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Intensification of the Plant Products Drying Process by Improving Solar Dryer Design
摘要： The article presents the rationale for production of dried fruits and vegetables using a solar drying unit. To intensify the drying process, convection of drying agent ?ow in the proposed drying chamber is studied using Navier–Stokes equations. Numerical methods are used for solving equations describing the process of convective heat transfer. As a result, graphical interpretations of isolines of drying agent ?ow are obtained and location of passive zones in the dryer chamber are identi?ed. Uniformity of the temperature zones in the chamber is ensured by supplying additional drying agent into the passive zones. Temperature values at various levels of the drying chamber are experimentally obtained. Results for drying cut-up mass of vegetables and fruits are presented.
关键词： solar drying,passive zones,convective heat transfer,Navier–Stokes equations,temperature uniformity
更新于2025-09-23 15:19:57
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[ASME ASME 2018 International Mechanical Engineering Congress and Exposition - Pittsburgh, Pennsylvania, USA (Friday 9 November 2018)] Volume 8A: Heat Transfer and Thermal Engineering - Infrared Thermography to Measure Heat Transfer of a Heated Curved Thin Sheet
摘要： Heat transfer measurements on a heated curved thin sheet are performed by infrared thermography. The evolution of the temperature field is recorded to calculate the heat flux by using the two-dimensional unsteady heat balance equation. The thermal conduction term is estimated by the projection relationship between the curved surface of the thin sheet and the horizontal plane. Natural convection is neglected during the estimation of this heat flux. Unlike the traditional means of heat flux measurement, this method is non-intrusive and can measure the heat flux distribution within a curved space, allowing an easier evaluation of the errors due to radiation and tangential conduction. An electrical resistance foil with known power are applied as the heating source to compare the calculated heating power with the actual recorded power, the max relative error for different heating powers is about 10 %, which verified of the feasibility of the method. Considering possible applications, three different domestic gas cookers are used to heat three different curved thin pans, and then, in each case, the heat flux of the burners is analyzed. From the heat flux distribution of the three gas cookers, some heating characteristics such as heating power, maximum and average heating flux are investigated to help optimize the designs of the gas cookers, avoiding local over-heating and low uniformity of heat distribution.
关键词： Heat transfer measurements,infrared thermography,heating characteristics,gas cookers,curved thin-sheet
更新于2025-09-19 17:15:36
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Study of infrared thermal application for detecting defects within tunnel lining
摘要： With the aging of tunnels, additional maintenance and assessment procedures are required to monitor their working conditions. The passive thermal infrared method, which is a nondestructive contact-free method, is used to find defects in a box-type and shield tunnels with concrete lining. In this study, this method is numerically applied to detect defects in an unhealthy concrete structure. The thermal field data measurements are reviewed and the governing heat transfer mechanisms for a defected concrete surface are presented. The heat transfer in the concrete segment, tunnel air, and the air inside the void due to the conduction, convection, and radiation mechanisms is explained. Further, the type of cavity, the temperature difference between the healthy and unhealthy concrete surfaces, the temperature difference between the tunnel air and concrete surfaces, and the influence of the void depth on the detection accuracy are investigated. The results show that the temperature difference between the concrete surface and the tunnel air is more than 0.35 °C, which is an ideal condition for detecting the voids with an approximate depth of 30 mm or less.
关键词： Hammering test,Heat transfer,Infrared thermography,Defected lining,RC tunnel lining
更新于2025-09-19 17:15:36
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Analysis and Optimization of a Microchannel Heat Sink with V-Ribs Using Nanofluids for Micro Solar Cells
摘要： It is crucial to control the temperature of solar cells for enhancing e?ciency with the increasing power intensity of multiple photovoltaic systems. In order to improve the heat transfer e?ciency, a microchannel heat sink (MCHS) with V-ribs using a water-based nano?uid as a coolant for micro solar cells was designed. Numerical simulations were carried out to investigate the ?ows and heat transfers in the MCHS when the Reynolds number ranges from 200 to 1000. The numerical results showed that the periodically arranged V-ribs can interrupt the thermal boundary, induce chaotic convection, increase heat transfer area, and subsequently improve the heat transfer performance of a MCHS. In addition, the preferential values of the geometric parameters of V-ribs and the physical parameters of the nano?uid were obtained on the basis of the Nusselt numbers at identical pump power. For MCHS with V-ribs on both the top and bottom wall, preferential values of V-rib are rib width d/W = 1, ?are angle α = 75°, rib height hr/H = 0.3, and ratio of two slant sides b/a = 0.75, respectively. This can provide sound foundations for the design of a MCHS in micro solar cells.
关键词： nano?uid,heat transfer enhancement,micro solar cell,microchannel heat sink,V-ribs
更新于2025-09-19 17:13:59
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Radiative Thermal Diode Mediated by Nonreciprocal Graphene Plasmon Waveguides
摘要： A thermal diode based on the asymmetric radiative heat transfer between nanoparticles assisted by nonreciprocal graphene plasmon waveguides is proposed in this work. The thermal diode system consists of two particles and a drift-biased suspended graphene sheet in close proximity of them. Nonreciprocal graphene plasmons are induced by the drift currents in the graphene sheet, and then couple to the waves emitted by the particles in near-field regime. Based on the asymmetry with respect to their propagation direction of graphene plasmons, the thermal rectification between the two particles is observed. The performance of the radiative thermal diode can be actively adjusted through tuning the chemical potential or changing the drift currents in the graphene sheet. With a large drift velocity and a small chemical potential, a perfect radiative thermal diode with a rectification coefficient extremely approaching 1 can be achieved within a wide range of interparticle distance from near to far field. The dispersion relations of the graphene plasmons are adopted to analyze the underlying physics of the rectification effect. In addition, due to the wide-band characteristic of nonreciprocal graphene plasmons, drift-biased graphene can act as a universal platform for the thermal rectification between particles. The particles with a larger particle resonance frequency are preferable to achieve a better thermal diode. This technology could find broad applications in the field of thermal management at nanoscale.
关键词： graphene plasmon waveguides,nonreciprocal,nanoparticles,radiative heat transfer,thermal diode
更新于2025-09-19 17:13:59
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Experimental study on two-phase boiling in wavy copper microchannels fabricated with ultrafast laser micromachining
摘要： In this study, the sinusoidal wavy (SW) copper microchannels with triangular cross section were fabricated with the ultrafast laser micromachining approach. The flow boiling of de-ionized water in SW microchannel were experimentally studied under mass fluxes of 43.43-217.15 kg/(m2s) and heat fluxes of 0-590 kW/m2. The flow patterns in the SW microchannels were visually observed and the boiling heat transfer characteristics were analyzed based on the obtained data. It shows the SW microchannel has a maximum enhancement of 127.7% in local heat transfer coefficient with an acceptable increase of pressure loss compared to the straight one in present work. In SW microchannel, a low degree of superheat can trigger the onset of nucleate boiling. A slow decreasing tendency of local heat transfer coefficient under a high effective heat flux or a high vapor quality was observed. The heat transfer mechanism of flow boiling in SW microchannel was analyzed based on the experimental visualization. Nucleate boiling and thin film evaporation are the dominant modes under different thermal boundary conditions. The flow boiling instability phenomenon in microchannels can be diminished using the wavy structures.
关键词： Boiling heat transfer,Sinusoidal wavy microchannel,Flow instability,Ultrafast laser micromachining
更新于2025-09-19 17:13:59
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A three dimensional meshfree-simulation of the selective laser sintering process with constant thermal coefficients applied to nylon 12 powders
摘要： 3D printing is an intersting process in the context of creating original objects.Selective laser sintering printers use a laser to fuse polyamide particles together with specific resin and heat. The difference in temperature between the different areas in the process causes the appearance of deformations, the objective of this work is the modeling of the thermal SLS phenomenona, by following the evolution of the temperature as a function of time.This model is based on the resolution of the heat conduction equation coupling with convection and radiation conditions with a distribution heat source and constant thermal coefficients by the meshless method based on radial basis function , the result of this study,will be presented and compared with other works.
关键词： heat transfer,Meshfree method,radical basis function (RBF),thermal modeling,selective laser sintering(SLS)
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Research on Fabrication Method of High Stability Long Period Fiber Grating
摘要： We investigate thermal effects of pulmonary cooling which was induced by cold air through an endotracheal tube via a ventilator on newborn piglets. A mathematical model was initially employed to compare the thermal impact of two different gas mixtures, O2-medical air (1:2) and O2-Xe (1:2), across the respiratory tract and within the brain. Following mathematical simulations, we examined the theoretical predictions with O2-medical air condition on nine anesthetized piglets which were randomized to two treatment groups: 1) control group (n = 4) and 2) pulmonary cooling group (n = 5). Numerical and experimental results using O2-medical air mixture show that brain temperature fell from 38.5 ?C and 38.3 ?C ± 0.3 ?C to 35.7 ?C ± 0.9 ?C and 36.5 ?C ± 0.6 ?C during 3 h cooling which corresponded to a mean cooling rate of 0.9 ?C/h ± 0.2 ?C/h and 0.6 ?C/h ± 0.1 ?C/h, respectively. According to the numerical results, decreasing the metabolic rate and increasing air velocity are helpful to maximize the cooling effect. We demonstrated that pulmonary cooling by cooling of inhalation gases immediately before they enter the trachea can slowly reduce brain and core body temperature of newborn piglets. Numerical simulations show no significant differences between two different inhaled conditions, i.e., O2-medical air (1:2) and O2-Xe (1:2) with respect to cooling rate.
关键词： brain,bio-heat transfer,Pulmonary cooling,piglet,numerical simulation
更新于2025-09-19 17:13:59
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Numerical modelling of heat transfer, mass transport and microstructure formation in a high deposition rate laser directed energy deposition process
摘要： In laser directed energy deposition (L-DED) processes, by applying a converged powder stream, relatively high laser power and larger laser spot, the powder utilisation efficiency and processing speed can be increased. There is, however, lack of mathematical models for L-DED. In this paper, a three-dimensional numerical model is established to study the mass transport and heat transfer in the melt pools in high deposition rate (HDR) L-DED of 316L stainless steel. The Volume of Fluid (VOF) method is employed to track the melt pool free surfaces, and enthalpy-porosity method is used to model the solid-liquid phase change. A discrete powder source model is developed by considering the non-uniform powder feed rate distribution. Results show that this model can well predict the deposited track dimensions (width, height and dilution depth). Different from conventional L-DED processes, the impact of higher mass addition on the melt pool fluid flow and temperature distribution is significant. In the regions where filler powder is injected, a downward mass flow is observed, and the temperature is slightly reduced. With the extracted temperature distribution and geometry at the solidification front, the solidification conditions are also calculated, as well as the primary dendrite arm spacing (PDAS) of the solidified tracks. Due to the high laser energy input, the temperature gradient is lower, and coarser microstructures are formed compared with conventional L-DED. The simulated results are in good agreement with experimental results.
关键词： Heat transfer,High deposition rate laser directed energy deposition,Mass transport,Primary dendrite arm spacing
更新于2025-09-19 17:13:59
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Conductive and convective heat transfer during welding of AISI316L stainless steel using pulsed Nd: YAG laser
摘要： Conductive and convective heat transfers during an autogenous butt joint welding of AISI 316L stainless steel sheets using pulsed Nd: YAG laser have investigated. An FEA based three-dimensional model was developed to receive the transient thermal responses across the weld pool and the predicted results are compared with experimental observations. The heat transfer in the keyhole region, melt ?ow directions around the keyhole and heat affected zone are computed for consecutive pulse irradiation during laser welding and the same was investigated on far with experiment. The temperature distribution have predicted in terms of inward heat ?ux and Paclet number to investigate the heat and mass transportation in the weld pool. These results have taken for discussion and found that has a close association with experimental results.
关键词： Peclet Number,Pulsed laser welding,Melt ?ow,316L Stainless steel,Moving heat source,Heat transfer
更新于2025-09-16 10:30:52