Chapter 4

Question 1

Heating and Cooling Foods

Answer 1

Prevents microbiological and enzymatic degradation

Question 2

Systems for heating and cooling food products

Answer 2

Heat exchangers

Question 3

Non-contact heat exchanger

Answer 3

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

Question 4

Contact heat exchanger

Answer 4

Direct physical contact between product and heating/cooling system

Question 5

Plate heat exchanger

Answer 5

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

Question 6

Parallel Flow

Answer 6

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

Question 7

Counter-current flow

Answer 7

Product stream vs heating/cooling stream travel in opposite directions

Question 8

Fouling

Answer 8

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

Question 9

Tubular heat exchanger

Answer 9

(Non-contact) check it out

Question 10

Scraped surface heat exchanger

Answer 10

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

Question 11

Steam infusion heat exchanger

Answer 11

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

Question 12

Specific heat

Answer 12

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

Question 13

Sensible heat

Answer 13

Temperature change with no state change

Question 14

Latent heat

Answer 14

Addition/removal of heat during state change

Question 15

Relationship between specific heat and moisture content

Answer 15

Specific heat increases and moisture content increases

Question 16

Apparent specific heat

Answer 16

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

Question 17

Thermal conductivity

Answer 17

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

Question 18

Thermal diffusivity

Answer 18

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

Question 19

Forced convective heat transfer

Answer 19

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

Question 20

Free convective heat transfer

Answer 20

Density differences caused by temperature gradients within the system

Question 21

Conduction

Answer 21

Heat transfer by within solids by molecular movement

Question 22

Convection

Answer 22

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

Question 23

Radiation

Answer 23

Transfer of heat by electromagnetic waves

Question 24

Steady state heat transfer

Answer 24

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

Question 25

Unsteady state heat transfer

Answer 25

Temperature changes with location and time

Question 26

Two layers develop in pipe during convective heat transfer

Answer 26

hydrodynamic boundary (Near wall)
thermal boundary (farther from wall)

Question 27

Reynold’s Number

Answer 27

Indication of inertial forces and viscosity of the fluid

Question 28

Nusselt number

Answer 28

Enhancement in rate of heat transfer caused by convection

Question 29

Prandtl Number

Answer 29

Thickness of the hydrodynamic boundary layer compared with the thermal boundary layer

Question 30

Log mean temperature difference

Answer 30

Determines area and overall resistance to heat transfer