Liquid-liquid separation by disc bowl centrifuge
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Centrifugation is an old technique which is characterized by application of centrifugal instead of gravitational acceleration with instant to increase sedimentation velocities of partiicles to be separated from a mixture.The principle of centrifugation was applied in Liquid-liquid separation by using disc-bowl centrifuge in dairy industry to ease separation of liquid milk into cream and skim milk.Apart from that,it was useful in diluting coconut milk to coconut cream and water.Nowadays, milk can be skimmed more efficiently.
The technique centrifugation involve separating mixtures into two or more phase,one involved continuous phase.The driving forc behind the separation is the density between the hases.The centrifugal forces separation process to be accelerzted.Centrifugal forces are generated by rotating the materials.Forces generated highly depend on the speed and radius of rotation.When difference in density are large and time is not a limiting factor, separation can take place by gravity(knowm as sedimentation and skimming).
Therefore,in this experiment,we are about to separate cream from dairy millk of 250g and 500g and coconut milk.Apart from that,we are about to measure the quantity and density of cream and skimmed milk.
Materials and method
Dairy milk powder and coconut milk
Firstly, the disc and bowl were washed and cleaned with tap water. It was ensured that the rubber-o-ring was placed at the base of bowl. The disc was arranged in a way that the holes lie on a line.The ring was screwd tightly.Next, the bowl with ring was tighten using special tool provided. The heavy phase outlet was first fixed and followed by light phase outlet. The collection fixture, distribution float, and collection beaker was placed.Next, 250 g of full cream milk powder was dissolved with water in 1 L beaker to form a liquid milk.After that, the liquid milk was poured into feed receiver. The switch was turned on and the the speed knob was fixe.The knob of feed stopper was turned to feed position sa that milk can flow through the centrifuge. The quantities of feed (milk),cream, and skim milk was recorded. The density of cream and skim milk was measured using 25 ml specific gravity (SG) bottle.All the steps was repeated to dilute a coconut milk.
The mechanism responsible for removal of cream by centrifugation is based on fact liquid of different specific gravities revolved around same centre at the same distance with a same angular velocity.If raw milk were allowed to stand,the fat globules would begin to rise to the surface in a phenomena called creaming. Raw milk in rotating container has centrifugal force exerted on the heavier liquid compared to the lighter one.This will eventually allow rapid separation of milk fat from the skim milk portion and removal of solid impurities from the milk.
The sample of 250g full cream milk powder is easier to separate.This is due to the fact when more milk weight (gram) of milk powder was added,the fat globules or cream form is more,therefore its harder to separate into cream and skim milk for full cream milk powder, and to separate into cloudy water and cream in coconut milk. Next, density is a factor which can affect the separation process. The cream (fat globules) thoeretically have lower density compared to skim milk. Therefore,when raw milk allow to stand,the cream (fat globules) would begin to rise in surface. As the cream is less dense than skim mlik,therefore it settles inwars in the channels toward the axis of rotation and passes to an axial outlet.The skim milk moves outward to the space outside the plate stack and pass through the separator bowl.However,in our experiments,the were some error in the result obtain for 250g milk and 500 g milk,the cream density should be less than skim milk but it occurs to be otherwise.Therefore,they are some precaution step should be taken into account like avoid too much spills of milk as it may affect the
1. R L EARLE (1983) Unit Operations in Food Processing,Pergamon press 2. FRANK O’MAHONY, Rural Dairy Technology Experience in Ethiopia retrieve from books.google.my/books.