Reservoir (2P)

Boundary conditions for two-phase fluid network

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Libraries:
Simscape / Foundation Library / Two-Phase Fluid / Elements

Description

The Reservoir (2P) block sets boundary conditions in a two-phase fluid network. The reservoir is assumed infinite in size, causing its pressure and specific internal energy to remain constant.

Port A represents the reservoir inlet. The flow resistance between port A and the reservoir interior is assumed negligible. The pressure at port A is therefore equal to the pressure inside the reservoir.

The specific enthalpy and specific internal energy at the reservoir inlet depend on the direction of flow. Fluid leaves the reservoir at the reservoir pressure and specific internal energy. Fluid enters the reservoir at the reservoir pressure, but the specific internal energy is determined by the two-phase fluid network upstream.

The block provides independent selection of pressure specification and energy specification, by using the Reservoir pressure specification and Reservoir energy specification parameters. Depending on the selected options, the block exposes additional parameters to specify values for the selected quantities. You specify the reservoir pressure and specific internal energy with block parameter values or physical signals.

This block also serves as a reference connection for the Pressure & Internal Energy Sensor (2P) block. In this case, the measured pressure and specific internal energy are relative to the reservoir pressure and specific internal energy.

Assumptions and Limitations

• The flow resistance between port A and the reservoir interior is negligible. Pressure is the same at port A and in the reservoir interior.

Examples

Cavitation in Two-Phase Fluid

How two-phase fluid components can be used to simulate cavitation. The model is a translational mechanical converter driven by an oscillating pressure source. During the negative portion of the pressure source cycle, the fluid cavitates, reducing the force produced by the converter. As a result, the converter displacement drifts and does not return to the starting position.

• Open Model

Fluid Vaporization in Pipe

Model the vaporization of water to generate steam. Liquid water enters the pipe at 370 K at a rate of 1 kg/s. The pipe is heated to 1000 K, causing the water flowing inside pipe to saturate.

• Open Model

Ports

Input

P — Pressure control signal, MPa

physical signal

Physical signal port that provides the reservoir pressure control signal.

Dependencies

To enable this port, select Provide input signal for the selected pressure specification and set Reservoir pressure specification to Specified pressure.

Tc — Reservoir condensing temperature control signal, K

physical signal

Physical signal port that provides the reservoir condensing temperature control signal.

Dependencies

To enable this port, select Provide input signal for the selected pressure specification and set Reservoir pressure specification to Saturation pressure at specified condensing temperature.

Te — Reservoir evaporating temperature control signal, K

physical signal

Physical signal port that provides the reservoir evaporating temperature control signal.

Dependencies

To enable this port, select Provide input signal for the selected pressure specification and set Reservoir pressure specification to Saturation pressure at specified evaporating temperature.

T — Temperature control signal, K

physical signal

Physical signal port that provides either the subcooled liquid temperature or the superheated vapor temperature control signal, based on the Reservoir temperature specification parameter setting.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Temperature.

X — Mass fraction of vapor control signal, unitless

physical signal

Physical signal port that specifies the mass fraction of vapor in the reservoir.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Vapor quality.

a — Volume fraction of vapor control signal, unitless

physical signal

Physical signal port that specifies the volume fraction of vapor in the reservoir.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Vapor void fraction.

H — Specific enthalpy of the fluid control signal, kJ/kg

physical signal

Physical signal port that specifies the specific enthalpy of the fluid in the reservoir.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Specific enthalpy.

U — Specific internal energy of the fluid control signal, kJ/kg

physical signal

Physical signal port that specifies the specific internal energy of the fluid in the reservoir.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Specific internal energy.

SC — Degree of subcooling of the fluid control signal, deltaK

physical signal

Physical signal port that specifies the degree of subcooling of the fluid in the reservoir, that is, the difference between the liquid saturation temperature and the fluid temperature.

This input signal specifies a temperature difference, in units of deltaK, rather than an absolute temperature. Therefore, if you connect a Simulink-PS Converter block directly to this port, do not select the Apply affine conversion check box.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Degree of subcooling.

SH — Degree of superheating of the fluid control signal, deltaK

physical signal

Physical signal port that specifies the degree of superheating of the fluid in the reservoir, that is, the difference between the fluid temperature and the vapor saturation temperature.

This input signal specifies a temperature difference, in units of deltaK, rather than an absolute temperature. Therefore, if you connect a Simulink-PS Converter block directly to this port, do not select the Apply affine conversion check box.

Dependencies

To enable this port, select Provide input signal for the selected energy specification and set Reservoir energy specification to Degree of superheating.

Conserving

A — Reservoir inlet

two-phase fluid

Two-phase fluid conserving port associated with the reservoir inlet.

Parameters

Provide input signal for the selected pressure specification — Method to specify pressure

off (default) | on

Method to use to specify the pressure in the reservoir. If you clear this check box, the block models pressure based on the value of the corresponding block parameter. If you select this check box, the block models pressure based on the value of the signal at the corresponding input port.

Reservoir pressure specification — Specification method for reservoir pressure

Specified pressure (default) | Saturation pressure at specified condensing temperature | Saturation pressure at specified evaporating temperature

Specification method for the reservoir pressure:

• Specified pressure — Specify a value by using the Reservoir pressure parameter or the signal value at port P, or use the atmospheric pressure specified by a Two-Phase Fluid Properties (2P) block connected to the circuit.

• Saturation pressure at specified condensing temperature — Use the pressure along the liquid saturation curve that corresponds to the temperature specified by the Reservoir condensing temperature parameter or the signal value at port Tc.

• Saturation pressure at specified evaporating temperature — Use the pressure along the vapor saturation curve that corresponds to the temperature specified by using the Reservoir evaporating temperature parameter or the signal value at port Te.

Specify reservoir pressure as atmospheric — Reservoir pressure

on (default) | off

If you select this check box, the block uses the atmospheric pressure specified by a Two-Phase Fluid Properties (2P) block connected to the circuit. If you clear this check box, the block uses the Reservoir pressure parameter value.

Dependencies

To enable this parameter, clear the Provide input signal for the selected pressure specification check box and set Reservoir pressure specification to Specified pressure.

Reservoir pressure — Pressure in reservoir

0.101325 MPa (default) | positive scalar

Absolute pressure inside the reservoir. This pressure remains constant during simulation. The default value corresponds to atmospheric pressure at mean sea level.

Dependencies

To enable this parameter, clear the Specify reservoir pressure as atmospheric check box.

Reservoir condensing temperature — Specify saturation pressure in terms of condensing temperature

373.15 K (default) | positive scalar

Pressure of the fluid inside the reservoir is equal to the saturation pressure, along the liquid saturation curve, that corresponds to this condensing temperature. The condensing temperature must be less than the critical temperature because the saturation curves are not defined above the critical point.

Dependencies

To enable this parameter, clear the Provide input signal for the selected pressure specification check box and set Reservoir pressure specification to Saturation pressure at specified condensing temperature.

Reservoir evaporating temperature — Specify saturation pressure in terms of evaporating temperature

373.15 K (default) | positive scalar

Pressure of the fluid inside the reservoir is equal to the saturation pressure, along the vapor saturation curve, that corresponds to this evaporating temperature. The evaporating temperature must be less than the critical temperature because the saturation curves are not defined above the critical point.

Dependencies

To enable this parameter, clear the Provide input signal for the selected pressure specification check box and set Reservoir pressure specification to Saturation pressure at specified evaporating temperature.

Provide input signal for the selected energy specification — Method to specify specific internal energy

off (default) | on

Method to use to specify the specific internal energy in the reservoir. If you clear this check box, the block models energy based on the value of the corresponding block parameter. If you select this check box, the block models energy based on the value of the signal at the corresponding input port.

Reservoir energy specification — Thermodynamic variable to use to define reservoir conditions

Temperature (default) | Vapor quality | Vapor void fraction | Specific enthalpy | Specific internal energy | Degree of subcooling | Degree of superheating

Thermodynamic variable to use for energy specification:

• Temperature — Specify the absolute temperature inside the reservoir by using the Reservoir temperature parameter or the signal value at port T. You can specify a state that is a subcooled liquid or superheated vapor. You cannot specify a liquid-vapor mixture because the temperature is constant across the liquid-vapor mixture region.

• Vapor quality — Specify the mass fraction of vapor in the reservoir by using the Reservoir vapor quality parameter or the signal value at port X. You can use this option only when the pressure is less than the critical pressure because this quantity does not exist above the critical point. You can specify a state that is a liquid-vapor mixture. You cannot specify a subcooled liquid or a superheated vapor because the vapor quality is 0 and 1, respectively, across the whole region. Additionally, the block limits the pressure to below the critical pressure.

• Vapor void fraction — Specify the volume fraction of vapor in the reservoir by using the Reservoir void fraction parameter or the signal value at port a. You can use this option only when the pressure is less than the critical pressure because this quantity does not exist above the critical point. You can specify a state that is a liquid-vapor mixture. You cannot specify a subcooled liquid or a superheated vapor because the vapor quality is 0 and 1, respectively, across the whole region. Additionally, the block limits the pressure to below the critical pressure.

• Specific enthalpy — Specify the specific enthalpy of the fluid in the reservoir by using the Reservoir specific enthalpy parameter or the signal value at port H. This option does not limit the fluid state.

• Specific internal energy — Specify the specific internal energy of the fluid in the reservoir by using the Reservoir specific internal energy parameter or the signal value at port U. This option does not limit the fluid state.

• Degree of subcooling — Specify the degree of subcooling of the fluid in the reservoir by using the Reservoir subcooling parameter or the signal value at port SC. You can use this option only when the pressure is less than the critical pressure because the saturation curves are not defined above the critical point.

• Degree of superheating — Specify the degree of superheating of the fluid in the reservoir by using the Reservoir superheating parameter or the signal value at port SH. You can use this option only when the pressure is less than the critical pressure because the saturation curves are not defined above the critical point.

Reservoir temperature — Temperature in reservoir

293.15 K (default) | positive scalar

Absolute temperature inside the reservoir. This temperature remains constant during simulation. The specified temperature maps to a specific enthalpy in either the subcooled liquid region or the superheated vapor region. For most fluids, the temperature in the liquid-vapor mixture region of a P-H diagram is constant, therefore a temperature value does not correspond one-to-one to a specific enthalpy value within the liquid-vapor mixture region.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Temperature.

Reservoir temperature specification — Type of temperature at input port T

Subcooled liquid temperature (default) | Superheated vapor temperature

Specify whether temperature control signal at port T provides the subcooled liquid temperature or the superheated vapor temperature value.

Dependencies

To enable this parameter, select the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Temperature.

Reservoir vapor quality — Mass fraction of vapor in reservoir

0.5 (default) | scalar in range [0 1]

Mass fraction of vapor in the reservoir. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Vapor quality.

Reservoir vapor void fraction — Volume fraction of vapor in reservoir

0.5 (default) | scalar in range [0 1]

Volume fraction of vapor in the reservoir. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Vapor void fraction.

Reservoir specific enthalpy — Specific enthalpy of fluid in reservoir

1500 kJ/kg (default) | positive scalar

Specific enthalpy of the fluid in the reservoir. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Specific enthalpy.

Reservoir specific internal energy — Specific internal energy of fluid in reservoir

1500 kJ/kg (default) | positive scalar

Specific internal energy of the fluid in the reservoir. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Specific internal energy.

Reservoir subcooling — Degree of subcooling in reservoir

5 deltaK (default) | positive scalar

Degree of subcooling of the fluid in the reservoir, that is, the difference between the liquid saturation temperature and the fluid temperature. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Degree of subcooling.

Reservoir superheating — Degree of superheating in reservoir

5 deltaK (default) | positive scalar

Degree of superheating of the fluid in the reservoir, that is, the difference between the fluid temperature and the vapor saturation temperature. This value remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for the selected energy specification check box and set Reservoir energy specification to Degree of superheating.

Cross-sectional area at port A — Area normal to flow path at reservoir inlet

0.01 m^2 (default) | positive scalar

Flow area of the reservoir inlet, represented by port A.

Inputs outside valid range — Action to take when signal values are outside of valid range

Warn and limit to valid values (default) | Limit to valid values | Error

Action for the block to take when the input signal values are outside of valid range:

• Limit to valid values ― The block limits the input signal to the minimum or maximum valid values, but does not issue a warning.

• Warn and limit to valid values ― The block issues a warning and limits the input signal to the minimum or maximum valid values.

• Error ― Simulation stops with an error.

Dependencies

To enable this parameter, select at least one of these check boxes:

• Provide input signal for the selected pressure specification

• Provide input signal for the selected energy specification

Extended Capabilities

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

Version History

Introduced in R2015b

R2026a: Model a controlled reservoir

The Controlled Reservoir (2P) and Reservoir (2P) blocks have been combined into the Reservoir (2P) block. Select the Provide input signal for the selected pressure specification and Provide input signal for the selected energy specification check boxes to control the reservoir conditions by using input signals. Otherwise, you can control the reservoir conditions by using the block parameters.

If you use a Controlled Reservoir (2P) block in your custom composite components, you must update the composite component code:

• Old syntax: source = foundation.two_phase_fluid.elements.controlled_reservoir;

• New syntax: source = foundation.two_phase_fluid.elements.reservoir;