Question

# 2. a) i) ii) b) i) A thin-walled concentric tube heat exchanger has a uniform overall heat transfer coefficient, and operates under the following conditions in Table 1. ii) Cold fluid Hot fluid Mass flow Specific heat rate [kg-s¹] capacity [J-kg-¹-K¹] 3850 1900 Inlet Outlet temperature temperature [°C] [°C] 0.2 0.25 Table 1: Heat exchanger conditions for question 2a. 25 240 110 Calculate the maximum possible heat transfer rate between the fluids, describing fully the assumptions you must make. [7 marks] Calculate the hot outlet temperature, assuming the heat exchanger operates in the mode that maximises the heat transfer rate. [5 marks] Write a chemical equation for the complete combustion of 1 kmol of cetane (C16H34) in air assuming stoichiometric conditions. Take air to be 79% nitrogen and 21% oxygen by volume. Substance Carbon Dioxide Water Oxygen Pentane 5 kilomoles of pentane (CsH12) are burned completely in pure oxygen under stoichiometric conditions with temperature and pressure being constantly maintained at standard conditions of 25°C and 105 Pa respectively. Calculate how much energy is available for external heating. Enthalpies of formation are available in Table 2 and you may take the chemical equation for the combustion of pentane to be C5H12 +80₂5 CO₂ + 6H₂0 Enthalpy of Formation [kJ.kmol ¹] -393,522 [5 marks] -241,827 0 -146,800 Table 2: Enthalpy values for question 2b. [8 marks]  Fig: 1