共查询到20条相似文献,搜索用时 31 毫秒
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《Drying Technology》2013,31(10):1895-1917
ABSTRACT The present study proposes the development of a complete mathematical modelling transfer phenomena involving at the same time heat, mass and momentum transfer during the drying process of clay. Clay is a generic example of colloid materials forming particulate gels. That can be considered as bi-constituent, homogeneous, isotropic, and highly deformable. The model was numerically solved by the finite difference method and validated by comparison of the numerical results with a previous set of experiments data. The simulation has allowed the determination of spatio-temporal evolution within the solid of different variables: temperature fields, moisture contents, displacement, deformation and stresses. The parametric sensibility has been analyzed in the case of thermophysical properties and the external heat transfer coefficient. Various values of external conditions have been analyzed. 相似文献
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Divya Srivastava Bikash Mohanty Ravindra Bhargava 《Chemical Engineering Communications》2013,200(8):1089-1101
In this work, a generalized steady-state mathematical model has been developed for simulation of the multiple effect evaporator (MEE) system, used in the Indian sugar industry. The developed model is capable of handling exhaust steam (saturated/superheated) inputs in more than one effect, vapor bleeding from desired effects, heat loss from each effect, and variations in boiling point rise as well as specific heat capacity with combination, heat transfer coefficient through external empirical correlations, and condensate flashing. The developed model has been solved by the globally convergent method. The results of present investigations have been validated against the data obtained from the Indian sugar industry with seven effects. The predicted exit liquor concentration, vapor body temperature, and amount of vapor bleed from each effect shows close agreement with the industry data within a maximum error band of ±2%. Further, a correlation has been developed for the prediction of overall heat transfer coefficient (OHTC) of each effect. The developed model can be further used to improve the steam economy of the MEE system by the incorporation of flash vapors from condensate stream. 相似文献
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Simultaneous heat and mass transfer, which arises from injecting a gas (helium or hydrogen) from or through the solid surface into a flowing external stream, has been studied for a rotating disc geometry. The effects of concentration levels of the injected gas in the external stream on the thermodynamic coupling in the presence of centrifugal force have been investigated over a wide range of Tw/Te.
Boundary layer equations for heat and mass transfer were solved numerically. Exact and linearized approximate solutions were obtained. The results have shown that the thermal diffusion effect on mass transfer becomes increasingly important as the free stream concentration increases and as Tw/Te departs from unity. The diffusion thermo effect on heat transfer was found to be the most important when the free stream concentration is zero and as Tw/Te approaches unity. 相似文献
Boundary layer equations for heat and mass transfer were solved numerically. Exact and linearized approximate solutions were obtained. The results have shown that the thermal diffusion effect on mass transfer becomes increasingly important as the free stream concentration increases and as Tw/Te departs from unity. The diffusion thermo effect on heat transfer was found to be the most important when the free stream concentration is zero and as Tw/Te approaches unity. 相似文献
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After some genera] remarks about liquid/solid fluidization, various aspects of liquid fluidization hydrodynamics and heat transfer have been analyzed on a coherent basis. For each of these cases, the state-of-the-art has been reported, together with some indication of areas that deserve further attention. Major emphasis is placed on the hydrodynamic behavior of fluidized beds, heat transfer mechanisms from surface-to-bed and on the effect of various parameters on the type of fluidization and heat transfer coefficient. This review covers the various correlations developed over the years for the prediction of bed voidage, heat transfer coefficient and optimum conditions of liquid/solid fluidized beds. 相似文献
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采用金属内衬外部缠绕纤维增强复合材料,可减轻纯金属身管重量,提高身管刚度.为了详细分析复合材料身管分界面接触热阻对身管热性能影响,本文建立考虑复合材料身管分界面接触热阻效应的瞬态传热模型,运用有限差分法编制通用程序对接触热阻效应对复合材料身管热性能影响进行数值定量分析.结果表明,接触热阻对于复合材料身管的传热性能有较大影响,必须采取措施来减小接触热阻,这在复合材料身管的热性能设计中必须重点考虑. 相似文献
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N. M. Ghasem 《化学工程与技术》2005,28(8):915-922
A mathematical model has been developed to simulate a gas‐phase ethylene polymerization reactor with internal cooler. The model was analyzed to determine the effects of reactor operating conditions on dynamics and stability. The reactor model employed assumed that both the gas and polymer phase in the reactor are well mixed. Comparing the present model to one with external heat exchanger confirms that, in either form, gas‐phase polyethylene reactors are prone to show unstable steady states, limit cycles and excursions toward unacceptably high temperature steady states. It was also observed that, with internal cooler, minor design changes in the cooler area available for heat transfer and in the inlet temperature of the coolant have a significant effect on the low stable steady state range of catalyst feed rates. With internal cooler, the suitable operating range increased with the increase in the area available for heat transfer. This effect is insignificant in the case of a reactor with external heat exchanger. Manipulating the reactor coolant inlet temperature and/or gas velocity can increase the stability range in the reactor with internal cooler as against one with external heat exchanger. 相似文献
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The effect of a solid presence on global hydrodynamic parameters and heat transfer in an external loop airlift reactor has been experimentally investigated. Results obtained in both two- and three-phase flow are presented in this study. Two different external loop airlift reactor sizes have been used and local hydrodynamic characteristics including local gas hold-up and bubble velocity have been obtained in two-phase flow. Optical and ultrasound probes have been used to obtain this information, respectively. It was found that an increase of solid hold-up leads to a decrease of liquid velocity and heat transfer coefficient. Measured in a two- and three-phase reactor using a horizontal-heating probe, a correlation of the average gas hold-up and heat transfer coefficient is proposed. Correlation parameters are identified in homogeneous and heterogeneous flow regimes, which have been derived from the gas slip velocity concept. The experimental liquid velocity and gas hold-up in the riser have been represented in a satisfactory way by a hydrodynamic model, either in the absence or in the presence of solid particles. 相似文献
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An analysis is presented for the main factors which control the intensity of vapor condensation in plate condenser channels, such as heat transfer both in single-phase stream of the coolant and in the condensate film, heat and mass transfer in gas-vapor phase, thermal resistance of fouling at heat transfer surface and pressure drop in condensing stream. On the basis of a relationship between the heat transfer and the wall shear stress, an approximate equation is obtained for calculating heat transfer from the pressure drop data. For calculation of heat transfer in condensate film during the condensation of high speed vapor, an analogy between heat and momentum transport has been used. An analysis of fouling deposition on heat transfer surface has been performed and an equation is presented for calculating the reduction of the fouling thermal resistance as compared with shell and lube heat exchangers. Experimental data are in good agreement with theoretical results. These data have shown the improvement of all the mentioned factors, which determine the intensity of the whole condensation process compared to the same factors in shell and tube condensers. Under the equal conditions, the required area of the heat transfer surface is reduced by 1.6 to 3 limes for the plate condenser, as compared with conventional shell and tube units. 相似文献
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Mass and heat transfer of a falling liquid film on an external screw grooved surface of perpendicular tubes were studied and correlations by similarity parameters were obtained. The mechanism for enhancement of the transfer rate by screw grooved surface was analysed. Applying Danckwerts surface renewal model to mass transfer and heat transfer, the frequencies of renewal were evaluated and compared. 相似文献
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Mass and heat transfer of a falling liquid film on an external screw grooved surface of perpendicular tubes were studied and correlations by similarity parameters were obtained. The mechanism for enhancement of the transfer rate by screw grooved surface was analysed. Applying Danckwerts surface renewal model to mass transfer and heat transfer, the frequencies of renewal were evaluated and compared. 相似文献
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An analysis is presented for the main factors which control the intensity of vapor condensation in plate condenser channels, such as heat transfer both in single-phase stream of the coolant and in the condensate film, heat and mass transfer in gas-vapor phase, thermal resistance of fouling at heat transfer surface and pressure drop in condensing stream. On the basis of a relationship between the heat transfer and the wall shear stress, an approximate equation is obtained for calculating heat transfer from the pressure drop data. For calculation of heat transfer in condensate film during the condensation of high speed vapor, an analogy between heat and momentum transport has been used. An analysis of fouling deposition on heat transfer surface has been performed and an equation is presented for calculating the reduction of the fouling thermal resistance as compared with shell and lube heat exchangers. Experimental data are in good agreement with theoretical results. These data have shown the improvement of all the mentioned factors, which determine the intensity of the whole condensation process compared to the same factors in shell and tube condensers. Under the equal conditions, the required area of the heat transfer surface is reduced by 1.6 to 3 limes for the plate condenser, as compared with conventional shell and tube units. 相似文献
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Vincenza Antonucci Michele Giordano Sabato Inserra Imparato Luigi Nicolais 《Polymer Composites》2002,23(5):902-910
Autoclave manufacturing of thermoset composites is determined mainly by heat transfer phenomena. As a matter of fact, the consolidation of composite laminates takes place by the progress of the polymerization, which is activated thermally. The design and control of the autoclave process relies on the capability to manage the relationship between the temperature-pressure cycle of the heat carrier fluid and the temperature distribution through the manufacturing part. In particular, in industrial cases, the main limitations reside in the correct evaluation of the local convective heat transfer conditions through the autoclave and in the evaluation of the local thermal inertia arising from the bagging-tooling system. In this study, the autoclave manufacturing of thick laminates has been addressed by modeling the heat transport phenomena occurring through the composite, the bagging and the tooling system. A new methodology for the evaluation of the energy transfer regimes has been proposed accounting for the heat fluxes from the bag and the tool side, the temperature through-the-thickness gradients and the heat generated by the resin polymerization reaction. The proposed approach enables the prediction of the temperature history of the autoclave assembly without knowledge of the effective thermal inertia of the two external layers, which could be difficult to evaluate owing to possible deformations of the bag during the manufacturing cycle and nonuniform shape of the metallic tool along the part. Experimental data from industrial autoclave runs have been collected and analyzed to validate the method. 相似文献
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对离子束动态混合注入(DIMI)技术制备的黄铜、紫铜、不锈钢和碳钢管基聚四氟乙烯(PTFE)表面的冷凝传热实验发现,用不同加工条件制备的表面具有不同的化学组成、不均匀的表面状态以及不同的物理化学性质,从而导致不同的冷凝成滴面积和传热性能,而且表面加工条件对滴状冷凝传热的寿命有至关重要的作用,不同基体材料应有不同的最佳制备工艺条件.不同工艺条件下制备黄铜基PTFE表面水蒸气竖直管外冷凝传热通量比相应的膜状冷凝提高0.3-4.6倍,冷凝传热系数提高1.6-28.6倍.实验结果也表明冷凝表面基体材料对冷凝传热性能有一定的影响. 相似文献
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EFFECTS OF HEATING METHODS ON VACUUM FREEZE DRYING 总被引:4,自引:0,他引:4
The heat and mass transfer during freeze drying of raw beef by different heating methods is studied theoretically and experimentally. The difference between radiant heating and microwave heating in freeze drying process has been analyzed. The results obtained are important for the selection of the heating methods in practical freeze dryers. 相似文献