Spiral tube heat exchangers combine compact size, resistance to thermal stress and high heat transfer efficiency.

Figure 1. Spiral Tube Cross-Section A spiral tube heat exchanger uses multiple parallel tubes connected to pipe-like manifolds to create a tube-side flow path. When the coiled assembly is bolted to a shell, the space between the coils acts as the shell-side flow path.

A spiral heat exchanger is a useful alternative to shell-and-tube de-signs in severe service applications. Compact design and optimized heat transfer performance are features that make this heat exchanger worth consideration.

A spiral tube heat exchanger is a compact, coiled assembly. The design uses multiple parallel tubes connected to pipe-like manifolds to create a tube-side flow path. For heat exchange, the multiple tube bundle is spirally wound to form a spring-like coil and create two flow paths. This coil assembly is connected to a round, flat plate that also serves as the head of the shell assembly.

When the coiled assembly is bolted or welded to a shell, the space between the coils acts as the shell-side flow path. Tube manifolds protrude through the head to provide tube-side connections; shell-side connections are made directly through the head. With this design, threaded, flanged or welded connections are possible, and connections can be made on the bottom of the shell assembly for different flow path configurations.

The number, size and length of tubes selected directly affect heat transfer optimization. Bundle and shell diameter also influence optimization.

Explore the Benefits

Because of the spiral flow paths of the tube-side and shell-side fluids, centrifugal force and secondary circulating flow enhance heat transfer on both sides in a true counterflow configuration. The design eliminates potential for plugging on both the shell and tube sides of the heat exchanger. In cases where shell-side heat transfer media has high fouling characteristics, bolted shells can be removed for cleaning without disconnecting piping.

Spiral tube heat exchangers have a square, box-like profile that allows it to fit in a small footprint. Because the tube bundle is a coiled assembly, space requiremnts for tube bundle removal are minimized.

Difference in Design

Heat transfer performance is optimized because no baffles are used or dead spots created to lower velocities and coefficients. Additionally, because several multiple parallel tube configurations are possible (diameter, number and length), efficiency is not compromised by limited shell diameter sizes. Therefore, in many applications, a spiral tube heat exchanger may be more efficient than a shell-and-tube heat exchanger.

A number of features set a spiral-tube design apart from a shell-and-tube design. The shell-and-tube design has a long rectangular dimensional profile; the spiral design has a square, box-like profile. The compact profile of the spiral allows it to fit in a smaller footprint.

The tube bundle is a coiled assembly, so space requirements for tube bundle removal are minimized. Shell-side baffles and pass dividers are not required, eliminating alignment obstacles when maintenance requires replacement of the tube bundle. Also, because of its square dimensional profile, the bundle does not sag.

Conventional shell-and-tube heat ex-changers can experience tube-sheet leakage when subjected to continuous surging from positive-displacement compression such as in an interstage cooler in a multiple-stage reciprocating compressor. Spiral tube heat exchangers have welded tube-to-manifold joints, making them resistant to both thermal and pressure pulsation cycling. The multiple parallel tube and welded manifold design can handle tube-side pressures as high as 15,000 psig. Generally, spiral tube heat exchangers are suited for applications where tube-side pressure exceeds 500 psig.

Spiral tube heat exchangers use manifolds instead of the channels, heads and tube sheets found in shell-and-tube designs. The shell side of a spiral heat exchanger does not require tube supports or pass dividers. Higher heat transfer coefficients also can reduce the total required heat transfer area, resulting in less tubing. Reduced system size and overall parts count decrease shipping weight on packaged assemblies and makes them appealing for mobile applications.

Many OEMs and end users still are not acquainted with spiral tube heat exchangers and the associated application advantages. Good heat transfer efficiency and compact size make this design well suited for industrial cooling applications.

Putting Spiral Tube Heat Exchangers to Work

Spiral tube heat exchangers achieve good heat transfer in a range of applications. Here are a few:

Interstage, After and Bypass Cooling for Gas Compressors
With its compact size and resistance to pressure pulsation, the spiral tube heat exchanger often is used on positive-displacement compressors for interstage and after cooling of compressed gas, especially for high pressure applications. Other types of compressors use spirals for bypass coolers on capacity control loops. The spiral has a small footprint that fits within the skid size of the compressor package.

Process Fluid Sample Cooling
The multiple tube capability of the spiral tube heat exchanger makes it appropriate for cooling process samples before analysis when sample flow exceeds 1.5 gal/min. The compact size allows it to fit inside or outside an analyzer enclosure, or on small sample cooling and analysis panels.

Acid/Caustic Coolers
Like a shell and tube, a spiral tube heat exchanger can be manufactured with exotic metals as well as heavier wall tubes and other pressure parts for added corrosion resistance.

Vent Condensers
A spiral tube bundle can be configured to connect directly to a tank or vessel. Chilled water or other process fluid is passed through the tubes, and condensed product falls back directly to the vessel while allowing noncondensibles to be exhausted. Because either of the tube manifolds can be extended through the shell to provide a third tube-side connection, product-laden vapors can be passed through the unit and the condensate drained back to the vessel easily.

Pump-Seal Cooling
Dynamic pump seals create frictional heat. This heat must be dissipated to prevent overheating of the seal surfaces. Frequently, the pumped fluid is used as the seal-cooling medium. A spiral tube heat exchanger is suited for such high pressure applications and can handle corrosive or high purity fluids.

Boiler Blowdown Coolers
A spiral tube heat exchanger is a compact and efficient way to reduce blowdown temperature prior to discharge or recovery. Equally important, it can handle thermal shock and can be cleaned.

Other applications include demineralized water, oil, refrigerants and cryogenic coolers.