3 replies to this topic

[KS2010]

Dear friends/engineers,

I am here once again to seek your help / suggestions.

As we know minimum of 19.5% [by v/v %] Oxygen in air is required for human breathing i.e. maximum of 80.5% Nitrogen in air is allowable to prevent Nitrogen Asphyxiation.

I want know what happens if the pipe carrying high pressure and low temperature nitrogen [pressure: 35barg and -80 oC] gets leaked through pinhole of diameter, 0.5mm and an operator is unaware let's say for 24 hrs.

Basically I am interested in finding the distance of pure nitrogen plume from leak point and composition of surroundings i.e. composition of nitrogen and oxygen around pure nitrogen centre plume. Assume pipe is located in a small room of total volume 125m3 [i.e. 5m x 5m x 5m] and room is not ventilated and no fan therefore no much mixing occurs.

You may assume the wind speed in the room about 5m/sec.

I have carried out gas orifice calculation with the orifice diameter of 0.5mm and the resulting volumetric flow rate of nitrogen leakage at above condition is 0.002 m^3/sec.

I have attached the hand drawn sketch for better explanation. Sorry for messy sketch.

I think such problem can be solved using CFD software but there should be some calculation methology for the same.

Any help will be appreciated.

Thanks in advance.

Attached Files

•  Gaseous Nitrogen Leak through Pinhole.doc   218.5KB   47 downloads

Edited by KS2010, 24 May 2010 - 04:55 PM.

[kkala]

Before looking into sophisticated dispersion models, we can see that the 125 m3 room can be full of nitrogen in a 24 hours period (0.002x3600x24=173 m3/d).
There is no fan or natural ventilation (but wind of 5 m/s?); heavy cold nitrogen tends to displace ambient air pushed out through the clefts. Even so there will be some mixing, so some N2 will be displaced too. But it seems that in 24 hours most of the original air will have been replaced by N2. Dangerous situation would have been created before (asphyxia due to N2 is reported in wikipedia).
I think it is difficult to reliably apply a dispersion model in a room (experience limited to Gausian models in atmosphere).

Note: N2 leakage was briefly estimated 0.002 kg/s = 0.0016 Nm3/s which (at any case) does not change conclusions.

Edited by kkala, 25 May 2010 - 03:25 PM.

[KS2010]

Before looking into sophisticated dispersion models, we can see that the 125 m3 room can be full of nitrogen in a 24 hours period (0.002x3600x24=173 m3/d).
There is no fan or natural ventilation (but wind of 5 m/s?); heavy cold nitrogen tends to displace ambient air pushed out through the clefts. Even so there will be some mixing, so some N2 will be displaced too. But it seems that in 24 hours most of the original air will have been replaced by N2. Dangerous situation would have been created before (asphyxia due to N2 is reported in wikipedia).
I think it is difficult to reliably apply a dispersion model in a room (experience limited to Gausian models in atmosphere).

Note: N2 leakage was briefly estimated 0.002 kg/s = 0.0016 Nm3/s which (at any case) does not change conclusions.

Thanks kkala,

I understand that there will be all N2 in 24 hrs with no ventilation/fan. However it doesn't answer my questions. OK let's see problem this way: how far N2 plume will travel and surrounding air & N2 mixture in various small intervals eg 2min,4min,6min ....upto 20 hrs.

Any clue?

[Qalander (Chem)]

Before looking into sophisticated dispersion models, we can see that the 125 m3 room can be full of nitrogen in a 24 hours period (0.002x3600x24=173 m3/d).
There is no fan or natural ventilation (but wind of 5 m/s?); heavy cold nitrogen tends to displace ambient air pushed out through the clefts. Even so there will be some mixing, so some N2 will be displaced too. But it seems that in 24 hours most of the original air will have been replaced by N2. Dangerous situation would have been created before (asphyxia due to N2 is reported in wikipedia).
I think it is difficult to reliably apply a dispersion model in a room (experience limited to Gausian models in atmosphere).

Note: N2 leakage was briefly estimated 0.002 kg/s = 0.0016 Nm3/s which (at any case) does not change conclusions.

Thanks kkala,

I understand that there will be all N2 in 24 hrs with no ventilation/fan. However it doesn't answer my questions. OK let's see problem this way: how far N2 plume will travel and surrounding air & N2 mixture in various small intervals eg 2min,4min,6min ....upto 20 hrs.

Any clue?

To me this seems very risky condition for human survival as

• The Capillary shaped fine almost invisible jet stream of Nitrogen may touch the top ceiling immediately considering the 35 barg pressure and
• This jet will induce whirlpool agitation of inside room atmospheric air and a much faster intermixing rate I assume
• moreover the cool highly dense Nitrogen will also push-away/displace all nearby air radially
• Whereas the wind low speed current will contribute to richer Nitrogen concentrations towards down stream side

This is all what I could envisage from your image and data thereon, hope this is someway guiding/helpful for way forward!