Chapter 4 Flashcards

1
Q

Heating and Cooling Foods

A

Prevents microbiological and enzymatic degradation

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2
Q

Systems for heating and cooling food products

A

Heat exchangers

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3
Q

Non-contact heat exchanger

A

Product and mechanism are kept physically separated usually by a thin wall

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4
Q

Contact heat exchanger

A

Direct physical contact between product and heating/cooling system

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5
Q

Plate heat exchanger

A

Stainless steel plates, better heat transfer from pressed patterns to increase turbulent, Simple maintenance, sanitary

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6
Q

Parallel Flow

A

Product stream vs. heating/cooling stream travel in the same direction

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7
Q

Counter-current flow

A

Product stream vs heating/cooling stream travel in opposite directions

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8
Q

Fouling

A

Deposition of solids, such as milk protein, onto the plate. It decreases heat transfer

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9
Q

Tubular heat exchanger

A

(Non-contact) check it out

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10
Q

Scraped surface heat exchanger

A

scraping action allows for rapid heat transfer to a relatively small product volume. scrapes film build up on tube wall

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11
Q

Steam infusion heat exchanger

A

(contact) direct addition of steam to product, amount of water added

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12
Q

Specific heat

A

(Cp) measures the total amount of thermal energy needed to raise the temperature of a
material

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13
Q

Sensible heat

A

Temperature change with no state change

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14
Q

Latent heat

A

Addition/removal of heat during state change

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15
Q

Relationship between specific heat and moisture content

A

Specific heat increases and moisture content increases

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16
Q

Apparent specific heat

A

When a change in state occurs, incorporates heat involved in the change of state in addition to the sensible heat.

17
Q

Thermal conductivity

A

(k) measures the rate of heat transfer per unit time across a
given cross section of the material (W/mC)

18
Q

Thermal diffusivity

A

(alpha) Ratio involving thermal conductivity, density, and specific heat. high thermal diffusivity means that heat travels through it quickly

19
Q

Forced convective heat transfer

A

Use of some mechanical means such as a pump, fan, or stirring to induce movement of the fluid

20
Q

Free convective heat transfer

A

Density differences caused by temperature gradients within the system

21
Q

Conduction

A

Heat transfer by within solids by molecular movement

22
Q

Convection

A

Heat transfer in liquids by movement of molecules due to density difference

23
Q

Radiation

A

Transfer of heat by electromagnetic waves

24
Q

Steady state heat transfer

A

Time has no influence on the temperature distribution within an object, although temperatures may be different at different locations within the object

25
Unsteady state heat transfer
Temperature changes with location and time
26
Two layers develop in pipe during convective heat transfer
``` hydrodynamic boundary (Near wall) thermal boundary (farther from wall) ```
27
Reynold's Number
Indication of inertial forces and viscosity of the fluid
28
Nusselt number
Enhancement in rate of heat transfer caused by convection
29
Prandtl Number
Thickness of the hydrodynamic boundary layer compared with the thermal boundary layer
30
Log mean temperature difference
Determines area and overall resistance to heat transfer