Complete Question
A large power plant heats 1917 kg of water per second to high-temperature steam to run its electrical generators.
(a) How much heat transfer is needed each second to raise the water temperature from 35.0°C to 100°C, boil it, and then raise the resulting steam from 100°C to 450°C? Specific heat of water is 4184 J/(kg · °C), the latent heat of vaporization of water is 2256 kJ/kg, and the specific heat of steam is 1520 J/(kg · °C).
J
(b) How much power is needed in megawatts? (Note: In real power plants, this process occurs under high pressure, which alters the boiling point. The results of this problem are only approximate.)
MW
Answer:
The heat transferred is ![Q = 5.866 * 10^9 J](https://tex.z-dn.net/?f=Q%20%3D%205.866%20%2A%2010%5E9%20J)
The power is ![P = 5866\ MW](https://tex.z-dn.net/?f=P%20%3D%205866%5C%20%20MW)
Explanation:
From the question we are told that
Mass of the water per second is ![m = 1917 \ kg](https://tex.z-dn.net/?f=m%20%3D%201917%20%5C%20kg)
The initial temperature of the water is ![T_i = 35^oC](https://tex.z-dn.net/?f=T_i%20%20%3D%2035%5EoC)
The boiling point of water is ![T_b = 100^oC](https://tex.z-dn.net/?f=T_b%20%3D%20100%5EoC)
The final temperature ![T_f = 450^oC](https://tex.z-dn.net/?f=T_f%20%3D%20450%5EoC)
The latent heat of vapourization of water is ![c__{L}} = 2256*10^3 J/kg](https://tex.z-dn.net/?f=c__%7BL%7D%7D%20%3D%202256%2A10%5E3%20J%2Fkg)
The specific heat of water ![c_w = 4184 J/kg^oC](https://tex.z-dn.net/?f=c_w%20%3D%204184%20J%2Fkg%5EoC)
The specific heat of stem is ![C_s =1520 \ J/kg ^oC](https://tex.z-dn.net/?f=C_s%20%3D1520%20%5C%20J%2Fkg%20%5EoC)
Generally the heat needed each second is mathematically represented as
![Q = m[c_w (T_i - T_b) + m* c__{L}} + m* c__{S}} (T_f - T_b)]](https://tex.z-dn.net/?f=Q%20%3D%20m%5Bc_w%20%28T_i%20-%20T_b%29%20%2B%20m%2A%20c__%7BL%7D%7D%20%20%2B%20m%2A%20c__%7BS%7D%7D%20%28T_f%20-%20T_b%29%5D)
Then substituting the value
![Q = m[c_w [T_i - T_b] + c__{L}} + C__{S}} [T_f - T_b]]](https://tex.z-dn.net/?f=Q%20%3D%20m%5Bc_w%20%5BT_i%20-%20T_b%5D%20%2B%20c__%7BL%7D%7D%20%20%2B%20C__%7BS%7D%7D%20%5BT_f%20-%20T_b%5D%5D)
![Q = 1917 [(4184) [100 - 35] + [2256 * 10^3] +[1520] [450 - 100]]](https://tex.z-dn.net/?f=Q%20%3D%201917%20%5B%284184%29%20%5B100%20-%2035%5D%20%2B%20%5B2256%20%2A%2010%5E3%5D%20%20%2B%5B1520%5D%20%20%5B450%20-%20100%5D%5D)
![Q = 1917 * [3.05996 * 10^6]](https://tex.z-dn.net/?f=Q%20%3D%201917%20%2A%20%5B3.05996%20%2A%2010%5E6%5D)
![Q = 5.866 * 10^9 J](https://tex.z-dn.net/?f=Q%20%3D%205.866%20%2A%2010%5E9%20J)
The power required is mathematically represented as
![P = \frac{Q}{t}](https://tex.z-dn.net/?f=P%20%3D%20%5Cfrac%7BQ%7D%7Bt%7D)
From the question ![t = 1\ s](https://tex.z-dn.net/?f=t%20%3D%201%5C%20s)
So
![P = \frac{5.866 *10^9}{1}](https://tex.z-dn.net/?f=P%20%3D%20%5Cfrac%7B5.866%20%2A10%5E9%7D%7B1%7D)
![P = 5866*10^6 \ W](https://tex.z-dn.net/?f=P%20%3D%205866%2A10%5E6%20%5C%20W)
![P = 5866\ MW](https://tex.z-dn.net/?f=P%20%3D%205866%5C%20%20MW)