Mechanical Engineering Answers

A refrigerator unit working on Bell Coleman cycle takes air from cold chamber at -10 °C and compresses it from 1 bar to 6.5 bar with index of compression being 1.2. The compressed air is cooled to a temperature of 25 °C before it is expanded in the expander where the index of expansion is 1.35, determine,

a. COP

b. Quantity of air circulated per minute for production of 2000 kg of ice per day at 0 °C from water at 20 °C

c. Capacity of the plant in tons of refrigeration Assume, C₂ = 1 kJ/kg k for air.

An air refrigerator works between pressure limits of 1 bar and 4 bar. The temperature of the air entering the compressor is 15 °C and entering the expansion cylinder is 30 °C. The expansion follows the law PV^1.25= constant. The compression follows the law PV^1.35 = constant. Take for air, Cp = 1 kJ/kg k and Cv = 0.7 kJ/kg k. Find the following

a. COP of the refrigeration cycle

b. If the air circulation through the system is 25 kg/min, find the refrigeration capacity of the system

8.) The energy required to punch a square from 30mm thick plate is 20KJ. If the ultimate strength of plate is 450Mpa, determine the maximum sides of square that can be punch. (Please show the solution of answer)

Answer: S=24.69mm

6.)  The power required to shear a plate 60mm thick for 20sec is 8KW. If the ultimate strength of plate materials is 4oo Mpa, How wide should the plate be? (Please show the solution of answer)

Answer: b= 222.22mm

5.)  A plate 400mm wide and 0.03 mm thick with strength of 400Mpa is to shear. During shearing process a 1000mm mean diameter flywheel changes its speed from 220 to 200 rpm. Determine the weight of flywheel to be used. (Please show the solution of answer)

Answer: W=61.34KN

3.   During a punching process of 350 kg flywheel the speed varies 250 to 220 rpm with 1.2m mean diameter. Determine the kinetic energy needed. (Please show the solution of answer)

Answer: 9.74 kN-m    

2. Compute the maximum deflection of a 15 coils helical spring having a load of 80 kgs. The spring is a square and ground ends w/ modulus of elasticity in shear of 80 GPa, outside diameter of 100mm, wire diameter of 10mm. (Please show the solution of answer)

Answer: a. 74.375mm

3.) A machine costs P20,000 today. If inflation rate is 6% per year and interest is 10% per

year, what will be the appropriate future value of the machine, adjusted for inflation, in

five years?

 In a porter governor the mass of the central load is 18 kgand the mass of each ball is 2kg. the top arms 250 mm while the bottom arms are 300 mm long. The friction of the sleeve is 20 N. If the top arms make 45 deg with the axis of rotation in the equilibrium position, find the range of the speed of the governor in that position