Dry Expansion Evaporator Tubes | Internally Grooved Straight Tubes

Dry expansion evaporator tubes (also known as DX evaporator tubes within the industry) are specially designed for dry-type shell-and-tube evaporators. In a dry expansion evaporator, refrigerant flows inside the tubes while water or secondary coolant circulates outside the tubes on the shell side.

Kenergy's DX evaporator tubes feature an internally grooved straight tube design. The helical grooves on the inner wall continuously disturb the two-phase refrigerant flow during evaporation, breaking the laminar boundary layer and significantly enhancing the tube-side heat transfer coefficient. Compared to smooth tubes, the heat transfer efficiency is improved by over 40% under the same refrigerant flow rate. These tubes are ideally suited for heat pump units, industrial water chillers, and refrigerated air dryers.

Core Advantages

Optimized Tooth Profile for Dry Expansion Conditions

Specially designed groove geometry maintains excellent heat transfer performance even at low refrigerant mass flux, while ensuring proper oil return to the compressor.

Compatible with Multiple Refrigerants

Optimized groove parameters for R134a, R404A, R407C, R22, and other common refrigerants. Custom matching available for alternative refrigerants upon request.

Multi-Start Thread Options

Available in 1, 2, 4, 6, and 8 thread starts to meet varying requirements for heat transfer intensity and pressure drop across different operating conditions.

Straight Tube Supply

Standard lengths of 3–6 meters, with custom cut-to-length service available to match your specific heat exchanger design requirements.

Technical Parameters

Standard outer diameters, wall thicknesses, and groove configurations. Custom specifications available upon request.

Outer Diameter (mm)	Bottom Wall (mm)	Fin Height (mm)	Thread Starts	Helix Angle (°)	Weight (g/m)	Heat Transfer Area (m²/m)	Material
12.70	0.35–0.50	0.15–0.22	1/2/4/6/8	15–35	125–165	0.045–0.050	TP2, T2
15.88	0.40–0.55	0.18–0.25	1/2/4/6/8	15–35	175–225	0.056–0.062	TP2, T2
19.05	0.45–0.60	0.20–0.28	1/2/4/6/8	15–35	235–290	0.067–0.075	TP2, T2
25.40	0.50–0.70	0.22–0.30	1/2/4/6/8	15–35	355–440	0.090–0.100	TP2, T2

Typical Applications

Air Source Heat Pump Evaporators

Dry expansion evaporators for air-to-water heat pumps in residential heating, domestic hot water, and commercial heating applications.

Industrial Water Chiller Evaporators

Water-cooled and air-cooled industrial chiller evaporators for process cooling, precision machinery, and factory temperature control.

Refrigerated Air Dryer Evaporators

DX evaporators for冷冻式空气干燥器 (refrigerated air dryers) in compressed air systems to remove moisture efficiently.

Modular Air-Cooled Heat Pumps

Multi-circuit evaporators for modular chiller and heat pump systems requiring compact heat exchanger design.

Frequently Asked Questions

Q: What is the difference between tubes used in dry expansion evaporators vs. flooded evaporators?

In dry expansion evaporators, refrigerant flows inside the tubes and evaporates progressively along the tube length. The groove design must promote nucleate boiling while handling two-phase flow with increasing vapor quality. In contrast, flooded evaporators have refrigerant on the shell side with water inside the tubes, requiring enhanced boiling surfaces on the outside diameter. DX tubes focus on internal groove optimization for flow boiling, while flooded tubes typically feature external enhancements for pool boiling heat transfer.

Q: How do internally grooved straight tubes ensure a proper seal after tube expansion into the tube sheet?

Our tubes feature tight wall thickness tolerance of ±0.02mm, ensuring uniform expansion into the tube sheet without excessive thinning or cracking. The consistent bottom wall thickness across the tube circumference and along its length guarantees reliable mechanical-rolled joints. For high-pressure applications, we recommend our O-temper (annealed) tubes which provide optimal ductility for expansion. Groove geometry is designed to maintain structural integrity during the expansion process without groove collapse.

Q: How do you match groove profiles for low-GWP refrigerants like R290 (propane)?

Low-GWP refrigerants such as R290 have different thermophysical properties and lower mass flow rates compared to traditional HFCs. For R290 and similar hydrocarbons, we recommend groove designs with lower fin height and optimized helix angles to maintain efficient heat transfer at reduced refrigerant charge. Kenergy's engineering team can develop custom groove profiles tailored to your specific low-charge system requirements. We have successfully supplied DX tubes for R290 heat pump projects with charge reductions of up to 40%.

Q: Can you provide anti-corrosion coating for the tubes?

Yes, we offer several anti-corrosion treatment options depending on the application environment. For seawater or high-humidity applications, we can apply a specialized epoxy coating on the tube exterior surface. For enhanced corrosion resistance in aggressive water conditions, we also offer tin plating services. Please specify your water chemistry and operating conditions when inquiring, and our technical team will recommend the most suitable protective treatment.

Dry Expansion Evaporator Tubes — Internally Grooved Straight Tubes