Mechanical Engineering Answers

A heavy cylindrical mass is supported at the end of a close-coiled helical spring and is
located concentrically in a cylinder of oil as shown, with a small annular clearance
between the cylinder wall and mass. The mass has a value of 6 kg. When released
from the spring, the mass is observed to sink to the bottom of the cylinder at a steady
speed of 1.4 m/s. When secured to the spring, the spring is observed to extend 16 mm
when the mass was being immersed in the oil. The system is now caused to vibrate.
Determine the frequency of free response and the ratio of two successive amplitudes.
The specific gravity of the oil is 0.86 and that of the mass is 7.35.

A room A/C in a house operates with R-12 between 1.2368 bar and 13.672 bar. The vapour is dry and saturated at the compressor inlet. Assuming isentropic compression, determine the theoretical C.O.P of the plant is 80% of the theoretical, calculate the power required to run the compressor to obtain a refrigerating capacity of 1 TR. If the liquid is sub-cooled through 10oC after condensation, calculate the power required. The properties of R-12 are given below: Saturation Temperature oC Enthalpy, kJ/kg Entropy, kJ/kgK Saaturation pressure (bar) Liquid Vapour Liquid Vapour 1.2368 13.672 -25 13.33 176.48 0.0552 0.7126 55 90.28 207.95 0.3197 0.6774

Temperature (oC) Pressure(bar) Enthalpy(kJ/kg) Entropy(kJ/kgK) 64.86 13.672 220.6 0.7126 Assume specific heat of liquid to be 1.055 kJ/kgK

In a 15 TR ammonia refrigeration plant for cooling a large warehouse, the condensing temperature is 25oC and evaporating temperature -10oC. The refrigerant ammonia is sub-cooled by 5oC before passing through the throttle valve. The vapour leaving the evaporator is 0.97 dry. Find: 1. Coefficient of performance 2. Power required Saturation Temperature oC Enthalpy, kJ/kg Entropy, kJ/kgK Specific Heat, kJ/kgK Liquid Vapour Liquid Vapour Liquid Vapour 25 298.9 1465.84 1.1242 5.0391 4.6 2.8 -10 135.37 1433.05 0.5443 5.4770 - -

A chemical laboratory uses an air refrigeration cycle system operating between pressures of 4 bar and 16 bar. The air temperature after heat rejection to surrounding is 37oC and air temperature at exit of refrigerated lab is 7oC. The isentropic efficiencies of turbine and compressor are 0.85 and 0.8 respectively. Determine compressor and turbine work per TR; C.O.P; and power per TR. Take

Assume a large primary system that consist of a vessel containing warm water in the system with a temperature of 350,001k. An infinitesimal amount of its heat of 1050j is transferred to a secondary system consisting of a room air at a temperature of 350k. Consequently the water temperature drops to 349,999k. What is the entropy generation: A) If the system is cooled in air. B) If the heat removed from the primary system is used to run a cannot engine process and that rejected by the engine is transferred to the secondary system.

A restaurant food storage air conditioning working on air refrigeration cycle of 10 tonnes capacity works between 4 bar and 16 bar. The air leaves the cold chamber at 0oC and discharges air at 25oC to the expansion cylinder after air cooler. The expansion and compression cylinders are double acting. The mechanical efficiency of compressor and expander are 85% and 80% respectively. The compressor speed is 250 r.p.m and has a stroke of 250mm Determine: 1. C.O.P 2. Power required 3. Bore of compression and expansion cylinder (Assume isentropic compression and expansion as polytropic with n = 1.25)

An aircraft air conditioner works between the pressure limits of 1 bar and 5 bar. The temperature of the air entering the compressor from the cabin and expansion cylinder are 10oc and 25oC respectively. The expansion and compression follow the pv1.3=constant. Find the following: 1. The theoretical C.O.P of the refrigeration cycle: 2. If the load on the system assuming the actual C.O.P is 50% of the theoretical C.O.P 3. The stroke length and the piston diameter of single acting compressor running at 300 r.p.m and the volumetric efficiency is 85%. (Take L/d = 1.5 : cp = 1.005 kJ/kgK ; cv = 0.71 kJ/kgK )

A house initially at a temperature 310k during a hot summer day must be cooled to a temperature 294k while the ambient temperature is 310k. Obtain an expression for the minimum workdone required and determine the minimum work also required to cool a room containing the total area of 200 meter square with equivalent mass of 50 kilogram meter square of the living room.

A house initially at a temperature 310k during a hot summer day must be cooled to a temperature 294k while the ambient
temperature is 310k. Obtain an expression for the minimum workdone required and determine the minimum work also
required to cool a room containing the total area of 200 meter square with equivalent mass of 50 kilogram meter square of the
living room.

A house initially at a temperature 310k during a hot summer day must be cooled to a temperature 294k while the ambient temperature is 310k. Obtain an expression for the minimum workdone required and determine the minimum work also required to cool a room containing the total area of 200 meter square with equivalent mass of 50 kilogram meter square of the living room.