Mechanical Engineering Quiz # 9

Thermal diffusivity is a

All of these

Physical property of a substance

Function of temperature

Dimensionless parameter

A pressure gauge on the discharge side of a refrigerant compressor reads too high. The reasons will be

All of these

Lack of cooling water

Water temperature being high

Dirty condenser surface

The difference between dry bulb temperature and wet bulb temperature, is called

Wet bulb depression

Dew point depression

Degree of saturation

Dry bulb depression

The relative humidity is defined as

The mass of water vapour present in 1 kg of dry air

The ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

The mass of water vapour present in 1 m3 of dry air

The ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.

During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

A heat pump working on a reversed Carnot cycle has a C.O.P. of 5. It works as a refrigerator taking 1 kW of work input. The refrigerating effect will be

2 KW

3 kW

1 kW

4 kW

In an impulse turbine, the jet of water impinges on the bucket with a low velocity and after flowing over the vanes, leaves with a high velocity.

True

False

A Pelton wheel develops 1750 kW under a head of 100 metres while running at 200 r.p.m. and discharging 2500 litres of water per second. The unit power of the wheel is

0.25 kW

0.75 kW

3.75 kW

1.75 kW

When the speed of the pump increases, its net positive suction head (NPSH) requirement decreases.

Agree

Disagree

The specific speed from 160 to 500 r.p.m. of a centrifugal pump indicates that the pump is

Slow speed with radial flow at outlet

High speed with radial flow at outlet

Medium speed with radial flow at outlet

High speed with axial flow at outlet

If the ratio of all the corresponding linear dimensions are equal, then the model and the prototype are said to have

Dynamic similarity

Kinematic similarity

None of these

Geometric similarity

The maximum number of jets, generally, employed in an impulse turbine without jet interference are

Eight

Four

Two

Six

In a reciprocating pump, air vessels are fitted to the suction pipe and delivery pipe close to the cylinder of the pump.

False

True

Which of the following statement is wrong?

The reaction turbines are used for low head and high discharge.

An impulse turbine is generally fitted slightly above the tail race.

The angle of taper on draft tube is less than 8°.

A Francis turbine is an impulse turbine.

Slip of a reciprocating pump is negative, when

Delivery pipe is long and pump is running at high speeds

Suction pipe is short and pump is running at low speeds

Suction pipe is short and delivery pipe is long and the pump is running at low speeds

Suction pipe is long and delivery pipe is short and the pump is running at high speeds

The speed of a turbine runner is

Directly proportional to H3/2

Inversely proportional to H1/2

Directly proportional to H1/2

Inversely proportional to H3/2

Manometric head, in case of a centrifugal pump, is equal to

Workdone per kN of water - Losses within the impeller

All of these

Energy per kN at outlet of impeller - Energy per kN at inlet of impeller

Suction lift + Loss of head in suction pipe due to friction + Delivery lift + Loss of head in delivery pipe due to friction + Velocity head in the delivery pipe

A Francis turbine is used when the available head of water is

25 m to 250 m

Above 250 m

None of these

0 to 25 m

In the casing of a centrifugal pump, the kinetic energy of the water is converted into pressure energy before the water leaves the casing.

False

True

For centrifugal pump impeller, the maximum value of the vane exit angle is

10° to 15°

25° to 30°

15° to 20°

20° to 25°

The efficiency of a reaction turbine for a given head __________ with the increase in speed.

Decreases

Increases

A reciprocating pump is also called a __________ displacement pump.

Positive

Negative

The static head of a centrifugal pump is equal to the __________ of suction head and delivery head.

Product

SUM

Difference

Power required to drive a centrifugal pump is directly proportional to __________ of its impeller.

Square of diameter

Fourth power of diameter

Diameter

Cube of diameter

The overall efficiency for a Pelton wheel lies between

0.50 to 0.65

0.75 to 0.85

0.65 to 0.75

0.85 to 0.90

Discharge (Q) of a centrifugal pump is given by (where D = Diameter of impeller at inlet, b = Width of impeller at inlet, and Vf = Velocity of flow at inlet)

Q = π.b.Vf

Q = π.D.Vf

Q = π.D.b.Vf

Q = D.b.Vf

The velocity corresponding to Reynold number of 2800, is called

Higher critical velocity

Lower critical velocity

Sub-sonic velocity

Super-sonic velocity

Viscous force is the __________ of shear stress due to viscosity and cross-sectionar area of flow.

Ratio

Product

SUM

Different

Which of the following statement is wrong?

The length of divergent portion in a venturimeter is equal to the convergent portion.

A flow whose streamline is represented by a curve, is called two dimensional flow.

A pitot tube is used to measure the velocity of flow at the required point in a pipe.

The total energy of a liquid particle is the sum of potential energy, kinetic energy and pressure energy.

A water tank contains 1.3 m deep water. The pressure exerted by the water per metre length of the tank is

9.28 kN

28.9 kN

2.89 kN

8.29 kN

Quiz:	Mechanical Engineering Quiz # 9
Subject:	Heat Transfer Refrigeration And Air Conditioning
Total Questions:	1465 MCQs
Time:	1465 Minutes