Heat Dispersion Research Articles

A miniaturized cooling system for trans-esophageal echocardiographic probes may improve patients safety in minimally invasive cardiac surgery or trans-catheter percutaneous interventions

Abstract Introduction The recent development of real-time three-dimensional trans-esophageal echocardiography (RT-3D TEE) has favoured a wider transition from open-heart to minimally invasive surgery (MIS) or various trans-catheter percutaneous interventions, minimizing surgical risks and allowing faster post-operative and procedural discharge [1]. However, recent studies have highlighted the potential risk of oesophageal lesions partly related to thermal injury caused by the heat of the TEE probe during cardiac interventions [2]. Purpose This work aims to design a cooling system for trans-esophageal echocardiographic probes to be used during MIS or trans-catheter procedures. Currently during those interventions, fluoroscopic and RT-3D TEE images are simultaneously used, since commercial TEE probes automatically switch off at a temperature threshold of approximately 42.5°C [3], to avoid potential thermal oesophageal lesions. Additionally, ultrasound (US) image quality tends to decrease as temperature increases. The creation of a cooling device for TEE probes would therefore increase the reliability of US images in the intraoperative context, also considering their complete harmlessness to the patient. Methods The proposed cooling system design is a silicone cap – thus potentially sterilisable and reusable - into which the probe is inserted. The cap has an inner tube in which water flows at 25°C, constituting the cooling fluid. Heat exchange was studied through thermo-fluid dynamic simulations to analyse the cooling phenomenon. The hydraulic flow is controlled by a pumping device that activates when the probe temperature reaches a specific threshold deemed to be critical, also for image quality. Temperature trends are constantly monitored by means of two thermistors. Results The cooling system was extensively tested (5 repetitions for each experimental condition: Probe alone, Passive silicone and Active cooling system) on a probe produced by GE Healthcare, setting 38°C as the activation temperature threshold for the pump. Considering the duration of MIS or transcatheter interventions (about two hours) [2], it was experimentally observed that by using the cooling system the probe never exceeded the temperature of 39°C. From experimental tests, it is possible to state that the insulating properties of silicone result in a dual effect: a) silicone passively hinders heat dispersion produced by the probe due to the Joule effect - Passive silicone condition ; b) once the system is activated the cooling effect is maintained by the precence of water inside the cap - Active cooling system condition. Conclusions In conclusion, based on numerical simulations and experimental results, this novel tool seems promising, increasing the safety and potentially also the reliability of US images in the intraoperative and intraprocedural scenario. Cooling system design Experimental results

Influences of urban shape on city-scale heat and pollutants dispersion under calm and moderate background wind condition

Influences of urban shape on city-scale heat and pollutants dispersion under calm and moderate background wind condition

EXPERIMENTAL INVESTIGATION OF A CONVERGENT NOZZLE FOR THERMAL HOMOGENIZATION OF AIR

This study employed a 2 kW<sub>th</sub> solar air tower simulator system for experimental validation, explicitly focusing on the effectiveness of a custom-designed mixer assembly under conditions of even and uneven heat flux distribution. Non-uniform heat dispersion within the absorbers can create localized hotspots and temperature disparities, resulting in thermal stress within the pipeline system. To address this challenge, a mixer assembly was devised to equalize the temperature differential in the heated air. The study concentrates on scrutinizing the temperature variance along both the axial and azimuthal axes within the mixer assembly, examining scenarios with aperture power of 1000 W and 1500 W, as well as mass flow rates of 6.37 g/s and 14.87 g/s. Notably, the study identified a maximum temperature differential of 7°C at the mixer's outlet when the initial temperature variance at the inlet stood at 37°C.

The effect of TIG welding technology parameters on the weld quality of copper material joints for heat pipe applications

Copper is a commonly used material for heat pipe fabrication using the welding process. However, welding copper to copper presents significant challenges due to its inherent material properties. Its exceptionally high thermal conductivity facilitates rapid heat dispersion, complicating the maintenance of a stable melting zone. Furthermore, copper is prone to oxidation, which generates brittle oxides that can adversely affect weld quality. This research paper examines the relationship between TIG welding parameters—specifically current, voltage, shielding gas flow rate, and filler rods—and the mechanical properties of the resulting heat pipe material. The study involves varying the welding current at levels of 120 A, 135 A, and 150 A, along with different types of filler rods. The results indicate that both the selection of welding current and the type of filler rod significantly influence the tensile strength of copper welded joints. Notably, the use of higher currents in ERCuSi-A welding tends to decrease hardness in the HeatAffected Zone (HAZ), while producing more complex variations in hardness within the Weld Metal (WM), dependent on the interplay between heat and the chemical composition of the filler rod. Additionally, nickel in the ERCuNi filler rod contributes to an increase in weld hardness.

Hazard Identification of Ammonia FSS for Ammonia Fuelled Ammonia Carrier

Ammonia is a zero-carbon fuel that has attracted considerable interest. The compound has high volumetric energy density and is easy to store and transport. Despite this, a proper study is necessary to ensure safety because ammonia fuel will likely be applied first to ammonia carriers. In this study, hazard identification (HAZID) was performed to identify the risk of the ammonia fuel supply system and preventive/mitigation measures were suggested to minimize the risk. The analyzed system scope was the ammonia fuel supply system from a fuel service tank on the deck to the front of the engine. The nodes with the most scenarios were the fuel service tank and the fuel supply line. The main factors included internal factors, such as design defects, malfunctions, and operational errors, and external factors, such as impact, thermal stress, hogging, and sagging. Recommendations are provided to reduce the risk of accident scenarios, including safety devices/alarm devices in process systems, system layout configurations, and heat and gas dispersion analysis. The results are expected to help predict/minimize damage regarding ammonia fuel supply system design, operational safety, and potential risks.

Comparative analysis of transient thermal behaviour and efficiency in longitudinal metal porous fin with combined heat and mass transfer under dehumidification conditions

This investigation explores the transient thermal characteristics of longitudinal porous fins made of Aluminium (Al) and Copper (Cu), exposed to a dynamic moist airstream under dehumidification conditions. Heat and mass transfer processes are initiated when the fin surface temperature falls below the dew point temperature of the surrounding air, driven by differences in temperature and humidity ratios. Heat transfer within the porous structure is modelled using temperature-dependent convective coefficients and Darcy’s flow model, with the governing nonlinear partial differential equation transformed into dimensionless form and solved using the Finite Difference Method (FDM) to analyse the fin thermal profile and efficiency over time. These results reveal that Cu fin due to their superior thermal conductivity exhibit higher temperature profile and efficiency compared to Al fin across all pertinent parameters. A key finding is the significant impact of Relative Humidity (RH) on the thermal behaviour of the fin: as RH increases by 400%, the temperature distribution from base to tip decreases by 138% in Al due to its higher specific heat capacity, which enables it to absorb more latent heat and 85% in Cu, where the superior thermal conductivity allows for faster heat dissipation. As Darcy number (Da) decreases by 99%, the temperature distribution along the fin from base to tip increases by 0.058% in Al due to its lower thermal conductivity and 0.041% in Cu, where its higher thermal conductivity enables more efficient heat dispersion. These insights are pivotal for advancing fin design and optimization, facilitating improved thermal management in industrial applications under transient and dehumidifying conditions.

Industrial Dry Heat Island and Dispersion of Air Pollutants Induced by Large Coal-Fired Activities.

Notable anthropogenic heat sources such as coal-fired plants can alter the atmospheric boundary layer structure and the pollutant dispersion, thereby affecting the local environment and microclimate. Herein, in situ measurements inside a coal-fired steel plant were performed by multiple advanced lidars from 21 May to 21 June of 2021 in Yuncheng, Shanxi Province, China. Comparing with an adjacent meteorological site, we found a prominent nighttime dry heat island overhead of the factory, which was 3-10 °C hotter and 30%-60% drier than the surrounding fields. Large-eddy simulations constrained by the measured thermal contrast suggested that the heat-island-induced circulation could upward transport factory-discharged pollutants and horizontally spread them below the residual layer top, forming a mushroom-shaped cloud. The shape, size, and pollutant loading of the cloud were highly determined by thermodynamic variables such as aerodynamic wind and anthropogenic heat flux. Furthermore, these retained residual-layer pollutants can be convected downward to the ground after sunrise through the fumigation effect, causing the peaking phenomena aboveground. These peaks were statistically evidenced to be common in major urban agglomerations in China. The study provides a new insight regarding the origins of residual-layer pollutants and highlights the needs for programming representations of coal-fired heat emissions in mesoscale air-quality models.

CFD analysis of rotation effect on flow patterns and heat transfer enhancement in a horizontal spiral tube heat exchanger

This study explores the enhanced thermal performance of heat exchangers utilizing spirally coiled tubes, particularly in applications such as heating saltwater in solar desalination plants, which require elevated heat transfer coefficients. A numerical investigation is conducted to assess the impact of mechanically rotating horizontal spiral tubes on flow patterns and temperature profiles along their length. A detailed physical model was developed using COMSOL Multiphysics software. The findings from computational fluid dynamics simulations indicate that mechanical rotation significantly modifies both velocity and temperature gradients at each cross-section of the tube. This rotation effectively reduces the formation of thermal hotspots in the outer regions, thereby improving and accelerating heat dispersion. Notably, substantial variations in velocity and temperature profiles occur at rotation speeds up to 4 rpm; however, these changes diminish beyond this speed threshold. The study reveals that rotation increases the Nusselt number of the heated flow within the tube by over 145 %. Furthermore, the effects of rotation are more pronounced in smaller diameter tubes compared to larger ones. Ultimately, the performance factor indicates that the benefits of enhanced heat transfer outweigh the increased pressure drops associated with tube rotation, validating the effectiveness of the proposed heating system.

Laser Oscillation Diameter Variation Effect on Laser Wire Additive Manufacturing Deposition Morphology

A high-speed camera was employed to capture the melting process and investigate the impact of laser beam oscillation diameter on weld pool fluctuation and deposition morphology during laser wire additive manufacturing (LWAM) of 316L wire. The transient fluctuations of the weld pool caused by the laser beam were observed at different oscillation diameters. Additionally, 3D morphology measurements were conducted on the deposited layer to assess the effects of different oscillation diameters on its morphology. Further analysis examined the heat dispersion resulting from beam oscillation by plotting the energy distribution for various oscillation diameters. The key findings are as follows: Changes in oscillation diameter resulted in fluctuations within the weld pool that impacted the surface morphology of the deposit and refinement of pore condition as well as alterations in the energy distribution of the weld pool that influenced its contour geometry. Increasing the laser oscillation diameter can effectively make the keyhole shallower, weaken the bottom protrusion of the weld pool, and reduce the curvature of the top surface of the bead. Simultaneously, it can promote the stirring of the liquid solution, effectively refining the porosity area, reducing porosity within the weld pool, and improving the specimen’s density. However, larger oscillation diameters lead to more-significant hump arch formation on the deposited surface and larger roughness values.

Double-diffusive convection in flow of Carreau fluid with variable density inside converging and diverging channels of rectilinear walls

In this article, the effects of double-diffusive convection have been seen on the flow of Carreau fluid of variable density, maintained inside straight and converging (diverging) channels. Note that the channel walls exhibit variable porosity and undergo stretching or shrinking at non-uniform velocities. In the flow domain, we have taken into account the convective transport of both heat and species mass concentrations. The pseudo-similarity solutions of previous investigation for such type flows are not used here; however, a new set of similarity transformations has been formed, which reduced the governing system (PDEs) into an exact set of ordinary differential equations (ODEs), whereas the longstanding issues of semi-similarity solutions have been successfully resolved in this particular case and in general for all situations of Carreau fluid flow. In a nutshell, a unified mathematical approach has been devised in this paper. We strictly emphasized the simulation of flow of Carreau fluid and double diffusive convection in flow inside a channel with multiple dynamical behaviours and structures (both Jeffery Hammel and Poissuielle flow types) of walls. The boundary layer approximation and stream function assumptions have not been used in the study's execution. The shear thinning and shear thickening features of Carreau fluids with variable density cause them to exhibit lower axial velocity in the centre of a horizontal channel than Newtonian fluids due to variable wall configurations and complex flow conditions. By enhancing buoyancy driven convection, which promotes effective heat dispersion, increasing the solutal and thermal Grashof numbers (GrS=GrT>0) lowers the temperature field. It has been found that in channel with diverging walls (a1=2.0), increasing the modified Reynolds numbers (σ1,σ2>0) increases concentration profiles, i.e. ϕ(η), while decreasing them in channel with rectilinear walls (a1=0.0).

Insight on physical–mechanical properties of one-part alkali-activated materials based on volcanic deposits of Mt. Etna (Italy) and their durability against ageing tests

In recent years, there has been a growing interest in one-part alkali-activated materials, which utilize solid-form alkali activators, within the construction industry. This approach is becoming popular due to its simpler and safer application for cast-in-situ purposes, as compared to the conventional two-part method. At this purpose, we have pioneered the use of volcanic deposits of Mt. Etna volcano (Italy) as precursor for the synthesis of a unique one-part formulation. This was done to assess its performance against both traditional and two-part alkali-activated materials. The study employed a comprehensive range of investigative techniques including X-ray powder diffraction, Fourier transform infrared spectroscopy, hydric tests, mercury intrusion porosimetry, ultrasound, infrared thermography, spectrophotometry, contact angle measurements, uniaxial compressive strength tests, as well as durability tests by salt crystallization and freeze–thaw cycles. The key findings on the studied samples are as follows: i) small size of pores and slow absorption-drying cycles; ii) satisfying compactness and uniaxial compressive strengths for building and restoration interventions; iii) high hydrophily of the surfaces; iv) lower heating dispersion than traditional materials; v) significant damage at the end of the salt crystallization test; vi) excellent resistance to freeze–thaw cycles. These newly developed materials hold promises as environmentally friendly options for construction applications. They offer a simplified mixing process in contrast to the conventional two-part alkali-activated materials, thus providing an added advantage to this class of materials.

Effect of hydroxylated boron nitride and boron nitride nanosheets on the properties of doped organosilicone rubber composites

As the electronic industry develops rapidly, the miniaturisation, integration and multifunctionality of electronic devices have resulted in a dramatic increase in power density, and the heat dispersal of electronic devices has attracted much attention. In this work, hydroxylated hexagonal boron nitride (BN-H) was obtained by hot alkali treatment, and boron nitride nanosheets (BNNS) with a thickness of about 4 nm were obtained by boric acid-assisted ball milling stripping. The effects of different types of fillers as well as filler contents on the thermally conductive and mechanical performance of organosilicon composites were also compared. Notably, when BN-H and BNNS thermally conductive fillers were added at 12 wt%, the thermally conductive coefficients of the composites were 0.4831 W·m−1·K−1 and 0.7131 W·m−1 K−1, respectively, which were 183% and 318% of higher than that for the pure silicone rubber (SR, with a thermally conductive coefficient of 0.1706 W·m−1·K−1). In addition, in respect of mechanical performance, the tensile strengths of SR/BN-H and SR/BNNS composites with a filling level of 12 wt% were 3.59 MPa and 3.89 MPa, respectively, and the storage moduli were 4501 MPa and 4583 MPa, respectively, which were improved to a certain extent compared with pure SR. The present work provides an effective way to develop organosilicone rubber composites with good thermal conductivity and mechanical properties by boric acid assisted ball milling to strip boron nitride in the field of electronics packages.

Effective lateral dispersion of momentum, heat and mass in bubbling fluidized beds

The lateral dispersion of bed material in a bubbling fluidized bed is a key parameter in the prediction of the effective in-bed heat transfer and transport of heterogenous reactants, properties important for the successful design and scale-up of thermal and/or chemical processes. Computational fluid dynamics simulations offer means to investigate such beds in silico and derive effective parameters for reduced-order models. In this work, we use the Eulerian-Eulerian two-fluid model with the kinetic theory of granular flow to perform numerical simulations of solids mixing and heat transfer in bubbling fluidized beds. We extract the lateral solids dispersion coefficient using four different methods: by fitting the transient response of the bed to (1) an ideal heat or (2) mass transfer problem, (3) by extracting the time-averaged heat transfer behavior and (4) through a momentum transfer approach in an analogy with single-phase turbulence. The method (2) fitting against a mass transfer problem is found to produce robust results at a reasonable computational cost when assessed against experiments. Furthermore, the gas inlet boundary condition is shown to have a significant effect on the prediction, indicating a need to account for nozzle characteristics when simulating industrial cases.

Influence of sub-zero coolant circulation and additive nanoparticles on performance characteristics of FSPed Al6061 alloy

ABSTRACT Al6061 alloy has become prevalent in the industrial sector because of its low density, excellent machinability, and corrosion resistance but it lacks properties like hardness and wear. Therefore, surface modifications by friction stir processing (FSP) are done with additive nanosized particles like multi-walled carbon nanotubes (MWCNT), Titanium oxide (TiO2), and Graphene nanoparticles (GNP) To perform 2-pass FSP, a uniquely engineered fixture with coolant circulated underneath the plate at sub-zero temperatures is used. Grain refinement has been observed in micrographs as a consequence of 2-pass FSP. The coolant circulated beneath carries the heat generated and enhances the heat dispersion rate, culminating in finer grains. The calculated mean grain size of the Al6061 alloy was considerably decreased in all the surface composites. There is a substantial improvement in the microhardness profile, which has increased by nearly 70–90%, as well as a significant enhancement in tensile strength of almost 20–30% in all the composites. The ductile type of failure during tensile load is revealed by SEM fractography. The process of dynamic recrystallisation is responsible for the development of equiaxed grains. The wear resistance of all the composites is also enhanced, and the COF of Al6061/GNP composite is found to be lowest at 0.23.

Dynamic industrial risks assessment for enhanced safety in the oil and gas industry: a methodological innovations and applications

In recent years, continued and accelerated growth in the oil and gas sector has significantly contributed to catastrophic accidents in various regions of Algeria, especially those with high population densities. Therefore, assessing the risks associated with these industries is crucial to prevent such disasters. This study introduces a methodology integrating several Quantitative Risk Assessment techniques, such as Failure Modes and Effects Analysis, Fault Tree Analysis, Event Tree Analysis, and the Bow-Tie method, coupled with simulation tools (ALOHA and FLUENT). This integration created a Dynamic Industrial Risk Assessment Methodology (DIRAM), a comprehensive approach to assessing industrial risk consequences in the oil and gas industries. The study demonstrates DIRAM's effectiveness in understanding the dynamics of catastrophic events. It provides a visual representation of CO2 plume and heat dispersion after a Boiling Liquid Expanding Vapor Explosion (BLEVE), emphasising the importance of spatial-temporal awareness in risk assessment and emergency response. DIRAM offers a valuable basis for preventing and managing potential risks and reinforcing safety measures at hydrocarbon plants.

GaN microdisks with a single porous optical confinement layer for whispering gallery mode lasing

This paper details the fabrication of GaN-based microdisks with a single porous n-GaN layer positioned beneath the multiple quantum wells region on a modified green light-emitting diode epiwafer. Simulations of the longitudinal light field distribution reveal effective confinement of the light field within the multiple quantum wells region due to the presence of the single porous layer. The porous layer also demonstrates sufficient conductivity as determined through calculations and serves as an effective method for thermal dispersion. Under optical pumping, all microdisks exhibit clear whispering gallery mode (WGM) lasing at room temperature, with the lowest threshold of 13.50 μJ/cm2 achieved in a 2-μm-diameter microdisk. These findings suggest that integrating the single porous layer into GaN microdisks is a highly promising approach for achieving high-efficiency WGM micro-laser diodes with effective electrical injection and heat dispersion.

Thermal criticality and two-step diffusion-reaction of electromagnetic Casson-Williamson fluid flow along a vertical channel with convective cooling under bimolecular kinetic

The need to examine diverse conditions involving industrial working fluids and improving thermal transfer efficiency cannot be overstated. Every thermal system must monitor and control excessive heat production and propagation to avert disruptions in various engineering processes. Therefore, the study investigated the theoretical significance of thermal criticality and a two-step exothermic reaction on Casson-Williamson fluid dynamics behaviour through a fixed vertical channel driven by an electromagnetic field, axial pressure gradient, and heat buoyancy force under a generalized bimolecular chemical kinetic. The heat exchange at the convective wall surface is adhered to Newton’s law of cooling. The Galerkin weighted residual method (GWRM) was utilized to solve the dimensionless nonlinear equations governing the flow within the boundary layer, yielding graphical representations of momentum and energy distributions. The results show that higher values of the activation energy, Frank-Kamenetskii parameter, electric field loading, activation ratio term, Weissenberg number, and second step term led to better heat dispersion and, eventually, complete combustion of hydrocarbons in the Casson-Williamson fluid. To avoid system disruptions, the study underscores the crucial need for continuous monitoring of all factors that stimulate internal heat generation to prevent system failures, emphasizing the importance of vigilance in the field of thermal systems.

On the Role of Radial Dispersion in the Behavior of a Cooled Fixed‐Bed Reactor: Numerical Investigation of Fischer–Tropsch Synthesis with a Cobalt‐Based Catalyst

AbstractThe impact of radial dispersion of both heat and mass on the behavior of cooled fixed‐bed reactors was explored using a two‐dimensional reactor model. This study accounted for dispersion through an effective radial thermal conductivity (λrad) and a radial dispersion coefficient of mass (Drad), with Fischer–Tropsch synthesis serving as an illustrative process example. Under moderate reaction conditions and hence still rather gentle radial temperature profiles, the effect of mass dispersion on reactor performance was found to be minimal, even if disregarded (Drad = 0), whereas dispersion of heat (λrad) always significantly impacts reactor behavior. Nevertheless, for precise thermal runaway predictions by a reactor model, incorporating mass dispersion by a realistic Drad value is essential.

Exploration of linear and exponential heat source/sink with the significance of thermophoretic particle deposition on ZnO-SAE50 nano lubricant flow past a curved surface

The present research focuses on exploring the impact of linear and exponential heat source/sink on double-diffusive MHD convective flow heat and mass transport of ZnO – SAE50 nano lubricants in an exponentially stretching curved sheet along with the effect of thermophoretic particle deposition. The heat transmission is considered to be caused by both radiation and convection. The mathematical modelling of the considered problem results in a coupled system of partial differential equations, using suitable similarity transformation variables these equations are reduced to a coupled non-linear system of ordinary differential equations and are solved numerically by adopting the finite difference method to obtain the solution for the field variables. The quantity and spatial distribution of linear heat sources/sinks affect the physical dynamics and optimum status of the entire system and the application of exponential heat sources/sinks can improve heat dispersion and energy efficiency in industrial operations such as nuclear reactors and steel production. The thermophoretic particle deposition parameter controls particle concentration by allowing particles to accumulate on surfaces or in specific areas of the fluid. A rise in Hartmann number causes a mechanical damping force to act in the opposite direction of the fluid motion, lowering the speed of the fluid in the curved sheet. The heat and mass transmission properties are analyzed through the Levenberg – Marquardt backpropagating algorithm and the correlation coefficient has ideal values of unity for training, validation, testing, and overall. In light of this, the anticipated behaviour of the LMNN-BPA indicated that the heat transfer profile numerical data and the network output are in good consensus.

Physiological and structural traits contribute to thermotolerance in wild Australian cotton species.

Five species of cotton (Gossypium) were exposed to 38°C days during early vegetative development. Commercial cotton (Gossypium hirsutum) was contrasted with four wild cotton species (G. australe, G. bickii, G. robinsonii and G. sturtianum) that are endemic to central and northern Australia. Plants were grown at daytime maxima of 30°C or 38°C for 25 d, commencing at the four-leaf stage. Leaf areas and shoot biomass were used to calculate relative rates of growth and specific leaf areas. Leaf gas exchange measurements revealed assimilation and transpiration rates, as well as electron transport rates (ETR) and carboxylation efficiency (CE) in steady-state conditions. Finally, leaf morphological traits (mean leaf area and leaf shape were quantified), along with leaf surface decorations, imaged using scanning electron microscopy. Shoot morphology was differentially affected by heat, with three of the four wild species growing faster at 38°C than at 30°C, whereas early growth in G. hirsutum was severely inhibited by heat. Areas of individual leaves and leaf numbers both contributed to these contrasting growth responses, with fewer, smaller leaves at 38°C in G. hirsutum. CO2 assimilation and transpiration rates of G. hirsutum were also dramatically reduced by heat. Cultivated cotton failed to achieve evaporative cooling, contrasting with the transpiration-driven cooling in the wild species. Heat substantially reduced ETR and CE in G. hirsutum, with much smaller effects in the wild species. We speculate that leaf shape, as assessed by invaginations of leaf margins, and leaf size contributed to heat dispersal differentially among the five species. Similarly, reflectance of light radiation was also highly distinctive for each species. These four wild Australian relatives of cotton have adapted to hot days that are inhibitory to commercial cotton, deploying a range of physiological and structural adaptations to achieve accelerated growth at 38°C.