INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Chamber Acting Like Outside Air

Chamber Acting Like Outside Air

(OP)
Hello,

I have the task of experimentally measuring the radiator performance according to varying outdoor temperature degrees.

My plan for the test setup is to equip one box in another bigger box. The inner box (the heated space) will involve a radiator. While the volume between the inner box and the outer box will be cooled so the heat loss from the heated space will be satisfied.

The problem here is that how large the space between the inner and outer box should be so that the medium there can represent the outside air medium i.e. equipping a small volume there can cause unusual high local temperature increase close to the heat losing wall and/or continuous supply of chilled air to this space may deteriorate the temperature change pattern (as it should be through the heat loss). What I plan is to have a large gap between the boxes as maximum possible. But any method to determine that space volume? Or any idea with different approach of mine generally for the whole experimental setup?

Regards.

RE: Chamber Acting Like Outside Air

I can't help with your specific question, but just a few thoughts:

Will trapping your radiator in a fixed "small" volume of the inner box cause problems? You probably can't remove the heat through wall conduction fast enough. Walls may have to be so cold that condensate will occur.

What about varying humidity levels of the real world? Do you need to consider those in your test chamber?

I'm just throwing out ideas here but what about putting your radiator in the middle of a piece of ductwork? You could vary the inlet conditions (temp, humidity, airflow, etc.) with the proper air handling equipment, and measure the outlet conditions downstream of the radiator.


RE: Chamber Acting Like Outside Air

What sort of "radiator"?

The one you fix to the wall of a house or the one you have in the front of a car?

I suspect having read it a few times that you mean the former.

If you want to simulate the outside then you really want it as big as you can get, but my guess, for what it's worth, is that you should have 10 times the inner volume at least in the outer box and also create some sort of small circulation to reduce impact of cold or hot spots

That probably strikes the balance between a space that is too big to efficiently cool or heat up and one too small and hence you have insufficient heat sink for the inner space (house) to emit heat form the air heated by the internal radiator.

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

RE: Chamber Acting Like Outside Air

(OP)
Hey Guys,
I will try to reply your comments/suggestions. The purpose of my reply is to have discussion not positive/negative feedback. So feel free to comment more.

My recent solution in my question (how big the outside-air-like volume should be) is with calculating the temperature distribution through the wall. So I need to find the distance of the temperature gradient from the wall to the infinite outside air medium (according to my temperature range). Let's say I will calculate the distance δ1 as shown in the below figure. After finding this temperature gradient distance I will choose a width between boxes more than that. Any suggestions how to do that or another ideas are welcome!



Quote (BronYrAur)

Will trapping your radiator in a fixed "small" volume of the inner box cause problems? You probably can't remove the heat through wall conduction fast enough. Walls may have to be so cold that condensate will occur.

I guess that having a small volume for the heated space will lead to low thermal inertia, so quick heat up can be possible. I have to point that I will determine the material and the thickness of the wall with the aim of having a heat demand (for the inner chamber) as similar to a real case building room. So setting the outer temperature (of the volume between the outer and inner chambers) as equal to the outdoor air temperature will result in the same heat demand of a real case room. The conduction through the wall will be enough for the heat loss as expected from a real case room as a result of the material and thickness selection of the wall while the small volume in the inner chamber will lead to quick heat up or cool down.

Quote (BronYrAur)

What about varying humidity levels of the real world? Do you need to consider those in your test chamber?

That is another good point. I am at the beginning of designing the experimental setup. I quickly check for a small scale chiller for the outer volume (between the boxes) and found one with the ability of setting a specific humidity level together with the temperature. I need to check the literature to see how the effect of humidity will be in my temperature range.

Quote (BronYrAur)

I'm just throwing out ideas here but what about putting your radiator in the middle of a piece of ductwork?

This experimental setup is due to the request as stated in the project proposal that I based on. So I need to build this setup in the company lab and we don't have those ductwork (I guess that you mean large-scale air simulating devices). What I will build at last will be like this duct but in a cheap way.

Quote (LittleInch)

If you want to simulate the outside then you really want it as big as you can get, but my guess, for what it's worth, is that you should have 10 times the inner volume at least in the outer box and also create some sort of small circulation to reduce impact of cold or hot spots

That probably strikes the balance between a space that is too big to efficiently cool or heat up and one too small and hence you have insufficient heat sink for the inner space (house) to emit heat form the air heated by the internal radiator.

The inner chamber is with the aim to represent a house (more specifically a room) not a car. I will avoid of having a circulation for the case with natural convection outside (of course in real life there is forced convection due to the wind). The spots (local temperature change close to the wall) is a must but the infinite temperature of the outer volume (which is far from the wall of the inner chamber) should not get affected from these spots (then I think that I will build a medium as similar to outside air ambient). 10x bigger sounds big enough but I want to calculate the distance of δ1 (as shown in the above figure), the distance of the temperature degradation in the outer convective part.

Thanks for your comments/suggestions. Looking forward for more!

Regards.

RE: Chamber Acting Like Outside Air

Your distance will not be very big, but after a few minutes the temperature of the outer space will rise and affect your heat flow / temperature.

Depending on how you cool your air down in the space or just let it heat up, but less than the inner house temp will impact your experiment. If you're artificially cooling it again you want a big volume so you don't get hot or cold spots in the annulus space. you will need some sort of breeze in the space to get the air through the chiller

If you want to get natural like convection on the outer wall then you need space, much much more than the distance you quote

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

RE: Chamber Acting Like Outside Air

(OP)

Quote (LittleInch)

Your distance will not be very big, but after a few minutes the temperature of the outer space will rise and affect your heat flow / temperature.

I suppose that if the outer chamber in which the atmospheric condition is to be formed will be big enough, the heat loss will be as same as how it occurs naturally in the real case i.e. the heat loss from the heated room to the atmosphere. I will put some safety factor leading to a bigger space involving of high volume of cool air (let's say a gap between the boxes being 10x bigger than the calculated temperature gradient distance that is due to the convective heat loss -outside-). Also, I plan to supply the chilled air to this volume in low flow rate at a location far from the wall of the heated space (but close to the inner part of the wall of the outer box). The chilled air supply will be activated according to the temperature measure on this far supply zone. As you mentioned in your comment.

“In life, the truest guide is science” – Mustafa Kemal Atatürk

RE: Chamber Acting Like Outside Air

Quote (teknomania)

experimentally measuring the radiator performance according to varying outdoor temperature degrees.

As you currently describe things your test does not accomplish this.

You will at best be able to determine the performance of a radiator inside a specific box vs. outdoor temperature.

The real performance of a radiator vs. outdoors is entirely dependent on what separates radiator from outdoors.

RE: Chamber Acting Like Outside Air

(OP)

Quote (MintJulep)

The real performance of a radiator vs. outdoors is entirely dependent on what separates radiator from outdoors.

I will determine the material and its thickness in accordance with the heat loss from a real case building/house/room. Hence, with your words, what separates radiator from outdoor will be fulfilled with the correct material thickness of the inner chamber. Isn't this true?

Regards.

“In life, the truest guide is science” – Mustafa Kemal Atatürk

RE: Chamber Acting Like Outside Air

Quote (teknomania)

Isn't this true?

No.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close