Heat Transfer Research Articles

The Role of Thermal Conductivity on Opposed Flow Flame Spread

ABSTRACT Quantifying the magnitude of solid-phase and gas-phase heat transfer for opposed flow flame spread has been the subject of research, and debate, for decades. Many studies neglect the contribution of longitudinal conduction through thermally thick solids for opposed flow flame spread. This study demonstrates the role of thermal conductivity with the addition of unidirectional conductive elements (copper, steel, and carbon fiber) in 12-mm-thick polymethylmethacrylate (PMMA) substrates. A layer of conductive elements was placed either or 3 or 6 mm from the surface of the solid. The addition of conductive elements in the direction of flame spread was found to increase the rate of both downward and lateral flame spread. The addition of copper elements in particular was found to increase the downward flame spread rate by nearly 60%. The subsequent increase in flame spread rate for each sample orientation (lateral and downward) was contextualized using the ratio of gas-phase and solid-phase heat transfer, as determined in previous studies. Additionally, the flame spread rate was correlated to the effective thermal conductivity in the longitudinal direction and the spread rate was found to follow an approximately linear relationship with effective thermal conductivity.

Transient Modeling and Simulation of a Generic Stable Salt Reactor

A SAM system-level model of a generic stable salt reactor has been developed to investigate thermal-hydraulic behavior and safety performance under steady and transient conditions. The model integrates information generated from a reactor physics analysis using PROTEUS and PERSENT, and a computation fluid dynamics (CFD) analysis using STAR-CCM+. A loose, iterative coupling scheme between PROTEUS and SAM is implemented to calculate the equilibrium power and temperature distributions in the steady-state critical core condition. The converged steady-state model is then used in PERSENT to calculate the four reactivity feedback temperature coefficients (Doppler, fuel density, coolant density, and core radial expansion) and kinetic parameters that are needed in SAM to model the temperature feedback effects in transient simulations. Within the fully enclosed liquid fuel pins, natural convection is the dominant heat transfer mechanism. The STAR-CCM+ model of the fuel pin considers conjugate heat transfer from the liquid fuel salt to the pin cladding and external reactor coolant. The CFD results of the axial and radial temperature profiles are used to empirically determine an effective fuel salt thermal conductivity in the SAM fuel pin model so that the temperatures predicted by the SAM model match as closely as possible the CFD results. In the central region of the fuel pin, the effective thermal conductivity is as high as ~60 times the physical fuel salt thermal conductivity. The whole-plant SAM model is then used to simulate an unprotected station blackout transient. The results of this simulation showed that the large negative fuel axial expansion reactivity feedback reduces fission power to ~2.4% nominal power. The core is cooled by natural circulation, which removes heat in the core to the emergency heat removal system, and ultimately, to the ambient. However, peak fuel salt and cladding temperatures can potentially reach as high as 1500 K, albeit briefly, if the shutdown mechanism fails to operate.

Heat transfer analysis of a fully wetted inclined moving fin with temperature-dependent internal heat generation using DTM-Pade approximant and machine learning algorithms

Heat transfer analysis of a fully wetted inclined moving fin with temperature-dependent internal heat generation using DTM-Pade approximant and machine learning algorithms

Investigation on the design and heat transfer performance of dry-grinding heat pipes grinding wheels

Investigation on the design and heat transfer performance of dry-grinding heat pipes grinding wheels

Heat transfer visualization of transitional growth of turbulent spot on a wedge in Mach 5.2 hypersonic flow using fast-response TSP

Heat transfer visualization of transitional growth of turbulent spot on a wedge in Mach 5.2 hypersonic flow using fast-response TSP

Impact of non-linear motion on convective heat transfer induced by oscillating thermal waves in the presence of heat source and sink

Impact of non-linear motion on convective heat transfer induced by oscillating thermal waves in the presence of heat source and sink

Experimental and numerical studies of laminar natural convection heat transfer from an isothermally heated narrow flat plate oriented at different angles of rotation

Experimental and numerical studies of laminar natural convection heat transfer from an isothermally heated narrow flat plate oriented at different angles of rotation

Drop Dynamics during Condensation on Superhydrophobic Surfaces in Vapor Shear Flow.

Accurate models for predicting drop dynamics, such as maximum drop departure sizes, are crucial for estimating heat transfer rates during condensation on superhydrophobic (SH) surfaces. Previous studies have focused on examining the heat transfer rates for SH surfaces under the influence of gravity or vapor flowing over the surface. This study investigates the impact of surface solid fraction and texture scale on drop mobility in a condensing environment with a humid air flow. Experiments recorded condensation with varying surface feature sizes from micro- to nano scale under different flow rates. Video analysis detected the drop-size distribution and maximum drop departure sizes. Particle image velocimetry (PIV) provided accurate shear force representations. Results showed that the maximum drop departure sizes decreased with lower surface solid fractions and higher flow rates. A force balance analysis revealed that coalescence-induced drop jumping aids drop departure. Different drop behaviors due to coalescence were linked to surface characteristics. The study quantified drop jump distances under shear force during condensation on SH surfaces, and found that jump distances increased when coalescing drop sizes were similar. Based on these findings, a method for tuning SH surfaces to control drop size at coalescence and departure was suggested. Drop mobility was measured in terms of Bond and Capillary numbers, showing a dependence on surface solid fraction and pitch size. By combining these into surface slip length, it was shown that drop mobility increases with increasing slip length.

Investigation of heat transfer and pressure loss of bio-based functionalized multi-walled carbon nanotubes nanofluid in separation flow passage

Investigation of heat transfer and pressure loss of bio-based functionalized multi-walled carbon nanotubes nanofluid in separation flow passage

Wire-droplet-substrate integrated model for heat transfer and deposition geometry prediction in GMAW-based wire arc additive manufacturing

Wire-droplet-substrate integrated model for heat transfer and deposition geometry prediction in GMAW-based wire arc additive manufacturing

The impact of different shaped pin‐fins on the flow and heat transfer in the internal cooling structure of gas turbine blades trailing edges

The impact of different shaped pin‐fins on the flow and heat transfer in the internal cooling structure of gas turbine blades trailing edges

Multiphysics Modeling of Heat and Mass Transfer for Photoelectrochemical CO2 Reduction to CO

Multiphysics Modeling of Heat and Mass Transfer for Photoelectrochemical CO₂ Reduction to CO

Dynamic-Wetting Liquid Metal Thin Layer Induced via Surface Oxygen-Containing Functional Groups.

Enhancing the wettability of liquid metals (LMs) to address their high surface tensions is crucial for practical applications. However, controlling LMs wetting on various substrates and understanding the underlying mechanisms are challenging. Here, we present a facile dynamic-wetting strategy to modulate eutectic gallium-indium (EGaIn) wettability via chemical surface modification, spontaneously forming a stable and thin (∼18 μm) EGaIn layer. Polymer substrates exhibiting varying EGaIn wetting behaviors can be categorized by their sliding angles and adhesion force. X-ray photoelectron spectroscopy results demonstrate that the dynamic-wetting process occurs only on surfaces with sufficient oxygen-containing functional groups (content ≥18%) and confirm coordination interactions between the EGaIn oxide layer and surface functional groups. Furthermore, in EGaIn thermal management systems, the heat transfer rate in the wetting group is increased by up to 20% compared to that of the nonwetting group. This work will hasten the application of LMs in flexible circuits and thermal management.

A Portable Hybrid Photovoltaic Thermal Application: Shape-Stabilised Phase-Change Material with Metal Flakes for Enhanced Heat Transfer

A Portable Hybrid Photovoltaic Thermal Application: Shape-Stabilised Phase-Change Material with Metal Flakes for Enhanced Heat Transfer

Influence of radiative heat transfer on hybrid nanofluid across a curved surface with porous medium

Influence of radiative heat transfer on hybrid nanofluid across a curved surface with porous medium

Determination of Heat Transfer Coefficient in a Film Boiling Phase of an Immersion Quenching Process

Determination of Heat Transfer Coefficient in a Film Boiling Phase of an Immersion Quenching Process

Scalable and Precise Synthesis of Structurally Colored Bottlebrush Block Copolymers: Enabling Refined Color Calibration for Sustainable Photonic Pigments.

Self-assembled bottlebrush block copolymers (BBCPs) offer a vibrant, eco-friendly alternative to traditional toxic pigments and dyes, providing vivid structural colors with significantly reduced environmental impact. Scaling up the synthesis of these polymers for practical applications has been challenging with conventional batch methods, which suffer from slow mass and heat transfer, inadequate mixing, and issues with reproducibility. Precise control over molecular weight and dispersity remains a significant challenge for achieving finely tuned color appearances. Here, we present an alternative strategy to overcome the challenges by integrating a rapid continuous flow technique with an in-line self-assembly procedure. This strategy enables the rapid, stable and large-scale synthesis of narrow-dispersed BBCPs, exceeding 2 kg/day, a significant improvement over conventional gram-scale methods. Furthermore, precise control over the degree of polymerization is achieved with an unprecedented interval accuracy of four repeat units. This level of precision enables refined color calibration in the resulting photonic pigments, effectively eliminating the need for labor-intensive and costly multiple batch syntheses.

Thermal Analysis of Electromagnetic Induction Heating for Cylinder-Shaped Objects.

Induction heating is one of the cleanest and most efficient methods for heating materials, utilizing electromagnetic fields induced through AC electric current. This article reports an analytical solution for transient heat transfer in a three-dimensional (3D) cylindrical object under induction heating. A simplified form of Maxwell's equations is solved to determine the heat generation inside the cylinder by calculating the current density distribution within the body. The temperature within the solid is found from the solution of the unsteady heat equation based on Green's function. Owing to multiple spatial dimensions and time, a separation of variables technique is used to find Green's function. In addition, an innovative algorithm is proposed to take care of the variable material properties in analytical treatment. The analytical solution for temperature is verified with the data obtained from experiments for identical operating conditions. The analytical solution is used to study the impact of heat transfer coefficient and input AC current frequency and amplitude during transient heat diffusion. Our analytical solution suggests that the temperature-dependent material properties significantly affect the thermal response within the solid. Unlike many other conventional heating methods, the thermal boundary condition changes with time in induction heating, which makes our solution much more challenging.

Numerical analysis of natural convective heat transfer with porous medium using JUPITER

ABSTRACT Japan Atomic Energy Agency (JAEA) has developed a numerical method with the JUPITER code with a porous medium model to calculate the thermal behavior in primary containment vessels (PCVs) of Fukushima Daiichi nuclear power stations of Tokyo Electric Power Company (1F). In this study, we performed an experiment and numerical simulation of the natural convective heat transfer with the porous medium and compared those results. In comparison of the temperature and velocity distributions between the experiment and simulation, the temperature distribution in the simulation was in good agreement with the distribution in the experiment except the temperature near the top and side surface of the porous medium. The velocity distribution also agreed qualitatively with the experimental result. In addition, we also performed the numerical simulations with various effective thermal conductivity models to discuss the effect of the conductivity based on the internal structure of porous media on the natural convective heat transfer. The result indicated that the temperature distribution in the porous medium and the velocity distribution of the natural convection were significantly different for each model, and the simulation result with the Kunii–Smith model was close to the experimental results.

Biochar-Aided Heat Transfer in Ground Source Heat Pumps: Effects on Water Capillary Rise and Carbon Storage Capability

Biochar-Aided Heat Transfer in Ground Source Heat Pumps: Effects on Water Capillary Rise and Carbon Storage Capability