Extended Performance Evaluation Criteria Research Articles

Performance evaluation of ducts with non-circular shapes: Laminar fully developed flow and constant wall temperature

Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through bundle of ducts with non-circular shape – rectangular, isosceles triangular, elliptical, trapezoidal and hexagonal. The bundle of circular tubes has been used as a reference heat transfer unit. Constant wall temperature has been selected as the thermal boundary condition. The performance characteristics of the bundles with non-circular ducts have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the hydraulic diameter of the duct has been specified.The results clearly show that the rectangular, trapezoidal or hexagonal duct configuration can compete, in some cases, with the circular tube configuration. The choice of the tube shape and geometrical details depends on the constraints imposed and the objectives pursued. The results obtained from the present study revealed that they differed from those obtained with a common constraint of specified cross sectional area.

Estimation of entropy generation by heat transfer from a liquid in an enclosure to ambient

This study outlines the estimation of entropy generation of a stored liquid-vapour combination. A salient feature of the present study is the incorporation of a separated flow model for the calculation of entropy generated by a diabatic two phase system. Equations of state corresponding to different thermodynamic equilibria are used for these calculations. Two distinct expressions are proposed for the determination of the total entropy generated by the diabatic saturated two phase system that comprise liquid and ullage regions. The dissipative energy losses in various liquid-ullage systems is quantified through the derived mathematical relations obtained for the overall entropy generated by the system. These developed expressions form the basis of an experimental determination of the entropy generation rate. A parametric study on temperature influencing entropy generation has been performed in the context of different thermal transport mechanisms. The influence of fill levels on entropy generation was also analysed by considering a low and an intermediate filling ratio. The study concluded the influence of central zone of thermodynamic equilibrium with maximum wall convection and minimum concentration gradient on the overall entropy generated by the system. References A. Bejan. A study of entropy generation in fundamental convective heat transfers. ASME J Heat Transfer, 101, 1979, 718--725. doi:10.1115/1.3451063 A. Bejan. Second law analysis in heat transfer. Energy, 5, 1980, 721--732. doi:10.1016/0360-5442(80)90091-2 S. Sarangi. and K. Chowdhury. On the generation of entropy in a counter flow heat exchanger. Cryogenics, 22, 1982, 63--65. doi:10.1016/0011-2275(82)90095-9 P. K. Nag and P. Mukherjee. Thermodynamic optimization of convective heat transfer through a duct with constant wall temperature. Int J. Heat and Mass Transfer, 30, 1987, 401--405. doi:10.1016/0017-9310(87)90128-1 A. Bejan A thermodynamic optimization of geometry in engineering flow systems. Exergy Int. Journal, 4, 2001, 269--277. doi:10.1016/S1164-0235(01)00028-0 V. D. Zimparov Extended performance evaluation criteria for enhanced heat transfer surfaces: heat transfer through ducts with constant heat flux. Int J. Heat and Mass Transfer, 44, 2001, 169--180. doi:10.1016/S0017-9310(00)00074-0 H. Abbassi Entropy generation analysis in a uniformly heated micro channel heat sink. Energy, 32, 2007, 1932--1947. doi:10.1016/j.energy.2007.02.007 F. J. Collado The law of stable equilibrium and the entropy-based boiling curve for flow boiling. Energy, 30, 2005, 807--819. doi:10.1016/j.energy.2004.04.007 J. V. C. Vargas and A. Bejan Thermodynamic optimization of the match between two streams with phase change. Energy, 25, 2000, 15--33. doi:10.1016/S0360-5442(99)00052-3 P. K. Nag Engineering Thermodynamics. Tata McGraw-Hill Publishing Company Limited, 2nd Edition, 1996. W. M. Rohsenow, J. P. Hartnett, Y. I. Cho, Hand book of Heat Transfer. McGraw-Hill New York,3rd Edition, 1988. D. Rakshit, R. Narayanaswamy, T. Truong, K. P. Thiagarajan An experimental study on the interface mass transfer governing thermodynamics of stored liquids. Proceedings of the 20th National and 9th International ISHMT-ASME Heat and Mass Transfer Conference, January 4--6, 2010, Mumbai India. C. Balaji, M. Hˆlling, H. Herwig Entropy generation minimization in turbulent mixed convection flows. International Communications in Heat and Mass Transfer, 34, 2007, 544--552. doi:10.1016/j.icheatmasstransfer.2007.01.015 F. P. Incropera, D. P. Dewitt, T. L. Bergmen, A. S. Lavine Introduction to Heat Transfer. John Willey and Sons, 5th Edition, 2005. P.E. Liley, Steam Tables in SI Units, private communication. School of Mechanical Engineering, Purdue University, West Lafayette, IN., 1984. V. V. Malyshev and E. P. Zlobin Evaporation of liquid hydrocarbons in heated closed containers. Translated from Inzheneruo-Fizicheskii Zhurnal, 23, 4, 1972, 701--708. doi:10.1007/BF00835847

Performance Evaluation of Some Tube Inserts as Heat Transfer Enhancement Techniques

Different heat transfer enhancement techniques can be used successfully in the retrofit design of shell-and-tube heat exchangers that can lead to significant cost savings. Tube inserts are frequently used in such applications. Twisted tapes, wire coils, helically coiled ribbons (as tube inserts in smooth pipes), and rifled pipes have been evaluated as heat transfer enhancement techniques. To assess the benefit of using these kinds of techniques, extended performance evaluation criteria (PEC) have been implemented under different constraints. The decrease in entropy generation can be combined with the relative increase in the heat transfer rate or decrease of the heat transfer area to determine the geometrical parameters of the tubes for optimal thermodynamics performance.

Performance evaluation of tube-in-tube heat exchangers with heat transfer enhancement in the annulus

Different techniques as angled spiraling tape inserts, a round tube in side a twisted square tube and spiraled tube in side the annulus have been used to enhance heat transfer in the annulus of tube-in-tube heat exchangers. The heat transfer enhancement in the shell can be supplemented by heat transfer augmentation in tubes using twisted tape inserts or micro-finned tubes. The effect of the thermal resistance of the condensing refrigerant could also be taken into consideration. To assess the benefit of using these techniques extended performance evaluation criteria have been implemented at different constraints. The decrease of the entropy generation can be combined with the relative in crease of the heat transfer rate or the relative reduction of the heat transfer area to find out the geometrical parameters of the tubes for optimal thermodynamics performance. The results show that in most of the cases considered, the angled spiraling tube insert technique is the most efficient.

Energy conservation through heat transfer enhancement techniques

Enhanced heat transfer surfaces have been successfully used in the heat transfer industry to obtain more compact and efficient units. Conservation of the useful part of energy (exergy) can be reached through higher heat transfer than that for standard surfaces and flow configurations. There are numerous ways for heat transfer augmentation which have been marketed or tested in laboratories. In this paper, we review some of the passive techniques for single-phase flow. One of the most promising heat transfer enhancement techniques is the compound augmentation method, in which different enhancement techniques are used simultaneously. Extended performance evaluation criteria (PEC) equations for enhanced heat transfer surfaces based on the entropy production theorem are developed to include the effect of fluid temperature variation along the length of a tubular heat exchanger and assess two objectives simultaneously. The need for this more comprehensive treatment of PEC compared to previous references is illustrated by the analysis of heat transfer and friction characteristics of ten spirally corrugated tubes. These PEC are used to assess the multiplicative effect when a corrugated tube is combined with twisted tape insert. Copyright © 2002 John Wiley & Sons, Ltd.

Enhancement of heat transfer by a combination of a single-start spirally corrugated tubes with a twisted tape

Abstract Heat transfer and isothermal friction pressure drop results have been obtained experimentally for two single-start spirally corrugated tubes combined with five twisted-tape inserts with different relative pitches in the range of Reynolds number 4×10 3 −6×10 4 . The characteristic parameters of the tubes are: height-to-diameter ratio, e / D i =0.0371 and 0.0441; and relative pitch, H / D i =7.7,6.25,3.95,2.95,2.4. Significantly, higher friction factor and inside heat transfer coefficients than those of the smooth tube under the same operating conditions have been observed. Extended performance evaluation criteria (PEC) equations for enhanced heat transfer surfaces have been used to assess the multiplicative effect. Thermodynamic optimum can be defined by minimizing the entropy generation number compared with the relative increase of heat transfer rate or relative reduction of heat transfer area.

Enhancement of heat transfer by a combination of three-start spirally corrugated tubes with a twisted tape

Heat transfer and isothermal friction pressure drop results have been obtained experimentally for two three-start spirally corrugated tubes combined with five twisted tape inserts with different relative pitches in the range of Reynolds number 3×10 3–6×10 4. The characteristic parameters of the tubes are: height to diameter ratio, e/ D i=0.0407 and 0.0569; and relative pitch, H/ D i=15.3, 12.2, 7.7, 5.8, 4.7. Significantly, higher friction factor and inside heat-transfer coefficients than those of the smooth tube under the same operating conditions have been observed. Extended performance evaluation criteria (PEC) equations for enhanced heat transfer surfaces have been used to assess the multiplicative effect. Thermodynamic optimum can be defined by minimizing the entropy generation number compared with the relative increase of heat transfer rate or relative reduction of heat transfer area.

Extended performance evaluation criteria for enhanced heat transfer surfaces: heat transfer through ducts with constant heat flux

Extended performance evaluation criteria equations for enhanced heat transfer surfaces based on the entropy production theorem are developed to include the effect of fluid temperature variation along the length of a tubular heat exchanger. The equations originate from various design constraints and generalize the performance evaluation criteria (PEC) for enhanced heat transfer techniques obtained by means of first law analysis. The general evaluation criteria add new information to Bejan’s entropy generation minimization method assessing two objectives simultaneously. The application of this more comprehensive treatment of PEC compared with previous references is illustrated by the analysis of heat transfer and fluid friction characteristics of 10 spirally corrugated tubes assessing the benefit of these tubes as an augmentation technique. The results for different design constraints show that the optimum rib-height-to-diameter ratio ( e/D) for these tubes is about 0.04.

Extended performance evaluation criteria for enhanced heat transfer surfaces: heat transfer through ducts with constant wall temperature

Extended performance evaluation criteria equations for enhanced heat transfer surfaces based on the entropy production theorem have been developed to include the effect of fluid temperature variation along the length of a tubular heat exchanger with constant wall temperature as a boundary condition. The equations originate from various design constraints and generalize the performance evaluation criteria (PEC) for enhanced heat transfer techniques obtained by means of first-law analysis. The general evaluation criteria add new information to Bejan’s entropy generation minimization (EGM) method assessing two objectives simultaneously. The application of this more comprehensive treatment of PEC compared to previous references is illustrated by the analysis of heat transfer and fluid friction characteristics of 10 spirally corrugated tubes assessing the benefit of these tubes as an augmentation technique. The results for different design constraints show that the optimum rib-height-to diameter ratio ( e/ D) for these tubes is about 0.04.

Extended performance evaluation criteria for enhanced heat transfer surfaces

Extended performance evaluation criteria for enhanced heat transfer surfaces

Extended performance evaluation criteria for enhanced heat transfer surfaces

Extended performance evaluation criteria for enhanced heat transfer surfaces