## Modelica.Thermal.HeatTransfer

1-dimensional heat transfer with lumped elements

### Information

This package contains components to model 1-dimensional heat transfer with lumped elements. This allows especially to model heat transfer in machines provided the parameters of the lumped elements, such as the heat capacity of a part, can be determined by measurements (due to the complex geometries and many materials used in machines, calculating the lumped element parameters from some basic analytic formulas is usually not possible).

Example models how to use this library are given in subpackage Examples. For a first simple example, see Examples.TwoMasses where two masses with different initial temperatures are getting in contact to each other and arriving after some time at a common temperature. A more realistic example is provided in Examples.Drive where the heating of an electrical motor is modelled, see the following screen shot of this example:

The filled and non-filled red squares at the left and right side of a component represent thermal ports (connector HeatPort). Drawing a line between such squares means that they are thermally connected. The variables of a HeatPort connector are the temperature T at the port and the heat flow rate Q_dot flowing into the component (if Q_dot is positive, the heat flows into the element, otherwise it flows out of the element):

       Modelica.SIunits.Temperature  T  "absolute temperature at port in Kelvin";
       Modelica.SIunits.HeatFlowRate Q_dot  "flow rate at the port in Watt";

Note, that all temperatures of this package, including initial conditions, are given in Kelvin. For convenience, in subpackages HeatTransfer.Celsius, HeatTransfer.Fahrenheit and HeatTransfer.Rankine components are provided such that source and sensor information is available in degree Celsius, degree Fahrenheit, or degree Rankine, respectively. Additionally, in package SIunits.Conversions conversion functions between the units Kelvin and Celsius, Fahrenheit, Rankine are provided. These functions may be used in the following way:

      import SI=Modelica.SIunits;
      import Modelica.SIunits.Conversions.*;
         ...
      parameter SI.Temperature T = from_degC(25);  // convert 25 degree Celsius to Kelvin

This package contains the following model components:

       Examples               (subpackage) Examples of library usage.
       Interfaces             (subpackage) Interface definitions.

       HeatCapacitor          Lumped thermal element storing heat.
       ThermalConductor       Lumped thermal element transporting heat without
                              storing it.
       Convection             Lumped thermal element for heat convection.
       BodyRadiation          Lumped thermal element for radiation heat transfer
                              between two bodies

       FixedTemperature       Fixed temperature boundary condition.
       PrescribedTemperature  Variable temperature boundary condition
       FixedHeatFlow          Fixed heat flow boundary condition.
       PrescribedHeatFlow     Variable heat flow boundary condition.

       TemperatureSensor      Absolute temperature sensor.
       RelTemperatureSensor   Relative temperature sensor.
       HeatFlowSensor         Sensor to determine the heat flow rate
                              between two ports.

       Celsius                (subpackage) Elements with Celsius interface.
       Fahrenheit             (subpackage) Elements with Fahrenheit interface.
       Rankine                (subpackage) Elements with Rankine interface.

There are several other components available, such as AxialConduction (discretized PDE in axial direction), which have been temporarily removed from this library. The reason is that these components reference material properties, such as thermal conductivity, and currently the Modelica design group is discussing a general scheme to describe material properties.

For technical details in the design of this library, see the following reference:
Michael Tiller (2001): Introduction to Physical Modeling with Modelica. Kluwer Academic Publishers Boston.

Release Notes:

- July 15, 2002 by Michael Tiller, Martin Otter and Nikolaus Schürmann:
  Implemented.

Acknowledgements:
Several helpful remarks from the following persons are acknowledged: John Batteh, Ford Motors, Dearborn, U.S.A; Anton Haumer, Technical Consulting & Electrical Engineering, Austria; Ludwig Marvan, VA TECH ELIN EBG Elektronik GmbH, Wien, Austria; Hans Olsson, Dynasim AB, Sweden; Hubertus Tummescheit, Lund Institute of Technology, Lund, Sweden.

Copyright © 2001-2002, Modelica Association, Michael Tiller and DLR.

The Modelica package is free software; it can be redistributed and/or modified under the terms of the Modelica license, see the license conditions and the accompanying disclaimer in the documentation of package Modelica in file "Modelica/package.mo".

Name | Description
--- | ---
Examples | Example models to demonstrate the usage of package Modelica.Thermal.HeatTransfer
Interfaces |
HeatCapacitor | Lumped thermal element storing heat
ThermalConductor | Lumped thermal element transporting heat without storing it
Convection | Lumped thermal element for heat convection
BodyRadiation | Lumped thermal element for radiation heat transfer
FixedTemperature | Fixed temperature boundary condition in Kelvin
PrescribedTemperature | Variable temperature boundary condition in Kelvin
FixedHeatFlow | Fixed heat flow boundary condition
PrescribedHeatFlow | Prescribed heat flow boundary condition
TemperatureSensor | Absolute temperature sensor in Kelvin
RelTemperatureSensor | Relative Temperature sensor
HeatFlowSensor | Heat flow rate sensor
Celsius | Components with Celsius input and/or output
Fahrenheit | Components with Fahrenheit input and/or output
Rankine | Components with Rankine input and/or output

## Modelica.Thermal.HeatTransfer.HeatCapacitor

Lumped thermal element storing heat

### Information

This is a generic model for the heat capacity of a material. No specific geometry is assumed beyond a total volume with uniform temperature for the entire volume. Furthermore, it is assumed that the heat capacity is constant (indepedent of temperature).

The temperature T [Kelvin] of this component is a state. A default of T = 25 degree Celsius (= SIunits.Conversions.from_degC(25)) is used as start value for initialization. This usually means that at start of integration the temperature of this component is 25 degrees Celsius. You may, of course, define a different temperature as start value for initialization. Alternatively, it is possible to set parameter steadyStateStart to true. In this case the additional equation 'der(T) = 0' is used during initialization, i.e., the temperature T is computed in such a way that the component starts in steady state. This is useful in cases, where one would like to start simulation in a suitable operating point without being forced to integrate for a long time to arrive at this point.

Note, that parameter steadyStateStart is not available in the parameter menue of the simulation window, because its value is utilized during translation to generate quite different equations depending on its setting. Therefore, the value of this parameter can only be changed before translating the model.

This component may be used for complicated geometries where the heat capacity C is determined my measurements. If the component consists mainly of one type of material, the mass m of the component may be measured or calculated and multiplied with the specific heat capacity cp of the component material to compute C:

       C = cp*m.

       Typical values for cp at 20 degC in J/(kg.K):

          aluminium   896
          concrete    840
          copper      383
          iron        452
          silver      235
          steel       420 ... 500 (V2A)
          wood       2500

### Parameters

Name | Default | Description
--- | --- | ---
C |  | Heat capacity of part (= cp*m) [J/K]
steadyStateStart | false | true, if component shall start in steady state

### Modelica definition

    model HeatCapacitor "Lumped thermal element storing heat"
      parameter SI.HeatCapacity C "Heat capacity of part (= cp*m)";
      parameter Boolean steadyStateStart=false
        "true, if component shall start in steady state";
      SI.Temperature T(
                       start=from_degC(25)) "Temperature of part";
      Interfaces.HeatPort_a port;
    equation
      T = port.T;
      C*der(T) = port.Q_dot;

    initial equation
      if steadyStateStart then
        der(T) = 0;
      end if;
    end HeatCapacitor;

## Modelica.Thermal.HeatTransfer.ThermalConductor

Lumped thermal element transporting heat without storing it

### Information

This is a model for transport of heat without storing it. It may be used for complicated geometries where the thermal conductance G (= inverse of thermal resistance) is determined by measurements and is assumed to be constant over the range of operations. If the component consists mainly of one type of material and a regular geometry, it may be calculated, e.g., with one of the following equations:

- Conductance for a box geometry under the assumption that heat flows along the box length:

          G = k*A/L

          k: Thermal conductivity (material constant)
          A: Area of box
          L: Length of box

- Conductance for a cylindrical geometry under the assumption that heat flows from the inside to the outside radius of the cylinder:

          G = 2*pi*k*L/log(r_out/r_in)

          pi   : Modelica.Constants.pi
          k    : Thermal conductivity (material constant)
          L    : Length of cylinder
          log  : Modelica.Math.log;
          r_out: Outer radius of cylinder
          r_in : Inner radius of cylinder

        Typical values for k at 20 degC in W/(m.K):

          aluminium   220
          concrete      1
          copper      384
          iron         74
          silver      407
          steel        45 .. 15 (V2A)
          wood         0.1 ... 0.2

### Parameters

Name | Default | Description
--- | --- | ---
G |  | Constant thermal conductance of material [W/K]

### Modelica definition

    model ThermalConductor
      "Lumped thermal element transporting heat without storing it"
      extends Interfaces.Element1D;
      parameter SI.ThermalConductance G "Constant thermal conductance of material";

    equation
      Q_dot = G*dT;
    end ThermalConductor;

## Modelica.Thermal.HeatTransfer.Convection

Lumped thermal element for heat convection

### Information

This is a model of linear heat convection, e.g., the heat transfer between a plate and the surrounding air. It may be used for complicated solid geometries and fluid flow over the solid by determining the convective thermal conductance Gc by measurements. The basic constitutive equation for convection is

       Q_dot = Gc*(solid.T - fluid.T);

       Q_dot: Heat flow rate from connector 'solid' (e.g. a plate)
          to connector 'fluid' (e.g. the surrounding air)

Gc = G.signal[1] is an input signal to the component, since Gc is nearly never constant in practice. For example, Gc may be a function of the speed of a cooling fan. For simple situations, Gc may be calculated according to

       Gc = A*h

       A: Convection area (e.g. perimeter*length of a box)
       h: Heat transfer coefficient

where the heat transfer coefficient h is calculated from properties of the fluid flowing over the solid. Examples:

Machines cooled by air (empirical, very rough approximation according to R. Fischer: Elektrische Maschinen, 10th edition, Hanser-Verlag 1999, p. 378):

        h = 7.8*v^0.78 [W/(m2.K)] (forced convection)
          = 12         [W/(m2.K)] (free convection)

        where
          v: Air velocity in [m/s]

Laminar flow with constant velocity of a fluid along a flat plate where the heat flow rate from the plate to the fluid (= solid.Q_dot) is kept constant (according to J.P.Holman: Heat Transfer, 8th edition, McGraw-Hill, 1997, p.270):

       h  = Nu*k/x;
       Nu = 0.453*Re^(1/2)*Pr^(1/3);

       where
          h  : Heat transfer coefficient
          Nu : = h*x/k       (Nusselt number)
          Re : = v*x*rho/mue (Reynolds number)
          Pr : = cp*mue/k    (Prandtl number)
          v  : Absolute velocity of fluid
          x  : distance from leading edge of flat plate
          rho: density of fluid (material constant
          mue: dynamic viscosity of fluid (material constant)
          cp : specific heat capacity of fluid (material constant)
          k  : thermal conductivity of fluid (material constant)

       and the equation for h holds, provided
          Re < 5e5 and 0.6 < Pr < 50

### Modelica definition

    model Convection "Lumped thermal element for heat convection"
      SI.ThermalConductance Gc "Convective thermal conductance of element";
      SI.HeatFlowRate Q_dot "Heat flow rate from solid -> fluid";
      SI.Temperature dT "= solid.T - fluid.T";
      Modelica.Blocks.Interfaces.InPort G(
                                          final n=1, redeclare type SignalType = SI.ThermalConductance)
        "Signal representing the convective thermal conductance in [W/K]";
      Interfaces.HeatPort_a solid;
      Interfaces.HeatPort_b fluid;
    equation
      Gc = G.signal[1];
      dT = solid.T - fluid.T;
      solid.Q_dot = Q_dot;
      fluid.Q_dot = -Q_dot;
      Q_dot = Gc*dT;
    end Convection;

## Modelica.Thermal.HeatTransfer.BodyRadiation

Lumped thermal element for radiation heat transfer

### Information

This is a model describing the thermal radiation, i.e., electromagnetic radiation emitted between two bodies as a result of their temperatures. The following constitutive equation is used:

        Q_dot = Gr*sigma*(port_a.T^4 - port_b.T^4);

where Gr is the radiation conductance and sigma is the Stefan-Boltzmann constant (= Modelica.Constants.sigma). Gr may be determined by measurements and is assumed to be constant over the range of operations.

For simple cases, Gr may be analytically computed. The analytical equations use epsilon, the emission value of a body which is in the range 0..1. Epsilon=1, if the body absorbs all radiation (= black body). Epsilon=0, if the body reflects all radiation and does not absorb any.

       Typical values for epsilon:

       aluminium, polished    0.04
       copper, polished       0.04
       gold, polished         0.02
       paper                  0.09
       rubber                 0.95
       silver, polished       0.02
       wood                   0.85..0.9

Analytical Equations for Gr

Small convex object in large enclosure (e.g., a hot machine in a room):

        Gr = e*A

        where
           e: Emission value of object (0..1)
           A: Surface area of object where radiation
              heat transfer takes place

Two parallel plates:

        Gr = A/(1/e1 + 1/e2 - 1)

        where
           e1: Emission value of plate1 (0..1)
           e2: Emission value of plate2 (0..1)
           A : Area of plate1 (= area of plate2)

Two long cylinders in each other, where radiation takes place from the inner to the outer cylinder):

        Gr = 2*pi*r1*L/(1/e1 + (1/e2 - 1)*(r1/r2))

        where
           pi: = Modelica.Constants.pi
           r1: Radius of inner cylinder
           r2: Radius of outer cylinder
           L : Length of the two cylinders
           e1: Emission value of inner cylinder (0..1)
           e2: Emission value of outer cylinder (0..1)

### Parameters

Name | Default | Description
--- | --- | ---
Gr |  | Net radiation conductance between two surfaces (see docu) [m2]

### Modelica definition

    model BodyRadiation
      "Lumped thermal element for radiation heat transfer"
      extends Interfaces.Element1D;
      parameter Real Gr(unit="m2")
        "Net radiation conductance between two surfaces (see docu)";
    equation
      Q_dot = Gr*Modelica.Constants.sigma*(port_a.T^4 - port_b.T^4);
    end BodyRadiation;

## Modelica.Thermal.HeatTransfer.FixedTemperature

Fixed temperature boundary condition in Kelvin

### Information

This model defines a fixed temperature T at its port in Kelvin, i.e., it defines a fixed temperature as a boundary condition.

### Parameters

Name | Default | Description
--- | --- | ---
T |  | Fixed temperature at port [K]

### Modelica definition

    model FixedTemperature
      "Fixed temperature boundary condition in Kelvin"

      parameter SI.Temperature T "Fixed temperature at port";
      Interfaces.HeatPort_b port;
    equation
      port.T = T;
    end FixedTemperature;

## Modelica.Thermal.HeatTransfer.PrescribedTemperature

Variable temperature boundary condition in Kelvin

### Information

This model represents a variable temperature boundary condition. The temperature in [K] is given as input signal to the model. The effect is that an instance of this model acts as an infinite reservoir able to absorb or generate as much energy as required to keep the temperature at the specified value.

### Modelica definition

    model PrescribedTemperature
      "Variable temperature boundary condition in Kelvin"

      Interfaces.HeatPort_b port;
      Modelica.Blocks.Interfaces.InPort T(
                                          final n=1, redeclare type SignalType = SI.Temperature);
    equation
      port.T = T.signal[1];
    end PrescribedTemperature;

## Modelica.Thermal.HeatTransfer.FixedHeatFlow

Fixed heat flow boundary condition

### Information

This model allows a specified amount of heat flow rate to be "injected" into a thermal system at a given port. The constant amount of heat flow rate Q_dot is given as a parameter. The heat flows into the component to which the component FixedHeatFlow is connected, if parameter Q_dot is positive.

### Parameters

Name | Default | Description
--- | --- | ---
Q_dot |  | Fixed heat flow rate at port [W]

### Modelica definition

    model FixedHeatFlow "Fixed heat flow boundary condition"
      parameter SI.HeatFlowRate Q_dot "Fixed heat flow rate at port";
      Interfaces.HeatPort_b port;
    equation
      port.Q_dot = -Q_dot;
    end FixedHeatFlow;

## Modelica.Thermal.HeatTransfer.PrescribedHeatFlow

Prescribed heat flow boundary condition

### Information

This model allows a specified amount of heat flow rate to be "injected" into a thermal system at a given port. The amount of heat is given by the input signal into the model. The heat flows into the component to which the component PrescribedHeatFlow is connected, if the input signal is positive.

### Modelica definition

    model PrescribedHeatFlow "Prescribed heat flow boundary condition"
      Modelica.Blocks.Interfaces.InPort Q_dot(
                                              final n=1);
      Interfaces.HeatPort_b port;
    equation
      port.Q_dot = -Q_dot.signal[1];
    end PrescribedHeatFlow;

## Modelica.Thermal.HeatTransfer.TemperatureSensor

Absolute temperature sensor in Kelvin

### Information

This is an ideal absolute temperature sensor which returns the temperature of the connected port in Kelvin as an output signal. The sensor itself has no thermal interaction with whatever it is connected to. Furthermore, no thermocouple-like lags are associated with this sensor model.

### Modelica definition

    model TemperatureSensor "Absolute temperature sensor in Kelvin"
      Modelica.Blocks.Interfaces.OutPort T(
                                           redeclare type SignalType = SI.Temperature);
      Interfaces.HeatPort_a port;
    equation
      T.signal[1] = port.T;
      port.Q_dot = 0;

    end TemperatureSensor;

## Modelica.Thermal.HeatTransfer.RelTemperatureSensor

Relative Temperature sensor

### Information

The relative temperature "port_a.T - port_b.T" is determined between the two ports of this component and is provided as output signal in Kelvin.

### Modelica definition

    model RelTemperatureSensor "Relative Temperature sensor"
      extends Modelica.Icons.TranslationalSensor;
      Interfaces.HeatPort_a port_a;
      Interfaces.HeatPort_b port_b;
      Modelica.Blocks.Interfaces.OutPort T_rel(
                                               redeclare type SignalType = SI.Temperature);
    equation
      T_rel.signal[1] = port_a.T - port_b.T;
      0 = port_a.Q_dot;
      0 = port_b.Q_dot;
    end RelTemperatureSensor;

## Modelica.Thermal.HeatTransfer.HeatFlowSensor

Heat flow rate sensor

### Information

This model is capable of monitoring the heat flow rate flowing through this component. The sensed value of heat flow rate is the amount that passes through this sensor while keeping the temperature drop across the sensor zero. This is an ideal model so it does not absorb any energy and it has no direct effect on the thermal response of a system it is included in. The output signal is positive, if the heat flows from port_a to port_b.

### Modelica definition

    model HeatFlowSensor "Heat flow rate sensor"
      extends Modelica.Icons.RotationalSensor;
      output SI.HeatFlowRate Q_dot "Heat flow rate from port_a to port_b";
      Modelica.Blocks.Interfaces.OutPort heat(
                                              redeclare type SignalType = SI.HeatFlowRate) "Heat flow from port_a -> port_b";
      Interfaces.HeatPort_a port_a;
      Interfaces.HeatPort_b port_b;
    equation
      port_a.T = port_b.T;
      port_a.Q_dot + port_b.Q_dot = 0;
      Q_dot = port_a.Q_dot;
      heat.signal[1] = Q_dot;
    end HeatFlowSensor;