Heat Flow Research Articles

Research progress on aero-optical effects of hypersonic optical window with film cooling

AbstractIn recent years, the demand for optical imaging and detection in hypersonic aircraft has been on the rise. The high-temperature and high-pressure compressed flow field near airborne optoelectronic devices creates significant interference with light transmission, known as hypersonic aero-optical effects. This effect has emerged as a key technological challenge, limiting hypersonic optical imaging and detection capabilities. This article focuses on introducing the thermal effects and optical transmission effects of hypersonic aero-optical effects, as along with corresponding suppression techniques. In addition, this article critically reviews and succinctly summarizes the advancements made in hypersonic aero-optical effects testing technology, while also delineating avenues for future research needs in this field. In conclusion, there is an urgent call for further exploration into the study of aero-optical effects under conditions characterized by high Mach, high enthalpy, and high Reynolds number in the future.

Insights Into Pool Boiling Heat Transfer on Minichannel Surfaces Through Point and Field Measurements

Abstract In this study, saturated pool boiling experiments were conducted on copper minichannel and flat surfaces at atmospheric pressure using water as the working fluid. The heat transfer performance was assessed through point measurements with a heater block, cartridge heaters, and thermocouples, as well as field measurements using a thin-foil heater and infrared thermography. Two copper minichannel surfaces with square cross sections of 1 mm (minichannel-1) and 2 mm (minichannel-2) side lengths were tested and compared to a flat surface. Minichannel-1 and minichannel-2 enhanced the critical heat flux (CHF) by 17% and 45%, respectively, and improved the heat transfer coefficient by 24–40% and 51–75%, respectively, compared to the flat surface. Minichannel-2 exhibited the lowest and most uniform boiling surface temperature, making it the best performer among the three. There was no significant change in departure frequency among the surfaces, and no significant change in departure diameter for the flat surface and minichannel-1. However, minichannel-2 had lower departure diameters due to its deeper channels, which prevented bubble coalescence and maintained low departure diameters. Additionally, minichannel-2 delayed vapor film formation by breaking it with its deeper fins, thereby improving CHF and slightly enhancing bubble dynamics. The enhancement in boiling heat transfer is primarily attributed to the increased surface area provided by the minichannels, with a minor contribution from improved bubble dynamics. However, the dominant factor in enhancing pool boiling heat transfer on minichannel surfaces is the increase in surface area.

Synergistic Impact of Magnets and Fins in Solar Desalination: Energetic, Exergetic, Economic, and Environmental Analysis

This study investigates the effectiveness of combining magnets with parabolic and truncated fins in enhancing the distillation process of solar stills. The integration of magnets accelerated evaporation rates, while the fins increased the heat absorption area, resulting in improved output, vis-à-vis traditional solar stills. A comparative assessment revealed that the parabolic fin solar still (PFS) with magnets outperformed the truncated fin solar still (TCFS), producing 20%, 15%, and 16% more distillate at three different depths (1, 2, and 3 cm). The superior performance of the PFS is attributed to the magnetism of the water and the fins’ more extensive surface area for heat absorption. Efficiency measurements at a water depth of 1 cm showed that the PFS achieved the maximum energy and exergy efficiencies at 30.49% and 8.85%, respectively, compared with TCFS’s 25.23% and 6.22%. Economically, the PFS setup proved more feasible, with a 20.9% lower cost per liter of distilled water than TCFS. Additionally, the environmental impact assessment indicated a significant reduction in CO2 emissions, potentially generating revenues of approximately USD 1242.32 through carbon credits. These results reflect a considerable margin to enhance the efficiency of solar desalination through well-planned adjustments, which bodes well for the future of optimized solar distillation systems from an economic and environmental perspective.

A scientific report on heat transfer analysis due to generated and absorbed heat over an oscillatory stretching sheet: a finite difference-based study.

A non-Newtonian liquid motion across a stretchable surface is relevant to various industrial applications, including extruding plastic sheets and stretching plastic films. In connection with this, the impact of endothermic and exothermic chemical reactions on the flow of rate-type liquid via an oscillatory stretching sheet in the presence of permeable media with the Maxwell liquid model is elucidated in the present study. Scientists and engineers may enhance the efficiency of chemical reactions or heat transmission by optimising system flow and investigating the effect of reactions on flow dynamics. The present study's governing partial differential equations (PDEs) are transformed into their non-dimensional form using similarity variables. The resulting equations are numerically solved using the finite difference method (FDM). Outcomes disclose that the temperature profile declines as the activation energy and unsteadiness parameters increase. The influence of the Maxwell and unsteadiness parameters on the fluid's velocity with respect to time is represented. The rise in the values of chemical reaction parameter upsurges the thermal profile. As the activation energy and unsteadiness parameters upsurge, the thermal profile declines. As the chemical reaction parameter and the ratio of oscillation frequency to stretching rate values rise, the concentration profile falls.

Computational role of homogeneous–heterogeneous chemical reactions and a mixed convective ternary hybrid nanofluid in a vertical porous microchannel

Abstract This article mainly scrutinizes the heat transfer and flow characteristics of a mixed convection ternary hybrid nanofluid in a porous microchannel considering the catalytic chemical reaction and nonuniform heat absorption/generation. Using appropriate similarity transformations, the modeled equations are converted into reduced ones and then solved via the Runge–Kutta–Fehlberg 4th/5th order method. To strengthen this analysis, the convection mechanism has been deployed. The effect of pertinent physical parameters on the fluid motion and thermal field is displayed, including some important engineering variables like the Nusselt number, Sherwood number, and drag force. The novel outcomes display that the flow reduces with porous permeability and nanoparticle volume fraction. The temperature of the nanofluid improves with nonuniform heat absorption/generation. The concentration decreases in the presence of both homogeneous and heterogeneous reaction intensities. The heat transfer rate enhances for the Eckert number, and a similar influence on the mass transfer rate is noticed for homogeneous reaction parameters. Further, the drag force declines for the Grashof number. The outcomes show that, in all cases, the ternary hybrid nanofluid shows a greater impact than the nanofluid. The attained findings represent applications in the era of cooling and heating systems, thermal engineering, and energy production.

Optimization of heat transfer in a double lid-driven cavity with isoperimetric heated blocks using GFEM.

This article is concerned with the examination of flow dynamics and heat transfer characteristics in a 1:4 double lid driven cavity in presence of isoperimetric heated blocks of various shapes. The focus is to identify the optimal shape that enhances the heat transfer in a tall cavity. The parametric settings are chosen in such a way that all the convection regimes including natural, forced and mixed convection could be generated. This cavity has lids positioned at the top and bottom, moving in opposite directions along the x-axis. The physical system is represented as a set of coupled partial differential equations incorporating the rheological properties of the power-law fluids (PL). The governing equations in conjunction with various non-dimensional physical parameters are simulated via Galerkin's Finite Element Method (GFEM) on a very fine hybrid grid. The study includes the computation of the Kinetic Energy and Average Nusselt number to determine the optimal shape. It is concluded that the circular block is superior to the other two in terms of heat transmission efficiency.

Development of a near infrared region based non-invasive therapy device for diabetic peripheral neuropathy.

Diabetic Peripheral Neuropathy (DPN) is a nerve damage that is treated with painkillers and steroids which have the drawback of interference with other medications and the dangers of side effects. Novelty of the proposed work is to develop a Near Infrared Region (NIR) based non-invasive therapy device called 'DPNrelief-1.0V'developed with a 890 nm wavelength diodes. DPNrelief-1.0V delivers a total dosage of 6.174 J/cm2 with heat absorption by tissue of 61.74 Joules at 30 minutes. The device was tested by carrying out a pilot study with 8 patients where 4 were treatment group and control group. The DPNrelief-1.0V is validated by Nerve Conduction Study (NCS) test. The degenerated nerves pre-therapy showed less amplitude, Conduction Velocity (CV) and latency which was improved post-therapy by 100% in amplitude of nerve signal, 100% in CV and a decrease of 36.2% in latency. Independent t-test was conducted to find the difference between control and treatment, wherein a p value < 0.05 was obtained depicting significant difference between two groups. Furthermore, the performance of the device is validated by one-way test repeated measures Analysis of Variance (ANOVA), wherein a p value of < 0.05 was obtained depicting a difference in nerve condition pre-and post-therapy. The performance of DPNrelief-1.0V has outperformed Anodyne therapy device with lesser dosage, treatment time and portability and in curing the symptoms of DPN. DPNrelief-1.0V finds its potential in the field of medicine for treating DPN.

Harmonic and Heat Flow Representations of the Gaussian White Noise

Harmonic and Heat Flow Representations of the Gaussian White Noise

Temperature‐dependent heat transfer deterioration in ordered graphene/ceramic composites

AbstractBoosting heat transfer of ultrahigh temperature ceramics (UHTCs) with dimensional‐crossover graphene has become an increasing challenge for improving the thermal protective performance of new‐generation spacecraft. Yet its characteristics of anisotropic and high interfacial thermal resistance inevitably cause heat transfer deterioration at high temperatures. Here we develop a few ZrB2/graphene/ZrB2 interface‐dominated diffuse models that are driven by bonding configurations and thermal converger. It has been found that forming stronger bonding configurations by Zr‐C interfacial bonding and designing a preferred thermal converger by ordered graphene are both unarguable ways of suppressing high‐temperature heat transfer deterioration. Each Zr‐C interfacial bonding serves as an independent sluice gate to accelerate heat flow. More high‐frequency phonons are excited at high temperature, which augments the interfacial thermal conductance from 38.5 to 335.4 MW·m−2·K−1 at 700 K. Impressively, a concept of thermal converger inspires us to adopt ordered graphene for changing the diverging behavior in isotropic ZrB2 composites. Its convergent process combines with anisotropic characteristics to transform the isotropic heat flow into the highly ordered graphene. Their thermal conductance can be regulated from minimum (2.5) to maximum (80.8 W·m−1·K−1) by rotating the ordered graphene from 90° to 7.5°. This work paves an optimal way for manipulating the heat transfer of UHTCs.

Study on the Effect of Heat Transfer Characteristics of Energy Piles

The thermal performance of energy piles equipped with new metal fins to improve heat transmission is examined in this research. The solid heat transfer module of COMSOL Multiphysics was used to create a 2D numerical model of the energy pile, utilizing the energy pile at a field test site in Nanjing as an example. By contrasting the experimental data, the COMSOL Multiphysics model’s correctness was confirmed. After that, a new kind of energy pile fin was created to improve the heat transfer of the pile. The impact of the new fin type on the energy pile’s heat transfer efficiency was assessed, and the temperature change within the soil surrounding the pile before and after the fin was set was examined by contrasting the parameters of pipe configuration, buried pipe depth, and concrete thermal conductivity. The results indicate that after setting the fins to run for 336 h, the temperature of the concrete area increases by 10.8% to 12.3%, and the temperature of the region surrounding the pile increases by 5.3% to 8.7% when the tube diameter is chosen to be between 20 and 40 mm; The fins maximize the heat transfer temperature between the surrounding soil and the concrete, and as the tube diameter increases, the temperature drops. For 336 h of pile operation, the temperature of the concrete may be raised by 10.8% to 12.3% after the fins are set, and the temperature around the pile can be raised by 5.3% to 8.7%. The heat transmission efficiency of the energy pile can be improved by raising the temperature of the soil surrounding the pile through an increase in the concrete’s thermal conductivity; however, the degree of improvement diminishes as the conductivity rises. It is intended that this study will offer insightful information on the best way to design energy pile heat transfer efficiency.

Dicke superradiant heat current enhancement in circuit quantum electrodynamics

Controlling the flow of energy and heat at the microscale is crucial to achieve energy-efficient quantum technologies, for on-chip thermal management, and to realize quantum heat engines and refrigerators. Yet, the efficiency of current quantum technologies is affected by thermal noise, and efficient cooling of quantum devices remains challenging in various solid-state implementations such as superconducting circuits. Collective effects, such as the Dicke superradiant emission, have been exploited to enhance the performance of quantum devices. However, the inherently transient nature of Dicke superradiant emission raises questions about its impact on steady-state properties. Here, we study how to enhance the steady-state heat current flowing between a hot bath and a cold bath through an ensemble of N qubits, that are collectively coupled to the thermal baths. Remarkably, we find a regime where the heat current scales quadratically with N in a finite-size scenario. Conversely, when approaching the thermodynamic limit, we prove that the collective scenario exhibits a parametric enhancement over the noncollective case. We then consider the presence of a third uncontrolled bath, interacting locally with each qubit, that models unavoidable couplings to the external environment. Despite having a nonperturbative effect on the steady-state currents, we show that the collective enhancement is robust to such an addition. Finally, we discuss the feasibility of realizing such a Dicke heat valve with superconducting circuits. Our findings indicate that in a minimal realistic experimental setting with two superconducting qubits, the collective advantage offers an enhancement of approximately 10% compared to the noncollective scenario. Published by the American Physical Society 2024

Tectonostratigraphic models of an extensional back-arc basin: inferences for the evolution of the Pannonian Basin System

The subsidence history and sedimentary architecture of extensional basins are controlled by the interplay between tectonics, mantle dynamics and climatic variations. Observations from outcrop to regional seismic scales coupled with numerical modelling techniques, including basin-scale stratigraphic, crustal-scale tectonic and mantle-scale subduction models, contribute to the quantification of basin evolution. Here, we review and discuss both tectonic and stratigraphic applications of such models and compare them with observations from the Pannonian Basin system of Central Europe. We show that diachronous localization of back-arc extension, crustal thinning, asthenospheric upwelling and subsequent thermal relaxation are superimposed on an overall slow plate convergence. These processes result in contrasting subsidence and uplift patterns and a variable heat flow evolution in different parts of the basin system. The crustal stress-field of the sub-basins does not always reflect their contrasting vertical motions. Extensional deformation generally migrates from the basin margins towards the basin centre. Structural inversion is localized along hot and weak inherited zones from the Middle Miocene to Present. Tectonic subsidence focuses sedimentation along deep depocentres, sourced by exhumed footwalls and from the neighbouring orogens. The overall post-rift sediment progradation is influenced by inherited bathymetries from the preceding syn-rift stage and by enhanced differential vertical motions.

Effect of agitation during the early-age hydration on thixotropy and morphology of cement paste

AbstractThe effect of agitation during the early-age hydration on thixotropy and morphology of cement paste prepared with and without superplasticizers (SP) is investigated by applying penetration test, small amplitude oscillatory shear sweep test (SAOS), isothermal calorimetric test, scanning electron microscopy (SEM) and energy dispersive X-ray analyses (EDX). The results show that the agitation of cement paste during the induction period increases the heat flow rate and destroys existing structures of samples without changing the mineral composition of samples. Yet, if the agitation is applied during the acceleration period, the heat flow rate is significantly lowered and the morphology and mineral composition of samples undergo irreversible change, freshly formed syngenite is destroyed and no longer restored. The penetration force and the static yield stress grow linearly during the induction period and exponentially during the acceleration period. Agitation during the induction period destroys the structure, which causes the static yield stress and the penetration force values becoming nearly equal to zero. However, during the acceleration period, even after agitation the static yield stress and the penetration force exhibit high residual values, which indicates the impact of hydration to the structural build-up.

Experimental investigation of pool boiling on Ti-Cu composite coated surfaces prepared using Electric Discharge Coating

Boiling heat transfer has become a very potent two-phase heat transfer mechanism for cooling high heat-producing devices such as microelectronic devices, fusion reactors or turbine blades. Increasing research has shown that micro/nano-structures on surfaces increase the number of nucleation sites for bubble formation, which ultimately results in a major improvement in boiling performance. This led to studies on developing various coated surfaces in order to generate micro/nano-structures on surfaces. In the current study, microstructured boiling surfaces were prepared using the Electric Discharge Coating (EDC) process. Titanium-copper (Ti-Cu) composite microparticles were coated on copper surface under reverse polarity in the Electric Discharge Machine. Four surfaces were prepared by using current settings of 3 A, 4 A, 5 A and 6 A. It was followed by characterisation of the surfaces which included, wettability analysis, porosity, pore size estimation, mean roughness measurement and elemental analysis, in order to better understand the boiling results on the surfaces. The surfaces formed were hydrophilic in nature, with contact angles varying from 47° to 65°. Pool boiling were performed with the developed surfaces and critical heat flux (CHF) and nucleate boiling heat transfer coefficient (NBHTC) improvement of 37.17 % and 172 % respectively were observed with the best performing surface compared to the bare surface. The best performing surface was also compared with relevant published literature to determine its standing against the present state of the art.

Temperature Distribution in a Two-Scale Porous Structure of a Catalyst Made of Spherical Particles

The research deals with the determination of the temperature distribution in a two-stage porous catalytic medium when the heat flow passes through. The peculiarity of the proposed model of heat and mass transfer in a porous catalyst is to consider the change in the volume of the spherical particle that makes up the catalyst.A program for calculating the temperature distribution in a two-scale porous structure of a catalyst made of spherical particles that change in volume with time has been developed. It should be noted that the temperature gradient is rather high, and the temperature in the central region of the particle becomes high enough for the process of catalytic reaction initiation only after 3.25 s. The developed program together with analytical and empirical studies allow to find the range of temperature and time of heat treatment at which the given thermophysical characteristics of porous material will be observed.The work will be useful for engineers and scientists studying the problems of thermochemical reactors and heat transfer in catalytic fills.

An experimental investigation examining the usage of a hybrid nanofluid in an automobile radiator

AbstractSeveral modifications have been made to the radiator’s dimensions and materials as part of the evolution of the automotive cooling cycle. Coolant is an important factor that greatly affects the efficiency of the cooling cycle. In applications involving heat transmission, nanofluids have become a viable possibility coolant. Two distinct types of nanoparticles floating in the base fluid make up the hybrid nanofluid, a newly invented class of nanofluids. Tests of hybrid nanofluids as a working fluid substitute for conventional fluids have been assisted by the current study. In the radiator of a 2005 Honda, the MWCNT–Al2O3/water nanofluid was tested at various volumetric concentrations (Φ) using a 50:50 mixing ratio. The outcomes of the experiments were compared with those obtained by using pure water. The radiator’s performance was evaluated by adjusting the fluid flow rate and operating the fluid at two distinct temperatures (60, 80 °C). The outcomes demonstrated that the convection heat transfer coefficient increased with a ratio reached 28.5% over the distilled water at the same temperature and flow rate. Both effectiveness and the Nusselt number had improved, coming in at 22.54% and 23.74%, respectively. Depending on the fluid concentration there is an increase in the pressure drop up to 24% than ordinary fluid. It discovered considerable agreement between the research outcomes by comparing them with earlier publications. An experimental correlation was inferred from the results to estimate the Nusselt number as a function of the Reynolds number and (Φ).

Effects of Fly Ash Particle Size and Chemical Activators on the Hydration of High-Volume Fly Ash Mortars

This study investigated the effects of the fly ash (FA) particle size and chemical activators on the hydration reactions of high-volume fly ash (HVFA) cement pastes and the mechanical properties of HVFA mortars, with five types of FA with varying proportions of particles smaller than 10 μm prepared to assess the influence of particle size. In addition, the effect of chemical admixtures on the early-age hydration of the HVFA cement paste was evaluated. Quartz powder with the same fineness as that of normal FA was prepared to specifically examine the pozzolanic reaction of FA. The hydration reactions of the HVFA cement pastes were analyzed using isothermal calorimetry to measure the heat of hydration for 72 h. The results showed that an increase in the contents of FA particles with a diameter lower than 10 μm increases specific heat flow. Chemical activators, including Na2SO4, triethanolamine (TEA), and triisopropanolamine (TIPA), promote early-age hydration of HVFA cement pastes. The mechanical properties of the HVFA mortar were evaluated by measuring its compressive strength at 3 d, 7 d, and 28 d, with the findings revealing that the compressive strength of HVFA mortar improved with an increased proportion of FA particles smaller than 10 μm. Na2SO4, TEA, and TIPA consistently increased the compressive strength of the HVFA mortars.

Impact of Thermal Energy on Water and Ethylene Glycol (50:50)-Based Rotating Hybrid Nanofluid Past A Riga Surface with Radiation, Homogeneous and Heterogeneous Reactions

Hybrid nanofluid is crucial in improving the efficiency of heat transmission in thermal engineering applications, particularly the cooling of electrical equipment, heat exchangers, fuel cells, printing machines, etc. This study sought to investigate the augmentation of heat and mass transmission by the use of a rotating hybrid nanofluid consisting of a mixture of gold and silver nanoparticles suspended in water and ethylene glycol (50:50) past a heated Riga surface with velocity slip and suction. The energy equation is constructed using nonlinear radiation and heat consumption. The impact of both homogeneous and heterogeneous processes on the hybrid nanofluid is also explored. The governing mathematical model begins with partial differential equations that are converted into ordinary differential equations using a suitable conversion technique. The results of numerical computations are recorded as graphs and tables using the bvp4c scheme in MATLAB. It is noticed that both directional velocities undergo significant negative changes as a result of enhanced values of the rotational parameter. The higher levels of the radiation parameter resulted in significant enhancements in the thermal profile. The falling behavior of the nanoparticle concentration profile is recorded against a greater quantity of both chemical reaction parameters. Based on our analysis, when the Biot number changes from 0.4 to 0.8, the most significant heat transmission gradient occurs.

The influence of lymphatic vessels on nanoparticle distribution and heat transfer within tissue

AbstractThis study analytically investigates the dynamics of nanoparticle transport within a three‐dimensional porous cylinder simulating a lymphatic vessel, without external heat sources. The governing equations and boundary conditions are transformed to yield a system of ordinary differential equations, which are solved numerically using MATLAB built‐in function, bvp4c. Key parameters are visually examined and physically interpreted in relation to temperature, velocity, concentration, and Nusselt number profiles. The study reveals that the distribution of temperature and Nusselt number are maximized by increasing the heat transfer coefficient, whereas NP concentration is increased by decreasing it. Furthermore, the Brownian motion parameter enhances both heat transmission and NP concentration. It is also observed that simpler extravasation into lymphatics decreases tissue nanoparticle levels and heat conduction. Ultimately, optimal intra‐lymphatic nanoparticle distribution pathways are achieved by specifically varying heat transfer and interstitial mass flux patterns. By simulating biological barriers and lymphatic drainage, this model enhances our understanding of the underlying transport mechanisms controlling nanoparticle mobilization.

Improvement in an Analytical Approach for Modeling the Melting Process in Single-Screw Extruders

Most single-screw extruders used in the plastics processing industry are plasticizing extruders, designed to melt solid pellets or powders within the screw channel during processing. In many cases, the efficiency of the melting process acts as the primary throughput-limiting factor. If the material melts too late in the process, it may not be sufficiently mixed, resulting in substandard product quality. Accurate prediction of the melting process is therefore essential for efficient and cost-effective machine design. A practical method for engineers is the modeling of the melting process using mathematical–physical models that can be solved without complex numerical methods. These models enable rapid calculations while still providing sufficient predictive accuracy. This study revisits the modified Tadmor model by Potente, which describes the melting process and predicts the delay-zone length, extending from the hopper front edge to the point of melt pool formation. Based on extensive experimental investigations, this model is adapted by redefining the flow temperatures at the phase boundary and accounting for surface porosity at the beginning of the melting zone. Additionally, the effect of variable solid bed dynamics on model accuracy is examined. Significant model improvements were achieved by accounting for reduced heat flow into the solid bed due to the porous surface structure in the solid conveying zone, along with a new assumption for the flow temperature at the phase boundary between the solid bed and melt film.