Heat Transfer最新文献

Compact heat exchangers are critical components in various industries, including cooling air conditioning devices, automotive, aerospace, enabling efficient heat transfer between fluids or between fluids and solids. This study investigates the influence of fin angles (0°, 30°, 60°, and 90°) on the performance of compact heat exchangers. A combined 3D-CFD simulation and experimental analysis approach was used under a constant airflow rate of 0.05 kg/s and an inlet temperature of 294 K. Both the numerical simulations and experimental tests showed that a 60° louvered fin angle delivered the best heat transfer performance. Numerically, we found an average heat transfer coefficient of about 28.964 W/m²·K for the front side and 27.978 W/m²·K for the back side. The experimental results closely matched this, with the maximum average heat transfer coefficient reaching 28.4 W/m²·K for the front side and 26.6 W/m²·K for the back side on fin 2. The highest heat transfer coefficient values were detected on fin surfaces directly exposed to the airflow, while the backside surfaces presented notably lower heat transfer coefficients. The percentage differences for numerical and experimental results for the front side and back side are 1.98% and 5.18%. These findings underscore the importance of fin orientation in maximizing heat exchanger efficiency. This analysis provides a detailed look at heat transfer on both the front and back surfaces of the fins, offering insights that were not available in previous studies.

An experimental and numerical study has investigated the heat transfer (HT) and friction characteristics of a solar air heater (SAH) duct roughened using a rectangular S-shaped artificial roughness arrangement (inline and staggered). The thermal performance of SAH is studied with design variables such as the length of the relative roughness (d/H = 1.33), the height of the relative roughness (e/H = 0.271), and the distance between S (b/H = 0.667) remaining constant as the Reynolds number (Re) ranges from 3000 to 10,000 and the angle of attack 60°. Relative roughness of pitch range p/H (1.667, 3.33, 5, and 6.667) for inline with relative roughness of length (l/H) (0.8335, 1.666, 2.5, and 3.335) for staggered. A three-dimensional computational fluid dynamics (CFD) simulation is carried out using the CFD code, ANSYS Fluent, and the renormalization group k–ε turbulence model for solving turbulence terms in governing equations. It has been found that HT enhancement can be achieved by using an artificial roughness staggered arrangement at l/H = 0.8335 and e/D = 0.271 with an angle of attack (α) of 60°. Also offers the best thermal performance factor for the investigated range of 3.12.

The current investigation objective is to employ a semianalytical method to observe the micropolar fluid flow dynamics in the vicinity of a stretched surface through a chemical reaction of medium that is nonlinear, nonlinear radiation, heat dissipation, variable viscosity, and modified Fourier heat flux effects influenced by convective boundary conditions. The Chebyshev collocation technique is employed to solve the dimensionless ordinary differential equations, which are converted from dimensional partial differential equations using similarity transformations. The research also examines the performances of velocity, temperature, microrotation, and concentration fields due to the effects of various flow-influencing supervisory parameters within the boundary layer by representing these findings through graphical diagrams. The comparison of the couple-stress, friction factor, and mass and thermal rates has been done by the computed numerical data presented in the table. The final results show that velocity profiles decreased by increasing the microgyration factor and material parameter, whereas microrotation exhibited the opposite trend. An upsurge in the first-order slip parameter leads to fluid velocity and microrotation depreciation. The potency of the magnetic field impelled to deflate the fluid moment, but the increased porosity parameter intensified fluid velocity. The thermodiffusion effect leads to an expansion concentration field, but the chemical reaction and Schmidt number have opposite impacts. The magnetic and temperature ratio parameters are driven to intensify the skin friction and couple stress, but thermal relaxation and radiation parameters have evidenced opposite effects.

Heat pipes (HPs) are becoming increasingly popular because they are efficient heat transfer technologies. This study investigates the potential application of an HP as an air-cooling system at the gas turbine (GT) inlet as a viable solution to increase GT power output. In particular, a case study is conducted on real GT engines operating in Kerman, Iran. First, a theoretical model is constructed using the established HP technologies to design a wick structure as a thermal control element. MATLAB-based simulations are utilized for HP design and analysis to specify the impact of HP structural factors on heat transport capabilities, emphasizing the significance of operating orientation and the utilization of gravity to augment heat transport capacity. To validate the methodology, selected results from previous research are replicated and compared. The HP design is optimized to maximize thermal effectiveness, while the tube bank or heat exchanger system is optimized to minimize inlet air pressure drop. Computational results indicated that the optimal tilt angle is 15°. The proposed method shows that the heat transfer rate per HP reaches a maximum of 1.4878 kW at 40°C. Then, the case study results indicated that a net power output of up to 18.6% is achievable when utilizing HP heat exchangers, which maintains its effectiveness even at temperatures below the design threshold. Consequently, this system proves suitable for peak load conditions during hot seasons and year-round performance. This technology offers a promising new approach to GT design, with significant implications for enhancing energy efficiency and power stabilization.

Drying dates to a semi-dried, soft, preferred by most consumers, remains a challenge for small-scale processors due to limited control, longer drying time, quality degradation, and other inefficiencies of traditional methods such as open-sun drying. This study investigated the mechanical hot-air drying kinetics and characteristics and evaluated quality changes after drying of Biser dates from 57% to 30% moisture content (wet basis) at various temperatures using a state-of-the-art computer vision system (CVS). This study findings revealed that drying time decreased with increasing temperature, with the shortest drying time observed at 70°C (14.5 h) and the drying occurred predominantly in the falling rate period. Additionally, among the three thin-layer drying models investigated in this study, Page model stands out as the best fitting model to describe the mechanical hot-air drying behavior of Biser dates, having an uppermost coefficient of determinations (R²) of (0.9899–0.9984) and least standard error (SE). The effective moisture diffusivity (D_eff) followed second Fick's diffusivity model and fall between a range from 3.50 × 10⁻¹⁰ to 5.84 × 10⁻¹⁰ m²/s across the temperatures studied (50°C, 60°C, and 70°C). Higher temperatures led to greater shrinkage but helped prevent surface cracking. Notably, CVS measurements showed significant differences (p < 0.05) in shrinkage across samples, with 60°C and 70°C yielding higher volumetric shrinkage. Rehydration capacity was highest at 60°C (45.47%), followed by 70°C (34.21%) and 50°C (20.99%). Overall, drying at 70°C provided the most efficient balance between drying time and product quality, making it the optimal condition for small-scale processors already transitioning to mechanical hot-air drying. It also reduced drying period, minimized quality losses, improved operational consistency, and product standard in the shift away from traditional methods. Future research should focus on sensory evaluation to assess consumer acceptance of semi-dried Biser dates processed under these conditions.

This paper reviews how tubular solar still designs can enhance thermal output and offer a sustainable desalination solution powered by solar energy. Conventional solar stills typically produce only 2–5 L/m²/day, highlighting the need for more efficient and practical designs for widespread adoption. Studies categorize performance improvement methods into two primary approaches, with particular emphasis on phase change materials due to their demonstrated efficacy. Experimental data shows that phase change materials can improve the system energy efficiency to a maximum of 30% and boost manufacturing capacity notably while reaching production quantities greater than 6 L/m²/day within optimal operating parameters. The review demonstrates how advanced wick materials, vacuum insulation together with reflective surfaces have enhanced both thermal performance and productivity of these systems. Geographical conditions, together with climate variables, influence the success of these enhancement methods; so, specific optimization measures must be developed for different locations. Recent experimental and theoretical research synthesis delivers important pathways for future development, which proves tubular solar stills as sustainable water scarcity solutions that produce less carbon than traditional desalination approaches.

This study introduces a novel Y-shaped twisted insert with trapezoidal perforations, a numerical study was performed to investigate the thermal-hydraulic performance of circular pipes equipped with Y-shaped inserts, for heat transfer enhancement in circular heat exchanger pipes. employing computational fluid dynamics (CFD) with Ansys 2022-R2 (finite volume method, k–ε turbulence model). Five geometric configurations cases (A, B, C, D, and E) variations included twisted Y-strips (twist ratios 2 or 7), and trapezoidal perforations were analyzed under constant heat flux (1000 W/m²) with air as the working fluid across Reynolds numbers (Re) range (3000–21,000). Results demonstrated significant heat transfer enhancement, with case E (twisted Y-strip, twist ratio 7, 30 trapezoidal holes) achieving a peak Nusselt number (Nu = 197.673 at Re = 21,000), a 258% increase over the plain pipe (Nu = 55.23). Thermal Performance Factor (TPF) peaked at 3.863 (Re = 3000, case E), indicating superior efficiency at lower Re. Flow resistance reduction was observed, with case E exhibiting the lowest friction coefficient (f = 0.016 at Re = 21,000). The synergistic effects of twisted geometries and perforations enhanced turbulence, fluid velocity, and heat dissipation. These findings underscore the efficacy of Y-shaped inserts with optimized twist ratios and perforations in augmenting passive thermal performance while mitigating hydraulic losses, positioning case E as a promising configuration for energy-efficient heat exchange systems. The results showed remarkable agreement with previous research on Y-shaped inserts, reinforcing the credibility of the findings, which reflect scientific consensus in the field of heat transfer.

This piece of work provides an in-depth analysis of magnetohydrodynamics (MHD) fluid flow and heat transport near a continuously moving vertical plate in the presence of nonlinear thermal radiation with convective boundary condition. A nonlinear dependence of thermal radiation on temperature enhances thermal transport, while convective boundary conditions govern heat transfer at the plate surface. The governing partial differential equations (PDEs) are transformed into ordinary differential equations (ODEs) through the application of a similarity transformation. To numerically solve these ODEs, we have used bvp4c method in MATLAB. The influences of dimensionless parameters on heat transfer and fluid flow are presented using tables and graphs. The key novelty of this study lies in analyzing the impact of nonlinear thermal radiation on MHD flow over a constantly moving vertical plate using the bvp4c method. When the fluid flows in the positive x-direction and the plate moves in the opposite direction, the coefficient of skin friction decreases. Moreover, when the direction of the fluid and the plate is the same, both the velocity and the temperature profiles increase with greater nonlinear thermal radiation. Near the wall, the temperature gradient decreases as nonlinear thermal radiation intensifies, while it increases in the free stream. The thickness of the thermal boundary layer decreases, while the thickness of the velocity boundary layer increases with increasing magnetic parameter. Similarly, when the Grashof number increases, the velocity boundary layer becomes thicker, while the thermal boundary layer tends to become thinner. However, when the Prandtl number increases, the thermal boundary layer becomes thicker, whereas the velocity boundary layer tends to become thinner. Practically, these findings aid in optimizing heat transfer in engineering applications such as cooling systems, heat exchangers, aerospace thermal protection, and biomedical devices.

Researchers are driven to explore alternative and environmentally friendly energy sources due to the significant impacts of environmental degradation. Thermal energy storage utilizing phase change materials (PCMs) has developed as a novel option for mitigating environmental pollution. This study numerically proposes an approach to enhance the energy storing and heat transmission rates of PCMs in a triangular space. Within the space, there is a rotating cylinder that maintains a consistent speed, resulting in the production of forced heat transfer. Natural convection occurs due to the thermal gradient between the space's partially hot left wall and the remaining cold walls. To achieve optimal outcomes, an investigation was performed to assess the impact of various elements on mixed convection in the given region. The elements that need to be considered are the Reynolds number Re (10–100), which represents the speed of the inner cylinder, the Darcy number represents the permeability Da (10⁻⁵–10⁻²), the Hartmann number Ha (0–100), which represents the intensity of the magnetic field, and the volumetric percentage of the nanoparticles ɸ (0–0.08). The obtained findings demonstrated a notable augmentation in heat transfer rates when the Da value increased and the position of the heated section on the left wall was altered. Conversely, the heat transmission rates decreased with a rise in Ha and ɸ. The study found that increasing the values of Ha and ɸ to their maximum levels resulted in a reduction of 20% and 15% in Nu_avg, respectively. By raising Da and shifting the heated area of the left wall lower, Nu_avg experienced a significant rise of 320% and 162.5%, respectively.