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Y1S1_FST1101B > CHAP 14 : FOOD ENGINEERING > Flashcards

CHAP 14 : FOOD ENGINEERING Flashcards

1
Q

What does a unit operation refer to?
Give examples.

A

It refers to any processing step that involves a physical or chemical transformation of the material.

  • e.g. homogenisation, pasteurisation, packaging
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2
Q

What is a process made up of ?

Which 2 classes can processes be classified as?

A

It is when unit operations are grouped in a specific sequence.

  • batch processing and continuous processing
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3
Q

What is batch processing?

What is continuous processing?

A

Batch processing : a fixed set of raw materials is input through the sequence of unit operations and a fixed set of finished products is produced at the end

Continuous processing : raw materials are constantly being put into the process and products are constantly being removed from the process

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4
Q

What are the 2 advantages of batch processing over continuous processing?

(scenario : producing milk and filling into bottles. In batch, milk is pasteurised in a batch in a batch pasteuriser while in continuous, the milk is continously fed into and removed from a pastueriser in a continuous pasteuriser such as the heat plate exchanger)

A
  1. Batch - much easier to control, just need to measure temperature and control time in the pastuerisation of milk ;; continuous process is more complicated, control flow rate of milk
  2. Batch processing is cheaper –> investment in sensors and equipment for continuous process is much higher
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5
Q

What are the 3 advantages of continous processing over batch processing?

A

1.sensors and equipment for continuous process are more sophisticated

  1. higher throughput and efficienc because once process has started, production line will remain operational for long time before shutting down for maintenance and cleaning ;; and no pause or downtime between batches
  2. Easiest to make quantitative assessments and predictions of the process when in a steady state (properties of process like temp, pressure, flow rate constant)
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6
Q

What is throughput?

A

It refers to the amount of product that can be produced per unit time

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7
Q

Why are process flow diagrams useful? [2]

A
  1. To study critical components of the process (e.g. during HACCP analysis)
  2. To visualise how materials flow within a food processing plant.
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8
Q

What law is material balance based on?
What is the definition of material balance?

A
  • It is based on the law of conservation of mass
  • Mass balance : the mass of the material that enters the process must be equal to all the mass of the stream of materials exiting the process

In physics and chemistry, the law of conservation of mass or principle of mass conservation states that for any system closed to all transfers of matter and energy, the mass of the system must remain constant over time, as the system’s mass cannot change, so the quantity can neither be added nor be removed

Material stream is the direction and route of material movement along with the sequence of material distribution in the supply chain.

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9
Q

Mass balance / material balance (refer to the same thing) is useful for studying the raw material demand, product _____, waste streams and possible _____.

A

yield; losses

  • With a material balance diagram, we can compare the theoretical yield of product against the actual yield, and to determine where there might have been unexpected product losses etctetc
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10
Q

What is Molarity?

what is the unit for molarity to express concentrations of solutions?

A

Molarity is defined as the number of moles of solute per liter of solution.

  • The symbol for molarity is M or moles/liter
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11
Q

How much is millimolar, micromolar, and nanomolar and their units?

A

Millimolar : mM
- 1 x 10^ -3 M

Micromolar : μM
- 1 x 10^ -6 M

Nanomolar : nM
- 1 x 10^ -9 M

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12
Q

Another common way of expressing concentration are mass and volume percentages. What is the formula for mass percent, volume percent and mass|volume percent and their units?

A

Refer to fst1101b notes pg 7-8

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13
Q

What does 1 ppm and 1 ppb stand for and their numerical values?

A

1 ppm : 1g of solute in 1 million ml of solution (1mg per L / 1 mg per kg)

  • 1 Litre : 1 thousand ml ; 1 mg = 10^ -3g

1ppb : 1g of solute in 1 billion (10^9) ml of solution (1μg per L / 1μg per kg)

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14
Q

What is heat transfer?

A

Heat transfer is the energy exchanged between materials (solid/liquid/gas) as a result of a temperature difference.

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15
Q

Give some examples where heat transfer is used.

A
  1. Cooling of fruits and vegetables
  2. Freezing of foods
  3. Roasting of coffee beans
  4. Pasteurising of milk
  5. Drying of foods with heat
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16
Q

Heat transfer is analagous to mass balance. Write out the equation which describes all the energy that is entering and leaving a process.

A

Heat in + Reaction heat = heat out + heat accumulation + heat loss

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17
Q

Heat transfer is analagous to mass balance. Write out the equation which describes all the energy that is entering and leaving a process.

A

Heat in + Reaction heat = heat out + heat accumulation + heat loss

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18
Q

What is reaction heat?

A

It is the energy that is produced or absorbed during a chemical reaction or change of phases (e.g. change of ice to water or water to steam)

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19
Q

What is the equation to describe heat transfer for continuous process when it is under a steady state.

A

Heat in + Reaction heat = heat out + heat loss

  • There is no net accumulation of material or heat in a process. In stady state, properties (temp, pressure etc) are all constant
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20
Q

What is the sensible heat? What is the equation and units?

A

It is the amount of energy needed to increase the temperature by ΔT degrees celcius for a given mass (m, kg).

q = mcΔT

unit of q : Joules

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21
Q

What are fluids and what state(s) do they exist in?

A

Fluids are substances tht have no fixed shape and yield easily to exernal pressure

  • Includes gasses and liquids
22
Q

What are the 3 modes of heat transfer and how do they work?

A
  1. Conduction – form of heat transfer in which heat energy from one body is transferred to another via direct contact by interchanging molecular kinetic energy. No transfer of molecules in the 2 bodies. Primary mechanism of heat transfer in solids.
  2. Convection – Transfer of heat from one place to another due to movement of fluid. The actual transfer of material is the basis of heat transfer.
  3. Radaition – when energy is transferred via electromagnatic radiation. No mtter needs to be in physical contact / transfered for thermal radiation.
23
Q

What is the equation for heat flux (rate of heat transfer by CONDUCTION)?

A

fst notes pg16

24
Q

In the equation, k, the thermal conductivity, has units of J s^-1 m^-1 K^-1.

What 3 things does units the equation imply about heat conduction?

A
  1. Heat conduction is fastest when material is thin (less m)
  2. Heat conduction is fastest when there is a large temperature difference
  3. Heat conduction is the fastest when material is a good conductor of heat (high thermal conductivity)
25
Q

What is the equation for rate of heat transfer by CONVECTION?

A

refer to fst notes pg17

26
Q

The rate of heat transfer in a plate heat exchanger is often dependent on conduction and convection. True or False?

A

True.

In a plate heat exchanger, the hot fluid transfers heat via convection to the metal plate and the metal plate heats the cold fluid/liquid food via convection. When heat travels across the metal plate, it is done via conduction.

27
Q

What is the difference between the symbol Q and q?

What does it mean when there is a dot above the Q/q symbol respectively?

A
  • Q represents heat energy while q represents heat energy PER UNIT AREA
  • The dot above Q means that it is a derivative of time, how heat energy changes w time (RATE of heat transfer)
  • The dot above q means that it is the RATE of heat transfer PER UNIT SURFACE AREA
28
Q

In the plate heat exchanger, how do food manufacturers reduce the amount of heat wastage?

A

The heated liquid product (e.g. hot pasteurised milk) coming out of the plate exchanger is used as the heating medium to pre-heat the incoming cold liquid product (e.g. cold raw milk)

29
Q

Give an example of radiative heat transfer.

A
  1. Transfer of sun to heat accross the vacuum of space
  2. Baking in oven, where heat is transferred to heating element via radiation and convection
30
Q

What is mass transfer?

A

It is the transport of molecules within physical systems. It can take place within one phase or it can be at the interphase between 2 phases

31
Q

Give an example of a mass transfer process.

A
  • Evaporation, which occurs at the interphase between 2 phases (liquid and gas)
32
Q

The process of diffustion can be explained by Fick’s law. Give the equation for Fick’s law.

A

refer to fst notes pg22

33
Q

Applications of mass transfer to the food industry : evaporation

Give examples of some foods made by evaporation.

A

Dried fruits (soaked in syrup then dehydrated), powdered beverages

34
Q

What is membrane filtration?

A

It is the process by which liquid food is passed through a semi permeable membrane under high pressure

35
Q

In membrane filtraton, the molecules that are small enough to pass through the pores of the membrane forms the _____ while larger molecules retained by the membrane are known as the _____.

A

permeate, retentate

36
Q

When we are consuming food, we are also perceiving the flow of fluids in our mouth. This is known as _____. The field of study that studies the flow behavior of foods is known as _____.

A

mouthfeel ;; rheology

37
Q

What is the equation of resitance to flow?

A

fst notes pg 25-26

38
Q

What is shear stress and its units?

A

It is the force per unit area applied that causes fluid to flow. Units is Pascal (Pa)

39
Q

What is yield shear stress and its units?

A

The MINIMUM amount of shear stress to start the liquid flowing. Units is Pa

40
Q

What is the shear rate?

A

It measures how fast the fluid deforms / flows

41
Q

What are newtonian fluids? Give an example.

A

They are fluids that :
1. Do not have a shear stress
2. Shear rate increases proportionately with their shear stress

Pure water is an example

42
Q

The consistency coefficient for Newtonian fluids is also known as ____, with units of _____

A

Viscocity
Pa.s. (pascal second)

43
Q

What are shear thinning / pseudoplastic fluids?

A

They are fluids where once the flow has started (more stress placed on them), it is easier for them to flow faster

  • Shear stress proportionate to shear rate
44
Q

What are shear thickening fluids?

A

In such a fluid, the more shear stress is applied, the more it resists deformation

  • Shear stress increase, viscocity increases, leading to an increase in the resistance to flow –> flow slower. This results in an increase in the shear rate to maintain the same level of shear stress.
45
Q

What is Bingham Plastic? Give examples

A
  • Fluids that have positive shear stress, whose flow is like a Newtonian fluids where shear stress and shear rate are linearly proportional
  • e.g. tooth paste, tomatopaste
46
Q

If a fluid has positive yield stress and shear stress and shear rate are not linearly proportional, they are known as the ______ ______ or _____ _____. Give examples

A

Bingham pseudoplastic ;; Herschel-Bulkley platstic

Examples : minced fish paste, cream cheese

47
Q

Rheology is applied to understand the flow of fluids during processing. Fluids can flow in a pipe in a laminar flow / turbulent flow. What is laminar flow and turbulent flow?

A
  • Laminar flow conditions : fluids flow in multiple parallel layers, no mixing
  • Turbulent flow : layers moving in all directions, resulting in mixing of different layers
48
Q

Often, do we want to achieve laminar flow or turbulent flow during food processing and why?

A

Tubrulent flow to ensure adequate mixing during the heating process

49
Q

What is the equation of Reynolds number?

A

Refer to fst notes pg30

50
Q

When reynold’s number is below ____, it is said to be in laminar flow. When it is higher than ____, it is said to be in a turbulent flow. Fluids with reynold’’s number in between are said to be in _____ where their flow patterns are in between laminar and turbulent flow patterns.

A

2100 ;; 4000

Y1S1_FST1101B (12 decks)

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