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ADVANCES IN FOOD REFRIGERATION Tuan Pham School of Chemical Engineering and Industrial Chemistry University of New South Wales tuan.pham@unsw.edu.au. History of Food Refrigeration. Harrison - ice making (1860), frozen meat export (1873) China 1000BC - ice harvesting
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ADVANCES IN FOOD REFRIGERATIONTuan PhamSchool of Chemical Engineering and Industrial ChemistryUniversity of New South Walestuan.pham@unsw.edu.au
Annual investment in refrigerating equipment: US$170
Annual refrigerated foodstuffs: US$1200 billion
(3.5 times USA military budget)
700-1000 million household refrigerators
300 000 000 m3 of cold-storage facilities
and causes big problems!
Ozone-depleting effects - Montreal protocol
Global-warming effects - Kyoto agreement
Part I: Common industrial problems
- Chillers and freezers
- Cold stores
- Refrigerated transport
- Retail display
Chillers and freezers can be classified into
air-cooled
immersion
spray
cryogenic
surface contact chillers.
Immersion and Spray Chillers/Freezers
faster than air chilling, especially for small products
absorption of liquid or solutes by the product, leading to undesirable appearance or other quality losses
cross-contamination between products
leaching of food components such as fat
effluent disposal problem
Include plate chillers/freezers, mould freezers, belt chillers, scraped surface freezers
High heat transfer rate (similar to immersion freezers) - only metal bw refrigerant & product
No absorption of liquid
No liquid effluent.
Need products with flat surfaces, such as cartons Preferably thin or small products such as fish and peas.
Labor intensive or need sophisticated automation.
Freezing time
Surface resistance
Internal resistance
Problems with transport vehicles & containers are same as in cold rooms, but multiplied several-fold (because of high A/V ratio and fluctuating ambient conditions)
Food remains safe and wholesome according to specifications.
Ability to handle different products or production rates
Freezers and chillers:
An undersized cooling coil or freezer will require oversized compressors, condensers etc.
Objectives: to predict changes in
- finite differences
- finite elements
- finite volumes
Accuracy of predictions by various models
(based on 70 beef chilling tests)
Can simulate the flow field outside the product (air, water, cryogen...) as well as inside
Computationally expensive (fast computers, lots of memory, days of runtime)
Software expensive (especially for non-U)
Need lots of expertise to use properly
Need lots of time for data preparation
Accuracy NOT guaranteed even when all the above are satisfied!
Why is CFD not quite accurate?
Weight loss, dry appearance
Water absorption, bloated appearance
Drip
Crystal growth (ice cream)
Water penetration (bakery products)
Tenderness (beef, lamb)
Fat rancidity flavour
PSE (pale soft exudative) (pork)
DFD (meat)
Flavour (fish)
Colour (meat)
Browning, spots, freezing injury (fruit)
Tissue breakdown (fruit)
Growth Rate = Optimum rate
× Temperature Inhibition Factor
× Water Activity Inhibition Factor
× pH Inhibition Factor
× Other Inhibition Factors
Optimizer
Results:
Product quality
Cost
Reliability
etc...
Process inputs:
Air temperature
Washing, cleaning
Product shape, wrap...
etc.
Process model
Gradient (classical) methods
- fast & methodical
- ends up at nearest local optimum
Stochastic methods (SA, GA...)
- methods with madness
- can be time consuming - 100,000 trials?
- better at obtaining global optimum
- better at dealing with errors
- can perform multi-objective optimisation
A variable temperature regime is the answer:
Css weight
Air T, v
Controller
FREEZER
(16-h lag)
Process
Model
Optimizer
Frozen csses
