An alternative criterion in heat transfer optimization

Abstract

Entropy generation is recognized as a common measurement of the irreversibility in diverse processes, and entropy generation minimization has thus been used as the criterion for optimizing various heat transfer cases. To examine the validity of such entropy-based irreversibility measurement and its use as the optimization criterion in heat transfer, both the conserved and non-conservative quantities during a heat transfer process are analysed. A couple of irreversibility measurements, including the newly defined concept entransy, in heat transfer process are discussed according to different objectives. It is demonstrated that although thermal energy is conserved, the accompanied system entransy and entropy in heat transfer process are non-conserved quantities. When the objective of a heat transfer is for heating or cooling, the irreversibility should be measured by the entransy dissipation, whereas for heat-work conversion, the irreversibility should be described by the entropy generation. Next, in Fourier's Law derivation using the principle of minimum entropy production, the thermal conductivity turns out to be inversely proportional to the square of temperature. Whereas, by using the minimum entransy dissipation principle, Fourier's Law with a constant thermal conductivity as expected is derived, suggesting that the entransy dissipation is a preferable irreversibility measurement for heat transfer.

Entransy - a Novel Theory in Heat Transfer Analysis and Optimization

“…This loss or dissipation of the energy can be used as the measurement of irreversibility in these transport processes. However, an irreversible heat transfer process seems to have its own particularity, for the heat energy always remains constant during transfer and it doesn't appear to be readily clear what the non-conserved quantity is in a heat transfer process (Chen et al, 2011). Based on the analogy between electrical and heat conductions, Guo et al (2007) made a comparison between electrical conduction and heat conduction as shown in table 1.…”

“…1. Two-dimensional heat conduction with a uniformly distributed internal heat source (Chen et al, 2011) According to the new extremum principle based on entransy dissipation, for this volumepoint heat conduction problem, the optimization objective is to minimize the volumeaverage temperature, the optimization criterion is the minimum entransy dissipation, the optimization variable is the distribution of the HTCM, and the constraints is the fixed amount of the HTCM, i.e., ( )…”

“…Table 2. Optimized results obtained by the optimization criterions of minimum entropy generation and entransy dissipation extremum (Chen et al, 2011) …”

“…Recently, Guo et al (2007) introduced the concepts of entransy and entransy dissipation to measure, respectively, the heat transfer capacity of an object or a system, and the loss of such capacity during a heat transfer process. Moreover, Guo et al (2007) proposed the entransy dissipation extremum and the corresponding minimum entransy dissipation-based thermal resistance as alternative optimization criterions for heat transfer processes not involved in thermodynamic cycles, and consequently, developed the minimum entransy dissipation-based thermal resistance principle to optimize the processes of heat conduction (Guo et al, 2007;Chen et al, 2009aChen et al, , 2011, convective heat transfer (Meng et al, 2005;Chen et al, 2007Chen et al, , 2008Chen et al, , 2009b, thermal radiation (Cheng & Liang, 2011), and in heat exchangers (Liu et al, 2009;Guo et al, 2010). This chapter summarizes the entransy theory in heat transfer, such as the definitions of entransy, entransy dissipation and its corresponding thermal resistance with multitemperatures, the minimum entransy dissipation-based thermal resistance principle for heat transfer, etc., and introduces its applications in heat transfer optimization.…”

Application of entransy theory in the heat transfer optimization of flat-plate solar collectors

“…Moreover, Guo et al proposed the entransy dissipation extremum principle to optimize the processes of heat conduction [11][12][13][14][15], heat convection [16,17], and thermal radiation [18].…”