Explanation:
The given data is as follows.
Volume of water = 0.25 ![m^{3}](https://tex.z-dn.net/?f=m%5E%7B3%7D)
Density of water = 1000 ![kg/m^{3}](https://tex.z-dn.net/?f=kg%2Fm%5E%7B3%7D)
Therefore, mass of water = Density × Volume
= ![1000 kg/m^{3} \times 0.25 m^{3}](https://tex.z-dn.net/?f=1000%20kg%2Fm%5E%7B3%7D%20%5Ctimes%200.25%20m%5E%7B3%7D)
= 250 kg
Initial Temperature of water (
) = ![20^{o}C](https://tex.z-dn.net/?f=20%5E%7Bo%7DC)
Final temperature of water = ![140^{o}C](https://tex.z-dn.net/?f=140%5E%7Bo%7DC)
Heat of vaporization of water (
) at
is 2133 kJ/kg
Specific heat capacity of water = 4.184 kJ/kg/K
As 25% of water got evaporated at its boiling point (
) in 60 min.
Therefore, amount of water evaporated = 0.25 × 250 (kg) = 62.5 kg
Heat required to evaporate = Amount of water evapotaed × Heat of vaporization
= 62.5 (kg) × 2133 (kJ/kg)
=
kJ
All this heat was supplied in 60 min = 60(min) × 60(sec/min) = 3600 sec
Therefore, heat supplied per unit time = Heat required/time =
= 37 kJ/s or kW
The power rating of electric heating element is 37 kW.
Hence, heat required to raise the temperature from
to
of 250 kg of water = Mass of water × specific heat capacity × (140 - 20)
= 250 (kg) × 40184 (kJ/kg/K) × (140 - 20) (K)
= 125520 kJ
Time required = Heat required / Power rating
=
= 3392 sec
Time required to raise the temperature from
to
of 0.25
water is calculated as follows.
![\frac{3392 sec}{60 sec/min}](https://tex.z-dn.net/?f=%5Cfrac%7B3392%20sec%7D%7B60%20sec%2Fmin%7D)
= 56 min
Thus, we can conclude that the time required to raise the temperature is 56 min.