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ENGR5003 / Week 2
Old spec L18 Question 4TutorialOld spec ENGR2172:210 min

ENGR217 (old spec) Thermo L18 tutorial, Question 4 official answers

A compressor takes in air at the rate of 0.29 kg/s at 12 C and 100 kPa. It delivers air at 302 C and 640 kPa. Conditions are steady and adiabatic. For air assume cp=1.005c_p = 1.005 kJ/(kg K); for water cp=4.19c_p = 4.19 kJ/(kg K). Neglect kinetic and potential energy changes.

Formulas you may need
  • SFEE Q˙−W˙=m˙[(h2−h1)+12(C22−C12)+g(z2−z1)]\dot Q - \dot W = \dot m\left[(h_2 - h_1) + \tfrac{1}{2}(C_2^2 - C_1^2) + g(z_2 - z_1)\right] (on the formula sheet)
  • Ideal gas / liquid Δh=cpΔT\Delta h = c_p\Delta T (on the formula sheet)
  1. (a)
    What is the power requirement for the compressor?
  2. (b)
    Cooling water is now supplied around the compressor casing at 0.30 kg/s and 31 C, leaving at 72 C. The intake conditions and mass flow rate are unchanged, but the delivery temperature of the air falls to 109 C. What is the new power requirement of the compressor?