The magnetic field can serve as a proper controlling parameter for heat transfer and fluid flow; it can be also employed to maximize the thermodynamic efficiency in various fields. Nanofluids and ...porous inserts are among the conventional approaches of heat transfer enhancements. Porous media, in addition to improving the heat transfer, can enhance the pressure drop. This research presents a numerical investigation on the magnetohydrodynamics forced convection effects of Al
2
O
3
–CuO–water nanofluid inside a partitioned cylinder within a porous medium. The calculations were carried out for a broad range of governing parameters. The nanofluid flow is modeled as a two-phase flow using two-phase mixture model, and the Darcy–Brinkman–Forchheimer equation is employed to model fluid flow in porous media. Simulation was also conducted under the laminar flow regime by finite volume method. Furthermore, the thermal boundary condition of constant uniform heat flux was imposed on the cylinder walls. The average Nusselt number as well as the performance evaluation criteria (PEC) were examined for diverse Darcy numbers (0.0001 < Da < 0.1) and Hartmann numbers (0 < Ha < 40). The results indicate the significant impact of Hartmann and Darcy number enhancement on the elevation of heat transfer coefficient. Additionally, incorporation of nanoparticles to the base fluid increased the PEC in all cases. Moreover, the PEC reached to its maximum value in configurations involving permeable porous media (i.e., a medium with Da = 0.1 and Ha = 40).
•Energy and exergy analyses are evaluated.•Comparative analysis on geothermal and solar-driven multi-generation systems is applied.•Parametric study is represented to specify the impacts of diverse ...design parameters on the system performance.•The maximum and minimum exergy destruction of the system components are related to the evaporator and the pump, respectively.•System produces 352,816 kWh and 174.913 kg of electrical power and hydrogen during one year.
Given the limited sources of fossil fuels, mankind should find new ways to meet its energy demands. In this regard, geothermal and solar energy are acknowledged as reliable, safe, promising, and clean means for this purpose. In this research study, a comparative analysis is applied on geothermal- and solar-driven multi-generation systems for clean electricity and hydrogen production through energy and exergy assessments. The systems consist of an organic Rankine cycle, a proton electrolyte membrane electrolyzer, and a thermoelectric generator subsystem. The Engineering Equation Solver software has been utilized in order to model the system and obtain the output contours, sensitivity analysis, and exergy destruction. The results were obtained considering the ambient temperature of Bandar Abbas city as a case study. The geothermal system was performant over the solar system, with 11.21% higher hydrogen production and 0.17 % higher exergy efficiency. According to the sensitivity analysis, the turbine efficiency, evaporator inlet temperature, thermoelectric generator suitability criterion, pump efficiency, and evaporator inlet mass flow rate were the most influential parameters. Also, the exergy analysis showed that the utmost system's exergy destruction is pertinent to the evaporator and the least is related to the pump. In addition, the system produces 352,816 kWh and 174.913 kg of electrical power and hydrogen during one year.
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This current paper presents the experimental investigation of pool boiling enhancement for surface structuring using wire electric discharge machine (WEDM) method in saturated water at atmospheric ...pressure. Further, the effects of 45° inclination, geometry dimensions, cross-sectional angle of fins (15°, 45° and 90°) and WEDM current which are used in fabrication surfaces on copper surface were examined. The experimental results showed that the heat dissipation increases with higher WEDM current, lower cross-sectional fin angle (CFA) and deeper channel. Sample # 9 with more depth and high CFA reached a maximum heat flux of 120 W cm
−2
which corresponds to an enhancement of 200% in heat transfer coefficient compared to the plain surface. The improved heat transfer is attributed to bubble dynamics, heat transfer area, bubble slide and scrape, and capillary flow.
Owing to their safety, stability and controllability, diffusion flames have found extensive applications in medicine and power generation. Regarding the significance of recirculation impact on ...micro-combustors, an efficient method should be developed for better analysis of the micro-combustors performance. In this paper, an asymptotic method is developed to model diffusion flames propagation through a biofuel in counterflow configuration with the consideration of heat recirculation effect. The flame structure includes pre-heat, post-vaporization and oxidizer zones. Micron-sized lycopodium particles and air can be regarded as biofuel and oxidizer, respectively. Mass and energy conservation equations are investigated in each zone. For evaluation of the thermal recirculation impact, a specific term is included in the energy conservation equation. Furthermore, the effects of changes in the flame temperature, mass fraction of the gaseous fuel and oxidizer (relative to fuel and oxidizer Lewis numbers), mass particle content, particle radius and equivalence ratio were examined considering and ignoring the thermal recirculation effect. The results indicate that increase of heat recirculation coefficient will rise the flame temperature and shift the flame position to the fuel nozzle side. Also, consideration of thermal heat recirculation will enhance the gaseous fuel production in the pre-heat and post-vaporization zones.
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Corrugating channel wall is considered to be an efficient procedure for achieving improved heat transfer. Further enhancement can be obtained through the utilization of nanofluids and porous media ...with high thermal conductivity. This paper presents the effect of geometrical parameters for the determination of an appropriate configuration. Furthermore, the optimization of forced convective heat transfer and fluid/nanofluid flow through a sinusoidal wavy-channel inside a porous medium is performed through the optimization of entropy generation. The fluid flow in porous media is considered to be laminar and Darcy-Brinkman-Forchheimer model has been utilized. The obtained results were compared with the corresponding numerical data in order to ensure the accuracy and reliability of the numerical procedure. As a result, increasing the Darcy number leads to the increased portion of thermal entropy generation as well as the decreased portion of frictional entropy generation in all configurations. Moreover, configuration with wavelength of 10 mm, amplitude of 0.5 mm and phase shift of 60° was selected as an optimum geometry for further investigations on the addition of nanoparticles. Additionally, increasing trend of average Nusselt number and friction factor, besides the decreasing trend of performance evaluation criteria (PEC) index, were inferred by increasing the volume fraction of the nanofluid (Al
O
and CuO).
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air ...conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can ameliorate the ultimate heat usage and delay or even avoid the occurrence of system failures, thus leading to remarkable economic, environmental and energy efficiency outcomes. A century of research on ameliorating critical heat flux (CHF) has focused on altering the boiling surface characteristics, such as its nucleation site density, wettability, wickability and heat transfer area, by many innovative techniques. Due to the remarkable interest of using nanoparticle deposition on boiling surfaces, this review is targeted towards investigating whether or not metal oxide nanoparticles can modify surface characteristics to enhance the CHF. The influence of nanoparticle material, thermo-physical properties, concentration, shape, and size are categorized, and the inconsistency or contradictions of the existing research results are recognized. In the following, nanoparticle deposition methods are presented to provide a worthwhile alternative to deposition rather than nanofluid boiling. Furthermore, possible mechanisms and models are identified to explain the amelioration results. Finally, the present status of nanoparticle deposition for CHF amelioration, along with their future challenges, amelioration potentials, limitations, and their possible industrial implementation, is discussed.
Digital light processing (DLP) as a vat photopolymerization technique is one of the most popular three-dimensional (3D) printing methods, where chains are formed between liquid photocurable resin ...molecules to crosslink them and solidify the liquid resin using ultraviolet light. The DLP technique is inherently complex and the part accuracy depends on the process parameters that have to be chosen based on the fluid (resin) properties. In the present work, computational fluid dynamics (CFD) simulations are presented for top-down DLP as photocuring 3D printing. The effects of fluid viscosity, travelling speed of build part, travelling speed ratio (ratio of the up-to-down traveling speeds of build part), printed layer thickness, and travel distance considering 13 various cases are scrutinized by the developed model to obtain a stability time of fluid interface. The stability time describes the time it takes for the fluid interface to show minimum fluctuations. According to the simulations, a higher viscosity leads to prints with higher stability time. However, lower stability times in the printed layers are caused by a higher traveling speed ratio (TSR). The variation in settling times with TSR is extremely small in comparison to that of viscosity and travelling speed variations. As a result, a declining trend can be detected for the stability time by increasing the printed layer thickness, while by enhancing the travel distance values, the stability time demonstrated a descending pattern. In total, it was revealed that it is essential to choose optimal process parameters for achieving practical results. Moreover, the numerical model can assist in the optimizing the process parameters.
Porous inserts and nanofluids are among the conventional methods for the amelioration of heat transfer in industrial systems. The heat transfer rate could also be improved by utilizing porous ...substances with a higher thermal conductivity in these systems. This research work presents a two-dimensional (2D) numerical examination of the laminar forced convection of an Al2O3-CuO-carboxy methyl cellulose (CMC) non-Newtonian hybrid nanofluid within an annular pipe in a porous medium. The porous medium was inserted within two inner or outer wall cases. For hybrid nanofluid flow modeling in porous media, a Darcy–Brinkman–Forchheimer formulation was employed. Additionally, a power-law technique was utilized as a fluid viscosity model for the considered non-Newtonian fluid. The governing equations were discretized according to the finite volume method (FVM) using the computational fluid dynamics (CFD) software package ANSYS-FLUENT. The cylinder walls’ thermal boundary conditions were exposed to a constant heat flux. For various Darcy numbers, the impacts of different volume fractions of the hybrid nanofluid (0% to 5%), the total Nusselt number, the pressure drop, and the performance number (PN) were evaluated. The outcomes indicate that the heat transfer coefficient increases considerably with a decrease in the Darcy number (0.1 to 0.0001), as well as with an increase in the porous thickness ratio. Moreover, it was found that the nanoparticles’ increased volume fraction would ameliorate the heat transfer and, more considerably, the PN factor. Furthermore, according to the outcomes in both cases I and II for a constant porous thickness ratio and Darcy number (rp=1,Da=0.0001) and a high volume fraction (φ=5%), the maximum total Nusselt number reached 1274.44. Moreover, applying a volume fraction of 5% with Da=0.1 and rp=1 reached the highest value of the PN index equal to 7.61, which is augmented as roughly 88% compared to the case of a zero volume fraction.
•Coating heat transfer surfaces utilizing micro/nanoparticles through spin-coating process are assessed.•An experimental heat transfer in nucleate pool boiling considering surface modification method ...is investigated.•Impacts of roughness and material concentration on pool boiling heat transfer are evaluated.•Optimum heat transfer coefficient enhancement can be obtained by changing surface morphology.•Pool boiling improvement mechanism based on visualization of bubble dynamics on surfaces is presented.
Pool boiling has gained tremendous attention in an efficient transferring of high thermal energy for diverse industrial applications. Surface coating is considered as a common approach for achieving an enhanced boiling heat transfer. In this paper, spin-coating technique is scrutinized experimentally for modifying the surface and enhancing the heat transfer in nucleate pool boiling of distilled water at atmospheric pressure. The images of Scanning Electron Microscopy (SEM) as well as Atomic Force Microscopy (AFM) are utilized for obtaining the phase structure and surface morphology in the prepared materials. Regarding the results of experimental tests, considerable improvements in surface roughness and porosity were achieved by the use of surface coating. Furthermore, the positive effect of adding an appropriate amount of material in achieving the enhanced overall performance of pool boiling was found. Also, higher nucleation sites densities (NSD) were formed by coating the surface, and consequently, improved boiling performance was reached.
The maximum heat flux of 101.78 W/cm2 was associated with sample 4 regarding the highest roughness as well as the highest NSD. In addition, it was inferred that the superior surface characteristics of the micro/nanostructured coatings resulted in an enhanced heat transfer coefficient (HTC) value.
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This research investigates a numerical simulation of swirling turbulent non-premixed combustion. The effects on the combustion characteristics are examined with three turbulence models: namely as the ...Reynolds stress model, spectral turbulence analysis and Re-Normalization Group. In addition, the P-1 and discrete ordinate (DO) models are used to simulate the radiative heat transfer in this model. The governing equations associated with the required boundary conditions are solved using the numerical model. The accuracy of this model is validated with the published experimental data and the comparison elucidates that there is a reasonable agreement between the obtained values from this model and the corresponding experimental quantities. Among different models proposed in this research, the Reynolds stress model with the Probability Density Function (PDF) approach is more accurate (nearly up to 50%) than other turbulent models for a swirling flow field. Regarding the effect of radiative heat transfer model, it is observed that the discrete ordinate model is more precise than the P-1 model in anticipating the experimental behavior. This model is able to simulate the subcritical nature of the isothermal flow as well as the size and shape of the internal recirculation induced by the swirl due to combustion.
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•A PDF approach is used to predict the turbulent non-premixed combustion.•Three turbulent models (RSM, STA and RNG) are employed for modeling the swirling flows.•P-1 and DO models are implemented for the simulation of the radiative heat transfer.•The use of the RSM and DO models to predict turbulence and radiative heat transfer, respectively, show better accuracy.•Increasing the swirl number augments the turbulence intensity and fluid recirculation.
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