Gas-Charged Accumulator (IL)
Accumulator with gas chamber in isothermal liquid network.
Description
Unit Gas-Charged Accumulator (IL) is an accumulator with a gas chamber in an isothermal liquid network. The accumulator consists of a gas pre-filled chamber and a liquid chamber. The chambers are separated by an orifice plate, piston or any other separator.
When the fluid pressure at the inlet to the accumulator becomes greater than the pressure in the gas pre-filled chamber, the fluid enters the accumulator and compresses the gas by a polytropic process. The decrease in fluid pressure causes the gas to decompress and the accumulated fluid is released into the system. The movement of the separator is restricted by a rigid restrictor when the liquid volume is zero or when the liquid volume is equal to the capacity of the liquid chamber. The fluid chamber volume is defined as the difference between the total accumulator volume and the minimum gas volume.
Fluid inlet resistance and divider properties such as inertia and damping are not modelled. The flow rate is positive if the liquid enters the accumulator.
The diagram shows an accumulator with a gas chamber. The total volume of the accumulator is divided by a vertical divider into a liquid chamber on the left and a gas chamber on the right. The distance between the left side and the divider defines the liquid volume . The distance between the right side and the divider determines the gas volume . The working volume of the liquid chamber is less than the total volume of the accumulator, so the gas volume never goes to zero:
where
-
- is the total volume of the accumulator, including the liquid chamber and the gas chamber;
-
- is the volume of liquid in the accumulator;
-
- volume of gas in the accumulator;
-
- volume of the liquid chamber;
-
- minimum gas chamber volume, the small portion of the chamber that remains filled with gas when the liquid chamber is full.
The contact pressure of the rigid restrictor is modelled by usage of elasticity and damping coefficients. The pressure and gas volume dependence between the current state and the precharge state is polytropic, and the pressure is balanced on the divider:
where
-
- is the gas pressure in the gas chamber;
-
- is the pressure in the gas chamber when the liquid chamber is empty;
-
- is the specific heat capacity coefficient (adiabatic index).
Conservation of mass
Conservation of mass is represented by the following equations:
where
-
- is the pressure in the fluid chamber, which is equal to the pressure at the inlet to the accumulator;
-
- mass flow rate of liquid entering the port A;
-
- density of liquid in the chamber.
where is the stiffness coefficient of the limiter.
Ports
Conserving
#
A
—
isothermal liquid inlet 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.
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Parameters
Parameters
#
Total accumulator volume —
total 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 total volume of the accumulator, including the liquid chamber and the gas chamber, it is equal to the sum of the volume of the liquid chamber and the minimum volume of the gas chamber.
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| Evaluatable |
Yes |
#
Minimum gas volume —
minimum gas chamber volume
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
Minimum gas chamber volume, the small portion of the chamber that remains filled with gas when the liquid chamber is full.
The value of this parameter must be non-zero to avoid dividing by zero when the liquid chamber is full.
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Yes |
#
Precharge pressure —
gas chamber pressure
Pa | GPa | MPa | atm | bar | kPa | ksi | psi | uPa | kbar
Details
Pressure in the gas chamber when the fluid chamber is empty.
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| Evaluatable |
Yes |
# Specific heat ratio — specific heat capacity coefficient
Details
Specific heat capacity coefficient (adiabatic value).
The parameter is necessary to account for heat transfer, and its value is usually between 1 and 2, depending on the properties of the gas in the chamber.
For dry air at 20°C, the value of the adiabatic exponent for an isothermal process is 1, and for an adiabatic (and isoentropic) process it is 1.4.
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| Evaluatable |
Yes |
#
Hard stop stiffness coefficient —
stiffness factor
MPa/m^3
Details
The stiffness coefficient of the contact pressure of a rigid restrictor in relation to the volume of fluid penetrating the restrictor. Rigid restrictors are used to limit the volume of fluid between zero and the volume of the fluid chamber.
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| Default value |
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| Evaluatable |
Yes |
# Fluid dynamic compressibility — fluid compressibility
Details
Whether it is necessary to model the change in density of a fluid due to its compressibility.
If Fluid dynamic compressibility is checked, changes due to the mass flow rate of the fluid in the block are calculated in addition to density changes due to pressure changes.
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| Evaluatable |
No |