I have one question which is not related to any software. I want to know when flow will take place between two points, say 1 and 2. There are three heads, pressure, elevation and velocity (total head=phead+zhead+vhead).

Is there any possibility of flow when the total head at 1 and 2 is same? If no, how can we prove this statement if there is velocity head? velocity is there means flow is there, but total heads are same. Is there any possibility of such case, i.e. total heads are same at 1 & 2 which has non zero velocity heads? Kindly help to remove my confusion.

Thanks

hi i think yes. under microgravity. what is your idea?

Again in case of microgravity, as I understood there will be minute elevation head difference. Then heads at 1 & 2 are not same, which is primary requirement of the case. Thanks for your reply.

IF YOU CHOOSE THE DIRECTION OF THE FLOW PEPENDICULARE RESPECT TO THE GRAVITY, I THINK IT CAN BE THE SAME HEAD. ISN'T?

It is possible for inviscid fluid, because in this case total head is conserved (Bernulli equation!).

Hi Javadi, If the direction of flow is perpandicular to gravity, Gravity force will act perpandicular to flow, means it will not help in flowing the fluid. Then wich head is there causing the flow? Do not forget the total head at 1 & 2 is same. I am just confused.

Thaks Javedi for ur interest.

You're simply converting one form of energy to another - think of inviscid flow in a nozzle. The total head is conserved, but in the upstream portion the pressure is high, velocity is low. Downstream the pressure is low and the velocity is high. The total energy is the same however. Of course, if you have no area change then the pressure would be uniform and the velocity would be zero. It seems like your confusion stems from considering purely 1D flow without any area change or other boundary condition that can enforce a change in flow conditions.

Thanks a lot for your kind comments.

I agree with you. Now which factor decides the direction of flow if the head is conserved. Analytically I want to prove to somebody the direction of flow when total head is same at 1 & 2. If velocity head is zero there, will not be any flow, but for non-zero velocity head and equal total head at 1 & 2 what decides the direction of flow?

That would be the pressure gradient.

Thanks, Here we can conclude that it is the pressure gradient which decides the flow direction (provided that total heads at 1 & 2 are same). However this does not prove correct in divergent section of nozzle where flow takes place in opposite direction of pressure gradient.

One more thing shall I conclude from that if there is loss (difference in total heads at 1 & 2), this is the cause of flow (total head difference causing flow).

Thanks a lot