tutorial aire acondicionado

8/12/2019 Tutorial Aire Acondicionado

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ROOM AIR CONDITIONING

PROBLEM DESCRIPTION:The problem considered here is a closed room with a heat generation source

inside. The conditioned air injected into the room to maintain proper conditions which alternately cools

down the component and prevents overheating. The model consists of an inlet vent at the bottom of a

wall. There is an outlet vent on the ceiling and a heat source in the middle of the room as shown.

Software used are GAMBIT and FLUENT.

GEOMETRY:

1) Open GAMBIT, under operation panel select GEOMETRY COMMAND BUTTON,

. select create vertices create 4 vertices at (0,0,0)

(7,0,0) (7,7,0) (0,7,0)enter these values in global -> APPLY.


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2) Select EDGE COMMAND BUTTON next to vertices, select CREATE EDGE .selecttwo vertices (hold shift+left click every time to select the specific vertex,edge,face,volume etc)->

APPLY. Join all the vertices to make a square.

3) NEXT, select FACE COMMAND BUTTON next to edge button. Select . Select allfour edges (holding shift+left click)-> APPLY.

4) To generate the room volume, create one more edge by repeating steps 1 and 2. USE MOVE/COPY

. Pick the vertex at origin (0, 0, 0)select copy and enter (0, 0, 7)in global

window. This will create vertex at (X=0 Y=0 Z=7). Join them.


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5) Select volume next to face button. Right click on . Selectsweep face from drop-down list. Select the FACEin face, then, click in window next to edge to

activate it (it will turn into yellow)and select just drawn edge, (to change the direction to be

extrude hold shift+middleclick) -> APPLY.this case is extruded inve Z Direction.

6) Now, create Heat source (repeat the steps 1-5 with some changes).6.1) create vertices at (X=2.5, Y=0, Z=-2.5)and (X=4.5, Y=0, Z=-2.5)in global. Copy both vertices

by entering global values (0, 3, 0).

6.2) join all the vertices using by EDGE COMMAND BUTTON.

6.3) Form a FACE.

6.4) create vertex at (0, 0, 2) (use copy functions) and join them.


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6.5) Repeat step 5 to extrude it.

7) Creating inlet and outlet vent.

7.1) For inlet vent create two vertices at (3, 0.3, 0)and (4, 0.3, 0)

7.2) copy them at (0, 1, 0)

7.3) For outlet vent make two vertices at (1, 7, -2.75)and (1.5, 7, -2.75)

7.4) copy them at (0, 0, -1)

7.5) join all the vertices and form faces.


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8)Before generating mesh, split the faces and volume.

8.1) Go to face panel, select SPLIT/MERGEfaces . Select face1and under that select

face14-> APPLY. NEXT select face6and under that face15-> APPLY.

8.2) Go to volume in geometry. Select SPLIT/MERGEvolume, . Select volume1 in the

above, then, select volume2 in the lower volume window-> APPLYand save the model.

MESHING:

1) Select mesh button in operation panel . Under thisselect edge mesh then select . Select all the edges of theroomand define the

interval count 20units(interval count can be obtained by right click on interval size bar).

2) Assign 10nos(interval count) for longer edgesand 6for the samller edgesof HEAT SOURCE.3) for inlet vent assign 4nos(interval count) for all edges.4) Assign 4 nos for longerand 3for smaller edges of outlet vent.


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5) Select volume command button , under this panel select, mesh volumeskeeping interval size default, change ELEMENTS--- to TET/HYBRIDmesh the volume1and

volume2.


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APPLYING BOUNDARY CONDITIONS:

1) Select ZONE COMMAND BUTTON , select SPECIFY

BOUNDARY TYPES COMMAND select the faces of the room, assign them

according to their position(right, left, top etc), select the appropriate FACE(top, bottom, front) in

ENTITY,select WALLin TYPE(right/left click and hold to scroll beteween BCs)-> APPLY.

2) Apply the same BC for the server.3) Select INLETface and apply VELOCITY INLET and PRESSURE OUTLET for OUTLETvent.4) Select solidin typeand volume2 in volumesin SPECIFY CONTINUUM TYPE , name as

HEAT SOURCE.

5) Select solver as FLUENT5/6in SOLVERin MAIN MENU.6) Now save and EXPORTthe mesh

MAIN MENU> FILE> EXPORT

Save as XXXXX.msh

SOLVING THE PROBLEM:

OPEN FLUNT, Select 3ddpfrom the list of options and click Run.

The "3ddp" option is used to select the 3-dimensional, double-precision solver. In the double-precision

solver, each floating point number is represented using 64 bits in contrast to the single-precision solver

which uses 32 bits. The extra bits increase not only the precision but also the range of magnitudes that

can be represented. The downside of using double precision is that it requires more memory.

1) Import the saved mesh FILE->READ-> CASE (navigate to saved folder).2) Check for any errors in the gridGRID->CHECK.

Check the grid to make sure that there are no errors.

3) Scale the mesh GRID->SCALE-> SCALE(it is important to scale the mesh as fluent reads it inmeters).


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4) EXAMINEthe imported mesh DISPLAY->GRID.

DEFINING SOLVER PROPERTIES:

1) MAIN MENU-> DEFINE-> MODELS-> SOLVER-> select GREEN-GAUSS NODE BASED.1.1)MAIN MENU-> DEFINE-> VISCOUS->K-epsilon, STANDARD and STD. WALL FUNCTIONS.

Under Model, select the K-epsilonturbulence model. We will use the STANDARD model in

the k-epsilon Model box ( because Realizable k-epsilon model produces more accurate

results for boundary layer flows) Near-wall treatment box, check forstandard wallfunctionsbecause of no boundary layers.


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1.2)MAIN MENU-> DEFINE-> MATERIALS-> in DENSITY selectIncompressible-ideal-gas and inVISCOSITY select SUTHERLAND (three equation method).

DEFINE HEAT SOURCE MATERIAL.

MAIN MENU-> DEFINE-> MATERIAL->under material type change to SOLID(change the name

and formula)-> CHANGE/CREATE(do not over wirte aluminium).

OPERATING CONDITIONS:

FLUENT uses gauge pressure internally. Any time an absolute pressure is needed, it is generated by

adding the operating pressure to the gauge pressure. We'll use the default value of 1 atm (101,325 Pa)

as the Operating Pressure.


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Specifying Boundary contition for HEAT SOURCE

1) select Heat-source-> SET->check that heat-source is selected in drop-down (material name)2) check-> SOURCE TERMS.

2) source term-> edit-> assign no of energy source to 1->none to constant-> 1000-> OK.


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Outlet

In the Boundary Conditionswindow, look under Zones. Select Outletto check the details of the

boundary condition. The boundary condition type should be default selected topressure-outlet:

if it didn't, select it. Click Edit,and ensure that the Gauge Pressureis default to 0. If it is, close

this window.

SOLVE:

The order of discretization that we just set refers to the convective terms in the equations; the

discretization of the viscous terms is always second-order accurate in FLUENT. Second-order

discretization generally yields better accuracy while first-order discretization yields more robust

convergence. If the second-order scheme doesn't converge, you can try starting the iterations with

the first-order scheme and switching to the second-order scheme after some iterations.

MAIN MENU->SOLVE-> SOLUTION-> SECOND ORDER(in discrization panel) and rest default-> OK

RESIDUALS:Plotting of residuals-> SOLVE-> MONITERS-> RESIDUAL-> PLOT-> NONE(convergence

criterion)-> OK.

Change the residual under Convergence Criterion to NONE. Also, under Options,select Printand Plot.

This will print the residuals in the main window and plot the residuals in the graphics window as they are

calculated.


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INITIALIZING:

SOLVE-> INITIALIZE-> select INLETin compute from drop-down-> INITIALIZE.


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POST PROCESSING:

CREATING ISO-SURFACE

1) MAIN MENU->SURFACE-> ISO-SURFACE1.1)Select GRIDand X-COORDINATEin SURFACE OF CONSTANTdrop-down list1.2)Click COMPUTE and retain 3.5value in ISO-VALUES.1.3)Enter name for appropriate ISO-SURFACE.1.4)Click CREATE.1.5)REPEAT THE SAME FOR Y(iso-value 0.9)AS WELL AS Z-Coordinate(iso-value -3.5).

DISPLAY CONTOURS FOR DIFFERENT PARAMETERS:

1.1)Make sure that FILLEDis selected inOPTIONS1.2)Check DRAW GRID is selected and select OUTLINEin EDGE TYPE.


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1.3)Select PRESSUREAND STATIC PRESSURE in Contours of drop-down list.1.4)Select X-CoordinateISO-SURFACE.1.5)Click DISPLAY.1.6)Contours for VELOCITY, TEMPERATURE, and TURBULENCEetccan be obtained.

REPEAT THE SAME FOR CONTOURS OF;

1) TOTAL TEMPERATURE.2) VELOCITY.3) PRESSURE (static and total).

DISPLAY VECTORS FOR VELOCITY PROFILE.

1) MAIN MENU-> DISPLAY-> VECTORS.

2) Keep everything default

3) To increase the sizeof the vector arrows modify

range in SCALE.

4) Select any ISO-SURFACE (FLUENT displays interior by

default) and click DISPLAY.


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