Thermal Mass
Mass in thermal systems.
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Description
The Thermal Mass block represents thermal mass. This value reflects the ability of a material or combination of materials to store internal energy, it depends on the mass of the body and its heat capacity.
Thermal mass is described by the following expression:
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where:
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- heat flux;
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- specific heat capacity of the material mass;
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- mass;
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- temperature;
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- time.
The Variable mass parameter allows you to specify whether the mass remains constant or changes during the simulation:
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`Off' - thermal mass remains constant during the simulation.
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On- the thermal mass can be changed during the simulation. When this option is selected, the Mass parameter is replaced by the Minimum mass parameter, and the block has two additional input ports: Mdot, which sets the change in thermal mass, and Tin, which sets the temperature of the incoming mass. The value of the signal on the Tin port does not affect the results if the mass does not change or decreases.
Use the Variable mass option to model systems where the mass changes but geometric effects remain negligible, e.g. a washing machine is filled, heated and then emptied with different amounts of liquid per cycle.
By default, the block has one heat port. Since the positive direction of the block is from the port to the block, the heat flow will be positive if it flows into the block.
In some tasks, it is common to display the mass in series with other elements in the block diagram. To support this option, the Number of graphical ports parameter can be used to allow another port to be displayed. The two-port option is purely graphical: both ports have the same temperature, so the block functions the same whether it has one or two ports. The block icon changes depending on the value of the Variable mass and Number of graphical ports parameters.
Ports
Input
Mdot - mass control, kg/sec
scalar
Input port that defines the change in thermal mass. Use the high-priority variable Mass to set the initial value of thermal mass.
Dependencies
To use this port, set Variable mass to `On'.
Tin - temperature of the incoming mass, K
scalar
Input port that determines the temperature of the incoming mass. The value in the Tin port has no effect if the value in the Mdot port is less than or equal to 0.
Dependencies
To use this port, set the Variable mass parameter to `On'.
Non-directional
M is the port that connects the mass to the thermal network
heat
Heat port that connects the mass to the heat network.
N is the second graphics port
heat
A second thermal port that allows the mass to be connected in series with other elements of the block diagram. This port has the same temperature as the M port, so the difference between block representations with one and two ports is only graphical.
Dependencies
To use this port, set the Number of graphical ports parameter to 2.
Parameters
Variable mass - specify whether the mass remains constant or changes during the simulation
Off (by default) | On
The Variable mass parameter allows you to specify whether the mass remains constant or changes during the simulation:
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Off- thermal mass remains constant during the simulation. -
On- the thermal mass can be changed during the simulation.
Mass - constant mass
1.0 kg (by default) | `positive scalar'.
Mass value. Mass is constant during the simulation.
Dependencies
To use this port, set Variable mass to `Off'.
Specific heat is the specific heat capacity of the material
447.0 J/(K*kg) (by default) | `positive scalar'.
Specific heat capacity of the material.
Minimum mass - minimum mass allowed
1e-6 kg (by default) | positive scalar
Minimum thermal mass value.
Dependencies
To use this port, set Variable mass to `On'.
Number of graphical ports - number of visible ports
1 (by default) | 2.
Options for connecting the block to other parts of the circuit:
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1- the unit has one non-directional port that connects it to the thermal network. If the unit has one port, connect it to the connection line between the other two units. -
2- selecting this option opens a second port that allows the unit to be connected in series with other units in the loop. Since both ports have the same temperature, the unit operates as if it had one port.