What Is an Inner Grooved Copper Tube

The purpose of using inner grooved copper tubes is to improve the energy efficiency ratio (EER) of air conditioners or heat exchangers, thereby achieving energy-saving performance.

The most effective solution is to enhance the heat transfer performance of air conditioner heat exchangers, including both evaporators and condensers.

In air conditioners, refrigeration units, and other cooling equipment, the most effective technical approach to controlling raw material cost of heat exchanger coils is the research and application of enhanced heat transfer technology.

This is typically achieved by:

• Increasing heat transfer per unit area

• Controlling the volume of the heat exchanger

• Improving the overall heat transfer coefficient

This is the reason why inner grooved copper tubes were developed.

Relationship Between Copper Tube Diameter and Heat Transfer Efficiency

Selection of Inner Grooved Copper Tube Diameter

The heat transfer efficiency of a heat exchanger and the cost-performance ratio of an air conditioner are highly related to:

• The diameter of the inner grooved copper tube

• The geometric shape of the internal grooves

In early heat exchanger designs, the copper tube diameter was approximately φ9.52 mm, which was later reduced to φ7.0 mm.

With smaller-diameter tubes:

• The spacing between tubes is reduced

• Fin efficiency is improved

• The effective heat transfer area is increased

As a result:

• Airflow resistance through the heat exchanger is reduced

• Overall heat transfer performance is significantly improved

• The performance of evaporator coils and condenser coils is enhanced

Structure and Heat Transfer Performance of Inner Grooved Copper Tubes

Internal Structure of Inner Grooved Copper Tubes

Inner grooved copper tubes can be classified into:

• Conventional inner grooved copper tubes

• Non-conventional inner grooved copper tubes

Common conventional types include:

• Trapezoidal inner grooved copper tubes

• M-type inner grooved copper tubes

Non-conventional groove types mainly refer to:

• Cross-grooved inner copper tubes

In general, cross-grooved copper tubes provide higher heat transfer efficiency than single-helix trapezoidal grooved tubes, especially when mixed refrigerants are used.

Different refrigeration systems have different requirements for the structure of inner grooved copper tubes.

Below is a discussion of the relationship between inner groove structures and refrigerants.

Trapezoidal Inner Grooved Copper Tube

As shown, trapezoidal inner grooved copper tubes significantly enhance heat transfer performance.

• When used with R410A refrigerant:

  • Condenser heat transfer coefficient is 1.5 times that of standard inner grooved tubes

  • Evaporator heat transfer coefficient is 1.4 times higher

• When used with R407C refrigerant:

  • Condenser heat transfer coefficient is 1.3 times higher

  • Evaporator heat transfer coefficient is 1.3 times higher

This enhanced performance is mainly due to:

• Small apex angle of the trapezoidal grooves

• Thin groove tips

• Larger groove bottom width

During condensation, the refrigerant liquid film at the groove bottom becomes thinner, effectively reducing thermal resistance.

These tubes are commonly used in high-pressure refrigeration systems, such as:

• Condensing units

• Evaporators and condensers

• Bitzer condensing units

• Outdoor condensing units

• Air-cooled condensers

• Cooling coils

M-Type Inner Grooved Copper Tube

Multiple grooves create more evaporation nucleation sites, but excessive rib height can reduce fin efficiency and increase flow resistance.

To address this issue, M-type inner grooved copper tubes were developed by adding small grooves on trapezoidal ribs.

Experimental results show:

• Under low mass flow rates, M-type tubes exhibit a significant increase in condensation heat transfer coefficient

• Wider groove bottoms facilitate refrigerant drainage

• Liquid film thickness is reduced

System-level testing shows:

• Cooling capacity increases by 70–80 W under identical conditions

• Heating capacity in heat pump systems increases by approximately 100 W

Composite Inner Grooved Copper Tube

Composite inner grooved copper tubes are most suitable for R407C refrigerant.

R407C is a non-azeotropic mixture of three refrigerants, which tends to stratify when flowing through conventional single-groove tubes or smooth tubes.

In composite inner grooved copper tubes:

• Turbulence is generated in two directions

• Refrigerant components are thoroughly mixed

• Gas-liquid phase change is enhanced

This internal structure effectively eliminates heat transfer degradation caused by refrigerant stratification.

Although cross-grooved tubes can also improve mixing, they result in higher pressure drop losses.

Therefore, V-type inner grooved copper tubes are recommended for R407C refrigerant systems.

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Cross-Grooved Inner Copper Tube

• Features of Cross-Grooved Copper Tubes

  • Increases liquid superheat and internal heat transfer area

  • Creates more evaporation nucleation sites

  • Enhances turbulence

  • Suitable for evaporator tubes

  • Ideal for R410A refrigeration systems

  These systems typically operate at higher flow velocities to offset the pressure drop associated with cross-groove structures, while fully utilizing the large internal surface area.

  As a result, cross-grooved copper tube heat exchangers are particularly suitable for R410A refrigerant units and compressors.

Limitations in the Application of Inner Grooved Copper Tubes

Although V-grooved and cross-grooved copper tubes outperform conventional single-helix trapezoidal grooved tubes, their application is limited due to:

• Higher material requirements

• More complex manufacturing processes

• Higher production costs

As a result, these tubes have not yet been widely adopted on a large scale.

Different types of inner grooved copper tubes vary significantly in groove geometry and structural combinations.

Therefore, when designing groove profiles and geometric parameters, the impact of different inner groove structures on heat transfer performance must be considered first.