Gas-Charged Accumulator (IL)
A battery with a chamber for gas in an isothermal fluid network.
blockType: EngeeFluids.IsothermalLiquid.Volumes.GasChargedAccumulator
|
Path in the library: |
Description
Block Gas-Charged Accumulator (IL) It is a battery with a chamber for gas in an isothermal liquid network. The battery consists of a chamber pre-filled with gas and a chamber for liquid. The chambers are separated by a diaphragm, piston, or any other separator.
When the pressure of the liquid at the battery inlet becomes greater than the pressure in the gas-filled chamber, the liquid enters the battery and compresses the gas as a result of a polytropic process. A decrease in liquid pressure leads to decompression of the gas and the release of accumulated liquid into the system. The movement of the separator is limited by a rigid limiter when the volume of the liquid is zero or when the volume of the liquid is equal to the capacity of the liquid chamber. The volume of the liquid chamber is defined as the difference between the total volume of the battery and the minimum volume of gas.
The fluid resistance at the inlet, as well as separator properties such as inertia and damping, are not modeled. The flow rate is positive if liquid enters the battery.
The diagram shows a battery with a gas chamber. Total battery capacity It is divided by a vertical separator into a liquid chamber on the left and a gas chamber on the right. The distance between the left side and the separator determines the volume of the liquid . The distance between the right side and the separator determines the volume of gas . Working volume of the liquid chamber It is smaller than the total volume of the battery, so the gas volume never becomes zero.:
where
-
— total battery capacity, including liquid chamber and gas chamber;
-
— the volume of liquid in the battery;
-
— the amount of gas in the battery;
-
— volume of the liquid chamber;
-
— the minimum volume of the gas chamber, the small part of the chamber that remains filled with gas when the liquid chamber is full.
The contact pressure of the rigid limiter is modeled using the coefficients of elasticity and damping. The dependence of gas pressure and volume between the current state and the pre-charging state is polytropic, and the pressure is balanced at the separator:
where
-
— gas pressure in the gas chamber;
-
— pressure in the gas chamber when the liquid chamber is empty;
-
— coefficient of specific heat capacity (adiabatic index).
Conservation of mass
The conservation of mass is represented by the following equations:
where
-
— the pressure in the liquid chamber, which is equal to the pressure at the inlet to the battery;
-
— the mass flow rate of the liquid entering the port A;
-
— the density of the liquid in the chamber.
where — the stiffness coefficient of the limiter.
Conservation of momentum
Conservation of momentum is represented by the following equation:
where — contact pressure of the rigid limiter.
Variables
Use the parameter group Initial Targets to set the priority and initial target values for the block parameter variables before modeling. For more information, see Configuring physical blocks using target values.
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.
| Program usage name |
|
Parameters
Parameters
#
Total accumulator volume —
total battery capacity
m^3 | um^3 | mm^3 | cm^3 | km^3 | ml | l | gal | igal | in^3 | ft^3 | yd^3 | mi^3
Details
The total volume of the battery, including the liquid chamber and the gas chamber, is equal to the sum of the volume of the liquid chamber and the minimum volume of the gas chamber.
| Units |
|
| Default value |
|
| Program usage name |
|
| Evaluatable |
Yes |
#
Minimum gas volume —
minimum volume of the gas chamber
m^3 | um^3 | mm^3 | cm^3 | km^3 | ml | l | gal | igal | in^3 | ft^3 | yd^3 | mi^3
Details
The minimum volume of the gas chamber, the small part 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 division by zero when the liquid chamber is full.
| Units |
|
| Default value |
|
| Program usage name |
|
| Evaluatable |
Yes |
#
Precharge pressure —
pressure in the gas chamber
Pa | uPa | hPa | kPa | MPa | GPa | kgf/m^2 | kgf/cm^2 | kgf/mm^2 | mbar | bar | kbar | atm | ksi | psi | mmHg | inHg
Details
The pressure in the gas chamber when the liquid chamber is empty.
| Units |
|
| Default value |
|
| Program usage name |
|
| Evaluatable |
Yes |
# Specific heat ratio — coefficient of specific heat capacity
Details
Coefficient of specific heat capacity (adiabatic index).
The parameter is necessary to account for heat transfer, usually its value is 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 index for the isothermal process is 1, and for an adiabatic (and isentropic) process — 1.4.
| Default value |
|
| Program usage name |
|
| Evaluatable |
Yes |
#
Hard stop stiffness coefficient —
stiffness coefficient
Pa/m^3 | MPa/m^3
Details
The coefficient of rigidity of the contact pressure of the rigid limiter in relation to the volume of liquid that has penetrated the limiter. Rigid limiters are used to limit the volume of liquid between zero and the volume of the liquid chamber.
| Units |
|
| Default value |
|
| Program usage name |
|
| Evaluatable |
Yes |
# Fluid dynamic compressibility — compressibility of liquid
Details
Is it necessary to simulate a change in the density of a liquid due to its compressibility?
If the check box is selected Fluid dynamic compressibility, then the changes associated with the mass flow rate of the fluid in the block are calculated in addition to the density changes associated with pressure changes.
| Default value |
|
| Program usage name |
|
| Evaluatable |
No |