soil heat transfer/temperature change air drain

[xiloergos]

Hello everyone. I'm new here. Really cool website. I'm just a carpenter, don't ask too much of me! = )

I'm designing a geothermal system for a possible greenhouse I'll build, but I don't have much money, so I need to make calculations very precisely.

I find myself in need of help, to figure out what the temperature change in air flowing through a corrugated pipe underground would be.

I have this information:

Air: Air will be entering the pipe at 10 degrees Fahrenheit.
Pipe: High density Polyethylene corrugated (solid - without any piercing or knifing) with a thermal conductivity coefficient of 0.5 W/m^K (temperature of the pipe is negligible - meaning it's not insulated or heated)
Surface area of the pipe: The pipe is 100' long with a diameter of 4" (so I believe the surface area is 2.777778 square feet - contact with the ground surrounding it)
Flow: The air is moved by a 270 CFM fan (so I believe traveling at 270 cubic feet per minute)
Surface: The surface surrounding the pipe is soil (I'm going to assume the soil will have a thermal conductivity coefficient of 1.5 W/m^K) and the temperature of the soil is permanently 45 degrees Fahrenheit.

I have attached a very simple diagram with most of this information.

I need to know at what temperature will the air come out?

I really tried to use my head for this, and even tried the chatgpt thingy online, but I think I need the help of real engineers!

Thank you in advance!

Xilo

 

[Pinwards]

It's not in his profile directly, but if you go to the Google Drive link in his profile, then his e-mail address is at the top.

#

 

[xiloergos]

Thank you, it is there, how did I miss it!? I checked several times before, and it was only dates and places. Oh well, it's there now, thanks Pinwards!

 

[1503-44]

I had my email in my profile on Dropbox, but people didn't like Dropbox, so I changed to the link on Google drive. That one didn't have my email until I revised it yesterday. Apologies.

Physics doesn't get too deep into heat transfer. To find these tables its better to look for thermodynamics [heat transfer] textbooks. The book in the picture is the best one I've found. "Heat Transfer" by J.P. Holman - McGraw Hill Mechanical Engineering Series is another. I have almost as many stick on notes marking the pages on that one as I do the other.

I had a really good basic physics book, but I can't seem to find it. "Spacecraft Dynamics and Control". Its probably not going to be very practical.

I think you take a real chance on finding good understandable textbooks today. My father's textbooks from the 1940s were really great for capturing basic principles. Probably none of those left anymore. I used to buy up all the old used books I could find at Brown's Book Store, in Houston. I spent many a Saturday morning there. They were famous for their technical stock. Wonder if it still exists.

There are some good places to learn about serious subjects on the internet. You just have to be determined to find it in all the rubbish that Google lists first. A number of universities maintain free learning sites.

Of course you can get some good practical answers here too.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[1503-44]

OK Point #6 Solved

This solution method is not dependent on the maximum length of your pipeline. It simply finds how long a pipeline must be to reach any temperature of interest less than the soil temperature, given only all the other data. It doesn't need an entry for L, because it solves for whatever length is needed to reach Tm. It doesn't really care how much of it you might decide to build, which allows quite a bit of liberty for you to decide what temperature is good for your pocketbook.


You can enter any temperature (less than your 45 degree soil temperature) into the last box in row 28 and it will tell you how long a pipeline must be to get to that temperature. To heat it up to 44.99 degrees you must build a pipeline 89,756 feet, or 17 miles long. 45 degrees gives a divide by 0, or infinite length answer, so I really recommend you don't build that one.

BTW, thanks for appreciating my teaching style.
Unfortunately I'm still too busy learning new stuff (and trying to remember old stuff) to have enough time for teaching. You seemed to be truely interested with a real need for a practical solution and I do like solving those kinds of problems. Thanks for your patience. We're installing a new kitchen and bathroom this week, so I was a bit distracted.



--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[xiloergos]

Is it sort of saying, if you eat 'x' cookies you'll gain 'y' kilograms, but you are not actually gaining 'y' kilograms, you need to put a value instead of 'x'.

Or did I not get it at all? = )




Sounds like you could use me over there (kitchen and bathroom) I'm a carpenter = )

 

[1503-44]

The F team.
500 ton pipeline anchor block.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[xiloergos]

Impressive, I guess you don't just lay it on the floor = )

 

[1503-44]

Posted to the wrong thread. should I leave it here?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[xiloergos]

If no one starts worshiping it we should be fine I think = )

 

[1503-44]

No. We are looking for a place along our pipeline model where Tm will equal the temperature of the air we need. Just solving the problem "backwards" if you will, many times. Rather than looking for L, given Tm, I solve for Tm assuming some L, which it is important to remember it is a distance from the pipe inlet, not a particular Length of any given pipeline. That's what you will decide. Terminating the pipeline at the temperature that is acceptable.


--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[xiloergos]

Wonderful explanation, now I get it, I don't think I could have cracked this one one my own. My spiritual gifts are others, clearly this is one of yours!

 

[1503-44]

Right
That's the biggest pipeline anchor that I'd ever seen. Weighs 500 Tonnes.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[xiloergos]

Why so chunky at that particular place?

 

[1503-44]

Not even Allah knows the answer to that.
It's a waste of good concrete.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."