Special Issue "Selected Papers from XII International Conference on Computational Heat, Mass and Momentum Transfer (ICCHMT2019)"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Thermal Management".

Deadline for manuscript submissions: closed (31 January 2020).

Special Issue Editors

Prof. Dr. Inż Jan Taler
Website
Guest Editor
Politechnika Krakowska, Institute of Thermal Power Engineering, 31-864 Krakow, Poland
Interests: power engineering; thermodynamics; heat transfer; inverse heat transfer problems; steam boiler dynamics; thermal stresses
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Prof. Dr. Abdulmajeed A. Mohamad
Website
Guest Editor
Department of Mechanical and Manufacturing Engineering, University of Calgary, T2N 1N4 Calgary, AB, Canada
Interests: complex transport phenomena; fluid saturating porous medium; energy systems; double diffusion systems; micro-gravity; nanofluids; microfluidics
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Prof. Dr. Andrea Vallati
Website
Guest Editor
Department of Astronautics, Electrical, and Energetics Engineering DIAEE; Sapienza University of 00185 Rome, Italy
Interests: thermodynamics; heat transfer; numerical methods
Special Issues and Collections in MDPI journals
Prof. Dr. Roberto de Lieto Vollaro
Website
Guest Editor
Department of Engineering, Università Degli Studi Roma Tre, 00146 Roma, Italy
Interests: energy engineering; energy systems; heat transfer
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

ICCHMT is an international conference series that is widely recognized and respected in the international scientific community. ICCHMT was founded by Professor Abdulmajeed A. Mohamad from University of Calgary, and for nearly 20 years it has taken place in different parts of the world: Magusa, Cyprus (1999); Rio de Janeiro, Brazil (2001); Banff, Canada (2003); Paris, France (2005); Canmore, Canada (2007); Guangzhou, China (2009); Istambul, Turkey (2011 and 2015); Cracow, Poland (2016); Seoul, South Korea (2017); and Cracow, Poland (2018). In 2019, the Conference will be held in Rome (Italy). The conference topics dedicated to energy topics are as follows:

  • Heat Exchangers/heat pipe;
  • Fluid machinery;
  • Internal flow and heat transfer;
  • Micro/nano heat and mass transfer;
  • Mixing devices and phenomena;
  • Multi-phase flows;
  • Reactive flows and combustion;
  • Steam and gas turbines;
  • Technology for renewable energy sources;
  • Thermal flow visualization;
  • Thermal fluid machinery;
  • Transport phenomena in porous media;
  • Waste management and waste disposal.

Therefore, the manuscripts within these research area are most welcome.

Prof. Dr. Jan Taler
Prof. Abdulmajeed Mohamad
Prof. Dr. Andrea Vallati
Prof. Roberto de Lieto Vollaro
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Energy systems
  • Energy machinery
  • Thermal power plants
  • Thermodynamics
  • Energy efficiency in buildings.

Published Papers (20 papers)

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Research

Open AccessArticle
Gasification of Coal Dust in a Cyclone Furnace in an O2/H2O Atmosphere
Energies 2020, 13(9), 2253; https://doi.org/10.3390/en13092253 - 04 May 2020
Abstract
This paper presents the results of the modeling of coal dust gasification using oxygen and steam in a cyclone furnace. The combustion process leads to the release of gas composed mainly of CO and H2. The composition of this gas can [...] Read more.
This paper presents the results of the modeling of coal dust gasification using oxygen and steam in a cyclone furnace. The combustion process leads to the release of gas composed mainly of CO and H2. The composition of this gas can be controlled through changes in the content of O2 and H2O in the gasifying agent. It is possible for the process conditions adopted in the study to obtain the CO content at the level of 50% with the content of the gasifying agent O2/H2O of 50/50. In the case of the composition of the gasifying agent O2/H2O of 80/20, the H2 content was 50%. The maximal calorific value of the gas was obtained for O2/H2O 50/50 (11.2 MJ/kg). Full article
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Open AccessArticle
Experimental Validation of a Heat Transfer Model in Underground Power Cable Systems
Energies 2020, 13(7), 1747; https://doi.org/10.3390/en13071747 - 06 Apr 2020
Abstract
This paper presents the laboratory test stand that is used for experimental validation of underground power cable system models. Determination of temperature distribution in the vicinity of the cable is the main goal of the study. The paper considers a system of three [...] Read more.
This paper presents the laboratory test stand that is used for experimental validation of underground power cable system models. Determination of temperature distribution in the vicinity of the cable is the main goal of the study. The paper considers a system of three power cables, situated in the in-line arrangement, and buried in sand. Three electrical heaters of special construction are used in order to simulate the heat flux that is generated in the power cables during their operation. The test stand is designed to be placed in a thermoclimatic chamber, which allows testing the system in various thermal conditions when the ambient temperature changes by 20 °C to 30 °C. Numerical computations of the steady-state temperature fields are performed using the finite element method. Full article
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Open AccessArticle
Transient Natural Convection in a Thermally Insulated Annular Cylinder Exposed to a High Temperature from the Inner Radius
Energies 2020, 13(5), 1291; https://doi.org/10.3390/en13051291 - 10 Mar 2020
Abstract
Extensive numerical analysis was performed for the unsteady state, natural convection in the annular cylinders. The cylinder’s boundaries were thermally insulated, except the inner surface. The fluid (water) in the cylinder initially was assumed at a cold temperature while the inner surface was [...] Read more.
Extensive numerical analysis was performed for the unsteady state, natural convection in the annular cylinders. The cylinder’s boundaries were thermally insulated, except the inner surface. The fluid (water) in the cylinder initially was assumed at a cold temperature while the inner surface was subjected to a high temperature. The time history for the heat transfer by diffusion and advection was studied. The time needed for fully charging the storage tank and rate of heat transfer was calculated. The predicted results were compared with the pure heat diffusion process and with a steady-state convection system. Therefore, CFD simulations were performed for natural convection in the storage tank. The main objective of this study was to establish correlations for the rate of heat transfer as a function of time and other controlling parameters. The correlation is needed in designing a thermal energy storage system for domestic and industrial heating processes. One of the drawbacks of the conventional thermal storage systems is the slow charging and discharging, where the heat transfer is mainly diffusion dominated. To overcome such a problem, a system was designed based on the natural convective heat transfer mechanism. Therefore, the heat transfer and fluid flow in a cylindrical storage tank were simulated for a range of Rayleigh numbers (104 to 108) and radius ratio. It was found that a convection-operated storage tank reduces the thermal charging process time drastically compared with the thermally diffusion charging process. The rate of reduction in the charging time mainly depends on the rate of heating and geometric parameter of the tank. To the best of the authors’ knowledge, the work is novel. Full article
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Open AccessArticle
A Linear Regression Thermal Displacement Lathe Spindle Model
Energies 2020, 13(4), 949; https://doi.org/10.3390/en13040949 - 20 Feb 2020
Abstract
Thermal error is one of the main reasons for the loss of accuracy in lathe machining. In this study, a thermal deformation compensation model is presented that can reduce the influence of spindle thermal error on machining accuracy. The method used involves the [...] Read more.
Thermal error is one of the main reasons for the loss of accuracy in lathe machining. In this study, a thermal deformation compensation model is presented that can reduce the influence of spindle thermal error on machining accuracy. The method used involves the collection of temperature data from the front and rear spindle bearings by means of embedded sensors in the bearing housings. Room temperature data were also collected as well as the thermal elongation of the main shaft. The data were used in a linear regression model to establish a robust model with strong predictive capability. Three methods were used: (1) Comsol was used for finite element analysis and the results were compared with actual measured temperatures. (2) This method involved the adjustment of the parameters of the linear regression model using the indicators of the coefficient of determination, root mean square error, mean square error, and mean absolute error, to find the best parameters for a spindle thermal displacement model. (3) The third method used system recognition to determine similarity to actual data by dividing the model into rise time and stable time. The rise time was controlled to explore the accuracy of prediction of the model at different intervals. The experimental results show that the actual measured temperatures were very close to those obtained in the Comsol analysis. The traditional model calculates prediction error values within single intervals, and so the model was divided to give rise time and stable time. The experimental results showed two error intervals, 19µm in the rise time and 15µm in the stable time, and these findings allowed the machining accuracy to be enhanced. Full article
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Open AccessArticle
Numerical Solution of Axisymmetric Inverse Heat Conduction Problem by the Trefftz Method
Energies 2020, 13(3), 705; https://doi.org/10.3390/en13030705 - 06 Feb 2020
Abstract
In this paper, the issue of flow boiling heat transfer in an annular minigap was discussed. The main aim of the paper was determining the boiling heat transfer coefficient at the HFE-649 fluid–heater contact during flow along an annular minigap. The essential element [...] Read more.
In this paper, the issue of flow boiling heat transfer in an annular minigap was discussed. The main aim of the paper was determining the boiling heat transfer coefficient at the HFE-649 fluid–heater contact during flow along an annular minigap. The essential element of the experimental stand was a test section vertically oriented with the minigap 2 mm wide. Thermocouples were used to measure the temperature of the heater and fluid at the inlet and the outlet to the minigap. The mathematical model assumed that the fluid flow was laminar and the steady–state heat transfer process was axisymmetric. The temperatures of the heated surface and of the flowing fluid were assumed to fulfill energy equations with adequate boundary conditions. The problem was solved by the Trefftz method. The local heat transfer coefficients at the fluid–test surface interface were calculated due to the third kind boundary condition at the saturated boiling. Graphs were used to illustrate: the measurement of the heater surface temperature, 2D temperature distributions in the pipe and fluid, and the heat transfer coefficient as a function of the distance from the minigap inlet. The measurement uncertainties and accuracy of the heat transfer coefficient determination were estimated. Full article
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Open AccessArticle
Online Determining Heat Transfer Coefficient for Monitoring Transient Thermal Stresses
Energies 2020, 13(3), 704; https://doi.org/10.3390/en13030704 - 06 Feb 2020
Abstract
This paper proposes an effective method for determining thermal stresses in structural elements with a three-dimensional transient temperature field. This is the situation in the case of pressure elements of complex shapes. When the thermal stresses are determined by the finite element method [...] Read more.
This paper proposes an effective method for determining thermal stresses in structural elements with a three-dimensional transient temperature field. This is the situation in the case of pressure elements of complex shapes. When the thermal stresses are determined by the finite element method (FEM), the temperature of the fluid and the heat transfer coefficient on the internal surface must be known. Both values are very difficult to determine under industrial conditions. In this paper, an inverse space marching method was proposed for the determination of the heat transfer coefficient on the active surface of the thick-walled plate. The temperature and heat flux on the exposed surface were obtained by measuring the unsteady temperature in a small region on the insulated external surface of a pressure component that is easily accessible. Three different procedures for the determination of the heat transfer coefficient on the water-spray surface were presented, with the division of the plate into three or four finite volumes in the normal direction to the plate surface. Calculation and experimental tests were carried out in order to validate the method. The results of the measurements and calculations agreed very well. The computer calculation time is short, so the technique can be used for online stress determination. The proposed method can be applied to monitor thermal stresses in the components of the power unit in thermal power plants, both conventional and nuclear. Full article
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Open AccessArticle
Effect of Impeller Design on Power Characteristics and Newtonian Fluids Mixing Efficiency in a Mechanically Agitated Vessel at Low Reynolds Numbers
Energies 2020, 13(3), 640; https://doi.org/10.3390/en13030640 - 03 Feb 2020
Abstract
The mixing process is a widespread phenomenon, which plays an essential role among a large number of industrial processes. The effectiveness of mixing depends on the state of mixed phases, temperature, viscosity and density of liquids, mutual solubility of mixed fluids, type of [...] Read more.
The mixing process is a widespread phenomenon, which plays an essential role among a large number of industrial processes. The effectiveness of mixing depends on the state of mixed phases, temperature, viscosity and density of liquids, mutual solubility of mixed fluids, type of stirrer, and, what is the most critical property, the shape of the impeller. In the present research, the objective was to investigate the Newtonian fluids flow motion as well as all essential parameters for the mechanically agitated vessel with a new impeller type. The velocity field, the power number, and the pumping capacity values were determined using computer simulation and experimental measurements. The basis for the assessment of the intensity degree and the efficiency of mixing had to do with the analysis of the distribution of velocity vectors and the power number. An experimental and numerical study was carried out for various stirred process parameters and for fluids whose viscosity ranged from low to very high in order to determine optimal conditions for the mixing process. Full article
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Open AccessArticle
Modeling of a Combined Cycle Gas Turbine Integrated with an Adsorption Chiller
Energies 2020, 13(3), 515; https://doi.org/10.3390/en13030515 - 21 Jan 2020
Cited by 3
Abstract
Forecasts to 2030 indicate that demand for electricity will increase from 2% to 3% per year, and due to the observed high rate of development of the world economy, energy demand will continue to increase. More efficient use of primary energy has influence [...] Read more.
Forecasts to 2030 indicate that demand for electricity will increase from 2% to 3% per year, and due to the observed high rate of development of the world economy, energy demand will continue to increase. More efficient use of primary energy has influence on reduction emissions and consumption of fuel. Besides, reducing the amount of fuel burned, it reveals a beneficial effect on the environment. Since extraction-back pressure turbines have some limitations, including the restriction of electricity production due to limited heat consumption in summer. The paper discusses the possibilities of integrating the adsorption aggregate with a combined cycle gas turbine and its impact on the operation of all devices. Simulations are performed on Sim tech IPSEPro software. The obtained results confirm that the adsorption aggregate, using a low grade of thermal energy, does not affect the operation of the gas and steam cycle and allows the production of electricity at a constant level. The calculated chemical fuel energy utilisation factor was 85.7% in cogeneration and 75.6% in trigeneration. These factors indicated a reduced utilisation of chemical fuel energy; however, this reduction is caused by a lower COP for adsorption chillers. Besides, the adsorption aggregate additionally generates chilled water for air conditioning or other technological processes, which stands for an added value of the innovative concept proposed in the paper. Full article
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Open AccessArticle
Measurements Based Analysis of the Proton Exchange Membrane Fuel Cell Operation in Transient State and Power of Own Needs
Energies 2020, 13(2), 498; https://doi.org/10.3390/en13020498 - 20 Jan 2020
Abstract
Currently, fuel cells are increasingly used in industrial installations, means of transport, and household applications as a source of electricity and heat. The paper presents the results of experimental tests of a Proton Exchange Membrane Fuel Cell (PEMFC) at variable load, which characterizes [...] Read more.
Currently, fuel cells are increasingly used in industrial installations, means of transport, and household applications as a source of electricity and heat. The paper presents the results of experimental tests of a Proton Exchange Membrane Fuel Cell (PEMFC) at variable load, which characterizes the cell’s operation in real installations. A detailed analysis of the power needed for operation fuel cell auxiliary devices (own needs power) was carried out. An analysis of net and gross efficiency was carried out in various operating conditions of the device. The measurements made show changes in the performance of the fuel cell during step changing or smooth changing of an electric load. Load was carried out as a change in the current or a change in the resistance of the receiver. The analysis covered the times of reaching steady states and the efficiency of the fuel cell system taking into account auxiliary devices. In the final part of the article, an analysis was made of the influence of the fuel cell duration of use on obtained parameters. The analysis of the measurement results will allow determination of the possibility of using fuel cells in installations with a rapidly changing load profile and indicate possible solutions to improve the performance of the installation. Full article
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Open AccessArticle
Numerical Investigation of Pipelines Modeling in Small-Scale Concentrated Solar Combined Heat and Power Plants
Energies 2020, 13(2), 429; https://doi.org/10.3390/en13020429 - 16 Jan 2020
Cited by 1
Abstract
In this paper four different detailed models of pipelines are proposed and compared to assess the thermal losses in small-scale concentrated solar combined heat and power plants. Indeed, previous numerical analyses carried out by some of the authors have revealed the high impact [...] Read more.
In this paper four different detailed models of pipelines are proposed and compared to assess the thermal losses in small-scale concentrated solar combined heat and power plants. Indeed, previous numerical analyses carried out by some of the authors have revealed the high impact of pipelines on the performance of these plants because of their thermal inertia. Hence, in this work the proposed models are firstly compared to each other for varying temperature increase and mass flow rate. Such comparison shows that the one-dimensional (1D) longitudinal model is in good agreement with the results of the more detailed two-dimensional (2D) model at any temperature gradient for heat transfer fluid velocities higher than 0.1 m/s whilst the lumped model agrees only at velocities higher than 1 m/s. Then, the 1D longitudinal model is implemented in a quasi-steady-state Simulink model of an innovative microscale concentrated solar combined heat and power plant and its performances evaluated. Compared to the results obtained using the Simscape library model of the tube, the performances of the plant show appreciable discrepancies during the winter season. Indeed, whenever the longitudinal thermal gradient of the fluid inside the pipeline is high (as at part-load conditions in winter season), the lumped model becomes inaccurate with more than 20% of deviation of the thermal losses and 30% of the organic Rankine cycle (ORC) electric energy output with respect to the 1D longitudinal model. Therefore, the analysis proves that an hybrid model able to switch from a 1D longitudinal model to a zero-dimensional (0D) model with delay based on the fluid flow rate is recommended to obtain results accurate enough whilst limiting the computational efforts. Full article
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Open AccessArticle
Thermodynamic Analysis of Advanced Gas Turbine Combined Cycle Integration with a High-Temperature Nuclear Reactor and Cogeneration Unit
Energies 2020, 13(2), 400; https://doi.org/10.3390/en13020400 - 14 Jan 2020
Abstract
The EU has implemented targets to achieve a 20% share of energy from renewable sources by 2020, and 32% by 2030. Additionally, in the EU countries by 2050, more than 80% of electrical energy should be generated using non-greenhouse gases emission technology. At [...] Read more.
The EU has implemented targets to achieve a 20% share of energy from renewable sources by 2020, and 32% by 2030. Additionally, in the EU countries by 2050, more than 80% of electrical energy should be generated using non-greenhouse gases emission technology. At the same time, energy cost remains a crucial economic issue. From a practical point of view, the most effective technology for energy conversion is based on a gas turbine combined cycle. This technology uses natural gas, crude oil or coal gasification product but in any case, generates a significant amount of toxic gases to the atmosphere. In this study, the environmentally friendly power generation system composed of a high-temperature nuclear reactor HTR integrated with gas turbine combined cycle technology and cogeneration unit is thermodynamically analysed. The proposed solution is one of the most efficient ways for energy conversion, and what is also important it can be easily integrated with HTR. The results of analysis show that it is possible to obtain for analysed cycles thermal efficiency higher than 50% which is not only much more than could be proposed by typical lignite or hard coal power plant but is also more than can be offered by nuclear technology. Full article
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Open AccessArticle
Numerical Investigation on the Flow Characteristics in a 17 × 17 Full-Scale Fuel Assembly
Energies 2020, 13(2), 397; https://doi.org/10.3390/en13020397 - 13 Jan 2020
Abstract
In a previous study, several computational fluid dynamics (CFD) simulations of fuel assembly thermal-hydraulic problems were presented that contained fewer fuel rods, such as 3 × 3 and 5 × 5, due to limited computer capacity. However, a typical AFA-3G fuel assembly consists [...] Read more.
In a previous study, several computational fluid dynamics (CFD) simulations of fuel assembly thermal-hydraulic problems were presented that contained fewer fuel rods, such as 3 × 3 and 5 × 5, due to limited computer capacity. However, a typical AFA-3G fuel assembly consists of 17 × 17 rods. The pressure drop levels and flow details in the whole fuel assembly, and even in the pressurized water reactor (PWR), are not available. Hence, an appropriate CFD method for a full-scale 17 × 17 fuel assembly was the focus of this study. The spacer grids with mixing vanes, springs, and dimples were considered. The polyhedral and extruded mesh was generated using Star-CCM+ software and the total mesh number was about 200 million. The axial and lateral velocity distribution in the sub-channels was investigated. The pressure distribution downstream of different spacer grids were also obtained. As a result, an appropriate method for full-scale rod bundle simulations was obtained. The CFD analysis of thermal-hydraulic problems in a reactor coolant system can be widely conducted by using real-size fuel assembly models. Full article
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Open AccessArticle
Numerical and Experimental Study on Convective Heat Transfer Characteristics in Foam Materials
Energies 2020, 13(2), 348; https://doi.org/10.3390/en13020348 - 10 Jan 2020
Abstract
Foam materials are widely used in heat exchange because of their high porosity and large specific surface area. Correctly characterizing heat transfer characteristics is the key to ensuring efficient heat transfer. In this paper, single-blow transient test technology is used to experimentally measure [...] Read more.
Foam materials are widely used in heat exchange because of their high porosity and large specific surface area. Correctly characterizing heat transfer characteristics is the key to ensuring efficient heat transfer. In this paper, single-blow transient test technology is used to experimentally measure the temperature. Silicon carbide ceramics with various thicknesses ranging from 30 to 105 mm and different pore structures were used in the experiments. The test was carried out at the velocity ranging from 0.5 to 1.8 m/s. The air temperature distributions of the inlet and outlet were obtained by processing the experimental data, and the regularity of the average volumetric heat transfer coefficient was obtained and analyzed. Subsequently, the simplified tetrakaidecahedron models with a porosity of 0.85 and 0.75 were used to analyze the heat transfer characteristics. The local thermal equilibrium and local thermal non-equilibrium at the pore scale were analyzed. By comparing the simulation with the experiment, it shows that the larger thickness affects local thermal equilibrium and leads to a decrease in the volumetric heat transfer coefficient. The conclusion can be used to guide the optimization of the design of foam material-mediated heat exchange equipment. Full article
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Open AccessArticle
Analysis of Non-Equilibrium and Equilibrium Models of Heat and Moisture Transfer in a Wet Porous Building Material
Energies 2020, 13(1), 214; https://doi.org/10.3390/en13010214 - 02 Jan 2020
Abstract
In the proposed paper, non-equilibrium and equilibrium models of heat and moisture transfer through wet building materials are presented and compared. In the former, the mass transfer between liquid and gaseous moisture results from the difference between the partial pressure of water vapor [...] Read more.
In the proposed paper, non-equilibrium and equilibrium models of heat and moisture transfer through wet building materials are presented and compared. In the former, the mass transfer between liquid and gaseous moisture results from the difference between the partial pressure of water vapor and its saturation value. In the second model, the equilibrium between both phases is assumed. In the non-equilibrium model, liquid moisture can be in the continuous (funicular) or discontinuous (pendular) form. The transfer of moisture for each proposed model is tightly coupled with the energy transfer, which is assumed to be an equilibrium process. The time step and grid size sensitivity analysis of both numerical models are performed primarily. The verification of the model is based also on the numerical data available in literature. Finally, obtained with considered models, temporal variations of moisture content in three locations in the computational domain are compared. Reasonable conformity of results is reported, and discrepancies related to differences in formulations of models are discussed. Full article
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Open AccessFeature PaperArticle
Comparison of Combustion Models for Lifted Hydrogen Flames within RANS Framework
Energies 2020, 13(1), 152; https://doi.org/10.3390/en13010152 - 28 Dec 2019
Abstract
Within the framework of a Reynolds averaged numerical simulation (RANS) methodology for modeling turbulence, a comparative numerical study of turbulent lifted H2/N2 flames is presented. Three different turbulent combustion models, namely, the eddy dissipation model (EDM), the eddy dissipation concept [...] Read more.
Within the framework of a Reynolds averaged numerical simulation (RANS) methodology for modeling turbulence, a comparative numerical study of turbulent lifted H2/N2 flames is presented. Three different turbulent combustion models, namely, the eddy dissipation model (EDM), the eddy dissipation concept (EDC), and the composition probability density function (PDF) transport model, are considered in the analysis. A wide range of global and detailed combustion reaction mechanisms are investigated. As turbulence model, the Standard k-ε model is used, which delivered a comparatively good accuracy within an initial validation study, performed for a non-reacting H2/N2 jet. The predictions for the lifted H2/N2 flame are compared with the published measurements of other authors, and the relative performance of the turbulent combustion models and combustion reaction mechanisms are assessed. The flame lift-off height is taken as the measure of prediction quality. The results show that the latter depends remarkably on the reaction mechanism and the turbulent combustion model applied. It is observed that a substantially better prediction quality for the whole range of experimentally observed lift-off heights is provided by the PDF model, when applied in combination with a detailed reaction mechanism dedicated for hydrogen combustion. Full article
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Open AccessArticle
A Comprehensive Thermal and Structural Transient Analysis of a Boiler’s Steam Outlet Header by Means of a Dedicated Algorithm and FEM Simulation
Energies 2020, 13(1), 111; https://doi.org/10.3390/en13010111 - 24 Dec 2019
Abstract
Increasing the share of renewables in energy markets influences the daily operation of thermal power units. High capacity power units are more frequently operated to balance power grids and, thus, steam boilers are exposed to unfavorable transient states. The aim of this work [...] Read more.
Increasing the share of renewables in energy markets influences the daily operation of thermal power units. High capacity power units are more frequently operated to balance power grids and, thus, steam boilers are exposed to unfavorable transient states. The aim of this work was to perform thermal and structural analyses of a boiler’s outlet steam header, with a capacity of 650∙103 kg/h (180 kg/s) of live steam. Based on the measured steam pressure and temperatures on the outer surface of the component, transient temperature fields were determined by means of an algorithm that allows determination of transient stress distributions on the internal and external surfaces, as well as at stress concentration regions. In parallel, a finite element method simulation was performed. A comparison of the obtained results to a finite element analysis showed satisfactory agreement. The analyses showed that the start-up time could be reduced because the total stress did not exceed the allowed values during the regular start-up of the analyzed power unit. The algorithm was efficient and easy to implement in the real control systems of the power units. The numerical approach employed in the presented algorithm also allowed for determination of the time- and place-dependent heating rate value, which can be used as input data for the control system of the power unit. Full article
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Open AccessArticle
Evaluation of the Performance of the Drag Force Model in Predicting Droplet Evaporation for R134a Single Droplet and Spray Characteristics for R134a Flashing Spray
Energies 2019, 12(24), 4618; https://doi.org/10.3390/en12244618 - 05 Dec 2019
Abstract
Drag force plays an important role in determining the momentum, heat and mass transfer of droplets in a flashing spray. This paper conducts a comparative study to examine the performance of drag force models in predicting the evolution of droplet evaporation for R134a [...] Read more.
Drag force plays an important role in determining the momentum, heat and mass transfer of droplets in a flashing spray. This paper conducts a comparative study to examine the performance of drag force models in predicting the evolution of droplet evaporation for R134a single droplet and spray characteristics for its flashing spray. The study starts from single moving R134a droplet vaporizing in atomispheric environment, to a fully turbulent, flashing spray caused by an accidental release of high-pressure R134a liquid in the form of a straight-tube nozzle, using in-house developed code and a modified sprayFoam solver in OpenFOAM, respectively. The effect of the nozzle diameter on the spray characteristics of R134a two-phase flashing spray is also examined. The results indicate that most of the drag force models have little effect on droplet evporation in both single isolated droplet modelling and fully two-phase flashing spray simulation. However, the Khan–Richardson model contributes to different results. In particular, it predicts a much different profile of the droplet diameter distribution and a much lower droplet temperature in the radial distance. The nozzle diameter has a significant impact on the flashing spray. A smaller diameter nozzle leads to more internse explosive atomization, shorter penetration distance, lower droplet diameter and velocity, and a faster temperature decrease. Full article
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Open AccessArticle
Influences of the Flow Cut and Axial Lift of the Impeller on the Aerodynamic Performance of a Transonic Centrifugal Compressor
Energies 2019, 12(23), 4503; https://doi.org/10.3390/en12234503 - 27 Nov 2019
Abstract
In this study, the influences of the flow cut and axial lift of the impeller on the aerodynamic performance of a transonic centrifugal compressor were analyzed. The flow cut is a method to reduce the flow rate by decreasing the impeller passage height. [...] Read more.
In this study, the influences of the flow cut and axial lift of the impeller on the aerodynamic performance of a transonic centrifugal compressor were analyzed. The flow cut is a method to reduce the flow rate by decreasing the impeller passage height. The axial lift is a method of increasing the impeller passage height in the axial direction, which increases the impeller exit width (B2) and increases the total pressure. A NASA CC3 transonic centrifugal compressor with a backswept angle was used as a base compressor. After applying the flow cut, the total pressure at the target flow rate was lower than the total pressure at the design point due to the increase in the relative velocity at the impeller exit. After applying the axial lift, the total pressure at the design flow rate was increased, which was caused by the reduction in the relative velocity as the passage area at the impeller exit was increased. By applying the flow cut and axial lift methods, it was shown that the variation in relative velocity at the impeller exit has a significant effect on the variation in total pressure. In addition, it was found that the relative velocity at the impeller exit of the target flow rate is maintained similar to the base impeller when the flow cut and the axial lift are combined. Therefore, by combining the flow cut and the axial lift, three transonic centrifugal impellers with flow fractions of 0.7, 0.8, and 0.9 compared to the design flow rate were newly designed. Full article
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Open AccessArticle
Sensitivity of Numerical Predictions to the Permeability Coefficient in Simulations of Melting and Solidification Using the Enthalpy-Porosity Method
Energies 2019, 12(22), 4360; https://doi.org/10.3390/en12224360 - 15 Nov 2019
Cited by 1
Abstract
The high degree of uncertainty and conflicting literature data on the value of the permeability coefficient (also known as the mushy zone constant), which aims to dampen fluid velocities in the mushy zone and suppress them in solid regions, is a critical drawback [...] Read more.
The high degree of uncertainty and conflicting literature data on the value of the permeability coefficient (also known as the mushy zone constant), which aims to dampen fluid velocities in the mushy zone and suppress them in solid regions, is a critical drawback when using the fixed-grid enthalpy-porosity technique for modelling non-isothermal phase-change processes. In the present study, the sensitivity of numerical predictions to the value of this coefficient was scrutinised. Using finite-volume based numerical simulations of isothermal and non-isothermal melting and solidification problems, the causes of increased sensitivity were identified. It was found that depending on the mushy-zone thickness and the velocity field, the solid–liquid interface morphology and the rate of phase-change are sensitive to the permeability coefficient. It is demonstrated that numerical predictions of an isothermal phase-change problem are independent of the permeability coefficient for sufficiently fine meshes. It is also shown that sensitivity to the choice of permeability coefficient can be assessed by means of an appropriately defined Péclet number. Full article
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Open AccessArticle
Noise Reduction of an Extinguishing Nozzle Using the Response Surface Method
Energies 2019, 12(22), 4346; https://doi.org/10.3390/en12224346 - 15 Nov 2019
Abstract
An inert gas such as nitrogen is used as an extinguishing agent to suppress unexpected fire in places such as computer rooms and server rooms. The gas released with high pressure causes noise above 130 dB. According to recent studies, loud noise above [...] Read more.
An inert gas such as nitrogen is used as an extinguishing agent to suppress unexpected fire in places such as computer rooms and server rooms. The gas released with high pressure causes noise above 130 dB. According to recent studies, loud noise above 120 dB has a strong vibrational energy that leads to a negative influence on electronic equipment with a high degree of integration. In this study, a basic fire-extinguishing nozzle with absorbent was selected as the reference model, and numerical analysis was conducted using the commercial software, ANSYS FLUENT ver. 18.1. A total of 45 experiment points was selected using the design of experiment (DOE) method. An optimum point was derived using the response surface method (RSM). Results show that the vibrational energy of the noise was reduced by minimizing the turbulence kinetic energy. Pressure and velocity distributions were calculated and graphically depicted with various absorbent configurations. Full article
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