3 replies to this topic

[Raja Jani]

Dear all

Please help me for designing a Electric resistance duct (finned tube)heater to heat air from 85 to 100 C

I need book/study material for complete design. also if anybody have experience in modeling that in HTRI 5.0 would also be helpful( i heard that they include this in HTRI in may 2009, news letter from in this regard is in google )

please help me, I am already running out of time.

Raja

[kkala]

Unfortunately my experience is not enough to help. However I remember an urgent instruction to heat air upstream a bag filter from ~100 0C to 120 0C (to avoid water condensation) in a fertilizer company (1978). As Operators we only calculated the power of the electric resistance (mass airflow*Cp*Δt) and told electricians to install resistance of such kW in the air duct. The work was implemented in about three days, fortunately electricians did not asked for details and no fins were used.
You seem to require detailed design. Plant Electrical Engineer or Electricians could specify all the details required (as in the event above), or at least give substantial help.
Hope you will accomplish the task on time.

Edited by kkala, 01 January 2010 - 06:26 PM.

[Raja Jani]

thanks for the help . i am thankful to you. i did some calculation from basic fundamentals and got values for sheath temperature calculation ( that was the emergency)and will do rest of the calculation later . now what u suggest is giving me a clue to check my value through a running unit.

I am a freelancer and just started in process design and simulation that's why I really need this type of help . I would be happy if i could help you in future, regarding simulation of process plants

reply

Unfortunately my experience is not enough to help. However I remember an urgent instruction to heat air upstream a bag filter from ~100 0C to 120 0C (to avoid water condensation) in a fertilizer company (1978). As Operators we only calculated the power of the electric resistance (mass airflow*Cp*Δt) and told electricians to install resistance of such kW in the air duct. The work was implemented in about three days, fortunately electricians did not asked for details and no fins were used.
You seem to require detailed design. Plant Electrical Engineer or Electricians could specify all the details required (as in the event above), or at least give substantial help.
Hope you will accomplish the task on time.

[kkala]

Raja, I could not offer real help; you have already gone much "deeper" in the issue. At fertilizer industry I had not seen the electrical resistance installed due to other emergencies, but the electricians accomplished the work without difficulty. When you visit the running unit, be advised by the relevant Electrical Engineer (this Engineer would be mainly responsible for such a task over here).
Hoping of effective help by others, a few more (even trivial) on the subject (comments welcomed):
1. I was informed that (in case of fertilizer industry) the resistance was placed in a tube (sheath) like a coil, installed in the duct.
2. Fins were not used; but this would increase heat transfer coefficient (per m2 of "bare" tube) to air, hence resulting sheath temperature would be theoretically lower.
3. Process is self regulated to some extent: Heat produced by resistance is passing to the air with variation of sheath and tube temperature (heat capacity of the latter assumed insignificant).
4. Resistance, insulating material in sheath, tube, have a max acceptable temperature (usually advised by Electrical Engineer). A high high sheath temperature cutoff (of electricity) is needed to protect these materials, in addition to other controls.

Edited by kkala, 03 January 2010 - 02:56 AM.