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ABSTRACT Grain drying is a simultaneous heat and moisture transfer problem. The modelling of such a problem is of significance in understanding and controlling the drying process. In the present study, a mathematical model for coupled heat and moisture transfer problem is presented. The model consists of four partial differential equations for mass balance, heat balance, heat transfer and drying rate. A simple finite difference method is used to solve the equations. The method shows good flexibility in choosing time and space steps which enable the simulation of long term grain drying/cooling processes. A deep barley bed is used as an example of grain beds in the current simulation. The results are verified against experimental data taken from literature. The analysis of the effects of operating conditions on the temperature and moisture content within the bed is also carried out 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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对现行8.53MPa德士古渣油气化炉激冷室中热质传递过程进行了分析、研究,从数学模型着手,进行模拟计算,模拟结果与工业数据吻合良好。通过模拟揭示了激冷过程本质特征,探讨了现行激冷环损坏的主要原因。 相似文献
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The present paper deals with the periods of dif- ferent drying mechanism. A calculation method is pre- sented for the temperature distribution of the material during these periods and for distribution of moisture content in the falling rate period. The test material was a 100 x 100 x 30 mm gypsum plate. 相似文献
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用流程模拟软件对尿素生产的操作数据进行模拟计算,计算出所有物流的温度、压力、流量和组成,这些数据能够准确地反映工艺状况。通过对模拟结果进行分析,找出装置运行的瓶颈问题,并采取相应措施,解决问题,使生产操作达到增产、节能、降耗、优化的目的。 相似文献
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ABSTRACT The aim of this work was to analyze the simultaneous heat and mass transfer between air and soybean seeds in countercurrent and concurrent moving bed dryers by simulation. The technique chosen was based on modeling from mass and energy conservation equations for the fluid and particulate phases. The equilibrium, heat transfer and mass transfer equations were taken from specific studies. The equation representing drying kinetics was obtained by means of a thin-layer study, whereas the equilibrium equations was chosen from rival model discrimination, based on nonlinearity measures. Hence, the model parameters were defined by the respectives studies. The profiles for temperature and humidity of the fluid and the temperature and moisture of the seeds were obtained by numerical solution of the model. This model consisted of ordinary differential equations and the solution was obtained by a specific code. The simulated results indicated a significant. 相似文献
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建立了苯乙烯本体热聚合过程模型,分析讨论了苯乙烯在连续搅拌槽式反应器中进行热引发本体聚合行为.分别讨论了聚合温度和停留时间对苯乙烯的转化率、聚合速率、产物的相对分子质量及其分布、粘度和密度的影响,结果表明,聚合温度决定产物的相对分于质量及其分布,且对转化率、聚合速率及粘度均有较大影响;停留时间对产物的相对分子质量及其分布无明显的影响,对转化率、密度及粘度有较大影响.聚合温度和停留时间是苯乙烯本体聚合过程中的两个至关重要的操作条件,同时为方便工程应用提供了经验关联式. 相似文献
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蒽醌法双氧水生产中加氢反应原理及其控制 总被引:3,自引:0,他引:3
概述蒽醌法双氧水生产中催化加氢反应原理和控制要点,从实际生产的角度,着重介绍了优化反应条件,遏制副反应,保持蒽醌稳定性的主要途径和意义。 相似文献
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A control volume formulation for the solution of a set of two-way coupled heat and diffusive moisture transfer equations with an infrared source term is presented in three dimensions. The solution procedure developed uses a fully implicit time stepping scheme for the solution of the coupled set of equations and is applied to study the infrared drying of potato using two different drying systems. The maximum deviation between experimental and simulation results were 9.0°C in temperature for potato drying, and 10% (d.b.) for moisture predictions. The overall predictions agreed well with the available experimental data from the two systems and show a good potential for application in infrared drying of food grains and biomaterials. 相似文献
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《Drying Technology》2013,31(2):363-379
ABSTRACT A control volume formulation for the solution of a set of two-way coupled heat and diffusive moisture transfer equations with an infrared source term is presented in three dimensions. The solution procedure developed uses a fully implicit time stepping scheme for the solution of the coupled set of equations and is applied to study the infrared drying of potato using two different drying systems. The maximum deviation between experimental and simulation results were 9.0°C in temperature for potato drying, and 10% (d.b.) for moisture predictions. The overall predictions agreed well with the available experimental data from the two systems and show a good potential for application in infrared drying of food grains and biomaterials. 相似文献
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ABSTRACT In a previous study (Dostie and Navarri, 1994), experiments indicated that a non-uniform moisture distribution could develop in radio frequency drying depending on the applied power and initial conditions, making the design and scale-up of such a dryer a more difficult task. Consequently, a thorough study of the combined convection and RF drying process was undertaken. Experimental results have shown that the values of the neat and mass transfer coefficients decrease with an increase in evaporation rate caused by RF energy. This effect is adequately taken into account by the boundary layer theory. Furthermore, the usual analogy between heat and mass transfer has been verified to apply in RF drying. Experiments have also shown that a different mass transfer resistance on both sides of the product should not result in non-uniform drying. However, it appears that non-uniform drying is dependent upon the initial moisture distribution and the relative intensity of heal transfer by convection and RF- It was shown that the maximum drying rate occurs at a higher average water content and that the total drying time increases with non-uniformity of the initial moisture distribution. 相似文献
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The heat and mass transfer equations governing an adsorbent bed in an adsorption heat pump and the mass balance equation for the adsorbent particles in the adsorbent bed were solved numerically to simulate the cycle of a basic adsorption heat pump, which includes isobaric adsorption, isosteric heating, isobaric desorption, and isosteric cooling processes. The finite difference method was used to solve the set of governing equations, which are highly nonlinear and coupled. The pressures of the evaporator and condenser were 2 and 20 kPa, respectively, and the regeneration temperature of the bed was 403 K. Changes in the temperature, adsorptive pressure, and adsorbate concentration in the adsorbent bed at different steps of the cycle were determined. The basic simulated cycle is presented in a Clausius-Clapeyron diagram, which illustrates the changes in average pressure and temperature of the adsorbent bed throughout the cycle. The results of the simulation indicated that the most time-consuming processes in the adsorption heat pump cycle were isobaric adsorption and isobaric desorption. The high thermal resistance of the bed slows down heat transfer, prolonging adsorption and desorption processes. 相似文献
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液相法甲醇合成过程中机械搅拌反应器的模拟 总被引:1,自引:1,他引:0
本文对C301及C302两种不同催化剂条件下机械搅拌反应器内液相法甲醇过程进行了模拟,模拟中节气液之间的传质过程及催化剂气固相本征反应动力学,主要模拟条件:温度483K-528K,压力2.0MPa-6.0MPa,原料气中CO浓度0.06-0.45。模拟结果表明,在C301与C302催化剂条件,隆成总体速率的模拟计算与实测值相吻合,平均偏差分别为7.98%和11.92%,可以认为,气固相本征动力学模型应用于液相甲醇合成过程的工程设计与过程分析是适用和可靠的。 相似文献