Heat and Mass Transfer最新文献

Machining different types of complex parts requires changing speed of the motorized spindle to accommodate the various processes, resulting in temperature rise or decline and then causing thermal deformation of machine tool, which plays a significant impact on the machining accuracy of the parts. According to the Law of Conservation of Energy and Fourier's Law of Heat Conduction, the heat transfer mechanism of the motorized spindle is investigated. Based on the thermo-solid structure coupling theory, the analytic models of the temperature field and thermal deformation for the motorized spindle are established, and the thermal hysteresis phenomenon is explored by means of the case studies. The characteristic experiments were carried out under variable working conditions and the model parameters were identified using Genetic Algorithm (GA). The accuracy and effectiveness of the proposed models for predicting temperature and thermal deformation of the spindle are validated which is applicable to compensate the thermal errors. Moreover, compared with data-driven modeling approach, our study needs lesser data for parameter identification, greatly saving the computation time in modeling.

Bee bread is a value-added apiculture product produced from bee pollen by mixed lactic acid fermentation. Although many studies focused on the bioactive components and health effects of the bee bread, there is no study concerned with understanding its moisture adsorption properties. Herein, it was aimed to evaluate moisture adsorption properties and thermodynamics of bee bread using different sorption models at 25 and 35 °C. The water adsorption of bee bread had Type II characteristics, and the monolayer moisture content was calculated with BET, GAB, and Caurie models between 3.58 and 5.80 g/100 g. The Peleg and Caurie models ensured better prediction for adsorption. The stability of bee bread was high at 25 °C according to the smaller ratio of Type III to Type II-bound water. The entropy of adsorption was 16.01–25.78 kJ/mol.K and it decreased with the moisture adsorption. Besides, the moisture adsorption needs external energy from the environment because of ∆G > 0.

The performance of a PEM fuel cell that uses hydrogen as the fuel and pure oxygen as the oxidant strongly depends on water management, which has been primarily studied in a single-channel domain. Therefore, there is a need to examine water distribution throughout the entire fuel cell domain, including both the anode and cathode sides. Liquid water can cause flooding in the gas diffusion layer, catalyst layer, and channels, reducing the active surface area of the catalyst and, consequently, the reaction rate. Phase transfer between liquid water and water vapor influences the buildup of liquid water in these domains. In the present work, a three-dimensional, non-isothermal, two-phase numerical model incorporating both the cathode and anode domains has been developed to study water distribution. This model includes water phase transition in the gas diffusion layer, catalyst layer, and channels. The mixed flow distributor is used to analyze water formation and distribution throughout the domain. The study shows that using pure oxygen at the inlet increases the ohmic region in the polarization curve and decreases concentration losses, which could be important for applications such as spacecraft. Additionally, the effects of liquid water accumulation in the porous layers on reactant transport and cell performance are investigated.

In this study, the transient and steady-state heat transfer caused by an air jet impinging on a heated plate moving back and forth in the horizontal direction is investigated experimentally. The jet flow issuing form nozzle of various geometry (circular, triangle, square) is impinged on rough and smooth surfaces. In addition, Reynolds number (jet velocity), distance between the nozzle and the plate, plate velocity and stroke are considered as independent parameters that could affect the heat transfer.The optimum number of experiments is determined with the help of Taguchi design of experiment method. The transient and steady-state heat transfer are analyzed by means a high-technology thermal camera. Local and average Nusselt numbers representing the heat transfer characteristics are calculated in response to the variable parameters. Comparative graphs and ANOVA test results are presented and evaluated in order to determine the effects of parameters on heat transfer. As a result, it has been seen that Reynolds number (82%) is the most dominant parameter affecting heat transfer. Other parameters are listed as nozzle geometry (7.6%), surface roughness (4.9%), plate velocity (1%), stroke (0.6%) and nozzle-plate distance (0.1%) according to their degree of effect.

In this study, the effect of maltodextrin, powdered sugar, and corn starch carrier agents used at different ratios (5% and 10%) in the convective dryer at 65 ºC and hybrid dryer (microwave + convective) at 350 W + 65 ºC to produce blackberry powder was investigated. Drying kinetics, energy analyses, physical, flow properties, and biochemical analyses of blackberry powder production processes were investigated. Drying rates in drying processes varied between 0.0052–0.0477 g moisture/g dry matter minute. Effective moisture diffusion values were determined between 3.36 × 10^–8-2.57 × 10^–7 m²/s. Specific moisture absorption rate and specific energy consumption values were found to vary between 0.0019–0.0034 kg/kWh and 237.15–530.00 kWh/kg, respectively. Tapped density was determined in the range of 1.666–2.765 g/ml, while bulk density was determined in the range of 1.319–1.937 g/ml. The wettability values of blackberry powders were found to vary between 2.00–27.67 s. Drying processes did not preserve the color values of fresh blackberry puree (p < 0.05). In bioactive findings, total phenol content values were 16.756–25.876 µg GAE/g⁻¹ dw, total monomeric anthocyanin values were 229–1.469 µg cy⁻³-glu/g⁻¹ dw, total flavonoid values 3.958–5.080 mg KE/kg dw and total antioxidant activity values 406–500 µmol TE/g⁻¹ dw.

Reiner–Philippoff (RP) fluid flow above a heated sheet concluded the model of Cattaneo–Christov heat flux for Darcy-Forchheimer is implemented in this work. The influences of thermal radiation, heat source/sink, velocity, and thermal slip boundary conditions are also deliberated. The transformations are used to convert obtained partial differential equations into a set of ordinary differential equations, and they are solved numerically using the shooting method (RK-4) solver with the help of the computational software MATLAB. The dimensionless temperature and velocity numbers are further developed. More engineering curiosity of local Nusselt and Skin frictions are tabulated, depicted, and interpreted. The study presents graphical and tabular illustrations depicting flow parameters, velocity profiles, and temperature profiles. Key conclusions drawn include, When the inertia coefficient ({F}_{r}) increases, the velocity field (f^{prime}(eta )) decreases. Analytical calculations are performed for the flow of a Reiner-Philippoff fluid over a shrinking sheet, considering influences such as thermal radiation, velocity slip, and temperature fluctuations. Increased heat absorption correlates with higher Nusselt numbers, whereas temperature generation lowers wall temperatures. The skin friction magnitude gradually increases in the order of dilatant, viscous, and pseudo-plastic fluids, respectively.

The study is devoted to enhanced CeO₂ evaporation in the temperature range between 2130 and 2650 K from refractory crucibles made of different materials: molybdenum, tantalum, and tungsten. The composition datum of vapor and films deposited on collectors receiving evaporation products were obtained by quadrupole mass spectroscopy and by energy-dispersive X-ray spectroscopy. One of approximation coefficients of the temperature dependence of CeO₂ vapor in the range between 2150 and 2220 K was measured. The study is of interest for a variety of technologies utilizing refractory oxide evaporation with high productivity, including the plasma mass separation methods.

Through the analysis of hot oil carrying theory, the problem of oil film heat accumulation in hydrostatic bearing can be revealed, so as to avoid serious lubrication failure caused by heat accumulation. In this paper, the hot oil carrying factor is defined and the mathematical model of the thermal oil carrying characteristics of the oil film is established by taking the beveled double rectangular oil pad hydrostatic bearing as the object, and the hot oil carrying law under different working conditions is obtained by changing the inclination angle of the beveled oil pad at 0.0230°, 0.0250° and 0.0280°, respectively. Theoretical calculations and simulation studies show that within the range of the circumferential inclination of the oil pad with better dynamic pressure effect of the bearing, the inclination has little effect on the oil film hot oil carrying. When the speed of the workbench is lower than 10r/min, no oil film hot oil carrying phenomenon occurs. When the speed is in the range of 10r/min-100r/min, a part of the load will cause the phenomenon of oil film hot oil carrying. And when the speed exceeds 100r/min, the heat accumulation of the oil film is the most serious at this time. There are many reasons for the lubrication failure of hydrostatic bearings, and hot oil carrying is a new research direction, this paper starts from the oil film heating mechanism of beveled oil pads hydrostatic bearings, and describes the phenomenon of hot oil carrying.

SCADA systems play an important role in tracking the behaviour of critical process variables and connecting geographically dispersed subsystems at the industrial plant level. This article presents a PLC and SCADA-based control framework to automate and supervise the temperature control processes in the heat exchanger plant. The OMRON (NX1P2-9024DT1) PLC is interfaced with the Wonderware InTouch SCADA system to gather data, create a simulated temperature control prototype and carry out the necessary control operations within the heat exchanger plant. The PLC controls the entire process and programming of PLC is done using Sysmac studio automation software using the ladder programming language. The proposed system controls the temperature of the heat exchanger system through PID and Fractional Order PID (P ({text{I}}^{uplambda }{text{D}}^{upmu })) controllers with Integral Anti-windup technique. Various control strategies like Cascade Control, Feedforward Control and Smith Predictor for time delayed process are discussed for controlling the temperature of the process. The performance of both PID and fractional order PID controllers is optimized using adaptive heuristic optimization techniques like Genetic Algorithm (GA), Ant Colony Optimization (ACO) and Particle Swarm Optimization (PSO). In control system design and analysis, the calculated performance indices are used as quantitative measures for evaluating the performance of a system. The combined form of temperature controller with Cascade control, Feedforward control and dead-time compensator is modelled and examined for simulation using MATLAB. Simulation and real-time experimentation analysis of the developed controllers are executed with metaheuristic optimization techniques based on different performance indices like ISE, IAE and ITAE.

A numerical model based on the enthalpy method for solidification/melting that incorporates liquid-phase convection was established for a shell-and-tube phase-change thermal energy storage device with dispersed heat sources. This model optimized the heat source structure and simulated the phase change process, thermal storage performance, and evolution and effects of convection-induced vortices. To overcome the limitations of melting blind spots in traditional inner-tube heat sources, a dispersed heating approach was introduced to optimize the heat source distribution on the inner and outer tubes without changing the heat exchange area. The optimal heat source model demonstrated superior heat transfer performance, featuring an inner-tube top heat source and three uniformly distributed outer-tube bottom heat sources at a dispersion angle of 60°. It reduced the complete melting time by 70.88% compared to the inner-tube heat source alone and by 51.99% compared to the outer-tube bottom heat source. The dispersed heat sources effectively utilized the natural convection benefits at the upper inner side and enhanced the heat transfer at the lower sections to address the melting blind spots of the central heat source, thereby improving the uniformity of the process. The enhancement in heat transfer within the dispersed heat source model is primarily due to the optimized heat source distribution, which facilitates a more dispersed and uniform vortex evolution during the phase change. This promotes the development of the liquid-solid interface and reduces the mutual interference in convection vortex expansion. Hence, the internal heat transfer rate and thermal storage capacity of the system are improved.