CN100517342C - Method for numerical simulation of steam condensation containing incoagulable gas in pipe - Google Patents

Abstract

The invention relates to a simulation method of steam condensation number of non-condensable gas in a pipe and pertains to the mechanics field of computational fluid. The invention makes use of the CFX platform and sets source term of quality continuous equation of steam components to simulate the steam condensation process of non-condensable gas. The steps are: (1) the fluid in the flow field is set as gas mixture with changeable component mass percentage and all components respectively show steam and non-condensable gas and are in ideal state; (2) boundary conditions such as flow field area, inlet, outlet and wall are set; (3) the continuous governing equation of steam components is added with Uchida empirical correlation in the source phase of wall boundary conditions. The method of the invention makes a slight alteration on the basis of the existing calculation program of the finite volume method and accurately simulates the complex process of the change between the two phases of the steam condensation of the non-condensable gas. The treatment process is simple and efficient.

Description

Contain the not method for numerical simulation of the steam condensation of condensable gas in the pipeline

Technical field

The present invention relates to the method in a kind of Fluid Mechanics Computation field, specifically be a kind of in jet chimney to containing the not method for numerical simulation of the steam condensation of condensable gas, promptly by the fluid dynamics governing equations of additional condensation model is calculated.

Background technology

In many industrial occasions, the steam condensation that is accompanied by the energy transfer is a very important physical process.But, when existing not condensable gas in the steam (such as air),, refrigerant heat transfer is worsened even its content is extremely small.

Currently exist the research of the steam condensation under the situation mainly to be divided into theoretical research and experimental analysis two big classes: the governing equation model of (1) boundary layer and liquid film to condensable gas not, this theory thinks that concentration difference and the temperature difference in the steam just caused mass transfer and heat transfer, studies respectively so the boundary layer on the phase interface is divided into two parts: the condensable gas potpourri of the steam of condensation liquid and gas-not.Like this, under the situation that incoagulable gas exists, the boundary layer of a two-phase has been set up, proposed a cover numerical value computation model from the mass conservation and energy conservation theory again, explained on the basis of math equation that clearly condensable gas has not limited the mechanism that steam conducts heat.(2) empirical model, this theory be the technician on the basis of engineering practice, in conjunction with the field experiment result, a series of empirical correlation formula has been proposed.The core concept of these correlations is that steam-not condensable fluid-mixing is processed into single-phase polycomponent flow field, and will be wherein the mass loss that causes because of condensation of steam component and energy loss be loaded into as source item with algebraic expression and simulate in the fluid dynamics governing equations, what obtain is the analysis result that condensation influences whole flow field.

Mainly be to calculate to the simulation that contains not condensable vapors condensation at present by the programming of numerical evaluation instruments such as Fortran language.The discrete large-scale non-linear coupled differential group (particularly first kind model also needs to set up complicated two-phase governing equations) that loads two kinds of models often needs to expend and lacks to 1 year, the manpower of as many as several years, and process is numerous and diverse.

Find through literature search prior art, the paper " the stability of equilibrium analysis of liquid-gas phase transition system " that Wu Shuanying etc. delivered on " thermal power engineering " the 5th phase in 2005, available energy in the liquid-gas phase transition heat transfer process is analyzed, obtain phase balance condition, mechanical stability condition and the thermally-stabilised condition of liquid-gas phase transition system on this basis, but do not related to not condensable gas problem.This method calculated amount is very big, is applicable to scientific research, can not be applied to engineering reality.

Summary of the invention

The objective of the invention is at the deficiencies in the prior art, provide and contain the not method for numerical simulation of the steam condensation of condensable gas in a kind of pipeline, can be rapidly and simulate after the condensation in the flow field steam and condensable gas component concentrations change procedure not intuitively, make the technician utilize computing machine just can obtain the change of component situation of on-site steam equipment flow field, thereby for optimizing circuit design, avoiding not that condensable gas gathers the reference frame that provides important.

For realizing above-mentioned target, the present invention utilizes CFX (by the large scale business fluid software for calculation of Britain AEA Technology company exploitation) platform, by quality continuity equation source item is set to the steam component, have the not steam condensation process of condensable gas with simulation, comprise: the liquid that (1) is set in the flow field is the variable gaseous mixture of constituent mass percentage, each component is represented steam and condensable gas not respectively, and each component is perfect condition.(2) set border conditions such as territory, flow field, import, outlet and wall.(3) the continuity governing equations of steam component is increased Uchida empirical correlation formula in the source of wall boundary condition in mutually.

The inventive method concrete steps are as follows:

(1) utilizes ANSYS.ICEM.CFD software that the hexahedron structure grid is divided in the flow field of saturated vapour in the jet chimney, on the basis in gridding flow field, carry out numerical evaluation;

(2) set the Flow Field Calculation territory, set the density of reference pressure, Y saturated vapour under gravitate and this reference pressure;

(3) liquid of definition in the flow field is the variable gaseous mixture of constituent mass percentage, and the component of gaseous mixture is respectively steam and condensable gas not, and each component is perfect condition, promptly is in gas phase all the time;

(4) in the Flow Field Calculation territory, the steam group of setting variable mass in the gaseous mixture is divided into the diffusion transport equation, and the not condensable gas component of mass conservation is a conservation;

(5) select turbulence model according to the flow pattern in flow field; Foundation comprises the partial differential governing equations of each mesh quality, momentum and energy conservation information;

(6) boundary condition of import, outlet and the wall in definition Flow Field Calculation territory, comprising inlet fluid speed, steam component massfraction, fluid temperature (F.T.), wall surface temperature, outlet relative pressure, and, be carried in the wall boundary condition the source item of the mass equation in the Uchida empirical correlation formula as the quality control system of equations of steam component;

(7) the partial differential governing equations is carried out discretize, obtain Algebraic Equation set and utilize sealing with upper boundary conditions;

(8) utilize the Algebraic Equation set in the CFX software stream field computational fields to carry out iterative computation repeatedly, till satisfying the iteration precision that sets, finish the numerical simulation of steam condensation in the pipeline.

Turbulence model of the present invention, CFX platform provide the basic turbulence model that comprises laminar flow, k-ε model and RNGk-ε model, can choose according to the size of actual Renolds number.

Wall boundary condition of the present invention comprises that wall roughness and wall heat transmits, can be with the temperature value of on-the-spot or the outside wall surface that experiment records as thermal boundary condition.

Governing equations of the present invention, CFX platform provide time term wherein, convective term and diffusion term, and source item is defaulted as 0, only need call the Uchida empirical correlation formula of writing with CEL in the source item interface section and get final product.

Discrete method of the present invention, the High Resolution that the CFX platform provides are a kind of high precision mixed difference that integrates upwind difference and central difference, can be default during use.

The inventive method is done to change and can realize on existing finite volume method calculation procedure basis slightly, easy, solution efficiently that the problem how feasible not condensable gas is handled in the process of this complicated two-phase phase transformation of steam condensation has obtained has important practical value.

Description of drawings

Fig. 1 among the present invention in pipeline different cross section position through condensable gas mass concentration cloud charts not after calculating.

Fig. 2 is result who obtains and the comparison of testing measured value after calculating through the present invention.

Embodiment

In order to understand technical scheme of the present invention better, be further described below in conjunction with accompanying drawing and instantiation, embodiment is the support to the technology of the present invention feature, rather than limits.

The physical model that the present invention relates to is people such as the Revankar of U.S. Purdue university in order to study that vertical tube contains the steam condensation of condensable gas not and the vertical condenser pipe built.The physical Model Study of this experiment be that axial length (x to) is 640mm, the vertical condenser pipe of internal diameter (D) 32mm feeds 1 atmospheric saturated vapour from top to bottom, wherein contains the air of 1% quality, be massfraction α=0.01, mixed gas reynolds number Re=4 * 10 ⁴

Because this experimental physics model is simple, data are detailed and representative, the present invention carries out numerical evaluation to this experiment, and with result of calculation and experiment value comparison, with its accuracy, has very strong cogency.Its main performing step is as follows:

(1) utilize ANSYS.ICEM.CFD software (global general-use grid dividing and software for editing) stream field to carry out the hexahedron structure grid dividing after, the selection solver is CFX;

(2) select " territory " to be used for setting the territory, flow field in " establishment "-hurdle, setting reference pressure is the density 0.68kg/m of an atmospheric pressure, Y saturated vapour under gravitate and this pressure ³

(3) select " material " to be used for setting the medium in flow field in " establishment " hurdle: the liquid in the definition flow field is the variable gaseous mixture of constituent mass, the component of potpourri is respectively steam and condensable gas not, and each component is perfect condition, promptly be in gas phase all the time, title material can set up on their own, is made as mixture here;

(4) select mixture in " fluid " in " territory " one, and the steam group of setting variable mass is divided into the diffusion transport equation, the not condensable gas component of mass conservation is a conservation;

(5) select turbulence model according to the flow pattern in flow field, select general k-ε turbulence model here; Set up the partial differential governing equations that comprises each mesh quality, momentum and energy conservation information voluntarily by CFX software;

(6) in " establishment " hurdle, select " boundary condition " to be used for setting the boundary condition of import, outlet and the wall in flow field respectively, comprising inlet fluid speed 50m/s, steam component massfraction 0.99, fluid temperature (F.T.) 373K, wall surface temperature (from the Revankar experimental data, reading) with export relative pressure 0Pa;

(7) in " establishment " hurdle, select " expression formula " to be used for writing mass equation in the Uchida empirical correlation formula, the condensation rate m of Uchida empirical correlation formula definition steam ⁰For:

m ⁰＝C _u(ρ _steam/ρ _nc) ^0.8×(T-T _wall)/h _1g

Wherein: C _uBe to adjust coefficient, relevant with the air quality mark, be taken as 450W/ (m ²K); ρ _SteamAnd ρ _NcRepresent the steam and the density of condensable gas not respectively; T and T _WallThe temperature of representing gas and wall respectively; h _1gThe expression saturated vapour latent heat of vaporization (for superheated vapor, h _1gThe enthalpy difference of saturated vapour under expression superheated vapor and this pressure).

In the following formula, except T and T _WallOutward, all the other are the physical parameter of mixing flow field, can obtain by consulting pertinent literature.m ⁰Final unit be kg/ (m ²K), its physical meaning is the quality that the unit interval enters (or going out) CONTROL VOLUME by unit area on the condensation front.Owing to condense is that energy is transferred to extraneous process from computational fields, so, when the Uchida model being carried in the source item of steam compositional continuity equation of wall boundary condition as the area source item, m ⁰Before should add negative sign;

(8) utilizing CFX to find the solution controller disperses to the above partial differential governing equations of having sealed that comprises boundary condition, and to its iterative: difference scheme is chosen the High Resolution form of CFX platform acquiescence in " finding the solution control " hurdle, in physical model and uncomplicated, so iteration time is unsuitable oversize at interval, getting 0.5S gets final product, iteration precision reaches 0.00001, can think that just result calculated is near actual effect.

After having drawn separating on each computing node by above-mentioned solution procedure, need represent result of calculation by modes such as line value figure, polar plot, isoline figure, motion pattern, cloud atlas.

Fig. 1 be the flow field respectively at the x/D=0.2 place, the mass concentration cloud charts of the not condensable gas of x/D=2 place, x/D=10 place and four diverse locations of x/D=20.Therefrom as seen, fluid is in top-down flow process, because steam (is pressed m with quality of steam by condensation gradually from the unit area computational fields in the unit interval ⁰Ratio remove), make in the mixing flow field that the mass percent of condensable gas does not constantly increase.In the drawings, the condensable gas mass percent is not along with the increase of pipeline axial (X to) distance, and is high more the closer to its concentration of wall, illustrated that condensable gas is not easy to produce accumulation phenomena at the wall that condenses.This and theoretical analysis and engineering practice result match.

Fig. 1 has described the loading Uchida flow field concentration change behind the model of condensing qualitatively.From the CFX post processor, extract the concentration value of the different radial positions at x/D=0.2, x/D=2 place, four the diverse location places in x/D=10 place and x/D=20, and with it with experiment in the concentration value that measures of opposite position compare, obtain Fig. 2 quantitatively.Calculated value and experiment value have shown that all the condensable gas mass percent does not increase along with the increase of axial and radial distance, and no matter qualitative still quantitative, calculated value and actual value are coincide all relatively goodly.

As seen through the above analysis, what the present invention provided is the analysis result of condensation to the influence of whole flow field, be compared to other set up the two-phase governing equations at diffusion boundary layer and liquid film complicated approach, it will not considered condensate film, more help practical operation, and the numerical simulation whole structure is gratifying, especially when calculating aspects such as flow field concentration of component, flow field density, concentration gradient, have very high precision, show that the inventive method is a kind of economy, high-efficiency method.

Claims (1)

1, contains the not method for numerical simulation of the steam condensation of condensable gas in a kind of pipeline, it is characterized in that comprising the steps:

(1) utilizes ANSYS.ICEM.CFD software that the hexahedron structure grid is divided in the flow field of saturated vapour in the jet chimney, on the basis in gridding flow field, carry out numerical evaluation;

(2) set the Flow Field Calculation territory, set the density of reference pressure, Y saturated vapour under gravitate and this reference pressure;

(3) liquid of definition in the flow field is the variable gaseous mixture of constituent mass percentage, and the component of gaseous mixture is respectively steam and condensable gas not, and each component is perfect condition, promptly is in gas phase all the time;

(4) in the Flow Field Calculation territory, the steam group of setting variable mass in the gaseous mixture is divided into the diffusion transport equation, and the not condensable gas component of mass conservation is a conservation;

(5) select turbulence model according to the flow pattern in flow field; Foundation comprises the partial differential governing equations of each mesh quality, momentum and energy conservation information;

(6) boundary condition of import, outlet and the wall in definition Flow Field Calculation territory, the boundary condition of described import, outlet and wall comprises inlet fluid velocity, steam component massfraction, fluid temperature (F.T.), wall surface temperature, outlet relative pressure, and, be carried in the wall boundary condition the source item of the mass equation in the Uchida empirical correlation formula as the quality control system of equations of steam component;

(7) the partial differential governing equations is carried out discretize, obtain Algebraic Equation set and utilize sealing with upper boundary conditions;

(8) utilize the Algebraic Equation set in the CFX software stream field computational fields to carry out iterative computation repeatedly, till satisfying the iteration precision that sets, finish the numerical simulation of steam condensation in the pipeline.

Images