Central composite design to optimize the heat transfer rate in unsteady Boger hybrid nanofluid flow over a permeable slow rotating disk

Numerical simulation of motion characteristics and heat transfer enhancement of free particles in boiling heat transfer

Impact of pin-fin structural parameters on flow and heat transfer in embedded hybrid microchannel heat sinks based on a hotspot-oriented comprehensive evaluation framework

Double-pipe heat exchangers (DPHEs) are vital in industrial applications, and improving their performance is crucial for sustainability. This study uses three-dimensional Computational Fluid Dynamics (CFD) simulations to investigate the impact of passive flow modifications, specifically geometrically spaced and perforated ring inserts, on heat transfer and pressure drop in a DPHE. The research involved developing a 3D numerical model whose accuracy was ensured through a comprehensive mesh independence study and rigorous validation against established empirical correlations and experimental data. Subsequent simulations explored the influence of geometric spacing ( G -factor) and the number of perforations per ring. Results demonstrated that for unperforated rings P = 0 , uniform spacing maximised heat transfer, reaching a Nusselt number of 177.4 at a Reynolds number of 12,000. In contrast, strongly biased configurations exhibited superior overall performance by balancing thermal enhancement with hydraulic losses. These biased cases achieved a Performance Evaluation Criterion (PEC) of 1.065, equivalent to a 6.5% improvement compared with the uniform arrangement. The introduction of perforations significantly altered performance; a four-hole configuration with G = 1 . 00 consistently achieved the highest heat transfer and overall performance, with the Nusselt number rising to 195.8 and the PEC reaching 1.176, indicating an optimal balance between fluid mixing and flow resistance. By comparison, increasing the number of perforations further to eight reduced the pressure drop from 171 . 9 Pa for solid rings to 132 . 0 Pa , but had a less pronounced positive impact on heat transfer performance. For this configuration, the Nusselt number remained close to that of the unperforated case. Analysis of both turbulent kinetic energy (TKE) and velocity vector fields provided critical insights into the underlying mechanisms, illustrating how ring geometry and perforations disrupt boundary layers and generate beneficial turbulence. Furthermore, regression-based multivariate correlations for both the Nusselt number and friction factor were formulated as functions of Reynolds number, G -factor, and porosity. Validation against the full set of 75 CFD simulation cases demonstrated high accuracy, with 96% of the correlation-predicted Nusselt numbers deviating by less than ± 5 % from the corresponding CFD results, and the equivalent friction factor values deviating by less than ± 10 % . • Non-uniform ring spacing significantly affects DPHE thermo-hydraulic behaviour. • Four-hole perforated rings provide the best heat-transfer and pressure balance. • Strongly biased ring spacing yields higher overall PEC than weakly biased layouts. • CFD reveals mixing patterns driven by combined spacing and perforation effects. • Correlations predict Nusselt number and friction factor for 75 DPHE cases.

Methodology to assess the influence of thermocouple measurement errors on unsteady heat transfer characteristics in aero-engine experiments

Thermal management of electronic chips using microencapsulated phase change material slurry in a taenidia-inspired spiral channel heat exchanger

• Flame stability with heat transfer and NOx pathways of ultra-lean NH 3 /H 2 blends. • Hydrogen enrichment extends ammonia’s lean flammability limit. • Radical pool strength (H, O, OH) increases with Re and ϕ. • Intermediate species (NH 2 , NH, HO 2 , HNO) exhibit distinct equivalence-ratio trends. Ammonia’s narrow flammability and low reactivity limit its use in micro-combustors, but hydrogen enrichment offers a pathway to stable ultra-lean operation. Hydrogen enrichment has been proposed as a viable strategy to overcome these limitations, yet systematic mapping of lean NH 3 /H 2 flames under micro-scale confinement remains scarce. In this work, a two-dimensional numerical study was conducted on a planar micro-combustor fuelled with an NH 3 /H 2 blend (10/90 vol%) to quantify flame stability, heat transfer, and NOx chemistry over a broad range of Reynolds numbers Re = 191–1330 and ϕ = 0.65–0.20. Hydrogen addition extends the lean limit from ϕ = 0.65 to ϕ = 0.2, with ultra-lean flames ( ϕ = 0.20–0.25) stabilized only at Re = 572 and 381, respectively. Outlet temperatures rise with Re and approach adiabatic values, while heat loss ratio ( Q loss /HoR) reduces below 0.065 once Re exceeds 953 across the entire equivalence ratio range. Radiative coupling provides an additional stabilizing effect, with incident radiation increasing from 3.6 × 10 4 W/m 2 ( ϕ = 0.20, Re = 572) to 76 × 10 4 W/m 2 ( ϕ = 0.65, Re = 1330). Radical pool analysis revealed that H, O, and OH intensify with both Re and ϕ , sustaining chain branching and flame anchoring, while intermediate species showed distinct behaviours. Kinetic pathway analysis confirmed that NO formation is dominated by HNO decomposition and NO 2 reduction, whereas consumption proceeds mainly through reactions with HO 2 and HNO cycling. The findings provide the first integrated stability–heat transfer–reaction pathway analysis of NH 3 /H 2 micro-planar flames, demonstrating how hydrogen extends ammonia’s lean limit to ultra-lean regimes while reshaping the NO/N 2 O distribution through radical-driven chemistry.

This study examines the influence of freeze pipe design parameters on the thermal and hydraulic performance of artificial ground freezing (AGF) systems. A parametric analysis is conducted to evaluate the effects of geometric variables (inner and outer pipe diameters, wall thickness, and pipe length), material properties, and the heat transfer fluid’s flow regime. An analytical model is developed for steady-state heat transfer between the soil and circulating fluid, accounting for flow regime transitions and internal heat generation due to hydraulic resistance. Results demonstrate that thermal efficiency is highly sensitive to both geometry and operational conditions. The optimum inner pipe diameter generally ranges between 0.6 and 0.8 of the outer diameter, depending on the flow rate and fluid characteristics. While the material and thickness of the outer pipe have a strong effect on heat transfer, the properties of the inner pipe material exert only a minor influence. Additionally, extended pipe lengths and elevated flow rates may reduce performance due to self-heating of the circulating fluid, highlighting the need for integrated design optimization. The proposed framework offers practical guidance for enhancing freeze pipe configurations in AGF applications. • An analytical model for steady-state heat transfer in an ice wall, considering the coolant flow regime, is developed. • It is demonstrated that freeze pipe thermal efficiency is highly sensitive to its size, materials, and the coolant flow parameters. • It is shown that self-heating of coolant at high flow rates and long pipe lengths is a limiting factor for system performance. • A practical framework is provided to optimize freeze pipe design in artificial ground freezing systems.

Experimental study of flow boiling heat transfer in smooth and circular pin-fin minichannels

Stage-dependent performance and design criteria of functionally graded TPMS–PCM composites: Joint effects of gradient function and steepness

Strategic nanoparticle placement for remote enhancement of boiling heat transfer performance.

Numerical analysis of natural convection and entropy generation in a porous square enclosure using ECOP analysis: Effects of linear heating position and porosity

Optimization of heat exchanger design for third generation centralized solar power generation system: CFD and thermoeconomic coupling method for improving thermal performance and reducing storage costs of batteries

This study presents a multi-step approach to design and evaluate the cooling architecture of an actively cooled probe nacelle suitable for high-temperature supersonic flows. First, a 1D heat transfer model was used to determine the coolant pressure required for thermal protection of the nacelle at supersonic conditions. It incorporates conductive-convective heat transfer, effusion cooling, leading-edge effects, and high-speed boundary layer effects. A parametric analysis identified a minimum coolant pressure of 2.4 bar to satisfy the temperature limits of the nacelle at the most severe conditions of M 1 = 6 , T 01 = 1700 K . 3D RANS simulations were utilized to assess the accuracy of the 1D model giving average deviations in adiabatic cooling effectiveness and heat transfer coefficient below 6% and 15% respectively. Finally, the cooling performance of the nacelle was assessed in a transonic open jet. Cooling effectiveness was measured with high-resolution infrared thermography, and heat flux was measured with high-frequency Atomic Layer Thermopiles (ALTP). Uncertainties in cooling effectiveness and heat transfer coefficient were evaluated through Taylor propagation and Monte Carlo simulations, respectively. Oil-flow visualization was conducted to compare the surface flow behavior in the effusion cooled face between simulations and experiments, while Schlieren was used to compare the bow shock location and shape. A comprehensive comparison is conducted involving analytical models, simulations and experiments that validate the proposed methodology. • First unified 1D 3D experimental methodology for supersonic cooled-probe design. • Actively cooled probe enables optical tests from transonic to Mach 6 and 1700 K. • IR, thermopile, schlieren, and oil tests link heat flux, cooling, and flow topology. • 1D and 3D models agree within 15% for HTC and 7% for cooling effectiveness.

Continuous flow chemistry for the synthesis of highly energetic materials: A review of synthetic advancements, process intensification, and safety engineering

Heat transfer and instability characteristics of a two-phase thermosyphon loop with wide range of filling ratios

Coupled channel–electrode design for water transport and performance stability in proton exchange membrane fuel cells

Flow, heat transfer, and particle deposition in a novel corrugated impingement cooling channel with return holes: a numerical study

The dual role of local thermal non-equilibrium for mixed convective heat and mass transfer in porous media: Suppressing heat transfer while enhancing mass transfer

Effects of flow slip and temperature jump on heat transfer in a ribbed microfluidic channel using lattice Boltzmann method