Answer the following questions using the Psych chart provided and for water: spe

Question

Answer the following questions using the Psych chart provided and for water: specific heat = 1 Btu (lb_m middot degree F), heat of = 144 Btu/lb_m and heat of vaporization = 970 Btu/lb_m (at 212 degree F) and specific heat of ice = 0.44 Btu/(lb_m middot degree F). An 18 lb turkey is removed from a freezer at -5 degree F and put into a refrigerator to thaw. How much energy (Btu) is required to warm the turkey up to the 38 degree F temperature of the refrigerator? Assume the turkey has the thermal prosperities of water. Estimate the cost ($) of the energy required to heat the water for a 15 minute shower in which the flow rite is 2.6 gpm. A propane water heater is used to heat the water from 50 degree F to 108 degree F. Assume the heater is 70% efficient, that one gallon of propane costs $2.80 and contains 91, 200 Btu's.

Explanation / Answer

1.

mass of Turkey is m = 18 lb, the tempereature difference is dT = T2-T1 = 38-(-5) = 43 0F

heat energy required is dQ = m*c*dT

dQ = 18*1*43 Btu

Q = 774 Btu

so heat energy required is 774 Btu

2.

the flow rate of shower is 2.6 gpm

and about 15 minutes the water quantity would be V = 2.6*15 gallons = 39 gallons

The temperature difference is dT = T2-T1 = 108 -50 = 58 0F

one gallon of propane cost is $2.80 , whic contains 91200 Btu

so the total energy of the propane, for 15 minutes shower is Q = 39*91200 Btu = 3556800 Btu

cost is 3556800/2.8 $ = 1270285.7143 $

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