TITLE.PM5

706 ENGINEERING THERMODYNAMICS

dharm

\M-therm\Th13-6.pm5

Heat supplied per kg of air with regenerator

= cp(T 5 – T′) + cp(T 7 – T 6 ′)

= 1.005 [(1023 – 722) + (1023 – 872)]

= 454.3 kJ/kg

(i)ηthermal (without regenerator) =

146 73

807

= 0.182 or 18.2%. (Ans.)

(ii)ηthermal (with regenerator) =

146 73

454 3

. = 0.323 or 32.3%. (Ans.)
(iii)Mass of fluid circulated, m& :
Power developed, P = 146.73 × m& kW
∴ 350 = 146.73 × m&

i.e., m&=

350

146.73 = 2.38 kg/s

i.e., Mass of fluid circulated = 2.38 kg/s. (Ans.)

Highlights

1. A cycle is defined as a repeated series of operations occurring in a certain order.


2. The efficiency of an engine using air as the working medium is known as an ‘Air standard efficiency’.


3. Relative efficiency, ηrelative = Actual thermal efficiency
   Air standard efficiency
   .


4. Carnot cycle efficiency, ηCarnot = TT
   T

12

1

−.

5. Otto cycle efficiency, ηOtto = 1 –^11
   ()rγ−

.

Mean effective pressure, pm(Otto) =

prr r

r

(^1) p
(^111)
11
[( )( )]
()()
γ
γ
− −−
−−.

6. Diesel cycle efficiency, ηDiesel = 1 –^1111
   γ

ρ

γ ρ

γ

()r −

−

−

L

N

M

M

O

Q

P

P

Mean effective pressure, pm(Diesel) =

pr r

r

1 111

11

γγγρ ργ

γ

[( ) ( )]

()()

−− −

−−

−

.

7. Dual cycle efficiency, ηDual = 1 –^11
   ()^111

(. )

rγ ()()

βργ

− ββγρ

−

−+ −

L

N

M

M

O

Q

P

P

Mean effective pressure, pm(Dual) = pr^1 r r

111 1

11

γγβρ β βργ

γ

[( ) ( ) ( )]

()()

−+ −− −

−−

−

.

8. Atkinson cycle efficiency, ηAtkinson = 1 – γ.
   ()r
   r

−

−

α

γγα

where α = Compression ratio, r = Expansion ratio.