2. Read and translate the text into your native language: .Centrifugation

Centrifugation and decantation (sedimentation, settling, flotation) are processes for the separation of heterogeneous mixtures of phases that differ from each other in their density. The physical principles governing these processes are the same.

Decantation occurs under the effect of earth’s gravity. In the case of centrifugation, accelerated separation is made possible by the effect of centrifugal forces, which may be many times stronger than earth’s gravity.

Centrifugation and decantation may be used to separate solid particles from a liquid or two immiscible liquids of different densities from each other, or both. Centrifugal separation is achieved not only with centrifuges but in any system where a rotational movement is imparted to the mixture. One of the devices for centrifugal separation without a mechanical centrifuge is the cyclone, discussed briefly at the end of this chapter. However, the major part of the present chapter will deal only with mechanical centrifugation and centrifuges.

Centrifuges are relatively expensive machines, both in capital expenditure and in the cost of operation (energy consumption, wear of rapidly moving parts, need for sturdy construction capable of resisting the very high forces and pressures).

Notwithstanding their cost, centrifuges are used extensively in industry. Following

are a few of the many applications of mechanical centrifugation in the food industry:

● Milk separation: one of the oldest and most widespread uses of the centrifuge in the food industry is the separation of whole milk to skimmed milk and cream. The centrifuges used for this purpose are known as ‘separators’ (Walstra et al., 2005)

● Cheese production: in modern dairy plants, centrifuges are used for the rapid separation of curd from whey

● Pulp control in fruit and vegetable juices: centrifugation is used for the reduction of pulp content in fruit juices and for the production of clear juices by total removal of the pulp

Centrifugation

● Edible oil processing: several operations in the production and refining of edible oils involve the separation of the oil from an aqueous phase. Centrifugation

is the preferred method of separation

● Essential oil recovery: essential oils of citrus fruit are recovered by centrifugal separation of aqueous mixtures formed in the course of juice extraction

● Production of starch: one of the methods for the separation of starch from suspensions is mechanical centrifugation

● Production of yeast: centrifuges are used for the separation of commercial yeast from the liquid growth medium.

Basic Principles

As stated above, centrifugation is a process of ‘accelerated decantation’. It is therefore advantageous to analyze first the process of ‘natural’ decantation in the field of earth’s gravity. The following discussion deals with the critical conditions for the separation of solid particles from a liquid. The same reasoning and the same results are also applicable to the separation of liquid droplets dispersed in a fluid.

Specific engineering issues concerning liquid–liquid separation will be discussed separately.

3. Translate the following sentences from Russian into English:

1. Центробежная сепарация выполняется не только в центрифугах, но и в другой системе, где вращательное движение выделяет смеси.

2. Молочное разделение – один из старейших и наиболее распространенных видов использования центрифуги в пищевой промышленности является разделение цельного молока на обезжиренное молоко и сливки.

3. Производство сыра - в современных молочных заводах центрифуги используются для быстрого разделения творога от сыворотки.

4. Применение Pulp в фруктовых и овощных соках: центрифугирование используется для снижения содержания целлюлозы в фруктовых соках и для производства прозрачных соков путем полного удаления пульпы.