Augmentation And Optimization On Heat Conduction And Convection Processes

The goal of heat transfer augmentation established on the description and judge of the whole heat transfer performances can be stated as the desire to encourage or accommodate high heat fluxes. Almost all the augmentation techniques are used to vary the local behavior of heat transfer so as to improve the whole performance. Considering the constraint conditions, heat transfer augmentation appears the feature of optimizations from whole to local, namely, in order to realize the best whole heat transfer performances, how to design the local behavior of the heat transfer process? Taking heat conduction and convection optimizations as the research objects, this dissertation is to solve the above foundational problems by means of variation principle in the field of heat transfer augmentation, and explore some theoretical conclusions to direct the selection and actualization of augmentation techniques. For the augmentation of heat conduction, the principle of temperature-gradient uniformity governing the optimal distribution of the thermal conductivity is presented and proved theoretically. Based on this principle, bionic optimization technique is introduced to search the optimal spatial distribution of the high-conductivity material in pursuit of the maximum heat transfer at a given temperature difference. For connective heat transfer augmentation, the field-coordination equations are given and theoretically proved to achieve the optimal heat transfer performance at a constant flow resistance. For fin system, the spatial distributions of three defined physical quantities, filling ratio, extend measure and stretch direction, are described for general fin structures. Based on which the heat transfer between fin system and fluid is modeled mathematically. Finally, three foundational principles are presented for the optimal design of the fin system with lower flow resistance and higher heat transfer rate.To perform the optimization analysis, a new numerical simulation method, named as dual-velocity algorithm for flow calculation on collocated grids,is developed and the iterative formulas of the optimization principles are presented. Numerical simulations on specific heat transfer problems are performed to show theremarkable augmented effects resulting from process optimization, and to recognize the theoretical significances of process optimization to the study of heat transfer augmentation. Dominated by the deterministic simple principle, numerical simulations of bionic optimization show picturesquely the evolution procedure of numerous and complicated shapes of high-conductivity material. In the velocity field optimization, the optimal velocity fields are able to direct augmentation techniques how to blend or to mix fluid so as to realize the maximum effect of heat transfer augmentation. With the variations of the configurations, boundary conditions or flow resistance, the trend from quantitative variation to qualitative variation of the optimal flow state is full proof of the coordination between the velocity and heat flux fields, which enriches and develops further the field-coordination theory. In the fin-structure optimization, numerical results can offer detailed constructional information about the optimal fin system, for example, where fin needs to extend its surface, and how much area fin extends, etc. Furthermore, two kinds of heat transfer enhancement tubes with fiber fins are designed and tested. The results show that the two enhancement tubes developed by means of the fin system augmentation principle are of superior performances of lower flow resistance and higher heat transfer, which is coincident with the prediction in fin-structure optimization.