Spring-Loaded Accumulator (IL)

A spring-loaded accumulator used to store energy in an isothermal liquid system.

spring loaded accumulator (il)

Description

The Spring-Loaded Accumulator (IL) unit simulates a spring-loaded accumulator in an isothermal liquid network. The accumulator consists of a preloaded spring and a fluid chamber.

When the fluid pressure at the inlet to the accumulator becomes greater than the preload pressure (preload), the fluid enters the accumulator and compresses the spring. When the fluid pressure decreases, the spring uncompresses and releases the accumulated fluid into the system. The divider movement is restricted by a rigid stopper when the fluid volume is zero or when the fluid volume is equal to the fluid chamber capacity.

Fluid inlet resistance and spring characteristics such as inertia and damping are not modelled. The spring pressure is assumed to be linear with respect to the liquid volume. The flow rate is positive if the fluid enters the accumulator. The diagram shows a spring accumulator:

spring loaded accumulator 1

	Volume of liquid in the accumulator.
	Volume of the fluid chamber.
	Pressure at maximum capacity.
	Pressure in the fluid chamber equal to the inlet pressure of the accumulator.
	Contact pressure of the rigid stop.
	Stiffness coefficient of the stop.
	Spring stiffness coefficient.
	Mass flow rate of fluid entering port A.
	Density of the fluid in the fluid chamber.

Mass conservation

Mass conservation is described by the following equation:

where:

Conservation of momentum

Conservation of momentum is described by the following equation:

where:

Variables

To set the priority and target value for block variables before modelling, use the Initial Targets section in the block settings window.

Ports

Conserving

# A — isothermal liquid port
isothermal liquid

Details

isothermal liquid port, corresponds to the inlet to the accumulator. The flow rate is positive if the fluid enters the accumulator.

Program usage name

port

Parameters

# Liquid capacity — battery capacity
l | gal | igal | m^3 | cm^3 | ft^3 | in^3 | km^3 | mi^3 | mm^3 | um^3 | yd^3 | N*m/Pa | N*m/bar | lbf*ft/psi | ft*lbf/psi

Details

The amount of liquid the battery can hold.

Values	`l` \| `gal` \| `igal` \| `m^3` \| `cm^3` \| `ft^3` \| `in^3` \| `km^3` \| `mi^3` \| `mm^3` \| `um^3` \| `yd^3` \| `Nm/Pa` \| `Nm/bar` \| `lbfft/psi` \| `ftlbf/psi`
Default value	`8e-3 m^3`
Program usage name	`V_capacity`
Evaluatable	Yes

# Preload pressure — spring pressure
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Spring pressure when the fluid chamber is empty.

Values	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`1.0 MPa`
Program usage name	`p_preload`
Evaluatable	Yes

# Pressure at full capacity — spring pressure
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar

Details

Spring pressure when the fluid chamber is full.

Values	`Pa` \| `GPa` \| `MPa` \| `atm` \| `bar` \| `kPa` \| `ksi` \| `psi` \| `uPa` \| `kbar`
Default value	`3.0 MPa`
Program usage name	`p_max`
Evaluatable	Yes

# Hard stop stiffness coefficient — stiffness factor
MPa/m^3

Details

The stiffness coefficient of the contact pressure of a rigid stopper in relation to the volume of fluid that has penetrated the stopper. Rigid stops are used to limit the volume of fluid between zero and the volume of the fluid chamber.

Values	`MPa/m^3`
Default value	`1e4 MPa/m^3`
Program usage name	`k_hard_stop`
Evaluatable	Yes

# Fluid dynamic compressibility — fluid compressibility

Details

Whether the change in fluid density due to fluid compressibility should be modelled. If Fluid dynamic compressibility is enabled, changes due to the mass flow rate of the fluid in the block are calculated in addition to the density changes due to pressure changes.

Default value	`true (switched on)`
Program usage name	`dynamic_compressibility`
Evaluatable	No