Heat Transfer最新文献

Machine learning techniques are gaining momentum in the present-day context in most engineering applications due to their versatility and accuracy. They facilitate faster data processing coupled with a high degree of accuracy. They are extensively used in understanding and modeling engine combustion and emissions. Engine emissions significantly contribute to environmental degradation. In the current study, an effort has been made to compare the emissions recorded from a four-stroke single-cylinder biodiesel engine with those obtained using artificial neural network (ANN) models, where the hyperparameters have been optimized using nature-inspired metaheuristic optimization algorithms like JAYA, WOA, ROA, and WaOA. The study was conducted using diesel and cardanol-methanol-diesel blends of B10M10, B20M10, and B30M10, by varying the fuel injection pressure from 180 bar (standard injection timing) to 220 bar with an interval of 20 bar. Furthermore, experiments were conducted with oxygen enrichment at concentrations of 3%, 5%, and 7% w/w on the standard oxygen concentration of air. The study showed a remarkable reduction of 59% in CO emissions at 220 bar fuel injection pressure with 7% w/w oxygen enrichment for the B30M10 blend as compared to 180 bar without oxygen enrichment. A similar reduction of 32.6% and 16.6% were observed for HC emissions and smoke opacity for the same operating conditions. However, a rising trend of 50% was observed for NO_x emissions for the same blend and operating conditions. The findings indicate that the data recorded conforms with that obtained by using the ANN model optimized through these metaheuristic algorithms.

Evaluations were conducted on the thermal performance of an organic Rankine cycle (ORC) system using three fluids as the evaporative system at a low-grade heat source. The modified ORC evaporators were replaced with a three-fluid system, which included hot fluids at the top and bottom and an isopentane working fluid in the middle section. Furthermore, the thermal performance assessment with a hot fluid heat transfer ratio in the outer and inner tubes (Q₂/Q₁) varying from 25:75 to 75:25 has been investigated. The impact of the hot fluid's (Q₂/Q₁) heat transfer ratios to saturated steam on the modified ORC's thermal performance assessment was examined, with an evaporative temperature range of 45–65°C and a pinch point temperature difference (PPTD) of 3–10°C. The Taguchi technique solves multiparameter optimization using the L9 orthogonal array. The findings showed that in three-fluid-based modified ORC systems, the network output, exergetic efficiency, and irreversibility went down with PPTD for all three Q₂/Q₁ cases. For Q₂/Q₁ of 75:25, the ORC's energetic efficiency and overall irreversibility reached their optimum, while a PPTD of 3–10°C reduced the exergetic efficiency by 19.71%. Also, Q₂/Q₁ of 75:25 showed the highest and 200% higher ORC system work done at PPTD of 3°C than Q₂/Q₁ of 25:75—the lowest. Modified ORC network generation, energy output, and heat transfer rate showed excellent results at an evaporative temperature of 58.33°C. For optimal network productivity, Q₂/Q₁ of 75:25 was 160% and 40% greater than 50:50 and 25:75 at 58.33°C, respectively. The three-fluid-based modified ORC system performs better with a 75:25 Q₂/Q₁ ratio. According to Taguchi's analysis, evaporation temperature affects the improved ORC system's thermal, exergy, and network generation. Also, heat transfer ratios (F = Q₂/Q₁) largely affect system irreversibility.

This research looks at the impact of dielectric fluids and fluid speeds on cell temperature control in innovative cylindrical lithium-ion batteries during high-rate discharges (C-rate) using the multiscale multidomain battery model. The goal is to improve the battery thermal management system to increase battery performance, longevity, and safety. The present study includes reducing thermal strains, enhancing efficacy, and forestalling overheating risks across various applications in electrified systems. The assessment focuses on four dielectric fluids—ester, mineral, kerosene, and Novec 7200—flowing at 0.01 m/s to gauge their efficiency in managing cell temperatures. Results demonstrate the criticality of effective thermal management in maintaining optimal battery performance and longevity. Ester oil emerges as the most efficient coolant, maintaining cell temperatures at 305.84 K and showcasing a 44% reduction compared with scenarios without coolant. In contrast, kerosene oil, mineral oil, and Novec 7200 yield temperature reductions of 42.86%, 42.51%, and 43.11%, respectively. Furthermore, combining 1% v/v. MXene nanoparticles with ester oil enhance cooling capabilities, with remarkable cell temperature reductions of 50% at 0.01 m/s velocity. Subsequent increments in flow velocity lead to enhanced cooling effects: at 0.05 and 0.1 m/s, reductions reach 51.89% and 52.155%, escalating to 52.58% and 54% at 0.5 and 1.0 m/s, correspondingly.

Surface roughness has a great impact on the peristaltic motion of nanofluid flow and plays an important role in engineering, manufacturing, and material sciences. During tissue engineering, imaging techniques, implant surface finish, surgical instrument texture, and tissue engineering, and so forth. This study explores the effects of electrical double layers, surface roughness, velocity slip, and thermal slip to investigate the heat transfer rate of cobalt and alumina nanoparticles with water through uniform and nonuniform horizontal tubes. In the present study, the Jeffrey nanofluid flow model is chosen to investigate the heat transfer phenomenon of hybrid nanofluids based on alumina and cobalt nanoparticles suspension in water. The effects of electroosmosis, surface roughness, viscous dissipation, heat source/sink parameter, velocity, and thermal slips are also under consideration during the peristaltic motion of hybrid nanofluid in uniform and nonuniform tubes. The mathematical software MATHEMATICA 13.3 is utilized to find the exact solution and graphical results to investigate the complicated flow behavior. It is noticed that the velocity near the walls of the tube is lower for the surface roughness parameter and higher in the core part. The behavior of velocity for the remaining parameter is the opposite. The temperature of the current fluid flow increases for all parameters except the surface roughness parameter. The effects of velocity for hybrid nanofluid are prominent as compared with nanofluid in the core part. The temperature profile and heat transfer rate for hybrid nanofluids are lower as compared with nanofluids, which shows the cooling effects. This study is beneficial for hyperthermia, gene therapy, drug delivery, and tissue engineering.

The chief objective of the present investigation is to study experimentally the hydraulic and thermal performance of a corrugated tube with copper foam cylindrical inserts (MFCIs) containing a new type of inserts with the purpose to improve the procedure of heat transfer, which gives an elevated thermal enhancement factor more than that of smooth tube beneath the similar operating circumstances. Also, in this paper, the study of the effect on the number of cylindrical inserts was made from metal foam (10 PPI and porosity 0.9) on the Nusselt number and Nusselt number ratio as a double heat exchanger furnished with the suggested MFCI with various values of Reynolds numbers ranges from 1600 to 4000 via using water as the test fluid. The investigational outcomes revealed an enhancement in heat transfer as well as the thermal performance of the corrugated tube with MFCI, which being significantly augmented in comparison to those for the smooth tube. Additionally, the average rise in the value of heat transfer is within 225% and 400% at the test range, relying upon the number of cylindrical inserts as well as the Reynolds number, whereas the maximum thermal performance is obtained to be around 2.4 for utilizing the corrugated tube having (four) cylindrical inserts at low Reynolds number (1820). Furthermore, the outcome of the loss of pressure manifested that the corrugated tube's mean friction factor is between 96% and 97% more than the smooth tube.

This work has broad applications in areas such as materials engineering, particularly in the manufacturing of polymers, textile fibers, and nanocomposites, thus, inspired the study to examine a continuous two-dimensional flow of micropolar fluid steadily fluctuated in an oblique impinging on a stretched surface theoretically and computationally. In addition, heat radiation and chemical reactions are taken into account in this work. The flow is composed of a uniform shear flow parallel to the sheet surface and a stagnation-point flow. Assuming a linear variation in surface temperature, the sheet is extending at a velocity proportionate to the distance from the stagnation point. In terms of partial differential equations, the boundary-layer regime under discussion is modeled. The nondimensional ordinary differential equations were developed using appropriate similarity variables via a similarity transformation approach. The most effective and powerful too of the numerical approach, known as the pseudospectral collocation technique, is used to solve the micropolar flow model problem. The velocity, angular velocity, temperature, and concentration profiles are portrayed through graphs. Moreover, the impression of the input values on the wall drag coefficient, thermal, and solutal transfer rate are computed in a table. A table is used to compare the numerical findings with the results found in the literature to verify the correctness of the results. It is noted that there is great agreement between the found answer and the earlier investigations. Graphs are used to show the impacts of the relevant factors in the problem, which include the magnetic parameter, the impinging angle heat transfer characteristics, the Prandtl number, the Lewis number, Brownian motion, and the thermophoresis parameter.

In this article, the effect of different boundary conditions and different thermal and physical properties of walls and gas on flame characteristics and stability of hydrogen–air mixture are investigated using an analytical method. This method solves the gas–wall energy equation, and the hydrogen mass conservation equations. The jump conditions are obtained by integrating the energy and mass equation into a small control volume around the flame. For validation of this model, the temperature distribution on the outer surface of the wall is compared with experimental data that show the maximum relative error of 3.5% for Q = 400 mL/min and 4.9% for Q = 200 mL/min. The maximum variation of gas temperature is nearly 6.5 times of wall temperature variation. The wall can be considered one-dimensional for conventional wall materials with K > 10. For the existence of combustion inside the chamber, when the value of K is greater than 10, the Péclet number should also be considered greater than 10. In a constant equivalence ratio, increasing the medium temperature increases flame stability.

The present study investigates the gyrotactic microorganism flow in a rotating porous medium containing Newtonian fluid. Using gravity modulation, Darcy–Brinkman biothermal convection is examined. Linear theory describes the stationary convective mode which derives the expression for critical Rayleigh number. This indicates the onset of bioconvection. The system's marginal stability is demonstrated by graphical and tabular representation which has a good agreement with each other. The Ginzburg–Landau equation governs the Nusselt number, which is used to further explore heat transfer. The study provides an explanation and graphical representation of the effects of the following factors on heat transfer: cell eccentricity, modified Vadasz number and bioconvective Rayleigh–Darcy number, modulation frequency, and amplitude along with Taylor number. The mean Nusselt number has been plotted in the current study. The effect of rotating porous media and gravity modulation is explained in this work. Additionally, a comparison graph is plotted to examine the effects of gravity, both modulated and unmodulated, on the Nusselt number. This demonstrates how well gravity modulation on rotating porous media controls the system's heat transfer. A comparison between numerical and analytical results for unmodulated cases is also explained graphically.

The solar updraft tower power plant presents a promising renewable energy solution but faces limitations in thermal efficiency and energy production during nonsunny hours. This study addresses a critical gap in the literature by investigating the integration of latent heat storage systems utilizing paraffin wax as phase change materials (PCMs) to enhance solar updraft tower (SUT) performance. Two identical small-scale SUTs were constructed, both using the same tank configuration; however, the PCM device was filled with paraffin wax as a PCM, while the non-PCM device contained only atmospheric air. Three scenarios were explored, featuring varying PCM tank heights of 2, 4, and 6 cm (the full capacity of the PCM tank). Results indicated that, from 3 p.m. until sunset, the PCM-integrated SUT in Case 3 (with 6 cm of PCM) achieved the best performance, with an average absorber temperature rise of 25°C, compared with 12°C for the non-PCM device. During the same period, the average air velocity at the tower neck, where a wind turbine could be installed, was 1.21 m/s for the PCM device, versus 0.82 m/s for the non-PCM device. Notably, the nocturnal operating time extended significantly with PCM use, rising from 90 min for the 2 cm case to 125 min for the 6 cm case. In contrast, the non-PCM device exhibited no operational time after sunset. This research not only demonstrates the effectiveness of PCM in improving the thermal performance and operational longevity of SUTs but also introduces a novel tank configuration that allows for flexible PCM integration, representing a significant advancement in the development of more efficient SUT systems.