In order to achieve energy saving by improving the energy efficiency ratio of the air conditioner or radiator.
The best solution is to improve the heat transfer performance of the air conditioner heat exchanger (evaporator and condenser).
The most effective technical measure to control the cost of raw materials for heat exchanger coils in air conditioners, refrigeration units, or other refrigeration equipment is the research and application of powerful heat transfer technology.
Usually, this can be achieved by improving the heat transfer per unit area of the heat exchanger, controlling the volume of the heat exchanger, improving the heat transfer coefficient and other properties.
This is why the internally threaded copper pipe was created.
Relationship Between Copper Tube Diameter and Heat Transfer Efficiency
First of all, let’s look at the selection of the pipe diameter of the female threaded pipe
The heat transfer efficiency of the heat exchanger and the cost performance of the air conditioner are greatly related to the inner thread copper tube diameter and the geometry of the inner thread copper tube teeth.
At the beginning of the heat exchanger research, the heat exchanger copper tube diameter was about φ9.52mm, which was later refined to φ7.0mm.
This fine tube diameter heat exchanger, due to the distance between the tube and the tube is reduced, making the use of fins to improve efficiency, heat transfer effective area increased.
As a result, the flow resistance of airflow through the heat exchanger is reduced and the heat transfer performance of the evaporator coil or condenser coil is strengthened.
Structure and Heat Transfer Properties of Internally Threaded Copper Pipes
Female threaded copper pipe is divided into “Common threaded copper pipe” and “non-common threaded copper pipe”
Common threaded copper pipe mainly refers to the Trapezoidal Internal Thread Copper Tube, M-shaped Internal Thread Copper Tube.
The non-common tooth refers to Cross Internal Threaded Copper Pipe.
Usually, the heat transfer efficiency of the cross-slotted copper pipe is higher than that of the common single-spin trapezoidal slotted copper pipe.
Especially when the refrigerant is mixed, the advantage of using the cross-slotted copper pipe is more.
The requirements of the refrigeration system are different for different constructions of copper tubes with internal threads.
Now, let us discuss the relationship between the different constructions of copper tubes with internal threads and refrigerants.
✓ Trapezoidal Internal Thread Copper Tube
The reinforced heat transfer coefficient of the trapezoidal female threaded copper tube as shown in the figure is greatly improved.
When it is used for R410A refrigerant, the condenser coil heat transfer coefficient is 1.5 times that of the ordinary female threaded tube, and the evaporator coil heat transfer coefficient is 1.4 times that of the ordinary female threaded tube.
When used for R407C refrigerant, the condensing heat transfer coefficient is 1.3 times that of a normal female threaded tube, and the evaporating heat transfer coefficient is 1.3 times that of a normal female threaded tube.
The main reason why this structure of female threaded tube produces such a good heat transfer enhancement effect is that the trapezoidal top angle is smaller, the trapezoidal tip is thinner, the higher trapezoidal structure can also have a larger groove bottom width.
And the refrigerant liquid film at the bottom of the trapezoidal groove becomes thinner during condensation, reducing the thermal resistance.
Related products you can refer to Miracle condensing unit or evaporator and condenser, such as Bitzer condensing units, outdoor condensing units, evaporator unit, air-cooled condenser, cooling coil, etc. due to the high system pressure.
✓ M-shaped Internal Thread Copper Tube
In addition, multiple threads form more evaporation cores, but the higher bulge will reduce the ribbing efficiency and increase the flow resistance.
In order to solve this contradiction, a copper tube with a small slot in the trapezoidal projection was developed, called an “M” shaped copper tube with internal thread.
Experiments show that the coefficient of M-type copper tube with internal threads rises significantly at a low mass flow rate when condensing, mainly because M-type copper tube with internal threads has a large width of the bottom of the slot, which is conducive to refrigerant discharge and reduces the thickness of the liquid film.
According to the test of the whole air conditioner, the M-type copper pipe with inner thread is used for the external machine, and the cooling capacity rises 70-80w under the same condition of the internal machine, and the heating capacity rises about 100w in the heat pump air conditioner test.
✓ Combined Internal Thread Copper Tube
Combined internal threaded copper tubes are most suitable for R407C refrigerants.
This is because R407C is a mixture of three non-azeotropic refrigerants, which are easy to be stratified when flowing in a common single-slotted female tube (especially a light tube).
However, when the refrigerant flows in the combined internal threaded copper tubes, turbulence occurs in both directions, allowing the three mixed substances to mix fully.
Gas-liquid conversion is also carried out, and this internal structure design effectively solves the problem of heat transfer efficiency caused by stratification.
Although R407C can also be fully mixed in the cross-grooved inner thread tube, the pressure drop loss in the cross-grooved inner thread tube is larger.
So it is better to use the V-type inner thread tube for R407C refrigerant products.
✓ Crossed Internal Thread Copper Tube
Features of cross internal threaded pipe
- Increase the superheat and heat transfer area of the liquid.
- More evaporation cores are formed.
- Intensified turbulence.
- Suitable for evaporator tubes.
R410A refrigerant products are used in refrigeration units.
These units operate at high flow rates to overcome the negative effects of pressure drop loss in cross-grooved tubes.
At the same time, the advantage of the large internal surface area of the cross-slotted copper tubes is used.
Therefore, heat exchangers with cross-grooved copper tubes are more suitable for R410A refrigerant units or compressors.
Limiting Factors for the Application of Internal Thread Copper Tube
Although V-groove and cross-groove copper tubes have advantages over ordinary single-spin trapezoidal grooved copper tubes.
However, due to the high material requirements and high production costs of V-slot and cross-slot copper tubes, these two types of copper tubes are not used on a large scale.
For different types of internally threaded copper tubes, the tooth structure parameters are very different, and there are more ways to combine them.
Therefore, when designing the tooth shape and geometric parameters.
The influence of different internal thread structures on the heat transfer performance of internally threaded copper tubes should be considered first.