Heat Transfer最新文献

Biomass boilers are widely used for sustainable heating, but combustion inefficiencies lead to significant emissions of CO, NO_x, and particulate matter, affecting both performance and air quality. Traditional control strategies like Fuzzy Logic Control (FLC) often rely on fixed rule sets, limiting adaptability in dynamic combustion environments. This study aims to optimize air-fuel balancing in a 10 kW domestic biomass boiler using the Artificial Bee Colony (ABC) algorithm, with the dual objective of minimizing harmful emissions and maximizing thermal efficiency. Combustion data was collected under varying operating conditions, and an optimization model was developed using ABC. A 50-iteration optimization process was executed, and the results were benchmarked against FLC. ABC achieved a 28% reduction in CO, 21% in NO_x, and 30% in particulate matter, with a 3.8% improvement in thermal efficiency. It also demonstrated a 54% enhancement in fitness score and faster convergence than FLC. The novelty of this study lies in the first-ever application of the ABC algorithm for real-time biomass combustion optimization. Unlike FLC, ABC dynamically explores optimal solutions, offering a more adaptable, computationally light, and globally optimized control mechanism. This establishes a new direction in intelligent emission control, advancing cleaner and more efficient biomass energy systems.

Heat transfer within granular materials is a complex multiphase process, often consisting of solid, gaseous, and potentially liquid phases. Conventional methods to determine heat transfer properties typically involve small-scale testing on a finely ground sample, which has the potential to introduce sample bias into the outcomes. This study presents a method to determine the thermal properties of granular materials from laboratory-scale experimental measurements, through the determination of the thermal diffusivity and the convective heat transfer coefficient (which is closely related to the Biot number) of the system. A series of experiments was conducted, and they were analyzed using the proposed method. It was shown that these properties can be accurately obtained by a two-stage process in which values are first estimated, assuming that only the lowest decaying mode dominates (as it does for long times), before fitting the complete analytic solution against the measured curves. The results show that this method gives a very accurate estimate of the diffusivity and Biot number, which may subsequently be used to determine key properties such as thermal conductivity and the convective heat transfer coefficient. This method is experimentally validated using sand as a proof-of-concept.

The purpose of the present study is to characterize the thermal performance of micropolar fluid flows on a vertically elongated permeable sheet in the presence of a heat source/sink. The additional physical aspects include a heat source/sink and the fluid flow across a permeable medium. The mathematical problem is governed by partial differential equations is transformed into a system of nonlinear ordinary differential equations using similarity transformations. The regulating transformed standard ordinary differential equations are subsequently simulated utilizing the Runge-Kutta fourth order method, accompanied by the shooting technique to evaluate numerical findings of dependent quantities of physical importance through MATLAB. The impact of varied parameters on the fluid momentum, angular momentum, and energy was analyzed and shown graphically. The results demonstrate that the porosity of the medium plays a critical role in regulating both flow resistance and heat transfer: higher porosity enhances permeability, leading to faster fluid motion and improved thermal transport, while low porosity increases drag and suppresses heat transfer. The applied magnetic field introduces Lorentz forces that dampen velocity profiles and increase fluid temperature through Joule heating, thereby thickening the thermal boundary layer. Increasing the micropolar parameter enhances coupling between microrotation and linear motion, resulting in higher velocity and microrotation profiles. The study further provides streamlined and isothermal plots to illustrate the interplay of magnetic and porous effects. These findings underline the novelty of combining porosity, slip, and heat source/sink effects in micropolar fluid dynamics and contribute to optimized designs for thermal management in porous and magnetized environments.

The present study explores the thermal insulating behavior of epoxy-based composites reinforced with ramie fiber and glass dust, using a combination of numerical analysis and experimental validation. To numerically assess the effective thermal conductivity (k_eff) of the composites, a finite element approach is applied to a 1-D heat conduction model under defined boundary conditions. The simulations are conducted to evaluate k_eff under two different conditions: with and without voids within the composite element. Hybrid epoxy composites of varying filler proportions, ranging volume fractions from 0% to 15.136% are then fabricated using the hand lay-up method. Using the guarded heat flow method, the k_eff of these composites is then measured. The numerical simulation outcomes are matched against experimental k_eff values, revealing good agreement with a maximum deviation of only 5.97%. The epoxy composites exhibited a decrease in k_eff by about 25.56% from 0.180 to 0.134 W/m K with an increase in filler content up to 17 wt.%, indicating enhanced thermal insulation performance of the composites. This study confirms that hybrid epoxy composites containing ramie fiber and glass dust provide a thermally insulating and economical alternative for various functional applications, such as in packaging, construction, and automotive parts.

The present numerical study focuses on investigating the effects of magnetohydrodynamic mixed convection and Joule heating in a lid-driven Z-shaped cavity containing double rotating cylinders in a comprehensive manner. An ample range of practical applications, including nuclear reactor cooling, magnetically controlled solar collectors, metallurgical processes, and electronic device cooling, makes it a captivating field of research. The current study considers a Z-shaped cavity that has a hot wall at the lower portion of the cavity and a cold wall at the top, which is a moving lid, and other walls are kept adiabatic. It comprises two rotating circular cylinders that can rotate in both clockwise (CW) and counterclockwise directions. The Galerkin finite element method-based computational process is utilized to resolve two-dimensional steady continuity, momentum, and energy equations under specified boundary conditions. Both quantitative and qualitative outcomes are assessed to predict the fluid flow and thermal behavior for a limited range of some pertinent parameters: Hartmann number (Ha = 20, 30, and 40), rotational Reynolds number (Re_c = −10 and 10), heat generation coefficient (∆ = 0, 2, and 5), Grashof number (10³ ≤ Gr ≤ 10⁶), and Reynolds number (100 < Re < 700). Results reveal a maximum 40% and 45% reduction in the Nusselt number occurring for enhancing the magnetic effect and heat generation coefficient, respectively. Moreover, CW rotation of the cylinders or aiding flow facilitates over 38% elevation in the Nusselt number by improving overall flow circulation in the cavity. Increasing the fluid Reynolds number leads to a 150% augmentation in the Nusselt number due to intensified turbulent flow. Hence, the comparative results of this meticulous numerical study, blended with novel geometrical contour, can be utilized to improve the thermal efficiency of other intricate systems.

The current work explores the reflection behavior of coupled plane waves from the stress-free boundary of a half-space made of a fiber-reinforced orthotropic nonlocal thermoelastic voided composite, employing Lord and Shulman's generalized thermoelastic theory. Four coupled time-harmonic waves with distinct velocities are found to propagate through the medium, considering well-suited boundary conditions. The explicit form of the expressions for the amplitude ratios and the energy ratios of the reflected coupled plane waves is derived. Numerically quantitative analysis for a magnesium-like crystal is performed using MATLAB software, with the results visually interpreted through graphs. Nonlocal parameter, void parameter and material's anisotropy due to different levels of fiber reinforcement significantly affect the amplitude ratios of the reflected waves. It is verified that, during reflection phenomena, there is no dissipation of energy, that is, at every angle of incidence, the total of energy ratios remains conserved and sums to one.

This study investigates the significant influence of various flow parameters on hybrid nanofluids and ternary hybrid nanofluids, modeled as non-Newtonian fluids with symmetric behavior, an essential characteristic in advanced heat transfer applications. The analysis is conducted within the framework of steady, two-dimensional flow over a rotating disk, incorporating the effects of nonlinear thermal radiation and sticky (viscous) dissipation. The governing partial differential equations are transformed into a system of ordinary differential equations (ODEs) using appropriate similarity transformations. These equations are solved numerically using the Runge–Kutta–Fehlberg method along with the shooting technique through MATLAB 2021(a). Additionally, asymptotic solutions for the wall shear stress are obtained to validate the numerical results. The impact of key physical parameters on velocity, temperature, and thermal performance is examined through detailed graphical illustrations. The results reveal that increasing magnetic field strength leads to a noticeable suppression of velocity profiles, while nonlinear current emission enhances the Nusselt number, temperature distribution, and flow intensity, and concurrently reduces local skin friction.

This study focused on analyzing the thin-layer drying characteristics of both cooked and soaked chickpeas using a forced convection solar dryer, with experiments conducted at different drying temperatures (50°C, 60°C, 70°C, and 80°C) and air flow velocities (0.25, 0.50, 0.75, and 1.00 m/s). Drying in both types occurred entirely with the falling rate period, indicating diffusion control of moisture. Increased drying temperature and air velocity decreased drying time, while temperature having a stronger impact. The Exponential as well as Page models were fitted to each experimental run, with Page's model demonstrated superior performance, consistently achieving a higher coefficient of determination (r² = 0.998–0.999) and lower reduced chi-square values (χ² = 0.565 × 10⁻⁴ to 2.268 × 10⁻⁴) across all drying conditions for both cooked and soaked chickpeas. The drying constants k and n of Page's model were estimated under all conditions. The dependence of the drying constant k on drying air temperature and velocity was described using both the Arrhenius equation and Power law models which shows, increasing from 0.1396 to 0.4541 h⁻¹ for cooked chickpeas as the temperature rose from 50°C to 80°C at a constant air velocity of 0.25 m/s. Arrhenius equation provided better fit compared to the Power model, as evidenced by higher r² and lower Chi-square (χ²) values. Cooked chickpeas had a higher initial moisture content (205%–215% d.b.) compared to soaked chickpeas (139%–148% d.b.) and required longer drying durations (6–21 h depending on conditions). However, cooked samples showed better rehydration behavior, with rehydration ratios up to 2.42, whereas soaked samples achieved a maximum of 1.89, indicating greater structural integrity post-drying. Sensory evaluation favored drying at with moderate temperature and airflow. Cooked chickpeas had better texture and flavor, while soaked ones retained more color and taste.