cooling copper pipes after braizing

[rbartlett]

what would cool copper pipes down quicker

water at 1 deg c or water at 99 deg'c ?

and why??

cheers

richard

[Peter_1]

Cold water, larger DT between water and copper tube but I think this answer will be to easy.
I do it most of the time just after soldering because that cleans also the soldering.

[mrchatts]

If you pour hot water onto the copper pipe wouldn’t the water boil off quicker and take the heat with it? But hay 99 deg’c is still too hot for my hands

[rbartlett]

i'd better make it a bit clearer

i mean to say water applied with a wet rag

soory about that

cheers

richard

[Argus]

I don't think that cooling a hot joint with water is best practice.

Let the joint cool naturally - you will affect the hardness of the metal, also if there is a pin hole leak in the braze that you may not know about, it will drag water into the pipe.

If you must cool it with water, keep it to the surrounding pipe.
________
Suzuki Boulevard S50 specifications

[iceman007]

I also let my joints cool naturally first and then apply a damp rag later to finish the cooling process, but I reckon that the water at 99 degrees would cool the pipe quicker, because at 1 degree, the water is taking sensible heat to raise it's temperature. Water at 99 degrees is virtually at it's boiling point, and will take mostly latent heat, to change it's state and evaporate. The energy needed is greater for latent heat than for sensible heat, so this water will be able to remove heat energy faster from the pipe. (maybe?)

Regards
James

[chemi-cool]

hi richard,

when you cool copper instantly, it goes hard and loose some of its flexibility.

when you let it cool slow by air, it stays soft and again not flexible like it should be.

manufacturers do not recommend cold shock to hot joint.

to learn more, go to http://www.copper.org/applications/p...h/cth_main.htm
and download the copper tube handbook.
its at the bottom of the page and full of usefull information, better keep it on a CD.

chemi

[rbartlett]

iceman is on the right track as to the nature of my question

the should/shouldn't etc of using a wet rag is secondary and of interest too but for another thread maybe

cheers

richard

[adacus1]

As everyone has said dont do this as joints should be allowed to cool naturally to retain ductility, BUT

A wet rag at 1°C will cool the joint faster because

a. Heat transfer occurs fastest with the greatest Dt AND
b. The amount of heat required to boil a given quantity of water is the sum of the sensible heat to raise the water from its initial temperature plus the latent heat to boil the water.

[hhbref2003]

You may have a point Richard. But, hey, imagine getting the 99 deg. water on you. The less risk you can achieve the better for you. Practice have shown that the cooler the water the quicker the cooling rate of the copper. After all will you carry a container of 99 deg. water on top of a skyrise roof? I'm talking about safety here.

[rbartlett]

also if there is a pin hole leak in the braze that you may not know about, it will drag water into the pipe.






this is an interesting point -care to elaborate why,how etc?

cheers

richard

[electricstuff]

OK, this is one of those trick questions, right....
Like the one about whether ice cubes freeze faster if you fill the tray with warm water (they do, as the warm water melts ice on the bottom of the freezer compartment, making a better thermal path)

[shogun7]

If you have 1-lb of copper pipe at 1200*f and want to drop the temp to 200*f how many btu would you need to remove? anyone?

[frank]

Over what time scale Shogun?

[rbartlett]

Over what time scale Shogun?

ooo you got me there frank..what has time got to do with quantity?

cheers

richard

[electricstuff]

Time is only relevant in that more of the btus will be removed by radiation & convection if it's done over a longer period of time - the total btus removed will be the same.
The answer is <the specific heat capacity of copper> * <the temperature change> - can't put a number to it as I don't know the SHC of Cu in pounds/BTUs/DegF...

[electricstuff]

According to This handy website, the answer is 92.01715643656176 BTUs
Of course this doesn't take into account whatever may be inside the pipe...

[shogun7]

Frank, that’s an interesting question. I believe there are many answers. For example, if we start at 1200*f and we use an eyedropper that would take an X amount of time to get to 200*f. On the other hand if we throw it in a tub of cold/hot water ...well you can see what I’m driving at. By the way I got 90 BTU

[Gary Collins]

Cooling the copper tubes as quickly as possible has another benefit. If the system is not GN2 purged during the brazing procedure, rapid cooling after the brazing material has set will minimize the copper oxide formation on the tube interior which makes for a cleaner system. Quench only the outside of the tube and fitting unless you plan on using a micron gauge to measure the vacuum depth to verify the system is dry.

[satig]

100% d'accord (agree) with Adacus1

(As everyone has said dont do this as joints should be allowed to cool naturally to retain ductility, BUT

A wet rag at 1°C will cool the joint faster because

a. Heat transfer occurs fastest with the greatest Dt AND
b. The amount of heat required to boil a given quantity of water is the sum of the sensible heat to raise the water from its initial temperature plus the latent heat to boil the water.)