Investigation Of Flow And Heat Transfer In Mini/Micro Tubes And Related Basic Physical Properties

Due to the broad applied prospects of microchemical technology in many fields such as production of high added value product, design of high efficient equipment in heat and mass transfer, flammable and explosive reaction, production of hazardous or toxic chemicals, strong exothermic reaction, and miniaturization of fuel cell and its vehicle-mounted system etc, the investigations of fluid flow and heat transfer in microtubes have been receiving more and more recognition. Problems such as if the conventional theory are still valid in micro scale, what factors which are negligible in conventional scale will have effect on the fluid flow and heat transfer in micro scale, and so on should be analyzed and discussed. In this paper, the liquid flow characteristics of deionized water, ethanol, and six ionic liquids (ILs) aqueous solutions and the heat transfer characteristics of nine common chemical fluids were studied. Meanwhile, the related theory and modeling in these subjects were investigated.The main contents are generalized as follows:1. Based on the Guggenheim equation, a corresponding-states group-contribution method was developed to estimate the surface tension of ionic liquids. For a database of1224data points for105ILs, the calculated surface tensions agree well with the experimental data from literatures, it satisfied the need of engineering appliance; Based on the absolute rate and free volume theories, a new hybrid model was developed to estimate the viscosity of ionic liquids. For a database of1073data points for156ILs, this model can provide a higher estimation accuracy than other models proposed before; Based on the Reidel equation, a new model was developed to estimate the thermal conductivity of ionic liquids. For a database of296data points for36ILs, the estimation accuracy is less than the experimental uncertainty (3-5%). All the three models proposed here are based on the principle of group contribution method with a simple form. Only the critical temperature Tc or normal boiling temperature Tb which can be obtained from the literature are needed during the calculation.2. The surface tensions σ (278.15-313.15) K and densities ρ (278.15-313.15) K of aqueous solutions of1-ethyl-3-methyl-limidazolium bromide and1-butyl-3-methyl-limidazolium bromide and the dynamic viscosity η(283.15-313.15) K of aqueous solutions of1-ethyl-3-methyl-limidazolium bromide and1-butyl-3-methyl-limidazolium bromide have been measured at atmospheric pressure. The modified exponential decay equation, Masson-type equation, and Thomas-type equation were used to correlate the surface tension, density, and dynamic viscosity of aqueous solution of ionic liquids, respectively. From these experimental data, the related surface excess properties, apparent molar volumes and hydrodynamic molar volume were determined.3. The experiments were carried out to examine the flow characteristics of deionized water, ethanol, three kinds of [Emim][Br] aqueous solutions, and three kinds of [Bmim][Br] aqueous solutions in stainless steel microtubes with inner diameter of0.353mm. The Reynolds number varied from25.1to542.6. The effect of polarity and electric viscous on liquid flow was also investigated. It is observed that, in the scale of experiments, the results taking the inlet and exit losses and the developing region loss in account are in good agreement with conventional theory. The influence of polarity and electric viscous is at a level within the experimental uncertainty.4. A series of systematic experiments were carried out under laminar flows (Re=52-527) in stainless steel microtubes using deionized water,5wt%ethanol aqueous solution,50wt%ethanol aqueous solution, ethanol, ethyl acetate, cyclohexane, nhexane, cyclohexanone, and cyclopentanone as working fluids. The inner diameters of stainless steel microtubes are0.353,0.597, and1.045mm, respectively. The characteristics of heat transfer in these microtubes differ significantly from those in conventional tubes. According to the experimental results, an empirical equation based on the Gnielinski equation was proposed to correlate the heat transfer in our microtubes. The effect of solid-liquid interfacial tension was also incorporated. In light of engineering applications, the solid-liquid interfacial tension cannot be easily obtained, thus, the data of liquid surface tension were used to represent the magnitude of interaction of solid-liquid interface. The calculation results are in good agreement with our experimental results, it satisfied the need of engineering appliance.