Please enable JavaScript.
Coggle requires JavaScript to display documents.
Week 16: Fluid (2) & Pump (Fluid Mechanics (Static Fluid vs Fluid…
Week 16: Fluid (2) & Pump
Fluid Mechanics
Static Fluid vs Fluid Dynamics
Static fluid (no movement) ~ Pascal’s principle , Archimedes Principle
Fluid dynamics (movement of fluid) ~ Equation of continuity, Bernoulli equation
Viscosity: measure of the resistance of a fluid to flow. It is micro and is expressed in Pa.s or mPa.s or cP
Factors affecting product viscosity
Temperature ( usually increase temp, decrease μ)
Concentration of solutes ( usually increase conc. , increase μ)
Molecular weight of solutes ( usually increase Mw, increase μ)
Suspended matters ( usually increase suspended matters, increase μ)
Flow Characteristics
Reynolds Number
In Newtonian fluid, viscosity is constant whereas in non-Newtonian fluid the viscosity changes with time or magnitude of stress
Pumps: provides energy (head) to overcome forces that oppose transportation of fluid
2 Types
Positive displacement pumps
4 features
Have a cavity that expands and contracts
Fluid is drawn into the expanding cavity on the suction side (inlet) and is expelled from discharge side (outlet) when cavity collapsed
Can develop high pressure head but cannot tolerate blockages at the discharge
Suitable for high viscosity fluid or shear-sensitive products
Advantages
Flow is independent of pressure
Suitable for high viscosity fluid
Consistent in delivery
Low space requirement (small dimension)
Disadvantages
Not suitable for crystal products
Not suitable for suspended products / particulates
Relatively high maintenance cost
Cannot tolerate blockage at discharge outlet
Centrifugal/kinetic pumps
4 properties
Have a rotating impellor inside a stationary casing
Based on hydrodynamic pumping principle
Fluid enters the pump at the centre of impeller rotation and due to the centrifugal force, moves to the impeller periphery and discharge via the outlet
Suitable for low viscosity fluid (e.g. milk and fruit juices) whereby flow rates are high and pressure requirements are moderate
Advantages
Simple in construction low operating cost
Suitable for low viscosity fluid
Continuous operation ( High output flow rate)
Low space requirement (small dimension)
High reliability in operation (lesser moving parts)
Pulseless and smooth flow
Disadvantages:
Operates at high efficiency over limited conditions
Poor suction power
Factors to consider
Properties of fluid (e.g. viscosity, shear sensitivity)
Product flow rate, temperature, suction and discharge pressure
Efficiency of pump
Continuous operation/ frequent start-stop
