Accumulator Sizing - Thermal Expansion 2

[slickstyles5]

Hi,

Does anyone know of any software that can be used to size an accumulator for thermal expansion?

As a side question, when the trapped liquid pressure increases, the nitrogen side of the accumulator will increase in pressure. Does the liquid side pressure increase? For example, let's say the precharge pressure of nitrogen is 75 psi, and the system pressure max is 50 psi, but when the temperature causes the trapped fluid to increase in pressure, the accumulator will start to fill at 75 psi. Will the liquid pressure also increase constinuously at that point?

Thanks
Gabriel

 

[Pumpsonly]

If I understand you correctly, you are asking whether the liquid pressure will increase beyond the 75 PSI?

The answer is YES. The filling liquid will compress the bladder and the N2 gas inside until they are the same.

 

[slickstyles5]

I just found in the Parker catalogue # HY10-1630/US a method for calculating the accumulator volume required for thermal expansion. All that ends up happening is that the accumulator is oversized slightly such that the pressure doesn't increase past the max allowable.

It all makes sense now!

 

[ione]

You can build your own spreadsheet using the following formula:

V = (P2/P1)^(1/k)/[1-(P2/P3)^(1/k)]*(? - 3alpha)*(T2 – T1)*Vfluid

Where:

V: minimum required accumulator volume
P1: precharge pressure
P2: nominal hydraulic system pressure
P3: maximum allowable hydraulic system pressure
T1: fluid temperature prior to thermal expansion
T2: fluid after thermal expansion
Vfluid: hydraulic fluid in the system subject to thermal expansion
alpha: coefficient of linear expansion for the pipe material
?: coefficient of expansion (volumetric) for the hydraulic fluid
k: ratio of specific heats (1.4 for air and nitrogen at low temperatures)

This formula assumes the gas endures an isentropic process. If the gas expansion/contractions of the gas is slow you can assume an isothermal process takes palce and the formula above becomes:

V = (P2/P1)/[1-(P2/P3)]*(? - 3alpha)*(T2 – T1)*Vfluid

 

[slickstyles5]

Hi,
I am just trying to confirm the units ...

The pressures P1, P2, P3 have to be in psia? Temperature in degF? Alpha & Beta has unit of degF^-1?

Is this correct? This will give me an accumulator volume with the same units as the fluid volume?

What's confusing me is that in the parker catalogue, the temperatures are in Kelvin, which would cancel out the units. See the link...

 

[slickstyles5]

EDIT : The parker catalogue would NOT cancel out the units because T2-T1 in Kelvin will not equal the same value in degF. For example a delta temp of 8.33K would be 15 degF delta Temp.

 

[ione]

The temperature difference unit and the expansion coefficients unit must cancel each other otherwise how you can get a consistent unit for volume?
So if T1 and T2 are in Kelvin, convert the unit of the expansion coefficients in 1/K.

Pressures are absolute pressures