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BTU's needed

Member Posts: 7
Are needed to maintain wax at 140 deg. (The wax
has almost the same heat transfer properties as water.)

A client has a 5000 gal tank insulated at R-28. The tank is 9 Ft. in diameter and 9 Ft. tall. The wax is brought into the tank at 120 deg. so we need to raise the temp 20 deg in about 10 hours. Once at 140 deg we only need to maintain that temp.

Thanks,
Craig

• Member Posts: 4

• Member Posts: 6,928
This might help a bit...

http://www.hvac-toolbox.com/38_286.html

Not the best table. No ambient temperature. Insulation listed in inches, not actual values.

ALWAYS VERIFY MY MATH! I do this quick and when I make a simple math error I tend to do it over and over and not see it...

But...assuming product is 8' deep in the tank:

64 sq.ft. surface looses about 64 * 160 = 10,240 btu/hr @ 140° via radiation. Water has emissivity of about 0.96. Couldn't find values for wax but did find reference that a crayon has extremely high emissivity... At least with the 0.96 value there's not much chance that the wax would loose more heat via radiation...

226 sq. ft. of wall surface (again product 8' deep) looses about 226 * 12 = 2,712 btu/hr. This using the 3" thick insulation column.

Since wax isn't evaporating at 140° I did not include evaporative loss. I'm presuming that the tank is filled with pure product--not scented or with other things that WOULD evaporate!

10,240 + 2,712 = 12,952 btu/hr STANDBY heat loss.

For the heat required to raise the product to usage temp you REALLY need to know the actual specific heat of the type of wax involved. Specific heat of paraffin wax is 0.69 but since you said "very similar to water" will use specific heat of water (1.0) to make the REALLY easy.

To raise each pound of product 20°F you need to add 20 btu. If done over a period of 10 hours you would need to add 2 btu/hr for each pound.
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