Engee documentation

Thermal Mass

Mass in thermal systems.

blockType: AcausalFoundation.Thermal.Elements.Mass

thermal mass

Thermal Mass

Path in the library:

/Physical Modeling/Fundamental/Thermal/Elements/Thermal Mass

variable thermal mass

Variable Thermal Mass

Path in the library:

/Physical Modeling/Fundamental/Thermal/Elements/Variable Thermal Mass

Description

Block Thermal Mass represents the thermal mass. This value reflects the ability of a material or combination of materials to accumulate internal energy, it depends on the mass of the body and its heat capacity.

The thermal mass is described by the following expression:

Where

  • — heat flow;

  • — specific heat capacity of the mass of the material;

  • — mass;

  • Т — temperature;

  • — Time.

Parameter Variable mass allows you to specify whether the mass remains constant or changes during the simulation:

  • If the check box is unchecked, the thermal mass remains constant during the simulation.

  • If the check box is checked, the thermal mass may change during the simulation. When selecting this option, the parameter Mass replaced by the parameter Minimum mass, and the unit 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 option Variable mass for modeling systems in which the mass changes, but the geometric effects remain insignificant, for example, a washing machine is filled, heated, and then emptied with different amounts of liquid per cycle.

By default, the unit has one thermal 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 customary to display the mass sequentially with other elements in the block diagram. To support this option, you can use the parameter Number of graphical ports, which allows you to display another port. The two-port option is purely graphical: both ports have the same temperature, so the unit functions the same way, regardless of whether it has one or two ports. The block icon changes depending on the value of the parameters Variable mass and Number of graphical ports.

Variables

Use the parameter group Initial Targets to set the priority and initial target values for the block parameter variables before simulation. For more information, see Configuring physical blocks using target values.

Ports

Conserving

# A — the port connecting the mass to the thermal network
heat

Details

A thermal port that connects the mass to the thermal network.

Program usage name

port_reference_a

# B — the second graphic port
heat

Details

The second thermal port allows you to connect the mass in series with other elements of the flowchart. This port has the same temperature as port A, so the difference between the representations of a block with one and two ports is only graphical.

Dependencies

To use this port, set the parameter Number of graphical ports value 2.

Program usage name

port_reference_b

Input

# Mdot — weight control, kg/s
scalar

Details

The input port that determines the change in thermal mass. Use a variable Mass from the parameter group Initial Targets to set the initial value of the thermal mass.

Dependencies

To use this port, check the box Variable mass.

Data types

Float64
Complex numbers support

I don’t

# Tin — the temperature of the incoming mass, K
scalar

Details

The 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, check the box Variable mass.

Data types

Float64
Complex numbers support

I don’t

Parameters

Parameters

# Variable mass — specify whether the mass remains constant or changes during the simulation

Details

Parameter Variable mass allows you to specify whether the mass remains constant or changes during the simulation.:

  • If unchecked, the thermal mass remains constant during the simulation.

  • If this option is selected, the thermal mass may change during the simulation.

Default value

—
Program usage name

variable_mass
Evaluatable

No

# Mass — constant mass
kg | mg | g | t | lbm | oz | slug

Details

The mass value. The mass is constant during the simulation.

Dependencies

To use this port, uncheck the box. Variable mass.

Units

kg | mg | g | t | lbm | oz | slug
Default value

1.0 kg
Program usage name

mass_const
Evaluatable

Yes

# Specific heat — specific heat capacity of the material
J/(kg*K) | kJ/(kg*K) | cal/(kg*K) | kcal/(kg*K) | cal/(g*K) | kcal/(g*K) | Btu_IT/(lbm*deltadegR)

Details

Specific heat capacity of the material.

Units

J/(kg*K) | kJ/(kg*K) | cal/(kg*K) | kcal/(kg*K) | cal/(g*K) | kcal/(g*K) | Btu_IT/(lbm*deltadegR)
Default value

447.0 J/(kg*K)
Program usage name

c
Evaluatable

Yes

# Minimum mass — minimum permissible weight
kg | mg | g | t | lbm | oz | slug

Details

The minimum value of the thermal mass.

Dependencies

To use this port, check the box Variable mass.

Units

kg | mg | g | t | lbm | oz | slug
Default value

1e-6 kg
Program usage name

min_mass
Evaluatable

Yes

# Number of graphical ports — number of visible ports
1 | 2

Details

Options for connecting the unit to the rest of the circuit:

  • 1 — the unit has one non-directional port that connects it to the heating network. If the unit has one port, connect it to the connecting line between the other two units.

  • 2 — when this option is selected, the second port opens, which allows you to connect the unit in series with other units in the circuit. Since both ports have the same temperature, the unit works the same as if it had a single port.

Values

1 | 2
Default value

1
Program usage name

port_count
Evaluatable

No

Examples