Heat Exchanger Sizing 7

[ClydeMule]

I am looking for some simple equations or rules of thumb for determining the straight length of tubing required to acheive a desired amount of heat transfer. The tubing would be formed into a coil. The coil would be immeresed in both still or agitiated water.

I would like to analyze both single phase and two phase flow. The two phase analysis would be used to make low cost evaporators.

The knowns are evap. temp, water final and initial temp, cooling medium mass flow rate, and tubing diameter.

In a nutshell:

"I want to make a 2 ton evaporator out of 1/2" coppper tubing in a tank of water. I am using R22, need 60 deg F water, and the water in the tank is not moving. What is the total length of tubing required"

Thanks,

Jeff Johnson

 

[TBP]

Track down a copy of "Handbook Of Data Sheets For Solution of Mechanical Systems Problems" by Roose & Roose. ISBN 0-442-27804-7. I believe it's out of print, but it has a formula and nomograph for solving exactly this kind of problem.

This is a handy book - you can look up solutions for odd problems like the minumum flow of water through an above ground pipe to prevent freezing. It provides a couple of pages each for 150 or so problems. One page is a short write-up, with a formula, and the other page is a nomograph showing the solution. Just plug your numbers in, and it'll give you a quick answer that in most cases is "close enough". If nothing else, you'll have a good indication of whether or not it makes sense to persue something further.

 

[235zzzo]

Hi ClydeMule

I suggest you a kind of bible for heat-exchangers:
"Heat-Exchangers-Thermal-Hydraulic Fundamentals and Design"
Edited by S.Kakaç, A.E.Bergles and F.Mayinger, MacGRAW-HILL,1980, ISBN 0-07-033284-3 .

Just go to the 559 through 700 pages, and you will find anything about any kind of heat-exchanger, even unsolved problems, at that time.
Good luck!
zzzo

 

[pardal]

If you want to do it without regarding the calcs , just check for window air conditioner , size the pipe length at evaporator, that´s what you need , do not worry about puting more pipe than needed. It will work.

feel free to contactme at k281969@hotmail.com but keep posting here .
Pardal

 

[235zzzo]

Hi Fellows!

To Pardal: "It will work", but allow me, if you put more than you need, then you have to pay more than for it! After all, what the engineering process serves for??
zzzo

 

[JeanAlesi]

I appoligize if this sounds a little immature or off topic, but can someone identify some of the very basic pros and cons of cooling air using above method over using intercoolers (air instead of waters)?

 

[pardal]

water is more efective so more energy eficient.
Air is aviable any where.
Water could be "hard" so it need water pretreatment.
Pardal

 

[JeanAlesi]

Thank you pardal, could you please explain what you meant by "water could be hard".?

 

[phex]

hard water = high contents of calcium and magnesium salts (ions)

 

[25362]

I'm sorry I failed to read phex's short and effective comment before sending my own long "dissertation". Please forgive me. Water that is rich in salts of calcium, magnesium or iron is called hard water. In regions where the water is particularly hard, you can see the precipitates of salts formed with these cations and fatty acid anions, as gray rings, called curd or soap curd, around bathtubs and sinks, after washing with soap. The hardness of water by Ca, Mg, or Fe ions is expressed as ppm CaCO₃ equivalent.

Chemically, CaCO₃ is found in nature in chalk, in limestone, coral, stalactites, stalagmites, shell, marble, etc. Most common forms of pure CaCO₃ are calcite and aragonite.

Cooling (hard) water problems start when these salts deposit on warm H/E surfaces due to their very low solubility (CaCO₃: less than 10 ppm at 25^oC) fouling them, and increasing resistance to heat transmission. CaCO₃ and CaSO₄ have negative coefficients of solubility as function of temperature, meaning they are less soluble as temperature rises.

On hot surfaces, as in boilers, the crust thus formed is mainly composed of CaSO₄ and CaCO₃ accompanied by varying proportions of Ca(OH)₂, Mg(OH)₂, complex calcium phosphates, silicates, etc. Part of the precipitation of calcium carbonate in boilers is done by the bicarbonate's decomposition in the water proper, thus it tends to form a sludge rather than a crust. Bicarbonate's is called temporary hardness.

There is a whole chapter in Chemistry dealing with water hardness and softening procedures.

 

[phex]

As always, 25362 gives the most complete answer possible =). thanks for sharing, just to be sure to have said it finaly. this place would be dead without ppl like you.

 

[JeanAlesi]

Agreed, thanks to all for the answers.