Generally speaking, most air conditioner heat exchanger is made of copper inner groove tube and outside use aluminum fins to expand on it to enhance the heat exchange efficiency.
But there is a metal potential difference between the inner copper tube and the outer aluminum fin, which causes electrochemical corrosion to easily occur, denatures the aluminum fin, and reduces heat exchange efficiency.
1. What is the aluminum groove tube?
Inner grooved tube for air conditioning & refrigeration heat exchangers is available in two designs
Straight inner groove tube: extruded tube with longitudinal grooves
Helical inner groove tube: extruded tube, precision drawn, and grooved with helical inner grooves.
the two tube-type have their own characteristics, but they will both give a significant increase in heat transfer coefficient compared to a smooth tube. This makes them perfect for the design of new high-performance fin & tube heat exchangers as well as for the replacement of copper inner groove tube used in the past.
2. The production method of aluminum inner grooved tube
It needs 4 steps of production processing to produce the aluminum inner groove tube.
- Tooth pressing treatment
Aluminum ingots are extruded and the first drawing dies to be the aluminum belt which is used for tooth pressing treatment to form grooves on the aluminum belt.
- Inner tooth formed treatment
Shaping the aluminum strip after the toothing treatment to form an internal thread tube blank after the first drawing steps.
- Tube blank gap welding
There is an internal thread tube blank gap after the first drawing steps and start to weld the tube blank completely and utterly.
- Shaping and heat treatment
After finishing gap welding, we are doing shaping and heat treatment for tubing itself and finally get the aluminum inner grooved tube.
The method includes two twisting-drawing steps, The first twisting-drawing step forms an intermediate twisted tube, the second twisting-drawing step forms the inner spiral grooved tube.
3.Why do we choose to use the helical inner groove tube?
We choose samples of smooth copper tube and aluminum inner groove tube to do a comparison as follows:
| Item | Smooth copper tube | Aluminum inner groove tube |
| NO. | A | B |
| OD/mm | 7 | 7 |
| Bottom wall thick (Tw / mm) | 0.3 | 0.47 |
| Groove height (Hf/mm) | – | 0.15 |
| Groove top angle | – | 6 0° |
| Helical angel | – | 1 8° |
| Groove number | – | 55 |
| Internal surface area | 201.06 | 291.63 |
| T. wall thick | 0.3 | 0.62 |
a. Evaporation experimental data and analysis
The test refrigerant is R22, the sample tube length is 3 m, the heat conductivity coefficient of aluminum is 237 W/(m·K), and the heat conductivity coefficient of copper is 398 W/(m·K).
when the refrigerant mass flow velocity is 150~500 kg/(m2 ·s), we can see Evaporation heat transfer performance
The thermal conductivity of aluminum is only about 60% of that of copper, but the heat transfer coefficient of the inner surface of tube B is nearly 2 times higher than that of tube A
we can make a conclusion that affects the heat transfer coefficient of the inner surface tube is not the thermal conductivity but the flow boiling heat transfer.
b. Condensation experiment data and analysis
The heat transfer coefficient of tube B is more than 2 times higher than that of tube A.
The condenser tube is mainly condensation heat transfer, internal surface tooth profile strengthening increases the internal surface area, and the internal wetting perimeter of the tube wall. At the same time, the rib teeth formed on the internal wall cause the “Gregoring” effect.
c. Mechanical properties of copper and aluminum tubes
Comparison of the mechanical parameter between the copper tube and aluminum tube and choose samples tube as follows:
Aluminum tube: 3003 anti-corrosion Aluminum Manganese Alloy grade
Copper tube: TP2 copper
The wall thickness of aluminum pipes is almost twice that of copper pipes. The biggest difference between aluminum and copper can be clearly seen from the item of tensile strength: the tensile strength of aluminum pipe is less than half of that of copper pipe
| Item | OD|mm | Wall thickness (mm) | Tensile strength (N|mm2) | Elongation (%) |
| Smooth copper tube | 7 | 0.31 | 238 | 45 |
| Inner groove aluminum tube | 7 | 0.66 | 109 | 51 |
The defect directly reflected in the heat exchanger is that the heat exchanger has poor pressure resistance and easy leakage. This is also the biggest bottleneck in the application of aluminum tubes in the field of refrigeration and air conditioning.
In terms of elongation, the two sample tubes are basically the same. above is our analysis of Comprehensive Performance.
The inner groove Aluminum Tube has good application Prospect in the heat exchanger in the HVAC industry. It is the better replacement material for smooth copper pipe
4.The highest performance in heat transfer
The inner grooves are following a helical pattern and have been optimized to improve heat transfer. The improvement in the heat transfer coefficient of the tube is two times what can be achieved with the traditional smooth copper tube.
This increased efficiency can help achieve a more compact design of the heat exchangers and a reduction in refrigerant load. Different grooves depth and geometry satisfy the specific regional requirements and refrigerants in use.
So precision drawin aluminum tubes represent an economic alternative to copper.
