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Reservoir (2P)

Two-phase fluid reservoir at constant temperature and pressure

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  • Reservoir (2P) block

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

Description

The Reservoir (2P) block sets pressure and temperature 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.

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 pressure and specific internal energy of the fluid are assumed constant in the reservoir.

  • 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

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.

Fluid Vaporization in Pipe

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.

Ports

Conserving

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

Parameters

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Specification method for the reservoir pressure:

  • Atmospheric pressure — Use the atmospheric pressure specified by a Two-Phase Fluid Properties (2P) block connected to the circuit.

  • Specified pressure — Specify a value by using the Reservoir pressure parameter.

  • 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.

  • 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.

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, set Reservoir pressure specification to Specified pressure.

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, set Reservoir pressure specification to Saturation pressure at specified condensing temperature.

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, set Reservoir pressure specification to Saturation pressure at specified evaporating temperature.

Thermodynamic variable to use for energy specification:

  • Temperature — Specify the absolute temperature inside the reservoir by using the Reservoir temperature parameter. 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. 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. 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. 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. 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. 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. 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.

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, set Reservoir energy specification to Temperature.

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

Dependencies

To enable this parameter, set Reservoir energy specification to Vapor quality.

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

Dependencies

To enable this parameter, set Reservoir energy specification to Vapor void fraction.

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

Dependencies

To enable this parameter, set Reservoir energy specification to Specific enthalpy.

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

Dependencies

To enable this parameter, set Reservoir energy specification to Specific internal energy.

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, set Reservoir energy specification to Degree of subcooling.

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, set Reservoir energy specification to Degree of superheating.

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

Extended Capabilities

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

Version History

Introduced in R2015b

See Also