Entropy Analysis On Process Of Fluid Flow And Heat Transfer

Using the low position waste heat energy to reduce environment thermal pollution is one new field of technology development on clean production. Deciding its economic key is the using efficiency of waste heat energy. It needs special methods to overcome the disadvantage factor: lacking driving force for heat transfer of low potential energy, in order that the irreversible loss of system can be furthest reduced. Based on the second law of thermodynamics, the article focuses on two sides: thermodynamics entropy analyzes and temperature field entropy. According to researches on system irreversible loss for heat transfer and fluxion, it finds out the influence factors of driving force for heat transfer. It is valuable to assess the thermodynamics perfect degree of heat transfer and fluxion system and improve thermal performance of heat transfer system.According to the open system entropy production expression, depended on the"entropy production" conception and non-equilibrium state for thermodynamics process which had been demonstrated by Prigogin with the second law of thermodynamics, the analysis method of entropy generation is applied to thermal analysis of falling film evaporation. Through the introduction of unit entropy generation number it can be deduced the mathematical formula of unit entropy generation number in the tube of falling film evaporation. On the condition of Re>1450(C_pμ/λ)^-1.06(0.5-0.25ω)^-1, it obtains the relationships between unit entropy production number and the Reynold's number or theδ/R which obeys the following rules according to the numerical value calculating result:(1) In the tube of falling film evaporation process, entropy generation reduces firstly along with the increasing of fluid Reynold's number, then increases. There exists minimum unit entropy generation number which corresponds Re_opt, and this point is optimal working point;(2) Entropy generation complies the similar rule along with the reducing ofωlike Re. There also exists minimum unit entropy generation number which correspondsω_opt.In order to confirm the theoretical analysis model, the industrial experiment of DAP tail gas partial condensation combined with phosphoric acid falling film flow evaporation was carried out, and experimental data could be collected under long-term work conditions. Taking 30% phosphoric acid dilute solution as the working substance, it is proved that the theoretical analysis model and the experimental result tallies good through the empirical datum contrast of falling film flow evaporation experiment in theΦ30×2×6000 pipe that the phosphoric acid passing on. This mathematical formula can express the entropy generation rule in falling film evaporation process, and it has the actual applications for strengthening the force for the heat transfer process and enhancing the thermodynamic efficiency.On researches of Boltzmann law and information entropy theory, this article defined the temperature field entropy concept based on the definition of physical field entropy, and deduced the normal calculating formula about temperature field entropy. Compared with thermodynamics entropy, the analysis on thermodynamics entropy generation and the application on temperature field entropy are coherence, though they are different in levels and methods. Both of them can reflect the irreversible dissipation of driving force for heat transfer and fluxion.This formula can be applied in the thermal research of rectangular fin radiator to calculate the temperature field entropy according to the fin radiator temperature distribution function. It can quantitively express the irreversible loss of rectangular fin radiator for heat transfer by the irreversible dissipation of driving force in process. This article has also studied the influence factors to temperature field entropy. In the certain scope, a quantitative relationship is deduced that temperature field entropy is proportional with heat conduction coefficient and thickness or it is inverse proportional with length.According to formula of fin efficiency, we obtained the working curves ofηvs. L andηvs.σat different materials: steel, cadmium and aluminum. Compared with the change tendency of temperature field entropy along with the fin radiator characteristic parameter, it may be known that the temperature field entropy of rectangular fin radiation can not only reflect system's thermodynamics capability but also find out the change mechanism of fin efficiency. It is valuable for the actual application to optimize thermal system design.The results of the study can be summarized as the following: the entropy generation analysis may express the irreversible dissipation of driving force and the thermodynamics perfect degree of heat transfer and fluxion system which was proved by experimental data like as the temperature field entropy. According to these obtaining conclusions it is useful for heat transfer and fluxion system to improve the using ratio of driving force and to enhance heat transfer efficiency.