Who knows the answer? Heat Transfer Problem

Beezil

Member #Nay
NAXJA Member
Folks....

who here can provide an answer for me on something.....

I'm putting together a production powder-coating line...The washing equipment requires heated water for wash chemicals to be most effective. Wash stage tanks will be emptied/re-filled periodically.
City water fills the tanks, and washing cannot (should not) continue until washing stage water is up to temp.

An idea was presented that I'm skeptical of, i don't think it will have much effect.

The idea was, run the 1 1/2" city line along the upper ceiling of the cure oven. Another manufacturer/end user we toured claims to have done this with measured results. This is supposed to take the edge off the 52-55 degree city water temp on its way to the washer tank. Tabnk water heater supposedly doesn't have to burn as much gas. I call BS.

So here's what info I'd like, and I don't know if there is some simple equation. I cannot find an online calc anywhere....


let's take 1 1/2" water pipe, schedule 40. Let's figure 60 GPM flow rate. water temp at the point of entry into the oven space (hot air) is 55 degrees. ambient air temp in the oven is 425 degrees. water travels in the pipe for 100 feet.

what is the temperature rise as it exits the oven after 100 feet?


I'm expecting the answer to be minimal. My guess is only a few degrees of rise.

I'd just like to know what the calculation ends up being.

I am very much aware that I can do all sorts of clever things to increase transfer efficiency....that naturally comes at the cost of introducing exchangers, pumps, plumbing, copper, etc,etc. It also introduces the opportuntiy for the line to fail, drenching the oven and production parts, and most definitly damage the oven itself from the effects of flash-cooling.

I just need the answer to "chill" someone less-knowledgeable out....

because really.......if it were a cost effective innovation, the equipment manufacturer would build them like this and market the hell out of it as some kind of "green initiative"....

what say you naxja science geeks?
 

old_man

NAXJA Member
NAXJA Member
You would need 200,000BTU to heat a 40 gpm water stream 10 degrees F. That is given 100% heat transfer into the tube and no heating of the oven or heat loss in the oven. 200,000 BTU converts to roughly 60,000 watts. Give the heat transfer, even with this large amount of power, I would be surprised if you raised it more than a half degree since the each gallon of water is in the pipe less than 14 seconds.
 
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XJEEPER

NAXJA Member # 13
NAXJA Member
Throw a burrito on your engine manifold for 5 minutes and feed it to the "less-knowledgable".......this will be a good example of how much heat transfer will result from simply running the supply pipe over the oven.

I talked to my buddy who owns an HVAC business with 20ys experience, and Tom's post backs up his feedback. He knows of shops that use the exhaust heat from their ovens to heat water and for heating their office spaces.

Common sense says that simply running a water feed pipe over the oven will do little to increase the water temp. You would need to design a heat exchange system (think car radiator in reverse) to collect the heat from the oven and concentrate it to pre-heat the water.

A tankless water heater is a much more efficient solution, with less risk.
 

lesslimited

Official MWC Brewmeister
NAXJA Member
The best answer would be to expand beer brewing operations and use wort chillers to heat the wash water...
 

superdave

New member
Even if it heated the water 10 degrees, what about in the winter when the water temp is lower? Better method is like a tankless water heater that uses coils to heat the water in the line.
 

Beezil

Member #Nay
NAXJA Member
The best answer would be to expand beer brewing operations and use wort chillers to heat the wash water...
I've spec'd a second 12 million BTU medium pressure gas service that got installed a few weeks ago....

i think I should have enough nat gas to fire a few more banjo burners, don't you think?

:flame:

:D
 
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