SECOND LAW OF THERMODYNAMICS

INTRODUCTION:

Thermodynamics has become part and parcel of our life. Whether travelling in a bus, sitting comfortably in an AC room or enjoying a cold coffee from the cafe , we observe and experience the applications of thermodynamics and its laws everywhere either directly or indirectly.

When sadi carnot , father of thermodynamics proposed theorems and cycles of thermodynamics hardly anyone had imagined that his proposals would someday play such a significant role in the developement  of automobile , which has become an iseperable part of our life today. Lord Kelvin and Rudolf Clausius developed the second law of thermodynamics in 1850's.

Second Law of Thermodynamics :

• General statement:

Heat always moves from hotter object to colder object , unless energy in some form is supplied to reverse the direction of heat flow.

• Kelvin Plank Statement :

A heat engine cannot convert total heat supplied into the mechanical work. OR No heat engine can have 100% efficiency.

fig. Kelvin Plank statement

• Clausius Statement:

No transfer of heat from lower temperature to higher temperature without aid of external work.

The Clausius statement of the second law of thermodynamics states that " It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a cooler to a hotter body".

fig. Clausius statement

Applications :

1. Removing heat from food items :

Removing heat from food item in refrigerator and throwing it away to the higher temperature atmosphere doesn't happen automatically. We need to supply external work via compressor to make this happen in refrigerator.

 

fig. Removing heat from food item  

2. Sweating in crowded room :

in a crowded room, everybody starts sweating. The body starts cooling down by transferring the body heat to the sweat. Sweat evaporates adding hreat to the room. Again this happens due to the first and second law of thermodynamics.

fig. Sweating in crowded room

3. Melting of ice cubes :

Ice cubes in drink absorb heat from the drink and make the drink cooler. If we forget to drink it, after sometime , it again attains room temperature by absorbing the atmospheric heat. All this happens cause of the second law of thermodynamics.

fig. Melting of ice cubes in drinks

4. Refrigerators and Heat pumps:

Another application of this law is refrigerators and heat pumps based on Reversed Carnot Cycle. If you want to move heat from body at a lower temperature to a body at higher temperature , then you have to supply external work. 

In the original Carnot cycle, heat produces work while in the reversed carnot cycle, work is provided to transfer heat from lower temperature reservoir to a higher temperature reservoir.

fig. Refrigerators an Heat pumps

5. Air conditioner and Heat pump :

Air conditioner and Heat pump follow the similar law of thermodynamics. The air conditioner removes heat from the room and maintains it at a lower temperature by throwing the absorbed heat into the atmosphere. 

The heat pump absorbs heat from the atmosphere and supplies it to the room which is cooler in winters. in both cases above external work/ energy in the form of electricity has to be supplied; larger the temperature difference, larger is the exernal work required.

fig. Air conditioner and Heat pump 

6. All types of Heat engine cycles:

According to the law, heat always flows from a body at a higher temperature to a body at the lower temperature. This law is applicable to all types of engine cycles including Otto, Diesel, etc. for all types of working fluids used in the engines. This law has led the progress of present day vehicles.

fig. All types of Heat engine cycles

CONTRIBUTERS:

1. DIPAK KHATALE

2. SHARAYU KHANDAGALE

3. YUKTA KHAIRNAR

4. ROHAN KHEKADE

5. KAUSTUBH BORSE