 대한기계학회논문집B
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• 제22권7호
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• pp.980-991
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• 1998

In this study, nucleate pool boiling heat transfer coefficients of alternative refrigerants on a plain, low fin, and two enhanced tubes were measured and compared against each other. To obtain data at conditions similar to the actual evaporator, a fluid heating method was employed instead of an electric heating method in the experiments. R123, R134a, R22 and R410a were used as working fluids and data were taken at 7 deg.C ar heat fluxes of 20 ~ 100 kW/m$\^$2/. Comparison of the plain tube data against some correlations showed that the simplest correlation of Cooper based on reduced pressure predicted the data for all fluids tested with a 10% deviation. For all refrigerants, enhanced tubes composed of subsurface and subtunnels, especially Thermoexcel-E tube, showed the highest heat transfer coefficients among the tubes tested with one exception that the low fin tube's performance was better than those of enhanced tubes for high vapor pressure fluid such as R410a at high heat flux. Finally, a low fin and enhanced tubes showed higher heat transfer enhancement for low vapor pressure of R123 than for high vapor pressure fluisd. For R123, the enhancement factors for Turbo-B and Thermoexcel-E tubes were 2.8 ~ 4.8 and 4.6 ~ 8.1 respectively.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권1호
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• pp.9-14
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• 2008

In this study, pressure drop and heat transfer characteristics of plain finned heat exchangers having 5.0 mm diameter (fin collar 5.3 mm) tubes were investigated. Six samples having different fin pitches (1.1 to 1.3 mm) and tube rows (1 and 2 row) were tested. The fin pitch had a negligible effect on j and f factors. Both j and f factors decreased as the number of tube row increased, although the difference was not significant for the f factor. When compared with the j and f factors of the samples having 7.3 mm diameter tubes, the present j and f factors yielded lower values. However, the j/f ratio was larger at low Reynolds numbers. Possible reasoning is provided from the flow pattern consideration. Comparison with existing correlations were made.