Question

Chlorine gas is to be heated from 125 °C and 1 atm to 175 °c. (a) Calculate the heat input ( W) required to heat a stream of the gas flowing at 5.0 kg's (b) Calculate the heat input (kJ) required to raise the temperature of 5.0 kg of chlorine in at constant pressure. a closed rigid vessel from 125 °C and 1 atm to 175 °C. (Suggestion: Evaluate the change in specific internal energy directly from the result of the first calculation, so that you do not have to perform another integration.) What is the physical significance of the numerical difference between the values calculated in parts (a) and (b)? (c) To accomplish the heating of part (b), you would actually have to supply an amount of heat to the vessel greater than the amount calculated. Why? A gas mixture contains equimolar quantities of methane and oxygen at 300 °C and 3 bar. Calculate the specific enthalpy of this stream in kJ/kg (not per kmol) relative to the pure components at 30 °C and 1 atm. State clearly all assumptions.

Answer 1

Specific heat of chlorine as a function of temperature is given by CP/R = 4.442 + 0.089 * 10^-3 T R = gas constant = 8.314 J/mole.k Mass flow rate of chlorine = 5 kg/s = 5 * 1000 g/s Molar mass of chlorine = 71 g/mole, Given T1 = 125 deg. c = 125 + 273 = 398 k and T2 = 175 deg. c = 175 + 273 = 448 k Molar flow rate of chlorine = mass flow rate/molar mass = 5000/71 moles/s = 70.42 moles/sec At constant pressure (is obelic process), delta H = Q = moles of chlorine * integral^448_398 cpdT Q = 70.42 * 8.314 {4.442 * (448 - 398) + 0.089 * 10^-3 * (448 * 448 - 398 * 398)/2} = 131135 joules/sec = 131135 watts = 131.135 kw for the case of heating in a rigid vessel becomes a constant volume process and for constant volume process, Q = moles of chlorine * integral ^448_398 (cp - R) dT