[sania]

Respected Sir/Madam
I want to know what is the impact of transporting fluids of different density through PD pumps, let say we have one of the  Positive displacement pump anytype (rotary, plunger or piston), having all the parameter is same i.e the volume of the cylinder, the length of the piston, the stroke of the piston, of any of these pumps. We have to transport three fluids having different density e.g Water 1.0, Sulphuric acid 1.8, and honey. Here are my few questions
1) Which fluids have more discharge pressure, while using the same pump having same parameter?
2) Which fluids give less friction losses?
3) either the density factors contribute in discharge pressure? (as far as centrifugal pump the densitfy difference does not affect the head of the pump, but it only affects upon power consumption). How PD pumps affects this behaviour?
waiting for your detailed answer
with kind regards
thankyou

[eugenedakin]

Hello sania,

These are common (and great) questions which are commonly asked . Here are the answers assuming the pumps are pushing a fluid upwards (against gravity):

1. All pumps will have the same head, but the lowest density will have the highest pressure (as psi) at a given (but constant) height at the outlet with the same pump.
2. The highest friction losses will occur with the most viscous fluid.  This is assuming a Newtonian fluid. 
3. The lowest density fluid will have the highest pressure (as psi), where as the highest density fluid will have the lowest pressure at a given (but constant) height above the pump.

I wish you the best,

Eugene

[sania]

Thankyou Sir for your kind reply.
in your first answer you said that ALL pumps will have the same head (as gravity is concerned), i heard it for only centrifugal pumps in the past, so i asked this question for pd pumps also. One thing which is confusing me is the head we define head as pressure in terms of lenght,

Head = pressure x 2.31/Specific gravity.
one thing i understand that as a defination of head  and it's formula if we increase the specific gravity the pressure also increases and viceversa.
but just clarify me how positive displacement pumps gives same head. I heard it about centrifugal pumps, for pd pumps i learnt it's give constant flow rate and work at high pressure. Hopefully  you understand my question. may be my thinking is not right. waiting for your precious response. With kind regards.

[eugenedakin]

Hello sania,

I am attempting to understand the depth at which we would like to explore your question.  Please have patience while I try and help. 

You are correct, centrifugal pumps provide the same head (in terms of height).
Lets put some numbers to an example...lets say a centrifugal pump is able to provide 10 feet of head with light crude oil (s.g. = 0.7)
10 = pressure x 2.31/0.7 = 3.03 psi.

With the same pump (providing 10 feet of head) we are going to pump water (s.g. = 1.0)...
10 = pressure x 2.31/1.0 = 4.33 psi

I found a quote on wiki mentining
Head is used to describe the energy in incompressible fluids. Head has units of distance and equals the fluid's energy per unit weight. Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density. This is found at http://en.wikipedia.org/wiki/Hydraulic_head

You are correct. There is a signifacent difference in centrifugal pump compared with positive displacement pumps:
Kinetic Pumps
Continuous energy addition
Conversion of added energy to increase in kinetic energy (increase in velocity)
Conversion increased velocity to increase in pressure
Conversion of Kinetic head to Pressure Head.
Meet all heads like Kinetic , Potential, and Pressure

Positive Displacement
Periodic energy addition
Added energy forces displacement of fluid in an enclosed volume
Fluid displacement results in direct increase in pressure which can be further viewed here: http://en.wikipedia.org/wiki/Pump.

My apologies, I thought that you were asking a general question, and not a specific one.

I hope this helps,

Eugene