CN105138736A - Numerical simulation method of lignite microwave drying furnace flow field - Google Patents

Abstract

The invention discloses a numerical simulation method of a lignite microwave drying furnace flow field. The numerical simulation method is characterized by comprising the following steps: step 1: establishing a physical model of a microwave drying furnace cavity via a gambit software, dividing a grid and setting a boundary condition of the model, wherein the size of the physical model is as same as the size of the experiment microwave drying furnace; step 2: introducing the physical model of the cavity into a fluent software, setting a solving model in the fluent software, and adding an UDF source term that absorbs heat with water vapor via a custom option; and and step 3: computing the solving model in the fluent software. According to the method disclosed by the invention, a heat absorption source term is added to the water vapor of the air inside the microwave drying furnace cavity; a flow field distribution inside the cavity is obtained via the numerical simulation of the microwave drying furnace, providing theory and application references for the microwave drying of the lignite.

Description

A kind of brown coal microwave drier Field Flow Numerical Simulation method

Technical field

The present invention relates to a kind of brown coal microwave drier Field Flow Numerical Simulation method.

Background technology

China's explored brown coal available reserves accounts for 13% of national coal total reserves, but the high-moisture of brown coal (20%-50%) brings problems to the application of brown coal.In order to improve the utilization ratio of brown coal, improving the quality of brown coal, usually needing to carry out drying to brown coal.

Microwave drying is the thermal effect utilizing microwave, imports the energy of microwave into dielectric material, the technology discharged as water vapor after making to increase in it.Compared with traditional drying mode, microwave drying has fast, in time, optionally dried material, be an important development direction of following dry materials.

In the research of microwave drying, under different drying condition, dry run can be divided into 4 stages:

1. warm-up phase brown coal temperature rises rapidly, and water percentage is substantially constant;

2. pressure buildup phase internal vapor pressure raises rapidly, and form higher total pressure difference, impel osmotic flow to occur, dehydration rate enlarges markedly;

3. constant speed drying section, the speed of flow of water vapor is by the impact of internal mass transfer resistance with the watt level absorbed;

4. falling rate drying period, dehydration rate declines, and temperature raises.Lower in the utilization ratio of falling rate drying period microwave, but but can not ignore in order to last stage of aridity of improving brown coal.

Microwave current drying mechanism and applied research major part are in food service industry, as RamiY.Jumah and G.S.V.Raghavan studies the heat and mass behavior of microwave and hot air combined drying wheat in spouted bed, mathematical model is established according to nonequilibrium kinetics theory, the behavior of researching microwave drying wheat, shows that microwave and hot blast combination have higher drying efficiency than simple heated-air drying; The Shi Mingheng of Southeast China University take Chinese patent pills as object, has carried out experimental study to microwave and hot blast combination drying, obtains microwave power, material size, accumulation degree, gas flow temperature and gas velocity to the impact of Micro-wave convection drying speed.Li Tao take rubber as object, numerical simulation rubber microwave heating change process, analysis show that efficiency is higher in short-term when microwave heating time, after sizing material heated by microwave, its inside joule heating density distribution and temperature distributing disproportionation even, joule heating density size and temperature level increase along with the increase of microwave power.And adopt microwave to carry out dry main at present or laboratory stage to coal, if the research and utilization microwave fields such as poplar Roar are to the research of brown coal drying characteristic, obtain the relation of brown coal rate of water loss and microwave power.

When on microwave to brown coal, the operation of polar molecule will be moved with microwave field effect, due to the interaction between hydrone in brown coal and adjacent molecule, create the effect of similar friction, water temperature is raised rapidly, depart from brown coal.Because the moisture evaporated in coal might not be discharged cavity in time, will be trapped in cavity by some steam, also can continue to absorb microwave, impel temperature to rise, thus reduce the drying efficiency of microwave.

Summary of the invention

For the problems referred to above, the invention provides a kind of brown coal microwave drier Field Flow Numerical Simulation method, heat absorption source item is added to the water vapor in microwave drier inside cavity air, by to microwave drier numerical simulation, obtain inside cavity Flow Field Distribution, for the Theory and applications of the microwave drying of brown coal provides reference.

For realizing above-mentioned technical purpose, reach above-mentioned technique effect, the present invention is achieved through the following technical solutions:

A kind of brown coal microwave drier Field Flow Numerical Simulation method, is characterized in that, comprise the steps:

Step one: the physical model being set up microwave drying furnace cavity by gambit software, and grid division, arranges the boundary condition of model, and wherein, the size of physical model is identical with test microwave drier;

Step 2: the physical model of cavity is imported in fluent software, solving model is set in fluent software, and add the UDF source item of water vapour heat absorption by self-defined option;

Step 3: calculate solving model in fluent software.

Preferably, in step one, the concrete steps of grid division are as follows:

First divide cavity surface grids, step-length is 0.1-0.5m;

Divide cavity volume mesh again, step-length is 0.1-0.5m;

Finally divide cover surfaces grid, mesh refinement is carried out to cover surfaces part, carry out when entirety divides closeer the closer to sheathing portion grid simultaneously.

Preferably, in step one, the boundary condition of model is as follows:

Chamber inlet is set to speed entrance, cavity outlet is set to free flow export, and pump discharge is set to pressure export, mends wind entrance and is set to pressure inlets, entry and exit up and down between the single cavity of adjacent two joint are set to internal interface, and arrange initial value by fluent software to boundary condition.

The invention has the beneficial effects as follows: this patent proposes to add heat absorption source item to water vapour in drying oven cavity, adopts numerical method that microwave drying brown coal cavity flow field is carried out to modeling and solved, and with comparison of test results analysis, verify the reliability of numerical method; Numerical analysis cavity body structure changes the mechanism of action to brown coal drying speed and microwave efficiency, draw the Changing Pattern of inside cavity temperature, water percentage, flow velocity, may be used for analyzing the reason of microwave drying efficiency with flow field change, draw the cavity body structure and operation method that improve microwave dehydration efficiency.

Accompanying drawing explanation

Fig. 1 is the structural representation of microwave drier list cavity model of the present invention;

Fig. 2 is that the present invention 20 saves cavity front view;

Fig. 3 is that exhaust port temperatures trial value and calculated value contrast;

Fig. 4 is that exhausr port water ratio test value and calculated value contrast;

Fig. 5 is operating mode a and b cavity temperature change curve;

Fig. 6 is operating mode a and b cavity water-cut variation curve;

Fig. 7 is operating mode a and b cavity change in flow curve;

The mark implication of accompanying drawing is as follows:

1. mend wind entrance, 2. microwave entrance, 3. pump discharge, 4. upper inlet, 5. dividing plate, 6. lower inlet, 7. upper outlet, 8. cover, 9. coal seam, 10. time outlet.

Embodiment

Below in conjunction with accompanying drawing and specific embodiment, technical solution of the present invention is described in further detail, can better understand the present invention to make those skilled in the art and can be implemented, but illustrated embodiment is not as a limitation of the invention.

A kind of brown coal microwave drier Field Flow Numerical Simulation method, comprises the steps:

Step one: the physical model being set up microwave drying furnace cavity by gambit software, and grid division, arranges the boundary condition of model, and wherein, the size of physical model is identical with test microwave drier.

Wherein, microwave drier single-unit cavity model as shown in Figure 1, the long 3m of single-unit cavity is established in embodiment, wide 3m, high 1.7m, form microwave drier production line by 20 joint single-unit cavitys, as shown in Figure 2, total length 60m, in production line operational process, brown coal are transported in cavity from left to right by belt, and belt is positioned at cavity bottom.On coal seam 9, adopt water conservancy diversion cover 8, water conservancy diversion cover 8 is connected with the pump housing by pump discharge 3, forms the water vapor in negative pressure extracting cavity; And be provided with two benefit wind entrances 1 at the top of cavity, for preventing chamber pressure too low; Often save cavity and have upper and lower two entrances, namely between upper inlet 4 and lower inlet 6, two entrances, dividing plate 5 is set; Also there are upper and lower two outlets (upper outlet 7 and lower outlet 10), between two outlets, also dividing plate are set.Entry and exit up and down between adjacent single-unit cavity are that wherein single-unit cavity is provided with microwave entrance 2 for the ease of gas flowing in cavity.

The model of cavity is set up and the division of grid completes in Gambit.In model, cavity size is identical with the drying oven size of test.In finite element analysis, whether suitable precision and the counting yield of and the result of calculation of stress and strain model closely bound up, stress and strain model thinner, and computational accuracy is higher, and the time spent is longer; Otherwise computational accuracy step-down, the time spent is also shorter.First divide cavity surface grids in this patent, then divide volume mesh, finally divide cover surfaces grid.Concrete operations are as follows: during division cavity surface grids, Elements selects unstructured grid Tri (triangular mesh unit), Type selects pave (unstructured grid division), step-length is 0.1-0.5m (preferably 0.1m), confirmation can generate required grid, by required each face grid division all in this way.The division of volume mesh select from Elements list Tet Hybrid (mixed cell), Tgrid (hybrid grid) is selected from Type, step-length is 0.1-0.5m (preferably 0.1m), can generate required volume mesh after confirmation.

Mesh quality plays very important effect for the correct of numerical evaluation with stablizing, the feature of mesh quality is the distribution of node, smooth and deflection, Fluent calculates the several major requirements to mesh quality: mesh quality parameter Skewness can not higher than 0.95, preferably below 0.90, the smaller the better, otherwise discrete equation rigidity is increased, iteration convergence is slowed down, even difficulty; AlignmentwiththeFlow estimates that whether mesh lines is consistent with flow direction exactly, requires as far as possible consistent, to reduce false diffusion; Require will there be abundant grid cell etc. near flow surface, this carries out stress and strain model according to above-mentioned requirements completely.

Due to, near cover, flowing is comparatively complicated, the SizeFunction button in Gambit need be adopted to carry out mesh refinement to cover surfaces part when dividing cover surfaces grid, carry out requiring when entirety divides that close cover peripheral part is close, the integral grid numbers of 20 joint brown coal microwave drying furnace cavities are about 1,000 ten thousand simultaneously.

Boundary condition is exactly the mathematical physics condition that flow field variable should meet on computation bound, and boundary condition is together with starting condition and be called definite condition, and only after boundary condition and starting condition are determined, the solution in flow field just exists, and is unique.The starting condition of FLUENT completes in initialization procedure, and boundary condition then needs to set separately.The boundary condition of this model directly sets in Gamhit: chamber inlet is set to speed entrance, cavity outlet is set to free flow export, pump discharge is set to pressure export, mends wind entrance and is set to pressure inlets, and the entry and exit up and down between the single cavity of adjacent two joint are set to internal interface.Wherein, define->boundaryconditions in fluent ... inside Zone option, select corresponding border, just initial value can be set to boundary condition.

Step 2: the physical model of cavity is imported in fluent software, solving model is set in fluent software, and adds UDF (Userdefinefeature user defined feature) source item (source item will be written as UDF program by adding heat equation) of water vapour heat absorption by self-defined option.

Preferably, the concrete steps arranging solving model in fluent software are as follows:

A () turbulence model selects K-epsilon model, and add the UDF source item of water vapour heat absorption by self-defined option;

B the coupling of () pressure-velocity adopts Simple algorithm, convective term difference scheme adopts second order form;

C () boundary condition initial value, according to the amendment of test measurement parameter, carries out couple solution to governing equation, when in flow field, residual error is less than 10 ^-4time think convergence, governing equation is specific as follows:

Mass-conservation equation:

$\frac{\∂}{\∂x_i}\left(u_i\right)=0---\left(3\right)$

Constituent mass conservation equation:

div(ρuc _s)＝div(D _sgrad(ρc _s))+S _s(4)

Momentum conservation equation:

$\frac{\∂\left({\mathrm{\ρu}}_k{u}_i\right)}{\∂x_k}=-\frac{\∂P}{\∂x_i}+{\mathrm{\ρf}}_i+\frac{\∂}{\∂x_k}\left(\mathrm{\μ}\frac{\∂u_i}{\∂x_k}\right)---\left(5\right)$

Energy conservation equation:

$div\left({\mathrm{\ρu}}_{i}T\right)=div\left(\frac{k}{C_p}gradT\right)+S_T---\left(6\right)$

In formula (3)-(6), u _i, u _krepresent the flow velocity of different directions, wherein, when subscript equals 1, represent the flow velocity in x direction, when subscript equals 2, represent the flow velocity in y direction, when subscript equals 3, represent the flow velocity in z direction; x _i, x _krepresent different directions, wherein, when subscript equals 1, represent x direction, when subscript equals 2, represent y direction, when subscript equals 3, represent z direction; ρ: density; U: rate of flow of fluid; S: represent component (water vapor or air); c _s: the quality of unit volume component s; D _s: coefficient of diffusion; S _s: the production rate of component s in unit volume; K: turbulence pulsation kinetic energy; T: fluid temperature (F.T.); C _p: specific heat at constant pressure; S _t: unit volume endogenous pyrogen; Div (): ask divergence of a vector in bracket; Grad (): ask bracket inside gradient; P: pressure; f _i: different directions fluid acceleration, wherein, when subscript equals 1, represents the fluid acceleration in x direction, when subscript equals 2, represents the fluid acceleration in y direction, when subscript equals 3, represents the fluid acceleration in z direction;

Turbulent viscosity μ _tthe function of the dissipative shock wave ε of k and turbulence pulsation kinetic energy can be expressed as, namely

${\mathrm{\μ}}_t={\mathrm{\ρC}}_{\mathrm{\μ}}\frac{k^2}{\mathrm{\ϵ}}---\left(7\right)$

Wherein, C _μ=0.09; In standard k-ε model, k and ε is as two fundamental unknown variables, and for incompressible fluid, the transport equation corresponded is:

$\frac{\∂\left({\mathrm{\ρk}}_i{\mathrm{\μ}}_i\right)}{\∂x_i}=\frac{\∂}{\∂x_j}\[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_k})\frac{\∂k}{\∂x_j}\]+G_k-\mathrm{\ρ}\mathrm{\ϵ}---\left(8\right)$

$\frac{\∂\left({\mathrm{\ρ\ϵ\μ}}_i\right)}{\∂x_i}=\frac{\∂}{\∂x_j}\[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_{\mathrm{\ϵ}}})\frac{\∂\mathrm{\ϵ}}{\∂x_j}\]+\frac{C_{1\mathrm{\ϵ}}\mathrm{\ϵ}}{k}{G}_k-C_{2\mathrm{\ϵ}}\mathrm{\ρ}\frac{{\mathrm{\ϵ}}^2}{k}---\left(9\right)$

In formula (8) and (9), μ _i, μ _krepresent the turbulent viscosity of different directions, wherein, when subscript equals 1, represent the turbulent viscosity in x direction, when subscript equals 2, represent the turbulent viscosity in y direction, when subscript equals 3, represent the turbulent viscosity in z direction; k _irepresent the turbulence pulsation kinetic energy of different directions, wherein, when subscript equals 1, represent the turbulence pulsation kinetic energy in x direction, when subscript equals 2, represent the turbulence pulsation kinetic energy in y direction, when subscript equals 3, represent the turbulence pulsation kinetic energy in z direction; G _k: be the Turbulent Kinetic produced by laminar velocity gradient; C _{1 δ}=1.44, C _{2 ε}=1.92, σ _k=1.0, σ _ε=1.3; x _i, x _j, x _krepresent different directions, wherein, when subscript equals 1, represent x direction, when subscript equals 2, represent y direction, when subscript equals 3, represent z direction.

As further improvement, brown coal microwave drying cavity relates in the flow and heat transfer problem of different component, also can relate to component transportation problem, component transport model (SpeciesTransport) can be adopted, cavity different boundary can arrange the water vapor of different quality hundred ratio, selects H ₂o and Air two kinds of components, because water-vapour density is less than atmospheric density, need H in arranging ₂o is placed on before Air.In cavity, radiation patterns selects DiscreteOrdinates model.In addition, in the equation of momentum, density with temperature changes and changes, and can count buoyancy item, also add Gravity calculation model in computation process in thus solving.

The hot source term model more complicated of microwave heating, this patent adopts short-cut method, and add the thermal source item of microwave energy conversion according to mass component, preferably, it is as follows that water vapour adds hot source term model:

ΔQ＝mC _pΔT(1)

$S_T={\mathrm{Ar\ρ}}_{mixture}{m}_{H_{2}O}\frac{|T_{mixture}-T_{sat}|}{T_{sat}}---\left(2\right)$

In formula (1) and (2), Δ Q: absorb or liberated heat; M: steam quality; C _p: specific heat at constant pressure; Δ T: absorb heat or temperature difference before and after heat release; A: add thermal constant; R: coefficient of latent heat, gets 1000KJ/Kg; ρ _mixture: mixture density; T _mixture: mixture temperature; the massfraction of water in potpourri; T _sat: saturation temperature.

Suppose that the steam in cavity flow field does not undergo phase transition, the temperature impact of water vapor absorption microwave on cavity shows as sensible heat.The selection of coefficient A is the key determining thermal source item size, according to test measuring tempeature value as boundary condition, by increasing and decreasing source item constant A and calculating simulation, the measuring tempeature that the temperature that calculating simulation is obtained and cavity are tested is close, thus determines source item expression formula.

Above-mentioned model equation is written as UDF and heats source item program, save as .c file, user-define->functions->comp iled-UDFs in fluent below define function, .c file is added, and in arranging, heating source item is set to water vapor.

Step 3: calculate solving model in fluent software.

By modeling and the setting of above-mentioned flow process, according to following operation: Solve button->Monitors->Residual ... select in frame at Options and select Plot, to show dynamic residual in computation process; All filling out in AbsoluteCriteriaofcontinuity (continuity of an absolute standard) hurdle is 0.0001, and this represents calculating convergence precision; Model is started iterative in Fluent, iterations is set: Solve->Iterate ..., number of times is set to 2000 times, and then clicking Iterate can carry out computing.Result of calculation measured value and trial value contrast sees Fig. 3,4, and cavity numbering correspond to the position of the pump opened in 20 joint cavitys.As can be seen from the figure relatively, Changing Pattern is consistent, proves to calculate relatively rationally, and model is reliable for the temperature of the experiment and computation simulation of operating mode a, b and water cut value.The change curve of inside cavity Flow Field Calculation result is shown in Fig. 5,6,7, as can be seen from the figure cavity flow field Changing Pattern, the Changing Pattern of temperature under different cavity, water percentage, flow velocity can be drawn, microwave drying efficiency with the reason of flow field change, thus can analyze the cavity body structure and operation method that draw and improve microwave dehydration efficiency.This patent can provide theory and practice foundation for the application of microwave drying brown coal, can save lot of experiments expense by the method for this patent simultaneously.

These are only the preferred embodiments of the present invention; not thereby the scope of the claims of the present invention is limited; every utilize instructions of the present invention and accompanying drawing content to do equivalent structure or equivalent flow process conversion; or be directly or indirectly used in the technical field that other are relevant, be all in like manner included in scope of patent protection of the present invention.

Claims (6)

1. a brown coal microwave drier Field Flow Numerical Simulation method, is characterized in that, comprise the steps:

Step one: the physical model being set up microwave drying furnace cavity by gambit software, and grid division, arranges the boundary condition of model, and wherein, the size of physical model is identical with test microwave drier;

Step 2: the physical model of cavity is imported in fluent software, solving model is set in fluent software, and add the UDF source item of water vapour heat absorption by self-defined option;

Step 3: calculate solving model in fluent software.

2. a kind of brown coal microwave drier Field Flow Numerical Simulation method according to claim 1,

It is characterized in that, in step one, the concrete steps of grid division are as follows:

First divide cavity surface grids, step-length is 0.1-0.5m;

Divide cavity volume mesh again, step-length is 0.1-0.5m;

Finally divide cover surfaces grid, mesh refinement is carried out to cover surfaces part, carry out when entirety divides closeer the closer to sheathing portion grid simultaneously.

3. a kind of brown coal microwave drier Field Flow Numerical Simulation method according to claim 2,

It is characterized in that, in step one, the boundary condition of model is as follows:

Chamber inlet is set to speed entrance, cavity outlet is set to free flow export, and pump discharge is set to pressure export, mends wind entrance and is set to pressure inlets, entry and exit up and down between the single cavity of adjacent two joint are set to internal interface, and arrange initial value by fluent software to boundary condition.

4. a kind of brown coal microwave drier Field Flow Numerical Simulation method according to claim 3,

It is characterized in that, in step 2, the concrete steps arranging solving model in fluent software are as follows:

A () turbulence model selects K-epsilon model, and add the UDF source item of water vapour heat absorption by self-defined option;

B the coupling of () pressure-velocity adopts Simple algorithm, convective term difference scheme adopts second order form;

C () boundary condition initial value, according to the amendment of test measurement parameter, carries out couple solution to governing equation, when in flow field, residual error is less than 10 ^-4time think convergence, governing equation is specific as follows:

Mass-conservation equation:

$\frac{\∂}{\∂x_i}\left(u_i\right)=0---\left(1\right)$

Constituent mass conservation equation:

div(ρuc _S)＝div(D _Sgrad(ρc _S))+S _S(2)

Momentum conservation equation:

$\frac{\∂\left({\mathrm{\ρu}}_k{u}_i\right)}{\∂x_k}=-\frac{\∂p}{\∂x_i}+{\mathrm{\ρf}}_i+\frac{\∂}{\∂x_k}\left(\mathrm{\μ}\frac{\∂u_i}{\∂x_k}\right)---\left(3\right)$

Energy conservation equation:

$div\left({\mathrm{\ρu}}_{i}T\right)=div\left(\frac{k}{C_p}gradT\right)+S_T---\left(4\right)$

In formula (3)-(6), u _i, u _krepresent the flow velocity of different directions, wherein, when subscript equals 1, represent the flow velocity in x direction, when subscript equals 2, represent the flow velocity in y direction, when subscript equals 3, represent the flow velocity in z direction; x _i, x _krepresent different directions, wherein, when subscript equals 1, represent x direction, when subscript equals 2, represent y direction, when subscript equals 3, represent z direction; ρ: density; U: rate of flow of fluid; S: represent component (water vapor or air); c _s: the quality of unit volume component s; D _s: coefficient of diffusion; S _s: the production rate of component s in unit volume; K: turbulence pulsation kinetic energy; T: fluid temperature (F.T.); C _p: specific heat at constant pressure; S _t: unit volume endogenous pyrogen; Div (): ask divergence of a vector in bracket; Grad (): ask bracket inside gradient; P: pressure; f _i: different directions fluid acceleration, wherein, when subscript equals 1, represents the fluid acceleration in x direction, when subscript equals 2, represents the fluid acceleration in y direction, when subscript equals 3, represents the fluid acceleration in z direction;

Turbulent viscosity μ _tthe function of the dissipative shock wave ε of k and turbulence pulsation kinetic energy can be expressed as, namely

${\mathrm{\μ}}_t={\mathrm{\ρC}}_{\mathrm{\μ}}\frac{k^2}{\mathrm{\ϵ}}---\left(7\right)$

Wherein, C _μ=0.09; In standard k-ε model, k and ε is as two fundamental unknown variables, and for incompressible fluid, the transport equation corresponded is:

$\frac{\∂\left({\mathrm{\ρk}}_i{\mathrm{\μ}}_i\right)}{\∂x_i}=\frac{\∂}{\∂x_j}\[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_k})\frac{\∂k}{\∂x_j}\]+G_k-\mathrm{\ρ}\mathrm{\ϵ}---\left(8\right)$

$\frac{\∂\left({\mathrm{\ρ\ϵ\μ}}_i\right)}{\∂x_i}=\frac{\∂}{\∂x_j}\[(\mathrm{\μ}+\frac{{\mathrm{\μ}}_t}{{\mathrm{\σ}}_{\mathrm{\ϵ}}})\frac{\∂\mathrm{\ϵ}}{\∂x_j}\]+\frac{C_{1\mathrm{\ϵ}}\mathrm{\ϵ}}{k}{G}_k-C_{2\mathrm{\ϵ}}\mathrm{\ρ}\frac{{\mathrm{\ϵ}}^2}{k}---\left(9\right)$

In formula (8) and (9), μ _i, μ _krepresent the turbulent viscosity of different directions; k _irepresent the turbulence pulsation kinetic energy of different directions, wherein, when subscript equals 1, represent the turbulence pulsation kinetic energy in x direction, when subscript equals 2, represent the turbulence pulsation kinetic energy in y direction, when subscript equals 3, represent the turbulence pulsation kinetic energy in z direction; G _k: be the Turbulent Kinetic produced by laminar velocity gradient; C _{1 ε}=1.44, C _{2 ε}=1.92, σ _k=1.0, σ _ε=1.3; x _i, x _j, x _krepresent different directions, wherein, when subscript equals 1, represent x direction, when subscript equals 2, represent y direction, when subscript equals 3, represent z direction.

5. a kind of brown coal microwave drier Field Flow Numerical Simulation method according to claim 4, it is characterized in that, in step 2, it is as follows that water vapour adds hot source term model:

ΔQ＝mC _pΔT(1)

$S_T={\mathrm{Ar\ρ}}_{mixture}{m}_{H_{2}O}\frac{|T_{mixture}-T_{sat}|}{T_{sat}}---\left(2\right)$

In formula (1) and (2), Δ Q: absorb or liberated heat; M: steam quality; C _p: specific heat at constant pressure; Δ T: absorb heat or temperature difference before and after heat release; A: add thermal constant; R: coefficient of latent heat, gets 1000KJ/Kg; ρ _mixture: mixture density; T _mixture: mixture temperature; the massfraction of water in potpourri; T _sat: saturation temperature.

6. a kind of brown coal microwave drier Field Flow Numerical Simulation method according to claim 5, is characterized in that, in step 3, arranges iterations and calculates convergence precision, model is started iterative in fluent.