5 kg of wet steam of dryness fraction 0.8, passes from a boiler to a superheater at a constant pressure of 1MPa absolute. In the superheater the temperature increases to 350oc . Determine the amount of heat supplied in the superheater. The specific heat of super-heated steam Cps = 2.25 KJ/KgK

2. B]5 kg of wet steam of dryness fraction 0.8, passes from a boiler to a superheater at a constant pressure of 1MPa absolute. In the superheater the temperature increases to 350^oC. Determine the amount of heat supplied in the superheater. The specific heat of super-heated steam Cps = 2.25 KJ/KgK.

Given:

Wet steam = m_w= (m_f+m_g) = 5kg

Dryness fraction = x = 0.8

Temperature of Superheated steam = T_sup =350⁰c

Specific heat of Superheated steam = C_ps = 2.25 KJ/KgK

Pressure = 1mg = 1 × 10⁶ p but 1 bar = 10⁵ pascal

So, P = 10bar

From Steam table A1 at P =10bar:

Saturated steam = T_sat = 179.83^oc

Specific enthalpy of saturated water = h_f = 762.6 KJ/Kg

Latent heat of steam = h_fg = 2013.6 KJ/Kg

Specific enthalpy of dry saturated steam = h_g = 2776.2 KJ/Kg

Amount of heat added in Superheated = ( h_sup – h )

we know that the steam coming out of boiler is wet steam hence

h = ( h_f + x h_fg ) KJ/Kg

h = 762.6 + 0.8 × 2013.6

h = 2373.48 KJ/Kg

after heat addition the temperature is increase to superheated temperature that T_sup = 350^oc

h_sup = h_g + C_ps ( T_sup – T_sat )

h_sup = 2776.2 + 2. 25 (350 – 179.83 )

h_sup = 3159.08 KJ/Kg

Amount of heat Supply = ( h_sup – h )

Amount of heat Supply = 3159.08 – 2373.48

Amount of heat Supply = 785.5 KJ/Kg

Therefor amount of heat added for 5Kg of Steam = 785.5 × 5

amount of heat added for 5Kg of Steam = 3927.5 KJ