Coolant Phase Change Research Articles

S1720104 反応器のダイナミックオペレーション設計の効率化を目指したモジュール型プロセスシミュレーション方法の検討([S172]プロセスセイフティマネージメント,産業・化学機械と安全部門)

Applicability of three models for rector simulation at different levels of details is investigated, from the viewpoint of design of dynamic operation to perform the unsteady operation for dealing with the catalyst deterioration and the emergency stopping operation safely and efficiently. In this study, we develop three simulation systems by combining the standard unit models in the Visual Modeler, which are the fixed bed reactor model, the heat exchanger model and so on, in order to investigate influence of the number of spatial divisions of the model on dynamic simulation results. Then, methods for extension of submodels concerned with the reaction and the heat transport phenomena are developed by considering the catalyst deterioration and the phase change of coolant. When three case studies for load down in the vinyl acetate monomer process are performed by the developed simulation systems, application of a simulation method of expressing the divided heat transfer wall by a series of heat exchanger models is demonstrated to be useful for examination of dynamic operation by comparing with the conventional simulation method that is described in the previous paper.

A Numerical Investigation of Transpiration Cooling with Liquid Coolant Phase Change

This article presents a numerical approach to investigate the transpiration cooling problems with coolant phase change within porous matrix. A new model is based on the coupling of the two-phase mixture model (TPMM) with the local thermal non- equilibrium (LTNE), and used to describe the liquid coolant phase change and heat exchange processes in this article. The effects of thermal conductivity, porosity, and sphere diameter of the porous matrix on the temperature and saturation distributions within the matrix are studied. The results indicate that an increase in the porosity or sphere diameter can lead to an area dilation of two-phase region and a rise of liquid temperature; whereas an increase in the thermal conductivity of the porous matrix results only in a rise of liquid temperature, but drops of solid temperature and temperature gradient on the hot surface. The influence of hot surface pressure on cooling effect is discussed by numerical simulations, and numerical results show that the effect of the transpiration cooling will be worse under higher pressure. The investigation also discovers an inverse phenomenon to the past investigations on the transpiration cooling without coolant phase change, namely in two-phase region, coolant temperature may be higher than solid temperature. This inversion can be captured only by the new LTNE–TPMM.

Application of flexibility model in modeling of flow boiling heat transfer

The mathematical modeling and computer simulation have been widely used in the analysis of system's dynamic characteristics, and often useful for system control. One of the popular methods for this purpose is the lumped parameter method. For flow boiling heat transfer system, the traditional lumped parameter modeling method has a problem that the heat transfer coefficients change suddenly at the boundary of coolant phase change. It can cause error. In this paper, an idea of flexibility model is developed to deal with the boundary problem and to improve the model of flow boiling heat transfer. The segments of coolant phase change's boundary are identified, and the membership functions which are derived from Fuzzy Mathematics are used to derive approximate expressions of heat transfer coefficient in those regions. The continuity of heat transfer coefficient can be described by those expressions. The membership functions are derived from mathematical analysis and transformation. The result shows that this idea is feasible and the conclusion is practicable.

Zum Ausscheiden von Borsäure aus dem borierten Primärmedium von Druckwasserreaktoren / On the segregation of boric acid from the primary coolant of pressurized water reactors

The possibilities of segregation of boric acid from the borated primary coolant in pressurized water reactors are investigated on the basis of temperature-dependent boric acid solubility in water and two-phase mixtures of saturated water and vapor. The fundamentals for the evaluation of possibilities of boric acid segregation in combination with throttling and phase change of primary coolant are presented, and critical conditions for the segregation are formulated. No segregation of boric acid is to be expected for the operating conditions of the primary coolant; but segregation may occur in certain cases when the primary coolant is throttled to lower temperatures and a change of phase takes place