Entransy is a parameter proposed in recent years to describe the potential of heat in an object. Its balance equation was established based on the energy equation of heat transfer, which contains entransy, entransy flow, entransy dissipation and entransy production due to heat source. It has been proved that the total entransy must be reduced whenever there is heat transfer in an isolated system, leading to entransy dissipation. Entransy dissipation and entransy-based thermal resistance can be used to optimize heat conduction, heat convection, thermal radiation and the design of heat exchangers and heat exchanger networks. On the other hand, the entransy balance equation was also established for heat-work conversion processes. With the equation, entransy loss, which is the difference between the input and output heat entransy flows, was defined and related to thermodynamic processes. For the discussed thermodynamic cycles, it was found that larger entransy loss leads to larger output work.
A quasi-one dimensional calculation was carried out to figure out supersonic combustor performances. Three flow tubes were considered in the combustor region. Those were an air-flow-tube, a combustion-flow-tube and a fuel-flow-tube. A Mach=1 condition was assumed in the combustion-flow-tube. The estimation of a mode-transition was considered as a result of thermal choking. Both clean and vitiated inflows were tested with the calculation model. Experimental combustion tests were also carried out to compare and confirm the validity of calculated results. Mode-transition equivalence ratios and combustor wall pressure distributions were focused to compare between calculated and experimental results. The calculation model estimated the mode-transition equivalence ratio and the thrust performance with the relative errors at about 11% and 6% compared to the experimental results, respectively.
The polymer melts flow behaviors through nanopores are investigated by using the nanoporous template wetting technique in our study. The experimental observation indicates that the meniscus rises according to a (time)1/2 law which agrees with the Lucas-Washburn law. Comparing the experimental results with the Lucas-Washburn equation, we also demonstrate that the viscosities of polymer melts decrease in their flows through nanopores and the induced rheological behavior is caused by the nanoconfinement of nanopores.
A combustion-driven thermal transpiration-based combustor is presented. The combustor was successfully applied in a self-sustaining gas pump system having no moving parts and using readily storable hydrocarbon fuel. Thermal transpiration was accomplished by meeting two essential conditions: (1) gas flow in the transitional or molecular regime using glass microfiber filters as transpiration membranes and (2) a temperature gradient through the membrane using catalytic combustion downstream of the membrane. The effect of the transpiration membrane pore size on the performance of the gas pump was studied, and the experimental result which was quantitatively consistent with theoretical predictions was reported. The gas pump system was then converted to a novel, complete portable power generation system by incorporating a single-chamber solid-oxide fuel cell (SOFC). The SOFC exhibited a maximum power density of 40 mW/cm2 at the temperature and fuel/oxygen concentrations within the transpiration gas pump.
The low-frequency unstable combustion of hybrid rocket motors was investigated using the transfer function of the full thermal-combustion-gasdynamic coupled system that was coupled with a liquid oxidizer feed system. This transfer function was obtained based on the method developed by Karabeyoglu et al. The transfer function is applicable to the motors that have a long fuel port length. The linear stability limits and the frequencies of pressure oscillations in hybrid rocket motors were obtained theoretically using the transfer function. In addition, we compared these results with the results obtained under the assumption that various physical quantities change in bulk mode.
This paper describes an inverse method for estimating the local thermal diffusivity of biomaterials such as meats and vegetables using a thermophysical handy tester. A thermophysical handy tester is a fast, non-invasive, in-situ, local device for measuring the thermophysical properties of a material. However, it cannot be applied to soft or liquid materials precisely. In this study, an inverse analysis of this device was conducted to make it applicable to the measurement of the thermophysical properties of these materials. In the proposed inverse analysis, a real coded genetic algorithm (GA) was used to minimize the objective function. First, a calibration experiment of the device was conducted by using water to determine the apparatus constant. Then, this inverse method was validated by measuring the thermal diffusivity of some materials such as agar-gelled water, silicone oil, and glycerol. It was found that, the estimated thermal diffusivity shows good agreement with the reference value. Moreover, the thermal diffusivity of various biomaterials such as vegetables and meats was estimated, and reasonable values could be obtained by a proposed method.
The study of the relationship between the material, its structure, its behavior on one hand and its processing conditions on the other hand is a multidisciplinary science. Its modeling requires multiphysical couplings and considerations at various scales: microscopic for the chemical structures of the macromolecules forming the material and macroscopic for the global behavior and the process — materials interactions. Such studies often require important experimental developments to understand the basic aspects of these interactions, as well as mathematical modeling often inspired by experimental observations. Laboratory experimental conditions are unfortunately not representative of those the material experiences during processing. Mathematical modeling in this case is therefore an essential tool to explore varied or extreme conditions and offers detailed optimization parametric studies of the process — structure — properties triangle. The heat transfer during processing of polymeric and/or composites materials plays an important role. The molds are truly heat exchangers that are determinant for the quality of the finished products. Hence, it is necessary to model the mold thermal behavior, taking into account several physical phenomena which occur, due to the interactions between this sort of heat exchanger and the material. In the present work, extensive theoretical developments on the crystallization of polymers under non-isothermal flow are presented. An illustration of the process-structure relationship is proposed through recent theories and the results are dealing with the effect on crystallization kinetics in the case of injection molding of thermoplastic polymers.
This paper explores the mechanisms for dissociation of atomic clusters in terms of internal energy flow and driving forces. We employ the hyperspherical coordinates to investigate internal dynamics of atomic clusters. The hyperspherical coordinates consist of three gyration radii and 3n-9 hyperangular degrees of freedom that parameterize the shape of an n-atom system in the three-dimensional physical space. The latter 3n-9 hyperangular degrees of freedom are further classified into three twisting modes and 3n-12 shearing modes. We numerically characterize the patterns of energy flow among the internal degrees of freedom leading to dissociations. It is shown that a large amount of kinetic energy tends to accumulate in the largest gyration radius upon dissociations of the cluster. We also identify some of the twisting and shearing modes that are active right at the instant of dissociation. These modes may be regarded as the triggers that drive dissociation of the cluster by pumping energy into the largest gyration radius. Physically, this pumping of energy is mediated by the internal centrifugal forces that originate from twisting and shearing motions of the system. These results are consistent with theoretical expectations from the equations of motion for gyration radii, and could be an initial step towards the control of large-amplitude collective motions of complex molecular systems.
The paper presents numerical simulations of the discharge and near outlet regions of the hybrid-stabilized argon-water electric arc. Calculations were carried out for the assumption of laminar and turbulent plasma flow models, respectively. Results of calculations for currents 300-600 A show that the influence of turbulence is weak and the maximum difference for all the monitored physical quantities is less than 10%. Comparison with available experiments exhibits good agreement.