Thermal relief valve flow rate
Thermal relief valve flow rate
(OP)
Hi all,
I've got a question here about how to calculate the mass flow / volume flow through a Thermal Relief valve (I don't know the size or orifice, but assume it's the smallest ones anyone makes for piping so maybe 1/2" x 1"?).
The piping in question had a surge type event a few weeks ago and it popped all the TRVs set at ~30 barg in cryogenic propane for approx 30 seconds duration.
Now people want to estimate the volume which escaped into the closed drain / vent system. So nothing escaped, but the volume needs to be reported.
Any clues?
Or things to try and find out?
I've had a look on line and on this site, but nothing obvious pops up for thermal relief valves.
Thanks
LI
I've got a question here about how to calculate the mass flow / volume flow through a Thermal Relief valve (I don't know the size or orifice, but assume it's the smallest ones anyone makes for piping so maybe 1/2" x 1"?).
The piping in question had a surge type event a few weeks ago and it popped all the TRVs set at ~30 barg in cryogenic propane for approx 30 seconds duration.
Now people want to estimate the volume which escaped into the closed drain / vent system. So nothing escaped, but the volume needs to be reported.
Any clues?
Or things to try and find out?
I've had a look on line and on this site, but nothing obvious pops up for thermal relief valves.
Thanks
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Thermal relief valve flow rate
From Internet (ref API 521 edition7th)
For liquid-full systems, expansion rates for the sizing of relief devices that protect against
thermal expansion of the trapped liquids can be approximated using Equation (1) in SI units
(1) q = alpha*phi/(1000 *d*c)
where
q is the volume flow rate at the relieving conditions, expressed in m3/s;
alpha is the cubic expansion coefficient for the liquid at the expected relieving conditions,
expressed in 1/°C;
phi is the total heat transfer rate, expressed in watts;
d is the relative density referred to water (d = 1.00 at 15.6 °C), dimensionless;
NOTE Compressibility of the liquid is usually ignored.
c is the specific heat capacity of the trapped fluid, expressed in J/kgꞏK
Pierre
RE: Thermal relief valve flow rate
(* although a TRV, major manufacturers have had their TRV types type tested. If you can advise the manufacturer and model, the orifice and coefficient should be easy enough to find in the National Board NB-18 on-line document)
*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***
*** 'Pressure-relief Valve' is the equivalent ASME/API term ***
RE: Thermal relief valve flow rate
Inlet pressure 30 barg, outlet <1 barg.
It's a triangle 1/2" x 3/4". No model no but will be ancient. UK supply so might not be in the NB system. But anything similar will do.
It's liquid at this stage, about 560 kg/m3.
It was used as an inadvertent relief valve during a process upset so not a classic what flow have I got - this is a what flow did it do with 30 odd bar inlet across a small orifice for 30 seconds??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Thermal relief valve flow rate
Liquid coefficient = 0.64
D orifice (0.110 in2)
27.3 barg set pressure
10% OP (30 barg sizing pressure)
Rated flow = 13,677 lb/hr (6204 kg/hr)
Actual flow = 15,197 lb/hr (6893 kg/hr)
If you want the IO file, email me.
Good Luck,
Latexman
RE: Thermal relief valve flow rate
Thank you very much - I really just needed an OOM estimate. That's great.
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Thermal relief valve flow rate
Good Luck,
Latexman
RE: Thermal relief valve flow rate
*** Per ISO-4126, the generic term 'Safety Valve' is used regardless of application or design ***
*** 'Pressure-relief Valve' is the equivalent ASME/API term ***
RE: Thermal relief valve flow rate
(0.06/0.11)2 x 6204 = 1846 kg/hr rated and 2051 kr/hr actual
LI, ASSuME wisely.
Good Luck,
Latexman
RE: Thermal relief valve flow rate
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Thermal relief valve flow rate
A friend pointed out he got different numbers than I above. Turns out after I overrode the defaults in my program, with what I thought the defaults were, I got the same numbers as he:
Nozzle area = 0.110 in2; Rated coeff. = 0.640
Flowrate (lb/hr) = 20923 (rated) 23248 (actual)
Nozzle area = 0.060 in2; Rated coeff. = 0.640
Flowrate (lb/hr) = 11413 (rated) 12681 (actual)
Sorry for the confusion!
Good Luck,
Latexman
RE: Thermal relief valve flow rate
It still results in less mass going through the system than the amount that triggers certain regulatory actions and reporting.
Still great that you did this - many thanks.
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.