Steamfitter Instructor

ERP

When 25 gallons of water are heated from 40 degrees F to 200 degrees F, the volume of this water increases to 26 gallons. If the weight of water at 40 degrees F is 8.33 lbs per gallon, then the weight of water at 200 degrees F is MOST NEARLY

A 8.42    B. 8.23     C. 8.02     D. 7.33

C is the answer, but how do you arrive at this choice??



Thank you for your time and help

Gene

Alan (California Radiant) Forbes

It's all about

knowing the density and doing the math.



http://mathforum.org/library/drmath/view/56355.html

Eugene_Silberstein

Here You Go!

The density of water can be found by the following:



Density = 62.56 + (0.0003413 x Water Temp) - (0.00006255 x Water Temp x Water Temp)



So, for your 200 degree F water, we get:



Density = 62.56 + (0.00003413 x 200) - (0.00006255 x 200 x 200)



Density = 62.56 + 0.06826 - 2.502



Density = 60.12626 pounds/cubic foot



Since there are 7.5 gallons of water per cubic foot, the weight of one gallon of 200 degree water is found by:



60.12626/7.5 = 8.016, which is rounded to 8.02



Hope this helps!



P.S. It's on page 730 of:



http://www.heatinghelp.com/products/Heat-Pumps-A-C-Books/29/106/Residential-Construction-Academy-HVAC-Second-Edition-br-by-Eugene-Silberstein

Gordo

I would have

divided 25 gal. (the volume at 40*) by 26 gal. (the volume at 200*) and multiplied that ratio by 8.33 lbs./gal to give approx. 8.01 lbs./gal. which is closest  to answer C.