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FDSC 310 > 3 Transpiration and Psychrometry > Flashcards

3 Transpiration and Psychrometry Flashcards

1
Q

define transpiration

A

evaporation of water from produce to air

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2
Q

true or false: produce transpires at all times

A

false: when the air is saturated, it cannot transpire

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3
Q

transpiration has a (heating/cooling) effect on produce. explain.

A

cooling

the energy required to create vapor is removed from the plant the water

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4
Q

what is L of water?

A

2260 kJ/kg

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5
Q

what are the pros and cons or transpiration?

A

pros during plant growth:

  • cooling effect
  • enables mineral and water absorption
  • distributes minerals

cons:

  • decreases sellable weight due to water
  • quality loss from damage (wilting, shriveling, shrinkage, drying)
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6
Q

transpiration is a ______ phenomenon

A

diffusion

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7
Q

transpiration obeys the basic law of _____ _____ also known as _____ law

A

gas diffusion; Fick’s

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8
Q 
Here are the variables of Fick's Law. Tell me what they are, and which ones are directly proportional to J:
J
A
D
Pi
Pa
dx
R
T
A 
J = gas (vapor flux)
A = Surface Area
D = Diffusivity (diffusion coefficient)
Pi = Partial Pressure inside produce
Pa = Partial Pressure of water vapor in air
dx = thickness of surface layer/film
R = Gas constant
T = Absolute temperature

A, D, (Pi-Pa) are directly proportional to J

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9
Q

Where can you find Pws?

A

steam tables. as T increases, so does Pws.

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10
Q

the percentage ratio of Pwa to Pws is the:

A

relative humidity

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11
Q

expand WVPD

A

waver vapor pressure deficit

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12
Q

the difference between the saturated water vapor pressure and the partial pressure of water vapor in the air is:

A

WVPD

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13
Q

when WVPD is positive…

A

produce will transpire and lose moisture

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14
Q

produce with a higher WVPD will undergo (greater/less) transpiration losses than produce with a lower WVPD

A

more

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15
Q

placing warm produce in a cold room will result in a (greater/smaller) WVPD than warm produce at room temperature

A

greater

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16
Q

what happens when you have a positive WVPD but the RH is 100?

A

sweating

17
Q

what’s a good way to reduce WVPD without making it negative?

A

bring cool (not cold) produce (harvested during cool weather) to room temperature, and RH of 50%

18
Q

what happens to WVPD when you have cold produce brought to room temperature?

A

negative WVPD (condensation)

19
Q

under what 2 undesirable conditions related to WVPD promotes the growth of mold?

A

sweating and condensation

20
Q

differentiate between sweating and condensation

A

sweating: produce attempts to transpire, but the moisture can’t enter the saturated atmosphere so it stays on the surface of the produce
condensation: moisture attempts to enter the produce but the skin’s too good at its job, so it just collects on the surface

21
Q

what is curing?

A

treatment for some roots, tubers and bulbs to extend their PH shelf life. helps surface layer to dry, offering resistance to moisture loss and decay via bacteria and fungi

22
Q

what two mathematical methods are used to determine moisture loss

A

WVPD and TC

23
Q

what is TC?

A

transpiration coefficient

24
Q

what are the units for the TC?

A

mg/H2O/kg produce/MPa WVPD/s

25
Q

as produce respires, the temperature will (increase/decrease) causing the transpiration rate to (increase/decrease)

A

increase, increase

26
Q

what 5 methods are used to control transpiration losses?

A
  • maintaining high humidity
  • maintaining low temp difference between cooling coils and produce
  • protect from mechanical and physical injuries
  • regulate moisture loss (permeability)
  • prepackage in polymeric films (allow CO2 escape, regulate oxygen levels)
27
Q

the study of the thermodynamic properties of air water vapor mixtures is known as:

A

psychrometry

28
Q

on the psych chart, what does the horizontal axis delineate?

A

dry bulb temp

29
Q

on the psych chart, what do the curved liens delineate?

A

RH

30
Q

on the psych chart, what do the diagonal lines delineate?

A

wet bulb temp

31
Q

how is dew point read on the psych chart?

A

intersection of horizontal line through state point and 100% humidity line

32
Q

stay at same dry bulb temp but increase RH, dew point, and humidity ratio

A

isothermal humidification

33
Q

stay at same dry bulb temp but decrease RH, dew point and humidity ratio

A

isothermal dehumidification

34
Q

stay at the same humidity ratio but increase dry bulb temp, decrease RH,

A

adiabatic dehumidification

35
Q

stay at the same humidity ratio but decrease dry bulb temp, increase RH

A

adiabatic humidification

FDSC 310 (11 decks)

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