Entropy

When work is in transit, orderly motion of molecules is involved. Work is thus a high grade energy.

But when work is converted into heat, the order which was seen earlier in the molecules, disappears. Just like that. The molecules now move in a random and completely disorderly fashion. Thus, heat is a low grade energy.

When heat flow or transfer occurs, the molecular chaos increases. But this is not seen in the case of work flow.

The tendency of the universe (which is an isolated system) is always to reach a state of greater disorder, or in other words entropy. (Second law)

The entropy of a system is a measure of the degree of molecular disorder existing in the system

The above also indicates that even though energy is conserved quantity-wise (from first law ), energy gets degraded quality-wise (second law). This is the law of degradation of energy.

(In case of a perfectly crystalline solid at absolute zero temperature, its entropy is zero - Third law)



Source : "Engineering Thermodynamics" - P K Nag
Image source : boundless.com

Mechanical engineering interview

Q) What is mechanism?

Q) Zeroth Law of Thermodynamics

Q) What is DTS-i engine?

Mechanism and Machine

Mechanism:

A kinematic chain is an assembly of links ( or elements )  where links have relative motions and the motion of each link relative to each other is definite. A mechanism is obtained when one of the links in a kinematic chain is fixed.

In other words,

 A mechanism is a combination of rigid or restraining bodies so shaped and connected that they move upon each other with a definite relative motion.

Eg : Slider-crank mechanisms , gear mechanisms


Machine:

When two or more mechanisms are arranged in a special way to obtain a required motion and transfer of energy, it is called a machine.

Eg: IC engine, lathe

(A machine is anything that reduces human effort.. Aasaan bhasha me.. :D )

Zeroth Law of Thermodynamics

Zeroth law :

Consider three systems A, B and C.

Suppose A and B happened to be in thermal equilibrium.

Also, B and C are in thermal equilibrium.

Then, the above conditions imply that A and C are in thermal equilibrium..!!

If two systems are both in thermal equilibrium with a third then they are in thermal equilibrium with each other.

Why is zeroth law important?

It is because, temperature measuring instruments work based on zeroth law. For eg, when a thermometer is in contact with your body, heat flow occurs until both systems are in thermal equillibrium. At this point, we know, the temperature indicated by the thermometer is same as that of your body..!! As simple as that..!!

(In case of mercury thermometer, change in volume of mercury is the thermometric property)

Zeroth law was introduced later than other laws. But it was much more basic than the other laws, and hence the term "Zeroth".

DTS-i engine

DTS-i stands for “Digital Twin Spark Ignition”

In a 4 stroke petrol engine (‘petrol’ implies spark ignition), if only a single spark plug is incorporated, then air-fuel mixture will not burn completely. Hence power and efficiency are low.

This technology incorporates two spark plugs which helps in faster and efficient burning of air-fuel mixture (improved mileage). And more power..!!

The bike has a longer life, and is resistant to breakdowns and temperature fluctuations

(Since microchip is used for spark timing, the term “Digital”)

DTS-Si, DTS-Fi and DTS-I Triple spark engine are a further advanced models of DTS-i.

Watch the following video of DTS-i Triple spark engine: