P-H Diagram (2P)

Thermodynamic scope for two-phase fluid networks

Since R2021a

• 

Libraries:
Simscape / Fluids / Two-Phase Fluid / Utilities

Description

The P-H Diagram (2P) block plots a p-h diagram of the pressure with respect to the specific enthalpy of a thermodynamic, two-phase fluid. A p-h diagram indicates the fluid state at key points during a thermodynamic cycle.

Each numbered point on the diagram indicates the fluid state after a dynamic process in the refrigeration cycle:

1. Cool vapor at low pressure

2. Hot vapor at high pressure

3. Hot liquid at high pressure

4. Mixed vapor and liquid at low pressure

To use the P-H Diagram (2P) block:

1. Place a Thermodynamic Properties Sensor (2P) and a Pressure, Temperature & Internal Energy Sensor (2P) block at each location you want to monitor.

   Note

   The Pressure & Internal Energy Sensor (2P) block measures a differential pressure. Connect port A to the monitor point and port B to an Absolute Reference (2P) block.

2. Convert the Simscape physical signals to Simulink signals with a PS-Simulink Converter block.

3. Use a Mux block to combine the pressure signals. Connect the output signal to the P-H Diagram (2P) p port.

4. Use a Mux block to combine the converted specific enthalpy signals and connect the output signal to the h port.

5. Before running the simulation, double-click the P-H Diagram (2P) block, then click the Select fluid properties button to set the network fluid properties.

   If you do not select the fluid properties, the block uses the default two-phase network fluid, which is water.

Settings

Click the Settings button to specify the pressure, specific enthalpy, and temperature units and the element order. Clear the Array element order of inputs p and h with closed loop check box to use the Array indices of inputs p and h parameter to specify the order in which the block connects the cycle points.

P-H Diagram Playback

You can also replay the animation from the most recent simulation. After running the model, double-click the block and use the buttons at the top of the window to control the animation. Use the drop-down menu to the right of the Time field to control the rate of the playback. The replay controls are disabled before you run a simulation, when the model is loaded, and when the simulation is running.

Use the playback slider or Time field to control the simulation cycle. If you enter a time that is not a model time step, the block displays the next closest time step.

To save the current iteration of the plot, point to the plot area. From the icons in the top-right corner of the plot, click the Export icon and select the Save As button to save the plot.

Examples

Two-Phase Fluid Refrigeration

Models a vapor-compression refrigeration cycle using two-phase fluid components. The compressor drives the R-134a refrigerant through a condenser, an expansion valve, and an evaporator. The hot gas leaving the compressor condenses in the condenser via heat transfer to the environment. The pressure drops as the refrigerant passes through the expansion valve. The drop in pressure lowers the saturation temperature of the refrigerant. This enables it to boil in the evaporator as it absorbs heat from the refrigerator compartment. The refrigerant then returns to the compressor to repeat the cycle. The controller turns the compressor on and off to maintain the refrigerator compartment temperature within a band around the desired temperature.

Refrigeration Cycle (Air Conditioning)

A refrigeration cycle for a home air conditioning system. See Model a Refrigeration Cycle for the recommended steps to build this model in the two-phase fluid domain.

• Open Model

Residential Refrigerator

Models a basic refrigeration system that transfers heat between the refrigerant two-phase fluid and the environment moist air mixture. The compressor drives the R134a refrigerant through a condenser, a capillary tube, and an evaporator. An accumulator ensures that only vapor returns to the compressor.

• Open Model

Ports

Input

p — Pressure, MPa

vector

Vector of pressures. The vector must have same number of elements as the enthalpy signal at port h

h — Specific enthalpy, kJ/kg

vector

Vector of specific enthalpies. The vector must have same number of elements as the pressure signal at port p.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

This block can be used for simulation visibility in systems that generate code, but is not included in the generated code.

Version History

Introduced in R2021a

R2025a: Change units and specify cycle point order

Click the Settings button to specify the units and cycle point order. You can specify the pressure, specific enthalpy, and temperature units. Clear the Array element order of inputs p and h with closed loop check box to use the Array indices of inputs p and h parameter to specify the order in which the block connects the cycle points.

R2022b: Access playback capabilities

Use the controls at the top of the figure window to control and replay the animation from the most recent simulation.