Transfer Characteristics Research Articles

Flow mixing and heat transfer deterioration investigation of supercritical carbon dioxide in wire-wrapped bundles

As one selection of the fourth-generation reactors, the gas cooled reactor has received enormous attention such as high power conversion efficiency and simple cycle layout. In this paper, the flow mixing and heat transfer characteristics of supercritical carbon dioxide within a seven-pin wire-wrapped bundle were investigated. Due to the lack of more experiments data of velocity field, two experiments were selected to validate the uncertainty of different turbulence models from the view of temperature field. The analysis of mass exchange between different subchannels revealed that coolant flows consistently in a certain direction in edge and corner subchannels, whereas in center subchannels, the cross flow changes direction periodically. The mixing coefficients at three types of subchannel interfaces were fitted by a sine function with the R2 values are all greater than 0.96. For different mass flux and pressures, the root mean square error between correlations and simulations was less than 1 × 10-3, except when Re equals 15000. Additionally, the heat transfer deterioration of SCO2 was observed. While wire spacers can mitigate the extent of heat transfer deterioration, they cannot completely eliminate it. The Performance Evaluation Criterion (PEC) was introduced to assess the effectiveness of wire spacers in enhancing heat transfer. The results indicate that the PEC exceed unity, meaning that the enhanced heat transfer capability outweighs the additional resistance loss caused by wire spacers. With increasing pressure, the PEC decreases but remains greater than unity. The mixing of coolant between different subchannel induced by wire spacers can reduce the wall temperature of rods at the edge of the bundle. However, the seven-pin wire-wrapped bundle was investigated in this work, and the results may not accurately reflect the flow and heat transfer inside a real reactor rod bundle. In the future, a larger scale rod bundle should be conducted to obtain more universally applicable and realistic flow and heat transfer phenomenon for reactor assembly design.

Enhanced entropy generation and heat transfer characteristics of magnetic nano-encapsulated phase change materials in latent heat thermal energy storage systems

Enhanced entropy generation and heat transfer characteristics of magnetic nano-encapsulated phase change materials in latent heat thermal energy storage systems

Modeling of magneto bioconvection Williamson nanoliquid through modified heat flux: The significance of entropy

The combination of microbes and nanofluids has noteworthy consequences for technological and engineering progress, particularly in the realm of heat transfer applications. This study explains radiative flow with chemical reactions affect the emergence of microorganisms in magnetic mixed convective Williamson nanofluid flow. The Cattaneo-Christov heat flux theory and the effects of heat source/sink have been examined about the energy equation. The prime idea of this analysis is to enhance heat and mass transport. The modelled equations have been converted to dimensionless by considering suitable alteration. The dimensionless expression is then numerically tackled using MATLAB's bvp4c approach. The graphs for different profiles—that is, momentum, temperature, concentration and concentration of microorganisms that move—are made visible for particular nondimensional factors. Furthermore, entropy generation minimization has been obtained through law of thermodynamics. The drag friction, heat and mass transfer rate, and microbe density are also computed in a tabular manner. The most important findings that are pertinent to this study are that an increase in the values of the Brownian motion, thermal radiation and thermophoresis significantly enhance heat transfer characteristics. A consistent pattern can be observed when comparing the current results with earlier research.

Experimental study on the dynamic characteristics of biodiesel/ethanol droplets impacting upon the inclined heated wall

The investigation of droplet impingement plays a crucial role in understanding the dynamics of fuel impact on the walls inside engine combustion chambers. To study the dynamics and heat transfer characteristics of two-component mixed droplets impacting upon an inclined stainless steel heated wall, the effect of wall tilt angle (0°–40°), Weber numbers (We, ranging from 50 to 210), and wall temperatures (Tw, between 25 and 350 °C) on the heat transfer models and spreading diameters is conducted. Through quantitative analysis of high-speed images captured during the experiments, it is observed that the spreading diameter of droplet impact on the inclined wall is closely correlated with both the wall temperature and We of the droplet. The wall tilt angle is found to modify the heat transfer state transition of the droplet to some extent. Additionally, the influence of gravity results in significant differences between the front and back spreading coefficients of the droplet. Based on the available data, a new empirical model is proposed that incorporates temperature terms and inclination to predict the maximum spreading coefficient of droplets impact on an inclined heated wall. Compared with experimental data of this study and in the literature, the maximum prediction error is less than 12.3%.

Axial transfer characteristics of a drillstring in conjunction with bit penetration behavior in horizontal wells

Nonlinear friction and interaction between bit and rock often result in a lower weight on bit (WOB) than the intended design value. The analysis of the dynamic transmission mechanism of a drillstring in complex horizontal wells is a crucial engineering problem that aims to enhance drilling efficiency. In this paper, a mechanical model was developed, integrating nonlinear bit penetration behavior and variable axial loads, aiming to unveil the nonlinear axial vibration characteristics and elucidate the transmission mechanisms within the drillstring. Notably, the mean value of axial force distributed along the drillstring is dictated by wellhead pulling force, while the amplitude is shaped by the interaction between bit and rock, and rotary speed. In calculated examples for horizontal wells, the analysis reveals that significant losses in power axial transmission, resulting in WOB is only 38% of the intended value. And reducing the wellhead pulling force by 30 kN leads to a maximum increase in WOB only of 9.51 kN. Extended region in drillstring with negative axial forces exhibit maximum values 5–6 times higher than the WOB. Specific zones, such as 20 m–40 m and 0–20 m from the bit, experience axial force fluctuation amplitudes of 40.5% and 138.8% of the mean value respectively, with the latter identified as an intense vibration zone, while the acceleration values 0–10 m from the bit signal a high-risk zone. In prolonged horizontal section, stability issues manifest, with spiral buckling observed in the holding section and sinusoidal buckling in the horizontal section. Mitigating the synchronous vibrations between the bit and the surrounding drillstring can effectively reduce the intensity of axial vibration. To ensure successful drilling to target formation, adjusting the wellhead pulling force to keep the WOB in the range of 60–90 kN and limiting the rotary speed to 90 r/min are recommended practices. This comprehensive analysis offers valuable insights for optimizing drilling parameters, pinpointing high-vibration zones, and mitigating risks associated with drilling, providing a holistic approach to enhancing drilling efficiency.

Flow and heat transfer characteristics of hydrocarbon fuel in lightweight C/SiC regenerative cooling combustor

To meet the requirements of higher thermal protection ability and lower structural weight of regenerative cooling structures in advanced hypersonic vehicles, carbon-fiber-reinforced silicon carbide (C/SiC) composites with high permittable service temperatures and low densities are promising for application in thermal protection systems. In this study, four cylindrical regenerative cooling configurations applying C/SiC composites for a designated scramjet engine combustor are proposed, and the thermal protection performance under the influence of the cooling equivalence ratio (0.4∼1.0) and anisotropic thermal conductivity is studied. The results show that the C/SiC composites can significantly improve the heat resistance of the entire regenerative cooling structure owing to their relatively low thermal conductivity, which reduces the total heat flux transferred to the inner structure. The thermal protection ability can be maintained, whereas the coolant flow rate is reduced by 50%. C/SiC composites with higher thermal conductivities in the circumferential direction are beneficial for uniform temperature distribution. A flow distribution deterioration phenomenon caused by the thermal cracking of the coolant and the increasing flow resistance in the cooling channels can be observed under certain conditions, leading to a mass flow rate difference of 2.5 times among the cooling channels. Moreover, introducing C/SiC composites into the regenerative cooling structure design can significantly reduce the total structural weight by over 50% compared to traditional superalloys.

Efficient visible light-induced H2 production by g-C3N4/NiFe Prussian blue composites

Hydrogen (H2) produced via photocatalytic water splitting shows great potential as a renewable alternative to fossil fuels, as it uses clean and renewable resources (water and solar light). However, low efficiency remains a significant challenge for this technology. In this study, we synthesized novel graphitic carbon nitride (GCN)–Prussian blue analog (PBA) heterostructure composites using suitable PBAs for photocatalytic reactions, and explored their application in visible-light-induced H2 production. GCN-PBA heterostructure composites were synthesized using PBAs containing Ni, Co, and Fe, and their photocatalytic activities under visible light irradiation were compared. The visible-light absorption characteristics and H2 production efficiency of the GCN-PBA composites were characterized. The GCN-NiFe heterostructure composite showed excellent visible-light-induced H2 production efficiency, indicating effective charge separation and transfer characteristics that enhanced the photocatalytic activity of GCN. These findings contribute to the development of efficient photocatalytic materials for solar H2 production, thereby contributing to the advancement of renewable energy technologies.

Mechanofluorochromic behaviors and latent fingerprint detection of triphenylamine-based compounds with mono-/bis-BF2 fluorophores

To better understand the relationship between molecular structure of the mono-/bis-BF2-core compounds and mechanofluoroboron behaviors, two pyridine-based difluoroboron compounds with triphenylamine group (TPA-ts-BF2 and TPA-ts-2BF2) were designed and successfully synthesized, which TPA-ts-BF2 including a BF2 fluorophore and TPA-ts-2BF2 containing the bisBF2 fluorophores. Based on the photophysical properties measurements results, it was found that TPA-ts-2BF2 had more excellent intramolecular charge transfer characteristics than that of TPA-ts-BF2, and exhibited significant aggregation-induced emission activity, however, TPA-ts-BF2 displayed typical aggregation-caused quenching phenomenon. Meanwhile, the emission spectrum of the solid powders of TPA-ts-2BF2 was red-shifted 52 nm after grinding, that of TPA-ts-BF2 was red-shifted 46 nm, which was resulted from crystalline state switching to amorphous state. According to the theoretical calculations, we conjectured that TPA-ts-BF2 with uncoordinated amide linkage moiety had a tendency to forming a more twisted conformance and higher molecular polarity, which made that mechanofluorochromic behavior was worse than that of TPA-ts-2BF2. Additionally, TPA-ts-2BF2 was applied to latent fingerprint detection due to its prime aggregation-induced emission property.

Numerical study flow and heat transfer characteristics of superhydrophobic single tube bundle surface and wake flow

Numerical study flow and heat transfer characteristics of superhydrophobic single tube bundle surface and wake flow

Spatial–Temporal Variations of the Gross Ecosystem Product under the Influence of the Spatial Spillover Effect of Urbanization and Ecological Construction in the Yangtze River Delta Region of China

Rapid development of urbanization and intense human activities had a profound influence on the ecosystem service functions. As an integrated monetary index for the evaluation of final ecosystem services, the gross ecosystem product (GEP) is widely used in the quantification of ecosystem service value (ESV). This study initially assessed and analyzed the spatial distribution of the GEP at the county-level scale using multisource data spanning 2000, 2005, 2010, 2015, and 2020. Then, the spatial transfer characteristics of the GEP were measured. Finally, the study employed spatial panel econometric models and the geographically weighted regression (GWR) model to investigate the spatial effect of urbanization and ecological construction on the GEP. The results indicated that: (1) In 2020, the GEP in the Yangtze River Delta Region was RMB 15.24 trillion, and the GEP per unit area was RMB 42.58 million per square kilometer. It exhibited a cumulative decrease of RMB 298.72 billion from 2000 to 2020. (2) The spatial transfer efficiency of the GEP in urban agglomerations showed a clear decline trend. During the period of 2000–2020, over 96% of county-level units exhibited a decline with RMB 90,076,103.17/km2, indicating a consistent downward trend from the central regions towards the periphery. (3) Based on the decomposition effects of the spatial Durbin mode, urbanization and the ecological construction indicator showed spatial spillover effects on the GEP, but their impact mechanisms varied substantially. Among them, the urbanization rate (UR), population density (PD), and the proportion of impervious land (ILP) had the largest negative effect on the GEP, and a 1% rise in ILP locally resulted in a 0.044% decline in the local GEP and a 0.078% rise in the GEP of neighboring units. And the area of ecological land had a positive effect on the GEP of both local and neighboring areas. Those conclusions can offer evidence in favor of encouraging ecologically responsible building practices and sustainable growth in urban agglomerations.

Heat transfer and flow characteristics of a novel turbulator design in heat exchanger: Experimental and numerical analysis

Heat transfer and flow characteristics of a novel turbulator design in heat exchanger: Experimental and numerical analysis

Optical Microneedle-Lens Array for Selective Photothermolysis.

Photothermolysis is the process that converts radiation energy into thermal energy, which results in the destruction of surrounding tissues or cells through thermal diffusion. Laser therapy that is based on photothermolysis has been a widely used treatment for various skin diseases such as skin cancers and port-wine stains. It offers several benefits such as non-invasiveness and selective treatment. However, the use of light, e.g., laser, for safe and effective photothermolysis becomes challenging due to the limited penetration of light into skin tissue as well as the presence of melanin, which absorbs this light. To solve the current issues, we propose an optical microneedle-lens array (OMLA) coated with gold in this work to directly deliver light to targeted skin layers without being absorbed by surrounding tissues as well as melanin, which results in the improvement of the efficiency of photothermal therapy. We developed a novel fabrication method, frame-guided micromolding, to prepare the OMLA by assembling two negative molds with simultaneous alignment. In addition, evaluations of the optical and heat transfer characteristics of the OMLA were performed. We expect our developed OMLA to play a crucial role in realizing more effective laser therapy by allowing the precise delivery of photons to the target area.

Non-uniform boiling heat transfer characteristics and calculation evaluation in U-tube steam generator tube bundle

U-tube steam generator, as one of the core equipment in nuclear power plants, has lateral non-uniform heating on the secondary side, which complicates the progress of heat transfer on the secondary side of the evaporator by causing fluid cross mixing. However, there is relatively little research on the properties of transverse non-uniform heat transfer in the secondary side tube bundle of the evaporator under natural circulation conditions with the free liquid surface. Therefore, to conduct comparative experiments and studies between uniform and non-uniform heating, an experimental setup with the natural circulation of the free liquid surface and the ability of transverse non-uniform heating was constructed, considering the characteristics mentioned above for the secondary side of the evaporator. The results indicate that higher proportions of gas-phase distribution are frequently found in the tube bundle on the high-power side, and corresponding positions usually have higher water temperature, heat transfer capacity, and heat transfer coefficient. Besides, four heat transfer correlations that are suitable for pool boiling are estimated, and the results show that the Rohsenow correlation has the best applicability to compute the heat transfer coefficient for uniform heating experiments while performing worse in non-uniform heating experiments. The main reason is the lack of consideration for the factors of fluid cross mixing in traditional correlations.

Impact of Different Protrusions in Energy Transfer and Fluid Flow Characteristics Using Al₂O₃ Nanofluid in Pipe Flow

The study investigates how the protruded surface (the part sticking out of an otherwise flat surface) over the small channel affects flow characteristics and heat transfer within a circular flow regime, utilizing computational methods. This investigation uses an alumina nanofluid to compare and analyze the thermo-physical parameters of protruding pipes such as boxes, cylinders, dimples, and pyramids in pipe flow. Alumina nanofluid with varying volume fractions was evaluated as a thermo-fluid under laminar flow conditions, exploring its ability to enhance energy transmission (heat) over the protruded channels. The protruded surface induces turbulence around the protruded region, altering the coolant's physical characteristics. Since heat transfer predominantly occurs on surfaces, the alteration in surface geometry due to the protruded shape increases detectable heat transfer and the Nusselt number. With an increase in the volume percentage of nanofluids, there's a tendency for pressure loss to rise along the flow direction's centerline. The dimpled channel exhibits the highest Nusselt number among all protruding channels, indicating that increasing the Reynolds number also increases the surface heat transfer coefficient for all protrusions. When compared to the base fluid, cylindrical protrusions show the greatest pressure drop. Additionally, comparing a protruded channel with base fluid to one with a 4% volume of alumina nanofluid, it can be observed that the latter significantly improves heat transfer, followed by volume fractions of 1% to 3%.

Effect of ferro nanofluids on mixed convection in an open cavity with phase change material

Numerical analysis of mixed convection flow in an open channel cavity was performed by placing PCM and using ferro nanofluids (water based Fe3O4 nanofluid) with different volume fractions (1.0%, 3.0% and 5.0%) as working fluids. The effect of different Richardson numbers under laminar flow conditions with constant Reynolds number was analyzed to reveal how the nanofluid volume fraction and PCM position in the cavity affect the flow and heat transfer characteristics. The main reason for considering the use of nanofluid as a working fluid with the PCM layer is the thermal control of the cavity. It has been determined that the use of ferro nanofluids has a positive effect on the thermal control of the flow by increasing the thermal energy storage capacity of the PCM. As the Ri number increased, the importance of mixed convection effects increased, and for the highest Ri number, natural convection played a dominant role, causing a 65.5% decrease in the heated wall dimensionless temperature. Since the heat flux applied for pure water at highest Ri number is one third of that applied for 5.0% nanofluid, the specified temperature increase is quite lower by comparing heat flux thanks to the nanofluid high convection capability. Different than pure water, in all PCM cases the rate of melting is higher for 5.0% ferro nanofluid due to the higher convective heat transfer. In the case of the PCM on the bottom wall, the highest thermal energy storage capacity was obtained for each working fluid and 50% more energy was stored compared to the right heated wall at the same Ri number. Moreover, the maximum average Nu number was determined for the bottom heated case and for the same Ri number at 5.0% ferro nanofluid which was obtained approximately twice as much as pure water when flow reached steady state.

Computational 3D Simulations of Fluid Dynamics and Comparisons of Heat Transfer Characteristics of Various Flat-Plate Solar Collectors

Computational 3D Simulations of Fluid Dynamics and Comparisons of Heat Transfer Characteristics of Various Flat-Plate Solar Collectors

Dynamics of the ohmic heating and chemically reactive time-dependent flow of magnetized Casson fluid inside a rectangular pipe

Chemical reaction and ohmic heating can significantly influence the flow behavior and heat transfer characteristics in industrial processes involving non-Newtonian fluids. These processes include polymer processing, food processing, and manufacturing processes where non-Newtonian fluids are commonly encountered. Therefore, the impacts of chemical reaction and ohmic heating on the unsteady flow of an incompressible magnetized non-Newtonian Casson liquid through a rectangular pipe with a variable pressure gradient is scrutinized in this article. The impacts of heat generation/absorption and viscous dissipation are also incorporated through the energy equation. The numerical simulations of partial differential equations (PDEs) are acquired utilizing the finite difference method with the incorporating relaxation (SOR) algorithm. The impacts of dissimilar imperative parameters on various flow fields are scrutinized through graphs. Outcomes indicate that liquid velocity decreases with enhancing values of the Casson parameter. Furthermore, the liquid temperature has an enhancing behavior with the impact of the heat source/sink parameter. Comparisons of numerical results with previously published results show an excellent agreement. This kind of research may find specific industrial and medical utilizations such as glass manufacturing, crude oil purification, lubrication, paper production, blood transport study in cardiovascular design, etc.

Theory-based cryopreservation mode of mesenchymal stromal cell spheroids

Cryopreservation of spheroids requires development of new improved methods. The plasma membranes permeability coefficients for water and cryoprotectants determine time characteristics of mass transfer through the cell membranes, and therefore the optimal modes of cells cryopreservation. Here we proposed an approach to cryopreservation of multicellular spheroids which considers their generalized characteristics as analogues of the membranes’ permeability coefficients of the individual cells. We have determined such integral characteristics of spheroids from mesenchymal stromal cells (MSCs) as osmotically inactive volume; permeability coefficients for water and Me2SO molecules and the activation energy of their penetration. Based on these characteristics, we calculated the osmotic behavior of multicellular spheroids under cooling conditions to select the optimal cooling rate. We also determined the optimal cooling rate of spheroids using the probabilistic model developed based on the two-factor theory of cryodamage. From the calculation it follows that the optimal cooling rate of the MSC-based spheroids is 0.75°С/min. To verify the obtained theoretical estimates, we conducted experiments on freezing MSC-based spheroids under different modes. The obtained results of primary viability screening indicate that freezing at a constant linear cooling rate of 0.75–1.0°С/min gives a good result. Theoretical prediction of the spheroid osmotic behavior during cooling provided the basis for experimental verification of varying the temperature to which slow cooling should be carried out before immersion in liquid nitrogen. Slow freezing of spheroids to −40 °C followed by immersion in liquid nitrogen was shown to preserve cells better than slow freezing to −80 °C. Obtained data allow more effective use of MSC-based spheroids in drug screening and regenerative medicine.

Experimental Investigation of Thermal Prediction and Heat Transfer Characteristics of Two-Phase RDE during Long-Duration Operation

Experimental Investigation of Thermal Prediction and Heat Transfer Characteristics of Two-Phase RDE during Long-Duration Operation

Insights into Sub‐Thermionic Transport in Schottky Barrier FETs

AbstractBoltzmann carrier statistics restrict the sub‐threshold swing (SS ≥ 60 mVdec–1) and, consequently, the supply voltage (≈ 1 V) of the thermionic transistor. This primary bottleneck results in rapidly increasing power consumption, heating, and associated reliability/scalability challenges as more devices are packed into a small footprint. Despite significant efforts from the device community, a suitable sub‐thermionic alternative is yet to emerge. In this work, an attempt is made to understand the physics of Schottky barrier FETs demonstrating SS < 60 mVdec–1, as evident in some experimental results. Employing the in‐house TCAD tool, the electrostatic potential in the device is accurately modeled with the sweeping gate bias. Next, the Tsu–Esaki model is used to compute the tunneling current. The analysis shows that the steep SS results from an abrupt change in the tunneling barrier profile, from a step‐like to a triangular‐like. However, in the ON regime, the drift component begins to dominate the transfer characteristics. Thus, the subtle interplay between the drift and tunneling components of transport leads to SS < 60 mVdec–1 in OFF‐state with improved in ON‐state. Finally, using the calibrated model, the performance metrics of an all‐2D material‐based CMOS inverter operating at a low VDD ≈ 0.6 V are projected.