Industrial Oven Heat Gain
Industrial Oven Heat Gain
(OP)
I'm designing a ventilation system for an oven room and need to know what is the best way to account for the heat gain into the room from the ovens.
There are 5 ovens that are rated at 47kW and one gas fired at 250,000 btu/hr. I think that using the rated input will yield too much cfm's, so I'm thinking there is some divesity factor or "rule of thumb" to use for my estimate. In addition, I'm using a delta T of 15 degree F for my CFM calculations. Can anyone offer some insight. Thanks.
There are 5 ovens that are rated at 47kW and one gas fired at 250,000 btu/hr. I think that using the rated input will yield too much cfm's, so I'm thinking there is some divesity factor or "rule of thumb" to use for my estimate. In addition, I'm using a delta T of 15 degree F for my CFM calculations. Can anyone offer some insight. Thanks.





RE: Industrial Oven Heat Gain
TTFN
Eng-Tips Policies FAQ731-376
RE: Industrial Oven Heat Gain
The gas-fired oven probably has an exhaust. Is combustion air taken from inside the room, or outside?
RE: Industrial Oven Heat Gain
RE: Industrial Oven Heat Gain
What will be the internal temperature when the door is opened for unloading?
What temperature will the material be when it is unloaded and how much material will there be? In my experience, ovens are almost always unloaded at a temperature above fully ambient in order to reduce cycle time.
What it the internal temperature of the oven when the door is open.
We used to run a process where we ran the ovens up to 2,000 F, opened the door and loaded parts. When the ovens came back up to 1500F, we reopened the doors and unloaded about a pound of parts at 1500 F and let them cool in the room.
As the rest pointed out, most to the heat generated will be handled as part of the original design.
While you are doing this consider operator safety. When you open a door that is 12” x 12” at arms length on an oven at 2000 F the heat hits you in the chest with a force you can feel as a force as well as heat.
tom
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
RE: Industrial Oven Heat Gain
Depending on the temperatures you are running, don't forget to correct for density.
You could then assume that the difference between heat input - and here I mean real input, not nameplate rating - and heat in the exhaust is going into the room. At least under steady-state operation.
As others have pointed out, the material in the ovens will have heat when removed, so you need to consider where those parts go.
RE: Industrial Oven Heat Gain
Sometimes the operators leave the doors open to cool down the ovens faster. In some cases, the material is left in the oven with the door open or ajar to cool everything down at a gradual pace rather than subject it to thermal shock.
RE: Industrial Oven Heat Gain
RE: Industrial Oven Heat Gain
Tell the operators you need their help to keep them safe and comfortable. If you are lucky you work in a place where the company truly believes that operator comfort increases productivity. And the operators believe the company believes it. Check with the manager, foreman and unofficial team leader.
Spend a lot of time there making measurements. Ask the team when it gets hottest.
Maybe put in high capacity ducting with a thermostat. Be sure to give the operators the ability to override the thermostat.
Remember a room is hotter for guys working than for an engineer standing.
Check clothing. Recommend all cotton if they get hot. JC Penney Big Mac work shirts – all cotton, reasonable price, long lasting, catalog only. Get the blue chambray, not the hickory (mattress pattern fabric.)
Remember to allow for what the operator feel based on outside temperature. People seem to like rooms warmer in winter and cooler in summer.
Can you just ignore the ovens and go with the room in you calculations? Ignore why the room is warm and just calculate how much air you need to change to cool it.
Where does make up air come from?
tom
Thomas J. Walz
Carbide Processors, Inc.
www.carbideprocessors.com
RE: Industrial Oven Heat Gain
Note that the radiation coefficient is
hr=e*0.173[(T1/100)^4-(T2/100)^4]/(T1-T2)
T1,T2 in deg Rankine
e= emmisivity assumed = 1
For example if your area is 50 ft^2, you would get
Q=50*(850-70)*7.5=292,000 BTUH.
You then size the ventilation accordingly, to remove this heat.
If you can get better data on surface temps, then of course, these numbers would be smaller.