Primary Components. Types of Evaporators. Air Units: a common type of. t f d i ld t
evaporator found in cold storages, pre-coolers, and mechanical freezers.
Two Primary Types Types Of Refrigeration Systems Cryogenic System
Mechanical System
An open system that uses the refrigerant once and then vents it into the atmosphere. t h
A sealed system that uses the same refrigerant over and over.
Examples: A freezing system using liquid nitrogen (LN2) or carbon dioxide (CO2).
Examples: A system that uses Ammonia (NH3) or Freon as the refrigerant. We’ll focus on mechanical systems today.
How It Works How Does Mechanical Refrigeration Work? 1 TTo cool the air or liquid, it moves through a heat exchanger (evaporator), transferring its 1. l th i li id it th h h t h ( t ) t f i it heat into the refrigerant. 2. The refrigerant inside the evaporator must be maintained at a lower temperature than the air or liquid. Heat (high energy) moves to cold (low energy). i li id H t (hi h ) t ld (l ) 3. Temperature of refrigerant is controlled by the pressure inside the evaporator. (Pressure‐Temperature relationship) 4. The liquid refrigerant inside the evaporator absorbs the heat, changing state to vapor. (boiling)
How It Works How Does Mechanical Refrigeration Work?
Examples: At 33.5 PSIG, Ammonia boils at +20°F. At 3.6 PSIG, it boils at ‐20°F. All fluids have a “Pressure – Temperature” Relationship.
How It Works That means… By maintaining the desired pressure By maintaining the desired pressure inside the evaporator we get the inside the evaporator we get the desired temperature. The temperature at that boiling point determines how much heat is absorbed into the refrigerant, changing the liquid refrigerant to a vapor.
Primary Components Four Primary Components Of A Mechanical System
Evaporator: This is where the heat f from the product or space is th d t i transferred into the refrigerant. It’s main function is to remove heat from air or liquid. There are several types of evaporators used in food processing evaporators used in food processing industry.
Primary Components Types of Evaporators
Air Units: a common type of evaporator found in cold storages, t f di ld t pre‐coolers, and mechanical freezers. They are a combination of fans and a coil. Air is blown over the tubes which contains refrigerant. Other names: evaporators coils Other names: evaporators, coils
Primary Components Types of Evaporators
Shell And Tube Heat Exchangers: primarily i il used to cool fluids. Fluid dt l fl id Fl id being cooled is pumped through the tubes while the liquid refrigerant is in the shell. Applications: chill glycol, wine, water
Primary Components Types of Evaporators
Plate and Frame Heat Exchangers: plates stacked together containing l t t k d t th t i i refrigerant or product in alternating plates. These have extremely good heat transfer characteristics. Applications: chill glycol, wine, water
Primary Components Four Primary Components Of A Mechanical System
Compressor: the largest electrical user in a food storage facility is the i f d t f ilit i th compressor. It maintains the evaporator refrigerant pressure required to give desired evaporator temperature and to compress the refrigerant gas from the evaporator to a higher pressure the evaporator to a higher pressure. There are primarily three types of compressors…
Primary Components Types of Compressors
Rotary Screw Compressor: The most common type used. These units are t d Th it typical 100 HP to 1,000 HP. Wide range of applications and can be used in a single stage system or as the high stage or booster in a two‐ stage system.
Primary Components Types of Compressors
Reciprocating Compressor: these units have pistons going up and it h it i d down compressing gas, similar to a car engine. Typically 50 HP to 200 HP and can be used in a single stage system or as the high stage or booster in a two‐ stage system Limited compression stage system. Limited compression ratio.
Primary Components Types of Compressors
Rotary Booster Compressor: These are no longer manufactured but l f t db t there are still many in operation. They are used only as boosters in two stage systems.
Primary Components Four Primary Components Of Any Refrigeration System Condenser: high pressure gas is cooled and condenses back to liquid. This is where all of the heat from the cold storage and from the food product is transferred out of the refrigeration system. Fans blow air through coils as water is pumped over them. The water evaporates, absorbing the heat in the refrigerant gas, and the energy is rejected into the atmosphere.
Primary Components Four Primary Components Of Any Refrigeration System
Expansion Device: function is to control the flow of refrigerant from l h fl f fi f high (condensing pressure) to low (evaporating pressure) and controls the flow of liquid refrigerant into the q g evaporator. Several Types: hand expansion valve, motori ed modulating valve thermal motorized modulating valve, thermal expansion valve, etc.
Hand Expansion p Valve
Motorized Modulating g Valve
Thermal Expansion p Valve
Refrigeration System
Refrigeration System
Refrigeration System Commercial System ‐ Freon Only Ex: supermarkets, convenience stores, and small cold storages p , , g
Condensing Unit: The outdoor condensing unit contains both the d i it t i b th th compressor and condenser.
Air Unit: Standard air unit with thermal expansion valve and electric thermal expansion valve and electric defrost.
Applications Cold Storage
Cold Storage: Large rooms/buildings, typically 0°FF to ‐20 typically 0 to 20°FF, for storing for storing frozen foods. Found in large processing plants and as food distribution centers. Refrigeration systems can be shut off, sometimes for hours, without temperature gain that damages temperature gain that damages frozen food.
Applications Cooler
Cooler: Typically +32°F to +40°F for storing perishable refrigerated food storing perishable, refrigerated food products. Because product temperature has a very tight tolerance, length of time the refrigeration can be off is very limited.
Applications Types Of Mechanical Freezers
IQF Belt Freezer: A long tunnel type f freezer with one or two belts. ith t b lt To freeze mostly small, IQF products such as peas, cut corn, French fries, onions, pizza topping, shredded cheese, etc. Usual retention time is under 20 Usual retention time is under 20 minutes.
Applications Types Of Mechanical Freezers:
Spiral Freezer: spiral wound belt with many tiers to freeze items requiring a ti t f it ii longer retention time such as chicken parts, fish fillets, hamburger patties, potato co‐products, entrees, pizzas, etc. Usual retention time is 30‐60 minutes. minutes
Applications Types Of Mechanical Freezers:
Variable Retention Freezer: also called a carton freezer, is a large unit ll d t f i l it with moving conveyors or trays. For long retention time products like pies, tubs of ice cream, or turkeys and cartooned (boxed) products like chicken parts, turkey parts, meat. Retention time 2‐12 hours or possibly longer.
Applications Types Of Mechanical Freezers:
Blast Freezer: small room with large coil inside This is a batch operation coil inside. This is a batch operation with racks, loaded with product, manually put into and removed from the freezer. Retention time more than an hour, sometimes up to 20 hours.
Applications Types Of Mechanical Freezers:
Plate Freezer: vertical or horizontal plates Also called contact freezers plates. Also called contact freezers because the product is in direct contact with the heat exchange plate surface. Product is pumped or placed between the movable plates and refrigerant is pumped through the refrigerant is pumped through the plates. Vertical plate freezers are used to freeze meat, offal, and fruit products into 50‐60 lb blocks. Usual retention time is 2‐4 hours.
Horizontal
Vertical
Applications Types Of Mechanical Freezers:
Flat Product Freezer: specific type f freezer for quickly freezing thin f i kl f i thi product like hamburgers and fish fillets. Designed specifically to replace LN2 freezers.
Applications Food Freezing Load Calculation:
Product: Green Peas Quantity: 10,000 lbs/hr Temperature: Entering +70F Exiting: 0F (equilibrated)
Applications Food Freezing Load Calculation:
1) Product Load Specific Heat above freezing is
0.79 btu/lb F
39F (+70F ‐ +31F) x 0.79 Latent Heat (from chart) Latent Heat (from chart)
= 30.8 btu/lb = 106.0 btu/lb 106 0 btu/lb
Specific Heat below freezing is
0.42 btu/lb F
+31F (+31F ‐ 0F) x .42 TOTAL:
= 13.0 btu/lb = 139.8 btu/lb
10,000 lb/hr x 139.8 BTU/lb = 116.5 TR 12,000 BTU/TR
Applications Food Freezing Load Calculation:
2)Base Load Motors (116 HP x 3 000 btu/h/HP) Motors (116 HP x 3,000 btu/h/HP)
= 348 000 btu/h = 348,000 btu/h
Enclosure
= 60,000 btu/h
Other (lights, etc.)
= 84,000 btu/h TOTAL: = 492,000 btu/h 492,000 btu/h 12,000 btuh/TR
= 41.0 TR
3) Safety Factor 5% (water, uneven product feed):
= 6.0 TR
TOTAL LOAD
= 163.5 TR
