Formula/Math ?

[fishfanatic2]

What's the cooling rate of water? My problem is this, and I need a formula or an answer for it, plz. When I make my SW, i heat it to 80 degrees. room temp. is 70 degrees. I let the SW sit for 5-6 hrs. What temp. will it be after 5-6 hours since the water will cool do to the lower room temp. TIA for help and the formula.

 

[dhoch]

I can help you, but only in part.

The formula you desire is the following:

Q = mc(T1 -T2)/t

Where
m = mass of water (in grams)
c = specific heat of water (1 cal/g degree C)
T1 = Final Temperature (in C)
T2 = Inital Temperature (in C)
t = time in seconds
Q = Heating power

You have all the variables but the heating power, and this is not a simple thing to come up with. It has to do with variables dealing with air flow (how quickly air is moving across the surface area between the air and water), amount of surface area.

That is also assuming that your "bucket" is a perfect insulator (which of course it's not, so there is some heat transfer there).

I also believe that the heating power is not a constant as you have less power as the water get's closer to the rooms temp.

Basically this is not a simple problem (from a mathematical or physics perspective).

Dave

 

[hdtran]

FF2,

That depends on (a) how much water you have to start with, (b) the shape of your container, (c) what material your container is made of, (d) whether air is blowing against your container, or it's natural convection, (e) is the container covered, (f) is your water circulating with a pump, or natural convection, (g) if container not covered, relative humidity, etc.

Given the above information, and assuming no evaporative cooling, but assuming water circulation, a mechanical engineering or chemical engineering major should be able to provide you a numerical solution after having taken the required heat transfer course.

You're better off throwing a thermometer in your container, and pulling it out to check the reading every half-hour

 

[fishfanatic2]

wow, this is a lot more complicated than i thought. :lol:

Just curious to see as to what temp. i should have my water put into the bucket be to end up with a temp of 80 degrees after 5-6 hrs.

thnx anyway, ill probly just use the thermometer. :wink:

 

[Anonymous]

It'll probably just be room temp, unless you have a big bucket. A 10 degree difference on a small water change is really no big deal anyway, IMO.

 

[Anonymous]

Agreed Matt..its gonna cool down only to the temp of your indoors...honesty after 5-6hours it will be cooled down to room temp, it doest take long..i dont know any of the math formulas for it but try it out with regular tap water..heat it up and then throw in a thermometer and see how long it takes to cool down..the add salt shouldnt hinder its cooling too much from that.... HTH