Showing papers in "International Journal of Heat and Technology in 2021"
TL;DR: In this article, the authors defined a methodology for the optimal design of grid connected PV-battery systems in urban environments and evaluated the technical feasibility of combining multiple residential users at city level.
Abstract: Received: 10 December 2020 Accepted: 6 February 2021 In Europe, 70% of citizens live in urban areas and consume around 75% of the primary energy supply. In order to reduce the impact of energy consumption and improve the competitiveness of local energy systems, Energy Communities may help to address the challenges of urban sustainability and energy security through local energy production and self-consumption. Solar, biomass and wind are the main sources of renewable energy that are generally used in cities. However, not all the sources available in urban environment are usable, due to the limited availability, or other technical or non-technical limits and constraints. In order to promote renewable energy technologies in buildings it is necessary to consider architectural, cultural, energy, technical and economic feasibility. This work defines a methodology for the optimal design of grid connected PV-battery systems in urban environments. The model was applied to two districts located in the city of Turin with the aim of evaluating the technical feasibility of combining multiple residential users at city level. The purpose of this work is to promote self-consumption and self-sufficiency from the network, using the integration of solar energy with PVbattery systems, and to reduce electrical losses in favor of both the single user and the distribution system. Results show that different values of self-sufficiency and selfconsumption can be reached depending on the shape and dimension of each building. It was shown that it is possible to satisfy the current requirements to become an Energy Community in an urban environment with good levels of self-sufficiency.
14 citations
TL;DR: In this paper, the effects of nonlinear thermal radiation and Joule heating on MHD three-dimensional visco-elastic nanofluid flow due to a surface stretching in lateral directions are examined.
Abstract: Received: 23 September 2019 Accepted: 12 November 2020 This work examines the effects of non-linear thermal radiation and Joule heating on MHD three-dimensional visco-elastic nanofluid flow due to a surface stretching in lateral directions. A coupled nonlinear differential system is generated from the boundary layer equations by using self-similarity variables and is then solved numerically by using most powerful shooting technique with Runge Kutta method of fourth order. The computational results for the flow variables are plotted graphically and are discussed in detail for various governing parameters that emerged in the analysis. It is observed that the momentum of the visco elastic nanofluid is better than that of a viscous fluid. Thicker thermal and concentration boundary layers are formed for increasing nonlinear thermal radiation and temperature ratio parameters. Also the results are in very good agreement with the outcomes available in the literature as a particular case. This model may play a significant role in the field of manufacturing and engineering applications.
13 citations
TL;DR: In this paper, the performance of a conventional PV panel with two organic phase change materials (PCMs) was investigated and the results showed that the PV-PCM units allow achieving higher performances in comparison with a conventional photovoltaic module, especially during the hottest months.
Abstract: Received: 1 April 2021 Accepted: 20 April 2021 The electrical efficiency of photovoltaic (PV) modules can be improved through the cooling of the PV. Among the passive cooling strategy, one of the most promising concerns the use of phase change materials (PCMs) to decrease the operative temperature of a PV panel. This paper investigates the performances of a conventional PV panel in which two organic PCMs are added (PV-PCM) to reduce the temperature rise of PV cells and consequently to increase the electrical performances. With this aim, unsteady numerical simulations have been carried with Ansys Fluent software using a two-dimensional simplified geometry for the PV modules with the PCM is incorporated (PV-PCM), as well as for the benchmark PV module. The numerical simulations have allowed evaluating the PV cell temperatures, the power production, as well the PCM thermal behavior. As regards this latter aspect the dynamic analysis has evidenced the need to extend the time of simulation at least for two days in such way to take into account of the degree of solidification achieved during the night by the PCM materials. PCM with low melting temperature cannot complete solidifying during the night and so the heat stored during the day will be lesser than the theoretical one. The results of this study pointed out that the PV-PCM units allow achieving higher performances in comparison with a conventional PV module, especially during the hottest months. An increase in the peak power of 10% and of 3.5% of the energy produced all year round is attained.
12 citations
TL;DR: This paper attempted to launch a research on the multi-objective energy-saving optimization design of buildings based on the application of green building materials, and gave the green levels of a few candidategreen building materials and the scores of the environmental impact factors, which had verified the effectiveness of the proposed algorithm.
Abstract: Received: 29 October 2020 Accepted: 5 January 2021 Green building materials have brought fundamental changes to the traditional construction methods, enabling better environmental protection and energy-saving performance of the buildings. However, due to the various material types and the large property differences, until now there isn’t a uniform evaluation index system (EIS) for green building materials, the existing studies on the green-level evaluation of green building materials during production and use are insufficient, and the research on energy-saving design is just getting started. For this reason, this paper attempted to launch a research on the multi-objective energy-saving optimization design of buildings based on the application of green building materials. First, the quantification method for the environmental impact factors of green building materials was elaborated, and the intervals and standards of the quantification evaluation were given; then, a green building material optimization selection model was constructed, and a multi-objective energy-saving optimization algorithm was proposed; at last, experimental results gave the green levels of a few candidate green building materials and the scores of the environmental impact factors, which had verified the effectiveness of the proposed algorithm.
12 citations
TL;DR: In this paper, a simulation of turbulent flow with a range of Reynolds number from 1000 to 15000 using CFD methods was carried out for turbulent flow and the numerical outcomes illustrate that change twisted tape configurations have more effect on flow and heat performance.
Abstract: Received: 26 November 2020 Accepted: 5 March 2021 In various industrial applications, the high performance of heat exchanger demand is increasing. Subsequently, the energy resources depletion, for instance, in power plant, airconditioning system and food processing systems. The important field for saving energy was through improving thermal performance, which can provide high performance heat exchanger. Present enhancing approaches can be classified by three changed types, which are passive technique, active technique and compound technique. Dimple, twisted tape and corrugated pipe are the passive heat improvement technique which includes more surface extensions. Hence, this research work concentrates on verifying the computational calculations of flow in the heat exchanger pipe with different surface extensions in the pipe. It is carried out for turbulent flow with a range of Reynolds number from 1000 to 15000 using CFD methods. The numerical outcomes illustrate that change twisted tape configurations have more effect on flow and heat performance. Experimental and numerical results agreement can confirm the simulation technique reliability, which adopts in this investigation. The deviation errors are observed by less than 6% compared with the normal pipe. Pressure drop increases due to the rise of twisted tape dimensions (width and thickness), leading to more mixing of fluid, secondary flow, and swirl flow inside the pipe. As the tape geometrical parameters increase, the f value also increases due to more variance in velocities flow between liquid layers, which are adjacent to tape surfaces a pipe wall, and pipe core flow layers, become higher. Correspondingly, compared to the normal pipe, twisted configurations can rise f about 5.4 to 33.5%. The better thermal evaluation factor is at a twisted tape of 1x1 mm at Re number of about 1000. The range value of the thermal evaluation factor is more than 1.67.
8 citations
TL;DR: In this paper, a thermal comfort study has been carried out in the kitchen environment of a non-air-conditioned railway pantry car in Indian Railways by determining the standard effective temperature (SET) index.
Abstract: Received: 7 July 2020 Accepted: 21 October 2020 There are ample literature studies available, focusing on hot-humid built environment, which have achieved an increase in thermal comfort conditions by proper installation of ventilation-systems. The present thermal comfort study has been carried out in the kitchen environment of a non-air-conditioned railway pantry car in Indian Railways. The purpose is to enhance thermal comfort level under the currently applied ventilation system inside the kitchen of pantry car by determining the standard effective temperature (SET) index. During the summer and winter seasons, a field study was carried out to obtain the value of air temperature, globe temperature, relative humidity, and air velocity inside the pantry car for estimation of the SET index. A computational fluid dynamics (CFD) analysis was used to obtain a better-modified case model of the pantry car kitchen for the improvement of thermal comfort. The design interventions for the pantry car kitchen were created, with emphasis on increasing energy efficiency based on low-power consumption air ventilation system. The study results indicated that, modified case-I model has a better ventilation design concept as compare to the existing and other models, which increased the air velocity and significantly decreased the air temperature inside the kitchen of pantry car at all cooking periods. A value of SET (28.6–30°C) was found with a comfortable thermal sensation within all cooking periods, which is better for the pantry car workers. This finding suggests a sustainable improvement in the thermal environment of the \"non-airconditioned\" pantry car kitchen in the Indian Railways, which can be applied immediately.
6 citations
TL;DR: In this paper, an explanatory case study on the production process of an Italian SME is presented and discussed, where the authors demonstrate that using thermodynamic models as Exergy and Life Cycle thinking provides major benefits since it allows evaluation results more reliable and aims to develop a retrofitting approach that enhances the process.
Abstract: Received: 2 January 2021 Accepted: 10 February 2021 The continuously rising cost of energy and its impact on environmental policy are the primary boost for industry to stay global competitive in terms of maximizing productivity and raising operational costs. The prevailing goal in the height of industry 4.0 is to inspect and optimize manufacturing processes. The challenge is to consider thermodynamics as simulation and modelling solution that enables improve energy production and help efforts to shift towards a smart factory. The aim of this paper is to demonstrate that using thermodynamic models as Exergy and Life Cycle thinking provides major benefits since it allows evaluation results more reliable and aims to develop a retrofitting approach that enhances the process to avoid system failures efficiently. Any practitioner may pick suitable sensing networks in line with Industry 4.0, in order to develop a monitoring and control infrastructure and improve any manufacturing system, getting it smarter. In this article, an explanatory case study on the production process of an Italian SME will be presented and discussed.
6 citations
TL;DR: In this article, the authors investigated the influence of surface roughness of cylindrical heating tubes on the pool boiling heat transfer performance, and showed that the rough tube enhanced the heat transfer rate significantly compared to the smooth tube.
Abstract: Received: 21 May 2020 Accepted: 15 March 2021 This study investigates the pool boiling heat transfer of water over cylindrical heating tubes for different orientations and surface roughness of the tubes. First, two orientations of a smooth heating tube, horizontal and vertical, were used in the boiling chamber. For a given heat flux, the heat transfer coefficient achieved with the horizontal tube was always higher than that for the vertical tube. To investigate the influence of surface roughness, a rough heating tube with a fully rough outer surface was developed through a metal etching process. Under the same range of wall superheat, the rough tube enhanced the heat transfer rate significantly compared to the smooth tube. Finally, a modified heating tube (MHT) was developed by axially roughening half of the surface of an originally smooth tube. The orientation angle of the rough surface of this MHT was varied from 0° (horizontal-upward) to 180° (horizontal-downward) in the chamber. The heat flux increased significantly with the increase of orientation angles from 0° to 90° (the maximum of 80 kW/m at 90°), whereas the same decreased as the orientation angle is further increased from 90° to 180°. Results revealed that the bubble dynamics over the heating tubes play a vital role in pool boiling performance.
5 citations
TL;DR: In this article, the authors examined the flow development and the static wall pressure distribution along the circular duct from the convergent-divergent (CD) nozzle, and they found that mild oscillations in the flow field for correctly expanded flows.
Abstract: This article focuses on the flow development and the static wall pressure distribution along the circular duct from the convergent-divergent (CD) nozzle. The study aims to examine the quality of the stream in the conduit when the control is employed. The microjets are activated at the base at (PCD) of 13 mm, and the diameter of the microjets is 1 mm. Mach numbers of the investigation are 1.3, 1.9, and 2.4. The length of the duct considered was from L = 10D to 1D. The diameter of the enlarged tube was 16 mm. The experiments were conducted for NPRs from 3 to 11. The results revealed that the lowest duct length mandatory for the flow continued to attach with the circular duct wall are L/D = 1, 2, and 3 for Mach numbers 1.3, 1.9, and 2.4, respectively. The investigation outcome indicates that there are mild oscillations in the flow-field for correctly expanded flows. The oscillatory trend has a pronounced impact on the duct's flow when the jets are operated at higher NPRs. The control does not adversely affect the flow field, and the magnitude of wall pressure is nearly similar.
5 citations
TL;DR: In this paper, a 3D simulation of a flat air solar collector with transverse baffles was made to give a comparison between two types of solar collectors, so they made an improvement of Ben Slama Romdhane's solar collector by creating two air flow passages to increase heat transfer.
Abstract: Flat air solar collectors are used for heat transfer between the absorber and the heat transfer fluid, to improve this transfer there are several methods. Among these methods, the exchange surface lengthening and the creation of turbulence. In this work is done to give a comparison between two types of solar collectors, so we have made an improvement of Ben Slama Romdhane's solar collector by creating two air flow passages to increase heat transfer. We made a 3D simulation of a flat air solar collector with transverse baffles which causes turbulence and increases the exchange surface; we use the ANSYS calculation code to make the simulation and gives results with a brief time and minimal cost.
5 citations
TL;DR: In this article, a comparative study of turbine blade cooling from leading edge and its comparative study were reviewed and summarized along with their advantages and disadvantages with respect to their relative performance and performance.
Abstract: Received: 31 August 2020 Accepted: 21 December 2020 Developments in the gas turbine technology have caused widespread usage of the Turbomachines for power generation. With increase in the power demand and a drop in the availability of fuel, usage of turbines with higher efficiencies has become imperative. This is only possible with an increase in the turbine inlet temperature (TIT) of the gas. However, the higher limit of TIT is governed by the metallurgical boundary conditions set by the material used to manufacture the turbine blades. Hence, turbine blade cooling helps in drastically controlling the blade temperature of the turbine and allows a higher turbine inlet temperature. The blade could be cooled from the leading edge, from the entire surface of the blade or from the trailing edge. The various methods of blade cooling from leading edge and its comparative study were reviewed and summarized along with their advantages and disadvantages.
TL;DR: In this article, a pipe of internal diameter 50 mm and 6 m length with different orientations of 0, 30, and 45 degrees was used to identify pressure gradients and to study the fully developed flow patterns of oil-gas.
Abstract: The current investigation aimed to identify pressure gradients and to study the fully developed flow patterns of oil-gas as a blend in a pipe of internal diameter 50 mm and 6 m length with different orientations of 0, 30, and 45-degree. The study was performed at constant values of liquid superficial velocities 0.052, 0.157, 0.262, 0.314, 0.419, and 0.524 m/s, and inlet superficial velocities of gas were ranged from 0.05 to 4.7 m/s at atmospheric pressure. Two pressure transducers located up and downstream were used to measure pressure drops inside the tested pipe. Flow patterns were derived by using the correlation between pressure gradients and time series, the Probability Density Function of differential pressures, pressure gradients with gas superficial velocities, and total pressure losses with mean void fractions. The flow patterns of oil-gas were observed as a uniform stratified flow in the pipe on a 0-degree orientation at various superficial velocities. Stratified, wavy, and slug flow patterns were observed at 30-degree orientation, whereas, bubbly, slug, and churn flow patterns were observed in the pipe of 45-degree orientation. The experiment also showed that pressure drop gradients decreased with increased void fractions, gas superficial velocities, and degree rotations of the flow lines. Finally, the validation of using pressure transducers as a technique for estimating the flow patterns of two-phase flow showed acceptable results with some kind of patterns.
TL;DR: In this article, the experimental investigation of square micro-pin fin heat sink for identifying the most suitable pin fin geometry for heat removal applications under forced convection was presented, and the results showed that for large fin height lower thermal resistance was observed at the cost of large pressure drop.
Abstract: Received: 8 February 2020 Accepted: 30 November 2020 Thermal management of the new generation’s high performance electronic and mechanical devices is becoming important due to their miniaturization. Conventionally, the plate fin arrangement is widely used for removal of dissipated heat but, their effectiveness is not up to mark. Among different options, the most attractive and efficient alternative for overcoming this problem is micro pin fin heat sink. This paper presents the experimental investigation of square micro-pin fins heat sink for identifying the most suitable pin fin geometry for heat removal applications under forced convection. Twenty five square micro pin fin heat sinks were tested for three different heat load and Reynolds number. The results show that for large fin height lower thermal resistance was observed at the cost of large pressure drop. The dimensionless heat transfer coefficient increases with fin height and Reynolds number while it decreases with increasing fin spacing. The improvement in micro pin fin efficiency were observed by about 2 to 9% owing to presence of fins on the impingement surface, flow mixing, disruption of the boundary layers, and augmentation of turbulent transport.
TL;DR: In this article, the spontaneous combustion process of loose coal under constant air volume from normal temperature to 140 °C was tested by using large coal spontaneous combustion simulation test bench, so as to analyze the change law of oxygen consumption rate and heat release intensity in time and space.
Abstract: In order to study the dynamic development law of different regions in the spontaneous combustion process of coal, the spontaneous combustion process of loose coal under constant air volume from normal temperature to 140 °C was tested by using large coal spontaneous combustion simulation test bench, so as to analyze the change law of oxygen consumption rate and heat release intensity in time and space. The results showed that the temperature of the loose coal spontaneous combustion process varies with the height of the coal body at different temperature stages. The high temperature point moved from the upper middle position of the coal body to the air inlet side; the oxygen consumption rate and time of different coal body heights showed indexes Increase, and the rate of oxygen consumption coincided with the migration law of the high temperature point of the coal body height. The coal body exhibited slow and rapid growth in stages around 75 °C; the heat release intensity of the loose coal inlet gradually increased. After the temperature exceeds 75 °C, the heat release intensity of different coal heights gradually increased with time, and the intensity of heat release coincides with the migration law of the high temperature point of the coal body height.
TL;DR: The authors specified the steps of design and calculation for the hydraulic control cylinder, and the principles for determining the power of the diesel engine, and proved that the designed system is scientific and rational.
Abstract: Received: 5 October 2020 Accepted: 26 December 2020 The stability and reliability of hydraulic control system have a direct bearing on the overall dynamic performance of the press machine. Hydromechanical analysis on the hydraulic control system is of theoretical and practical significance to improving the transmission performance and structural design of the entire press machine. From a quantitative perspective, this paper firstly analyzes the fluid transmission features of the hydraulic control system for the press machine, and presents the fluid transmission route and design drawings of the hydraulic control system. The next step is the design of the hydraulic control system. The authors specified the steps of design and calculation for the hydraulic control cylinder, and the principles for determining the power of the diesel engine. After that, experiments were carried out to verify the dynamic and static features of the designed system, and prove that our system is scientific and rational.
TL;DR: In this paper, a LHTES material-based refrigerator was used to enhance the performance of a convectional refrigerator with the use of latent heat thermal energy storage (LHTES) material.
Abstract: Received: 13 September 2020 Accepted: 20 March 2021 The present research focuses on application of thermal energy storage on a convectional refrigerator to enhance its performance. Salt hydrate was used as latent heat thermal energy storage (LHTES) material to convert the convectional refrigerator to a LHTES materialbased refrigerator. The cabinet of the convectional refrigerator was loaded with 10 kg of water at a temperature of 28°C and experiments were conducted on it to know the time taken for the evaporator temperature (TE) to reach -5°C, and determine the performance characteristics of the convectional refrigerator. The experiments were repeated on the LHTES material-based refrigerator to compare its performance characteristics with those of the convectional refrigerator. The results reveal that the evaporator of the LHTES material-based refrigerator attains the temperature of -5°C forty minutes before the same temperature (-5°C) was attained in the evaporator of the convectional refrigerator. For the interval of evaporator temperature (−5 C ≤ TE ≤ −1 C) considered for evaluation of the performance characteristics of the refrigerators in this work, when TE drops from 1°C to 5°C, the coefficient of performance (COP) for the LHTES material-based refrigerator and convectional refrigerator decreases from 7.36 to 4.62 and 6.44 to 4.15, respectively; the refrigerating effect decreases from 118.41 kJ/kg to 111.80 kJ/kg and 113.37 kJ/kg to 106.69 kJ/kg, respectively; the compressor work increases from 15.10 kJ/kg to 23.18 kJ/kg and 17.60 kJ/kg to 25.68 kJ/kg, respectively. The higher value of the COP and refrigerating effect, and the lower value of the compressor work of the LHTES material-based refrigerator compared with those of the convectional refrigerator imply that there is an improvement in the performance of the refrigerator with the LHTES material. The current work broadens research on the use of a LHTES materials to enhance the performance of a refrigerator.
TL;DR: In this article, a simple geometry of shear flow in a channel is considered and the energy equation amenable to an analytic solution is simulated to extract the desired numerical findings in as much as for what parameters' values, the temperature has dual distribution /does not yield temperature distribution at all.
Abstract: Received: 21 September 2020 Accepted: 10 January 2021 The central stimuli of this brief note is to underscore the effect of the temperature dependent convection coefficient that give rise to a dual temperature regime facilitating dual entropy distribution. In order to avoid unwarranted complexities, a simple geometry of shear flow in a channel is considered. The energy equation amenable to an analytic solution is simulated to extract the desired numerical findings in as much as for what parameters’ values, the temperature has dual distribution /does not yield temperature distribution at all. In fact, a range of parameter values have been worked out for which dual temperature regime exists or not. The plots of entropy generation number Ns also show the dual regime. The findings reveal a qualitative and quantitative difference in dual systems of temperature and entropy. It further underlines that the thermal systems with the idealized uniform heat transfer coefficient may be far distinct from actual behaviour and even weak temperature dependence of convection coefficient need due attention while designing a system.
TL;DR: In this paper, the reliability performance of PV inverter is evaluated considering environmental factors and geographical locations for a 1-φ, 3-kW grid connected PV system in PLECS.
Abstract: Received: 7 December 2020 Accepted: 11 February 2021 Today inverter system is one of the enabling technologies for efficiently harnessing energy from renewable energy sources (Solar, Wind, etc.,) and also for high reliable grid interfacing systems. With the advancements in power electronics, inverter conversion efficiency pushed to 98%, also PV is becoming a major renewable energy source globally. Nevertheless, the reliability performance of PV inverter is of high concern. Different environmental factors like solar irradiance, ambient temperature (also called Mission Profile) affect the reliability performance of PV inverter. Environmental conditions vary from location to location. Hence to quantify the reliability performance of PV inverter all these factors need to be considered. In this paper reliability performance of PV inverter is evaluated considering environmental factors and geographical locations. For the reliability evaluation, a 1-φ, 3-kW grid connected PV system is developed in PLECS. Full bridge PV inverter with 600V/30A IGBT is employed as the interface between grid and PV source. Real time mission profile data of one-year logs at India (Relatively hot climate) and Denmark (Relatively cold climate) to account for environmental factors and geographical locations during the reliability performance evaluation of PV inverter. Monte Carlo simulation is used to generate a population of 20000 samples with 5% variation. Lifetime for 20000 samples is calculated and fitted in Two Parameter Weibull distribution. B10 lifetime is calculated at two locations. The results of this paper reveal that environmental factors and geographical locations have a significant impact on PV inverter reliability performance.
TL;DR: In this paper, a numerical study of the engine oil flow behavior of convective heat transfer through a concentric and an eccentric annulus formed between a heated inner rotating cylinder and a cooled outer stationary cylinder is presented.
Abstract: Received: 13 October 2020 Accepted: 20 January 2021 This numerical study details the engine oil flow behaviour of convective heat transfer through a concentric and an eccentric annulus formed between a heated inner rotating cylinder and a cooled outer stationary cylinder. The three-dimensional governing equations for continuity, momentum, and energy have been solved using a finite volume method (FVM). The computational simulations are developed using well-known commercial software ANSYS-FLUENT. Besides this, a sensitivity analysis is executed via response surface methodology (RSM) using the statistical software of Design-Expert 12 to predict the optimum design that improves the hydrothermal performance in an eccentric annular cylinder. The findings are reported for numerical calculations of the moment coefficient (Cmc), surface temperature (Ts) of the inner rotating cylinder and Nusselt number (Nu) for a range of values of (0.25 0.75) aspect ratio (R*), (0.5 2.5 cm) eccentricity (E), (0° – 180°) inclination angle of the inner rotating cylinder (θ) and a wide range of Taylor number (Ta) of (2 – 4.5×104). In the case of a concentric annular cylinder, the averaged Nusselt number increases by increasing the Taylor number and decreasing the aspect ratio. Also, increasing the Taylor number and decreasing the aspect ratio causes a gradual decrease in the moment coefficient and surface temperature of the inner rotating cylinder. Whereas in the case of the eccentric annular cylinder, the maximum averaged Nusselt number and minimum surface temperature with the moderate value of moment coefficient are obtained at the optimum case of 2.5 cm eccentricity and 180° inclination angle, which are considered the optimum-estimated parameters of the eccentric annular gap. The influences of these physical parameters are graphically depicted in terms of velocity contours and temperature fields. Therefore, the rotation of the inner cylinder is shown to have a significant impact on the thermal-flow field of confined fluid.
TL;DR: Wang et al. as mentioned in this paper proposed a Structural Safety and Disaster Prevention for Urban Underground Infrastructure (SDP-UIN) for urban underground infrastructure in China, which is based on the work of the University of Central South University of China.
Abstract: 1 Hunan Engineering Research Center of Structural Safety and Disaster Prevention for Urban Underground Infrastructure, Hunan City University, Yiyang 413000, China 2 School of Civil Engineering, Hunan City University, Yiyang 413000, China 3 Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environmental Monitoring, Ministry of Education, Central South University, Changsha 410083, China 4 Changsha Metro Group Co., Ltd., Changsha 410007, China 5 School of Resource, Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan 411201, China
TL;DR: In this paper, a 3D least squares mesh-less algorithm was proposed for modeling high-speed non-equilibrium reaction jets with multicomponent and large-displacement moving boundaries.
Abstract: Received: 15 September 2020 Accepted: 3 December 2020 The mesh-less method abandons the idea of traditional mesh method. In numerical calculation, it only needs the node information, and it’s not necessary to connect nodes into mesh cells. Aiming at the problem of non-equilibrium chemical reaction flows in a threedimensional muzzle with moving boundaries, this paper proposed a three-dimensional least squares mesh-less (3D-LSM) algorithm, and the ALE (Arbitrary Lagrangian-Eulerian) form multi-component Euler governing equations were adopted for fluid dynamics modeling; then, a finite-rate reaction model was used to deal with the chemical reactions in the flow field, a time-division method was applied to solve the stiff problem of chemical reactions, and multi-component AUFS (artificially upstream flux vector splitting) format was introduced to calculate the convective flux term of the governing equation. In addition, the weighted-point filling strategy and the dynamic point cloud method were employed to deal with the topological structure changes in the point clouds caused by the large displacement movement of the projectile in the three-dimensional muzzle flow field. Finally, the proposed mesh-less method was applied to calculate the muzzle of a 12.7mm gun, and accurately captured the bottle-shaped shock wave structure in the complex muzzle flow field and the second muzzle flame phenomenon; the calculation results were compared with the experimental results and obtained a good match, which had proved the feasibility of the proposed 3D-LSM method. The research findings of this paper provided a new solution for the simulation of high-speed non-equilibrium reaction jets with multicomponent and large-displacement moving boundaries.
TL;DR: In this paper, the free and forced vibration of a functional rectangular plate in contact with a turbulent fluid is investigated, and the results of analytical solution after solving the equations by coding in Wolfram Mathematica software have been compared with numerical solution of Abaqus software and then with accurate results in references.
Abstract: Received: 21 May 2020 Accepted: 15 December 2020 In this paper, the free and forced vibration of a functional rectangular plate in contact with a turbulent fluid is investigated. Functional plates have been considered due to their high thermal resistance to residual stresses. The geometry of the problem is that one side of the reservoir in which the fluid is placed is covered with a plate of Functionally Graded Material (FGM). In order to approximate the displacement of the plate, assuming the thirdorder theory of shear deformation, trigonometric harmonic test functions are used, which determine the boundary conditions of the simple and fixed plate support. In the equations governing fluid oscillating behavior, the potential velocity of the fluid is obtained by determining the boundary conditions of the fluid in the form of February series functions. To achieve the natural frequency of the plate in contact with turbulent fluid and the shape of the vibrating mode, the Rayleigh-Ritz energy method is used based on the minimum potential energy. In order to check the accuracy of the method used, the results of analytical solution after solving the equations by coding in Wolfram Mathematica software have been compared with numerical solution of Abaqus software and then with accurate results in references, which shows the appropriate accuracy of the solution. Finally, the effect of volumetric coefficient parameters, volume ratio, length ratio, plate thickness ratio, fluid height, reservoir width and boundary conditions on the natural frequency of the plate in contact with turbulent fluid has been investigated and analyzed.
TL;DR: In this article, the authors analyzed the influence of engineering geological factors, roadbed structural factors, and natural environmental factors on the thermal stability of frozen soil roadbed in permafrost regions.
Abstract: Received: 17 September 2020 Accepted: 8 December 2020 Many highways and railways in western China are built on permafrost roadbed. Frost heave and thaw settlement might cause diseases to frozen soil roadbed, such as deformation and cracking. For long-term operation, frozen soil roadbed should be kept stable and durable. Therefore, this paper analyzes the distribution law of temperature field of roadbed in permafrost regions, under the effect of thermal stability. Based on the thermodynamic properties of permafrost, the authors analyzed the influence of engineering geological factors, roadbed structural factors, and natural environmental factors on the thermal stability of frozen soil roadbed. Next, the antifreeze mechanism of frozen soil roadbed was described, together with the calculation methods for the relevant parameters. Afterwards, the temperature field of the roadbed with low thermal conductivity insulation material was analyzed by two methods, namely, steady-state thermal analysis and transient thermal analysis, and the solving process of roadbed temperature field was explained in details. The proposed analysis method and solving algorithm were proved valid through experiments. The research results provide a reference for the reasonable design of frozen soil roadbed.
TL;DR: In this paper, the authors used an experimentally validated two-dimensional numerical model, the objective was to study the air flow patterns and the thermal and hygrometric behavior of three screenhouses differentiated in their geometric configuration of the roof area and under four (4) outside wind speeds.
Abstract: Received: 4 May 2020 Accepted: 28 November 2020 Insect proof screenhouse is increasingly used in tropical countries with a warm climate, as this type of structure is more economical than greenhouses and gives farmers the opportunity to optimize their production systems. In this work we used an experimentally validated two-dimensional numerical model, the objective was to study the air flow patterns and the thermal and hygrometric behavior of three screenhouses differentiated in their geometric configuration of the roof area and under four (4) outside wind speeds. The results obtained allowed us to find that the airflow speed inside the screenhouse can be maximized with respect to the most critical scenario by 29% for a wind speed of 0.5 ms and up to 292% for a wind speed of 3.0 ms, which generates reductions in the average temperature inside the structure of -0.2°C (0.5 ms) and up to -2.2°C (3 ms). While the relative humidity presented values of 1.6% and 6.3% higher for these same speeds.
TL;DR: In this article, the temperature distribution during laser-induced thermotherapy in cancer treatment is investigated using a multilayered skin (epidermis, dermis, subcutaneous fat, and muscle) with an embedded tumor model, and the effects of related parameters systematically investigate; wavelength, laser intensity, beam area, tumor absorption coefficient, tumor position, tumor blood perfusion rate, and irradiation time.
Abstract: Received: 14 August 2019 Accepted: 6 September 2020 Laser ablation is gaining acceptance as a cancer treatment technique because of its localized energy delivery to the tumorous tissue. The combination of laser ablation with nanoparticles allows for more precise targeting of the ablative area with less damage to adjacent healthy tissue. Nevertheless, heat damage to adjacent tissue is still a potential concern. Therefore, mathematical modeling of laser-tissue interactions is a necessary part of clinical treatment planning. In this study, the temperature distribution during laserinduced thermotherapy in cancer treatment investigates using a multilayered skin (epidermis, dermis, subcutaneous fat, and muscle) with an embedded tumor model. The effects of related parameters systematically investigate; wavelength, laser intensity, beam area, tumor absorption coefficient, tumor position, tumor blood perfusion rate, and irradiation time. Mathematical modeling in this study is solved by finite element method (FEM) via COMSOL Multiphysics Software. Laser absorption and thermal phenomena are described by Beer-Lambert’s law and Pennes’s bioheat equation.
TL;DR: In this paper, a comprehensive mathematical equation suitable for all weight fraction of MWCNTs and volume percentages of Ethylene glycol was developed, which can forecast the temperature range.
Abstract: Received: 10 March 2020 Accepted: 16 October 2020 This article summarizes research involving the evaluation of the thermo-physical properties of ethyleneglycol-based solar thermic fluids oxidized multi-walled carbon nanotubes. Nanofluids were prepared with Ethylene glycol and water as base fluids in 100:0, 90:10 and 80:20 ratios. Base fluids of three categories were dispersed with surfactant-assisted multi-walled carbon nanotubes (MWCNTs) and oxidized MWCNTs in the weight fractions of 0.125, 0.25, and 0.5 percentages to check the influence of surface modification technique on the thermophysical properties. The variation in zeta potential is studied to examine the dispersion stability during 2 months. Thermal conductivity and dynamic viscosity were measured by hot disk method and Anton paar viscometer, respectively. Significant enhancement of thermal conductivity by 15 to 24 % was observed when the base fluids are dispersed with oxidized MWCNTs. In the case of nanofluids dispersed with surfactant-assisted MWCNTs, the improvement is significantly less compared to oxidized MWCNTs. Nanofluids' dynamic viscosity is found to be higher compared to base fluids in the temperature range of 50 to 70 C. A comprehensive mathematical equation suitable for all weight fraction of MWCNTs and volume percentages of Ethylene glycol was developed, which can forecast the temperature range. The correlation could fit well with the experimental data in reasonable limits.
TL;DR: In this paper, the authors carried out thermal design and evaluated the cooling performance of power electronic devices (PEDs) containing electronic equipment, and the experimental results rove the effectiveness of numerical simulation and electronic equipment cooling scheme.
Abstract: Received: 5 January 2021 Accepted: 11 March 2021 In electronic equipment, thermal failure and thermal degradation are two increasingly prominent problems of the devices, with the deepening integration and growing power density. Currently, there are relatively few reports on the heat transfer mechanism, heat source analysis, and numerical simulation of electronic equipment containing power electronic devices (PEDs). Therefore, this paper carries out thermal design and evaluates the cooling performance of PED-containing electronic equipment. Firstly, the basic flow was given for the thermal design of PED-containing electronic equipment; the heat transfer mode of PEDs and the equipment were detailed, so was the principle of thermal design; the cooling principles were introduced for ventilation cooling, heat pipe cooling, and closed loop cooling. Then, numerical simulation was carried out on the solid and liquid state heat transfer of PEDs and the equipment under different cooling modes. Based on an engineering example, the cooling scheme was finalized through heat source analysis on the proposed electronic equipment. The experimental results rove the effectiveness of numerical simulation and electronic equipment cooling scheme. The results provide a reference for the cooling scheme design for other fields of thermal design.
TL;DR: In this article, the authors explored the possibility of decreasing exergy reduction in thermal power plant components like boiler, turbine and condenser and thus increasing exergetic efficiency of power plants by redesigning the existing design of some important components like platen super heater, final super heaters, re heater, condenser, so that resource sustainability improves.
Abstract: Received: 1 March 2021 Accepted: 23 March 2021 Exergy analysis gaining importance as an engineering analysis tool for energy systems. This paper explores the possibility of decreasing exergy reduction in thermal power plant components like boiler, turbine and condenser and thus increasing exergetic efficiency of Power plants by redesigning the existing design of some important components like platen super heater, final super heater, re heater, condenser, so that resource sustainability improves. The method suggested for exergy destruction in condenser is by using Heat pipes and application of heat pipes for steam condensation has been validated with experimental results.
TL;DR: In this article, the authors elucidates heat together with mass transfer through a flat plate and variable temperature as well as dissipative effects, which resulted to steady flow equations which were simplified with appropriate similarity variables.
Abstract: Received: 5 March 2020 Accepted: 14 December 2020 This paper elucidates heat together with mass transfer through a flat plate and variable temperature as well as dissipative effects. The flow assumptions resulted to steady flow equations which were simplified with appropriate similarity variables. The simplified equations were numerically solved and results are presented both in graphs and tabular form. Effects of physical quantities of interest were presented graphically. The local skin friction is observed to increase because of increase in Schmidt number. Also, increase in Prandtl number is found to boast the local Nusselt number. The behaviour of increase in Prandtl number is found to be unstable within the boundary layer regime while increase in Eckert number produces heat energy within the fluid layers. Finally, the validation of the present problem is done by comparing with previous works and was in perfect agreement.
TL;DR: In this article, the effects of some wall functions on aerodynamic and turbulence behavior of air flow around a simplified high-speed train via OpenFOAM software are numerically investigated, and the results could be used for obtaining more accurate analysis of aerodynamic characteristics of fluid flow around high speed trains.
Abstract: Received: 15 May 2020 Accepted: 6 October 2020 Modelling of turbulence is a vital issue for flow forecasting which is of great interest for most of engineering applications like flow over planes, movement of pollutants and some industrial processes. Originally, via solving the government equations (Navier-Stokes equations) the flow field can be simulated. With developing PCs and high-performance computers, implementing of Navier-Stokes equations for numerical simulation is increasing. In this research, the effects of some wall functions on aerodynamic and turbulence behavior of air flow around a simplified high-speed train via OpenFOAM software are numerically investigated. In the following, first, the effects of some default and common wall functions of OpenFOAM on the flow and aerodynamic key parameters are analyzed and then, a relatively new wall function called “Enhanced Wall Function” was implemented from ANSYS FLUENT into OpenFOAM and improvement for comprehensive simulation. Variations of flow key parameters such as velocity, pressure distribution and aerodynamic significant components and parameters such as lift, drag and side coefficients under the influence of wall functions changes are illustrated. The results could be used for obtaining more accurate analysis of aerodynamic characteristics of fluid flow around high-speed trains.