6 replies to this topic

[danish]

sir,
i am a student of piping and extremely confused at one point while calculting pressure drop in pipe.
1> suppose steam enters in pipe at pressure 10bar with certain dryness fraction,for sake of easiness let us assume 0.8.while passing at certain point,the pressure is reduced to 8bar.at this point,we take the saturation temp. corresponding to 8bar for calculation purpose.why?why saturation temp. as tempreature at that point may be any value depending upon the type of path steam has crossed?
2>suppose saturated liquid is flowing at 10bar.saturted pressue i.e 10bar is the saturated vapour pressure as far as i know.as we all know,if pressure goes below the vapour pressure,the liquid will star vaporising.buti have seen with each pressure drop,we take the corresponding saturation temp. and do the calcultion.then which vapour pressure we r talking about at which liquid will start boiling and vaporize.
3>how the pressure of oil in thermic fluid heater increases without change in phase of the oil as the o/p of TFH is oil liquid.
conditions:
i/p of TFH : oil at 2 bar at 246 degree celsius
o/p of TFH : oil at 5 bar at 280 degree celsius.
oil property : flash point : 210 degree celsius
fire point : 255 degree celsius
autoignition tempreature : 375 degree celsius
oil : thermia plus

[shan]

1> I agree with you. It may be 8 bar superheated steam or 8 bar sub cooled water depending on the heat transfer through the piping wall.
2> I do not quite understand your question. It seems to me that you got confused fluid vapor pressure corresponding to fluid vapor temperature.
3> Liquid thermal expansion may result pressure increase in a confined container without phase change.

[danish]

thanx a lot jedi.
1.but can pressure rise by 3bar by means of thermal expansion for 34 degree celius rise in tempreature in TFH?
2.one more question realted to TFH package:-
a. what's the function of damping receiver in expansion tank?
b. is there any expansion in damping receiver and deaerator.if yes then will it isentropic?is there any expansion in expansion tank?if yes then by which process?
c.why vent is provided in expansion tank as that would be a loss of thermal fluid vapour which is very very costly and replaced once in 5 years.
d.the expanded oil is supplied to pump for further heating in TFH but that outlet comes from damper.which means that all the cooled processed liquid does not enter expansion tank.why?

Edited by danish, 25 November 2009 - 11:23 AM.

[shan]

The pressure increase value depends on the design of damping receiver. The increased pressure is the force needed to push out enough room from the damping receiver to contain the expanded hot oil due to temperature raise. This is not an isentropic process because the work is done by pushing damping receiver’s deform.

The vent on the expansion tank is to provide a release channel for the intruded air/gas.

You need to provide a process sketch for more detailed discussion.

[danish]

jedi, i m sending u the attached files related to process line diagram of expansion tank.but still some of my questions are unanswered.let me write it once more.
1.what exactly happens in deaerator?what type of expansion is there in deaerator?
2.the flud from deaerator then flow in expansion tank.what exactly happens in expansion tank?
3. what exactly the function of damping receiver?
3.why most of the cooled processed fluid passes out of damping receiver directly without going into deaerator hence expansion tank?is damping receiver enough for serving the purpose of process at that point?
4.can pressure rise by 3bars for just 34 degree celsius rise in tempreature in TFH by means of only thermal expansion?
5.the cooled processed fluid enters the damping reciver at 1.5 bar and 250 degree celsius.if vent is there in the expansion tank then pressure in there must be atmospheric.then what the use of expanding in expansion tank when the final pressure has to come ultimately at atmospheric pressure.will there be any expansion in tank?if yes then by which process?
6.what can be the max. temp. drop in baffled tank as the fluid enters TFH at 246 degree celsius?
actually i m from mechanical department and it's somewhat related to proces part.that's why i m facing this problem.the whole design of TFH package is by THERMAX.THERMAX people refused to entertain us?mechancal teachers had diffrent anwsers and said "it has to do with process and beyond our scope".tried to find out on net but cldn't get much on the process.
some properties i m writing down which may help u in answering:
oil: thermia plus
inlet condn. of TFH :2 bar at 246 degree celsius
outlet codn. of TFH: 5 bar at 280 degree celsius.
inlet condn. of baffled tank : 1.5 bar
let me know if u need chemical properties of oil.do refer the attached files as it has lot of informations on baffled tank and may help u in reaching final coclusion about ur answer.rest of the things are clear to me .ev thogh i can do the pipe sizing,MOC selection and other acivities based on just Pressure-tempreature-flow rate-corrosion information but that would not serve the purpose of project unless i know nook and corner of whle process.

Attached Files

•  BaffledTankDesign.pdf   11.43KB   42 downloads
•  Doc1.pdf   1.51MB   31 downloads

[joerd]

1.what exactly happens in deaerator?what type of expansion is there in deaerator?
2.the flud from deaerator then flow in expansion tank.what exactly happens in expansion tank?
3. what exactly the function of damping receiver?
3.why most of the cooled processed fluid passes out of damping receiver directly without going into deaerator hence expansion tank?is damping receiver enough for serving the purpose of process at that point?
4.can pressure rise by 3bars for just 34 degree celsius rise in tempreature in TFH by means of only thermal expansion?
5.the cooled processed fluid enters the damping reciver at 1.5 bar and 250 degree celsius.if vent is there in the expansion tank then pressure in there must be atmospheric.then what the use of expanding in expansion tank when the final pressure has to come ultimately at atmospheric pressure.will there be any expansion in tank?if yes then by which process?
6.what can be the max. temp. drop in baffled tank as the fluid enters TFH at 246 degree celsius?

Most of your questions are answered in the introduction of the patent that you attached.
1. The deaerator serves to remove dissolved gases from the oil, that may be picked up in the process heat exchangers.
2. The expansion tank serves to allow room for expansion of the oil, since it has a lower density when it is hot than when it is cold (at startup)
3. The damping receiver is used to dampen sudden fluctuations in the expansion tank, which could result from operations in the heat medium loop (valves opened/closed, etc.) For your second question 3, refer to shan's response.
4. That doesn't sound right. I have no reference point for these pressures in your sketches, but my feeling is that it is a static head effect, or a measurement error.
5. This is also static head, and possibly a little pressure drop that the vented gases encounter as they make their way out of the vent piping.
6. That all depends on size, location, insulation, ambient conditions. A good design should not have a lot of heat loss from the expansion tank.

[danish]

thanx a lot jedi.