5 replies to this topic

[chamatkar]

..

Edited by chamatkar, 28 July 2011 - 07:39 AM.

[ankur2061]

Chamatkar,

The following should be the cases for maximum and minimum pressure drop across the control valve:

Minimum delta P = (Min. level in source tank- dynamic losses in inlet line to CV) - (Min. level in destination tank - dynamic losses in outlet line from CV )

Note: For any flow to occur the min. level in source tank has to be still higher than the min. level in the destination tank. Once the level in the two tanks are equalized there should be no flow between the tanks which essentially means that the CV delta P has become zero.

Maximum delta P = (Max. level in source tank -dynamic losses in inlet line to CV) - (Min. level in destination tank - dynamic losses in outlet line from CV)

The above will give you the highest delta P as well as the highest flow rate which will decrease as the destination tank level starts increasing. Essentially flow will be the highest at the start of the transfer operation and will gradually decrease with time till it completely stops when the tank levels equalize.

The basic assumption in this scenario is that the tank vapor space pressure is equal for both the source tank and the destination tank.

Hope this explanation helps.

Regards,
Ankur.

[fallah]

Hello everyone,

I am new here. I have a situation and need your suggestions on it.

I have got two tanks connected through a pipe and a control valve (Level) in between. The flow between the tanks is purely by gravity. There is a constant incoming flow to the source while the pump is taking constant discharge from the destination tank. At steady state, total in flow to the system is equal to the out flow. The source and destination tanks have different liquid levels (HLL, NLL, LLL). I have to define the pressure drop across the control valve for different scenarios such as Max flow, Normal Flow and Minimum Flow. The source tank is at atm pressure while the destination one is at 3.5 kPag which is marginal. Static height of each tank is the only source to generate pressure upstream and downstream of a control valve.

The approach I consider is as follows. For max delta P across the control valve, flow rate is min. Considering this fact, the source static liquid head taken into account is the HLL and static liquid head considered to back calculate the pressure at control valve is LLL to get highest pressure drop. The dynamic pipe frictional losses in pipe is considered for each flowrate. Similarly, for min delta P across the control valve, flow rate is max. In that case, source static head considered is LLL while the destination one considered is HLL. Here also, dynamic pipe frictional losses calculated separately.

Please share your views and opinions on this and let me know if any one of you had ran into a situation similar to mine. If anyone of you have a good study material or an article that explains this kinda situation, pls share with me here.

Thanks a lot.

chamatkar,

Max flowrate (Control valve in max opening percent position)---->Min Dp across the valve ---->Source Tank at HHL and Destination Tank at LLL

Min flowrate (Control valve in min opening percent position)---->Max Dp across the valve ---->Source Tank at LLL and Destination Tank at HHL (Provided that Source Tank LLL>Destination Tank HHL otherwise there is no flow/reverse flow).

Fallah

Edited by fallah, 29 June 2011 - 07:11 AM.

[Padmakar Katre]

Hello everyone,

I am new here. I have a situation and need your suggestions on it.

I have got two tanks connected through a pipe and a control valve (Level) in between. The flow between the tanks is purely by gravity. There is a constant incoming flow to the source while the pump is taking constant discharge from the destination tank. At steady state, total in flow to the system is equal to the out flow. The source and destination tanks have different liquid levels (HLL, NLL, LLL). I have to define the pressure drop across the control valve for different scenarios such as Max flow, Normal Flow and Minimum Flow. The source tank is at atm pressure while the destination one is at 3.5 kPag which is marginal. Static height of each tank is the only source to generate pressure upstream and downstream of a control valve.

The approach I consider is as follows. For max delta P across the control valve, flow rate is min. Considering this fact, the source static liquid head taken into account is the HLL and static liquid head considered to back calculate the pressure at control valve is LLL to get highest pressure drop. The dynamic pipe frictional losses in pipe is considered for each flowrate. Similarly, for min delta P across the control valve, flow rate is max. In that case, source static head considered is LLL while the destination one considered is HLL. Here also, dynamic pipe frictional losses calculated separately.

Please share your views and opinions on this and let me know if any one of you had ran into a situation similar to mine. If anyone of you have a good study material or an article that explains this kinda situation, pls share with me here.

Thanks a lot.

Hi,
I have two basic questions here which are based on my contradictory understanding of your problem
1. To equalize the two tank levels why you need a control valve ( I understand the destination tank inlet is not at the top)
2. If the destination tank inlet is from the top then what is sanctity of different liquid levels in destination tank for hydraulics calculations?

P.S.-Your understanding for relation for Flow and relative DP is quite correct.

[LeilaR]

Hi everyone

I need to fill in the process data sheet of control valve on compressor surge line. Is there anyone to help me?

thanks

[Padmakar Katre]

Hi everyone

I need to fill in the process data sheet of control valve on compressor surge line. Is there anyone to help me?

thanks

Hi,
Before I answer your question in a single line i.e. how to arrive at the Delta P value, you first understand the concept of antisurge, the parameters involved and their sensitivity/sanctity. Surely I will answer your question if it still persists even after understanding the concept of Antisurge control in Centrifugal compressor machine.

Edited by Padmakar S Katre, 29 July 2011 - 12:11 AM.