Discuss the various stages involved in heating a 3 kg block of ice at a temperat

Question

Discuss the various stages involved in heating a 3 kg block of ice at a temperature of -20 degree C into 3 kg of steam at a temperature of 150 degree C, within a container of fixed volume. By considering the heat involved in each step of the process, calculate the total amount of heat required and the time taken to accomplish each step using a 15 kW power source. (Describe in words) (Specific heat of ice = 2010 J kg^-1 K^-1; specific heat of water = 4200 J kg^-1 K^-1; specific heat of steam at constant volume = 1890 J kg^-1 K^-1; latent heat of fusion of water = 3.3 times 10^5 J kg^-1; latent heat of vaporization of water = 2.25 times 10^6 J kg^-1)

Explanation / Answer

step 1

convert ice from -20 to 0 oC

Q = mcdT

Q = 3 * 2010 * 20 = 120600 J

P = Q/t

t = Q/P = 15 x 10^3 W

t = 8.04 s

step 2 )

phase change of ice ( convert into water )

Q = m*Lf = 3 * 3.3 x 10^5 = 990000 J

t = Q/P = 66 s

step 3

water goes from 0 to 100 oC

Q = mcdT

Q = 1260000 J

t = Q/P = 84 s

step 4

water chage the phase convert into steam

Q = m*Lv = 3 * 2.25 x 10^6 = 6.75 x 10^6 J

t = Q/P = 450 s

step 5

steam goes from 100 oC to 150 C

Q = mcdT

Q = 3 * 1890 * (150 -100)

Q = 283500 J

t = Q/P = 18.9 s

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