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Abstract
Heat transfer, friction factor and entropy generation from the inside surface of a horizontal circular tube fitted with trapezium - nozzle have been investigated experimentally. The heat transfer test section is heated electrically imposing axially and circumferentially constant wall heat flux. Three different pitch ratios (PR) of trapezium -nozzle arrangements in the test tube are introduced with PR=2, 4, and 7. The experiments covered a range of Reynolds numbers from 8000 to16000. Heat transfer and friction factor analyses are presented for different conditions of pitch ratios (PR) and Reynolds number. The results indicate that the trapezium - nozzle of different pitch ratios has a great effect on the results of heat transfer coefficient and friction factor. The Nusslet number increases with an increase in Reynolds number and it decreases with an increase in pitch ratios. It is found that using the trapezium -nozzle results in increasing the heat transfer rate compared with the plain tube. The maximum gain in Nusslet number is obtained for the smallest pitch ratio used, PR=2. This indicates that the effect of the reverse/re-circulation and surface flows can improve the heat transfer rate in the circular tube. For fixed Reynolds number, the friction factor increases with the decrease in pitch ratio for the circular tubes with trapezium -nozzle. The entropy generation number increases with increase Reynolds number at all cases, whereas the entropy generation number shows its highest value at pitch ratio of 2. From these results, it was found that the average enhancement in Nusselt number for circular tube fitted with trapezium - nozzle at pitch ratio (PR=2) is in the range of 202% to 257% compared with the plain circular tube for all tested conditions. Correlations of the Nusselt number and friction factor with Reynolds number and pitch ratio are presented.
Key words: Enhancement heat transfer; Circular tube; Re-circulation/Reverse flow; Turbulator; Entropy generation; Trapezium –nozzle
REFERENCES
[1] Bergles A., & Webb, R. (1985). Guide to the Literature on Convection Heat Transfer Augmentation. Advances in Enhanced Heat Transfer, 43, 81–89.
[2] Marner, W., Bergles, A., & Chenoweth, J. (1983). On the Presentation of Performance Data for Enhanced Tubes Used in Shell and Tube Heat Exchangers. Transaction ASME, Journal Heat Transfer, 105, 358–365.
[3] Eiamsa-ard, S., & Promvonge, P. (2005). Enhancement of Heat Transfer in a Tube with Regularly-Spaced Helical Tap Swirl Generators. Solar Energy, 78, 483-494.
[4] Yilmaz, M., Comakli, O., Yapici, S., & Sara O. (2003). Heat Transfer and Friction Characteristics in Decaying Swirl Flow Generated by Different Radial Guide Vane Swirl Generators. Energy Converse Management, 44(2), 283-300.
[5] Yilmaz, M., Comakli, O., & Yapici, S. (1999). Enhancement of Heat Transfer by Turbulent Decaying Swirl Flow. Energy Converse Management, 40(13), 1365-1376.
[6] Marner, W., & Bergles, A. (1978). Augmentation of Tube Side Laminar Flow Heat Transfer by Means of Twisted–Tap Inserts. Static Mixer Inserts and Internally Finned Tubes. J. Illum. Eng. Soc. Aug.7-11.Natl Res. Counc. of Can.
[7] Marner, W., & Bergles, A. (1985). Augmentation of Highly Viscous Laminar Tube Side Heat Transfer by Means of a Heat Twisted-Tap Insert and an Internally Finned Tubes. ASME.HTD, 43, 19-28.
[8] Mamer, W. J., & Bergles, A. E. (1989). Augmentation of Highly Viscous Laminar Heat Transfer Inside Tubes in Constant Wall Temperature. Experimental Thermal Fluid Science, 2(3), 252-267.
[9] Manglik, R., & Bergles, A. (1987). Correlation for Laminar Flow Enhanced Heat Transfer in Uniform Wall Temperature Circular Tubes with Twisted-Tape Inserts. ASME.HTD., 68, 19-25.
[10] Manglik, R., & Bergles, A. (1993). Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part 1-Laminar Flows. ASME.J. Heat Transfer. 115(4), 881-889.
[11] Manglik, R., & Bergles, A. (1993). Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part II-Transition and Turbulent Flows. ASME. J. Heat Transfer, 115(4), 890-896.
[12] Kedzierski, M., & Goncalves, J. (1999). Horizontal Convective Condensation of Alternative Refrigerants Within a Micro-Fin Tube. Enhanced Heat Transfer, 6, 161-178.
[13] Hsieh, S., Liu M.H., & Wu, F. Y. (1998). Developing Turbulent Mixed Convection in a Horizontal Circular Tube with Strip-Type Inserts. Int. J. Heat and Mass Transfer, 41(8-9), 1049-1063.
[14] Yakut, K., & Sahin, B. (2004). Flow-Induced Vibration Analysis of Conical Rings Used of Heat Transfer Enhancement in Heat Exchanger. Applied Energy, 78(3), 273–288.
[15] Yakut, K., Sahin, B., & Canbazoglu, S. (2004). Performance and Flow-Induced Vibration Characteristics for Conical-Ring Turbulators. Applied Energy, 79(1), 65–76.
[16] P r o m v o n g e , P, & E i a m s a - a r d S . ( 2 0 0 7 ) . Heat Transfer Augmentation in a Circular Tube Using V-Nozzle Turbulator Inserts and Snail Entry. Exp. Therm. Fluid Sci., 32(1), 332–40.
[17] Promvonge, P., & Eiamsa-ard, S. (2006). Heat Transfer Enhancement in a Tube with Combined Conical-Nozzle Inserts and Swirl Generator. Energy Convers. Manage., 47(18-19), 2867–82.
[18] Promvonge, P., & Eiamsa-ard, S. (2007). Heat Transfer in a Circular Tube Fitted with Free Spacing Snail Entry and Conical-Nozzle Turbulators. Int. Commun. Heat Mass Transfer, 34(7), 838–48.
[19] Promvonge, P, & Eiamsa-ard, S. (2007). Heat Transfer Behaviors in a Tube with Combined Conical-Ring and Twisted-Tape Insert. Int Commun Heat Mass Transfer, 34(7), 849–59.
[20] Promvonge, P. (2008). Thermal Augmentation in Circular Tube with Twisted Tape and Wire Coil Turbulators. Energy Convers. Manage., 49(11), 2949–55.
[21] Promvonge, P. (2008). Thermal Enhancement in a Round Tube with Snail Entry and Coiled-Wire Inserts. Int Commun Heat Mass Transfer, 35(5), 623–9.
[22] Promvonge, P., Teerapat, C., Sutapat, K., & Chinaruk, T.(2010). Enhanced Heat Transfer in a Triangular Ribbed Channel with Longitudinal Vortex Generators. Energy Conversion and Management, 51(6), 1242–1249.
[23] Eiamsa-ard, S., & Promvonge, P. (2006). Experimental Investigation of Heat Transfer and Friction Characteristics in a Circular Tube Fitted with V-Nozzle Turbulators. International Communications in Heat and Mass Transfer, 33(5), 591–600.
[24] Ibrahim, E. (2011). Augmentation of Laminar Flow and Heat Transfer in Flat Tubes by Means of Helical ScrewTape Inserts. Energy Conversion and Management, 52(1), 250–257.
[25] Qu, W. L., Mala, G. M., & Li, D. Q. (2000). Heat Transfer for Water Flow in Trapezoidal Silicon Micro Channels. Int. J. Heat Mass Transfer, 43(21), 3925–3936.
[26] Qu, W. L., Mala, G. M., & Li, D. (2000). Pressure-Driven Water Flows in Trapezoidal Silicon Micro Channels. Int. J. Heat Mass Transfer, 43(3), 353–364.
[27] Rahman, M., & Shevade, S. (2005). Fluid Flow and Heat Transfer in a Composite Trapezoidal Micro Channel. In: Proc. 2005 ASME Summer Heat Transfer Conference (pp. 411–417).
[28] Wu, H., & Cheng, P. (2003). Friction Factors in Smooth Trapezoidal Silicon Micro Channels with Different Aspect Ratios. Int. J. Heat Mass Transfer, 46(14), 2519–2525.
[29] Wu, H., & Cheng, P. (2003). An Experimental Study of Convective Heat Transfer in Silicon Micro Channels with Different Surface Conditions. Int. J. Heat Mass Transfer, 46(14), 2547–2556.
[30] Sadasivam, R., Manglik, R., & Jog, M. (1999). Fully Developed Forced Convection Through Trapezoidal and Hexagonal Ducts. Int. J. Heat Mass Transfer, 42(23), 4321–4331.
[31] Kamali, R., & Binesh, A. (2008). The Importance of Rib Shape Effects on the Local Heat Transfer and Flow Friction Characteristics of Square Ducts with Ribbed Internal Surfaces. International Communications in Heat and Mass Transfer, 35(8), 1032–1040.
[32] John, P., & Suresh, V. (2010). Heat Transfer in Trapezoidal Micro Channels of Various Aspect Ratios. International Journal of Heat and Mass Transfer, 53, 365–37.
[33] ANSI/ASME. (1986). Measurement Uncertainty (PTC 19, pp. 1-1985).
[34] Bejan, A. (1996). Entropy Generation Minimization. Boca Raton, FL: CRC Press.
[35] Ko, T., & Ting, K. (2005). Entropy Generation and Thermodynamic Optimization of Fully Developed Laminar Convection in a Helical Coil. Int Commune Heat Mass Transfer, 32(1-2), 214–23.
Heat transfer, friction factor and entropy generation from the inside surface of a horizontal circular tube fitted with trapezium - nozzle have been investigated experimentally. The heat transfer test section is heated electrically imposing axially and circumferentially constant wall heat flux. Three different pitch ratios (PR) of trapezium -nozzle arrangements in the test tube are introduced with PR=2, 4, and 7. The experiments covered a range of Reynolds numbers from 8000 to16000. Heat transfer and friction factor analyses are presented for different conditions of pitch ratios (PR) and Reynolds number. The results indicate that the trapezium - nozzle of different pitch ratios has a great effect on the results of heat transfer coefficient and friction factor. The Nusslet number increases with an increase in Reynolds number and it decreases with an increase in pitch ratios. It is found that using the trapezium -nozzle results in increasing the heat transfer rate compared with the plain tube. The maximum gain in Nusslet number is obtained for the smallest pitch ratio used, PR=2. This indicates that the effect of the reverse/re-circulation and surface flows can improve the heat transfer rate in the circular tube. For fixed Reynolds number, the friction factor increases with the decrease in pitch ratio for the circular tubes with trapezium -nozzle. The entropy generation number increases with increase Reynolds number at all cases, whereas the entropy generation number shows its highest value at pitch ratio of 2. From these results, it was found that the average enhancement in Nusselt number for circular tube fitted with trapezium - nozzle at pitch ratio (PR=2) is in the range of 202% to 257% compared with the plain circular tube for all tested conditions. Correlations of the Nusselt number and friction factor with Reynolds number and pitch ratio are presented.
Key words: Enhancement heat transfer; Circular tube; Re-circulation/Reverse flow; Turbulator; Entropy generation; Trapezium –nozzle
REFERENCES
[1] Bergles A., & Webb, R. (1985). Guide to the Literature on Convection Heat Transfer Augmentation. Advances in Enhanced Heat Transfer, 43, 81–89.
[2] Marner, W., Bergles, A., & Chenoweth, J. (1983). On the Presentation of Performance Data for Enhanced Tubes Used in Shell and Tube Heat Exchangers. Transaction ASME, Journal Heat Transfer, 105, 358–365.
[3] Eiamsa-ard, S., & Promvonge, P. (2005). Enhancement of Heat Transfer in a Tube with Regularly-Spaced Helical Tap Swirl Generators. Solar Energy, 78, 483-494.
[4] Yilmaz, M., Comakli, O., Yapici, S., & Sara O. (2003). Heat Transfer and Friction Characteristics in Decaying Swirl Flow Generated by Different Radial Guide Vane Swirl Generators. Energy Converse Management, 44(2), 283-300.
[5] Yilmaz, M., Comakli, O., & Yapici, S. (1999). Enhancement of Heat Transfer by Turbulent Decaying Swirl Flow. Energy Converse Management, 40(13), 1365-1376.
[6] Marner, W., & Bergles, A. (1978). Augmentation of Tube Side Laminar Flow Heat Transfer by Means of Twisted–Tap Inserts. Static Mixer Inserts and Internally Finned Tubes. J. Illum. Eng. Soc. Aug.7-11.Natl Res. Counc. of Can.
[7] Marner, W., & Bergles, A. (1985). Augmentation of Highly Viscous Laminar Tube Side Heat Transfer by Means of a Heat Twisted-Tap Insert and an Internally Finned Tubes. ASME.HTD, 43, 19-28.
[8] Mamer, W. J., & Bergles, A. E. (1989). Augmentation of Highly Viscous Laminar Heat Transfer Inside Tubes in Constant Wall Temperature. Experimental Thermal Fluid Science, 2(3), 252-267.
[9] Manglik, R., & Bergles, A. (1987). Correlation for Laminar Flow Enhanced Heat Transfer in Uniform Wall Temperature Circular Tubes with Twisted-Tape Inserts. ASME.HTD., 68, 19-25.
[10] Manglik, R., & Bergles, A. (1993). Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part 1-Laminar Flows. ASME.J. Heat Transfer. 115(4), 881-889.
[11] Manglik, R., & Bergles, A. (1993). Heat Transfer and Pressure Drop Correlations for Twisted-Tape Inserts in Isothermal Tubes: Part II-Transition and Turbulent Flows. ASME. J. Heat Transfer, 115(4), 890-896.
[12] Kedzierski, M., & Goncalves, J. (1999). Horizontal Convective Condensation of Alternative Refrigerants Within a Micro-Fin Tube. Enhanced Heat Transfer, 6, 161-178.
[13] Hsieh, S., Liu M.H., & Wu, F. Y. (1998). Developing Turbulent Mixed Convection in a Horizontal Circular Tube with Strip-Type Inserts. Int. J. Heat and Mass Transfer, 41(8-9), 1049-1063.
[14] Yakut, K., & Sahin, B. (2004). Flow-Induced Vibration Analysis of Conical Rings Used of Heat Transfer Enhancement in Heat Exchanger. Applied Energy, 78(3), 273–288.
[15] Yakut, K., Sahin, B., & Canbazoglu, S. (2004). Performance and Flow-Induced Vibration Characteristics for Conical-Ring Turbulators. Applied Energy, 79(1), 65–76.
[16] P r o m v o n g e , P, & E i a m s a - a r d S . ( 2 0 0 7 ) . Heat Transfer Augmentation in a Circular Tube Using V-Nozzle Turbulator Inserts and Snail Entry. Exp. Therm. Fluid Sci., 32(1), 332–40.
[17] Promvonge, P., & Eiamsa-ard, S. (2006). Heat Transfer Enhancement in a Tube with Combined Conical-Nozzle Inserts and Swirl Generator. Energy Convers. Manage., 47(18-19), 2867–82.
[18] Promvonge, P., & Eiamsa-ard, S. (2007). Heat Transfer in a Circular Tube Fitted with Free Spacing Snail Entry and Conical-Nozzle Turbulators. Int. Commun. Heat Mass Transfer, 34(7), 838–48.
[19] Promvonge, P, & Eiamsa-ard, S. (2007). Heat Transfer Behaviors in a Tube with Combined Conical-Ring and Twisted-Tape Insert. Int Commun Heat Mass Transfer, 34(7), 849–59.
[20] Promvonge, P. (2008). Thermal Augmentation in Circular Tube with Twisted Tape and Wire Coil Turbulators. Energy Convers. Manage., 49(11), 2949–55.
[21] Promvonge, P. (2008). Thermal Enhancement in a Round Tube with Snail Entry and Coiled-Wire Inserts. Int Commun Heat Mass Transfer, 35(5), 623–9.
[22] Promvonge, P., Teerapat, C., Sutapat, K., & Chinaruk, T.(2010). Enhanced Heat Transfer in a Triangular Ribbed Channel with Longitudinal Vortex Generators. Energy Conversion and Management, 51(6), 1242–1249.
[23] Eiamsa-ard, S., & Promvonge, P. (2006). Experimental Investigation of Heat Transfer and Friction Characteristics in a Circular Tube Fitted with V-Nozzle Turbulators. International Communications in Heat and Mass Transfer, 33(5), 591–600.
[24] Ibrahim, E. (2011). Augmentation of Laminar Flow and Heat Transfer in Flat Tubes by Means of Helical ScrewTape Inserts. Energy Conversion and Management, 52(1), 250–257.
[25] Qu, W. L., Mala, G. M., & Li, D. Q. (2000). Heat Transfer for Water Flow in Trapezoidal Silicon Micro Channels. Int. J. Heat Mass Transfer, 43(21), 3925–3936.
[26] Qu, W. L., Mala, G. M., & Li, D. (2000). Pressure-Driven Water Flows in Trapezoidal Silicon Micro Channels. Int. J. Heat Mass Transfer, 43(3), 353–364.
[27] Rahman, M., & Shevade, S. (2005). Fluid Flow and Heat Transfer in a Composite Trapezoidal Micro Channel. In: Proc. 2005 ASME Summer Heat Transfer Conference (pp. 411–417).
[28] Wu, H., & Cheng, P. (2003). Friction Factors in Smooth Trapezoidal Silicon Micro Channels with Different Aspect Ratios. Int. J. Heat Mass Transfer, 46(14), 2519–2525.
[29] Wu, H., & Cheng, P. (2003). An Experimental Study of Convective Heat Transfer in Silicon Micro Channels with Different Surface Conditions. Int. J. Heat Mass Transfer, 46(14), 2547–2556.
[30] Sadasivam, R., Manglik, R., & Jog, M. (1999). Fully Developed Forced Convection Through Trapezoidal and Hexagonal Ducts. Int. J. Heat Mass Transfer, 42(23), 4321–4331.
[31] Kamali, R., & Binesh, A. (2008). The Importance of Rib Shape Effects on the Local Heat Transfer and Flow Friction Characteristics of Square Ducts with Ribbed Internal Surfaces. International Communications in Heat and Mass Transfer, 35(8), 1032–1040.
[32] John, P., & Suresh, V. (2010). Heat Transfer in Trapezoidal Micro Channels of Various Aspect Ratios. International Journal of Heat and Mass Transfer, 53, 365–37.
[33] ANSI/ASME. (1986). Measurement Uncertainty (PTC 19, pp. 1-1985).
[34] Bejan, A. (1996). Entropy Generation Minimization. Boca Raton, FL: CRC Press.
[35] Ko, T., & Ting, K. (2005). Entropy Generation and Thermodynamic Optimization of Fully Developed Laminar Convection in a Helical Coil. Int Commune Heat Mass Transfer, 32(1-2), 214–23.