Welcome to Nikhil's world

ISRO 2019 Refrigeration and Air-Conditioning Questions, Answers and Explanation 1 . The highest value of thermal conductivity is expected for a) Solid ice b) Steam c) Water d) Superheated steam Answer c) Water Explanation As water is heated, much of the energy is used to bend the hydrogen bonds; a factor not available in the solid or gaseous phase. This extra energy causes the specific heat to be greater in liquid water. 4. Starting friction is low in which type of lubrication a) Hydrostatic lubrication b) Hydrodynamic lubrication c) Mixed (semi fluid) lubrication d) Boundary lubrication Answer a) Hydrostatic lubrication Explanation In hydrodynamic lubrication the outer surface of journal and inner surface of bearing always remain in contact. In hydrostatic lubrication when the bearing starts to move, the pump supplies oil at a pressure thereby creating a clearance between the journal and the bearing. This reduces the starting friction. 8. A circular...

ISRO 2018 Refrigeration and Air-Conditioning Questions, Answers and Explanation 1 . Carnot cycle consists of  a) Two constant pressure and two isentropic processes b) One constant isenthalpic, one constant volume and two constant pressure processes c) Two isothermal and two isentropic processes d) One constant pressure, one constant volume and two isothermal processes. Answer c) Two isothermal and two isentropic processes Explanation  [ Thermal Engineering ] The most efficient heat engine cycle is the Carnot Engine cycle and it is represented as a rectangle in T-S diagram Otto Cycle - 2 constant volume and 2 isentropic Diesel Cycle - 1 constant pressure, 1 constant volume and 2 isentropic 2. One reversible heat engine operates between 1600K and T 2 K and another reversible heat engine operates between T 2 K and 400K. If both engines have the same heat input and output, then the temperature T 2 is equal to a) 800K b) 1600K c) 1200K d) 6400K...

ISRO Mechanical Engineering Heat Transfer Questions, Answers and Explanation Conduction 2017.2.62.  The distribution of a temperature T, at a particular instant , across a large concrete wall, 1m thick, which is heated from one side is given by the equation T = 150-80x+16x 2 , where the distance x is in meters and T is in degree Celsius. Thermal conductivity of wall is 0.6W/mK, area of cross section is 10 m 2 . The heat accumulated in unit time at this instant in the concrete wall is a) 768J/sec b) 384J/sec c) 96J/sec d) 192J/sec Answer d) 192J/sec Explanation Heat accumulated = Heat conducted away - Heat conducted in Q = kA*[dT/dx] at x = 1 minus at at x = 0 = 0.6*10*(-80+32x) at x = 1 minus at x = 0 =6*32 = 192J/sec General 2017.2.29.  Which of the following is FALSE? a) Heat flow by conduction is directly proportional to the area and temperature gradient b) Heat flow by convection is directly proportional to the area and temperature differen...

ISRO 2015 Mechanical Engineering Questions, Answers and Explanation 11. Which of the following is applied to brittle materials? a) maximum principal stress theory b) maximum principal strain theory c) maximum strain energy theory d) maximum shear stress theory Answer a) maximum principal stress theory Explanation [ Strength of Materials ] Ductile Materials - Planes of maximum shear exist in the material at 45 o and the material begins to slide along these planes. Maximum shear stress theory/ Total strain energy theory can be used. Brittle Materials - When the normal stress in the material reaches the ultimate stress the material fails suddenly by fracture. Maximum principal stress theory can be used.

ISRO 2013 Mechanical Engineering Questions, Answers and Explanation 14 . The purpose of surge tank in a pipeline is to  a) smoothen the flow of water b) minimize friction loses in pipe c) prevent occurrence of hydraulic jump d) relieve pressure due to water hammer Answer d) relieve pressure due to water hammer Explanation [ Fluid Mechanics ] Surge tank is a small storage tank or reservoir required in the hydro power plants for regulating the water flow during load reduction and sudden increase in the load on the hydro generator (water flow transients in penstock) and thus reducing the pressure on the penstock. When the load on the generator is reduced suddenly (load throw-off), governor closes the turbine gates and thus create an increase in  pressure on the penstock. This may result in water " hammering effect" and may require pipe of extra ordinary strength this pressure, otherwise the penstock may burst. To avoid this positive water hammering pres...

ISRO 2014 Mechanical Engineering Questions, Answers and Explanation 18. Tension in the cable supporting a lift of weight 'W' and having an acceleration 'a' while going upward is (g is acceleration due to gravity) a) W(1+a/g) b) W(1-a/g) c) W(2+a/g) d) W(1+2a/g) Answer a) W(1+a/g) Explanation [ Engineering Mechanics ] Tension increases when the lift accelerate upwards and decreases when the lift accelerate downwards. Mass of the lift = W/g Increase in tension due to acceleration = mass of list * acceleration of lift = W/g*a Total tension = Tension due to gravity + Tension due to acceleration  = W + W/g*a = W(1+g/a) 2014. 80 . Which type of gear meshing should be employed to transmit torque to a linear force? a) Epicyclic gear b) Helical gear c) Bevel gear d) Rack and pinion Answer d) Rack and pinion Explanation [ Theory of Machines and Mechanical Vibrations ] Epicyclic gear trains have one or more axes of gears in motion. In all other gear ty...