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%.

Amass of m 1.5 kg of steam is contained in a closed rigid container. initially the pressure and temperature of the steam are: p 1.5 mpa and t 240°c (superheated state), respectively. then the temperature drops to t2= 100°c as the result of heat transfer to the surroundings. determine: a) quality of the steam at the end of the process, b) heat transfer with the surroundings. for: p1.5 mpa and t 240°c: enthalpy of superheated vapour is 2900 kj/kg, specific volume of superheated vapour is 0. 1483 m/kg, while for t 100°c: enthalpy of saturated liquid water is 419kj/kg, specific volume of saturated liquid water is 0.001043m/kg, enthalpy of saturated vapour is 2676 kj/kg, specific volume of saturated vapour is 1.672 m/kg and pressure is 0.1 mpa.

When using the ohmmeter function of a digital multimeter, the leads are placed in what position relative to the component being tested? a. parallel b. control c. series d. line

Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.