Throttling is a process in which the flow of fluid is restricted
by closing the valve partially. Now imagine their are students in a
class room and as the bell rungs they started moving out. Now if the
door is opened partially then their will be clusters form by the
students. Similarly in flow of fluid their is restriction to flow. now
as students form clusters they pushing other students and in the same
way fluid particles start rubbing with other molecules and as a result
friction is their and as we all know friction is one of the biggest reason for any process to make it irreversible.
Hence it is clear that Throttling is irreversible.
EXAMPLES OF THROTTLING PROCESS
1. Flow through a partially opened valve as in IC engines
2. Flow through a very small opening e.g orifice.
3. Flow through a porous plug.
Characteristics of Throttling
1. No Work Transfer
Explanation:
As we know their is work transfer in turbines due to very large pressure difference. but in the case of throttling their is very low pressure differences so the work we get is very small and this work is lost in overcoming friction. so here we generally neglect the work transfer.
2. No Heat Transfer
Explanation:
Lets see it with a example... imagine you open the freeze and took out your water bottle and just within the fraction of seconds you put back that bottle, now what is the temperature difference between the two states of the water bottle, it is approx. zero. It means heat transfer needs some time , now what happened in throttling is that device length is very small and the fluid is always pushed ahead due to the bulk coming and due this their is not much time for the heat transfer. As we are considering the steady flow and bulk is not accumulated in the device so heat transfer is also neglected.
3. Irreversible Process
4. Isenthalpic Process
Explanation:
The word ISENTHALPIC means same Enthalpy.
look we apply steady flow energy equation:
now neglecting potential energy changes and
heat transfer(q) and work transfer (w) are zero as the characteristics of throttling..
equation becomes:
now what we generally seen that practically velocities values (c1 and c2
) are very very small as compared to enthalpies values so c1 and c2 can
be neglected and finally
hence the process is Isenthalpic.
Hence it is clear that Throttling is irreversible.
EXAMPLES OF THROTTLING PROCESS
1. Flow through a partially opened valve as in IC engines
2. Flow through a very small opening e.g orifice.
3. Flow through a porous plug.
Characteristics of Throttling
1. No Work Transfer
Explanation:
As we know their is work transfer in turbines due to very large pressure difference. but in the case of throttling their is very low pressure differences so the work we get is very small and this work is lost in overcoming friction. so here we generally neglect the work transfer.
2. No Heat Transfer
Explanation:
Lets see it with a example... imagine you open the freeze and took out your water bottle and just within the fraction of seconds you put back that bottle, now what is the temperature difference between the two states of the water bottle, it is approx. zero. It means heat transfer needs some time , now what happened in throttling is that device length is very small and the fluid is always pushed ahead due to the bulk coming and due this their is not much time for the heat transfer. As we are considering the steady flow and bulk is not accumulated in the device so heat transfer is also neglected.
3. Irreversible Process
4. Isenthalpic Process
Explanation:
The word ISENTHALPIC means same Enthalpy.
look we apply steady flow energy equation:
heat transfer(q) and work transfer (w) are zero as the characteristics of throttling..
equation becomes:
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