Minimizing the entropy production in heat exchange

Johannessen, Eivind; Nummedal, Lars; Kjelstrup, Signe

doi:10.1016/s0017-9310(01)00362-3

Cited by 106 publications

(70 citation statements)

References 8 publications

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“…(30) is the same as the left side of Eq. (25). Hence, the condition corresponding to the minimum lost available work strategy is that corresponding to a constant rate of lost available work, not only valid for Newton's heat transfer law but also valid for the generalized convective heat transfer law, in which the conclusions in Refs.…”

Section: Effects Of Heat Transfer Lawsmentioning

confidence: 95%

“…6 shows dependence of the dimensionless system temperature z(ω) on the dimensionless time ω in case of the heat transfer law q ∝ (∆(T 4 )) 1. 25 . The highest dimensionless system temperature z(ω) during the whole heat transfer process corresponds to the strategy of T 1 = const, the dimensionless system temperature z(ω) for the strategy of q = const lies between that for the strategy of T 1 = const and that for the strategy of S = min, the lowest dimensionless system temperature z(ω) corresponds to the strategy of W l = min.…”

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

“…7 shows dependence of the ratio of the reservoir temperature to the system temperature u(ω) on the dimensionless time ω in case of the heat transfer law q ∝ (∆(T 4 )) 1. 25 . At the beginning of heat transfer process, the temperature ratio u(ω) for the strategy of W l = min is larger than that for the other strategies, while at the end of heat transfer process, the temperature ratio u(ω) for the strategy of W l = min is smaller than those for the other strategies.…”

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

“…8 shows dependence of the dimensionless rate of lost available workW l on the dimensionless time ω in case of the heat transfer law q ∝ (∆(T 4 )) 1. 25 . Compared to the results with the Dulong-Petit heat transfer law, the differences of the time variations ofW l among the strategies of q = const, S = min and T 1 = const are smaller.…”

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

“…Based on Ref. [24], Johannessen et al [25] further considered that the heat transfer coefficient is related to the local temperature changes, and showed that the local entropy generation rate is constant, i.e. equipartition of entropy production (EoEP).…”

Section: Introductionmentioning

confidence: 99%

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Optimal paths for minimizing lost available work during heat transfer processes with a generalized heat transfer law

Shao-Jun¹,

Chen²,

Sun³

2009

Braz. J. Phys.

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A common of finite-time heat transfer processes between high-and low-temperature sides with a generalized heat transfer law [q ∝ (∆(T n )) m ] are studied in this paper. The optimal heating and cooling configurations for minimizing lost available work are derived for the fixed initial and final temperatures of the working fluid of the system (low-temperature side). Optimal paths are compared with the common strategies of constant heat flux, constant source (reservoir) temperature and the minimum entropy generation operation by numerical examples. The condition corresponding to the minimum lost available work strategy is that corresponding to a constant rate of lost available work, not only valid for Newton's heat transfer law [q ∝ ∆T ] but also valid for the generalized convective heat transfer law [q ∝ (∆T ) m ]. The obtained results are more general and can provide some theoretical guidelines for the designs and operations of practical heat exchangers.

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Section: Effects Of Heat Transfer Lawsmentioning

confidence: 95%

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

Section: Numerical Example For the Heat Transfer Lawmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Optimal paths for minimizing lost available work during heat transfer processes with a generalized heat transfer law

Shao-Jun¹,

Chen²,

Sun³

2009

Braz. J. Phys.

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Optimal distribution of temperature driving forces in low‐temperature heat transfer

Austbø

Gundersen

2015

AIChE Journal

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A fairly extensive review of research on optimal distribution of driving forces in heat-transfer processes is provided. Four different guidelines for specifying the temperature profiles in heat exchangers have been compared. Not surprisingly, the irreversibilities due to heat transfer in a heat exchanger of given size were found to be minimized when the temperature difference is proportional to the absolute temperature. Comparing a design with an optimal temperature profile and a design with a uniform temperature difference throughout the heat exchanger, sensitivity analyses illustrated that savings in irreversibilities increase with decreasing temperature level and increasing temperature span for the cooling load. Heat exchanger size was found to be of negligible importance. The results indicated that optimal utilization of heat exchanger area is of little importance for processes operating above ambient temperature, while significant savings can be obtained by optimal distribution of temperature driving forces in processes below ambient temperature. V C 2015 American Institute of Chemical Engineers AIChE J, 61: 2447-2455, 2015 Keywords: process design, heat transfer, driving forces, exergy of heat, heat exchanger IntroductionBesides environmental and social aspects, process plants are designed and operated with the purpose of seeking return on investments.1 Hence, economic criteria are required to evaluate different design options and carry out optimization. 2In an early phase of process design, it is normally not possible to account for all fixed and variable costs.2 When comparing the relative merits of different structural options in a flow sheet and parameter settings, the economic criteria can be simplified by neglecting common items. 2The thermodynamic performance of a heat exchanger and thereby the energy cost related to operation can be improved by reducing its temperature driving forces. This does, however, require increasing the heat exchanger size and thereby the investment cost. In heat exchanger network synthesis and design, this conflict is often accommodated by assigning a minimum temperature difference in the heat exchangers.2,3 The minimum temperature difference is then used as an economic trade-off parameter, balancing the operating cost related to energy use and the investment cost of heat exchangers.This approach has been adopted in many studies for design of cryogenic refrigeration processes such as liquefaction of natural gas. 4 However, as pointed out by Jensen and Skogestad, 4 the use of a minimum temperature difference constraint in optimization of natural gas liquefaction processes leads to nonoptimal utilization of the heat exchanger area. This indicates that a design strategy aiming at uniform temperature difference throughout the heat-transfer process gives nonoptimal distribution of temperature driving forces. This is related to the behavior of exergy of heat, which increases steeply with decreasing temperature below ambient.Different design guidelines for optimal distribution of t...

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Equivalence between Minimum Entropy and Exergy Applied to Continuous Stirred‐Tank Reactors

Bispo

Manzi

2023

Chem Eng & Technol

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Minimum entropy and exergy concepts were applied to continuous stirred-tank reactors (CSTRs) to assess their effectiveness as analytical and optimization tools as well as to clarify some existing controversy regarding their practical applications. The second law of thermodynamics was used to establish in detail the concepts themselves or in the formulation of the exergy balance. Relevant information was extracted from both, in addition to which differences between them were revealed. By applying a commercial software package to the production of propylene glycol, the results of theoretical analysis and simulation showed that such concepts produced equivalent effects when applied to CSTRs and, due to the operating conditions, exergy proved to be independent of the so-called dead state. Therefore, it is concluded that both procedures lead to equivalent optimization strategies when applied to CSTRs and depending on the objectives, but the use of minimum entropy may be more advantageous for some approaches, as it does not depend on the dead state.

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Minimizing the entropy production in heat exchange

Cited by 106 publications

References 8 publications

Optimal paths for minimizing lost available work during heat transfer processes with a generalized heat transfer law

Optimal paths for minimizing lost available work during heat transfer processes with a generalized heat transfer law

Optimal distribution of temperature driving forces in low‐temperature heat transfer

Equivalence between Minimum Entropy and Exergy Applied to Continuous Stirred‐Tank Reactors

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