Elementary Heat Research Articles

Numerical simulation of 3D vorticity dynamics with the Diffused Vortex Hydrodynamics method

In this paper the three-dimensional extension of the Diffused Vortex Hydrodynamics (DVH) is discussed along with free vorticity dynamics simulations. DVH is a vortex particle method developed in-house and widely validated in a 2D framework. The DVH approach has been embedded in a new frontend to the open-source code PEPC, the Pretty Efficient Parallel Coulomb solver. Within this parallel Barnes–Hut tree code, a superposition of elementary heat equation solutions in a cubic support is performed during the diffusion step. This redistribution avoids excessive clustering or rarefaction of the vortex particles, providing robustness and high accuracy of the method. An ascending vortex dipole at various resolutions is selected as a test-case and heuristic convergence measurements are performed, taking into account the conservation of prime integrals and the energy–enstrophy balance.

Heat transfer model verification for thermal monitoring system of integral bridges

Thermal actions considered on abutments of integral bridges by the European standard (Eurocode 1) might be in variety of certain situations underestimated. Based on this assumption, thermal monitoring system has been designed and installed into structure of bridge No. 27-117. Temperature profiles in five certain spots are being measured to provide sufficient basis for evaluation of real thermal actions on abutments of integral bridges. For purpose of measurement verification, elementary heat transfer models for finite element method solver were created. These models are being loaded by simplified temperature profiles reached in real time in-situ. Evaluated models provide verification data to compare with measured temperature profiles in structure and might provide information about temperature profiles probably reached during extreme weather situations.

MODELING OF A DOUBLE CIRCULATION RECUPERATOR’S HEAT WORK

Utilization of heat from waste products of heat units’ combustion is one of the most important means of saving fuel and energy resources and improving the environmental performance of the enterprise. Improving the design of heat recuperators and increasing their energy efficiency by improving thermal performance is based primarily on the development of new and improvement of existing methods for calculating heat exchangers. In this paper, based on the method of elementary heat balances, a mathematical model of the thermal operation of a double-circulation recuperator is developed. The use of the described mathematical model of recuperator’s heat work makes it possible to analyze its design in terms of energy efficiency, durability, the ability to reduce heat emissions into the environment.

Cooling Load Estimation of a Multi-Storey Building: A Heat Transfer Approach

The key objective of this work is to maintain the pre-determined inside conditions & to establish thermal equilibrium the prime rate at which heat needs to be detached from the space. Nowadays one of the most serious problems is environmental issues. For this problem, energy utilization by buildings and enterprises are responsible. Markets, Residential houses, commercial buildings, industry, and Infrastructure consume approximately 72% of the world’s energy. Roughly 60 % of a building’s total energy necessity is distributed to the plant of air-conditioning installed in a big complex or building that is air acclimatized. To limit energy utilization, accurate prediction of the cooling load are important. The elementary heat transfer concepts are used to manually calculate the cooling load of a multi-storey building. This method is derived from CLTD technique of cooling load estimation. We estimate the cooling load at the extreme conditions. So, we have taken the outside conditions as relative humidity 54% and 450C DBT for the month of May during summer. The average outside air velocity during this period is 1.67 m/s. The significance of this work is to show that, actual cooling load prediction results in less capital cost, investment and energy consumed. Thus, accuracy should be paramount when load calculation is being performed.

Energetics and 3D Structure of Elementary Events in Solar Coronal Heating

Abstract Parker first proposed (1972) that coronal heating was the necessary outcome of an energy flux caused by the tangling of coronal magnetic field lines by photospheric flows. In this paper we discuss how this model has been modified by subsequent numerical simulations outlining in particular the substantial differences between the “nanoflares” introduced by Parker and “elementary events,” defined here as small-scale spatially and temporally isolated heating events resulting from the continuous formation and dissipation of field-aligned current sheets within a coronal loop. We present numerical simulations of the compressible 3D MHD equations using the HYPERION code. We use two clustering algorithms to investigate the properties of the simulated elementary events: an IDL implementation of a density-based spatial clustering of applications with noise technique, and our own physical distance clustering algorithm. We identify and track elementary heating events in time, both in temperature and in Joule heating space. For every event we characterize properties such as density, temperature, volume, aspect ratio, length, thickness, duration, and energy. The energies of the events are in the range of 1018–1021 erg, with durations shorter than 100 s. A few events last up to 200 s and release energies up to 1023 erg. While high temperatures are typically located at the flux tube apex, the currents extend all the way to the footpoints. Hence, a single elementary event cannot at present be detected. The observed emission is due to the superposition of many elementary events distributed randomly in space and time within the loop.

Analysis of capability for improvement of basic mathematical model of electrode of ferro-alloy furnace

The article analyzes the Mathematical Model of The Self-Baking Electrode which is defined as basic. Its advantages and disadvantages are determined. Criterias for creating more advanced mathematical model for equalizing the thermal field of the Electrode are proposed.
 The problem of calculating the thermal field is solved by the the method of elementary heat balances of electrode. For this goal the simulated area is divided into annular (cylindrical) elements along the radius and height of the electrode.The calculation of the temperature field of the electrode is carried out in two stages: I – with boundary conditions and currents for the parts of the electrode facing to the center of the smelting furnace; II – with boundary conditions and currents for the parts of the electrode facing to the lining. 
 The mathematical model takes into account an effect of the ribs and the hood on the distribution of electric current and Joule’s Heat over the cross section of the Electrode. In case heating ferromagnetic materials under impact of an electromagnetic field, the magnetic permeability at first decreases relatively slowly, and then droping down sharply as a certain temperature (Curie Point) is reached. The material loses its magnetic properties completely and goes into into a paramagnetic state.
 The value of the electrode current changes according to the graph from the starting value to the working value and then remains constant. The current density of the electrode along the radius is unequal due to the action of the surface effect, as well as due to existence of a metal hood and ribs, the electrical conductivity of which is higher than conductivity of special carbon paste.
 The goal of the work is to create modern mathematical model of the secondary current network of electric smelting furnace which could improve baking conditions of the Electrode and to reach the state of its temperature field to equable. This would create a stable mode of operation of the furnace.The paper analyzes the main features of the mathematical model of the secondary network of the smelting furnace, identifies the stages of development and formulates the main assumptionssimplifications that could be accepted wile creating this model.

Optimization Of Heat And Mass Exchange Processes In Processing A Cell Of Oil Crops

One of the promising areas in the technology of oilseed processing is electro physical processing methods. The use of electrophysical processing methods dramatically accelerates the flow of processes, increases labor productivity, reduces the need for production facilities, and in some cases reduces energy consumption. Based on the foregoing, it is possible to formulate the main goal of studying the process of heat treatment of cotton seed mint in a two-phase flow: to identify rational conditions for the process, to outline rational ways for effective structural design of the apparatus for heat treatment of cotton seed mint. Achieving this goal should ensure a reduction in the energy and material consumption of the process, an increase in the yield of black oil, an improvement in the quality indicators of the final products and working conditions of the staff. The analysis of technological processes occurring in a single biological cell of peppermint of cotton seeds is important, among other things, because it allows us to outline ways of choosing and synthesizing optimal process parameters, and to develop highly efficient plants. However, the solution to the problems of optimization of continuous heat and mass transfer (HMT) processes occurring in apparatuses or installations as a whole as L-optimization is labor intensive, since when considering complex HMT systems, the number of optimizing factors increases. In the systems under consideration, the number of main factors exceeds 20, even if they vary at two levels, more alternative options are required for optimization. The functional decomposition of optimization problems was carried out based on the hierarchical structure of the HMT systems, in which the hydrodynamic structure of the interacting flows is considered as the main central subsystem-processes, which are subsequently divided into more than elementary heat and mass transfer (HMT) processes. Optimization of the lower levels of technological plants for the implementation of solid-state processes is considered for IR - roasting in a solvent medium (IR-LCMSR).

Three-dimensional temperature prediction in cylindrical turning with large-chamfer insert based on a modified slip-line field approach

Chamfered inserts have found broader applications in metal cutting process especially in high-performance machining of hard-to-cut materials for their excellent edge resistance and cutting toughness. However, excessive heat generation and resulting high cutting temperature eventually cause severe tool wear and poor surface integrity, which simultaneously limits the optimal selection of machining parameters. In the present study, an analytical thermal–mechanical model is proposed for the prediction of the three-dimensional (3-D) temperature field in cylindrical turning with chamfered round insert based on a modified slip-line field approach. First, an innovative discretization method is introduced in a general 3-D coordinate system to provide a comprehensive demonstration of the irregular cutting geometry and heat generation zones. Then, a plasticity-theory-based slip-line field model is developed and employed to determine the intensities and geometries of every elementary heat sources in Primary Deformation Zones (PDZ), Secondary Deformation Zones (SDZ) and Dead Metal Zones (DMZ). At last, a 3-D analytical model is suggested to calculate the temperature increases caused by the entire heat sources and associated images. The maximum cutting temperature region predicted is found existing upon the chip-tool contact area rather than the tool edge. Moreover, the rationalities of cutting parameters employed are analyzed along with theoretical material removal rates and ensuing maximum cutting temperatures. The results indicate that the cutting conditions with large depth of cut and high cutting speed are more desirable than those with high feed rates. The proposed models are respectively verified through a series of 3-D Finite Element (FE) simulations and dry cutting experiments of Inconel 718 with chamfered round insert. Satisfactory agreement has been reached between the predictions and simulations as well as the measurements, which confirms the correctness and effectiveness of the presented analytical model.

Quasistatic magnetoconvection: heat transport enhancement and boundary layer crossing

We present a numerical study of quasistatic magnetoconvection in a cubic Rayleigh–Bénard (RB) convection cell subjected to a vertical external magnetic field. For moderate values of the Hartmann number $Ha$ (characterising the strength of the stabilising Lorentz force), we find an enhancement of heat transport (as characterised by the Nusselt number $Nu$). Furthermore, a maximum heat transport enhancement is observed at certain optimal $Ha_{opt}$. The enhanced heat transport may be understood as a result of the increased coherence of the thermal plumes, which are elementary heat carriers of the system. To our knowledge this is the first time that a heat transfer enhancement by the stabilising Lorentz force in quasistatic magnetoconvection has been observed. We further found that the optimal enhancement may be understood in terms of the crossing of the thermal and the momentum boundary layers (BL) and the fact that temperature fluctuations are maximum near the position where the BLs cross. These findings demonstrate that the heat transport enhancement phenomenon in the quasistatic magnetoconvection system belongs to the same universality class of stabilising–destabilising (S–D) turbulent flows as the systems of confined Rayleigh–Bénard (CRB), rotating Rayleigh–Bénard (RRB) and double-diffusive convection (DDC). This is further supported by the findings that the heat transport, boundary layer ratio and temperature fluctuations in magnetoconvection at the boundary layer crossing point are similar to the other three cases. A second type of boundary layer crossing is also observed in this work. In the limit of $Re\gg Ha$, the (traditionally defined) viscous boundary $\unicode[STIX]{x1D6FF}_{v}$ is found to follow a Prandtl–Blasius-type scaling with the Reynolds number $Re$ and is independent of $Ha$. In the other limit of $Re\ll Ha$, $\unicode[STIX]{x1D6FF}_{v}$ exhibits an approximate ${\sim}Ha^{-1}$ dependence, which has been predicted for a Hartmann boundary layer. Assuming the inertial term in the momentum equation is balanced by both the viscous and Lorentz terms, we derived an expression $\unicode[STIX]{x1D6FF}_{v}=H/\sqrt{c_{1}Re^{0.72}+c_{2}Ha^{2}}$ (where $H$ is the height of the cell) for all values of $Re$ and $Ha$, which fits the obtained viscous boundary layer well.

Numerical modelling and performance maps of a printed circuit heat exchanger for use as recuperator in supercritical CO2 power cycles

In heat to power systems with CO2 as working fluid in the supercritical state (sCO2), heat exchangers account for nearly 80% of the capital expenditure. Therefore, improved design, materials and manufacturing methodologies are required to enable the economic feasibility of the sCO2 technology. In this study, a comparison of different modelling methodologies for Printed Circuit Heat Exchangers (PCHE) is proposed to identify strengths and weaknesses of both the approaches. The elementary heat transfer unit of a PCHE recuperator for sCO2 applications is firstly modelled using 1D and 3D CFD methodologies respectively; implemented in GT-SUITE and ANSYS FLUENT software. After the comparison in terms of heat transfer performance and pressure drops, the 1D approach is used to model a 630kW PCHE recuperator. The PCHE model calibration on the design point, followed by its validation against off-design operating points provided by the manufacturer, eventually enabled to broaden the simulation spectrum and retrieve performance maps of the device. The CFD models comparison shows a good agreement between temperature profiles. However, the local heat transfer coefficient, modelled in the 1D approach through the Dittus-Boelter correlation, experiences a +10% offset on the hot side and a -20% on the cold one with respect to the 3D CFD calculations. Besides, the performance maps of the full scale PCHE recuperator show that the maximum temperature of the hot stream impose a greater influence than the maximum pressure of the cold one in terms of overall heat transfer coefficient. Nonetheless, both these operating parameters contribute to affect the heat exchanger effectiveness.

CFD modeling of macro-encapsulated latent heat storage system used for solar heating applications

This paper attempts to address and generalize the impact of elementary heat transfer aiding to phase transition of phase change material (PCM) enclosed within a thin cylindrical macro-encapsulate. A transient, three-dimensional solver with user-defined functions is modeled to study the solidification and melting characteristics of PCM aided by conduction heat transfer and external convection effects within a solar air heater system (SAHS). The conservative equations are discretized using Finite volume method (FVM). The effect of convection between the macro-encapsulate and the working fluid is captured by interface modeling. The present analysis is divided into two segments, namely, phase change assisted by conduction heat transfer alone and combined conduction-convection effects. The obtained results suggest that with conduction assisted heat transfer, only 27% of the PCM portion from the bottom of the macro-encapsulate has undergone complete melting. During the discharging cycle, as the bottom part of PCM gets solidified quickly, the heat contained within the upper regions cannot escape easily through the bottom face of macro-encapsulate. However, in the combined mode, over 70% of the PCM has undergone complete melting within the stipulated time. In addition, during the discharging cycle there was no entrapment of stored heat within the macro-encapsulate in the combined mode.

Impact of flux distribution on elementary heating events

This work used the COSMA Data Centric system at Durham University, operated by the Institute for Computational Cosmology on behalf of the STFC DiRAC HPC Facility (www.dirac.ac.uk. This equipment was funded by a BIS National E-infrastructure capital grant ST/K00042X/1, STFC capital grant ST/K00087X/1, DiRAC Operations grant ST/K003267/1 and Durham University. DiRAC is part of the National E-Infrastructure. I.D.M was funded by the Science and Technology Facilities Council (UK). The research leading to these results has also received funding from the European Research Council (ERC) under the European Union Horizon 2020 research and innovation programme (grant agreement No. 647214). J.O was funded by the Science and Technology Facilities Council (UK) by Doctoral Grant [ST/K502327/1].

Development of mathematical models and the calculations of elements of convective heat transfer systems

Despite the considerable number of papers on elaborating the methods of mathematical modeling of thermal power systems, at present little attention is paid to the development of methods of analysis of the influence of different factors on the performance indicators of work of an energy unit. In this article we substantiated principles of selection and mathematical modeling of the simplest elements of heat transfer systems, which clearly reflect the essence of processes in these systems and are convenient in terms of their mathematical modeling. The use of selection and mathematical description of elementary heat exchangers, mixers and dividers of flows may describe a variety of heat transfer system of any energy plants. These methods allow comparing various modes of operation of the equipment, its design peculiarities and their possible combination significantly faster and economically efficient. A proposed mathematical model of the elements of HTS in the form of a temperature characteristic provides unification of models of all elements, subsystems and HTS as a whole, as well as the clarity and convenience of the description of connections of elements. The calculations of heat transfer systems may be efficiently used for analysis of the work and different types of design and checking calculations of heat transfer convective surfaces. The use of generalized dimensionless parameters makes it possible to perform calculations based on different parameters of the initial information and to improve efficiency of analysis of the work of heat exchangers.

Logarithmic corrections toN≥2black hole entropy

We revisit the computation of logarithmic corrections to black holes with N equal or greater than 2 supersymmetry. We employ an on-shell method that takes advantage of the symmetries in the AdS(2) x S**2 near horizon geometry. For bulk modes interactions are incorporated through the spectrum of chiral primaries that we derive afresh. The spectrum of boundary states is computed explicitly by analyzing gauge variations. Elementary heat kernels in 4D and 2D then give the logarithmic corrections to the black hole entropy. Our computation represents a streamlined and simplified derivation that agrees with the results recently found by A. Sen.

Theoretical prediction of longitudinal heat conduction effect in cross-corrugated heat exchanger

In the elementary heat exchanger design theory, the longitudinal heat conduction through the heat transfer plate separating hot and cold fluid streams is neglected, and only the transverse heat conduction is taken into account for the conjugate heat transfer problem. In the cross-corrugated heat exchanger, the corrugated primary surface naturally leads to the highly non-uniform convective heat transfer coefficient distribution on opposite sides of the plate. In such a case, the longitudinal heat conduction may play a significant role in the thermal coupling between high heat transfer regions located on opposite sides of the plate. In the present study CFD is used to perform a quantitative assessment of the thermal performance of a cross-corrugated heat exchanger including the longitudinal heat conduction effect for various design options such as different plate thickness and corrugation geometry for a typical operating condition. The longitudinal heat conduction effect is then predicted by the theoretical method using the ‘network-of-resistance’ in the wide range of the heat exchanger design space.

Optical Measurement of Thermal Conductivity and Absorption Cross-Section of Gold Nanowires

A thin film of Al0.94Ga0.06N doped with Er3+ is used to measure the heat dissipation from lithographically prepared gold nanowires (330 nm × 20 nm × 1.6 −13.2 μm) excited at 532 nm with a Nd:YAG continuous wave laser. A temperature image of the optically excited gold nanowire is processed from the relative peak intensities from Er3+ photoluminescence. The thermal profile along the nanowire is fit using an elementary heat transfer model with the thermal conductivity as an adjustable parameter. We observe a reduction in the temperature dependent thermal conductivity of the nanowires compared to the bulk value that is attributed to an increase in scattering from grain boundaries having an average diameter of 8 nm. Energy balance yields the absorption cross-section at 532 nm, when the laser polarization is aligned with the nanowire, as 1.4 ± 0.5 × 10–13 m2.

A Practical Cost Model for Selecting Nonwoven Insulation Materials

Elementary heat transfer in the range of density, thickness, and temperature normally used for house insulation, has been described experimentally for nonwoven structures. A model relating cost, density, and thermal efficiency of nonwoven insulating materials has been developed to aid in insulation materials selection and optimization of cost. Intrinsic to this system are material specific thermal conductivity slope coefficients readily derived from thermal conductivity versus specific volume plots.

Effect of microribbing on the instantaneous convective heat transfer coefficient in the working chamber of an unlubricated piston compressor

Experimental comparative evaluation is performed for elementary heat flows and instantaneous convective heat transfer coefficients in the working chamber of a piston compressor with smooth and microribbed surfaces. An experimental procedure is developed, and an experimental test unit is manufactured. The experimental data obtained show that instantaneous convective heat transfer coefficients for the microribbed and smooth surfaces for the working chamber of an unlubricated piston compressor are approximately the same, but the elementary heat flow is directly proportional to the ribbing factor of the heat exchange surface and the temperature difference of the working gas and a given surface.

ON MODELLING HEAT AND MOISTURE TRANSFER IN SANDWICH WALL AND SLAB STRUCTURES

In real wall or slab structures made of capillary‐porous materials (such as masonry or concrete) exposed to ambient air, the unsteady processes of heat transfer and moisture migration as reciprocal phenomena are observed. Basing on the Fourier general differential equations and using the assumptions of the elementary heat balance method, the problem of heat and moisture transfer has been studied in multi‐layer wall structures, such as sandwich panels. As a result the general equations were proposed and transformed into formulas useful in the FDM approach (Finite Difference Method). On this basis a computer program was written to analyse the phenomena mentioned above. Some computational tests for a concrete sandwich panel wall with insulation made of foamed polyurethane were presented and discussed to illustrate a possible application of this approach. The paper shows that the improvement of computational accuracy of modelling the thermal engineering problems requires an assumption of real parameters which characterise capillary‐porous structural materials and result from moisture transfer.

Effect of uncertainties in physical properties on forced convection heat transfer with nanofluids

Nanofluids are considered to offer important advantages over conventional heat transfer fluids. However, at this early stage of their development, their thermophysical properties are not known precisely. As a result, the assessment of their true potential is difficult. This fact is illustrated by analyzing their thermohydraulic performance for both laminar and turbulent fully developed forced convection in a tube with uniform wall heat flux. Two different models from the literature are used to express these properties in terms of particle loading and they lead to very different qualitative and quantitative results in two types of problems: replacement of a simple fluid by a nanofluid in a given installation and design of an elementary heat transfer installation for a simple fluid or a nanofluid.