15 replies to this topic

[ummu]

The situation as follows:

 

I have two storage tank. Tank A is 2m elevated above ground level. Tank B is on the ground with inlet nozzle is 0.5m above ground.Tank B is being fed by Tank A with flowrate of 10m3/d.

 

The outlet piping from Tank A is vertical pipe from bottom of tank and bend into horizontal pipe respectively (like an L shape). The length of vertical pipe is 2m and horizontal part is 10m.

 

The question is,

 

1) at given flowrate, what is the time taken for liquid to flow from Tank A to Tank B?

2) what happen if the elevation of Tank A is being lowered down to 0.5m? Is time taken to reach tank B is longer?

 

 

What happen here, I'm not sure whether the time taken shall be rely fully on the velocity or any other consideration?

[Ajay S. Satpute]

Is this a home-work question?

[Aneken]

1) at given flowrate, what is the time taken for liquid to flow from Tank A to Tank B?

 

You should know the diameter of pipe connecting tank A to tank B. Than Apply following eqn.

 

Volumetric flow rate(10 m3/day)= Area x Velocity

 

Calculate Velocity. Than use time = Distance/Velocity. Distance will be the length of pipe.

 

2) what happen if the elevation of Tank A is being lowered down to 0.5m? Is time taken to reach tank B is longer?

 

Your volumertic flow rate will be lowered. So will be the velocity and as a result the time will increase.

[ummu]

Mr. Ajay, unfortunately this is not homework question.

[ummu]

Aneken,

Thanks for the rough idea on question 1. Pipe diameter is standard 2".

However for Question 2, why is it the flowrate will be lowered?

 

 

Anyway, since the pipe routing involved vertical gravity flow, should I consider Froude Number equation to get the velocity? 

[samayaraj]

Ummu,

 

As the head reduces, velocity & volumetric flow rate will reduce. Hence it will take additional time compared to the first case.

 

You can consider this link for your reference.

 

http://www.cheresour...ng-calculation/

 

 

#Samayaraj

[ummu]

Samayaraj,

Thanks for your sharing.

From the spreadsheet you share (which is same situation as mine), can you determine time taken for the fluid to flow from the storage tank

to reach the receiver ?  will you depends fully on velocity?

 

Lets velocity is 3m/s...is that means, for every seconds, the fluid will travel 3m..so if pipe length is 10m, the time taken is 3.3s to reach from storage tank to receiver?

[erj]

Dear Ummu,

 

First of all this is the of Gravity flow, then how do you get "10m3/d."

Second here we are not talking about 1 molecule of mass to travel from storage tank to receiver so you must have to consider mass flow rate or volumetric flow rate.

And at last the liquid level is changing every second so this must be the case of transient calculations. In my views you have to calculate time using some transient simulators for fluid flow analysis.

 

please let me know any further suggestions or corrections.

[ummu]

Erjainrachit,

 

The 10 m3/d is the second tank (Tank consumption rate, so Tank A should supply same, isn't it? Correct me if I should not consider it this way.

[samayaraj]

Ummu,

 

I think your intention is to calculate the time required for liquid to reach from Tank A to Tank B in the initial start of flow and we cannot say for continuous flow. Ya it depends on velocity and it takes about 3.3 sec to reach the bottom receiver from the start of flow. But the velocity is a function of head, friction, bends etc. As said by erjainrachit, 10 m³/day is very small. I think it may be 10 m³/hr.

 

The excel I have given above is meant for assuming constant level in the storage tank. However, in actual condition, storage tank level will keep reducing and thus there will be a reduction in head in the tank. This will also reduce the flow and velocity. It will come under transient condition.

 

Look at the following link

 

http://www.cheresour...ime-calculator/

 

 

#Samayaraj

Edited by samayaraj, 14 January 2015 - 12:46 AM.

[ummu]

For time being, I'm hoping for a logical answers...whether using velocity is enough to predict time taken for the liquid to travel from one point to another. Anyone?

[samayaraj]

Ummu,

 

Ya. Velocity is the only factor which decides the time taken for the liquid to travel from one point to another.

 

 

#Samayaraj

[ummu]

Samayaraj,

 

Thanks a lot. All this while I'm thinking about the same logic answers, searching the internet makes the method more complicated

and none of it answer my question.

 

if you or others having any other suggestions, I'm truly welcomed them.

[erj]

Dear Ummu,

 

Considering your case and tank elevations If I take the Tank capacities to 8 m3, then after 16 min. and 6 seconds. the flow will stop and both the tanks will be having liquid surface elevations. I think that this won't help you, But of course the time taken will be dependent on velocity (if you talk about a single molecule of water).

[ummu]

Yeah, I forget that gravity flow shouldn't have a constant flowrate, it'll depend on pressure drop.

What I've done is, from Bernoulli's theorem of P1=P2, we can have pressure drop across the line.

From here we can determine the flowrate and then velocity.

 

Any other advise are welcome..thanks all

[samayaraj]

Yeah, I forget that gravity flow shouldn't have a constant flowrate, it'll depend on pressure drop.

What I've done is, from Bernoulli's theorem of P1=P2, we can have pressure drop across the line.

From here we can determine the flowrate and then velocity.

 

Ummu,

 

I hope you understood the idea. Look at the excel "Gravity flow line sizing calculation" link which I have provided in the above post. It may help you to understand better.

 

#Samayaraj

Edited by samayaraj, 19 January 2015 - 12:10 PM.