models.heat.condensation electronic device

8/10/2019 Models.heat.Condensation Electronic Device

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Solved with COMSOL Multiphysics 4.4

1 | C O N D E N S A T I O N D E T E C T I O N I N A N E L E C T R O N I C D E V I C E

C o n d e n s a t i o n D e t e c t i o n i n a n

E l e c t r o n i c D e v i c e

Introduction

Many systems, for example electronic devices, risk being damaged if exposed tocondensation. Given an amount of moisture in the air, condensation occurs when the

temperature decreases to reach the dew point. Numerical simulations are useful forobtaining knowledge relevant for preventing the formation of condensation.

Changes in air properties are the primary cause of condensation in some systems. Thisexample simulates the thermodynamical evolution of moist air in an electronic box

with the aim of detecting whether condensation occurs when the external environmentproperties change. The model imports measured data for the air temperature, pressure,and water vapor concentration and represents it by interpolation functions. Theproperty data corresponds to conditions observed during a stormy day when thetemperature dropped and humidity increased.

In this simulation, you assume the water vapor concentration to be homogeneousinside the box and equal to the external concentration. Also, the model setup neglectsdiffusion but considers the external concentration changes during the simulation.

Note: An extension of this model solves for an inhomogeneous concentrationcomputed from the Transport of Diluted Species interface and takes transport anddiffusion of the water vapor into account, see Condensation Detection in anElectronic Device with Transport and Diffusion . It requires the Chemical ReactionEngineering Module.

Model Definition

A box with square cross section of side 5 cm is placed in a moist air environment. Itcontains a heated electronic component and two small slits (1 mm thick) located at theleft and right sides. The simulation is in a 2D cross section of the box, which issupposed to be long enough in the orthogonal direction. It is made of aluminum and
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the electronic component is made of silicon. Figure 1 shows the model geometry.

Figure 1: Geometry of the model.

The box is placed in a changing environment. This means that during the simulation,temperature, pressure, and water vapor concentration change. The data providedcorrespond to a storm with a fall of pressure. Figure 2 shows the temperature, pressure,

and water vapor concentration as functions of time.

In this simulation, assume the moist air concentration inside the box to be equal to theexternal concentration.

Outside the box, you apply a convective cooling condition with a heat transfercoefficient h equal to 10 W/(m 2K) and a time-dependent external temperature. Thecentral component produces a total power of 1 W during the simulation. At the slit

boundaries, set a condition of open boundary to let external moist air freely enter orexit from the box.


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The study computes a simulation over one day and the solution is stored every30 minutes. The goal is to observe if some condensation appears.

Figure 2: Temperature, pressure, and water vapor concentration interpolation curves overthe course of a day.

Results and Discussion

Figure 3 shows the temperature and relative humidity profiles at the final time step.


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Figure 3: Temperature and relative humidity profiles after 24 hours.


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While the temperature gradient is not very large, the power dissipated from theelectronic component clearly influences the temperature field: it heats the surrounding

air and the walls. Cold air enters through the slits by convection. In addition, the airinside the box is cooled by conduction through the walls. The relative humiditydepends on temperature, pressure, and moisture content. Moreover, the pressure fallis small enough to consider the relative humidity to be primarily influenced bytemperature and concentration. The relative humidity maximum is located where thetemperature is the lowest but also where the water vapor concentration is the highest.

Figure 4: Maximum relative humidity over time inside the box.

Figure 4 represents the evolution of the maximum relative humidity inside the boxover the simulation period. This curve reaches a maximum of 100%, meaning thatcondensation occurs. A Boolean condensation indicator is inserted in order to

distinguish the exact condensation period. The condensation indicator is set to 1 whencondensation is detected (relative humidity equals 1) and to 0 otherwise.


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Model Library path: Heat_Transfer_Module/Power_Electronics_and_Electronic_Cooling/

condensation_electronic_device

Modeling Instructions

From the File menu, choose New.

N E W

1 In the New window, click the Model Wizard button.

M O D E L W I Z A R D

1 In the Model Wizard window, click the 2D button.

2 In the Select physics tree, select Heat Transfer>Conjugate Heat Transfer>Laminar Flow

(nitf) .3 Click the Add button.

4 Click the Study button.

5 In the tree, select Preset Studies>Time Dependent .

6 Click the Done button.

G E O M E T R Y 1

Import 11 On the Home toolbar, click Import .

2 In the Import settings window, locate the Import section.

3 Click the Browse button.

4 Browse to the models Model Library folder and double-click the filecondensation_electronic_device.mphbin .

5 Click the Import button.

The imported geometry is represented in Figure 1 .

M AT E R I A L S

A material is only needed on the solid part as the fluid part is going to be defined atthe feature level through the moist air functionality.


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1 On the Home toolbar, click Add Material .

A D D M AT E R I A L1 Go to the Add Material window.

2 In the tree, select Built-In>Aluminum .

3 In the Add material window, click Add to Component .

M AT E R I A L S

Aluminum1 In the Model Builder window, under Component 1>Materials click Aluminum .

2 Select Domains 1 and 3 only.

A D D M AT E R I A L

1 Go to the Add Material window.

2 In the tree, select Built-In>Silica glass .

3 In the Add material window, click Add to Component .

M AT E R I A L S

Silica glass1 In the Model Builder window, under Component 1>Materials click Silica glass .

2 Select Domain 4 only.

D E F I N I T I O N SThis part is dedicated to defining the interpolation function of external temperature,pressure and water vapor concentration. The use of piecewise cubic interpolationsmooths the curves between measurement points.

Interpolation 11 On the Home toolbar, click Functions and choose Global>Interpolation .

2 In the Interpolation settings window, locate the Definition section.

3 From the Data source list, choose File.

4 Find the Functions subsection. Click the Browse button.

5 Browse to the models Model Library folder and double-click the filecondensation_electronic_device_temperature_data.txt .



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7 In the Function name edit field, type T_ext .

8 Locate the Interpolation and Extrapolation section. From the Interpolation list,choose Piecewise cubic .

9 Locate the Units section. In the Arguments edit field, type s .

10 In the Function edit field, type K.

11 Click the Plot button.

This figure should look like the left curve of Figure 2 .


2 In the Interpolation settings window, locate the Definition section.

3 From the Data source list, choose File.


5 Browse to the models Model Library folder and double-click the filecondensation_electronic_device_pressure_data.txt .


7 In the Function name edit field, type p_ext .

8 Locate the Interpolation and Extrapolation section. From the Interpolation list,choose Piecewise cubic .

9 Locate the Units section. In the Arguments edit field, type s .

10 In the Function edit field, type Pa .

11 Click the Plot button.This figure should look like the bottom graph in Figure 2 .

Next, define probes for the maximum relative humidity and the condensation indicatorat the solver time steps.


2 In the Interpolation settings window, locate the Definition section.3 From the Data source list, choose File.


5 Browse to the models Model Library folder and double-click the filecondensation_electronic_device_concentration_data.txt .



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7 In the Function name edit field, type c_ext .

8 Locate the Interpolation and Extrapolation section. From the Interpolation list,

choose Piecewise cubic .9 Locate the Units section. In the Arguments edit field, type s .

10 In the Function edit field, type mol/m^3 .

11 Click the Plot button.

This figure should look like the bottom curve of Figure 2 .

Then, two probes are defined in order to get the maximum relative humidity and

the condensation indicator at the solver time steps.12 On the Definitions toolbar, click Probes and choose Domain Probe .

13 In the Domain Probe settings window, locate the Source Selection section.

14 Click Clear Selection .


16 Locate the Probe Settings section. From the Type list, choose Maximum .

17 Locate the Expression section. In the Expression edit field, type nitf.phi .18 On the Definitions toolbar, click Probes and choose Domain Probe .

19 In the Domain Probe settings window, locate the Source Selection section.

20 Click Clear Selection .


22 Locate the Probe Settings section. From the Type list, choose Maximum .

23 Locate the Expression section. In the Expression edit field, type nitf.condInd .

C O N J U G AT E H E AT T R A N S F E R

Fluid 11 In the Model Builder window, under Component 1>Conjugate Heat Transfer click Fluid

1.


3 In the Fluid settings window, locate the Model Inputs section.

4 Clear the Reference pressure check box.

5 Locate the Thermodynamics section. From the Fluid type list, choose Moist air .

6 From the Input quantity list, choose Concentration .

7 Locate the Model Inputs section. In the c edit field, type c_ext(t) .


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Initial Values 11 In the Model Builder window, under Component 1>Conjugate Heat Transfer click Initial

Values 1 .2 In the Initial Values settings window, locate the Initial Values section.

3 In the p edit field, type p_ext(0) .

4 In the T edit field, type T_ext(0) .

Convective Heat Flux 11 On the Physics toolbar, click Boundaries and choose Convective Heat Flux .

2 Select Boundaries 1, 2, 5, 7, 21, and 23 only.3 In the Convective Heat Flux settings window, locate the Heat Flux section.

4 In the h edit field, type 10 .

5 In the T ext edit field, type T_ext(t) .

Heat Source 11 On the Physics toolbar, click Domains and choose Heat Source .


3 In the Heat Source settings window, locate the Heat Source section.

4 Click the Total power button.

5 In the P tot edit field, type 1 .

Open Boundary 11 On the Physics toolbar, click Boundaries and choose Open Boundary .

2 Select Boundaries 3 and 22 only.

3 In the Open Boundary settings window, locate the Boundary Condition section.

4 In the f 0 edit field, type p_ext(t) .

5 Locate the Exterior Temperature section. In the T 0 edit field, type T_ext(t) .

M E S H 1

Size1 In the Model Builder window, under Component 1 right-click Mesh 1 and choose Edit

Physics-Induced Sequence .

2 In the Model Builder window, under Component 1>Mesh 1 click Size.

3 In the Size settings window, locate the Element Size section.

4 From the Predefined list, choose Coarse .


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Temperature (nitf)The second default plot represents the temperature profile at the last time step, as

shown in the top panel of Figure 3 .

2D Plot Group 41 On the Home toolbar, click Add Plot Group and choose 2D Plot Group .

2 In the Model Builder window, under Results right-click 2D Plot Group 4 and chooseSurface .

3 In the Surface settings window, click Replace Expression in the upper-right corner ofthe Expression section. From the menu, choose Conjugate Heat Transfer (LaminarFlow)>Relative humidity (nitf.phi) .

4 On the 2D plot group toolbar, click Plot .

Compare with the relative humidity profile in the bottom panel of Figure 3 .

5 In the Model Builder window, right-click 2D Plot Group 4 and choose Rename .

6 Go to the Rename 2D Plot Group dialog box and type Relative Humidity in theNew name edit field.

7 Click OK.

Probe 1D Plot Group 3Follow the steps below to reproduce the relative humidity evolution shown inFigure 4 .

1 In the Model Builder window, under Results right-click Probe 1D Plot Group 3 andchoose Rename .

2 Go to the Rename 1D Plot Group dialog box and type Maximum Relative Humidity in the New name edit field.

3 Click OK.

Maximum Relat ive Humidi ty 1 In the Table Graph settings window, click to expand the Legends section.

2 Select the Show legends check box.

3 From the Legends list, choose Manual .

4 In the table, enter the following settings:

Legends

Maximum Relative Humidity - Study 1

Condensation Indicator - Study 1


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5 In the Model Builder window, click Maximum Relative Humidity .

6 In the 1D Plot Group settings window, click to expand the Legend section.

7 From the Position list, choose Lower right .

8 Click to expand the Window settings section. Locate the Window Settings section.From the Plot window list, choose Graphics .

9 On the 1D plot group toolbar, click Plot .


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