Documentation

# evaluateHeatRate

Evaluate integrated heat flow rate normal to specified boundary

## Syntax

``Qn = evaluateHeatRate(thermalresults,RegionType,RegionID)``

## Description

example

````Qn = evaluateHeatRate(thermalresults,RegionType,RegionID)` returns the integrated heat flow rate normal to the boundary specified by `RegionType` and `RegionID`.```

## Examples

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Compute the heat flow rate across a face of the block geometry.

`thermalmodel = createpde('thermal','steadystate');`

Import the block geometry.

```importGeometry(thermalmodel,'Block.stl'); pdegplot(thermalmodel,'FaceLabels','on','FaceAlpha',0.5)```

Specify the thermal conductivity of the block.

`thermalProperties(thermalmodel,'ThermalConductivity',80);`

Apply constant temperatures on the opposite ends of the block. All other faces are insulated by default.

```thermalBC(thermalmodel,'Face',1,'Temperature',100); thermalBC(thermalmodel,'Face',3,'Temperature',50);```

Generate mesh.

`generateMesh(thermalmodel,'GeometricOrder','linear');`

Solve the thermal model.

`thermalresults = solve(thermalmodel);`

Compute the heat flow rate across face 3 of the block.

`Qn = evaluateHeatRate(thermalresults,'Face',3)`
```Qn = 4.0000e+04 ```

Compute the heat flow rate across the surface of the cooling sphere.

Create a thermal model for transient analysis.

`thermalmodel = createpde('thermal','transient');`

Create a sphere of radius 1, and assign it to the thermal model.

```gm = multisphere(1); thermalmodel.Geometry = gm;```

Generate mesh.

`generateMesh(thermalmodel,'GeometricOrder','linear');`

Specify thermal properties of the sphere.

```thermalProperties(thermalmodel,'ThermalConductivity',80, ... 'SpecificHeat',460, ... 'MassDensity',7800);```

Apply a convection boundary condition on the surface of the sphere.

```thermalBC(thermalmodel,'Face',1,... 'ConvectionCoefficient',500, ... 'AmbientTemperature',30);```

Set the initial temperature.

`thermalIC(thermalmodel,800);`

Solve the thermal model.

```tlist = 0:100:2000; result = solve(thermalmodel,tlist);```

Compute the heat flow rate across the surface of the sphere over time.

```Qn = evaluateHeatRate(result,'Face',1); plot(tlist,Qn) xlabel('Time') ylabel('Heat Flow Rate')```

## Input Arguments

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Solution of a thermal problem, specified as a `SteadyStateThermalResults` object. Create `thermalresults` using the `solve` function.

Example: ```thermalresults = solve(thermalmodel)```

Geometric region type, specified as `'Face'` for 3-D geometry or `'Edge'` for 2-D geometry.

Example: ```Qn = evaluateHeatRate(thermalresults,'Face',3)```

Data Types: `char` | `string`

Geometric region ID, specified as a positive integer. Find the region IDs using the `pdegplot` function with the `'FaceLabels'` (3-D) or `'EdgeLabels'` (2-D) value set to `'on'`.

Example: ```Qn = evaluateHeatRate(thermalresults,'Face',3)```

Data Types: `double`

## Output Arguments

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Heat flow rate, returned as a real number or, for time-dependent results, a vector of real numbers. This value represents the integrated heat flow rate, measured in energy per unit time, flowing in the direction normal to the boundary. `Qn` is positive if the heat flows out of the domain, and negative if the heat flows into the domain.