Showing papers in "International Journal of Heat and Technology in 2020"
TL;DR: In this paper, the authors developed the applied aspects of the theory of solving nonlinear problems, provisions of the analytical methodology and the methods for regulating stepwise thermodynamic processes based on adapted tools for approximating generalized and step functions.
Abstract: Received: 9 October 2019 Accepted: 22 January 2020 The need to increase the accuracy of decisions and the depth of analysis of complex heat power systems determines the relevance of modeling and regulation of heat and mass transfer processes with the development of theoretical models and the development of a new methodology. Uncertainty of the environment increases the significance of the problems of insufficient efficiency of the available numerical approaches to the modeling of dynamic processes and the regulation of heating elements. Therefore, the aim of the article was to develop the applied aspects of the theory of solving nonlinear problems, provisions of the analytical methodology and the methods for regulating stepwise thermodynamic processes based on adapted tools for approximating generalized and step functions. The following tasks were solved: the structure of mechanisms was determined, including regulators of the energy efficiency of the flare device of the boiler unit with an expanded combustion zone; a model of integration-balancing regulation of heat transfer with four types of unsteady processes determined by indicators of changes in the direction and sign of the entropy of the effects of the regulators is proposed. Quantitative meters of energy efficiency of combustion and heat transfer processes in boiler units have been developed. Mathematical adapted and developed technical and organizational methods for solving problems: approximation of the original functions (generalized Dirac and stepwise) by a sequence of recursive periodic functions; simulation of spasmodic heat transfer processes based on step functions; structuring the mechanism for regulating heat transfer, including four types of regulators; empirical modeling of the assessment and regulation of energy efficiency, taking into account the directivity and severity of the effects of regulators displayed by derivatives of higher orders of approximation of energy efficiency functions. The results were obtained: mathematical ones were adapted and new approximation models for generalized functions were built; quantitative measuring instruments of process dynamics for regulating the technical and organizational mechanisms of heat transfer were obtained.
17 citations
TL;DR: In this article, the effect of thermal buoyancy on aerodynamic parameters such as drag and lift coefficients, Nusselt number and Strouhal number are also studied in the mixed convection regime.
Abstract: Received: 23 April 2019 Accepted: 10 February 2020 The present work aims to numerically investigate the upward flow of air past an inclined square cylinder with an incidence angle equal to 45 in the mixed convection regime at a fixed Reynolds number Re = 100. The governing equations are modelled by considering Boussinesq approximation. The critical Richardson number (Ric) for the suppression of vortex shedding (VS) is determined. By observing the instantaneous streamline patterns and the coefficient of lift plot with time near the critical value, it is found that VS suppression occurs at Ric = 0.78. Also, the aerodynamic characteristics such as lift and drag coefficient, the heat transfer characteristic, and the Strouhal number are studied by varying Ri in the range of [0.2, 1]. The role of thermal buoyancy on the aerodynamic parameters such as drag and lift coefficients, Nusselt number and Strouhal number are also studied in the mixed convection regime. It is found that mean drag coefficient and Nusselt number increases with the increase in Ri, and no lift is developed for any Ri, while the Strouhal number increases with increase in Ri and vanishes at a critical Richardson number. Further, the effect of thermal buoyancy on streamlines, isotherms and iso-vorticity contours are also presented.
13 citations
TL;DR: In this paper, the authors investigated the heat and mass transfer flow of gyrotactic microorganisms and nanofluids with allowance for chemical reaction and heat generation through a porous medium past a nonlinear stretching sheet.
Abstract: Received: 20 March 2020 Accepted: 2 June 2020 The insertion of microorganisms (microbes) in commonly used nanofluids is helpful to enhance the thermal efficiency in many systems such as bio-microsystems like chipshaped microdevices, microbial fuel cells, enzyme biosensor and microfluidics devices like micro-volumes and bacteria powered micro-mixers. The utilization of porous media is another way to enhance the thermal efficiency. Our concern in this article is to numerically investigate the heat and mass transfer flow of gyrotactic microorganisms and nanofluids with allowance for chemical reaction and heat generation through a porous medium past a nonlinear stretching sheet. The fully coupled nonlinear system of equations is solved by employing the SOR (Successive over Relaxation) method. The repercussions of preeminent parameters on the flow, heat and mass transfer as well as microorganisms diffusion rate are deliberated and shown through graphs and tables. The culminations evidently disclose that the bioconvection Peclet number and the motile microbes parameter enhance the density of the motile microorganisms. It is also found that porous medium has negligible effect on motile microbes’ concentration while it significantly enhances the shear stress.
12 citations
TL;DR: In this article, a case study of the life cycle assessment of the Palazzo del Sedile, an historical building located in Matera, Italy, is presented, where three methods of assessment are largely described, the choice has been made due to their significance in expressing the environmental effects from three different perspectives.
Abstract: Received: 19 November 2019 Accepted: 17 February 2020 For some years now the regulations in the sustainability field oriented the practitioners towards an increasing restraint concerning energy necessities, to reconsider the weight in terms of energy and environmental impacts associated with different phases of their life cycle. Among the reliable models to carry out the valuation, the Life Cycle Assessment remains a useful tool that determine the most impactful stages of the life cycle of any process and, thus, its environmental performances. This paper aims to develop and complete previous analyses on sustainability led on the historical heritage of the city of Matera, highlighting all the issues that are still unresolved and the possible solutions to be undertaken. Deep considerations on sustainability and its peculiarities are carried out. A reported analysis of literature and a description of the methods and tools used in the case study are shown. The case study consists in performing the LCA using SimaPro software, based on the assumptions aimed to the energetic retrofit for “Palazzo del Sedile”, an historical building located in Matera, Italy. In this section, three methods of assessment are largely described, the choice has been made due to their significance in expressing the environmental effects from three very different perspectives.
9 citations
TL;DR: In this paper, the authors focused on the estimation of convective heat transfer and friction factor of vacuum pump oil/Fe3O4 magnetic nanofluids flow in a tube under laminar flow at high Prandtl numbers experimentally.
Abstract: Received: 15 February 2020 Accepted: 23 April 2020 The work is focused on the estimation of convective heat transfer and friction factor of vacuum pump oil/Fe3O4 magnetic nanofluids flow in a tube under laminar flow at high Prandtl numbers experimentally. The thermophysical properties also studied experimentally at different particle concentrations and temperatures. The Fe3O4 nanoparticles were synthesized using the chemical reaction method and characterized using X-ray powder diffraction (XRD) and vibrating sample magnetometer (VSM) techniques. The experiments were conducted at mass flow rate from 0.04 kg/s to 0.208 kg/s, volume concentration from 0.05% to 0.5%, Prandtl numbers from 440 to 2534 and Graetz numbers from 500 to 3000. The results reveal that, the thermal conductivity and viscosity enhancements are 9% and 1.75-times for 0.5 vol. % of nanofluid at a temperature of 60°C, respectively, compared with base fluid data. The heat transfer enhancement is 13.1% and 17.8%, the Nusselt number enhancement is 8.95% and 13.48% for 0.5 vol. % of nanofluid at mass flow rates of 0.0416 kg/s and 0.208 kg/s, respectively, compared with base fluid data with a friction factor penalty of 1.21-times. The correlations of Nusselt number and friction factor were proposed based on the experimental data at high Prandtl numbers.
9 citations
TL;DR: In this article, the impact of magnetic parameter, Prandtl number, permeability coefficient, heat source/sink volumetric rate and temperature difference between heated plate and ambient temperature was examined adjacent to a moving heated vertical plate subjected to a magnetic field and a heat source.
Abstract: Newtonian steady state flow of fluids with electrical conduction properties was examined adjacent to a moving heated vertical plate subjected to a magnetic field and a heat source/sink. The impact of magnetic parameter, Prandtl number, permeability coefficient, heat source/sink volumetric rate and temperature difference between heated plate and ambient temperature. A reduced system of ODEs was created via group similarity method. The solution led to some important results. Increasing permeability coefficient of the plate material resulted in a significant increase in flow velocity and a slight increase in heat flux but the magnitude of shear stress and temperature distribution decreased. Moreover, increasing the magnetic parameter, M, led to a significant decrease in velocity and a decrease in heat flux, whereas shear stress and temperature distribution increased. Furthermore, increasing Prandtl number, Pr, reduced the velocity significantly and the heat flux slightly. On the other hand, the magnitude of shear stress and temperature distribution increased. In case of using heat source, the increase in its energy rate decreased the heat flux with no significant effect on shear stress. Finally, the increment of temperature difference led to noticeable increase in velocity and a slight increase in heat flux, whereas the shear stress decreased.
9 citations
TL;DR: In this article, the authors performed a comparative analysis of two-dimensional transient water-copper oxide nanofluid flow and heat transportation inside a right-, acute and obtuse-angled triangular cavity in the presence of a magnetic field.
Abstract: Received: 27 December 2019 Accepted: 20 February 2020 This paper performs a comparative analysis of two-dimensional transient water-copper oxide nanofluid flow and heat transportation inside a right-, acuteand obtuse-angled triangular cavity in the presence of a magnetic field. The vertical and inclined walls of the enclosure are maintained at a constant low temperature whereas the base wall is heated by a uniform thermal condition. The finite element method is used to solve the principal equations of nanofluid within the cavities along with the wall conditions. The outcomes of the present problem for a specific case are verified by the standard published numerical results. For comparative analysis, the isotherms, streamlines, the heat transfer distribution, the average heat transfer rate on the heated wall and within the cavities for the several pertinent parameters of the problem are demonstrated. The result shows that the nanofluid filled obtuse-angled triangular cavity exhibits a higher heat transfer rate for the lower and moderate values of the thermal Rayleigh number whereas for the higher thermal Rayleigh number acute-angled triangular cavity shows better heat transfer performance than that of the other two cases analyzed in the present study. The presence of a magnetic field lessens the heat transfer rate in nanofluid applications. The magnetic field inclination angle controls the flow and heat transfer of nanofluid. Nanofluid flow shows insignificant effects of the friction in cavities compared to that of the base fluid.
8 citations
TL;DR: In this paper, a computational fluid dynamics (CFD) study was conducted to analyse the flow structure and the effect of varying the coil pitch on the coil friction factor and wall shear stress, through utilising different models' configurations.
Abstract: A computational fluid dynamics (CFD) study was conducted to analyse the flow structure and the effect of varying the coil pitch on the coil friction factor and wall shear stress, through utilising different models’ configurations. Three coils were tested, all of them having the same diameter and coil diameter: 0.005m and 0.04m respectively. Pitch variations began with 0.01, 0.05, 0.25 m for the first, second and third model respectively. Two turbulence models, STD(k-ϵ) and STD(k-w), were utilised in this simulation in order to determine the turbulence model which could capture most of the flow characteristics. A comparison was made between the STD(k-ϵ) and STD(k-w) models in order to analyse the pros and cons of each model. The results were validated with Ito’s equation for turbulent flow and compared with Filonenko’s equation for a straight pipe. The governing equations were discretized using finite volumes method and the SIMPLE algorithm was used to solve the equations iteratively. All the models were simulated using the ANSYS Fluent solver CFD commercial code. The results showed that in turbulent flows, Dean number had a stronger effect on reducing coil friction factor than the increment in pitch dimension.
7 citations
TL;DR: In this article, the effects of Stefan blowing when a non-Newtonian Casson base fluid flows over a surface which stretches linearly, and the impact of pertaining parameters on the dimensionless velocity, temperature and concentration were presented explicitly.
Abstract: Heat transfer analysis in nanofluids is an active research field due to its extraordinary physical and chemical properties In the current study, the focus lies on the effects of Stefan blowing when a non-Newtonian Casson base fluid flows over a surface which stretches linearly A uniform transverse magnetic field is employed The chemical reaction in the fluid with activation energy and radiation effects have also been engaging the attention Fundamental laws of conservation are employed to model governing equations of flow Similarity transform is introduced to reduce the said system of partial differential equations to ordinary differential equations which are in turn tackled analytically using Homotopy Analysis Method with genetic algorithms to optimise the series solution The impact of pertaining parameters on the dimensionless velocity, temperature and concentration were presented explicitly This study relevant to remedies for malign tissues, cells or clogged arteries of the heart
7 citations
TL;DR: In this article, the authors aim to improve the traditional fin structure of the air-cooled heat exchanger (ACHE) and propose the use of corrugated fin structure.
Abstract: Received: 18 April 2020 Accepted: 9 July 2020 In view of the heat transfer and ventilation characteristics of the Insulated Gate Bipolar Transistor (IGBT) in the Electric Multiple Unit (EMU), the authors aim to improve the traditional fin structure of the air-cooled heat exchanger (ACHE) and propose the use of corrugated fin structure. Using the computational fluid dynamics (CFD) technology, the ACHE with new fin structure was numerically simulated, and the temperature field, velocity field and pressure field at different fin corrugation angles and the synergy between the fields were analyzed. The results show that the improved fin structure can make the fluid flow in a corrugated flow channel, effectively increase the flow distance, and thus significantly enhance the turbulence performance of the fluid in the ACHE; the fin corrugation angle of 120 degrees is the key design point; compared with the traditional fin structure, the new fin structure improves the synergy between the various fields and increases the heat exchange efficiency. The research findings provide new ideas for the design of this type of ACHE.
6 citations
TL;DR: In this paper, the effect of thermal radiation on natural convection of several water-based nanofluids H2O-(Cu, Al2O3, Ag, TiO2) in a partially heated cubical cavity where the left vertical side is heated by three identical and parallel elements.
Abstract: Received: 20 October 2019 Accepted: 14 January 2020 This study investigates the effect of thermal radiation on natural convection of several water-based nanofluids H2O-(Cu, Al2O3, Ag, TiO2) in a partially heated cubical cavity where the left vertical side is heated by three identical and parallel elements. The right vertical side is totally cooled, and the other ones are kept adiabatic. A developed code based on the finite volume method and the Rosseland approximation is used to solve the governing equations. Calculations were performed for three inclination angles of the rectangular heating elements 0°, 45° and 90°. The effect of governing parameters, namely, Rayleigh number, solid volume fraction, radiation parameter, dimensionless spacing of the three heating elements, their aspect ratio and different type of nanoparticles on the velocity contours, isotherms as well as local and average Nusselt number were considered. The results indicate that the inclination angle has a considerable effect on the dynamic and thermal fields, but its effect on the average heat transfer is insignificant. The total Nusselt number increases with the volume fraction of nanoparticles, the radiation parameter and the aspect ratio of the heated elements. The numerical results also revealed that the Cu and Ag-water nanofluid offer a better heat exchange.
TL;DR: In this paper, a numerical model for the rock-breaking and slag discharge of pipe jacking machine (PJM) with different tunneling parameters, and numerically analyzes the variations in the flow rate and speed of slags, and the stress and deformation of cutterhead, at different cutterhead speeds (1.0-4.0r/min) and jacking speeds (0.5- 4.0mm/s).
Abstract: Received: 21 June 2020 Accepted: 17 September 2020 During pipe jacking in unstable coal rock formation, it is difficult to ensure the stability of the workface and the structural safety of the equipment. To solve the problem, this paper establishes a numerical model for the rock-breaking and slag discharge of pipe jacking machine (PJM) with different tunneling parameters, and numerically analyzes the variations in the flow rate and speed of slags, and the stress and deformation of cutterhead, at different cutterhead speeds (1.0-4.0r/min) and jacking speeds (0.5-4.0mm/s). Based on the simulation results, the authors discussed how different tunneling parameters affect the tunneling safety. The simulation results highlight the importance of the matching between cutterhead speed and jacking speed to tunneling safety. As the jacking speed increased, the load of the cutterhead increased significantly, which may cause the cutter to wear. At the jacking speed of 4.0mm/s, the equivalent stress and deformation of cutterhead peaked at 397.43MPa, and 10.73mm, respectively. Excessive jacking speed may result in accidents, such as deformation and structural fracture of cutterhead, posing a serious threat to the structural safety of cutterhead. As the cutterhead speed increased from 1.0r/min to 4.0r/min, the mean axial speed of slags dropped by 68%, and the slag flow rate declined by 76%, due to the rapid discharge of slags from the cabin. In this case, the slag volume in the cabin cannot provide sufficient support to the workface rock, and the risk of collapse soars during the tunneling in unstable formation. In addition, an excessive cutterhead speed increased tunneling energy consumption and aggravated the wear of the cutterhead. The research results promote the setting of control parameters for the safe pipe jacking in unstable coal rock formation.
TL;DR: In this paper, the Darcy-Brinkman model was considered for modeling porous media with nano-fluid and the results have demonstrated the increasing in the value of the Rayleigh and Darcy numbers as well as nanofluid volume fraction enhances both fluid flow strength and average of heat transfer.
Abstract: Received: 22 December 2019 Accepted: 14 May 2020 The present work demonstrates the natural convection of two layers filled the space between inner circular cylinder located within wavy enclosure using finite element scheme. The right layer is filled with Ag nano-fluid while the left layer is filled saturated porous media and the same nanofluid. The governing equations of fluid flow and heat transfer (mass, energy and momentum of the fluid) have been formulated in dimensionless form with related initial and boundary conditions the numerical solution include the subdividing the fluid flow domain to two sets of transport equations. The Darcy-Brinkman model was considered for modeling porous media with nano-fluid. The considered dimensionless parameters are Rayleigh number (106≥Ra≥103), Darcy number (10-1≥Da≥10-5), cylinder’s radius (0.4≥R≥0.2), circular cylinder vertical position (+0.2≥δ≥-0.2), the number of undulation (3≥N≥0) and nano-particle volume fraction (0.1≥φ≥0). The nanofluid is combining of Ag solid particle and water as a main fluid. The results were presented according to the stream-lines, isotherms, local and the mean of Nusselt number. The results have demonstrated the increasing in the value of the Rayleigh and Darcy numbers as well as nanofluid volume fraction enhances both fluid flow strength and average of heat transfer. It has been concluded that when the number of undulations N = 1 gives better heat transfers enhancement. It is recommended that for better heat transfer average to move the internal circular cylinder with radius (R = 0.2) vertically downward (δ=-0.2) with undulations’ number (N=1).
TL;DR: In this article, the numerical simulation of natural convection in a closed model greenhouse heated by tubes was studied and the obtained results present a good agreement with the experimental data and show a strong dependence of the air climate in the greenhouse.
Abstract: Received: 15 September 2019 Accepted: 27 December 2019 In this work, we interested to the numerical simulation of natural convection in a closed model greenhouse heated by tubes. A greenhouse box subjected to different boundary conditions on the roof like the imposed temperature, convective flux and mixed flux was studied. The considered mathematical model is a system of partial differential equations formed by the continuity, the momentum and the energy equations. The commercial Computational Fluid Dynamics (CFD) code Fluent was used for numerical simulations based on a finite volume method. In each case, we have studied the thermal and dynamic flow parameters in the greenhouse, such as the average velocity and the average temperature. The obtained results present a good agreement with the experimental data and show a strong dependence of the air climate in the greenhouse. These results help the farmers to set up a greenhouse with materials and dimensions suitable for external conditions.
TL;DR: In this article, the authors presented a dynamic energy modeling based on an energy-balance of residential buildings which uses urban-scale data, taking into account the microclimate conditions and morphological urban scale parameters.
Abstract: Received: 20 June 2020 Accepted: 30 July 2020 The development of urban-scale energy modeling is currently the goal of many research groups as a result of to the increased interest in evaluating the impacts of energy efficiency measures in cities. These energy models are useful to explore consumption and emission distribution at district scale and to quantitatively assess renovation strategies and energy supply options. This work presents a dynamic energy modeling based on an energy-balance of residential buildings which uses urban-scale data. The model was designed to take into account the microclimate conditions and morphological urban-scale parameters. This methodology was calibrated, optimized and validated by applying it to a district in the city of Turin. In addition, a thermal-electricity analogy has been implemented in a software for scientific computation and simulation to manage big database. Therefore, a new model based on thermal-electrical analogies, which can be applied to a larger building stock, is presented. A sensitivity analysis has highlighted the different types of behavior of building considering their periods of constructions. The results of this work show that this model can also be applied at a district scale with good accuracy, especially for old buildings, to manage the existing large databases for analyses at an urban or territorial scale; for newer buildings needs to be improved.
TL;DR: In this paper, an extensive numerical investigation of the heat transfer characteristics and the pressure force of jet impingement from the single row and multiple rows on a fixed and moving flat surface are reported.
Abstract: Received: 20 September 2019 Accepted: 12 July 2020 In this paper extensive numerical investigation of the heat transfer characteristics and the pressure force of jet impingement from the single row and multiple rows on a fixed and moving flat surface are reported. The computations were carried out over a wide range of parameters: relative nozzle-to-surface distance (H/d) from 0.5 to 6, relative nozzle to nozzle distances (S/d) from 4 to 10, jet angle from 45° to 90°, relative velocity ratio (Vplate/Vj) i.e. ratio of surface velocity to jet velocity from 0 to 1. The jet Reynolds number (Re) of 2,500, 3,400, 10,000, 20,000, and 23,000 and the number of jet rows of 1, 2, 4, and 8 have been used. It was found that the numerical accuracy by SST k-ω model is reasonably high to allow for a discussion of the main flow and heat transfer characteristics. The jet impingement heat transfer performance is generally enhanced with the increase of jet Reynolds number and jet angle and with the decrease of surface distance (H/d), jet distance (S/d) and the relative velocity ratio (Vplate/Vj) within the range examined. The pressure force coefficients on the impingement surface are relatively insensitive to Re number and the velocity ratio within the range examined, while it has highly dependent on H/d, S/d and jet angle. For multiple rows of aligned jet holes, the flow pattern exhibited a different shape due to the different intensity of the interference between adjacent air jets. The effect of multiple rows with regards to the impact on average Nu and pressure force coefficient for different geometry variations such as Re, H/d, S/d, VR and ɵ is negligible compared to the single row by approximately 9 and 13% in average respectively. Based on the computed results, equations of dimensionless parameters are correlated.
TL;DR: In this paper, the authors analyzed the behavior of radiation heat flux emitted by materials of different linear densities and porosities, varying the rate of air/fuel mixture and the flame power.
Abstract: Received: 10 December 2019 Accepted: 15 February 2020 Porous media burners have been the focus of many studies due to the advantage in different applications in industry, which exhibit a directional emission of thermal radiation and low emission of pollutants. Indeed, these characteristics yields benefits regarding productivity by an environment friendly process. Thus, this work analyzes the behavior of radiation heat flux emitted by materials of different linear densities and porosities, varying the rate of air/fuel mixture and the flame power. In this way, was constructed an experimental setup that consists in a supply system of air/fuel, data acquisition, burner support for the radiation sensor, and the radiometer. This structure enables the displacement from 0°C to 90°C allowing the analysis of radiation in the area of a semisphere. The results shown that the silicon carbide has higher radiation efficiency than zirconia, due the higher thermal conductivity and emissivity. However, the silicon carbide degraded in one of the measurements. The ZrO2 media has proved challenging to stabilize for equivalence ratios below 0.6. Regarding the porosity, it is concluded that the higher the porosity, the greater the radiation efficiency, the expected result because there is a larger contact area for the reaction to occur within the pores.
TL;DR: In this paper, the effects of aerogel application on the thermal properties of textile packages intended for use in protective clothing were investigated, and the developed packages were tested for resistance to the three major types of heat: radiant, convective, and contact.
Abstract: Received: 15 June 2020 Accepted: 3 Spetember 2020 The aim of this study was to investigate the effects of aerogel application on the thermal properties of textile packages intended for use in protective clothing. The packages were prepared in the form of removable inserts filled with aerogel, differing in terms of fabric and design. The developed packages were tested for resistance to the three major types of heat: radiant, convective, and contact. The package variant with superior thermal performance was also evaluated for water vapor resistance. The package after incorporation of aerogel was found to approximately double radiant and convective heat resistance, with an approx. eightfold improvement for contact heat at the highest test temperature 250°C. Threshold time increased from (17.7±0.7) s to (139.9±4.9) s for the optimum aerogel-enhanced package variant with the greatest number of pouches, which met the criteria of the highest performance level. The thermal conductivity and thermal resistance of three fabrics selected for testing were tested in order to determine their basic thermal insulation properties. In general, packages containing a larger number of narrower pouches exhibited higher thermal protective performance. The results show that the developed textile packages with aerogel can be successfully used in thermal protective clothing.
TL;DR: In this paper, a simplified calculation method to evaluate the thermodynamic performance of two solar tower power plants of 50 MW is proposed, which consist in an open air Brayton cycle and a Brayton-Rankine combined cycle.
Abstract: Received: 2 July 2020 Accepted: 15 September 2020 In this study, a simplified calculation method to evaluate the thermodynamic performance of two solar tower power plants of 50 MW is proposed. The systems consist in an open air Brayton cycle and a Brayton-Rankine combined cycle. The electricity produced, the average annual efficiency of the heliostats field-receiver system, the efficiency of the thermodynamic cycle and of the entire plant have been determined for both systems. The performances of the two plants have been compared to conventional plants using molten salts. The analysis shows that both systems have better performances than conventional solar tower plants using molten salts. The specific annual electrical energy per square meter of heliostat is higher than that obtained for the plant using molten salts, by 11.5% and 38.7% for the Brayton and the Brayton-Rankine combined cycle respectively. Moreover, an economic analysis has been performed. The results show that a reduction of the Levelized cost of Electricity (LCOE) can be achieved compared to the traditional molten salt plants, with savings of 15% and 13.6% for the Brayton and combined cycle respectively.
TL;DR: In this paper, a numerical investigation of convection in ventilation square cavities contains parallel insulated baffles, where the opening slots are positioned at the top, bottom corners of the hot vertical walls, and the governing Navier-Stokes equations are formulated in the form of vorticity stream functions.
Abstract: This research reports the outcome of a numerical investigation of convection in ventilation square cavities contains parallel insulated baffles. The left and right walls of the cavity are kept at the high temperature. Whereas the top, bottom cavity walls, parallel baffles are adiabatic. The opening slots are positioned at the top, bottom corners of the hot vertical walls. The governing Navier-Stokes equations are formulated in the form of vorticity- stream functions. The finite difference method is used to find the values of the primitive variables. The effects of baffles size (Sb − 0.25, 0.50, 0.75), 3 various positions of the parallel baffle, Rayleigh number (103 − 106), Reynolds number (30, 300, 600) are discussed with the flow fields, isotherms, and Nusselt number. It is found that the behavior of ventilation cavities does not only depend on the size of the baffles and its positions. It highly depends on the configuration of the ventilation cavity too. Further, the flow fields are restricted by the largest baffles size of Sb = 0.75.
TL;DR: In this paper, an experimental study has been carried out to investigate a method to reduce the water tank temperature and used it in room air condition in the hot season (July and August) in Iraq.
Abstract: Received: 4 February 2020 Accepted: 17 May 2020 In the present work, an experimental study has been carried out to investigate a method to reduce the water tank temperature and used it in room air condition. The tests were conducted in the hot season (July and August) in Iraq. The results proved that the device succeeded in reducing the water tank temperature to 23°C, which is a low temperature in the summer and kept at this value by continuous work of the device. It was almost constant at the hot afternoon compared to the temperature of the uncooled tank, which reached its temperature at 2:00 pm to about 43°C and the difference was 46.5%. The dry air temperature of the test room is very close to the temperature of the house room air (3033) °C, compared to the ambient temperature (45-50) °C. Decrease in the relative humidity to (51-45) % for the test room compared with house room (94-90) %. The power consumption of the system is lower than traditional air evaporative cooler in a rate of 67%.
TL;DR: The LME Laboratory of Mechanics, Department of Mechanical Engineering, University of Laghouat, LaghOUAT 03000, Algeria as mentioned in this paper and the Laboratory of Electromechanical Systems, National School of Engineers of Sfax, Universityof Sfax Sfax 3038, Tunisia
Abstract: 1 LME Laboratory of Mechanics, Department of Mechanical Engineering. University of Laghouat, Laghouat 03000, Algeria 2 LABTHOP Laboratory, Faculty of Sciences, University of El Oued, El Oued 39000, Algeria 3 Kocaeli University, Engineering Faculty, Mechanical Engineering Department, Kocaeli 41001, Turkey 4 Laboratory of Electromechanical Systems, National School of Engineers of Sfax, University of Sfax, Sfax 3038, Tunisia
TL;DR: In this article, a nonlinear two-dimensional unsteady flow model is created to decompose heat and mass transfer of this fluid, which is shaped by taking appropriate boundary conditions.
Abstract: Magnetohydrodynamic (MHD) unsteady flow of incompressible, electrically conducting, and viscous fluid passing through a vertical porous plate is explored in this investigation where the impact of thermal radiation and chemical reaction are presented. A nonlinear two-dimensional unsteady flow model is created to decompose heat and mass transfer of this fluid, which is shaped by taking appropriate boundary conditions. The governing equations are solved analytically with satisfactory boundary conditions by using a two-term perturbation technique. The analytical outcomes are illustrated graphically by using MATHEMATICA 7.0. The fundamental equations are also solved numerically by utilizing explicit finite difference methodology (EFDM) with the help of Compaq Visual Fortran 6.6a. The numerical arrangement is also depicted graphically to examine the outcomes. The acquired pertinent parameters are analysed conveniently, including thermal Grashof number, thermal radiation parameter, and chemical reaction parameter, the permeability of the porous medium, magnetic parameter, Prandtl number, modified Grashof number, and Schmidt number. It is observed from our experiment that the velocity and concentric profiles decline when the reaction rate between the molecules is high. Furthermore, a suitable validation has been done with the previously published articles, and a favorable agreement is observed.
TL;DR: In this article, the authors used probability density functions based on the maximum entropy method to stand for the complete atomization characteristics of spray dynamics, and evaluated the capability of using the model for the initial predictions of the droplet size and velocity distribution for liquid nitrogen spray of solid-cone pressure swirl nozzle.
Abstract: Received: 26 March 2020 Accepted: 3 June 2020 The polydispersed nature of the spray is captured through the use of probability density functions based on the maximum entropy method to stand for the complete atomization characteristics of spray dynamics. The droplet and velocity size distributions are practical tools for the analysis of sprays cooling. The special benefit of the model is a Eulerian based which is less computationally intensive when compared to models that are based on the Lagrangian approach that tracks droplet parcel. The accuracy of using Lagrangian approach in polydispersed phase is always accurately less than Eulerian approach because it depends on the number of parcels while in Eulerian approach it depends on the proposed continuous distribution function. The main intent of the current work is to evaluate the capability of using the model for the initial predictions of the droplet size and velocity distribution for liquid nitrogen spray of solid-cone pressure swirl nozzle. The use of liquid injection pressure cases of up to 0.6MPa and spray cone angles of just 30◦ from three different sets of experimental data. The results being characterized are spray drop size distribution, liquid volume fraction and spray cone angle values. The unsteady analyses of the effect of injection pressure are studied on the cryogenic liquid nitrogen. The numerical results show that the maximum entropy method applies to liquid cryogenic spray and indicates that the model reacts correctly to changes in different injection pressures. Comparisons are also made with measured drop size distribution data that are reasonably captured and the spray cone angle is found to be in good agreement during initial and farfield spray angles.
TL;DR: In this article, the authors explore the thermal performance of prefabricated building wall under cold conditions, and study the energy-efficient technology by determining the optimal thickness of the insulation layer.
Abstract: Received: 18 August 2019 Accepted: 20 December 2019 At present, prefabricated buildings have been widely used in residential buildings and industrial plants. The energy-efficient design of their walls has increasingly become the focus of design in the construction industry. Taking the commonly used composite walls of prefabricated buildings in Inner Mongolia as the research object, the authors aim to explore the thermal performance of prefabricated building wall under cold conditions, and study the energy-efficient technology by determining the optimal thickness of the insulation layer. The study found that the external envelope structure such as the walls is the main heat dissipation method of the prefabricated building; as the thickness of the insulation layer increases, the thermal conductivity of the wall decreases, and the thermal inertia index increases, showing better insulation characteristics; the heat flux density of the composite wall designed with the external insulation layer was the smallest; the average daily heating power consumption of the composite wall with the polystyrene plastic interlayer was the minimum, and it reduced by 21.65% compared with the no-intermediary insulation layer. The research findings provide guidance and suggestions for the composite wall design and material selection of prefabricated buildings in Inner Mongolia.
TL;DR: In this paper, the authors focused on the study of natural convection in a porous square cavity saturated by a nanofluid (Al2O3-Water) in the presence of a corrugated heat source.
Abstract: Received: 27 January 2020 Accepted: 14 May 2020 The present paper is focused on the study of natural convection in a porous square cavity saturated by a nanofluid (Al2O3-Water) in the presence of a corrugated heat source. The horizontal walls and the hatched parts of the vertical walls are considered adiabatic. The corrugated portions of the vertical walls are maintained at uniform and constant temperatures. The basic equations describing the natural convection flow consist of mass conservation, Darcy-Brinkman and energy were solved by means of finite element method. For the physical parameters of (Al2O3-water) nanofluid, we use the Brinkman and Maxwell models. The results are presented as isotherms, streamlines, average Nusselt number, velocity and temperature profiles for various combinations of Modified Rayleigh number, volume fraction of nanoparticles, amplitude and both sources position. It is found that the heat transfer increases with the increase of Modified Rayleigh number, volume fraction and amplitude. The hot source is at the bottom and the cold source is at the top is the optimal position of the two sources to evacuate better the convection heat transfer.
TL;DR: In this paper, the role of roofing element in reducing solar gain was investigated in six test rooms with different roof types (RCC roof, galvanized iron sheet roof, lawn over RCC roof and thatched roof) under summer weather conditions.
Abstract: Received: 12 July 2019 Accepted: 25 January 2020 Six test rooms each with different roof type (RCC roof; galvanized iron sheet roof; lawn over RCC roof; wet-sand bed over RCC roof; clay tile roof and thatched roof) under summer weather conditions are studied to analyze and quantify the role of roof element in reducing solar gain. The study also addresses the effects of roofing element on the test room temperatures. Results have shown that, lawn over the RCC roof could be the best choice among the considered. On the other hand, clay tile roof and thatched roof are found to be better than RCC roof as far as heat gain is considered. It is also observed that, clay tile roof providing better breathing effects as compared to thatched roof.
TL;DR: In this paper, the combination of two types of fin was investigated to establish a scientific comparison between models, a constant weight of the heat sink has been imposed, for that the total size of the original model (longitudinal-fin) was stabilized.
Abstract: Received: 28 August 2019 Accepted: 14 December 2019 Each type of fin has been investigated separately in many researches that are concerned with finding its performance under varying operating conditions, enhancement of heat sink performance by using the combination between two types of fin was investigated in this study. To establish a scientific comparison between models, a constant weight of the heat sink has been imposed. For that the total size of the original model (longitudinal-fin) was stabilized. Converting part of the original size into spin fins led to the emergence of a hybrid design that was studied by analytical and computational simulation. Under natural convection and Ra=10, calculation process was performed for varying the surface area between (1-1.8) times. The strong agreement of the validation results (0.31 %-0.52 %) showed the reliability of the analytical model based on the ANSYS simulation. Hence, the results demonstrated that the hybrid designs have a discrimination in several aspects; reducing the fin temperatures is about (2.7% to 8.8%), lower thermal resistance by (24% to 46%) and augmentation of heat transferred by (31% -80%), compared with original heat sink. Improvement of thermal resistance and heat transferred does not behave in the same approach with all models (area ratio of greater than 1.6), because of the overlap between the negative effect of convection coefficient and increase of surface area. So, the approximate steady state can be happened.
TL;DR: In this paper, the impact of the vertical arrangement of two cylinders on flow with high Reynolds number has been investigated via numerical modeling, and the results indicated that the flow pattern is irregular and unstable for denser arrangements while the propagation of vortices does not have any tendency in different spacing.
Abstract: Received: 3 April 2019 Accepted: 26 December 2019 The fluid flow around a cylinder is one of the classic issues in fluid mechanics because of its various applications. Cylindrical structures, both single and in the group patterns, are present in the design of cooling systems of nuclear power plants, hydro-structures, heat exchangers, chimneys, high buildings, power lines, cables and networks in air and water. In many engineering applications, Karman's vortex shedding produces flow-induced vibrations. To comprehend the fluid structures surrounding the cylinders, it is vital to understand some fundamental issues such as boundary layers, flow separation, free shear layer, sequence and dynamics of vortices. According to the limited studies conducted for the vertical arrangement of two cylinders in a flow with the high Reynolds number, there is no evidence of oblique flow or bi-stable pattern except in the case where cylinders are close to each other. In this paper, the impact of the vertical arrangement of two cylinders on flow with high Reynolds number has been investigated via numerical modelling. The results indicated that the flow pattern is irregular and unstable for denser arrangements while the propagation of vortices does not have any tendency in different spacing.
TL;DR: In this paper, a model of the chaotic motion of a nanoparticle is presented taking into account surface tension forces in a liquid coolant, and the experimental results of the work of Malaysian and Iran authors on the effect of TiO2 nanoparticles with a concentration of 0.5%; 1.0% and 1.5% in the main liquid solution of ethylene glycol (EG) in water in a volume ratio of 40:60% in terms of heat transfer coefficient are compared with their theoretical studies.
Abstract: Received: 3 November 2019 Accepted: 16 Feburary 2020 This article analyzes the vast material of works devoted to the use of nanofluids in heat exchange equipment. It is proved that the use of the classical theories and equations for calculating the viscosities and thermal conductivities of nanofluids is not correct, since it does not coincide with the experimental results of most independent authors. A model of the chaotic motion of a nanoparticle is presented taking into account surface tension forces in a liquid coolant. The experimental results of the work of Malaysian and Iran authors on the effect of TiO2 nanoparticles with a concentration of 0.5%; 1.0% and 1.5% in the main liquid solution of ethylene glycol (EG) in water in a volume ratio of 40:60% in terms of heat transfer coefficient are compared with our theoretical studies. The results of the experiments presented in: an increase in heat transfer coefficients by 9.72%, 22.75%, 28.92% for 1.5% volume concentration of TiO2 nanoparticles at a coolant temperature of 30°C, 50°C, 70°C, respectively. Our theoretical result: increase in the obtained heat transfer coefficients by 9.79%, 22.22%, 29.09% according to our formulas (9, 10, 15) for calculating turbulent viscosities and thermal conductivities, which takes into account the effect of surface tension forces on the total flow of nanofluids in the channels of heat exchange equipment. A new method for calculating heat exchange equipment using nanofluids is presented, taking into account the action of surface tension forces, as well as predetermining the calculation of turbulent viscosities and thermal conductivity of nanofluids. A theoretical calculations a plate heat exchangers for a technological task performed by classical and new method is presented. Similar results were obtained, which differ by about 0.5 of a percent. The plate heat exchanger was calculated using a new method using TiO2 nanoparticles in water and in a mixture of EG in water in a ratio of 40:60%, as well as when pumpkin vegetable oil was added to milk with the optimal concentration.