Heat Transfer In Channel Research Articles

Noncovalent functionalization of boron nitride via chelation of tannic acid with Fe ions for constructing high thermally conductive polymeric composites

AbstractWith the advancement of integration and miniaturization of precise instruments, the heat accumulating in electronic components is urgently needed to dissipate for ensuring their service life. In this work, boron nitride (BN) was functionalized with tannic acid/ferric ions (TA/Fe) chelate complexes to synthesize high thermally conductive natural rubber (NR) composites (NR@TA/Fe‐BN). The stable TA/Fe chelate complexes improved the interfacial compatibility between BN and NR and enhanced the BN dispersion in the NR matrix, which led to the reduction of interfacial thermal resistance and the construction of heat transfer channels in NR composites. As a result, a relative high thermal conductivity (0.327 W/(mK)) by 30 vol% NR@TA/Fe‐BN composite was achieved, being 2.44 times that of pure NR (about 0.134 W/(mK)). In addition, the insulating NR@TA/Fe‐BN composites showed outstanding elongation at break (686%) and tensile strength (15.2 MPa). This highly efficient and green TA inspired modification is expected to find application in industrial manufacturing of thermally conductive polymeric composites.

Effect of splitter angles and orientations attached to pin fin on heat transfer and hydraulic characteristics in a jet impingement rectangular channel

Heat transfer improvement of heat sinks is very interesting in many applications including electronic devices cooling. In this study, the influence of rotational angle of splitters attached to pin fins for two cases of identical and opposite directions is investigated. Five angles including 0, 30, 45, 60 and 90 are considered in the analysis conducted for the rectangular channel. Air as the heat transfer fluid at 302 K and 35,000 Reynolds number enters the channel. The temperature of the bottom of the channel is assumed to be constant. 18 rows of circular pin fins on which splitters are attached for enhancement of heat transfer are examined. In the numerical analysis, Nusselt number, turbulent kinetic energy, friction factor and pressure drop are analyzed parameters. The simulation of the models presented in the current study is endeavored using ANSYS Fluent software, which employs finite volume method. Results revealed that, for the identical-direction case, as the angle rises, the average Nusselt number, turbulent kinetic energy, friction factor and pressure drop increase, in a way that for the case of 90 degree, Nusselt number is 9 % and turbulent kinetic energy is 96 % higher than the base case of zero angle. Moreover, friction factor and pressure drop of the vertical-splitter case are 4.8 and 4.6 times more than those of the base case. It is also concluded that increasing angle from 0 to 45° for the opposite-direction case, Nusselt number diminishes. However, extra increase in the angle from 45 to 90 degree results in Nusselt number enhancement. Similar trend of variation is also reported for turbulent kinetic energy. Results also indicated that for the opposite-direction case, friction factor and pressure drop rise; for the case of 90 degree, friction factor and pressure drop increase 4.4 and 4.32 times, respectively.

CFD of roughness effects on laminar heat transfer applied to additive manufactured minichannels

AbstractAdditive manufacturing has received significant interest in the fabrication of functional channels for heat transfer; however, the inherent rough surface finish of the additively manufactured channels can influence thermal performance. This study investigates the impact of roughness on the thermo-fluid characteristics of laminar forced convection in rough minichannels. A numerical model was developed to create 3D Gaussian roughness with specified root-mean-square height. The finite volume method was used to solve the conjugate heat transfer of developed laminar flow in square minichannels. For Reynolds numbers ranging from 200 to 1600, the simulation results indicated enhanced heat transfer and increased flow resistance as Reynolds number increases, compared to a smooth minichannel, where effects on heat transfer and flow friction were negligible. For channels with relative roughness (root-mean-square height to channel hydraulic diameter) of 0.0068, 0.0113, and 0.0167, increasing the Reynolds number led to increased friction factor by 1.56, 1.71, and 2.91%, while the Nusselt number was enhanced up to 0.03%, 32.74%, and 46.05%, respectively. Heat transfer reduced in roughness valleys due to the presence of local low-velocity fluid in these regions; however, recirculation regions can occur in deep valleys of high roughness, increasing heat transfer and flow friction. Heat transfer was enhanced over roughness peaks due to flow impingement on the windward face of roughness as well as intensified energy transfer to the channel wall from roughness. Moreover, surfaces with higher roughness have a greater number of high peaks providing a thermal-flow path of a larger area and a thermal conductivity greater than that of the fluid.

Extreme in-plane phonon blocking in simple chainlike crystals

Taking chainlike $\mathrm{Tl}X{\mathrm{Se}}_{2}$ $(X=\mathrm{Tl}, \mathrm{In}, \mathrm{Al})$ as examples, we find that weak in-plane atomic interactions in these crystals intrinsically lead to extreme in-plane phonon blocking and heat flux confinement. We explicitly evaluate the propagative and diffusive lattice thermal transports based on the unified theory on top of the fourth-order lattice anharmonicity, and the results manifest that high-frequency phonons make negligible contributions to two channel heat transfer along the in-plane directions. This phenomenon provides a feasible approach for an effective suppression of the overall lattice thermal conductivity $({\ensuremath{\kappa}}_{\mathrm{L}})$. The findings are also applicable to a series of quasi-one-dimensional solids with different crystal structures. This work provides fundamental insight into the understanding and minimization of low ${\ensuremath{\kappa}}_{\mathrm{L}}$ of quasi-one-dimensional crystals by focusing on their harmonic lattice dynamics.

Heat transfer in a rotating lateral outflow trapezoidal channel with pin fins under high rotation numbers and Reynolds numbers

Existing heat transfer research on wedge-shaped channels with pin fins at the trailing edge has mainly focused on Reynolds numbers below 40,000. Larger inlet parameters are rarely considered, resulting in uncertainties in this aspect. Therefore, in this study, the heat transfer characteristics in a rotating lateral outflow trapezoidal channel with pin fins, which is a typical model of the internal cooling passage in a turbine blade, were experimentally investigated under the Reynolds number range of 10,000–110,000, rotation number range of 0–0.5, and speed range of 0–1000 rpm. The differences in the heat transfer at different entry conditions were compared. For the non-rotating condition, the heat transfer at a high Reynolds number (110,000) was four to nine times that at a low Reynolds number (10,000). For the rotating conditions, when the dimensionless parameter X/D (coordinate in radial direction/channel hydraulic diameter) was greater than seven for the inner surface and equal to eight for the outer surface, the heat transfer on the leading surface exceeded that of the trailing surface. Moreover, the critical rotation number, which varied with X/D, was noted on the leading surface. Finally, the heat transfer under a high Reynolds number and high speed were investigated. The findings under a high Reynolds number were similar to those under a low Reynolds number. The research of this paper supplements the heat transfer of wedge-shaped pin fins channel at the trailing edge of turbine blade under the condition of high Reynolds number and rotation number.

Inverse estimation of heat flux under forced convection conjugate heat transfer in a vertical channel fully filled with metal foam

In this work, for the first time, a heat flux at the boundary is estimated for a conjugate heat transfer under forced convection in the presence of high porosity metal foams. For the forward problem a vertical channel experimental set up reported in the literature is considered. The metal foam placed in the vertical channel is subjected to constant heat flux through aluminum plate and airflow of various velocities is passed through vertical channel for removal of heat from the high porosity metal foam placed in the vertical channel. Six different velocities are considered and the required temperature distribution of the aluminum plate is obtained by solving Darcy extended Forchheimer and Local Thermal non-equilibrium models for metal foams. The forward problem, created using computational fluid dynamics in ANSYS-FLUENT, is substituted with Neural Network for faster computation of the forward problem. The maximum errors between the computational fluid dynamics and Artificial Neural Network models for the heat flux values of 466.66, 666.66 and 1133.3 W/m 2 are found to be 0.086, 0.043, 0.092 respectively. The heat flux to the forward problem is treated as unknown and the same is estimated using an inverse method that couples Particle Swarm Optimization with Bayesian framework. The result of inverse estimation of exact temperature data shows that for a heat flux of 1266.64 W/m 2 the error is found to be 1.6e−4%. Similarly, for the noise added temperature data, the absolute % error in heat flux of 599.985, 733.315 and 1266.635 W/m 2 is 4.80e−2%, 2.20e−2%, 2.30e−2% respectively. • Inverse estimation of boundary heat flux using particle swarm optimization method. • Forward problem is a conjugate heat transfer problem in a vertical channel. • Darcy–Forchheimer, Local Thermal Non-equilibrium models for modelling porous medium. • Different Artificial Neural Network models to facilitate faster computations. • Particle Swarm Optimization combined Bayesian framework to quantify modeling error.

A numerical study on the condensation heat transfer in a vertical channel with various wettability conditions and gap spacing

A numerical study was carried out to analyze the condensation phenomena in a vertical channel between two flat plates. To solve the three-dimensional governing equations including conservation of the mass, momentum, and energy, the Volume of Fluid model was adopted. For the phase change phenomena, the Lee model was used. The tuning for the model parameter was performed using existing experimental data. To obtain the heat transfer coefficients under desired conditions, a model based on machine learning using artificial neural network was developed, which shows good accuracy and the future possibility of using the model for the tuning and validation of the phase-change model. A super-hydrophilic (10°), hydrophilic (58°), and hydrophobic surface (130°) were considered together with the variation of the gap spacing and the inlet velocity. The different condensation behavior according to the various surfaces wettability conditions was clearly identified. The formation of a liquid bridge in the channel for the dropwise condensation was observed, and its effects on the thermal and pressure drop performance were assessed. Details on the its performance were summarized quantitatively. It is expected that the present result and numerical method could provide useful information for the fin-type heat exchanger design.

Probing the charge and heat transfer channels in optically excited graphene — transition metal dichalcogenide hybrids using Johnson noise thermometry

Graphene (Gr)–transition metal dichalcogenide (TMDC) hybrids are promising platforms for achieving sensitive and ultra-fast photodetection. The process of photo-detection in such van der Waals hybrids is usually dictated by the formation of excitons followed by the transfer of charge and energy from the TMDC layer to graphene, but they have not been explored simultaneously in the same device before. In this work, we have investigated optically excited Gr–WS2 (tungsten disulfide) heterostructures using both standard electrical transport and Johnson noise thermometry. At large negative gate voltages, the experimentally observed photoresponse cannot be explained from conventional photogating but was found to host an increase in electron temperature as large as ∼4 K. Time dependence of the transport and the noise reveals that the change in temperature and photoresistance can originate from distinct microscopic processes. The findings can be exploited for the development of Gr–TMDC based ultra-fast bolometers.

Performance enhancement of photovoltaic panel by using microencapsulated phase change slurry in channel with staggered pins

Microencapsulated phase change material (MPCM) in the form of particles suspended in conventional cooling fluids such as water has shown enhanced heat transfer characteristics when compared to conventional single phase heat transfer fluids. This is attributed to the latent heat of fusion of the MPCM, which results in higher heat capacity of the heat transfer fluid. The thermal performance of MPCM slurry as a heat transfer fluid can be further improved when used in a channel consisting of staggered pins. Use of MPCM slurry in heat transfer channels can result in efficient cooling performance of photovoltaic (PV) systems, where significant thermal loads are prevalent due to high levels of irradiance or working in hot climate conditions. The present work investigates numerically the impact of using MPCM slurry at different mass fractions on the cooling performance of a heat transfer channel attached to a PV panel. The numerical simulations were performed using the ANSYS-FLUENT solver in combination with user-defined functions used to account for the thermophysical properties of MPCM slurry. It was observed that the Nusselt number of MPCM slurry was much higher than for water as single-phase fluid, especially at higher mass fractions at the same flow rate. Moreover, the PV panel temperature was found to be significantly reduced when phase change material in the MPCM slurry experienced melting. Moreover, using staggered circular pins in the channel resulted in a significant reduction of the PV panel temperature even under concentrated irradiance conditions. However, an increase in pumping power was noticeable at high mass fraction of MPCM slurry. Finally, a remarkable increase in the PV panel efficiency was achieved under normal and concentrated irradiance levels by using MPCM slurry in the cooling channel with and without staggered circular pins.

Topology optimization of porous solid structures for heat transfer and flow channels in reactors with fluid-solid reaction coupling

In this paper, the optimization models for the heat transfer and flow channels with porous structures are developed. To enhance the heat transfer capacity of the thermal system, the topological optimization of the fin structure in the radial direction of the heat transfer unit is proposed and the influence of the initial conditions on the optimization of fins is studied. At the same time, the transient process of the heat transfer unit with topology optimization is investigated to verify the feasibility of the optimization model. The results show that the fins designed by topology optimization have coral-likestructure, and the width of the fin decreases as it moves outward from the center. For the optimization of flow channels, the optimum distribution of porous material with theoptimal reaction rate in laminar flow reactor is analyzed. The optimal structures for flow channels in porous media is obatined theoretically and simulatednumerically for obtaining the related transport characteristics. In addition, for the topologically optimized reactor, as the initial reaction parameters change, the fluid channels in the porous domain show different structures withtopology optimization.

Correction to: Intensification of heat transfer of a wavy channel with a series of detachable vortex generators; Numerical analysis with rans model modification

Correction to: Intensification of heat transfer of a wavy channel with a series of detachable vortex generators; Numerical analysis with rans model modification

The water fouling development in plate heat exchangers with plates of different corrugations geometry

The occurrence of fouling conditions in heat transfer equipment of industrial enterprises causes the change of process regimes and can lead to full blockage of heat transfer channels. The investigation of fouling dynamics in plate heat exchangers (PHEs) is observed. The transport and reaction type of fouling model is used for accounting for the fouling on the heat transfer surface. The mathematical model of PHEs with commercially produced plates is presented. The model accounts for the difference in pressure drop and heat transfer coefficients along with the heat carrier movement through the channel distinguishing the major corrugated field, the zones of flow distribution, ports and collector part, introducing the local hydraulic resistances for each zone. The PHE performance in fouling conditions for different plate corrugations geometry is analysed. The impact of the corrugations’ inclination angle to the vertical plate’s axis on fouling dynamics is analysed for the case when PHE is assembled with plates of non-uniform corrugations angles. The results of the case study, represented by modelling of PHE installed in a sugar factory for heating a thin juice coming to an evaporation station, are presented. The approach for fouling mitigation at PHE design through the optimisation of plate corrugation geometry is discussed. The economic analysis showed, that the purchase of additional plates for operating PHE allows for saving 220 kW of heat energy and ensures reliable operation during 120 d of the sugar campaign.

Investigation of Effects of Baffle Heights on Flow and Heat Transfer in a Trapezoidal Channel with Vertical Baffles

Bu çalışmada, üst duvarında dik bölmeler bulunan, alt duvarı trapez şeklinde dalgalandırılmış bir kanalda farklı bölme yüksekliğinin akış ve ısı transferine etkileri nanoakışkan ve taban akışkan akışı için sayısal olarak incelenmiştir. Nanoakışkan olarak TiO2 nanopartiküllerin su içerisinde süspansiyonu kullanılmış ve nanopartikül hacim oranı, φ=%1 sabit tutulmuştur. Sayısal çalışma, Hesaplamalı Akışkanlar Dinamiği (HAD) tabanlı FLUENT 15.0 programı ile iki boyutlu gerçekleştirilmiştir. Kanalın bölmeler içeren üst yüzeyinin adyabatik olduğu kabul edilmiş ve alt trapez yüzeyi Tw=360K sabit sıcaklıkta korunmuştur. İki farklı bölme yüksekliği (t=H/2 ve t=2H/3) kullanılarak farklı Reynolds sayıları (200≤Re≤1200) için nanoakışkanın ve taban akışkanın Nusselt sayısı (Nu), sürtünme faktörü (f) ve termo-hidrolik performansı (THP) hesaplanmıştır, ayrıca çalışma bölmelerin olmadığı kanal akışı ile de karşılaştırılmıştır. Kanal içerisinde farklı parametrelerde hız ve sıcaklık görüntüleri elde edilmiştir. Sayısal sonuçlar, trapez bir kanalda bölmelerin yüksekliğine ve nanoakışkana bağlı olarak ısı transferinin önemli ölçüde iyileştiğini, ancak sürtünmenin de bir miktar arttığını göstermiştir. En yüksek termo-hidrolik performans, bölmesiz kanalda taban akışkana göre, TiO2-su nanoakışkan akışında Re=400 ve t=2H/3 bölme yüksekliğinde 1,95 olarak elde edilmiştir.

Heat transfer and field synergy characteristics in a rectangular unit channel under mechanical vibration

The internal heat exchangers of a vehicle in driving are excited by forced vibration due to road bumps. But the effect of this phenomenon on the thermal-hydraulic performance of the heat exchanger has not been systematically studied. To investigate the influence of this vibration on the heat transfer characteristics, a numerical model of the rectangular heat exchanger unit channel under vibration excitation was established and verified by experiments. It is found that compared to frequency, amplitude of vibration has a greater effect in enhancing heat transfer but when it is more than 4 mm, which leads to a rapid increase in the friction factor f. An index (j/js)/(f/fs) and a thermal-vibration performance factor (TVPF) considering the frequency and amplitude are proposed to evaluate the effect of vibration on the heat transfer, and it is indicated that for real vehicle operation, an amplitude of 2 mm and frequency of 25 Hz can effectively enhance heat transfer. Besides, it was found that the velocity gradient field perpendicular to the main flow direction caused by vibration synergizes with the temperature gradient field. This work is meaningful and of significance to the practical design of the actual heat exchangers in the automotive application.

Comparison of single-phase Newtonian and non-Newtonian nanofluid and two-phase models for convective heat transfer of nanofluid flow in backward-facing step

The aim is to investigate the application of nanofluids for improving the heat transfer in a backward-facing step channel. Numerical simulations are performed using single-phase models for both Newtonian and non-Newtonian fluids in the Reynolds number range 280–470. Constant and temperature-dependent thermo-physical properties of different volume fractions (0–4%) of nanoparticles are considered. The thermal enhancement of the nanofluids within the channel is analyzed and compared with the experimental data. A detailed comparison of different CFD models is established. Numerical results are obtained with two types of single-phase models (Newtonian and non-Newtonian) and three types of two-phase models (mixture, volume of fluid (VOF), Eulerian) and compared with experimental results obtained for the Nusselt number. The finite volume method is used to solve the system of governing partial differential equations describing the steady-state, two-dimensional, laminar, mixed convective flow in a micro backward facing step channel with uniform heat flux. The single-phase and two-phase models predict practically equivalent hydrodynamic fields, but significantly different thermal fields are observed in our results. The performance efficiency coefficient (PEC) is determined using single-phase and two-phase methods for Al2O3-water nanofluids at different Reynolds numbers to investigate their thermal performance.

A relatively wide-ranged correlation of saturated flow boiling heat transfer within narrow rectangular channel for water

• Database of boiling heat transfer in narrow rectangular channel over a relatively wide parametric range obtained. • Corresponding transition of two-phase flow regimes with dominant heat transfer mechanisms observed and discussed. • A new, wide-ranged correlation proposed. A campaign of tests is performed for saturated boiling heat transfer characteristics of water in narrow rectangular channel. The test matrix covers a relative wide range of conditional parameters and 3142 test data are acquired, screened and selected for study. Meanwhile, visualization test has been conducted with three typical flow patterns, namely isolated bubbly, confined bubbly and irregular annular flows, being observed and identified, each pattern corresponding to a prevailing or a transitional combined boiling heat transfer mode. Study of the data trend indicates that two boiling heat transfer mechanisms, namely nucleate boiling and forced convective evaporation, are either one dominant or two combined transitional during different phases of saturated flow boiling within the channel. With the basic view obtained from the test campaign, and with related parametric effect and sensitivity study, as well as the existing correlation assessment with the test data, a new correlation for the saturated boiling heat transfer is proposed and regressed, which consists a modification factor composing the two basic boiling mechanisms and the transition function between. A preliminary assessment is performed for its statistical and predictive accuracy, from which a relatively satisfactory agreement is drawn. The new correlation applies to a heat flux range of 100 - 2300 k W / m 2 , a mass flux range of 500 2000 k g / m 2 · s , a system pressure range of 0.2 5.5 M P a and the equilibrium quality range of 0 0.72 . It might be used, in conjunction with the flow pattern and the related heat transfer mechanism, to predict the saturated boiling heat transfer coefficient over a wide range of heat flux, mass flux and pressures with better accuracy than previous correlations.

Intensification of heat transfer of a wavy channel with a series of detachable vortex generators; Numerical analysis with rans model modification

Intensification of heat transfer of a wavy channel with a series of detachable vortex generators; Numerical analysis with rans model modification

Experimental Study on Flow Condensation Heat Transfer in a Horizontal Rectangular Channel with Ellipse-shape Pin Fins

Experimental Study on Flow Condensation Heat Transfer in a Horizontal Rectangular Channel with Ellipse-shape Pin Fins

Fast parameterized fractal modeling of active heat transfer channel

This paper presents a fast parameterized modeling method for fractal channel and constructs a unified parametric model for Y-shaped, V-shaped, T-shaped fractal channels. This parametric model establishes the relationship between multiple parameters (levels ratio, bifurcation level, pipe diameter ratio, bifurcation angle, aspect ratio) and performance of fractal channel. Parameterized modeling method can reduce repetitive workload and time, improve efficiency. Meanwhile, parametric model allows for a more comprehensive study, and it is important for reduce the occasionality of results. Using the parameterized modeling method, the aspect ratio and fractal channel type are numerically studied. The numerical study of the aspect ratio reveals that with the increase of aspect ratio, Nusselt number decreases, the peak temperature rises and then falls, and the pressure drop first decreases and then increases. The numerical study of fractal channel types shows that the V-shaped channel has the best cooling performance and Y-shaped channel has the best flow performance. Compared to the T-shaped channel, Nusselt number of V-shaped channel increases by 11.29%∼19.74%, the thermal resistance of V-shaped channel decreases by 8.18%∼19.73%, and the pressure drop of Y-shaped channel decreases by 51.04%∼61.75%. The fractal channel parametric model can be applied not only for parameter studies, but also for parameter optimization.

Mechanical properties and failure characteristics of granite treated with a combined water–air cooling cycle

Granite is the main material used to enhance geothermal reservoirs, and its mechanical properties play a key role in the safe and efficient development of geothermal materials. High temperature and cold shock issues are often encountered during the process of geothermal development. For this reason, numerous studies have been conducted on the mechanical properties of granite treated at different temperatures and with various cooling methods. In addition, granite is often affected by combined water-air cooling, which affects the development direction and stability of reservoir heat transfer channels. However, few studies on the mechanical properties of granite treated with combined water-air cooling have been conducted thus far. In this study, uniaxial compressive tests were conducted on granite to study the effect of localized water cooling at different temperatures and numbers of heating-cooling cycles. The results show that the thermal cracks in granite subjected to combined cooling treatments exhibited regional distribution characteristics with temperature and cycle times; there were no apparent thermal cracks at 200 °C, thermal cracks were mainly distributed in the water-cooling zone between 300 and 400 °C, and thermal cracks were distributed throughout the granite specimens above 500 °C as the number of cycles increased. Within 300 °C, the peak axial stress and Young's modulus of the granite exhibited slow linear decreasing trends with temperature and cycle times, but the peak axial stress and Young's modulus exhibited nonlinear decreasing characteristics when the temperature exceeded 400 °C. The failure mode gradually changed from brittleness to ductility. Above 500 °C, thermal cracks near the interface of the water-cooling and air-cooling zones became denser than those in the other two areas (the water-cooling and air-cooling zones) as the number of cycles increased, and the splitting failure during loading failure shifted from the water-cooling zone to the interface of water cooling and air cooling. The temperature condition for fracture and peeling between the air-cooling and water-cooling zones of the granite was 600 °C.