custom phase changing material does not release heat.

Problem:

When I adjust the latent heat, there's no change in the temperature curve of the XPS material. I anticipate a stable temperature, ranging between 305K and 320K. So the problem is that the material does not release the absorbed heat.

equations

assert(Cps > 0 && Cpl > 0)

assert(T > 0, 'Temperature must be greater than absolute zero')

T == M.T;

if T >= Tmelt_start && T <= Tmelt_end

phaseChangeRate == {0.001, '1/s'};

else

phaseChangeRate == {0, '1/s'};

end

if phase < 1 && phase > 0

Q == m * Cps * T.der + m * L * phaseChangeRate;

phase.der == phaseChangeRate;

else

Q == m * Cpl * T.der;

phase.der == {0, '1/s'};

end

end

explanation of the full code:

This code describes a thermal component that models internal energy storage in a thermal network. Here's a breakdown of the main parts of this code:

1. **Nodes**: These are points where other components can connect. Two thermal nodes are defined: `M` (top) and `N` (bottom).

2. **Inputs**: These values can be supplied from outside. `Mdot` represents the mass flow rate (in kg/s) and `T_in` is the input temperature (in Kelvin).

3. **Parameters**: These values determine the behavior of the component. They include:

- `mass_type`: Type of mass (constant or variable).

- `mass`: The mass of the thermal component.

- `Cps` and `Cpl`: Specific heat capacity for solid and liquid, respectively.

- `Tmelt_start` and `Tmelt_end`: The temperature range where the material starts melting and stops melting.

- `L`: Specific latent heat.

- `mass_min`: Minimum mass.

- `num_ports`: The number of graphical ports.

4. **Annotations**: These are metadata that provide additional information about the component or dictate how it is displayed in a GUI. Here, it is primarily used to indicate which parameters can be modified externally and to define the component's icon.

5. **Variables**: These represent the internal states of the component. They include:

- `m`: The mass.

- `T`: The temperature.

- `phase`: The phase (0 for solid, 1 for liquid, and values in between for a mixed phase).

- `phaseChangeRate`: The rate of phase change.

- `Q`: Heat flow rate.

6. **Branches**: These are connections between different parts of the network. Here, the heat flow `Q` from node `M` to another part of the network is defined.

7. **Equations**: These describe the mathematical relationships between the different variables and parameters. They include:

- Relationships between `T`, `Q`, `m`, and other variables, especially around phase change.

- Constraints on certain values (like that `Cps`, `Cpl`, and `T` must be positive).

8. **Connections**: These are the actual connections between the different nodes within the component. Here, node `M` is connected to node `N`.

The essence of this component is that it models a thermal mass that can store and release energy. It also accounts for phase changes, meaning it can melt or solidify within a certain temperature range.

component derdecomponent
    % Thermal Mass
    % This block models internal energy storage in a thermal network.

    nodes
        M = foundation.thermal.thermal; % :top
    end

    inputs(ExternalAccess = none)
        Mdot = {0,   'kg/s'};    % Mdot:bottom
        T_in = {300, 'K'};       % Tin:bottom
    end

    nodes(ExternalAccess = none)
        N = foundation.thermal.thermal; % :bottom
    end

    parameters
        mass_type = foundation.enum.constant_variable.constant; % Mass type
    end

    parameters (ExternalAccess = none)
        mass      = {1,   'kg'};    % Mass
    end

    parameters
        Cps = {200, 'J/(kg*K)'}; % Specific heat solid
        Cpl = {1000, 'J/(kg*K)'}; % Specific heat liquid
        Tmelt_start = {320, 'K'}; % Start Melting Temperature
        Tmelt_end = {305, 'K'}; % End Melting Temperature
        L = {100, 'J/(kg)'}; % Specific Latent Heat
    end

    parameters (ExternalAccess = none)
        mass_min  = {1e-6,'kg'};    % Minimum mass
    end

    parameters 
        num_ports = foundation.enum.numPorts2.one;     % Number of graphical ports
    end

    if num_ports == 2
        annotations
            N : ExternalAccess=modify
        end
        if mass_type == foundation.enum.constant_variable.constant
            annotations
                % Icon = 'mass2.svg'
            end
        else
            annotations
                % Icon = 'mass4.svg'
            end
        end
    else
        if mass_type == foundation.enum.constant_variable.variable
            annotations
                % Icon = 'mass3.svg'
            end
        end 
    end

    if mass_type == foundation.enum.constant_variable.constant
        annotations
            mass : ExternalAccess=modify
        end
        equations
            m == {1,'kg'};
        end
    else
        annotations
            [Mdot, T_in, m, mass_min] : ExternalAccess=modify
        end
        equations
            assert(mass_min > 0)
        end
    end

    variables (ExternalAccess=none)
        m = {value = {1,'kg'}, priority=priority.high}; % Mass
    end

    variables
        T = {value = {300, 'K'}, priority = priority.high}; % Temperature
        phase = {value = {0, '1'}, priority = priority.high}; % Phase
        phaseChangeRate = {0, '1/s'}; % Rate of phase change
    end

    variables (Access=private)
        Q = {0, 'W'}; % Heat flow rate
    end

    branches
        Q : M.Q -> *;
    end

    equations
        assert(Cps > 0 && Cpl > 0)
        assert(T > 0, 'Temperature must be greater than absolute zero')

        T == M.T;

        if T >= Tmelt_start && T <= Tmelt_end
            phaseChangeRate == {0.001, '1/s'};
        else
            phaseChangeRate == {0, '1/s'};
        end

        if phase < 1 && phase > 0
            Q == m * Cps * T.der + m * L * phaseChangeRate;
            phase.der == phaseChangeRate;
        else
            Q == m * Cpl * T.der;
            phase.der == {0, '1/s'};
        end
    end

    connections
        connect(M,N)
    end

end

Answer 1

[Shishir Reddy]

Hi Berkay

The issue seems to be related to the logic in the phase change model.

‘Tmelt_start’ has been set to 320K and ‘Tmelt_end’is set to 305K. This is inverted, typically the melting process starts at a lower temperature and ends at high temperature. So, the values must be swapped.

Tmelt_start = {305, 'K'};
Tmelt_end = {320, 'K'};

In calculating ‘’phaseChangeRate‘ - (T >= Tmelt_start && T <= Tmelt_end)’ – This condition only checks if the temperature T is within the range where phase change can occur. But it should also be ensured that ‘phaseChangeRate’ should be applied only when the material is neither fully solid (phase == 0) nor fully liquid (phase == 1).

For example, consider a material that starts melting at 305 K and finishes at 320 K. If the temperature is 310 K, it is within the range, but if ‘phase’== 0’ or ‘phase == 1’, the material is not currently undergoing a phase change. Conversely, if ‘phase’ is between 0 and 1 but the temperature is outside 305-320 K, the phase change should not be active.

So, the code should be modified as follows.

if T >= Tmelt_start && T <= Tmelt_end && phase < 1 && phase > 0
    phaseChangeRate == {0.001, '1/s'};
else
    phaseChangeRate == {0, '1/s'};
end

I hope this helps.