Can an immersion heater reach 600 degrees Fahrenheit in a closed cylinder?

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Discussion Overview

The discussion revolves around the feasibility of using a 3500W immersion heater to raise the temperature of air in a closed cylindrical vessel to 600 degrees Fahrenheit. Participants explore the implications of heat loss, the heater's suitability for air versus water, and the challenges of achieving uniform temperature distribution.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes a closed cylindrical vessel filled with air and questions whether the immersion heater can achieve 600°F.
  • Another participant points out that heat can escape through the vessel walls, which are made of 316 stainless steel.
  • Concerns are raised about the heater's design, suggesting it may not function properly in air and could burn out.
  • Participants discuss the need for a heat transfer coefficient to estimate heat loss, noting that it depends on various factors such as orientation and air currents.
  • One participant provides a convection heat transfer coefficient and seeks further guidance on calculations.
  • There is a discussion about the correct units for heat transfer calculations, clarifying the distinction between Watts and Joules.
  • Some participants argue that achieving 600°F requires energy accumulation, indicating that heat loss must be less than heat supplied initially.
  • Others suggest that the system will eventually reach a steady state where heat loss equals heat supplied, but this may occur at a temperature below 600°F.
  • A participant shares their experimental results using sand as the heating medium, reporting uneven temperature distribution across thermocouples placed at different heights.
  • Suggestions are made for improving temperature uniformity, including the use of multiple heaters.
  • Clarifications are sought regarding the orientation of the cylinder, with participants confirming it is upright.

Areas of Agreement / Disagreement

Participants express differing views on whether the heater can achieve the desired temperature and the implications of heat loss. There is no consensus on the final outcome or the best approach to achieve uniform heating.

Contextual Notes

Limitations include the lack of specific information on heat transfer coefficients, the heater's maximum operating temperature, and the conditions under which the experiment is conducted. The discussion also highlights the complexity of calculating heat transfer in this context.

Who May Find This Useful

This discussion may be of interest to those involved in experimental heating applications, thermodynamics, and engineering design, particularly in contexts where temperature control and material limits are critical.

anolan23
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I have a closed 4" diameter cylindrical vessel with Volume=400in^3 filled with air at room temperature. A 3500W immersion heater with Watt Density=23.9W/in^2 will be used to heat the air. Can the air get up to 600 degrees Fahrenheit? How can I find out what temperature the air will get to?
 
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Hi, and welcome to the Physics Forums. :smile:

You have a closed volume to which you are constantly adding heat energy? is there any way for heat to be lost from this system?
 
Well, heat can escape through the vessel walls. The vessel material is 316 stainless steel.
 
Emerson heaters are generally designed to work in water. You may burn out your heater if you try to use it in air.

Computing final temperature of anything is non trivial given complete information. You have not given near enough info to get even a good guess.
 
To estimate the rate of heat loss from the cylinder, you need to know the heat transfer coefficient on the outside of the cylinder, from the cylinder surface to the room air. This depends on the orientation of the cylinder and also on whether there are air currents in the room. You can do better if you insulate the cylinder.

Chet
 
From this video:



I was able to get a convection heat transfer coefficient of 15 W/m^2*K.

What can I do? I've attached a photo of some of my work.
 

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I was told a watt density under 30W/in^2 shouldn't cause any problems with burnout
 
The equation to work with is:

hA(T-Tair)=Q

where h is the convective heat transfer coefficient, T is the final temperature, A is the surface area of the cylinder, Tair is the room air temperature, and Q is the rate of heating supplied by the immersion heater (W/sec). This doesn't say anything about how long it will take for the system to reach that temperature. Make sure everything is in consistent units.

Chet
 
This is Newton's Law of cooling...based on my work from my photo attachment is this the Qout?
 
  • #10
Chestermiller said:
and Q is the rate of heating supplied by the immersion heater (W/sec).
Chet

Do you mean just Watts instead of W/sec? Units of Q are in Joules and then Qdot is J/sec
 
  • #11
anolan23 said:
I was told a watt density under 30W/in^2 shouldn't cause any problems with burnout
If the heater is valuable, you might consider first testing it with reduced voltages to the heater element, afterwards inspecting for signs of heat intolerance. A VARIAC would be handy for this, but make sure you are not supplying reduced voltage to any control circuitry associated with the heater.
 
  • #12
anolan23 said:
Do you mean just Watts instead of W/sec? Units of Q are in Joules and then Qdot is J/sec
Yes.:redface:
 
  • #13
anolan23 said:
This is Newton's Law of cooling...based on my work from my photo attachment is this the Qout?
At steady state, the rate that the heater supplies heat is equal to the rate that heat is lost to the surrounding air.

Chet
 
  • #14
I want to heat the air to 600F so there has to be some sort of energy accumulation. Wouldn't this mean the heat rate lost to air would be less than heat rate supplied by the heater? Therefore, not a steady state problem?
 
  • #15
anolan23 said:
I want to heat the air to 600F so there has to be some sort of energy accumulation. Wouldn't this mean the heat rate lost to air would be less than heat rate supplied by the heater? Therefore, not a steady state problem?
Sure! But it does mean it will be a steady state once the contents reach 600F! :wink:
 
  • #16
anolan23 said:
I want to heat the air to 600F so there has to be some sort of energy accumulation. Wouldn't this mean the heat rate lost to air would be less than heat rate supplied by the heater? Therefore, not a steady state problem?
It depends. As the temperature rises, the rate of heat loss to the room increases until the system eventually reaches steady state. Do you want the 600F to be the final steady state temperature, or do you want to reach 600 F, and then have the possibility to get even higher if you continue supplying heat. The first thing to do is to see if the system can even reach 600F, or whether the steady state temperature would be below 600F, and you could never reach 600 F. So, the first thing to do is to determine what the steady state temperature would be.

Chet
 
  • #17
Aha! thanks for all your help
 
  • #18
Remember that the immersion heater in a water tank will,probably be sitting at a max of 180 F (ish), if the element is in air at greater temperatures the wiring will reach the same temperature as the element so make sure your insulation and fittings are good for high temperatures, and or provide a way of cooling your wiring. I suspect that the element will burn out well before you reach your required temperature, but it's probably a good idea to check the data sheets for max operating temp. Please have your electrical safety devices checked prior to running this, it might be a good idea to check the max working temp of any fixtures and fittings you are using. BTW what are you trying to make/demonstrate?
 
  • #19
Thanks Jobrag for your input on keeping things working properly. We are seeing what temperatures our instruments can withstand if they were attached to a heated chamber.

My goal is to achieve a uniform temperature of 600F on the outside of the metal chamber. Instead of air as the medium being heated, we decided on using sand to achieve a process temperature of 600F. We used three thermocouples one near the top portion on the outside of the chamber, one in the middle, and one on the bottom. The top thermocouple was hooked up to a temperature control that was set to 600F.

The results were:
Top Thermocouple- 600F
Middle Thermocouple- 856F
Bottom Thermocouple- 497F

How can I make these temperatures more evenly distributed to 600F? What would you do?
 
  • #20
Two smaller heaters in the chamber might come closer to giving a more even heat distribution. One nearer to the bottom.
 
  • #21
Only one heater will be used
 
  • #22
Dumb question, but is the cylinder upright or on its side
 
  • #23
Upright. Not Dumb.
 
  • #24
Can it be mounted horizontally?
 
  • #25
No sir-E bob
 

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