MULTIPLE CHOICE QUESTIONS ON REFRIGERATION AND AIR CONDITIONING

1-Which of the following refrigerant has lowest freezing temperature?

(A) Carbon dioxide

(B) Ammonia

(C) Freon-12

(D) Freon-22

(Ans: D)

2-The working fluid in Bell Coleman cycle is

(A) Freon-12

(B) Carbon dioxide

(C) Ammonia

(D) Air

(Ans: D)

3-In a vapour compression system, the compression of refrigerant follows the law

(A) PVr = C

(B) PV = C

(C) PVn = C

(D) None of the above

(Ans: C)

4-The dry bulb temperature lines of psychometric chart are

(A) Vertical

(B) Horizontal

(C) Inclined

(D) Curved

(Ans: A)

5-When the lower temperature is fixed, COP of a refrigerating machine can be improved by

(A) operating the machine at higher speeds

(B) operating the machine at lower speeds

(C) raising the higher temperature

(D) lowering the higher temperature

(Ans: D)

6-Evaporative air-cooler is used effectively when

(A) dry bulb temperature is very close to the wet bulb temperature

(B) dry bulb temperature is high and relative humidity is high

(C) dry bulb temperature is low and relative humidity is high

(D) dry bulb temperature is high and the relative humidity is low

(Ans: D)

7-Refrigerant Freon 12 belongs to

(A) methane family

(B) ethane family

(C) ketone family

(D) aldehyde family

(Ans: A)

8-Sometimes refrigerant plants use cooling towers. The water cooled in these towers is used

(A) for defrosting evaporator coils

(B) to cool compressor cylinder only

(C) to cool the evaporator coils

(D) to cool refrigerant in condenser

(Ans: D)

9-The statements concern Psychometric chart.

I-Constant relative humidity lines are uphill straight lines to the right

II-Constant wet bulb temperature lines are downhill straight lines to the right

III-Constant specific volume lines are downhill straight lines to the right

IV-Constant enthalpy lines are coincident with constant wet bulb temperature lines

Which of the statements are correct?

(A) II and II

(B) I and II

(C) I and III

(D) II and IV

(Ans: D)

10-In S.I. unit, one tonne of refrigeration is equal to

(A) 110 kJ/min

(B) 210 kJ/min

(C) 50 kJ/min

(D) non of the above

(Ans: B)

11-Subcooling occurs when the vapour

(A) has high latent heat

(B) removes sensible heat from refrigerant

(C) has low latent heat

(D) has high thermal conductivity

(Ans: B)

12-The refrigerant used in vapour absorption refrigerator is

(A) Freon-12

(B) Ammonia

(C) CO2

(D) Aqua-ammonia

(Ans: D)

13-In a window air conditioner, the expansion device used is

(A) Capillary tube

(B) Thermostatic expansion valve

(C) Automatic expansion valve

(D) Float valve

(Ans: A)

14-Formula for R134a refrigerant is

(A) CH Cl F2

(B) C2 Cl3 F3

(C) C2 Cl2 F4

(D) C2 H2 F4

(Ans: D)

LEARN HOW TO READ ENGINE OIL SPECIFICATIONS !!

You might have seen something like 20W-50 or 10w40 on engine oil bottles.

Lets check out its meaning !!

Your engines rotating parts are protected from heat and friction by a thin layer of oil. Understanding the viscosity ratings and detergents used in today's modern oils is critical to keeping your engine running. As an owner there is no more critical maintenance item than regular oil changes with the proper oil for your car or truck.

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. This is the best of both worlds and is accomplished by using special additives to increase viscosity with increase temperature.

In a 10w-40 for example the 10w bit (W = winter, not weight or watt or anything else for that matter) simply means that the oil must have a certain maximum viscosity/flow at low temperature. The lower the "W" number the better the oil's cold temperature/cold start performance.

The 40 in a 10w-40 simply means that the oil must fall within certain viscosity limits at 100°C. This is a fixed limit and all oils that end in 40 must achieve these limits. Once again the lower the number, the thinner the oil: a 30 oil is thinner than a 40 oil at 100°C etc. Your handbook will specify whether a 30, 40 or 50 etc is required.

For more clarification watch the video :

CHECK OUT THE NEED OF MULTIPLE CYLINDERS IN ENGINE INSTEAD OF A SINGLE BIG ONE OF SAME VOLUME

What is the need of multiple cylinders in engine instead of a single big one of same volume?

Suppose we have a Chevrolet Spark of 1 litre (998 cc to be exact!) displacement. It has a 4 cylinder engine. So let's see what if we replace it with a single cylinder engine.

Let's do some basic calculations to find out the bore and stroke of this hypothetical engine. Assuming square type of engine ( bore equals stroke) we get bore=stroke=10.9 cm as opposed to original stroke of approx 5.8 cm. ( Assuming stroke of 7.7 cm ) So that is quite a big stroke length! So now let's discuss a few things about this-

1. With this big stroke, we need longer crankshaft. Longer is the crankshaft lesser is the maximum RPM achieved by the engine. This hampers the power output of engine. Hence the single cylinder will never be able to produce the same power as that of multi cylinder for the same compression ratio. Although some might argue that this will fetch good low end torque, which is true.
2. Single cylinders are impossible to balance! They will produce vibrations which are difficult to damp. You will definitely not like your car vibrating like a Royal Enfield bullet. Although flywheels and anti vibration mounts will come to the rescue, but mounts ( not flywheels) require periodic maintenance.
3. You will need to redesign the clutch which was designed to handle smaller bursts of power than a huge single one! Hence the clutch needs to be bigger and stiffer to avoid slipping which will increase clutch pedal effort enormously and break drivers legs. ( Assuming rest remind same). Moreover the transmission gears needs to be reinforced to handle rough shifting. This is not at all good for a nice passenger car!!
4. Single cylinder engines are difficult to keep cool, since the coolant jacket is far from the centre of combustion chamber and piston centre, overheating is more probable.
5. You will be burning all the fuel in one cylinder only which was earlier burnt in four chambers. Complete combustion is difficult to achieve. Also higher in-cylinder temperatures will aggravate NOX formation. Your car is less likely to pass pollution checks unless you invest in expensive Cat-cons. Not at all good for a cheap passenger car.
6. With single cylinder engine your car will start sounding like a oversized Bullet with utterly no respect for refined exhaust note. No one will buy such sounding car.
7. If at all you plan to turbocharge your engine, it will not be recommended by turbo manufacturers for turbo and engine safety. Such huge single cylinder's exhaust putts are capable to destroy a turbines of perfectly matched turbo. Singles are definitely not turbo friendly.
8. Now at this point let's assume you successfully replace the engine overcoming all difficulties. Now there will be such engine parts which you have custom made eg- high Flow fuel injectors, fuel pumps, ECU, also including engine Mechanical parts such as big end bearings and small end bearings etc. But these parts are not even remotely available in any spare parts shop if in case you damage any. If Chevrolet makes such engine they will have to face a lot of difficulties in arranging spares for their angry customers.

CHECK OUT THE DIFFERENCE BETWEEN A GAS TURBINE, A STEAM TURBINE, A WATER TURBINE AND AN INTERNAL COMBUSTION ENGINE

What is the difference between a gas turbine, a steam turbine, a water turbine and an internal combustion engine?

Turbine:

Turbine is a class of turbo machinery used to convert the energy in a flowing fluid into mechanical energy by the use of rotor mechanisms. Turbines, in general, convert either thermal or kinetic energy of the fluid into work.

Steam Turbine:

• The steam turbine uses pressurized steam from a boiler as the working fluid.

• The super-heated steam entering the turbine loses its pressure (enthalpy) moving through the blades of the rotors, and the rotors move the shaft to which they are connected.
• Steam turbines deliver power at a smooth, constant rate, and the thermal efficiency of a steam turbine is higher than that of a reciprocating engine but lower than gas turbine engines due to higher operating temperatures of the gas turbines (Gas turbines ~1500°C and steam turbines ~550°C).
• In modern days, primary use of the steam turbines is for the electrical power generation, but at the early 20th century steam turbines was used as the power plant for ships and locomotive engines. As an exception, in some marine propulsion systems where the diesel engines are impractical, such as aircraft carriers and submarines, the steam engines are still used.

Gas Turbine:

• Gas turbine engine or simply a gas turbine is an internal combustion engine, using gases such as air as the working fluid.

• Gas turbine engine, unlike the steam turbine, consists of several key components; those are the compressor, combustion chamber, and turbine, which are assembled along a rotating shaft, to perform different tasks of an internal combustion engine.
• Gas turbines can be used to produce torque, thrust (which powers the military fighter aircraft), or both in combination (used in turboprop engines).
• Gas turbines are more versatile, because many fuels can be used and working fluid, which has to be fed continuously, is readily available everywhere (air). Steam turbines, on the other hand, require large amounts of water for the operation and tend to cause problems in lower temperatures due to icing.
• They are preferred over other engines (mainly reciprocating engines) due to their high power to weight ratio, less vibration, high operation speeds, and reliability.

Internal Combustion Engine:

• The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases (generated by exothermic reaction of a fuel with an oxidizer) acting directly to cause movement, for example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.

• This contrasts with external combustion engines such as steam engines which use the combustion process to heat a separate working fluid, typically water or steam, which then in turn does work, for example by pressing on a steam actuated piston.
• Internal combustion engines are seen mostly in transportation. Several other uses are for any portable situation where you need an non-electric motor. The largest application in this situation would be an Internal combustion engine driving an electric generator. That way, you can use standard electric tools driven by an internal combustion engine.
• The advantages is the portability and the disadvantage is the pollution that they put out. Not only the obvious, air pollution, but also the Noise pollution, Some are so loud, that people need hearing protection to prevent damage their ears.
• Most internal combustion engines waste about 36 percent of the energy in gasoline as heat lost to the cooling system and another 38 percent through the exhaust. The rest, about six percent, is lost to friction. Thus most gasoline fueled internal combustion engines, even when aided with turbochargers and stock efficiency aids, have a mechanical efficiency of about 20 percent.

Water turbine:

• A water turbine is a rotary engine that takes energy from moving water. Now they are mostly used for electric power generation.

• The type of water turbine or hydro-power selected for a project is based on the height of standing water (referred to as head) and the flow, or volume of water, at the site, and there are a number of different hydro-power turbine types available that are suited to different heads and flows.
• Here a generator is placed at the top of a shaft that connects to the water turbine. As the turbine catches the naturally moving water in its blade and rotates, the generator receives the necessary force and begins to generate electrical energy.
• Hydroelectric power generation is by far the most efficient method of large scale electric power generation as the conversion process captures kinetic energy and converts it directly into electric energy hence there is no inefficient intermediate thermodynamic or chemical processes and no heat losses.
• The conversion efficiency of a hydroelectric power plant can be as high as 95% for large installations while for smaller plants with output powers less than 5 MW may have efficiency between 80 and 85 % which are much higher than the above three mechanisms.

CHECK OUT WHY DIESEL ENGINES DO NOT REQUIRE SPARK PLUG AS OF PETROL ENGINE

Why do diesel internal combustion engines require no spark plug to ignite the fuel unlike petrol engines?

To know the reason, we should first understand the processes in both engines.

In petrol engine, air-fuel mixture is administrated into the cylinder. The compression ratio of petrol engines is lower than diesel engines, i.e, 6–10. So when the charge is compressed inside the cylinder , the temperature of the charge will be less than the auto ignition point of the petrol and hence will not ignite. So a spark is produced by the spark plug to ignite the charge.

In diesel engines, the compression ratio is much higher,i.e 16–20. 

In this engine, only air is administrated into the cylinder. When the air is compressed in the compression stroke, the temperature of the air will be very high. Now when the fuel is injected by the fuel injector under high pressure, the fuel mixes with air in the cylinder and since the temperature of air is sufficiently high, the fuel will ignite without any external aid.

MULTIPLE CHOICE QUESTIONS ON CUTTING TOOLS

1-The ascending order of evolution of materials used for making the cutting tools is

(A) bronze – stone – steel – iron

(B) iron – steel – bronze – stone

(C) stone – bronze – iron – steel

(D) bronze – stone – steel – iron

(Ans: C)

2-The materials are added to cutting tools to increase their properties. Match the following

1. Tungsten      a. Hardness
2. Carbon         b. Hot hardness
3. Vanadium     c. Wear resistance

The correct order is

(A) 1-b, 2-a, 3-c

(B) 1-c, 2-a, 3-b

(C) 1-b, 2-c, 3-a

(D) 1-a, 2-b, 3-c

(Ans: A)

3-Which of the following is second hardest substance known?

(A) Ceramics

(B) Cermets

(C) Cubic Boron Nitride (CBN)

(D) Diamond

(Ans: C)

4-Which of the following tools are generally manufactured by Powder metallurgy?

(A) Low carbon steel

(B) Abrasives

(C) High carbon steel

(D) Cemented carbides

(Ans: D)

5-Which of the following is hardest known material?

(A) Cemented carbide

(B) Ceramics

(C) Cubic boron nitride (CBN)

(D) Diamond

(Ans: D)

6-Corrundum is a/an

(A) Diamond

(B) Abrasive

(C) Ceramic

(D) None of the above

(Ans: B)

7-The cutting tool wears due to

(A) Edge wear

(B) Crater wear

(C) Flank wear

(D) All of the above

(Ans: D)

8-The built up edge in cutting tools can be eliminated by

(A) Fast cutting speed

(B) Higher rake angles

(C) High pressure cutting fluid

(D) All of the above

(Ans: D)

9-The cutting speed of High speed steels is ___ times faster than Carbon steel

(A) 2

(B) 4

(C) 6

(D) 8

(Ans: B)

10-Which of the following cutting tool has highest hot hardness?

(A) Ceramics

(B) Cast alloys

(C) High speed steels

(D) Carbon tool steel

(Ans: A)

11-Which of the following cutting conditions greatly affects the tool wear?

(A) Cutting speed

(B) Feed

(C) Depth of cut

(D) None of the above

(Ans: A)

12-Which of the following is not a constituent of High speed steel?

(A) V

(B) Cr

(C) W

(D) Ni

(Ans: D)

13-In a single point turning operation with a cemented carbide and steel combination having a Taylor exponent of 0.25, if the cutting speed is halved, then the tool life will become

(A) Half

(B) Two times

(C) Eight times

(D) Sixteen times

(Ans: D)

14-A drill bit of 20mm diameter rotating at 500 rpm with a feed rate of 0.2 mm/revolution is used to drill a through hole in Mild Steel plate of 20mm thickness. The depth of cut in this drilling operation is

(A) 100 mm

(B) 20 mm

(C) 10 mm

(D) 0.2 mm

(Ans: C)

15-The tool life increases with the

(A) Increase in side cutting edge angle

(B) Decrease in side rake angle

(C) Decrease in nose radius

(D) Decrease in back rake angle

(Ans: A)

 16-Which one of the following grinding wheels (with grade, grit and bond) is suitable for cutter grinding?

(A) K 60 vitrified

(B) K 320 vitrified

(C) T 60 resinoid

(D) T 320 resinoid

(Ans: A)