Second_law_of_Thermodynamics_explaination.pptx

Second_law_of_Thermodynamics

1. Engineering Thermodynamics Mr. Vindhyachal Singh Assistant Professor , Department of Mechanical Engineering By Topic : Second law of thermodynamic (Basic concepts & Statements)

2. Limitation of “ FIRST LAW ” The first law of thermodynamic states that a certain energy flow takes place when a system undergoes a process or change of state . According to first law in ‘cyclic process’ Work is completely converted into heat or heat is completely converted into work. “HEAT” & “ WORK ” are mutually converted into each other. But from experience this is NOT TRUE !

3. Limitation of “ FIRST LAW ” First law does not help to predict whether the certain process is possible or not. The first law does not give info about Direction. It does not provide and specify sufficient condition to process take place. W or k ( W ) S y s t em H e a t ( Q ) Hot Reservoir T1 Cold Reservoir T2 H e a t Fl o w Hot Reservoir T1 Cold Reservoir T2 H e a t Fl o w Not possible

4. The “ SECOND LAW ” o f thermodynamic : The second low of thermodynamic gives more information about thermodynamic processes. Second law may be defined as – “ Heat can not flow itself from colder body to a hotter body ” . The Second law is also used to determine the theoretical limits for the performance of mostly used engineering systems like heat engines and heat pump….

5. “ Kelvin-Plank ” statement: The Kelvin-Plank statement of the second law of thermodynamic states that – “ It is impossible to any devi c e as heat engine that operates on a cycle to receive heat from a single reservoir and produce net equivalent amount of work ”. This statement means that only part of total heat absorbed by heat engine from a high temperature is converted to work, the remaining heat must be rejected at a lo w temperature .

6. Continued….. The heat engine as shown in fig.1is converting 100 % of heat into 100% work. This system is not satisfying second law. So, this statement can be also expressed as “ No heat engine has a 100 % of thermal efficiency ”. Q=100 kj w=100 kj Q=100 kj w=40 kj Heat Source Heat Engine Heat Source T1 Heat Engine Q2=60 kj Sink T2 1

7. “ Clausius ” statement : Clausius statement of second law of thermodynamic is as below – “ It is impossible to construct a device as heat pump that operates in a cycle and produces no effect other than the transfer of heat from lower temperature to higher temperature body ”. This statement means that heat cannot flow from cold body to hot body without any work input.

8. Heat Source T1 Heat Source T1 Heat sink T2 Heat sink T2 H P/RF Heat p ump Q1=100 kj Q2=100 kj Q2=60 kj Q1=100 kj No external work s u p p li ed 1 W=40 kj (external work s u p p li e d ) 2 IMPOSSIBLE POSSIBLE

9. SECOND LAW OF TD & PRINCIPLE OF REFRIGERATION EME new\PRINCIPLE OF RF.mp4

10. Co n tinued: The COP for fig. 2 , if it works as heat pump is- 100/40=2.5 . if it work as refrigerator is- 60/40=1.5. So, in other simple words this statement can be defined as – “ Heat cannot itself flow from a colder body to a hot body ”.

11. COMPARISON It is negative statement. It is based on experimental observations and no mathematical proof. Kelvin-Plank Statement Clausius Statement It is applied t o ‘H e a t Engin e’ . • It is applied to ‘Heat Pump’ and ‘Refrigeration’. It is also negative statement. It is based on experimental observations and no mathematical proof.

12. P erpetual M otion M achine PMM 2 If the engine exchange heat only single thermal reservoir , in which heat is supplied is completely converted into an equivalent amount of work and its efficiency becomes 100 % . This kind of machine is known as “ PMM 2 ”. Thermal Reservoir PMM 2 W=Q1 Q1

13. Co n tinued: The PMM 2 violates the second law of thermodynamic. Practically its IMPOSSIBLE to construct. The efficiency PMM 2 is W=Q N is 100 % for PMM 2.

14. Thank You..!