10 replies to this topic

[amitkatyal.asim]

We are pumping liquid through a pipe. After a pipe length, the flow area of pipe is reduced. As per bernoulli's equation, the velocity of flow will increase and pressure will decrease. In case the pipe area is reduced to a very low value then can the decrease in pressure due to reduction in flow area result in vaporization of liquid? Is this the working principle behind expansion valves used in refrigeration industry?

[Bobby Strain]

Use your favorite web search engine for refrigeration cycle.

 

Bobby

[Art Montemayor]

Please be specific and accurate in your wording.

The pipe you describe is not “thin”; it is reduced in diameter.  That's why I have corrected your thread title.

 

Bernoulli has little to do with what you describe as a liquid refrigerant flowing in a reduced diameter pipe.  Common sense should tell you that if you reduce the pipe diameter, you reduce the available flow area.  If you decrease the flow area, you increase the amount of driving force required to flow the same liquid quantity through a reduced conduit, while increasing the flow resistance on the pipe walls.  The increased flow resistance results in an increased pressure drop through the length of the reduced pipe diameter.

 

If you are dealing with a saturated liquid refrigerant, follow Bobby Strain’s advice: study and apply the saturated liquid’s pressure drop effect on a Temperature-Entropy Diagram for the refrigerant and you will get your answer: the drop in pressure causes a subsequent temperature drop of the lower-pressure liquid+vapor product.  You will probably find your product mixture inside the “saturated dome” on the T-S Diagram.

 

This is NOT the working principle behind expansion valves used in refrigeration industry.  (That is why it is important to heed Bobby Strain's advice and learn how and why a refrigeration system works)  The use of an expansion valve creates a rapid and controlled pressure drop - and thus, a refrigerating effect in the expanded refrigerant product mixture.  However, the use of pipe (or tubing) wall flow resistance is used in some low-cost, fixed capacity refrigeration cycles to produce the sought pressure drop.  This is often done in the form of a tubing coil of fixed dimensions.  I have used this type of simple, fixed device in some small Freon applications as well as inside cold boxes in cryogenic processes.  This is also used in relatively small refrigeration applications such as residential air conditioning units and commercial applications with a fixed capacity.

 

 

[amitkatyal.asim]

Dear Mr Montemayor,

As the pipe diameter decreases, for a non compressible flow, the velocity through the pipe increases as per equation of continuity. As the velocity increases, the dynamic pressure increases and static pressure decreases as the stagnation pressure is constant. What would happen if the diameter of the pipe is reduced to a very low value?

[Bobby Strain]

Is there some point to your query? Or context?

 

Bobby

[amitkatyal.asim]

I am trying to calculate energy used in pumping water through a coil. The coil id is 0.585 inches. I am taking the pressure at the start of coil as 0.5 bars. On taking the stagnation pressure as 50 bars, I am getting the volumetric flow rate = sqrt(4950000*sqr(Area of pipe)*2/1000) and energy used in pumping = stagnation pressure * volumetric flow rate/ pump efficiency.

Are my calculations correct?

[amitkatyal.asim]

I am trying to calculate energy used in pumping water through a coil. The coil id is 0.585 inches. I am taking the pressure at the start of coil as 0.5 bars. On taking the stagnation pressure as 50 bars, I am getting the volumetric flow rate = sqrt(4950000*sqr(Area of pipe)*2/1000) and energy used in pumping = stagnation pressure * volumetric flow rate/ pump efficiency.

Are my calculations correct?

[vaibhav]

Hi asim

 

pl. do not divert the  main topic of this thread - pumping of refrigerant .

 

use separate thread and submit the preliminary calculations for review.

 

regards

VP

[amitkatyal.asim]

It relates to the same topic ie. pumping of liquid through a pipe.

[vaibhav]

 you are talking about water. there was discussion about pumping of refrigerant.

 

 

 

 

 

 

[amitkatyal.asim]

It was for liquids in general