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Preservation of Food, Sustainability Examples,

Course SummaryHans Jonsson

Agenda• Preservation of food• Sustainability examples• Course summary

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Agenda - Preservation of Food• Basics• Storage time, storage temperature• Storing at low temperatures• Concentration of fruit juice• Freeze drying• Estimation of cooling demand• Freezing methods

Basics• Almost all processes in nature runs faster at

higher temperatures.

• This means that food is to be kept at low temperatures to allow a longer storage time.

• So, the cooler the better?• Yes and no!

• Since almost all food products contain water, there is a phase-change at (or around) 0 °C. Some food products are damaged by freezing!

• E.g. Tomatoes, Strawberries

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Basics, cont.• Damage due to freezing is caused by the ice

crystals during the freezing process. If the crystals are large, the cell membranes of the food is damaged and the texture is changed (or damaged).

• It has been shown that the size of the ice crystals become smaller if the freezing process is fast.

• However, some food products are quite insensitive to large ice crystals. E.g. meat, fish, etc.

• The nuitrition of the food is unaffected by freezing!

Storage time, storage temperature

The storage time depend on temperature!

To determine the storage time, the concept of High Quality Life (HQL) has been defined as:

HQL: Time of storage before first detectable change in quality occur.

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Storage time

Storage time, storage temperatureTo ensure high quality of the food:

1HQL t

<∑ ⎟⎟⎠

⎞⎜⎜⎝

⎛ τ

For the entire life span of the food, this ratio has to be summed.

1HQLHQLHQL C8

C8

C25

C25

C10

C10 <++τ

+τ

+τ

°

°

°−

°−

°

° L

Time of storage at temperature t

HQL of temperature t

where HQLt can be taken from the chart, or…

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Storage time, storage temperatureThe curves of the chart can be expressed by an equation, HQLt can hence be found by:

⎟⎟⎠

⎞⎜⎜⎝

⎛ −

⋅= ref,t

refD

tt

reft eHQLHQL

Dt,ref is determined by choosing two points on the curve, Dt,ref is hence found with:

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

refrefref,t HQL

HQLlnttD

Reference temperature

HQL of an arbitarily chosen reference temperature

Storage time

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Storage temperatures

Storing at low temperatures• Storing products containing water at low

temperatures will result in a certain weight loss (caused by diffusion of water). The product dries.

• Loss of weight means- Loss of quality- Loss of money (products sold per unit weight)

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Storing at low temperatures, cont.• This can be avoided by

- Using a system with a rapid cooling which makes the surface of the products freeze.- Storing products at high humidity (reduces diffusion)- Use wrapping of products to avoid diffusion.

Use of refrigeration in food industry• Common applications of refrigeration in

food industry:- Dairy products (Milk products)- Cheese- Ice cream- Breweries- Meat industry- Fishing industry- etc

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Concentration of fruit juice• Fruit juice is often concentrated in order to

save weight during transportation.• This can be done by:

- Concentration using a heat pump- Freeze concentration

Concentration of fruit juiceConcentration using a heat pump

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Concentration of fruit juiceFreeze concentration

Heat removal

Juice feed

Concentrated juice

Ice Use only about 1/7 of the energy required compared to ”Heat pump concentration”(ΔhFreeze=1/7·ΔhEvap)

Freeze drying• Very expensive• Used for special products where weight is

of importance- Pharmaceutical products- ”Hiking food”

• Other products:- Coffee powder- Soups- etc

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Freeze drying, cont.

Freeze drying, cont.• Product to be dried should be cut in thin

slices to allow for a good water vapor transport.

• Process requires a continuous evacuation of air.

• Requires more energy than freeze concentration since the water is removed by sublimation (ΔhSublimation= ΔhFreeze +ΔhEvap).

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Estimation of cooling demand

τΔ⋅

=hmQ&

Cooling demand can be estimated by:

Mass of product Enthalpy change

Time

Which may be rewritten as:

τ

Δ⋅⋅=

tcmQ p&

How do we get the enthalpy change and the specific heat?

Freezing of products involves a phase-change.

Figure 12.23a. Data also available in table 12.22.

Estimation of cooling demand

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Estimation of cooling demand

Freezing of products involves a phase-change.

Figure 12.23b

Products may also have ”internal heat generation” - Heat of curing (ripening)

Estimation of cooling demand

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Freezing methods• FloFreeze• GyroFreeze• Freezing tunnel• Liquid nitrogen freezer

FloFreeze

Air flow

Fluidized bed

Used for freezing small objects:

Berries, peas, french fries etc

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GyroFreeze

Products to be frozen transported on conveyor belt. Used for freezing larger objects:

Hamburgers, meat balls, etc

Air flow

Evaporator

Air flow

Freezing tunnel

Products to be frozen placed on carts. Sometimes products are already packed.

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Liquid nitrogen freezer

Used for freezing larger objects:Hamburgers, meat balls, etc

Agenda - Course Summary• Course objectives• Course requirements• Bonus points• About the exam

- When and where- Helping aids allowed

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Course objectivesAfter the course the student should be able to

Describe different sources of primary energy and assess their environmental impact.

Describe the utilisation of energy in the present day society.

Explain the physics that govern an indoor climate, and assess the changes needed to improve the indoor climate in existing buildings.

Perform heating/cooling load calculations for a single family residence.

Design heaters (radiators) and connecting tubing, and select a proper circulation pump.

Design a ventilation system to provide an adequate air flow of a proper temperature and humidity.

Explain the basic fundamentals of conventional refrigeration systems, including components like heat exchangers, compressors, and expansion valves.

Develop and describe a computer model of a conventional cooling system.

Describe different types of heating systems, and assess their applicability.

Describe and analyse the function of passive systems.

Briefly discuss alternative cooling processes.

Course objectives, cont.

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Course Requirements• One written exam, 5 credits• Seven project reports, 3 credits• Active participation at laboratory lessons, 1

credits

Project Reports• SEU-SEM1: Heating demand for a single

family residence• SEU-SEM2: Design of heating systems• SEU-SEM3: Design of ventilation systems

• Simulation of a refrigeration system (4 reports, SEU-CL1, SEU-CL2, SEU-CL3, SEU-CL4)

You are required to submit a written report for each of the assignments. SEM1-3 are individual, CL1-4 can be carried out in groups of 2-3 students.

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Laboratory Lessons

Active participation during the lab lessons:SEU-LAB1: Solar CollectorsSEU-LAB2: Flow MeasurementsSEU-LAB3: Basic Refrigeration SystemSEU-LAB4: Heat Transfer from a Tube and Fin Coil

For distance students, corresponding reports needs to be submitted through Bilda.

Bonus points for the exam!In order to promote continuous learning, you

will get bonus points on the exam if you submit the reports before the deadline and receive a passing grade.

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Exam - When and where

Tuesday December 16, 2008, 08.00-13.00Rooms M32-36, M263, + Extra room to be announced.Brinellvägen 64.

The exam starts without academic quarter!

Exam - Helping aids allowedAllowed:• Handouts available on the course homepage• Lecture notes• Summaries of Labs, Computer labs, Seminar assignments, Exercises• Course literature (SEU+Refrigeration book)• Calculator (not pre programmed)• Dictionaries, if permission given by Hans Jonsson

Not allowed:• Solved problems, including instructions and solutions to: Exams, Labs, Computer labs, Seminar assignments, and Exercises.• Books, other than the above stated.

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At the exam• Fill in the exam cover properly!• New question – New paper!• Write neatly!• Adhere to the rules! Attempts or suspicion of

cheating WILL be reported! Rules can be found at: http://www.kth.se/info/kth-handboken/II/11/3bil2.html

• Bring something to eat and drink!• Read through all the questions first!

Help with questions• Wednesday December 10

between 10.30-12.30 and 13.30-14.30

• Thursday December 11between 13.00-15.30

Session with Centra can be requested by email.

Brinellvägen 68, Level 4, Office K429.

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Online Course EvaluationAvailable on BILDA:

- Please help us improve!

Good luck on the exam!

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Agenda - Sustainability Examples• Cogeneration System in Brazil

Heat Exchanger

Micro Turbine

Absorption Chiller Thermax THWCooling Tower

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2

3

4

5

6 7

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9

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Cooling Load

Heat Exchanger

Micro Turbine

Absorption Chiller Thermax THWCooling Tower

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2

3

4

5

6 7

8

9

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Cooling Load

Combined Gas Turbine Cycle and Absorption Chiller for Electricity Supply and Cooling of a Supermarket

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Brazil map

Natal

Rio de Janeiro

Florianópolis

Cooling Load Coverage by Abs. Chiller, yearly

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

Florianopolis Rio de Janeiro Natal

[%]

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Global warming reduction in CO2 equivalents

500,00550,00600,00650,00700,00750,00800,00850,00900,00950,00

1000,00

Florianopolis Rio de Janeiro Natal

[tonn

es]

Electricity Load and Supply (December, Florianópolis)

0,005,00

10,0015,0020,0025,0030,0035,0040,00

0 2 4 6 8 10 12 14 16 18 20 22

Time [Hour]

Elec

tric

ity [k

W]

PloadPtotPout

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Urhuset

• House made of wood• Only a small amount of electricity used• Heated by fire wood, solar heating, and a

ground heat pump

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Snow CoolingBased on Lic.Eng. Thesis by

Kjell Skogsberg, Luleå Univ. Of Technology

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