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Join Date: Jan 2012
Posts: 12

Chaining Pressure Vessels and Outlet Temperature

02/26/2012 5:10 AM

Say I have a boiler with,

pressure = 86 bars

temperature = 573.15 K

overall heat transfer = 96 w/m2K

And there will be a pipe connecting the boiler to a pressure vessel

pipe length = 0.05m

pipe overall heat transfer = 0.146 w/m2K

The pressure vessel,

volume = 231cm3

pressure = 85 bars

overall heat transfer = 10kw/m2K

inlet steam temperature 573.08

Is the a way to find out the outlet steam temperature from the first pressure vessel, because I would like to connect another pressure vessel with the same data as the first pressure vessel.

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#1

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 10:21 AM

Are you sure what do you want do and what is your home work and what are you asking?

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Active Contributor

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Posts: 12
#2
In reply to #1

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 10:25 AM

I tried to make my question a bit clearer

Say I have a boiler with:
pressure relief valve = 86 bars
valve flow factor 0.007 kv
temperature of steam = 573.15 K
overall heat transfer of boiler = 96 w/m2K
steam mass flow = 1.4 kg/h

And there will be a pipe connecting the boiler and a pressure vessels:
pipe length = 0.05m
pipe overall heat transfer = 0.146 w/m2K

The pressure vessels 1 and to data:
volume = 231cm3
surface area = 0.21375
pressure relief valve = 85 bars
next pressure vessel relief valve = 84 bars
overall heat transfer of pressure vessels = 10kw/m2K
inlet steam temperature into first pressure vessel from boiler = 573.08 K

Is there a way to find out the outlet steam temperature from the first pressure vessel, to second pressure vessel.

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#3
In reply to #2

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 3:30 PM

Bionic,

If you truly have a boiler and it is producing steam that is flowing to a pressure vessel or device, very quickly the steam will heat the destination to 573+K.

The flow of steam will be determined by the pressure drop through the system.

You can determine the steam properties through the system via the use of a Mollier Diagram.

Where there is significant drop through your steam system, both the steam pressure and temperature will change.

The overall flow through your system will depend on the steam destination pressure(usually a steam surface condenser or the atmosphere)

Aside from completeing a homework problem, what is it you are trying to do !!???

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Active Contributor

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Posts: 12
#4
In reply to #3

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 3:39 PM

l am planing to make about 20 of these pressure vessels and need to know the temperature drop from one vessel to the next. so thank you for your help

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#9
In reply to #2

Re: Chaining Pressure Vessels and Outlet Temperature

02/27/2012 9:04 PM

Your boiler is giving less heat then you are loosing at your vessel. You have to do your home work first.

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#5

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 7:21 PM

In principle, you could use the enthalpy of the traversing fluid, calculate the heat conducted away, and find the new temperature from step to step. However, from a design point of view, it is much simpler to assume the same temperature and pressure throughout, because this will be conservative for the downstream vessels. The relief valve settings of 86/85/84 bars seem ridiculously prissy. If there is a purpose to this strange exercise, it hasn't been well explained yet.

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#7
In reply to #5

Re: Chaining Pressure Vessels and Outlet Temperature

02/27/2012 9:19 AM

Thank you for your input. Yes there is a purpose to this strange exercise. Let me try to explain my problem this way the steam flow will be 1.4 kg/h, so in a second it will be 1.4kg/h / 3600s = 3.89x10-4 kg/s. The energy contained in the steam per second will be enthalpy of saturated steam at 86 bars 2750kj/kg * 3.89x10-4kg/s = 1.07kj/s. 1.07kj/s will be the amount of energy going into the first pressure vessel. The pressure vessels volume will be 213.75cm3. I have used a real gas equation to determine that the 3.89x10-4kg/s of steam will exert about 4.9 bar of pressure in the volume of 213.75cm3. The pressure vessel relief valve will be 85 bar so it will take about (85 bar / 4.9 bar) = 17.35 seconds till fill the vessel and open the relief valve. The thing is as the vessel will be loosing heat of about 10 kw/s what will be the temperature of the steam leaving the pressure vessel

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#8
In reply to #7

Re: Chaining Pressure Vessels and Outlet Temperature

02/27/2012 3:28 PM

If I read this correctly your secondary pressure vessel is loosing heat at 10 kW and your total heat input is only 1.07kW. If that is the case you will never reach the lifting pressure of your safety valve. Your post is really not very well explained, sorry

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#6

Re: Chaining Pressure Vessels and Outlet Temperature

02/26/2012 10:59 PM

Could be that Bionic's got some goofy invention idea up his sleeve and needs some input without giving away any specifics. Wouldn't be the first time.

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