How should I work out Wattage for a heat exchanger pad heater?

[MechEng92]

I would like to size an adhesive pad heater to use on a brazed plate heat exchanger to prevent freezing in low ambient temperatures. How should I go about calculating the wattage?

 

[LittleInch]

Work out heat leakage from your HX in the lowest ambient conditions base don 5C or whatever temperature you need to stop the unknown fluid from going solid.

If this isn't insulated it could be significant.

Or use something which doesn't freeze.

Very vague questions result in very vague answers....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MechEng92]

Thank you, I know it's vague but I was hoping there was a generic method for calculating the Wattage which could be applied to any situation.

I know the freezing temperature of the fluid and the ambient temperature, I'm sure I can get the material properties of the heat exchanger with insulation. But should I also be considering surface area?

 

[LittleInch]

Surface area of what?

If its insulated it becomes a lot easier and less onerous, but why wasn't this considered in the design?

Could you wrap self limiting trace heating tapes around it? Will give amore overall protection whereas a pad heater requires internal convection to stop other bits freezing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MechEng92]

Surface area of the heat exchanger as I'm potentially looking to use a pad heater. Insulation is going to be used but we still require heating to prevent freezing at very low ambient temperatures.

Trace heating could work too.

 

[pierreick]

Hi,
Do we need to understand that flow rates will be discontinued during operation? leading to stagnation and freeze!
Regarding your brazed plate heat exchanger, the area to add heat is very minimum (side of the plates), better to keep the unit in service (recirculation) and if necessary, add some electrical tracing on pipes. Of course, Unit and pipes must be insulated.
Please clarify and provide some process data for us to understand.
BTY did you ring the HX supplier for advice?
My 2 cents
Pierre

 

[MechEng92]

Hi Pierre thanks for commenting, this particular scenario will be when the system is not operating when in standby and so the fluid will not be flowing and therefore we need the heating to prevent freezing in colder ambient temperatures.

I will speak with the HX supplier to see if they have recommendations specifically.

 

[LittleInch]

You should be able to get or calculate an overall U value for your heater with insulation in terms of W/m2/K.

So you need m2 of your HX and delta K.

You're probably looking somewhere in 5 to 10 W/m2/K range for thin insulation and maybe a bit less for thicker or better insulation.

At least will get you somewhere in the ball park if you use 5 as U, then whatever your DT is and your external square area.

So W = 5 x DT X square area.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MechEng92]

Amazing thank you

 

[pierreick]

Hi,
Better to contact supplier of HX and supplier of heat tracing, who have some experience to share with you. Don't rely on calculation, too many unknowns.
Consider flushing the equipment in case of shut down to mitigate the risks.

https://www.chromalox.com/en/solutions/heat-trace-solutions

https://thermon.com/chin/default.aspx#cookies-accepted

Good luck.
Pierre