All engineering studies of food processes are related to the basic unit operations of mass transfer and/or heat transfer.

These principles are applied to the numerous procedures of transporting, preparing, processing, packaging, and distributing of basic and value-added foods. Secondary unit operations include techniques of separating components, reducing particle size, mixing ingredients, and concentrating desired components. The unit separation operations, distillation, evaporation, dehydration, and filtration all involve the extraction of a component from a liquid, gas, or solid by physical or chemical means. However, each category listed has such different applications of scientific and engineering principles that it is too unwieldy to place them all under a combined unit operation. Thus, due to these complexities, the procedures have been divided into numerous categories related to the mechanisms of separation. This greatly simplifies the scientific and engineering studies of various unit operations and the subsequent engineering design, manufacture, and integration of the process facilities into an overall food process. Various separations of components in a basic harvested food or a partially processed product are the most important sequences of processing a food to a finished product for the market. The unit operation of extraction is considered to be the removal or separation of a component by material that has greater affinity for the component being removed.

Extraction, the separating of a component from a liquid or solid by another liquid is handled as a separate unit operation since the process is based on diffusion of one component from the base material to an extracting liquid. Since the mechanics of these processes are based on diffusion, study of the processes and design of extracting equipment is based on the diffusivities of the solute being removed from the base material. This differs from other separation processes such as distillation that involve a change of phase in one or more components requiring different scientific principles. The original applications of extraction processes began many years ago with application of gas absorption and solvent extraction in the industrial chemical industry. It has been in relatively recent years that the technology has been extensively applied to separating components in food (1).

Extraction as practiced in the food industry is essentially the operation of removing or separating a component from the food to ensure food safety or to alter the properties. A rudimentary form of extraction begins with the basic separation or removal of components from an as-received food. With the growing problems of microbiological contamination in harvested fruits, vegetables, and animals, the extraction operation of washing as-received raw materials has received much emphasis over the past few years. The simple washing of a vegetable or fruit is necessary to ensure that contamination from soil, fertilizers, living organisms, pesticides, and so on is removed or at least reduced to an acceptable level, making the vegetable safe to eat. Proper washing is particularly important in slaughtered animals since extremely dangerous microorganisms such as Escherichia coli and Salmonella contaminate many of them. A much more complex procedure for removing or extracting a component is found in the process for producing vegetable oils. For example, many vegetable and seed oils are extracted from the base material by solvent extraction. A solvent in which the corn oil is soluble

In order to cool the vapor to its condensing temperature of 220°F, 11.2 Btu/lb of heat is removed. This can be done by introducing condensate at 220°F from the steam side of the evaporator. The 11.2 Btu/lb of heat removed from the vapor is absorbed into the condensate, some of which will vaporize and give off what is known as "excess vapor." For every pound of vapor cooled, 11.2 Btu of heat is absorbed in the condensate, which requires 965.2 Btu/lb to boil. Therefore, for each point of vapor leaving the compressor, 11.2/965.2 or 0.0116 lb of excess vapor is available.

This excess vapor is used in several ways. Since there is a slight difference in latent heat between the steam and the vapor, slightly more steam is required than the vapor generated. Other excess vapor is used to cover losses due to radiation and venting, is made available in some instances for preheating, or is sent to a condenser. It is significant to note that the condenser on an MVR evaporator is responsible only for vent and excess vapors. This results in a much lower cooling requirements than is necessary for steam evaporators.

It is possible to calculate an equivalent steam economy for an MVR system. In this example, for every pound of water evaporated, 970.3 Btu is absorbed. The compressor supplies 14.1 Btu but with motor and gear losses, probably requires 14.5 Btu of energy. The equivalent economy (970.3/14.5) is 67 to 1. Since one horsepower is equivalent to 2545 Btu/h, the compressor in the example requires 14.5/2545 or 0.0057 hp/lb • h of evaporation.

It should be noted that pressure losses through the evaporator that must be absorbed by the compressor have not been considered in this example. These losses would be taken into account by either higher compressor horsepower or lower AT over the heat-transfer surface.

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

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