FLUID FLOW FOR CHEMICAL ENGINEERING Dr Mohd Azmier Ahmad Tel: +60 (4) EKC 212 CHAPTER 8 (Part 3) TRANSPORTATION SYSTEM & FLUID METERING ( (Fluid Moving Equipment)

Fluid Moving Equipment  Fluids are moved through flow systems using pumps, fans, blowers, and compressors.  Generally pumps move liquids while fans, blowers and compressors add energy to gasses.  Such devices increase the mechanical energy of the fluid.  Add energy to the fluid – they do work on the fluid.  The additional energy can be used to increase Velocity (flow rate) Pressure Elevation

A pump is a device used to move fluids. In general, 2 main forms are the positive displacement type & centrifugal pumps. Both of which are commonly used for delivery fluid against high pressures & where nearly constant delivery rates are required. PUMP

Positive displacement pump (PDP)  Force the liquid by changing volume. It delivers a pulsating / periodic flow as the cavity volume opens, traps & squeezes the fluid.  Deliver any fluid regardless of viscosity & operate at high pressure. However if pipe blocked, pressure will rises & damage pump  Mechanical efficiency varies from 40-50% for small pumps & 70-90% for large pumps.  PDP are classified into two general categories: (i) reciprocating pump (piston, plunger, diaphragm pumps) (ii) rotary pump (single rotor, multiple rotors – gear, lobe)

Typical positive displacement pumps: (a) Tire pump, (b) human heart, (c) gear pump.

a) Reciprocating pumps: (i) Piston pump:  Liquid is drawn through an inlet check valve into the cylinder by withdrawing of piston & forced out through discharge check valve on return stroke.  Piston may be motor driven through reducing gears.  Max. discharge for piston pumps ~ 50 atm.  Used for viscous fluids and oil wells.

ii) Plunger pump:  Use for higher pressure (≥ 1500 atm).  Contain heavy-walled cylinder with reciprocating plunger.  During its stroke, plunger fills all space of the cylinder.  Normally single acting and motor driven.  Not suitable for transferring toxic or explosive media.

(iii) Diaphragm pump:  Made of reciprocating flexible diaphragm metal / plastic/rubber.  Can handle toxic/corrosive liquids.  Handle only small to moderate amount of liquid ~ 100 gal/min.  Develop pressure up to 100 atm.

b) Rotary pump  Contains no check valve.  Minimise leakage due to close tolerance between moving & stationary parts.  Work well with clean and moderately viscous liquids.  Discharge pressure up to 200 atm or more. Rotary Lobe Pump Peristaltic Pump

Peristaltic Pump with 2 rollers Peristaltic Pump with 3 rollers

CENTRIFUGAL PUMPS  Most widely used in the chemical industries. It adds momentum to the fluid by means of fast moving blades (centrifugal force).  It can provide a higher flowrate (up to 300,000 gal/min) with moderate pressure rises compare to the PDP type.  Discharge is steadier but not effective in handling high viscosity liquids.

 Power from an outside source is applied to shaft A, rotating the impeller B within the stationary casing C.  The blades of the impeller in revolving produce a reduction in pressure at the entrance of the impeller. This cause liquid to flow into the impeller from the suction pipe D. This liquid is forced outward along the blades at increasing tangential velocity & exits the pump discharge at point E. Action of a centrifugal pump

An impeller attached to the rotating shaft. The impeller consists of a number of blades, also sometimes called vanes, arranged in a regular pattern around the shaft. (a) Open impeller, (b) enclosed or shrouded impeller

Pump positive displacement type centrifugal pumps reciprocatingrotary gear pump three-lobe gear pump peristaltic pump piston pump diaphragm pump