Phase-Change Thermal Mass

R2026b

Mass of two-phase material in thermal systems

Since R2026b

• 

Phase-Change Thermal Mass block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simscape / Foundation Library / Thermal / Thermal Elements

Description

The Phase-Change Thermal Mass block represents a mass of two-phase material in a thermal network. In each phase, the rate of temperature increase is proportional to the heat flow rate into the material and inversely proportional to the mass and the specific heat of the phase. Phase 1 has lower energy than phase 2. The material absorbs or releases latent heat during phase transition while maintaining its temperature at the phase transition temperature.

For example, this plot illustrates the phase change process for water, from the solid to the liquid state.

The block uses the equations

$$\begin{array}{l}Q=m\cdot c_1\frac{dT}{dt},\text{ if }T<T_t\\ Q=m\cdot L\frac{d{F}_2}{dt},\text{ if }T=T_t\\ Q=m\cdot c_2\frac{dT}{dt},\text{ if }T>T_t\end{array}$$

where:

• m is the mass.

• Q is the heat flow rate into the mass.

• T is the temperature of the mass.

• T_t is the Phase transition temperature.

• c₁ and c₂ represent the Phase 1 specific heat and Phase 2 specific heat, respectively.

• L is the Latent heat of phase transition.

• F₂ is the phase 2 mass fraction.

Use this block to model systems like ice storage air conditioners that freeze water at night, during off-peak hours, and then use this stored ice during the day to provide cooling. You can also use this block to model phase-change materials in electronics and battery cooling applications.

By default, the block has one thermal conserving port. Because the block positive direction is from the port toward the block, the heat flow is positive if it flows into the block.

In some applications, it is customary to display mass in series with other elements in the block diagram layout. To support this use case, the Number of thermal ports parameter lets you display a second port on the opposite side of the block icon. The two-port variant is purely graphical: the two ports have the same temperature, so the block functions the same whether it has one or two ports.

The physical signal port F2 outputs the mass fraction of phase 2 during simulation. If you start the simulation when the material is in transition between phase 1 and phase 2, you must specify the initial mass fraction of phase 2 by using the Initial mass fraction of Phase 2 parameter. If you start the simulation when the material is either in phase 1 or phase 2, you must specify the temperature at the start of simulation by using the Initial temperature parameter. Depending on the initial phase, the initial temperature must be either lower or higher than the phase transition temperature.

Ports

Output

F2 — Mass fraction of phase 2

physical signal

Physical signal output port that measures the mass fraction of phase 2 during simulation.

Conserving

M — Thermal port that connects mass to circuit

thermal

Thermal conserving port that connects the mass to the physical network.

N — Second thermal port

thermal

Second thermal conserving port that lets you connect the mass in series with other elements in the block diagram. This port has the same temperature as port M, therefore the difference between the one-port and two-port block representations is purely graphical.

Dependencies

To enable this port, set the Number of thermal ports parameter to 2.

Parameters

Mass — Mass of two-phase material

1 kg (default) | positive scalar

Mass of two-phase material. The mass is constant during simulation.

Phase 1 specific heat — Specific heat of material in phase 1

2090 J/(K*kg) (default) | positive scalar

Specific heat of the material in phase 1. The default value is for solid water.

Phase 2 specific heat — Specific heat of material in phase 2

4186 J/(K*kg) (default) | positive scalar

Specific heat of the material in phase 2. The default value is for liquid water.

Phase transition temperature — Temperature corresponding to phase transition

273.15 K (default) | positive scalar

Temperature at which the phase transition happens.

Latent heat of phase transition — Energy per mass transferred during phase transition

3.34e5 J/kg (default) | positive scalar

Energy per unit of mass that needs to be transferred in or out during phase transition. The default value is for transition of ice into water.

Initial phase — Material phase at start of simulation

Phase 1 (default) | Transition between Phase 1 and Phase 2 | Phase 2

Material phase at the start of simulation:

• Phase 1 — The two-phase material is completely in phase 1.

• Transition between Phase 1 and Phase 2 — The two-phase material is in transition between phase 1 and phase 2.

• Phase 2 — The two-phase material is completely in phase 2.

Initial temperature — Temperature at start of simulation

253.15 K (default) | positive scalar

Temperature at the start of simulation. The parameter value depends on the initial phase of material:

• If Initial phase is Phase 1, the initial temperature must be lower than the Phase transition temperature parameter value.

• If Initial phase is Phase 2, the initial temperature must be higher than the Phase transition temperature parameter value.

Dependencies

To enable this parameter, set the Initial phase parameter to Phase 1 or Phase 2.

Initial mass fraction of Phase 2 — Mass fraction of material in phase 2 at start of simulation

0.5 (default) | scalar between 0 and 1

Mass fraction of material in phase 2 at the start of simulation.

Dependencies

To enable this parameter, set the Initial phase parameter to Transition between Phase 1 and Phase 2.

Number of thermal ports — Number of visible thermal ports

1 (default) | 2

How to connect the block to the rest of the circuit:

• 1 — The block has one conserving port that connects it to the thermal circuit. When the block has one port, attach it to a connection line between two other blocks.

• 2 — Selecting this option exposes the second port, which lets you connect the block in series with other blocks in the circuit. Because the two ports have the same temperature, the block functions the same as if it had one port.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2026b