A refrigeration plant operates in Pretoria on refrigerant R134a at an evaporator pressure of 105kPa (gauge) and a condensing pressure of 920 kPa (gauge). There is a sub-cooling of 3K with a superheat of the gas entering the compressor of 8K. The compressor is a four-cylinder reciprocating compressor with a bore of 67mm and a stroke of 57mm with an estimated capacity of 35kW. The compressor is directly coupled to an electric motor running at 1470rev/min and a power consumption of 19,5 kW. Calculate: 1. The clearance volume efficiency if the compressor clearance is 3,6% 2. The actual volumetric efficiency 3. The compression efficiency when the mechanical efficiency is 85% and the motor efficiency 90%.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?