Heat Transfer Enhancement
• Higher tube-side heat transfer where plain tubes are limited by laminar or transitional flow.
• Better wall conditions where fouling, waxing, product degradation or poor controllability are linked to low shear and long wall residence times.
• More predictable exchanger performance across start-up, turndown and revamp conditions by eliminating the transition flow boundary – no sudden changes in heat transfer performance at different flow rates.
• Better use of available pressure drop than simply adding more passes and driving up velocity in a plain-tube design.
Where hiTRAN can be used in single-phase In single-phase applications, hiTRAN can deliver substantial heat-transfer gains across laminar, transitional and, in selected cases, turbulent flow regimes, with tube side improvements commonly ranging from around 4 times to as much as 16 times the plain-tube performance. The strongest gains are often seen in services with Reynolds numbers of 20,000 and below, including viscous fluids in the 2 cP to 200 cP viscosity range. hiTRAN can be used with great benefits for viscous oils, crude streams, heat transfer fluids and other services where a designer would otherwise add tube passes to increase velocity. In laminar flow, however, increasing velocity by adding passes gives only modest heat-transfer benefit while pressure drop rises sharply, so plain-tube designs can become thermally and hydraulically inefficient.
Where hiTRAN can be used in two-phase duties Two-phase applications are inherently more complex than single-phase services because performance depends not only on heat transfer, but also on phase change behaviour, vapour-liquid distribution, interface effects and pressure-drop sensitivity. In these duties, hiTRAN is most useful where tubeside performance is being limited by poor film heat transfer, weak vapour-side mixing, mass-transfer resistance, sub-cooled inlet regions, film boiling, or mist flow. In condensing duties, hiTRAN is generally most effective where vapour velocities are low and condensate films are thick, especially in multicomponent systems where vapour cooling and interfacial mass transfer become significant parts of the resistance. In boiling and reboiling services, it is commonly applied to improve the inefficient sub-cooled inlet region so that more tube length is available for effective boiling, while in vaporizers it can help mitigate film boiling and mist flow by strengthening liquid – vapor interaction, breaking up insulating vapor layers and accelerating droplet evaporation.
New designs In new equipment, hiTRAN is a tool that can be used to improve heat transfer performance without exceeding the pressure drop. Instead of relying on long tubes, many passes or multiple shells to force more performance from plain tubes, the exchanger can often be designed more compactly from the outset. This can reduce surface area, number of shells, tube length, weight, plot space and total installed cost. It can also make single- or low-pass designs practical in services where a plain-tube solution would otherwise become large, heavy or uneconomic. These benefits are illustrated in the case study below.
Case Study 1 In the preheat train at the Dos Bocas Terminal, wet crude was to be heated before oil-water separation by recovering heat from the hotter dry crude stream. Because both fluids were viscous, a plain-tube design resulted in very poor tube-side heat transfer and, consequently, an extremely large heat exchanger train. This has an impact on the length and time the fluid is pumped through the tubes in series. The more the tube length and greater the number of units in series, the higher the path length and residence time. Table 1 shows the two designs, with a 50 % cost reduction obtained using hiTRAN. The main issue was that the dry crude on the tube side remained in laminar flow, so the tube-side heat transfer coefficient was too low to produce a compact design. Simulations also showed temperature stratification within the tube, with fluid near the wall approaching wall temperature while the fluid core remained far less affected by heat transfer. This kept the overall heat transfer coefficient low and drove the design up to 20 shells, arranged as two in series and five in parallel. By applying hiTRAN, the tube-side thermal bottleneck was removed. The inserts increased radial mixing and heat transfer while still allowing the design to remain within the available pressure drop by reducing the number of passes from four to two. This made it possible to cut the exchanger train to 8 shells, each with fewer and shorter tubes, reducing the path length of the fluid while also reducing exchanger piping and installation costs by about 50 percent through the smaller, simpler overall design.
Retrofits Retrofit applications require a different approach to enhancement compared to new designs. Here, the question is more about extracting more value from existing shells, bundles or layouts with minimal disruption to the plant and plant equipment. hiTRAN is attractive because it can be applied selectively, whether across the full tube length, part of the tube length, or only in the sections where the limiting mechanism actually occurs without major alternations to the heat exchanger. That makes hiTRAN useful for debottlenecking, improving outlet conditions, increasing throughput or solving chronic operating problems without major plot-space expansion. In many cases, pass changes or part-length installation allow pressure drop to be reallocated more effectively so the exchanger delivers more duty from the same hardware. An example of a www. heat-exchanger-world. com Heat Exchanger World October 2026
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