Design for a Heat Exchanger 2

[Soinn]

anyone have a idea to built a heat exchanger which can heat up an airflow of 3kg/s from 20degree celcius to 28 celcius. The air is heat up by Aluminium pipes with finns which carry 95 degree celcius of water. Pretty hard to design an exchanger which is small size.
Cheers

 

[cdvk]

it seems like you should have no problem warming air up 8 degrees when you have 75 degrees temperature difference between the two fluids... you just have to find the best configuration for your application.

can you slow down the air at all?

 

[Soinn]

No. The air flow is fixed. What i need to consider is the arrangement of the finned tubes in order to get the smallest size of the exchanger. The size of the exchanger according to my calculation is too big (1.7mx0.8mx9m).
SO, any other idea to reduce the size?

 

[TD2K]

The controlling resistance is going to be on the air side.

How much are you trying to reduce the size of the exchanger? You can put in more rows of tubes but at the expense of course of pressure drop.

 

[Soinn]

if impossible, i would prefer an exchanger of size 0.5X 0.5X 1m.
The problems is adding more rows of tubes, the larger the size of the exchanger.

Thanks man

 

[TD2K]

You are going to need different technology than finned tubes for what you want to do and I don't know what that would be.

The amount of tubes and therefore area is related obviously to the volume. You have now a 12.24 m3 exchanger (the last 9 m is 9 m and not 0.9m?). You want to reduce this to 0.25 m3 meaning for discussion purposes 50 times more efficient heat transfer.

 

[Adam0012]

What fin count are you using? Is plugging an issue? dependant on how clean your air is you should try increasing your fin count. Try 22+ fpi

 

[Soinn]

Here's the tube i'm using Diameter 42mm, inner Diameter 38mm
Fin Length 0.02m, Fin pitch 0.01m, Fin Thickness 0.001m
Thanks Everybody !!

Cheers

 

[tickle]

I guess that the face velocity for the air is causing the large cross sectional area of the HE.

Can you bypass a fraction of the air around the HE in a duct? - this should allow you to get good control of the temperature as well.

If you increase the fins per inch, then you are adding more resistance to the air flow, you may want to consider bare tubes.

Can the HE be installed at an angle to reduce the footprint?

I would be interested to know what the air is used for and the current configuration in terms of air movers and ducting is to get a better idea. - have you spoken to air conditioning people, it sounds a bit air con like to me.

 

[22672]

The designs of the kind are carried out in sophisticated softwares like HTRI and HTFS.

This is a typical air cooled heat exchanger, wherein the air is being heated with hot water.

The coil configuration is the most important aspect. Depending on the flow of the hot water, you could have multiple passes on the tube side. However, the area of heat transfer is bound to be high due to large resistance observed on the cold fluid side.

Generally, as I have observed, two of the dimensions (Cross sectional area) of the flow is fixed and the length can be adjusted to suit the area required.

All the best.

 

[amirhirshfeld]

Building a heat exchanger to the current specification is no big deal.

I Suggest you use a fin plate heat exchanger.

You can find many manufacturers on the web.

If you need more help, contact me directly am_hirshfeld@coolingzone.com.


Amir

 

[speco]

Soinn,

I happen to have software which can solve this type of problem. I ran it through my program to see what it might look like. The program, by the way, is similar to HTRI or HTFS as mentioned by TEJU above. The flow area of .5 m X .5m is pretty small for this air flow and results in an extremely high air-side velocity. Along with it, would be a very high static pressure drop across the coil. The problem is compounded by using large diamter tubes, as you had intended to use. As Amirhirshfeld suggested, a plate-fin exchanger would be more appropriate for this application. I agree.

Using the normal finned tubing configuration for plate coil construction with tubes of 15.88 mm diameter, I believe that you can do this with a coil of .6 m X .6 m in face area. You should have about 4500 KG/hr of water flow at 95 deg. C. The air-side mass velocity is still high, but the static is reasonable at approx. 10 mm WG.

I can provide further details if you contact me directly.

Regards,

Speco (

http://www.stoneprocess.com)

 

[MobileHVAC]

Soinn,
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