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Evaporation
FPE Final Exam
What is evaporation used for? | To remove water from dilute liquid foods to obtain concentrated liquid products. |
How is evaporation different than dehydration? | Evaporation is for liquid foods whereas dehydration is for solid foods. |
The presence of _____ in an evaporator causes the temperature difference between steam and the product to _____, and the product boils at relatively ____ temperatures. | vacuum, increase, low |
What is the difference between a single-effect and a multiple-effect evaporator? | Single-effect: vapors are discarded; multiple-effect: vapors are reused for another evaporator chamber. |
Define a forward feed system. | The product from one effect becomes the feed for the next in a multiple-effect evaporator. |
T or F: As water is removed from a product, the liquid has increased rate of heat transfer. | False |
Define boiling-point elevation. | The increase in boiling point over that of pure water, at a given pressure. |
T or F: The relationship between boiling-point of a solution versus water is linear. | True |
The heat transfer area per unit volume in a pan evaporator is _____. | small |
Heating of the product in a pan evaporator occurs mainly due to natural ______. | convection |
T or F: Rising-film evaporators are primarily used for high-viscosity foods. | False |
A rising-film evaporator requires a temperature differential of at least ____ degrees between the product and the heating medium. | 14 |
T or F: A falling-film evaporator is more difficult to control uniform flowing than a rising-film evaporator. | True |
Falling-film evaporators utilize _____ _____. | spray nozzles |
T or F: A falling-film evaporator allows less effects than a rising-film evaporator. | False |
A forced-circulation evaporator utilizes a _____ heat exchanger. | noncontact |
T or F: Forced circulation evaporators are most cost effective. | True |
An agitated thin-film evaporator can be used for _____ viscosity foods. | high |
T or F: Agitated thin-film evaporators have relatively low rates of heat transfer. | False |
What are two disadvantages of agitated thin-film evaporators? | High cost, low processing capability |
Plate evaporators use principles from what other three types of evaporators? | Rising/falling-film, wiped-film, forced-circulation |