LAB VIVA/INTERVIEW QUESTIONS OF THERMODYNAMICS !!

LAB VIVA/INTERVIEW QUESTIONS OF THERMODYNAMICS :

1. A quantity of matter of fixed mass and identity which is bounded by a closed surface. 

2. An enclosure which permits thermal interaction. 

3. An enclosure which prevents thermal interaction.

4. A system in which all the measurable variables have the same value as they had inside an enclosure after a long time, irrespective of the interaction that may have taken place. 

5. A region of interest, that is involved in the analysis.

 6. Any change of state occurring in a system. 

7. A region in space or control volume or quantity of matter upon which attention is focussed for study. 

8. A change of state which occurs while the system is adiabatically enclosed. 

9. Any observable characteristic of the system. 

10. A type of reversible process, characterized by the fact that the system is at each instant arbitrarily close to equilibrium. 

11. A study of the transfer and conversion of energy. 

12. If a thermodynamic system undergoes an adiabatic process, the net amount of work performed by it depends only on its initial and final states, and not on the sequence of intermediate state or path. 

13. Depends solely upon the state of the system and not upon how that state was reached. 

14. A change in the state of a system which occurs without any work being done. 

15. It is impossible to construct a device which, working in a complete cycle, will produce no other effect than the transfer of a quantity of heat from a cooler to a hotter body. 

16. Two states of two systems characterized by an absence of heat flow even when there is no adiabatic wall between them.

17. The loci of points corresponding to states of the same temperature.

18. A system going through some process whose initial and final states are the same. 

19. A system which exchanges heat and work with its surroundings while operating in a cyclic process. 

20. A hypothetical machine whose operation would violate the laws of thermodynamics.

ANSWERS:

1. system 2. diathermic 3. adiabatic 4. equilibrium state 5. system 6. process 7. thermodynamic system 8. adiabatic process 9. property 10. quasistatic 11. thermodynamics 12. first law of thermodynamics 13. property 14. free motion 15. Clausius statement 16. thermal equilibrium 17. isotherms 18. cycle 19. thermodynamic machine 20. perpetual-motion machine

AFTER-MARKET ABS !! ARE THEY WORTH ??

ABS which simply means Anti-Locking Braking System prevents the rear or the front wheel or both in some case from locking up which if fails, ends in a disaster.

In technical terms,Anti-locking Braking System, is a complex technology in a motorcycle or a car that can help reduce the speed or stop the vehicle in an emergency situation without locking either of the two wheels or even all the four in case of cars. This is achieved by using speed sensors that is attached to the wheels that continuously monitor the wheel rotation speed and sends the data to the braking ECU which is in turn connected to the hydraulic unit that adjusts the hydraulic pressure of the brake fluid inside accordingly. In an emergency braking situation which is otherwise panic braking, one can be confident that the wheels wouldn’t lock up giving the rider a taste of the tarmac.

Can ABS System Purchased separately (After-market ABS)?

The answer is YES. But there are certain hitches in that too! You’ll have to figure out a way to calibrate the aftermarket ABS to your specific car/motorcycle. You must also understand that automakers spend thousands of hours testing and calibrating a car/motorcycle fitted with ABS, in order to fine-tune its working in real-world conditions. Obviously, this isn’t something that’s feasible for most owners. This is also a reason why after-market ABS systems, though available, are unpopular. Also after-market ABS are costly for example, Bosch makes an aftermarket ABS that costs a whopping Rs. 6 lakhs! 

It’s better to buy a motorcycle that has a factory fitted ABS system which would have been tested rigorously by the motorcycle manufacturer as an integrated part of the motorcycle itself.

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WHY MODERN ENGINES USE FORGED PISTON? CHECK OUT THE ANSWER !!

Now-a-days forged pistons are used by most of high end vehicles.The main characteristic that makes forged pistons excel in high performance applications is strength and durability. 

The high silicon content of cast pistons makes them brittle compared to forged pistons. Silicon gives the metal lubricity and is mixed in the alloy to limit heat expansion. This is primarily the reason why cast pistons require careful handling. 

Mild shock applied to it may cause the material to break. The process of forging compresses the molecules inside the alloy, which results in a denser surface area compared to a cast piston.

The Difference:

The difference between a normal or cast piston and a forged piston is the manufacturing technique. Traditional cast pistons are considered good enough by most engine manufactures when it comes to stock setups, and suffer no drawback in terms of compression and service life. The cast piston is most common on all mass-produced engines, because the casting process of making this type of piston presents a low cost opportunity to the manufacturer.

Forged pistons employ a single lump of billet alloy which is stamped by the use of a die. The shape of the die determines the size and shape of the piston.Forged pistons are also easy to manufacture as there is no need for big, heavy and expensive casting equipment as employed in the manufacture of cast pistons.

How Air Bags Work ?

Air Bags:-

An airbag is a type of vehicle safety device and is an occupant restraint system. The airbag module is designed to inflate extremely rapidly then quickly deflate during a collision or impact with a surface or a rapid sudden deceleration. 

The purpose of the airbag is to provide the occupants a soft cushioning and restraint during a crash event to prevent any impact or impact-caused injuries between the flailing occupant and the interior of the vehicle. The airbag provides an energy absorbing surface between the vehicle's occupant and a steering wheel, instrumental panel, A-B-C- structural body frame pillars, headliner and windshield/windscreen.

There are three parts to an airbag that help to accomplish this feature:

>The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.

>The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is flipped when there is a mass shift that closes an electrical contact, telling the sensors that a crash has occurred. The sensors receive information from an accelerometer built into a microchip.

>The airbag's inflation system reacts sodium azide (NaN3) with potassium nitrate (KNO3) to produce nitrogen gas. Hot blasts of the nitrogen inflate the airbag.

LAMINAR FLOW Vs.TURBULENT FLOW : DIFFERENCE EXPLAINED !!!

In fluid flows, there are two distinct fluid behaviors experimentally observed. These behaviors were first observed by Sir Osborne Reynolds.We will discuss this in detail in this article.

Laminar Flow

1. The fluid flow in which the adjacent layers of the fluid do not mix with each other and moves parallel to each other, is called laminar flow.
2. In the laminar flow, the fluid layer moves in straight line.
3. The laminar flow always occurs when the fluid flow with low velocity and in small diameter pipes.
4. The fluid flow having Reynolds number less than 2000 is called laminar flow.
5. The fluid flow is very orderly i.e. there is no mixing of adjacent layers of the fluid and they move parallel to each other and also with the walls of the pipe.
6. Shear stress in laminar flow depends only on the viscosity of the fluid and independent of the density.

Turbulent Flow

1. The fluid flow in which the adjacent layers of the fluid cross each other and do not move parallel to each other, is called turbulent flow.
2. In turbulent flow the fluid layers do not moves in straight line. They move randomly in zigzag manner.
3. The turbulent flow occurs when the velocity of the fluid is high and it flows through larger diameter pipes.
4. The fluid flow having Reynolds number greater than 4000 is called turbulent flow.
5. The fluid does not flow in definite order. There is a mixing of different layers and they do not move parallel to each other but crosses each other.
6. The shear stress in turbulent flow depends upon its density.

The difference is summarized in table below.

Hope,you got a clear picture of the difference between the two types of flow.Share this article with your friends.

PUMP Vs. COMPRESSOR : DIFFERENCE EXPLAINED !!!

Pump and compressor both are hydraulic machines used to increase the energy of fluid. Both of these devices used in industries and for domestic work. Pump is a device which is used to move the fluid (water, liquid and gases) and increase its elevation. It is mostly used to supply fluid from low elevation to high elevation. A compressor is a device which is a mechanical device just like pump but it increases the potential energy of fluid by compressing it in a closed container.

The main difference between pump and compressor is that the pump is used to increase kinetic energy of fluid which further increases the elevation or pressure energy of it.  It moves the fluid from one place to another. But the compressor is mostly used to increase the potential energy (pressure energy) of fluid by pressuring it into a container. It is used to compress the fluid which increases its density and pressure. There are many other differences which are described below.

Difference between pump and compressor:

FILLET AND CHAMFER : WHY AND WHEN TO USE IT ??

Fillet is a round corner whereas chamfer is a slant face created at the corner. 

Even though both perform same function selection of chamfer or fillet depends on how the component is manufactured.We will discuss why and when they are used while creating parts in this article.

Comparison Between Chamfer and Fillet for External Edges :

Whether we choose to select a chamfer edge, or a fillet edge, it will often depend on factors of project such as budget and time constraints. The chart below compares some of these considerations:

When to use them ?

Fillets give a part better flow and less resistance. Using a fillet also eliminates any sharp edges that can be easily damaged, or that could cause injury when the part is handled. This means there is less risk of failing an inspection for having a burr or sharp edge. Fillets also have lower stress concentration factors, meaning that they distribute stress over a broader area. This makes filleted parts more durable, and able to withstand larger loads.

Chamfers are more forgiving when designing to fit mating parts, but overall it appears that designs using fillets are preferred by senior management, industrial designers and many others.

The main points that help in deciding to choose a fillet or chamfer are the following:

1.When done manually one of the main factors that come in deciding which to apply is the machining time. A chamfer requires less machining time that a fillet radius.

2.When done on CNC both chamfer and fillet require the same time as only a tool change is required.

3.For fillets different radii of tools has to be stocked to create different radii, but a single tool can be used for creating different chamfers.

4.Higher machining time required translates into cost. Thus chamfers are less costly compared to fillets.

5.Industrial designers tend to prefer fillets compared to chamfers as these are considered to be visually pleasing.

6.One of the other reasons is that protective coating like paint are more uniformly distributed over a fillet compared to chamfer. Thickness of coating is reduced on sharp corners of chamfers so coating is lost first on these spots. Fillets have no such issues due to uniform distribution of coating.

7.Since non uniform distribution of coating can lead to accelerated rusting this may be a disadvantage.

8.Fillet gives better stress flow (less resistance) compared to chamfers. Fillets generally give a lower stress concentration factor than chamfers .

9. Chamfers are more forgiving when fitting mating parts. i.e. even if there are inaccuracies in a chamfer mating parts might fit together. But if the radius of fillet changes it will be difficult to fit the mating parts.