Pressure loss problem

Are you a nuclear physicist? why in heaven would you need such accuracy? sorry, I just wonder what is the heat source for the need of such accuracy! with what kind of instruments did you use to find the pressure difference in this one off so many channels. And what were the consequences that lead you to that discovery?generaly in paralell you have less presure than in series if I am not wrong.

I am curious

issa

Parallel or series - depends on the physical construction of the thing. If they're arranged like a bundle of drinking straws, they're in parallel. Pressure drop across one straw/channel = pressure drop across them all.

thanks ,none taken, you are Right. except that in series there are less straws thus more restrictions and more pressure to pass the same volume for the same time.the real problem is : when does the heat exchange is equalized than you need more straws and less pressure to allow time for a more efficient transfer.Otherwise you would be conducting heat to cool heat.( i misunderstood. I tough he had the capability to calculate the reduce velocity in one straw only! due to friction factors in that particular straw ) Never mind the problem does not t exist.

issa

Thanks for your response.

Yes they are bundled as straws.

So if I understand you correctly, number of straws does not change the pressure drop over the heat exchanger as long as all the straws are the same?

of course not, pressure will buildup or be lesser depending on the change of volume of air or coolant (water) that was initially meant to go trough. For example an heat exchanger clogged by limestone will have a pressure buildup at the entrance of the exchanger thus an increase in fluid or air velocity,but no lost in the amount of coolant passing trough. So If I understand well the pressure Will remain the same independently of the amount of straws as long as these straws allow the same amount of fluid or air to pass trough at the initially calculated pressure.simply put; tap a water hose with your thumb and you will increase pressure flow but wont change the volume. Take if off and you will have a lost of pressure but not of volume. the compensator are the pumps and the motor pumps.That is why they are rated. for ex; 35gals per minute at 700 psi.at such RPM. clog the circuit with a vane and you will have a pressure raise up to 3000psi,absorbed by the motor!

what the initial member comment said is contrary o these laws.( the more friction the more the pressure drop! that's flase.

issa

Issa

Correct -sort of. For a given setup, say 100 straws, the pressure difference between one end and the other will be the same for each straw (whether a straw is blocked or not).

If you change the configuration, packing in more (smaller) straws or fewer (bigger) ones, the pressure differential will (probably) change, due to the change in the 'resistance to flow' of the different sizes.

Don't know if you're up on electrical circuits, but if you have, say, 10 resistors all connected in parallel, whatever voltage drop you have across any one of them will be the same for all (since the ends are connected together).

Now if you take one resistor away (equivalent to blocking a straw), this increases the resistance. If you maintain the same voltage drop (equivalent to pressure difference), you'll decrease the current (equivalent to airflow).

Otherwise said, with fewer working straws/(resistors) in parallel, to maintain the same airflow/(current), you have to increase the pressure/(voltage).

Sorry if I've confused - I was hoping to illuminate.

John

This is fundamental :

• Pascal's Law
• Or Electric Analog Potential Difference (Your parallel straws example is so vivid/lucid).