The concept behind the study is elegantly practical. Crude oil arriving at a desalting unit is typically cold and viscous, and its water-oil emulsion is stubbornly stable, which makes salt removal difficult. Heating the crude before desalting reduces viscosity, destabilizes the emulsion, and improves separation. Meanwhile, the furnace exhaust leaves at approximately 973 kelvin, about 700 degrees Celsius, brimming with recoverable sensible heat. Rather than routing that heat through an intermediate conversion step, the researchers proposed transferring it directly to the crude stream through a shell-and-tube heat exchanger, avoiding the losses and complexity associated with boilers, organic Rankine cycles, or thermoelectric devices. Direct reuse, they argue, is the most attractive route when a compatible heat demand exists within the same plant.

Deciding which fluid goes where inside the exchanger was itself a consequential engineering choice. Following the guidance of industry specifications API 660 and IOGP S-614, the team assigned the crude oil to the tube side and the exhaust gas to the shell side. The rationale is rooted in mechanics and maintenance: the higher-pressure, fouling-prone crude benefits from the tube side, where mechanical cleaning and hydroblasting are straightforward, while the high-volume, pressure-drop-sensitive gas stream performs better on the shell side, where baffles can enhance heat transfer without excessive hydraulic penalty. This allocation reduces required shell thickness, controls fabrication cost, and keeps the dirtiest fluid in the easiest-to-clean passage.

What sets this work apart from earlier heat-exchanger studies is the sheer breadth of the design exploration. The researchers constructed a discrete design space of 192 configurations by combining four tube diameters ranging from 19.05 to 38 millimeters, four tube lengths from 1 to 3 meters, three segmental baffle types, and four tube arrangements including triangular and square patterns. Each configuration was simulated using three-dimensional, steady-state computational fluid dynamics with the RNG k-epsilon turbulence model, chosen for its established reliability in flows with curvature, recirculation, and strong strain rates. The simulations ran on the Simorgh supercomputer at Amirkabir University of Technology, with a final mesh of roughly 14 million cells verified through a Grid Convergence Index analysis showing discretization uncertainties below 0.6 percent.

The team deliberately avoided the classic trap of optimizing for a single metric. Instead, they evaluated four normalized indicators for every design: shell-side heat-transfer performance, total pressure drop, capital cost, and entropy generation, the last serving as a second-law measure of thermodynamic irreversibility. Entropy generation in a heat exchanger arises from two competing mechanisms, heat transfer across finite temperature differences and viscous friction, and minimizing it forces a design to respect both thermal and hydraulic realities simultaneously. Cost was estimated through established power-law correlations linking heat-transfer area and pumping power to equipment expense, providing a comparative economic yardstick across the 192 candidates.

The parametric results revealed a landscape of stubborn trade-offs. Increasing tube length reliably improved heat transfer by enlarging the exchange area and extending fluid residence time, but it simultaneously raised pressure drop and capital cost, and its effect on entropy generation was sometimes non-monotonic as thermal and frictional irreversibilities shifted in relative importance. Larger tube diameters eased hydraulic constraints but did not guarantee better overall performance; at the largest diameter tested, cost penalties mounted sharply. Baffle type emerged as a key lever on entropy generation, while tube arrangement played a comparatively minor role. Sensitivity analysis confirmed that tube diameter dominated the cost indicator, tube length governed thermal performance, and baffle configuration most strongly shaped thermodynamic losses.

To navigate this crowded trade-off space, the researchers applied Pareto analysis, identifying 141 non-dominated designs out of the 192 candidates, a large set that reflects how richly the objectives conflict in a discrete design space. They then ranked the Pareto solutions by their Euclidean distance to an ideal point representing perfect performance on all four normalized criteria, a transparent method that avoids the subjective weighting that can bias multi-objective decisions. The winning configuration, designated D2L4P4B1, pairs a 25.4-millimeter tube diameter with a 3-meter length, a 45-degree rotated square tube arrangement, and single-segmental baffles. It scored 0.903 on normalized heat transfer, 0.954 on entropy-generation performance, and a respectable 0.76 on pressure drop, with the shortest distance to the ideal point at 0.4433.

The CFD visualizations of the optimal design bring the physics to life. Temperature contours show a searing hot zone near the exhaust-gas inlet where the largest temperature gradients, and therefore the most intense heat transfer, occur, followed by a gradual cooling of the gas as it flows across the tube bundle. On the tube side, the crude oil warms steadily along its path, confirming effective absorption of the recovered heat, a rise that directly translates into lower viscosity and easier emulsion breaking downstream. Pressure contours reveal a smooth, gradual decline from inlet to outlet with no abnormal jumps, indicating that the optimized geometry keeps hydraulic losses within acceptable bounds for the viscous crude service.

The validation of the numerical framework lends credibility to the findings. Comparisons against published CFD data from Li and He showed maximum deviations of just 2.34 percent for the shell-side heat-transfer coefficient and 9.8 percent for pressure drop, good agreement for a system as geometrically complex as a baffled shell-and-tube exchanger. The authors are candid about the limits of their approach: the study relies on steady-state simulations with discrete design variables, excludes fouling evolution and transient operation, and validates against numerical rather than experimental data. They also note that a plant-specific design would need to impose the desalter’s required inlet-temperature range as an explicit constraint.

Even with those caveats, the study offers a compelling template for refineries seeking to squeeze value from their stacks. It demonstrates that the best heat-recovery design is never the one that maximizes heat transfer alone, nor the cheapest, nor the thermodynamically cleanest, but the one that balances all three against hydraulic reality. By coupling a rigorous CFD campaign with Pareto-based multi-objective selection and entropy-generation analysis, the researchers have shown that furnace exhaust at Marun can be converted from an environmental liability into a process asset, preheating crude oil, easing the burden on the desalting unit, and cutting the fuel that would otherwise be burned to do the same job. For energy-intensive industries worldwide, the message is that the geometry of a heat exchanger, down to the millimeter of a tube diameter and the angle of a baffle, can decide whether waste heat is truly recovered or merely relocated.

Subject of Research: Multi-objective CFD optimization of a shell-and-tube heat exchanger for recovering refinery furnace exhaust heat to preheat crude oil before desalting

Article Title: Multi-objective design and optimization of a shell-and-tube heat exchanger for recovering Marun furnace exhaust heat and preheating crude oil entering a desalting unit

Article References: Ghodrati, M., Deymi‑Dashtebayaz, M., Khoshnevis, A. B., & Yazdani, M. (2026). Multi-objective design and optimization of a shell-and-tube heat exchanger for recovering Marun furnace exhaust heat and preheating crude oil entering a desalting unit. Results in Engineering, 32, Article 113398. https://doi.org/10.1016/j.rineng.2026.113398

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113398

Keywords: waste heat recovery, shell-and-tube heat exchanger, CFD simulation, multi-objective optimization, entropy generation, Pareto front, crude oil preheating, refinery furnace, furnace exhaust gas, pressure drop, baffle design, energy efficiency

The research team, led by Dixit Arya together with Nisha Netam and Anuj Kumar Shukla, simulated the melting of a phase change material inside a closed rectangular enclosure fitted with conducting fins, comparing configurations with one, two, and three fins while holding the total fin area constant. Crucially, they ran the simulations not only at normal Earth gravity but also at five and ten times standard gravitational acceleration, conditions representative of aerial flight maneuvers and rotating machinery. The central insight is deceptively simple but consequential: gravity does not merely press down on the material, it fundamentally rewrites the physics of melting, and the fin geometry that works best at one gravity may underperform at another.

To understand why, one must appreciate the role of buoyancy-driven convection in latent heat thermal energy storage. When a phase change material melts next to a heated wall, the liquid layer that forms does not sit still. Warmer liquid is less dense, so it rises, while cooler liquid descends, creating circulating currents that ferry heat away from the melting front far more efficiently than conduction alone. The strength of this convective stirring is captured by the Rayleigh number, a dimensionless quantity that scales directly with gravitational acceleration. Multiply gravity by five or ten, and the Rayleigh number climbs accordingly, intensifying the internal flow and accelerating the melt. The simulations quantified this effect dramatically: maximum velocity magnitudes within the liquid increased by a factor of three to five under hypergravity compared with the baseline case.

The headline result concerns melting time. Under five times normal gravity, the finned configurations melted the material up to 47.8 percent faster than an unfinned enclosure, and at ten times gravity the improvement reached 48.2 percent. In practical terms, a thermal storage unit that would take minutes to fully charge at Earth gravity could accomplish the same task in roughly half the time during aggressive flight maneuvers. For aerospace engineers, this is more than a curiosity. Thermal management systems on high-speed aircraft and spacecraft must absorb transient heat loads quickly, and a storage medium that charges faster under acceleration effectively buys safety margin precisely when thermal stress is greatest.

Yet the study’s most provocative finding concerns fin placement and number, and here the conventional wisdom takes a beating. Engineers often assume that more fins mean better heat transfer, since each fin extends the heated surface into the material. The simulations tell a subtler story. A single, longer fin positioned in the lower region of the enclosure delivered the best performance among all cases examined. The reason lies in fluid dynamics: the lower fin sits where buoyant plumes originate, and its length allows it to channel warm liquid upward along its surface, feeding and reinforcing the convective circulation. Multiple shorter fins, by contrast, fragment the liquid domain into smaller cells, and fins placed in the upper region can act as barriers that suppress the very fluid motion that hypergravity amplifies. In effect, poorly placed fins strangle the convection that gravity is trying to supercharge.

This trade-off between conduction enhancement and convection suppression is the intellectual heart of the paper. Fins excel at conducting heat into solid regions that convection cannot reach, but every fin is also an obstacle in the flow path. Under hypergravity, where convective currents are the dominant heat-transfer mechanism, the penalty for obstructing flow grows correspondingly. The researchers’ comparative analysis of single-, double-, and triple-fin arrangements demonstrates that the optimal design is not the one with the most metal but the one that cooperates with the buoyant flow field. A long lower fin guides the flow; a cluster of short upper fins fights it.

The energy accounting reveals further nuances that any system designer must confront. Because fins displace a small volume of phase change material, the total energy stored in the finned enclosures decreased slightly, by between 0.38 and 1.32 percent, relative to the unfinned case. That loss is modest, but the gains in charging speed are not: the mean power delivered during melting increased by up to 90.8 percent in the best configurations. In other words, fins transform the storage unit from a slow, capacious reservoir into a fast, responsive one. However, the study also reports a reduction in energy storage density of roughly 7.5 percent, a metric that matters where every kilogram and every liter counts, as it always does in aerospace applications. The trade-off between storage capacity and heat-transfer performance is therefore not eliminated by hypergravity but reshaped by it.

These results arrive amid a growing body of research on phase change behavior across the gravity spectrum. Previous experimental work has documented accelerated melting under hypergravity in pin-fin heat sinks for airborne electronics, while other studies have explored the opposite extreme, where microgravity nearly eliminates buoyant convection and melting stalls into a slow, conduction-dominated process. Numerical investigations have examined metal foam composites, topologically optimized fins, and even magnetic field coupling under variable gravity. The new study contributes a systematic comparison of fin number and placement at constant total fin area, a controlled variable that isolates the geometric question from the material question. Its findings complement earlier work showing that fin length arrangements and enclosure inclination strongly influence melting at normal gravity, and extend that framework into a regime where the Rayleigh number is an order of magnitude larger.

The practical implications reach beyond aircraft. Rotating systems, from centrifugal thermal storage units to machinery on space stations with artificial gravity, all impose effective accelerations on their thermal storage media. Battery thermal management, a pressing concern for electric aviation, has already seen proposals combining phase change materials with fin structures under variable gravity environments. The new results suggest that such systems should be designed with the gravity vector in mind: orienting fins to nurture, rather than obstruct, buoyant circulation could yield charging-rate improvements approaching a factor of two, while naive fin layouts might deliver far less than expected. The finding that a single well-placed fin outperforms multiple shorter ones could also simplify manufacturing and reduce mass, a rare case where the better design is also the lighter one.

As with any numerical study, the results rest on modeling assumptions, and the authors note that the data underlying their findings are available upon reasonable request. Experimental validation under sustained hypergravity, which requires centrifuge facilities or parabolic flight campaigns, remains the necessary next step before these design rules enter flight hardware. Still, the study offers a clear and actionable principle for engineers racing to manage ever-growing heat loads in fast-moving machines: in the world of latent heat storage, gravity is not an obstacle to be engineered around but a fluid-dynamic resource to be harnessed, and the humble fin, placed with an eye on the flow, is the lever that unlocks it.

Subject of Research: Fin-enhanced melting of phase change materials for latent heat thermal energy storage under hypergravity conditions

Article Title: Impact of Multiple Fins on the Melting Characteristics of PCM in a Closed Enclosure Under Hypergravity Conditions

Article References: Arya, D., Netam, N., & Shukla, A. K. (2026). Impact of Multiple Fins on the Melting Characteristics of PCM in a Closed Enclosure Under Hypergravity Conditions. International Journal of Aeronautical and Space Sciences. https://doi.org/10.1007/s42405-026-01240-5

Image Credits: AI Generated

DOI: 10.1007/s42405-026-01240-5

Keywords: phase change material, hypergravity, latent heat thermal energy storage, fins, buoyancy-driven convection, Rayleigh number, thermal management, aerospace, melting time, energy storage density, CFD simulation, heat transfer

The research, published in the journal Results in Engineering, was carried out by Maziyar Moghtadaeifar, Ramin Farzadi, and Majid Bazargan, who built their design around a radical idea that has been gathering momentum in wind engineering: the J-shaped airfoil. A conventional blade cross-section, such as the standard NACA0021 profile used here as a baseline, is a closed teardrop shape. A J-shaped airfoil takes that profile and simply removes part of the pressure side, the face of the blade that faces away from the turbine’s rotation axis, leaving a hollow, scoop-like section bounded by a wall just one millimeter thick. The opening begins at the point of maximum thickness and runs all the way to the trailing edge, transforming the blade into something between a wing and a curved trough.

That hollow matters. When wind sweeps across a J-shaped blade, air circulates inside the concave cavity, and the resulting changes in pressure distribution alter how lift and drag act on the rotor. Earlier experimental and numerical work had shown that such profiles can improve self-starting, because the open cavity behaves somewhat like a drag device at low speeds, but often at a cost to peak efficiency. The innovation in the new study is to combine this profile with a helical configuration: three blades, each twisted sixty degrees around the rotation axis, mounted on a rotor with a radius of 0.99 meters and a height of 1.15 meters. Helical blades smooth the torque output because some section of some blade is always optimally positioned relative to the wind, reducing the violent fluctuations that plague straight-bladed designs and making the rotor less dependent on the angle at which it happens to have stopped.

To test the concept, the team ran three-dimensional unsteady Reynolds-averaged Navier-Stokes simulations using the shear-stress transport k-omega turbulence model, a combination that previous validation studies have identified as among the most accurate for capturing the complex, separated flows around vertical-axis rotors, including the transient phenomenon of dynamic stall. The computational domain stretched thirty-two rotor radii downstream and twelve radii in the other directions, with a blockage ratio of just 1.61 percent, and a sliding-mesh cylinder carried the spinning blades. The researchers verified their setup against published experimental data for two different variable-pitch turbines, then ran careful mesh and time-step independence studies, refining the grid until the cycle-averaged torque coefficient changed by less than one percent and settling on a time step of half a degree of rotation per step.

The first headline result concerns how the J-shaped profile itself performs. Across low and medium tip speed ratios, the ratio of blade speed to wind speed that governs rotor behavior, the J-shaped helical turbine outperformed a geometrically identical machine with conventional NACA0021 blades. At a tip speed ratio of 1.11, for example, the J-shaped rotor produced a torque coefficient 26.59 percent higher than the full-profile machine, with the advantage concentrated in the upwind passage between azimuth angles of thirty and one hundred twenty degrees, where dynamic stall dominates. The cavity appears to reshape the internal flow structure in a way that enlarges the pressure difference between the two sides of the blade, and the first torque peak shifts to a later azimuth angle and grows taller. Averaged across all the operating conditions examined, the profile swap alone was worth roughly a ten percent improvement in torque.

But the J-shape carried a hidden liability that emerged at high speed. At a tip speed ratio of 1.77, the open-tipped J-shaped turbine’s performance collapsed, falling more than fifty percent below the conventional rotor. The culprit was the blade tip. Because the J-profile is hollow, vortices do not merely shed from the tip the way they do on a solid wing; they can leak out through the open cavity itself, spilling high-energy flow and destroying the pressure difference the blade depends on. Tip vortices, the swirling structures that form wherever lift-generating surfaces end abruptly, are a familiar efficiency tax on all rotors, but the open J-section makes the leakage far more damaging precisely when the turbine is spinning fast enough to generate its best power.

The team’s fix was disarmingly simple: cap the tips. They added thin NACA0021-shaped plates, one millimeter thick, to both ends of each blade, sealing the hollow section like lids on a tube. The effect was enormous. At the problematic tip speed ratio of 1.77, the caps boosted the torque coefficient by roughly 122 percent compared with the uncapped J-shaped turbine, lifting it about eight percent above even the conventional full-profile machine. Averaged over all five tip speed ratios studied, from 0.44 to 1.77, the caps raised the J-shaped turbine’s torque coefficient by about 46 percent, and the capped J-shaped design beat the conventional helical turbine by about 48 percent overall. In power-coefficient terms, obtained by multiplying torque by tip speed ratio, the capped machine dominated across the operating range.

By slicing each blade into twenty sections along its height and tracking the torque of each, the researchers traced exactly where the gains came from. At a mid-range tip speed ratio of 1.33, the upwind half of the rotor improved by just over twenty percent with caps installed, while the downwind half gained a more modest eight percent, with the largest benefits near the tips themselves. Flow visualizations revealed the mechanism: without caps, the vortex forming inside the blade’s concave cavity escapes outward over the open edge; with caps in place, the vortex is redirected toward the trailing edge, and pressure builds inside the cavity, strengthening the force that drives rotation. The caps essentially convert a leaking bucket into a sealed one, letting the J-profile’s pressure advantage accumulate instead of draining away through the blade ends.

Perhaps most important for the urban applications that motivate this whole line of research, the capped design starts better. The team held the rotor stationary in a seven-meter-per-second wind and computed the starting torque at azimuth angles from zero to 105 degrees in fifteen-degree increments. The capped J-shaped turbine beat the conventional helical rotor at every single angle, with improvements ranging from about four percent to a striking 46.6 percent at ninety degrees, and an average gain of roughly 21.5 percent across all positions. For a technology whose central weakness has always been the dead zone where lift-based rotors cannot overcome their own drag, a design that simultaneously raises efficiency, smooths torque, and strengthens self-starting is a meaningful step forward. The authors caution that they fixed the cut ratio and cap thickness rather than optimizing them, so further gains may remain on the table. But the message of the study is clear: sometimes the path to better wind energy is not a bigger machine or a fancier material, but a hollow blade with its ends sealed shut, turning the city’s messy gusts into cleaner, steadier power.

Subject of Research: Aerodynamic performance and self-starting behavior of a helical J-shaped vertical-axis wind turbine with capped blade tips

Article Title: Aerodynamic performance and self-starting characteristics of a novel helical J-shaped vertical-axis wind turbine with blade-tip caps

Article References: Moghtadaeifar, M., Farzadi, R., & Bazargan, M. (2026). Aerodynamic performance and self-starting characteristics of a novel helical J-shaped vertical-axis wind turbine with blade-tip caps. Results in Engineering, 32, Article 113308. https://doi.org/10.1016/j.rineng.2026.113308

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113308

Keywords: vertical-axis wind turbine, J-shaped airfoil, helical blades, blade-tip caps, tip vortices, self-starting torque, CFD simulation, URANS, SST k-omega, dynamic stall, urban wind energy, power coefficient