3 replies to this topic

[bibidotcom]

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.

[Art Montemayor]

Paul:

I have to presume that this is a purely, impractical, student academic problem you present. The data you submit is flawed – or wrongly described – and leads to more questions than answers. For example:

• Where, specifically, is the 86 bars and 573.15 K in the boiler located at? Additionally, what KIND of pressure are you referring to – gauge or absolute? Please be specific; it makes a BIG difference.
• Heat transfer is not expressed in the units you furnish. Do you mean 96 kw/hour instead of 96 kw/m²K?
• A pipe length of 0.05 m is a ridiculously small and impractical length. Do you mean 5 meters? It is physically impossible to weld a pipe length of 0.05 m to both vessels – regardless of vessel size. You simply cannot fit a welding gun into such a confined space for full metal penetration.
• Regarding the vessel information, the same remarks as above apply.

If this is a theoretical academic problem, I can understand the question about finding the temperature drop in the pipe length from boiler to pressure vessel. Otherwise, it is an impractical question and one that is to be ignored in real life conditions because it is obvious that such a small pipe length is inconsequential. Additonally, if the steam produced is simply SATURATED steam, it is quite common sense to see that the lost, transferred heat in the connecting pipe will simply lead to a portion of steam condensation - but the steam temperature reaching the pressure vessel will be the same as the saturated steam generated in the boiler. If the generated steam is SUPERHEATED, that is totally another question. Now do you see why it is so important to report all pressures as either gauge or absolute? That is how we can look up the given conditions and find out if your steam is saturated or superheated.

Is there any insulation on the boiler, pipe, and vessel? Is this to be considered? Please be specific with the problem and the given data. Perhaps if you respond with the required additional, specific data our members might help you organize your answer to the problem.

[bibidotcom]

The pressures are all absolute, and the boiler will be insulated and the total heat transfer rate per unit area will be 96 w and the steam flow rate is 1.4kg/h. I know that the steam temperature will not change much from the boiler to the first pressure vessel, if you think of the first pressure vessel as a heat ex-changer which will also be insulated except for one part (area=0.21375m²) that will have total heat transfer rate per unit area of 10 kw. The steam flow to the first pressure vessel will be 1.4 kg/h / 3600 = 3.89_x10^-4kg/s. I have calculated the amount of energy in 3.89_x10^-4kg/s of steam to be, enthalpy of saturated steam at 86 bars 2750kj/kg * 3.89_x10^-4kg/s = 1.07kj/s. So per second there will be about 1.07kw entering the first vessel I used a real gas equation to determine that this amount of steam vapor will exert about 4.9 bars of pressure in the volume of 213.75m³. With the pressure vessel relief valve rated at 85 bars so it will take about 19 seconds to fill the pressure vessel and open the relief valve. So this is my question what will the temperature be inside the pressure vessel when taking into account the heat transfer rate per unit area of 10 kw of the vessel how do I calculate this since watts can not be converted to heat.

[bibidotcom]

The pressures are all absolute, and the boiler will be insulated and the total heat transfer rate per unit area will be 96 w and the steam flow rate is 1.4kg/h. I know that the steam temperature will not change much from the boiler to the first pressure vessel, if you think of the first pressure vessel as a heat ex-changer which will also be insulated except for one part (area=0.21375m²) that will have total heat transfer rate per unit area of 10 kw. The steam flow to the first pressure vessel will be 1.4 kg/h / 3600 = 3.89_x10^-4kg/s. I have calculated the amount of energy in 3.89_x10^-4kg/s of steam to be, enthalpy of saturated steam at 86 bars 2750kj/kg * 3.89_x10^-4kg/s = 1.07kj/s. So per second there will be about 1.07kw entering the first vessel I used a real gas equation to determine that this amount of steam vapor will exert about 4.9 bars of pressure in the volume of 213.75m³. With the pressure vessel relief valve rated at 85 bars so it will take about 19 seconds to fill the pressure vessel and open the relief valve. So this is my question what will the temperature be inside the pressure vessel when taking into account the heat transfer rate per unit area of 10 kw of the vessel how do I calculate this since watts can not be converted to heat.