What is an air conditioner evaporator?
Air conditioner evaporators are refrigeration devices.
Air conditioner evaporators are key components in refrigeration systems. They achieve cooling by absorbing heat and vaporizing low-temperature, low-pressure liquid refrigerant after throttling through the expansion valve. Their structure primarily consists of the evaporator core, expansion valve, and air duct.
Based on their design, air conditioner evaporators can be divided into three categories:
The tube-fin type uses aluminum fins wrapped around round tubes to form a condensed form, but this can lead to contact thermal resistance issues caused by differences in the thermal expansion coefficients of the tube-fins.
The tube-band type combines porous flat tubes with corrugated heat dissipation strips through brazing, requiring extremely high material uniformity to prevent cracking.
The plate-fin type uses stamped plates stacked together to form the refrigerant channels, with heat dissipation strips sandwiched between them. This provides the most compact structure and represents a future development trend.
How an Air Conditioner Evaporator Works:
Refrigerant from the expansion valve or throttling tube enters the evaporator, where it suddenly expands in volume, transforming into a low-temperature, low-pressure mist (particles of liquid). When this refrigerant comes into contact with the warmer evaporator walls, it easily absorbs heat and vaporizes.
When air flows over the evaporator surface, it contacts the evaporator tube sheet with extremely low surface temperature. The heat in the air is absorbed by the tube sheet and transferred to the refrigerant in the evaporator, causing the liquid refrigerant to vaporize, and the air becomes colder because the heat is taken away.
Air conditioning evaporator is the main working part in the refrigeration field and is widely used in various industrial equipment with refrigeration systems such as household air conditioners, ships, and automobiles.
In the ship air conditioning system, it is responsible for exchanging and updating the air outside and inside the ship.
In the automotive application scenario, the air conditioning evaporator is a component that directly generates cooling capacity, and its performance directly affects the comfort inside the car. Due to the strict installation space inside the car, the air conditioning evaporator must meet the requirements of miniaturization and lightweight.
The design must focus on the rationality of the condensate discharge path. The top-mounted evaporator also needs to solve the challenge of sealing and anti-leakage, and the expansion valve cooling capacity must reserve a margin to ensure compatibility with the entire vehicle air conditioning system.
Classification of Air Conditioner Evaporators
According to the type of cooled medium, evaporators can be divided into two categories:
(1) Evaporators that cool liquid refrigerants. They are used to cool liquid refrigerants such as water, brine or ethylene glycol aqueous solution. Commonly used evaporators of this type include horizontal evaporators, vertical tube evaporators and spiral tube evaporators.
(2) Evaporators that cool air. These evaporators have cooling pipes and air coolers.
Horizontal evaporators
Its structure is basically similar to that of horizontal shell and tube condensers. According to the liquid supply method, it can be divided into shell and tube evaporators and dry evaporators.
Horizontal shell and tube evaporators are widely used in closed brine circulation systems.
Its main features are: compact structure, good contact between liquid and heat transfer surface, and high heat transfer coefficient. However, it needs to be filled with a large amount of refrigerant, and the liquid column will have a certain impact on the evaporation temperature. And when the brine concentration decreases or the brine pump stops for some reason, the brine may be frozen in the tube. If the refrigerant is Freon, the lubricating oil dissolved in the Freon will have difficulty returning to the compressor.
The compressor must be shut down for cleaning. The main difference with a dry Freon evaporator is that the refrigerant flows inside the tubes, while the secondary coolant flows outside. The throttled Freon liquid enters the evaporator through the lower end cap on one side and, after several passes, is drawn out from the upper end cap. As the refrigerant evaporates as it flows through the tubes, a portion of the wall surface is occupied by vapor. Therefore, its heat transfer efficiency is not as good as that of a flooded evaporator. However, the liquid column does not affect the evaporation temperature, and the high Freon flow rate (≥4 m/s) improves oil return.
Because a large amount of secondary coolant is filled outside the tubes, the risk of freezing is reduced. This type of evaporator only requires 1/2 to 1/3 or less of the refrigerant charge of a flooded evaporator, hence the name “dry evaporator.”
Vertical Tube Evaporator
Both vertical and spiral tube evaporators share the same principle: the refrigerant evaporates within the tubes. The entire evaporator tube assembly is immersed in a chamber (or pool or tank) filled with refrigerant. To ensure the refrigerant circulates at a constant rate within the chamber, longitudinal baffles are welded inside and a spiral agitator is installed. The refrigerant flow rate is generally 0.3 to 0.7 m/s to enhance heat transfer.
These evaporators can only be used in open-circulation systems, so the refrigerant must be non-volatile, commonly used being brine or water. Using brine can easily oxidize the evaporator tubes, and the brine absorbs moisture, reducing its concentration. These evaporators allow for direct observation of the refrigerant flow and are widely used in brine refrigeration systems using ammonia as the refrigerant.
Air Conditioner Evaporator Tube Types
Cooling Tubes
Cooling tubes are a type of evaporator used to cool air. Widely used in low-temperature cold storage, refrigerant flows and evaporates within the cooling tubes, while the cooled air outside the tubes acts as a heat transfer medium through natural convection.
The greatest advantage of cooling tubes is their simple structure, ease of fabrication, and minimal dry-out of non-packaged food stored in the warehouse. However, the tubes have a low heat transfer coefficient and are difficult to operate during defrosting, making them difficult to automate. For direct ammonia cooling systems, seamless steel pipes are welded, using either plain tubes or wound finned tubes. For Freon systems, coiled or sleeved copper tube finned tubes are generally used.
Coil Tubes
Coil tubes can be fed with either gravity or ammonia pumps. Single-row and double-row coil wall tubes can be used in bottom-in, top-out ammonia pump feed systems and gravity feed systems. Single coil tubes can also be used in top-in, bottom-out ammonia pump feed systems and thermal expansion valve feed systems.
The advantages of serpentine ducting are its simple structure, ease of fabrication, low liquid storage volume, and wide applicability. However, its main disadvantage is that steam generated in the lower section of the duct cannot be promptly discharged and must travel the entire length of the duct before being discharged. This results in a low heat transfer coefficient and high resistance to vapor-liquid two-phase flow.
U-shaped ducting
Commonly used U-shaped ducting tubes are constructed from two or four layers of smooth, seamless steel pipe.
U-shaped top ducting tubes have the advantages of more uniform frost formation, ease of fabrication and installation, and a small liquid charge of approximately 50% of their volume. They are suitable for gravity-fed systems and ammonia refrigeration systems with bottom-in, top-out pumps, and are widely used in cold storage. However, they occupy more available warehouse space, and the upper ducting tubes are difficult to defrost.
Air Conditioner Evaporator Cooler
An air cooler is typically a complete unit consisting of an axial-flow fan and cooling ducts. The fan forces air from the warehouse to flow through the cooling ducts within the cabinet, exchanging heat and cooling the air, thereby lowering the warehouse temperature.
Air coolers can be categorized by the cooling method used: dry, wet, and a combination of dry and wet. Dry air coolers use a refrigerant or brine flowing through the ducts, cooling the air outside through the tube walls. Wet air coolers use a sprayed brine liquid for direct heat exchange with the air. Hybrid air coolers, in addition to cooling the ducts, also have a brine spray system. The following describes the dry air coolers commonly used in cold storage.
Common dry air coolers in cold storage can be categorized by their installation location into two types: ceiling-mounted and floor-standing. They all consist of air cooling ducts, a ventilator, and a defrost device, and the cooling ducts within the cooler are all sleeved. Large dry air coolers are often floor-standing.
Air Conditioner Evaporator Product Features
Product Features: This evaporator is for air conditioners. It features an internally threaded tube with a large internal surface area, louvers for excellent ventilation, and corrugated fins for a large heat dissipation area. It is constructed from a curved U-shaped tube that passes through fins, then undergoes expansion and welding.
Product Application: Air conditioning and refrigeration systems.
| Product Series | Air Conditioning Evaporator (GB) |
|---|---|
| Main Raw Materials | Evaporator: φ7 internally grooved copper tube; Condenser: φ7.94 or φ9.52 copper tube (internally grooved/smooth); Aluminum foil (smooth/hydrophilic film); Corrugated fin φ7 tube evaporator holes: row pitch 21mm, column pitch 12.7mm; φ9.52 tube evaporator/condenser holes: row pitch 25mm, column pitch 21.65mm; φ7.94 tube evaporator/condenser holes: row pitch 22mm, column pitch 19.05mm |
| Structural Form | Formed by bending U-shaped tubes through fins, followed by expansion and welding. |
| Heat Exchange Method & Performance | Refrigerant → copper tube → corrugated fin; Internally grooved tube provides larger surface area; Louvered window offers excellent ventilation; Corrugated fin increases heat dissipation area |
| Surface Treatment | None |
| Internal Quality | No rust debris, moisture content ≤50mg/m², dust content ≤30mg/m² |
| Product Specifications | 1. φ9.52 specification: 900mm×1000mm×21.65T; 2. φ7.94 specification: 794mm×1200mm×19.05T; 3. φ7 specification: 756mm×1200mm×12.7T; 4. Compatible with 1-6HP air conditioners, specific models: 23, 25, 32, 35, 45, 50, 60, 70, 76, 120, 130 |