Heat and mass transfer (Radiation mode)

Radiation :-


 Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region.

 Radiation emitted by a body is a consequence of thermal agitation of its composing molecules. Radiation heat transfer can be described by a reference to the so-called 'black body'.

The Black Body

A black body is defined as a body that absorbs all radiation that falls on its surface. 
Actual black bodies don't exist in nature - though its characteristics are approximated by a hole in a box filled with highly absorptive material.
 The emission spectrum of such a black body was first fully described by Max Planck.
A black body is a hypothetic body that completely absorbs all wavelengths of thermal radiation incident on it. Such bodies do not reflect light, and therefore appear black if their temperatures are low enough so as not to be self-luminous. All blackbodies heated to a given temperature emit thermal radiation.
The radiation energy per unit time from a blackbody is proportional to the fourth power of the absolute temperature and can be expressed with  

Stefan-Boltzmann Law as

q = σ T⁴ A         (1)

where
q = heat transfer per unit time (W)
σ = 5.6703 10^-8 (W/m²K⁴) - The Stefan-Boltzmann Constant
T = absolute temperature Kelvin (K)
A = area of the emitting body (m²)

The Stefan-Boltzmann Constant in Imperial Units

σ = 5.6703 10^-8 (W/m²K⁴)
    = 0.1714 10^-8 ( Btu/(h ft^{2 o}R⁴) )
    =  0.119 10^-10 ( Btu/(h in^{2 o}R⁴) )

Knocking in I.c Engine

Definition:-

knocking,  in an internal-combustion engine, sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder.


In a properly functioning engine, the charge burns with the flame front progressing smoothly from the point of ignition across the combustion chamber. However, at high compression ratios, depending on the composition of the fuel, some of the charge may spontaneously ignite ahead of the flame front and burn in an uncontrolled manner, producing intense high-frequency pressure waves. These pressure waves force parts of the engine to vibrate, which produces an audible knock.

Causes of knocking effect on engine:-

Knocking can cause overheating of the spark-plug points, erosion of the combustion chamber surface, and rough, inefficient operation. It can be avoided by adjusting certain variables of engine design and operation, such as compression ratio and burning time; but the most common method is to burn gasoline of higher octane number.

Rise: SIMPLE CARBURETOR : -The simple carburetor mainly...

Rise: SIMPLE CARBURETOR : -
The simple carburetor mainly...: SIMPLE CARBURETOR : - The simple carburetor mainly consist a float chamber,fuel discharge nozzle , a venturi, a throttle valve and a c...

SIMPLE CARBURETOR : -

The simple carburetor mainly consist a float chamber,fuel discharge nozzle , a venturi, a throttle valve and a choke.

A carburetor basically consists of an open pipe through which the air passes into the inlet manifold of the engine. The pipe is in the form of a venturi: it narrows in section and then widens again, causing the airflow to increase in speed in the narrowest part. Below the venturi is a butterfly valve called the throttle valve — a rotating disc that can be turned end-on to the airflow, so as to hardly restrict the flow at all, or can be rotated so that it (almost) completely blocks the flow of air. This valve controls the flow of air through the carburetor throat and thus the quantity of air/fuel mixture the system will deliver, thereby regulating engine power and speed. The throttle is connected, usually through a cable or a mechanical linkage of rods and joints or rarely by pneumatic link, to the accelerator pedal on a car or the equivalent control on other vehicles or equipment.
Fuel is introduced into the air stream through small holes at the narrowest part of the venturi and at other places where pressure will be lowered when not running on full throttle. Fuel flow is adjusted by means of precisely calibrated orifices, referred to as jets, in the fuel path.


As the throttle is opened up slightly from the fully closed position, the throttle plate uncovers additional fuel delivery holes behind the throttle plate where there is a low pressure area created by the throttle plate blocking air flow; these allow more fuel to flow as well as compensating for the reduced vacuum that occurs when the throttle is opened, thus smoothing the transition to metering fuel flow through the regular open throttle circuit.

Application of Gyroscope on bicycle>>>

1) Bicycle wheel:-
The angular momentum of the turning bicycle wheels makes them act like gyroscopes to help stabilize the bicycle. This gyroscopic action also helps to turn the bicycle.

 Having pointed to the gyroscopic nature of the bicycle wheel, it should be pointed out that experiments indicate that the gyroscopic stability arising from the wheels is not a significant part of the stability of a bicycle. The moments of inertia and the speeds are not large enough. The experiments  indicate that the stability of the bicycle can be described in terms of centrifugal force. A rider who feels an unbalance to the left will turn the handlebars left, producing a segment of a circular path with resulting centrifugal force which pushes the top of the bicycle back toward vertical and a balanced condition.

 2) Turning a Bicycle:-
A bicycle held straight up will tend to go straight. It is tempting to say that it stabilized by the gyroscopic action of the bicycle wheels, but the gyroscopic action is quite small.

       If the rider leans left, a torque will be produced which causes a counterclockwise precession of the bicycle wheel, tending to turn the bicycle to the left

       This is a good visual example of the directions of the angular momenta and torques, but the gyroscopic torques of bicycle wheels are apparently quite small  The gyroscopicly motivated descriptions like "leaning left turns it left" are more appropriate to motorcycles. 

3) Turning left:-
A rider leaning left will produce a torque which will cause the bicycle wheel to precess counterclockwise as seen from above, turning the bicycle left. The angulur momentum of the bicycle wheels is to the left. The torque produced by leaning is to the rear of the bicycle, as may be seen from the right-hand rule. This gives a rearward change in the angular momentum vector, turning the bicycle left.

Gyroscope a precessional angular motion.....

(1).
When a body moves along a curved path with a uniform linear velocity, a force in the direction of centripetal acceleration has to be applied externally over the body, so that it moves along the required curved path. This external force applied is known as active force.

(2).
When a body, itself, is moving with uniform linear velocity along a circular path, it is subjected to the centrifugal force radially outwards. This centrifugal force is called reactive force.

This two forces are acting on gyroscope. And make it balanced under gravitational forces.

free pc tricks