Reservoir (G)

R2026b

Boundary conditions for gas network at constant or time-varying pressure and temperature

• 

Reservoir (G) 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 / Gas / Elements

Description

The Reservoir (G) block sets boundary conditions in a gas network. Port A, a gas conserving port, represents the reservoir inlet.

The volume of gas inside the reservoir is assumed infinite. Therefore, the flow is assumed quasi-steady.

Gas enters and leaves the reservoir at reservoir pressure, but its temperature is determined by the direction of gas flow. If the gas flows out of the reservoir, its temperature equals the reservoir temperature. The reservoir acts as a heat source. If the gas flows into the reservoir, its temperature is determined by the gas network upstream. The reservoir acts as a heat sink.

You specify the reservoir pressure and temperature with block parameter values or physical signals. The block provides a choice of two modeling options:

• Static pressure and static temperature — To simplify the calculations, the block assumes that there is no difference between the pressure and temperature of gas inside the reservoir and at the exit port. This assumption is valid for applications with low-speed compressible flow, such as HVAC systems. You can also use it to simulate a portion of a system based on measured pressure and temperature at the boundary, that is, on the static pressure and static temperature.

• Total pressure and total temperature —This option assumes that the gas starts at rest and speeds up toward the exit port, which results in a reduction in pressure and temperature at the port. Use this modeling option for applications with high-speed compressible flows, such as aerospace, or for fluid dynamics analysis.

  Total pressure and total temperature are the pressure and temperature of gas at rest inside the reservoir. These quantities are also sometimes called stagnation pressure and temperature. They are related to the pressure and temperature at the reservoir port A by these equations

  $$\begin{array}{l}h\left(p_{total},T_{total}\right)=h\left(p_A,T_{outA}\right)+\frac{{\left[\min \left({\dot{m}}_A,0\right)\right]}^2}{2{\left[\rho \left(p_A,T_{outA}\right)S_A\right]}^2}\\ s\left(p_{total},T_{total}\right)=s\left(p_A,T_{outA}\right)\end{array}$$

  where:

  • p_total is the total, or stagnation, pressure.

  • T_total is the total, or stagnation, temperature.

  • p_A is the pressure at the reservoir port.

  • T_outA is the temperature at the reservoir port as the gas flows out of reservoir. If the gas flows into the reservoir, its temperature is determined by the gas network upstream.

  • h is the specific enthalpy.

  • s is the specific entropy.

  • $${\dot{m}}_A$$ is the mass flow rate of gas through the reservoir port. When the gas leaves the reservoir, $${\dot{m}}_A$$ is negative. The min term in the specific enthalpy equation assumes a value corresponding to the mass flow rate of gas when the gas leaves the reservoir. When the gas enters the reservoir, this term is 0.

  • ρ is density.

  • S_A is the cross-sectional area at the reservoir port.

This block also functions as a reference point for pressure and temperature measurements in a gas network. These measurements are relative to the reservoir static pressure and temperature, respectively. Connect the reservoir inlet to port B of a Pressure and Temperature Sensor (G) block to measure relative pressure and temperature of a node connected to the A port of the sensor.

Examples

Pneumatic Actuation Circuit

How the Foundation Library gas components can be used to model a controlled pneumatic actuator. The Directional Valve is a masked subsystem created from Variable Local Restriction (G) blocks to model the opening and closing of the flow paths. The Double-Acting Actuator is a masked subsystem created from Translational Mechanical Converter (G) blocks to model the interface between the gas network and the mechanical translational network.

• Open Model

Pneumatic Motor Circuit

How a pneumatic vane motor can be modeled using the Simscape™ language. The Pneumatic Motor component is built using the Simscape Foundation gas domain. It inherits from the foundation.gas.two_port_steady base class, which contains common equations that implement the upwind energy flow rate and the gas properties at the ports. The Pneumatic Motor subclass implements equations that describe behaviors specific to the component, such as the motor torque and flow rate characteristics and the mass and energy balance. The Pneumatic Motor block is inserted into the model using the Simscape Component block without the need to generate a separate library.

• Open Model

Choked Flow in Gas Orifice

The choking behavior of a gas orifice modeled by the Local Restriction (G) block. The Controlled Reservoir (G) blocks are used to set up controlled pressure and temperature boundary conditions from the Reservoir Inputs subsystem to test the gas orifice.

• Open Model

Ports

Input

P — Pressure control signal, Pa

physical signal

Physical signal port that provides the reservoir pressure control signal.

Dependencies

To enable this port, select Provide input signal for pressure.

T — Temperature control signal, K

physical signal

Physical signal port that provides the reservoir temperature control signal.

Dependencies

To enable this port, select Provide input signal for temperature.

Conserving

A — Reservoir inlet

gas

Gas conserving port associated with the reservoir inlet.

Parameters

Reservoir specification — Whether to use static or total quantities for pressure and temperature

Static pressure and static temperature (default) | Total pressure and total temperature

Select quantities to use for the reservoir pressure and temperature:

• Static pressure and static temperature — Specify pressure and temperature as boundary conditions at the reservoir port. Use this modeling option for applications with low-speed compressible flow, such as HVAC systems. You can also use it to simulate a portion of a system based on measured pressure and temperature at the boundary.

• Total pressure and total temperature — Specify pressure and temperature of gas at rest inside the reservoir. As the gas speeds up towards the exit port, its movement results in a reduction in pressure and temperature. Use this modeling option for applications with high-speed compressible flows, such as aerospace, or for fluid dynamics analysis.

Provide input signal for pressure — 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 Reservoir pressure parameter or atmospheric pressure. If you select this check box, the block models pressure based on the value of the signal at port P.

Pressure specification — Select specification method for reservoir pressure

Atmospheric pressure (default) | Specified pressure

Select a specification method for the reservoir pressure:

• Atmospheric pressure — Use the atmospheric pressure, specified by the Gas Properties (G) block connected to the circuit.

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

Dependencies

To enable this parameter, clear the Provide input signal for pressure check box.

Reservoir pressure — Pressure in the reservoir

0.101325 MPa (default) | scalar

Enter the desired pressure in the reservoir. This pressure remains constant during simulation.

Dependencies

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

Provide input signal for temperature — Method to specify reservoir temperature

off (default) | on

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

Reservoir temperature — Temperature in the reservoir

293.15 K (default) | scalar

Enter the desired temperature in the reservoir. This temperature remains constant during simulation.

Dependencies

To enable this parameter, clear the Provide input signal for temperature check box.

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

0.01 m^2 (default) | positive scalar

The cross-sectional area of the reservoir inlet, in the direction normal to gas flow path.

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 pressure

• Provide input signal for temperature

Extended Capabilities

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

Version History

Introduced in R2016b

R2026b: Model reservoir using total pressure and temperature

The new Reservoir specification parameter provides an option for specifying total pressure and temperature of gas, also known as stagnation pressure and temperature. The default, Static pressure and static temperature, is equivalent to the block functionality in previous releases.

Additionally, the Reservoir pressure specification parameter name has been shortened to Pressure specification. This change has no effect on block functionality.

R2026a: Model a controlled reservoir

The Controlled Reservoir (G) and Reservoir (G) blocks have been combined into the Reservoir (G) block. Select the Provide input signal for pressure and Provide input signal for temperature 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 (G) block in your custom composite components, you must update the composite component code:

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

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