Search Results (635)

This article presents the results of a numerical CFD study of heat exchanger channels with passive heat transfer enhancement methods. Two types of channel geometry were analyzed with different flow turbulization methods. In case I, internal micro-fins were applied to the tube wall, which disturbed the flow directly in the boundary layer; the investigated relative fin heights ranged from 0.01 h/D to 0.08 h/D, and the dimensionless longitudinal spacing varied from 0.92 L/D to 3.27 L/D. In case II, an insert with repeating drop-shaped elements was used, causing fluid turbulization in the tube core; the relative droplet diameter ranged from 0.38 d/D to 0.73 d/D, with the same longitudinal spacing as for the fins. The influence of the geometry and longitudinal spacing of the disturbance elements on the thermal–flow characteristics of such channels, namely, the friction factor, Nusselt number, and thermal efficiency evaluated using the PEC, was investigated over a Reynolds number range of 5000 to 400,000. The results show that the insert produces a larger increase in the Nusselt number, whereas the micro-finned tube generally achieves higher PEC values due to lower hydraulic losses. The results clearly indicate that, in most cases, the PEC is higher for the finned tube, particularly at low Reynolds numbers not exceeding 50,000. In turn, for the insert, the longitudinal distance between the elements, L, has a significant influence on the PEC; as L increases, the PEC also increase, reaching its maximum value for the largest L. Full article

To overcome the low heat-transfer efficiency on the seawater side of the intermediate fluid vaporizer (IFV), a triangular inner-finned heat-transfer enhancement tube suitable for low to medium-flow-velocity conditions was designed. The influence of triangular internal fins’ axial spacing, height, radial arrangement number, and inclination angle on the flow and heat transfer characteristics inside the tube was numerically investigated. The tube performance was evaluated and optimized by performance evaluation criteria (PEC). The results indicated that triangular internal fins induced vortex structures, which disrupted the boundary layer, thereby enhancing momentum and energy exchange between the hot fluid within the boundary layer and the cold fluid outside it. Heat transfer was improved with reduced fin distance, increased height, and increased the number of radial arrangements. The optimal comprehensive performance was achieved at an inclination angle of 75°. The Nusselt number (Nu) increased by 66.02%, the friction factor (f) increased by 162.23%, and PEC reached up to 1.203 when Re was 9545. The results provided a theoretical reference for the structural optimization of efficient heat-exchange tubes. Full article

This study presents a controlled three-dimensional conjugate CFD comparison of counter-flow and parallel-flow concentric tube heat exchangers under identical Reynolds number conditions (Re = 1000–2000). By isolating the flow configuration as the only varying parameter, the intrinsic influence of flow arrangement on thermo-hydraulic performance is systematically evaluated. Unlike enhancement-focused studies involving geometric modification or advanced working fluids, the present study focuses exclusively on the influence of flow arrangement under identical operating conditions. The analysis focuses on heat transfer rate, outlet temperature distribution, pressure drop, thermo-hydraulic performance index, and a normalized heat transfer ratio (Ψ). The results show that the counter-flow configuration consistently enhances heat transfer by 3.17–4.29% compared to parallel-flow operation, while maintaining nearly identical pressure-drop values. This improvement is attributed to the preservation of a higher logarithmic mean temperature difference (LMTD) along the exchanger length, sustaining the thermal driving force under laminar flow conditions. In contrast, the parallel-flow configuration exhibits a rapid decay in temperature difference near the inlet region, limiting effective heat transfer. Although heat transfer increases with Reynolds number in both configurations, the thermo-hydraulic performance index decreases due to the relatively higher increase in hydraulic resistance. Comparison with classical laminar flow behavior confirmed the physical consistency and reliability of the numerical model. The findings demonstrate that counter-flow arrangement provides a measurable thermal advantage without additional hydraulic penalty. The study offers a physically consistent and practically relevant framework for the design and optimization of concentric tube heat exchangers used in engine cooling and waste heat recovery applications. Full article

Bridging the gap between theoretical heat exchanger analysis and physical intuition remains a persistent challenge in engineering education, particularly when students are confronted with real-system effects such as pressure losses, measurement uncertainty, and deviations from simplified models. This work addresses this challenge through the coupled development of a pedagogical framework and an experimental platform. A modular heat exchanger test bench was conceived, designed, and constructed by graduate students within a structured project-based learning environment, in which competitive and cooperative phases were combined to emulate real engineering practice. This approach positions the test bench not only as a laboratory tool, but as the outcome of an active learning process that integrates system design, instrumentation, and modeling. The resulting platform enables the comparative study of multiple heat exchanger technologies—including three water-to-water heat exchangers (plate, shell-and-tube, and double-pipe) and one air-to-water fin-and-tube heat exchanger—under parallel, counterflow, and crossflow arrangements across a wide range of operating conditions. Comprehensive instrumentation (temperature, flow rate, and pressure measurements) supports rigorous energy balance analysis, effectiveness evaluation, and hydraulic performance assessment. Beyond undergraduate experimentation, the test bench provides a framework for advanced learning objectives, including uncertainty propagation, $\epsilon$-NTU analysis, model development, and experimental validation. The confrontation between model predictions and experimental data, including observed discrepancies, is shown to play a central role in developing critical engineering judgment. The proposed approach demonstrates how the integration of project-based learning with a reconfigurable experimental platform can create a sustainable and scalable environment for heat transfer education. Full article

To mitigate the spatiotemporal mismatch between renewable energy supply and building heating demand, this study proposes a novel non-pressurized shell-and-tube latent heat storage (NP-LHS) device coupled with an air-source heat pump (ASHP) system. To overcome the inherent low thermal conductivity of organic phase change materials (PCMs), the thermal performances of plain, corrugated, and finned tubes were systematically compared using both computational fluid dynamics (CFD) simulations and full-scale experiments. Numerical results indicate that the optimal tube spacing ratio ranges from 1.0 to 1.5. Among the evaluated geometries, the finned tube configuration exhibited superior comprehensive performance. It achieved an exceptionally high PCM volume fraction of 92.5% and dramatically reduced the complete melting time to 180 min—significantly faster than both corrugated (280 min) and bare tubes—while attaining a higher terminal temperature. Full-cycle dynamic experiments further demonstrated that integrating the finned tube NP-LHS into the ASHP system yielded a peak-shaving power reduction rate of 98.0%, effectively maintaining indoor thermal comfort. These findings conclude that expanding the conductive surface area via fins is practically more effective than inducing fluid turbulence for low-conductivity PCMs in non-pressurized storage applications. Full article

Nine sets of fin parameter combinations, including a plain tube control group, were modeled. Simulations were performed under steady-state conditions using the EWT Realizable k-ε turbulence model, with benzene and water as working fluids, while accounting for temperature-dependent thermophysical properties. Flow field distribution, temperature profile, Nusselt number, and pressure drop in the shell side of the heat exchanger were analyzed. Response surface methodology was employed to systematically evaluate the coupled effects of fin height and fin spacing on thermal performance. The results indicate that annular fins significantly enhance heat transfer by inducing secondary flow and disrupting the thermal boundary layer. Compared to the smooth tube, the finned tubes increased the Nusselt number (Nu) by up to 28.6% and the total heat transfer rate by 13.55%, while the pressure drop (ΔP) increased by approximately 9.81% to 16.5%. The analysis revealed that fin height is the dominant factor affecting performance, whereas fin spacing plays a regulatory role. As the fins became taller or denser, the temperature field evolved from stable stratification to intense mixing and eventually to local disorder. The study identified an optimal parameter range for engineering applications. A fin height of 2–3 mm combined with a spacing of 10–15 mm achieves the best balance between heat transfer enhancement and flow resistance. Specifically, the combination of h = 3 mm and s = 10 mm yielded the highest Energy Efficiency Coefficient (EEC) of 1.567. This configuration is recommended for large-flow, pressure-drop-sensitive systems, such as those found in petrochemical plants or long-distance heat transmission applications. Full article

Large-scale shell-and-tube heat exchangers operate for extended periods, critically affecting the energy efficiency and safety of hydrogen production processes. However, online condition monitoring on industrial distributed control systems (DCSs) is often hindered by an engineering trilemma: high-fidelity mechanistic models incur prohibitive computational latency; static constant-parameter models suffer from severe systematic bias; and purely data-driven models risk yielding non-physical predictions under out-of-distribution scenarios such as variable-load operations. To address these challenges, this study proposes a physics-guided adaptive digital twin tailored to high-noise industrial DCS environments. Energy conservation and the counterflow logarithmic mean temperature difference (LMTD) relation are embedded as hard constraints in a lightweight reduced-order model (ROM). On this basis, a closed-loop online adaptation strategy—comprising physical-bound checking, window-wise inverse estimation, anomaly rollback, and exponentially weighted moving average (EWMA) smoothing—treats the overall heat transfer coefficient U as an equivalent time-varying parameter that co-evolves with operating regimes. Validation on real plant DCS data under variable-load conditions shows that, compared with a conservative fixed-U baseline, the proposed online update eliminates massive systematic overestimations (up to tens of degrees Celsius) and suppresses inversion oscillations caused by small cold-side temperature differences and sensor noise. Relative to an overfitting-prone data-driven baseline, the framework retains millisecond-level inference latency while enforcing thermodynamic feasibility, thereby establishing a dynamic healthy baseline. This baseline provides a proxy indicator for distinguishing load-induced reversible variations from potential degradation-related residual trends. Full article

Frost buildup on copper tube-fin heat exchangers reduces their performance in cold, humid conditions. Fin length plays a key role in balancing heat transfer and frost resistance. This study experimentally examines how fin length affects thermal and frosting behavior. Four heat exchangers with fin lengths of $15.1$ $\mathrm{m}$$\mathrm{m}$, $18.53$ $\mathrm{m}$$\mathrm{m}$, $20.3$ $\mathrm{m}$$\mathrm{m}$, and $23.5$ $\mathrm{m}$$\mathrm{m}$ were tested at 2 °C/1 °C dry-bulb/wet-bulb air temperature and $-6$ °C coolant temperature under constant static pressure. Results show that longer fins increase total heat transfer—peak capacity rose from 512 $\mathrm{W}$ to 566 $\mathrm{W}$—but reduce heat transfer per unit area by about 30%. Operating time before defrosting increased by 30.6%, from $45.7$ $\min$ to $59.6$ $\min$, due to lower frost density. Total frost mass grew, but unit-area frost decreased by 12.7%. During defrosting, longer fins achieved greater absolute airflow recovery (from 195 to 213 ${\mathrm{m}}^3$h⁻¹), though defrosting efficiency per gram of frost declined. Short fins (15 $\mathrm{m}$$\mathrm{m}$) suit space-limited systems needing high surface efficiency. Long fins (23 $\mathrm{m}$$\mathrm{m}$) benefit large systems requiring long run times and strong post-defrost performance. Medium lengths (17 $\mathrm{m}$$\mathrm{m}$ to 20 $\mathrm{m}$$\mathrm{m}$) offer a practical balance for general use. These findings support better heat exchanger design in frost-prone applications. Full article

Shell-and-tube heat exchangers are critical components in oil refining, where their thermal and operational performance is strongly affected by fouling, corrosion-related deterioration, and deposit accumulation in tube-bundle cavities. This study investigates the technical condition of selected TK-type heat exchangers used in refinery services and proposes an integrated maintenance-oriented approach for the assessment and removal of severe deposits formed between tubes. The work first classifies heat-exchanger damage into structural and technological categories, emphasizing fouling as a key source of thermal performance degradation and operational inefficiency. A physical interpretation of compacted deposits is then combined with dynamic modeling to evaluate the response of the pollutant medium to pneumoshock excitation. Based on the analytical and simulation results, the main practical outcome of the study is the development of a pneumoshock cleaning device (PCD) for the mechanical removal of deposits from narrow inter-tube spaces. The proposed approach supports a more effective diagnosis of exchanger condition, helps identify suitable cleaning actions for heavily fouled bundles, and contributes to improved maintenance decision-making in refinery thermal systems, although quantitative before-and-after thermal performance validation is beyond the scope of the present study. As an applied developmental study, the work highlights the relevance of fouling-aware inspection and targeted cleaning technologies for extending equipment serviceability and supporting more reliable thermal management in industrial heat-exchange applications. Full article

This study reports the calculated values results of the shell-side heat transfer coefficient for a shell-and-tube heat exchanger with an inner shell diameter of 200 mm and a length of 518 mm, containing 85 tubes arranged in a staggered layout. Shell-side cross-flow was generated by nine standard segmental baffles with a 25% baffle cut and a baffle pitch of 48 mm. In particular, the effect of 13 combinations of shell-to-baffle and baffle-to-tube gaps on the heat transfer coefficient was investigated. Moreover, the influence of sealing strips and tube bundle diameter on the heat transfer coefficient was also examined. The calculations were carried out using three different approaches, namely the Gaddis-Gnielinski method, the extended Bell-Delaware method, and Aspen EDR code. Numerical simulations for an idealized heat exchanger were also conducted using Ansys Fluent and OpenFOAM. As far as the authors are aware, this is the first study to compare two computational methods widely regarded as reference approaches for shell-and-tube heat exchangers, namely the Bell-Delaware and the Gaddis-Gnielinski approaches. The results obtained using the Aspen EDR code, a widely recognized software tool for modeling and design of heat exchangers, were evaluated against the forecast of the Bell-Delaware and Gaddis-Gnielinski approaches. Full article

Non-insulated heat exchangers in gas-to-gas service lose substantial energy to the surroundings. This study evaluates Al₂O₃ and ZnO ceramic coatings (200 $\mathsf{\mu }$m) as passive thermal retention layers on the inner surface of the outer tube in a copper double-pipe heat exchanger, using 3D CFD simulations verified for internal consistency against Log Mean Heat Transfer Rate analytical solutions. Six cases were modelled: three coating conditions across parallel-flow and counter-flow configurations under laminar conditions ($R{e}_i\approx 525$, $R{e}_o\approx 192$) with air as the working fluid. The coating elevates the outer tube inner wall temperature $T_3$, increasing the convective driving force to the cold fluid while suppressing ambient dissipation. In parallel flow, Al₂O₃ increases the net inter-fluid heat transfer rate by 35.7% and reduces ambient losses by 81.4%; ZnO achieves 30.9% and 70.4%, respectively. In counter-flow, Al₂O₃ yields a 26.6% enhancement and 73.2% loss reduction. The coated parallel-flow configuration outperforms the uncoated counter-flow baseline. Thermal circuit analysis shows that Al₂O₃ superiority arises from its higher conductivity (40 vs. 19 W m⁻¹ K⁻¹), which sustains a higher equilibrium $T_3$ and a heat partition ratio of 11.84 versus 7.17 for ZnO. These results show that a single ceramic coating layer can recover a large fraction of the thermal energy lost through non-insulated walls, offering a low-cost, retrofit-compatible pathway to improve the energy efficiency of gas-to-gas heat exchangers in HVAC, building energy recovery, and industrial process heat applications. Full article

Organic Rankine Cycles (ORCs) are widely recognized as an effective solution for waste heat recovery (WHR). However, the design and optimization of these systems must address the tradeoff between computational efficiency and the need to capture complex component behavior. This requires moving beyond purely energetic 0D modeling approaches to account for constructional, spatial, and operational constraints. This work presents a novel modeling framework with a specific focus on the expansion device. Radial inflow turbine stages are selected for their capability to achieve high pressure ratios while maintaining compactness and high efficiency. Heat exchangers follow a generic one-dimensional counterflow configuration, with a shell-and-tube geometry adopted for sizing purposes. The turbine stages are modeled by resolving several internal sections in order to capture local thermofluid dynamic conditions. The framework predicts turbine efficiency and incorporates a newly developed formulation for shock-induced losses, improving performance prediction under trans-sonic flow conditions. After validation against experimental data, the model is applied to a WHR system integrated with an internal combustion engine fueled by biofuels. The results highlight the existence of optimal operating conditions arising from competing physical mechanisms. The analysis also shows the transition from single-stage to two-stage turbine configurations at high pressure ratios and emphasizes the role of real gas effects in determining stage performance and optimal expansion distribution. The results of simulations carried out for three different working fluids (ethanol, toluene, and R1234ze(E)) highlight that the available mechanical power ranges from 10 to 22 kW for single-stage turbine configurations and from 24 to 36 kW for two-stage configurations, with total system volumes varying between approximately 600 and 9000 L. Among the working fluids considered here, ethanol provides the best overall performance for the present case study. Overall, the proposed approach provides a reliable and computationally efficient tool for the preliminary design and optimization of ORC-based WHR systems. Full article

Flexible heat exchangers with intricate three-dimensional (3D) geometries exhibit superior mechanical and thermal performance compared with traditional two-dimensional (2D) designs. Their ability to offer greater design freedom and unique functionalities makes them particularly attractive for wearable medical devices. This study investigates flexible heat exchanger technologies in three main directions: (i) miniaturisation, (ii) integration of physical and mathematical models, and (iii) enhanced adaptability through heterogeneous design integration. Through a combination of literature review, mathematical modelling, and experimental analysis, the thermal efficiency of several configurations is compared, including basic thermoplastic polyurethane (TPU) tubes and 3D bio-inspired TPU tubes with aluminium-finned structures. The findings establish a foundation for the development of next-generation flexible wearable medical cooling devices with improved thermal management capabilities and practical applicability in industrial design. Furthermore, the outcomes of this research will directly support the development of improved wearable cooling devices within a UK-based medical device SME, Paxman Scalp Coolers, facilitating the translation of advanced heat exchanger designs into clinically relevant and commercially viable solutions. Full article

Phase change material (PCM)-based latent heat storage (LHS) systems help address the mismatch between renewable energy supply and thermal demand. However, their practical implementation is constrained by the strongly nonlinear and multiphysics nature of phase change, which makes high-fidelity simulations and real-time applications computationally expensive. This review examines mathematical reduced-order modeling (ROM) as an effective strategy to overcome this limitation by combining physics-based simplifications, projection methods, interpolation techniques, and data-driven models for PCM-based LHS systems. While physical simplifications (such as dimensional reduction and effective property approximations) represent an important first layer of model reduction, the primary focus of this work is on the mathematical ROM methodologies that operate on the governing equations after such physical simplifications have been applied. The review covers approaches including two-temperature non-equilibrium and analytical thermal-resistance models, Proper Orthogonal Decomposition (POD), CFD-derived look-up tables, kriging and ε-NTU grey/black-box metamodels, and machine-learning methods such as artificial neural networks and gradient-boosted regressors trained from CFD data. These ROM techniques have been applied to packed beds, PCM-integrated heat exchangers, finned enclosures, triplex-tube systems, and solar thermal components, achieving speed-ups from tens to over 80,000 times faster than full CFD simulations while maintaining prediction errors typically below 5% or within sub-Kelvin temperature deviations. A critical comparative analysis exposes the fundamental trade-off between interpretability, data dependence, and computational efficiency, leading to a practical decision-making framework that guides method selection for specific applications such as design optimization, real-time control, and system-level simulation. Remaining challenges—including accurate representation of phase change nonlinearity, moving phase boundaries, multi-timescale dynamics, generalization across geometries, experimental validation, and integration into industrial workflows—motivate a structured roadmap for future hybrid physics–machine learning developments, standardized validation protocols, and pathways toward industrial deployment. Full article

The steam generator is a core component of nuclear power plants that facilitates heat exchange between the primary and secondary circuits, directly impacting the overall operation of the plant in terms of safety and reliability. During prolonged operation, the heat transfer tubes of the steam generator are subjected to erosion, corrosion, and cracking due to high-temperature, high-pressure fluid impact and vibration. Existing in-service inspection strategies for heat transfer tubes generally employ fixed intervals and coverage, failing to effectively differentiate the actual risk of tubes in various regions, leading to wasted inspection resources or safety hazards. This paper proposes a dynamic inspection and plugging management strategy based on flow-induced vibration (FIV) analysis, specifically utilizing the flow stability ratio (FSR). By calculating the FSR of heat transfer tubes, the strategy categorizes them into high-risk, medium-risk, and low-risk regions, and dynamically adjusts inspection frequency and coverage based on these risk levels. Theoretical analysis and validation with actual data demonstrate that this strategy can improve inspection efficiency and ensure the safety of the steam generator. Full article