We were discussing the Otto cycle and the
Diesel cycle in our previous posts and we have seen there that these cycles are
not totally reversible cycles but also these cycles are internally reversible
cycles. Hence, thermal efficiency of an Otto cycle or Diesel cycle will be less
than that of a Carnot cycle working between similar temperature limits.

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During the process of regeneration, Heat will be transferred to the regenerator from the working fluid during one part of the cycle and heat will be transferred back to the working fluid during the second part of the cycle. Regenerator will be considered as reversible heat transfer device.

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Let us consider that we have one heat
engine which is operating between heat source having at temperature T

_{H}and heat sink having at temperature T_{L}. As we have already seen in our previous discussion that for a heat engine to be a complete reversible, difference between the working fluid temperature and heat source temperature or difference between working fluid temperature and heat sink temperature must never go beyond the differential amount of dT during any heat transfer process.
We can also say that heat addition or
heat rejection process must be carried out isothermally and this criterion is
fulfilled in Carnot cycle.

Now we will see here one more important
cycle i.e. Ericsson cycle, where heat addition process and heat rejection
process will be carried out isothermally. But we must note it here that Ericsson
cycle will be different from Carnot cycle. Because there will be two constant pressure
regeneration processes in Ericsson cycle instead of isentropic processes of Carnot
cycle.

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**So,
Let us see here Ericsson cycle**

First we will see here the PV and TS
diagram for Ericsson cycle, we will understand here the various processes
involved and finally we will determine the thermal efficiency of the Ericsson
cycle.

As we can see here from PV and TS
diagram, there will be two reversible isothermal processes and two reversible
constant pressure processes. Heat energy addition and rejection will be done at
constant temperature process and also at constant pressure process.

Advantage
of the Ericsson cycle over the Stirling cycles and Carnot cycles is its smaller
pressure ratio for a specific ratio of maximum to minimum specific volume with
higher mean effective pressure.

**Process, 1-2:**Isothermal expansion from state 1 to state 2. Heat energy will be added here from external source. Volume will be increased but pressure will be reduced during this process.

ΔU

_{1-2}= 0,
Q

_{1-2}= W_{1-2}= RT_{1}Log (V_{2}/V_{1})**Process, 2-3:**Constant pressure process, internal heat transfer from the working fluid to regenerator and therefore this process is also termed as constant pressure regeneration process.

ΔU

_{2-3}= C_{V}(T_{3}-T_{2})
W

_{2-3}= P_{2}(V_{3}-V_{2}),
Q

_{2-3}= (h_{3}-h_{2})**Process, 3-4:**Isothermal compression from state 3 to state 4. Heat energy will be rejected here to the external sink. Volume will be reduced but pressure will be increased during this process.

ΔU = 0,

Q

_{3-4}= W_{3-4}= RT_{3}Log (V_{4}/V_{3})**Process, 4-1:**Constant pressure process, internal heat transfer from the regenerator back to the working fluid.

ΔU

_{4-1}= C_{V}(T_{1}-T_{4})
W

_{4-1}= P_{1}(V_{1}-V_{4}),
Q

_{4-1}= (h_{1}-h_{4})During the process of regeneration, Heat will be transferred to the regenerator from the working fluid during one part of the cycle and heat will be transferred back to the working fluid during the second part of the cycle. Regenerator will be considered as reversible heat transfer device.

If we think the concept of regeneration
where, area under 2-3 i.e. Q

_{2-3 }and area under 4-1 i.e. Q_{4-1}are equal, Regenerative Ericsson cycle will become Carnot cycle because heat energy will be added from an external source at constant temperature and heat will be rejected too to an external sink at constant temperature and hence Regenerative Ericsson cycle will become Carnot cycle and therefore it will have similar efficiency as of Carnot cycle.
Therefore, efficiency of the Ericsson cycle will
be written as

Do you have any suggestions? Please
write in comment box.

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**Reference:**

Engineering thermodynamics, By P. K. Nag

Engineering thermodynamics, By S. K. Som

We will see another important topic in
the category of thermal engineering

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