Consider the evaporator section of an air-conditioning system (note: the evaporator may be considered as a shell and tube heat exchanger with refrigerant flowing through the tube and air flowing through the shell). air enters the evaporator at 32◦c and 1 bar with a volumetric flow rate of 50 m3/min and exits at 22◦c and 0.95 bar. refrigerant 134a at 5 bar with a quality of 20% enters the evaporator and leaves at 20◦c at the same pressure. assume steady state operation, negligible heat transfer at the outer surface of the heat exchanger, and negligible kinetic and potential energy effects. also, assume the air behaves as an ideal gas with constant specific heats. determine

An external consultant recommends that a plant installs a bank of capacitors for power factor correction. this will reduce the peak electrical demand charges by an average of 93 kw every month. the plant current pays $13 per kw in peak demand charges. the capacitor bank will include 223 kw of fixed capacitors, and 183 of variable capacitors. the fixed capacitors cost $59 per kw, and the variable capacitors will cost $65 per kw. the consultant charges 21% of the equipment costs to install the capacitors. because this project will reduce the demand for the electric utility, they are prepared to provide a one-time rebate of $42 per kw of reduced demand. what is the simple payback period for this project (in years)?