• Advances in Energy Research
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• v.8 no.3
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• pp.137-144
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• 2022

This study presents an experimental investigation of conventional and enhanced receiver tube performance for the application of a concentrated parabolic trough collector (CPC). The CPC system is fabricated and tested for the conventional and enhanced receiver tubes. The experiments were performed on both tubes for the change of flow rates. The temperature rise of the tube surface, as well as working fluid, were monitored for varying flow rates. The results were compared and discussed in view of enhanced CPC system performance. The results exhibited that the temperature rise of the working fluid passing through the tube was more in the case of the enhanced tube compared to the conventional receiver tube under the same flow rates.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.808-814
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• 1999

Pool boiling performance of a metal-formed enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a), at two different saturation temperatures $4.4^{\circ}C \;and \;26.7^{\circ}C$ .Heat flux was varied from 10㎾/$m^2\;to\ 50㎾/$m^2$. Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times higher for R-11, 6.0 tines higher for R-123 and 3.5 times higher for R-l34a. The enhancements are comparable with those of foreign products. The heat transfer coefficients of R-l34a were higher than those of R-11 and R-123, either for the enhanced tube or for the smooth tube. At $4.4^{\circ}Csaturation temperature, however, the heat transfer coefficients of R-l34a were approximately the same as those of R-11, The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube - the heat transfer coefficient increases as the saturation pressure increases.

• International Journal of Air-Conditioning and Refrigeration
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• v.8 no.2
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• pp.23-28
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• 2000

In this study, pool boiling performance of a structured enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a). Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times larger for R-11, 6.0 times larger for R-123 and 3.5 times larger for R-l34a, which are comparable with the performance of foreign products. The heat transfer coefficients of R-l34a was higher than those of R-11 or R-123, both for the enhanced tube and for the smooth tube. At 4.4$^\circ$C saturation temperature, however, the heat transfer coefficients of R-l34a was approximately the same as those of R-11. The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube-the heat transfer coefficient increased as the saturation pressure increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1267-1276
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• 1998

Falling-film evaporation experiments with aqueous lithium bromide (LiBr) solution were performed to investigate the heat transfer characteristics of enhanced copper tubes. Enhanced tubes (a knurled tube, a spirally grooved tube, and a tube coated with $20{\mu}m$ aluminum particles) and a bare tube were selected as test specimens. Averaged evaporation fluxes of water were obtained from horizontal tubes with various film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. The enhanced performance of steam generation was compared between tubes with varying parameters. The knurled tube geometry showed the most excellent performance among the tubes tested. The specified enhanced tubes were more useful for generating steam on a low grade heat source such as waste heat.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.5
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• pp.569-580
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• 1998

In this study, condensation heat transfer coefficients(HTCs) of a plain tube, low fin tube, and Turbo-C enhanced tube for CFC-11, HCFC-123, CFC-12, HFC-l34a are measured and compared against each other. All data are taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling temperature 3~8$^{\circ}C$. Test results show that HTCs of a low vapor pressure refrigerant, HFC-123, for a plain, low fin, and Turbo-C tubes are 10.5~20.5%, 8.2~12.2%, 16.5~19.2% lower than those of CFC-11, respectively. On the other hand, HTCs of a medium vapor refrigerant, HFC-l34a, for a plain, low fin, and Turbo-C tubes are 20.6~31.8%, 0.0~8.0%, 13.2~20.9% higher than those of CFC-12, respectively. For all refrigerants tested, HTCs of Turbo-C tube are the highest among the three tubes showing almost 8 times increase in HTCs as compared to those of a plain tube. Nusselt's prediction equation for a plain tube yielded 12% deviation for all plain tube data while Realty and Katz's prediction equation for a low fin tube yielded 20% deviation for all low tube data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.8
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• pp.613-619
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• 2006

The objectives of this paper are to study the characteristics of heat transfer for enhanced tubes (19.05 mm) used in the condenser with high saturation temperatures and to provide a guideline for optimum design of a condenser using HFC134a. Three different enhanced tubes are tested at a high saturation temperature of $59.8^{\circ}C$ (16 bar); a low-fin and three turbo-C tubes.. The refrigerant, HFC134a is condensed on the outside of the tube while the cooling water flows inside the tube. The film Reynolds number varies from 130 to 330. The wall subcooling temperature ranges from $2.7^{\circ}C$ to $9.7^{\circ}C$. This study provides experimental heat transfer coefficients for condensation on the enhanced tubes. It is found that the turbo-C(2) tube provides the highest heat transfer coefficient.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.710-719
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• 2001

Pool boiling heat transfer coefficients (HTCs) of HCFC123, HFC134a, HCFC22, HFC407C, HFC410A and HFC32 wre measured on a horizontal smooth tube, 26 fpi low fin tube, Turbo-B and Thermoexcel-E enhanced tubes. AN experimental apparatus was designed such that all tubes heated by cartridge heaters could be installed at the same time to save the refrigerant. Data were taken in the pool of $7^{\circ}C$ with the heat flux decreasing from 80 kW/$m^2\;to\;5kW/m^2$. Test results showed that HTCs of pure refrigerants and those of a azeotrope were greatly influenced by reduced pressure. HTCs of HFC407C were 21~25% lower than those of HCFC22 due to mass transfer resistance. For all refrigerants, enhanced tubes with sub-surface and sub-tunnels showed the largest heat transfer enhancement. Especially the largest heat enhancement was obtained for HCFC123 whose reduced pressure is the lowest among al the refrigerants tested. This indicates that either Turbo-B or Thermoexcel-E enhanced tube would be the best choice when used with a low vapor pressure refrigerant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.4
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• pp.289-298
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• 1992

Fouling is "a major unsolved" area in heat transfer research. Currently, fouling researches are performed in every directions-fundamental aspects, modeling and cumulating experimental data. In this study, an attempt was made to extend the knowledge in enhanced tube fouling. The Kern-Seaton fouling model which was originally proposed for smooth tube fouling was extended to repeated rib tubes. Key parameters-mass transfer coefficient and wall shear stress-were modeled for repeated rib tubes. Some critical points related with the enhanced tube fouling-uncertainties in the mass transfer rate, wall shear stress modeling, deformation of roughness shape during fouling-were discussed, and some quantitative evaluations were made.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.716-723
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• 2016

Enhanced tubes are used widely in the heat exchangers of absorption chillers. In regenerators, corrugated, ribbed or floral tubes are commonly used. In this study, the tube-side heat transfer coefficients and friction factors of enhanced tubes were obtained experimentally using the Wilson Plot method. The results showed that the heat transfer coefficients and the friction factors were the largest for the corrugated tube, followed by the ribbed tube. The heat transfer coefficients and friction factors of the floral tube matched those of the smooth tube within 4%, which suggests that the heat transfer and friction characteristics of the floral tube may be accounted for properly by the hydraulic diameter. The B(e+) and g(e+) were obtained from the experimental data of the corrugated and ribbed tube. The B(e+) and g(e+) of the corrugated tube matched those of the existing correlation within 20%. The present results may be used for an assessment of the heat transfer and friction characteristics of the enhanced tubes for regenerators.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1831-1843
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• 2001

In this study, convective boiling tests were conducted for enhanced tube bundles. The surface geometry consists of pores and connecting gaps. Tubes with three different pore sizes (d$_{p}$ = 0.20, 0.23 and 0.27 mm) were tested using R-123 and R-l34a for the following range: 8 kg/m$^2$s G 26 kg/m$^2$s, 10 kW/m$^2$ q0 40 kW/m$^2$and 0.1 $\chi$ 0.9. The convective boiling heat transfer coefficients were strongly dependent on heat flux with negligible dependency on mass flux or quality. For the present enhanced geometry (pores and gaps), the convective effect was apparent. The gaps of the present tubes may have served routes for the passage of two-phase mixtures, and enhanced the boiling heat transfer. The convective effect was more pronounced at a higher saturation temperature. More bubbles will be generated at a higher saturation temperature, which will lead to enhanced convective contribution. The pore size where the maximum heat transfer coefficient was obtained was larger for R-l34a (d$_{p}$ = 0.27 mm) compared with that for R-123 (d$_{p}$ = 0.23 mm). This trend was consistent with the previous pool boiling results. For the enhanced tube bundles, the convective effect was more pronounced for R-134a than for R-123. This trend was reversed for the smooth tube bundle. Possible reasoning is provided based on the bubble behavior on the tube wall. Both the modified Chen and the asymptotic model predicted the present data reasonably well. The RMSEs were 14.3% for the modified Chen model and 12.7% for the asymptotic model.model.