Entropy generation in combined heat and mass transfer

San, Jung‐Yang; Worek, William M.; Lavan, Z.

doi:10.1016/0017-9310(87)90168-2

Cited by 82 publications

(36 citation statements)

References 9 publications

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“…Selected conditions representative of condensers in HDH desalination and HVAC systems are studied. An HDH system has higher rates of mass transfer than contemplated in previous boundary layer analyses of noncondensable gas problems [26], and it involves condensation in the presence of much higher concentrations of noncondensables. However, the majority of the work presented here could be applied to any binary mixture with a single species diffusing out of the control volume of interest.…”

Section: Balancing and Entropy Generation Minimization In Heat Exchanmentioning

confidence: 96%

Entropy generation in condensation in the presence of high concentrations of noncondensable gases

Thiel

Lienhard

2012

International Journal of Heat and Mass Transfer

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The physical mechanisms of entropy generation in a condenser with high fractions of noncondensable gases are examined using scaling and boundary layer techniques, with the aim of defining a criterion for minimum entropy generation rate that is useful in engineering analyses. This process is particularly relevant in humidification-dehumidification desalination systems, where minimizing entropy generation per unit water produced is critical to maximizing system performance. The process is modeled by a consideration of the vapor/gas boundary layer alone, as it is the dominant thermal resistance and, consequently, the largest source of entropy production in many practical condensers with high fractions of noncondensable gases. Most previous studies of condensation have been restricted to a constant wall temperature, but it is shown here that for high concentrations of noncondensable gases, a varying wall temperature greatly reduces total entropy generation rate. Further, it is found that the diffusion of the condensing vapor through the vapor/noncondensable mixture boundary layer is the larger and often dominant mechanism of entropy production in such a condenser. As a result, when seeking to design a unit of desired heat transfer and condensation rates for minimum entropy generation, minimizing the variance in the driving force associated with diffusion yields a closer approximation to the minimum overall entropy generation rate than does equipartition of temperature difference.

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Section: Balancing and Entropy Generation Minimization In Heat Exchanmentioning

confidence: 96%

Entropy generation in condensation in the presence of high concentrations of noncondensable gases

Thiel

Lienhard

2012

International Journal of Heat and Mass Transfer

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“…Similarly, the augmentation of entropy generation rate due to 2 T , 3 T and 4 T in turbulent conditions in comparison to the corresponding laminar flames can be characterized by …”

Section: Mathematical Backgroundmentioning

confidence: 99%

“…Bejan [1] analysed the entropy generation mechanisms due to viscous action and heat transfer in channel flows. Local entropy generations due to heat and mass transfers in addition to viscous effects have been analyzed by San et al [2] and Poulikakos and Johnson [3]. Puri [4] analyzed entropy generation in the context of droplet combustion and identified the optimum transfer number for the purpose of minimization of entropy generation.…”

Section: Introductionmentioning

confidence: 99%

“…To analyze the relative contributions of viscous dissipation, heat conduction, mass diffusion and chemical reaction towards the overall entropy generation in turbulent premixed combustion. (2). To identify the effects of combustion regime, heat release parameter and global Lewis number on the different entropy generation mechanisms in turbulent premixed flames.…”

Section: Introductionmentioning

confidence: 99%

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A Direct Numerical Simulation-Based Analysis of Entropy Generation in Turbulent Premixed Flames

Farran

Chakraborty

2013

Entropy

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A compressible single step chemistry Direct Numerical Simulation (DNS) database of freely propagating premixed flames has been used to analyze different entropy generation mechanisms. The entropy generation due to viscous dissipation within the flames remains negligible in comparison to the other mechanisms of entropy generation. It has been found that the entropy generation increases significantly due to turbulence and the relative magnitudes of the augmentation of entropy generation and burning rates under turbulent conditions ultimately determine the value of turbulent second law efficiency in comparison to the corresponding laminar values. It has been found that the entropy generation mechanisms due to chemical reaction, thermal conduction and mass diffusion in turbulent flames strengthen with decreasing global Lewis number in comparison to the corresponding values in laminar flames. The ratio of second law efficiency under turbulent conditions to its corresponding laminar value has been found to decrease with increasing global Lewis number. An increase in heat release parameter significantly augments the entropy generation due to thermal conduction, whereas other mechanisms of entropy generation are marginally affected. However, the effects of augmented entropy generation due to thermal conduction at high values of heat release parameter are eclipsed by the increased change in availability due to chemical reaction, which leads to an increase in the second law efficiency with increasing heat release parameter for identical flow conditions. The combustion regime does not have any major influence on the augmentation of entropy generation due to chemical reaction, thermal conduction and mass diffusion in turbulent flames in comparison to corresponding laminar flames, whereas the extent of augmentation of entropy generation due to viscous dissipation in turbulent conditions in comparison to OPEN ACCESSEntropy 2013, 15 1541 corresponding laminar flames, is more significant in the thin reaction zones regime than in the corrugated flamelets regime. However, the ratio of second law efficiency under turbulent conditions to its corresponding laminar value does not get significantly affected by the regime of combustion, as viscous dissipation plays a marginal role in the overall entropy generation in premixed flames.

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“…A few researchers [2][3][4] have previously attempted to optimize the second law design of heat and mass exchange devices by studying the sources of irreversibilities at the local level. Carrington and Sun [4] presented the following expression for the volumetric entropy generation rate as a sum of the three components that arise in combined heat and mass transfer processes.…”

Section: Introductionmentioning

confidence: 99%

Entropy generation minimization of combined heat and mass transfer devices

Narayan

Lienhard

Zubair

2010

International Journal of Thermal Sciences

138

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This paper details a simple procedure by which the entropy generation in simultaneous heat and mass exchange devices can be minimized. Effectiveness for these devices is defined and a new parameter, 'modified heat capacity rate ratio' is introduced. It is found that the entropy generation of a combined heat and mass exchange device is minimized (at constant value of effectiveness) when the modified heat capacity rate ratio is equal to one irrespective of the value of other independent parameters. Several typical examples of the cooling towers have been studied to illustrate this concept. A practical application of the concept is also illustrated using a humidification-dehumidification desalination system.

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Entropy generation in combined heat and mass transfer

Cited by 82 publications

References 9 publications

Entropy generation in condensation in the presence of high concentrations of noncondensable gases

Entropy generation in condensation in the presence of high concentrations of noncondensable gases

A Direct Numerical Simulation-Based Analysis of Entropy Generation in Turbulent Premixed Flames

Entropy generation minimization of combined heat and mass transfer devices

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