UPSSSC JE Mechanical Paper 2 Mock Test - 6 - Mechanical Engineering MCQ

And W = Q_H - QC

Q_C = Q_H - W = 600 - 150 = 450kcal

An isobaric process is a thermodynamic process in which the pressure remains constant. This is usually obtained by allowing the volume to expand or contract in such a way as to neutralize any pressure changes that would be caused by heat transfer.

Young's modulus shows the rigidity of the material. when the temperature increases, the material starts to become soft. Therefore elasticity decreases with rise in temperature.

A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water boils at 100 °C (212 °F) at sea level, but at 93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) altitude. For a given pressure, different liquids will boil at different temperatures.

In a bending beam, a point is known as a point of contra flexure if it is a location at which no bending occurs. In a bending moment diagram, it is the point at which the bending moment curve intersects with the zero line. In other words, where the bending moment changes its sign from negative to positive or vice versa. It occurs in the overhanging beam.

1. Ammonia: It is the primary refrigerant that takes heat from brine. This ammonia changes phase while moving in the circuit.

2. Brine: It is the secondary refrigerant that takes heat from the water and produces ice.

There are three main circuits of working medium in ice plant:

Refrigeration circuit: Ammonia as working medium which actually produces the cold by changes its phase at a single degree of freedom with a different location

Cooling water circuit: Cooling water as a working medium to remove the heat of the condenser

Brine circuit: Brine solution as a working medium which transfers the cold from ammonia to water-filled cans where ice is to be formed.

Reaction Turbine: If at the inlet of the turbine, the water possesses kinetic energy and pressure energy, the turbine is known as a reaction turbine. e.g., e Francis and Kaplan turbine.

Tangential flow turbines: In this type of turbine, the water strikes the runner in the tangent direction to the wheel. Example: Pelton wheel turbine

Radial flow turbines: In this type of turbine, the water strikes in the radial direction. accordingly, it is further classified as

• Inward flow turbine: The flow is inward from periphery to the centre (centripetal type); Example: old Francis turbine

• Outward flow turbine: The flow is outward from the centre to periphery (centrifugal type); Example: Fourneyron turbine

Axial flow turbine: The flow of water is in the direction parallel to the shaft axis. Example: Kaplan turbine and propeller turbine

∴ Francis turbine is a radial inward flowing reaction turbine.

The compressor operates on a two-stroke cycle:

Stroke 1 (a – c): The piston withdraws, causing the air in the clearance volume to expand, and when the pressure in the cylinder falls below atmospheric pressure (at b), the inlet valve opens, and the air is drawn into the cylinder for the remainder of the stroke.

Stroke 2 (c – a): The piston moves inwards, compressing the air in the cylinder, and the inlet valve closes when the cylinder pressure reaches atmospheric pressure.

Further compression follows as the piston moves toward the top of its stroke until, when the pressure in the cylinder is more than that in the receiver, the delivery valve opens. The air is delivered to the receiver for the remainder of the stroke.

Effect of suction and discharge side pressure drops on P-V diagram of a reciprocating compressor.

Typical indicator card

Total energy line (T.E.L.) – Line representing the sum of pressure head, datum head, and velocity head.

∴ T.E.L. – H.G.L. = velocity head

P = 2πNT/60

In M.K.S units, horsepower transmitted by the shaft,

P = 2πNT/4500

Out of the given 4 options, only one option is the correct formula for power transmitted.

In the Power screw, the torque Mt required to lower the load is given by

M_t = Wd_m/2 tan (ϕ−α) where, W = load on the screw in N, d_m = the mean diameter of the screw-in m,

ϕ = friction angle and α = helix angle

Case 1. when ϕ ≥ α

tan (ϕ - α ) ≥ 0, thus M_t ≥ 0.

i.e., positive torque is required to lower the load. Thus the load will not turn the screw and will not descend on its own unless an effort is applied.

Such cases of screws are known as 'Self-locking screws.’ And the screw will hold the hold without any application of the brake.

Also, as ϕ ≥ α

tan ϕ ≥ tan α

Case 2. when ϕ < />

tan (ϕ - α ) < 0,="" thus="" />_t < />

i.e., negative torque is required to lower the load. The load will turn down the screw and will descend on its own unless a restoring torque is required to hold the load.

Such cases of screws are known as 'overhauling of the screw' or back drawing of the screw.

The velocity of free vortex flow ∝ 1/r

∴ In a free vortex, velocity decreases with radius.

Magnesium is a powerful inoculant in cast iron. When added in concentrations exceeding 0.04%, it produces a spheroidal form of graphite that improves the iron's strength and ductility. Magnesium is an abundant metal with a price roughly comparable to that of aluminum, albeit usually higher

A gas-turbine power plant operates on the simple Brayton cycle between the pressure limits of 100 and 1600 KPa. The working fluid is a mixture of air with 20% of carbon monoxide (CO). The mixture enters the compressor at 40^oC at a rate of 850 m3/min and leaves the turbine at 650^oC.

Surface tension is due to cohesion between liquid particles at the surface, whereas capillarity is due to both cohesion and adhesion. The property of cohesion enables a liquid to resist tensile stress, while adhesion enables it to stick to another body.

SI engine controls include Air/fuel ratio control, spark timing control, idle speed control. After treatment, system controls include thermal management to ensure rapid warm-up and high emission reduction efficiency; and air/fuel ratio control to ensure maximum conversion of the TWC.

The flame does not leap out during the opening of the inspection door because there is negative pressure in the combustion area. Negative pressure is achieved in balanced draft boilers by using forced draft fans to force air into the boiler (pressuring it) and Induced draft fans to remove air from the boilers to create negative pressure.

The solar energy received by the earth is approximately 1.4 kW/m². It is known as solar constant or Solar Irradiance.

Lubrication Principles:

If one surface is moving and inclined to the other, the viscous drag of the oil tends to draw the lubricant into the space between the surfaces and builds up a wedge. This develops an oil film; the pitch circle diameter usually specifies the size of the gear pressure that can support a load.

If the two surfaces were parallel or if they did not have relative motion, the oil–film pressure would not get developed, and a developed and load would not be supported by the lubricant.

There are three lubrication regions: Hydrodynamic lubrication, Boundary lubrication, and Mixed – film lubrication.

Boundary Lubrication:

With a lower relative velocity of the moving surfaces, adequate pressure cannot be developed to support the load by the oil film. At this point in time, boundary lubrication will exist. This will occur especially during starting and stopping of an engine.

As the speed increases, a sufficient film pressure is developed, and the load is supported by the oil film, which will shift to the hydrodynamic lubrication.

Hydrodynamic Lubrication:

If a film of oil completely separates the sliding surfaces, there is no metal–to–metal contact, and the wear on the surfaces is a minimum. This type of lubrication is developed when there is a relative motion between the two inclined surfaces separated by an oil film.

The thermite welding railroad method is especially suitable for broken steel rail repair, on-site joint welding on railway frog section of seamless railway line ball, and heavy transportation tasks.