cooling and cold chain technologies in general.
- 1. ADD YOUR TITLE HERE AGM301 COOLING AND COLD CHAIN Part 1 by: Quenan Gasana E-mail: qgasana@rica.rw
- 2. 0 Why this topic?
- 3. 0 ▪ Foods can become spoiled due to chemical reaction, physical reaction or action of microbes. ▪ Microbes are present in air, water, soil and also in the food we consume. ▪ Lowering the temperature slows down the rapid rate of these bacterial growth in foods. Most bacteria grow at a temperature of 4°C (40°F) to 60°C (140°F). This is the basic principle behind prolonging shelf life of the foods we consume through refrigerated storage. Why this topic?
- 4. 0 What is Cooling and Cold Chain?
- 5. 0 1. Define and explain the basic postharvest handling and treatment for smallholder farmers, achieved 5. Analyze and evaluate the feasibility of establishing and operating Agro-processing industries, 2. Analyze challenges and solutions in Cooling and cold chain management in developing countries, 6. Produce a product/Service to reduce postharvest-losses for smallholder farmers in Rwanda. 3. Innovate and implement mechanical solutions to effectively minimize postharvest losses, 4. Apply advanced technologies and techniques to enhance the value addition to agricultural produce, Learning outcome Upon successful completion of this course, students will be able to:
- 6. 0 Content Pre-cooling of horticultural crops Refrigerant Important terminologies and refrigeration system Refrigeration system accessories Cold storage design
- 7. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling-Purpose ▪ Removal of field heat ▪ Reduce energy required for cold storage ▪ Marketing flexibility ✓ Market at an optimum time (economy & quality) ✓ Market over a longer distance
- 8. 1 PRE-COOLING OF HORTICULTURAL CROPS Importance of pre-cooling ▪ Pre-cooling is the first step of good temperature management of fruits and vegetables after harvest. ▪ It is essential practice in any successful cool chain management of horticultural produce. ▪ However, time and temperature are the two most important features of pre-cooling. ▪ Speed of cooling depends upon: ✓ Accessibility of produce to the refrigerating medium, ✓ Difference between the temperature of produce and refrigerating medium, ✓ Velocity of refrigerating medium Pre-cooled - Alive & Happy Not-Precooled- Faster Sick and Die Effect of pre-cooling
- 9. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling temperature ▪ Generally, horticultural produce are cooled to their storage temperature i.e., ✓ For example, grapes are cooled to 1-4°C, potato to 5–9°C, ✓ Mango, tomato & banana to be cooled to > 10 °C. ▪ All fruits and vegetables are mostly cooled by room cooling and or mechanical refrigeration.
- 10. 1 PRE-COOLING OF HORTICULTURAL CROPS Advantages of Pre-cooling Benefit of pre-cooling ▪ Prevent wilting ▪ Slow the decay rate ▪ Prevent quality loss due to softening ▪ Reduce ethylene production ▪ Minimize the impact of ethylene Inhibition of the growth of decay causing organisms, Restriction of the enzyme activities, Reduction of water loss from the harvested produce, Reduction in rate of respiration and ethylene (C2H4) liberation, and Rapid wound healing.
- 11. 1 PRE-COOLING OF HORTICULTURAL CROPS Principles of cooling Selecting pre-cooling technique ▪ Cooling temperature 0 – 14°C ▪ Reduce temperatures via different means Direct cooling Heat sink medium e.g. cold water, ice and mixture Heat out Indirect cooling Heat sink medium e.g. cold air, cold metal Heat out ▪ Nature of the produce ✓ Temperature requirement ✓ Susceptibility to wetting ▪ Package design ▪ Production capacity ▪ Economic factors ▪ Social factors
- 12. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques Room cooling ▪ Air cooling ✓ Room cooling ✓ Forced air cooling ▪ Hydro cooling ▪ Ice cooling ✓ Top icing ✓ Liquid icing ✓ Individual package icing ▪ Vacuum cooling ▪ Evaporative cooling ▪ Insulated room equipped with refrigeration unit ▪ Disadvantage ✓ Slow cooling rate ✓ Not suitable for produce in large containers 1. Air Cooling
- 13. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques Forced-air cooling ▪ Fan assisted room-cooling ▪ The fan pulls cool air through packaged produce and forces the hot air to leave the package ▪ Cooling rate depends on temperature and the air flow rate ▪ 75 – 90% more efficient than room cooling Anona Coconut Mango Pumpkin Avocado Cucumber Melons Rhubarb Banana Eggplant Okra Strawberry Breadfruit Grape Orange Summer Squash Brussels sprout Grapefruit Papaya Tangerine Carambola Guava Passion fruit Tomato Cassava Kiwi Pepper Pineapple Cherimoya Kumquat Persimmon Pomegranate Litchi Prickly pear 1. Air Cooling
- 14. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques 2. Hydro-cooling ▪ The flow of chilled water over produce ▪ Disadvantages ✓ Limited to produce that are not sensitive to wetting ✓ Not energy efficient (20-40% efficiency) ▪ Critical point ✓ Good water sanitization practice ✓ Proper packaging Hydro-cooling-Packaging ▪ Wire-bound wooden crates ▪ Waxed fiberboard cartons ✓ Should not have solid top ▪ Mesh bags ▪ Bulk bin Hydro-cooling Produce
- 15. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques 3. Ice-cooling ▪ Ice continues to absorb heat as it melts ▪ Suitable for ✓ Produce with high respiration rate ✓ Dense product or palletized packages ▪ Relatively energy efficient ✓ 1 lb of ice cool 3 pounds of produce (85°F to 40°F) ▪ Maintain low temperature during transportation Liquid icing ▪ Crushed ice is added over the top of the produce Broccoli, Carrot, Leek Brussels sprouts, Chinese cabbage, Parsley Cantaloupe, Green onions, Peas Top-icing Individual package icing ▪ Add measured amount of crushed ice over the produce ▪ Disadvantages ✓ Uneven cooling ✓ Labor intensive ✓ Limited to low volume product ▪ Some automated system is available using ice dispenser & conveyor ▪ Injecting slurry of ice & water into the package through vents or hand holes ▪ Excellent cooling method for both large & small operation ▪ Disadvantages ✓ Limited to produce that are not sensitive to wetting ✓ Warm, wet produce is prone to post harvest diseases
- 16. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques 3. Ice-cooling Ice-cooling: packaging ▪ Hold strength after wetting ▪ Example ✓ Wax fiberboard cartons: o Minimal openings o Insulation properties ✓ Baskets ✓ Wooden wire-bound crates ✓ Hampers ✓ Perforated plastic liners Produce can be iced Produce can be damaged by direct contact with ice Artichokes Strawberries Asparagus Blueberries Broccoli Raspberries Leafy green Tomatoes Watermelon, cantaloupe Green beans Carrot Cucumbers Radishes Herbs Spinach Garlic Swe et corn Squash
- 17. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques 4. Vacuum cooling ▪ Vacuum around the produce causes water to evaporate rapidly thus reducing the temperature ▪ Vacuum is created by putting produce in the metal container. Then, the air is evacuated ▪ Disadvantage: wilting (if overdone) ▪ Hydro vacuum cooling o Spray water onto the produce before vacuum process Produce ▪ High surface: volume ratio ▪ Produce difficult to cool with Forced- air or Hydro-cooling Brussels sprouts Chinese cabbage Snap beans Carrot Leek Spinach Cauliflower Lettuce Sweet corn Celery Peas Swiss chard
- 18. 1 PRE-COOLING OF HORTICULTURAL CROPS Pre-cooling techniques 5. Evaporative cooling ▪ Misting/wetting in the presence of dry air stream (RH<65%) to cause evaporation ▪ Effective and inexpensive means of providing low temperature & high RH conditions ▪ Good for warm season crop such as tomatoes, pepper, cucumbers or eggplant Comparison of cooling method
- 19. 1 PRE-COOLING OF HORTICULTURAL CROPS ALTERNATIVE COOLING METHODS Solar assisted cooling chamber ▪ Temporary fruit storage at farm ▪ Hollow wall constructed from porous clay bricks ▪ The wall is kept moist ▪ Solar energy evaporated the water in the wall reduce temperature ▪ Can achieve o 4-5°C < ambient o 85-90% RH inside the structure High altitude storage ▪ Every 1000 m, the temperature decreases by 1.8°F (1°C) ▪ Storing produce at high altitude reduce energy required for cooling Night ventilation ▪ Requires o Large temperature difference between day and night o Well insulated structure o Close vents hole early in the morning
- 20. 2 Refrigerant Refrigerant ▪ Working fluid in the refrigeration ▪ It is capable of absorbing heat at lower temperature and rejecting heat at higher temperature in the form of sensible heat and latent heat. Ice Water Vapour Latent Heat of Melting Latent Heat of Freezing Latent Heat of Vaporization Latent Heat of Condensation Sensible Heat Sensible Heat Sensible Heat
- 21. 2 Sensible Heat (that can be sensed/felt) ▪ It is the energy moving from one system to another that changes the temperature without changing its phase. ▪ When the substance is heated, and the temperature rises, so the heat added is called sensible heat. ▪ This increase in heat can be felt physically or measured with ordinary thermometer. Latent Heat ▪ The heat needed to change one form of matter to another without change in temperature. So, it can be latent heat of vaporization or latent heat of condensation. Refrigerant
- 22. 2 Characteristics of Refrigerant • should be high Latent heat of vaporization • should be low Condensing pressure • should be low Freezing temperature • should be high Critical temperature • should be nontoxic, nonflammable, non-corrosive and chemically stable Toxicity, flammability, corrosion and chemical stability • should be low Cost • any leak of refrigerant to the environment should not cause any harm Environment friendly Refrigerant
- 23. 2 Classification Refrigerants Refrigerants Primary Refrigerants Used directly as working fluids. Undergo phase change. eg., R134a, R404a Secondary Refrigerants Liquids that are used to transport energy. Not undergo and phase change eg., Water , brines. Primary refrigerants ▪ Cool the substance or space directly by absorbing latent heat. ▪ It absorbs heat during evaporation in the evaporator and releases heat energy during condensation in condenser. ▪ E.g. Ammonia, Freon, SO2, CO2 etc. ▪ These fluids provide refrigeration by undergoing a phase change process in the evaporator. Secondary Refrigerants ▪ In refrigeration plant a secondary coolant is used as cooling medium which absorb heat from refrigerated space and transfer to primary refrigerant in evaporator. Secondary refrigerants are also known under the name brines or antifreezes Refrigerant
- 24. 2 Classification Of Primary Refrigerant Examples : o CFC’s : R11, R12, R113, R114, R115 o HCFC’s : R22, R123 o HFC’s : R134a, R404a, R407C, R410a 1. Halocarbon Refrigerants Are all synthetically produced and were developed as the Freon family of refrigerants. They contain 1 or more of these halogens (chlorine, bromine, fluorine) Composition: Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), Hydrofluorocarbons (HFCs) Types: Nontoxic, non-flammable, non-explosive, non- corrosive, non-irritant to human body and eyes, Odorless, colorless, Will not react with food product stored in the refrigerated space, Will not react with lubricating oil. Properties: Refrigerators and freezers, Air conditioning systems, Heat pumps, Industrial cooling processes Applications: CFCs and HCFCs deplete the ozone layer, Many halocarbon refrigerants are potent greenhouse gases Environmental concerns: Refrigerant
- 25. 2 Freon Group Refrigerants Application and ODP Values Refrigerant Areas of Application ODP CFC 11(R11) CFC 12 ( R 12 ) CFC 13 (R 13) CFC113 ( R113 ) CFC114 ( R114 ) Blend of R22 and R115 (R502) ▪ Air-conditioning Systems ranging from 200 to 2000 tons in capacity. It is used where low freezing point and non-corrosive properties are important. ▪ It is used for most of the applications. Air-conditioning plants, refrigerators, freezers, ice-cream cabinets, water coolers, window air-conditioners, automobile air conditioners. ▪ For low temp refrigeration up to – 90 C in cascade system ▪ Small to medium air-conditioning system and industrial cooling ▪ In household refrigerators and in large industrial cooling ▪ Frozen food ice-cream display cases and warehouses and food freezing plants. An excellent general low temp refrigerant 1.0 1.0 1.0 1.07 0.8 0.34 Refrigerant
- 26. 2 2. Inorganic Refrigerants ▪ Inorganic refrigerant were exclusively used before the introduction of halocarbon. ▪ These refrigerant are still in use due to there inherent thermodynamic and physical properties. • Carbon Dioxide • Water • Ammonia • Air • Sulphur dioxide Refrigerant
- 27. 2 2. Inorganic Refrigerants ▪ Used for commercial purposes mainly in cold stored and ice plants. ▪ The boiling temperature of NH3 at atmospheric pressure is -33 ºc and melting point from solid is -78ºC The low boiling points makes it possible to have refrigeration considerably below 0ºC without using pressure below atmospheric in the evaporator. ▪ Its latent heat of vaporization at -15ºC is 1315 k/kg ▪ It is colorless gas with a sharp pungent smell ▪ Has good thermodynamic properties ▪ It is neutral to all metals, highly soluble in oil. ▪ Volatile and non-toxic but in higher conc. Ammonia (NH3) R-717 Refrigerant
- 28. 2 2. Inorganic Refrigerants ▪ Previously used in household refrigerators ▪ Toxic, non-explosive and non-flammable, non-corrosive ▪ Irritant to human body ▪ Non mixable with oil ▪ Has pungent odor and low latent heat value Sulphur Dioxide (So2) Refrigerant
- 29. 2 3. Azeotrope Refrigerants ▪ This group of refrigerants consist of mixture of different refrigerants which can not separated under pressure and temperature and have fixed thermodynamic properties. ▪ A stable mixture of two or several refrigerants whose vapor and liquid phases retain identical compositions over a wide range of temperatures. ▪ Azeotropic mixtures are designated by 500 series ▪ Examples : • R-500 :( 73.8% R12 and 26.2% R152) • R-502 : (8.8% R22 and 51.2% R115) • R-503 : (40.1% R23 and 59.9% R13) Refrigerant
- 30. 2 4. Zeotropic Refrigerants ▪ A zeotropic mixture is one whose composition in liquid phase differs to that in vapor phase. Zeotropic refrigerants therefore do not boil at constant temperatures unlike azeotropic refrigerants. ▪ zeotropic refrigerants (e.g. non-azeotropic mixtures) are designated by 400 series. ▪ Examples : • R404a : R125 /R143a /R134a (44%,52%,4%) • R407c : R32/R125/R134a (23%, 25%, 52%) • R410a : R32/R125 (50%, 50%) • R413a : R600a/ R218/R134a (3%, 9%, 88%) Refrigerant
- 31. 2 5. Hydrocarbons ▪ Most of the hydrocarbon refrigerant are successfully used in industrial and commercial installation . They possess satisfactory thermodynamic properties but are highly flammable and explosive. ▪ Growing use in very small commercial systems like car air-conditioning system ▪ Examples: • R170, Ethane, C2H6 • R290 , Propane C3H3 • R600, Butane, C4H10 • R600a, Isobutane, C4H10 • Blends of the above Gases Refrigerant
- 32. 2 Secondary Refrigerant ▪ The refrigerants are brine which is used as intermediate fluid between evaporator and the substance or space to be cooled. They cool the substance and the space by absorbing their sensible heat. Also called indirect expansion system. • Eg. Brine solution made of calcium chloride or sodium chloride ▪ Water cannot be used as secondary refrigerant because at 0 ºC itself it will become ice and circulation is not possible. In brine solution CaCl2 is much preferred, it is very costly ▪ Choice of brine depends on temperature to which a material is to be cooled and industrial process in which it is to be used. The calcium chloride brine has eutectic temperature of -55 ℃ at salt concentration of 30% by mass. The sodium chloride brine has eutectic temperature of -21.1 ℃ at salt concentration of 23% by mass ▪ Freezing point of brine depends on its concentration. Cheapest secondary refrigerants are water and air but their application is limited. Since, water has a high freezing point (00C) and air has a low heat capacity. Refrigerant
- 33. 2 Designation of refrigerants: ▪ Since a large number of refrigerants have been developed over the years for a wide variety of applications, a numbering system has been adopted to designate various refrigerants. From the number one can get some useful information about the type of refrigerant, its chemical composition, molecular weight etc. All the refrigerants are designated by R followed by a unique number. Environmental and safety properties ▪ Ozone Depletion Potential (ODP) ▪ Global Warming Potential (GWP): ▪ Total Equivalent Warming Index (TEWI) ▪ Toxicity ▪ Flammability ▪ Chemical stability ▪ Compatibility with common materials of construction ▪ Miscibility with lubricating oils: Refrigerant
- 34. 2 Boiling Temperature Refrigerant Boiling Temperature at atm pressure R-11 +21.77 R-12 -29 R-21 +9 R-22 -41 R-30 +39.8 R-40 -23.7 R-113 +47.6 R-717 -33.3 R-764 -10 Refrigerant Freezing Temperature Refrigerant Freezing Temperature R-11 -111 R-12 -157.5 R-21 -135 R-22 -160 R-30 -96.9 R-40 -97.5 R-113 -35 R-717 -77.8 R-764 -75.6
- 35. 3 Important terminologies and refrigeration system 1. Cooling load ▪ Cooling load is the rate of removal of heat from a defined space in order to lower the temperature of that space to a desired level. ▪ The cooling loads of refrigeration systems are designated with a common unit called ton of refrigeration (TR). 2. Ton of refrigeration (TR) ▪ Amount of heat required to be removed from one ton of water at 0°C in order to convert it into ice at 0°C in one day (24 hours). ▪ 1TR= 12600 KJ/h or 210 KJ/min or 3.5 KW
- 36. 3 3. Coefficient of Performance (COP) ▪ The efficiency of the refrigeration system is also indicated as Coefficient of Performance of the system. ▪ It is the ratio of the heat extracted in the refrigerator to the work done on the refrigerant. ▪ COP =Amount of heat extracted in the refrigerator (Q) Amount of work done (W) COP = Q W Important terminologies and refrigeration system
- 37. 3 4. Relative Humidity ▪ It is the actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature. Important terminologies and refrigeration system
- 38. 3 Condenser Evaporator High Pressure Side Low Pressure Side Compressor Expansion Device 1 2 3 4 ▪ Refrigeration system is based on the principle that absorption of heat by a fluid (refrigerant) as it changes from a liquid to a gas, lowers the temperature of the objects around it. ▪ The most common type of refrigeration system applying this principle is Vapour Compression Refrigeration (VCR) System. ▪ The VCR System is widely used in refrigeration applications like refrigerator, water cooler, air conditioner and cold storage. ▪ The refrigeration effect is produced at the evaporator. Important terminologies and refrigeration system
- 39. 3 Low Pressure Low Temperature Vapour High Pressure High Temperature Vapour High Pressure High Temperature Liquid Low Pressure Low Temperature Liquid Compressor Condenser Expansion Valve Evaporator Refrigeration System Heat Important terminologies and refrigeration system
- 40. 3 Important terminologies and refrigeration system
- 41. 3 ▪ The low-pressure low temperature liquid refrigerant absorbs and removes heat from the inside cabinet. ▪ This low-pressure refrigerant from evaporator turns into saturated vapor which is then compressed water- or air-cooled high ▪ pressure and passed to the condenser. The heat is rejected in the condenser. Then the saturated liquid refrigerant enters the expansion valve, where it is undergoes pressure reduction. ▪ After expansion valve the refrigerant again enters the evaporator and the cycle continues. A fan is used to force the warm air over the evaporator coils. The condenser may be water or air-cooled type. Important terminologies and refrigeration system