Electrical Analogy Method Research Articles

Estimating the Impact of a Recuperative Approach on the Efficiency of Thermoelectric Cooling

Thermoelectric cooling is a prospective technology that has a lot of advantages; however, its main drawback is its low efficiency compared to other technologies. A lot of scientific research is aimed at the improvement of the efficiency of thermoelectric cooling, including the development of new thermoelectric materials, innovative structures, and better power management strategies. The present work further explores a self-developed recuperative power management approach, which takes advantage of the thermoelectric element’s ability to work as an electrical generator. This study relied on the thermal–electrical analogy method to develop a model that is capable of describing the impact of recuperation on the cooling performance while preserving the simplest configuration possible. The influence of different variables was estimated by three suggested quantities for evaluating the gains, losses, and rationality of the recuperative approach. A recovery of up to 10% of the electrical energy supplied to the thermoelectric element was observed experimentally. The ratio between the recovered energy and induced heat losses did not exceed a factor of 0.9. It is concluded that the recuperation process is reasonable only in the case of unavoidable interruption of the cooling process when average-performance thermoelectric elements are used.

Thermal performance enhancement in the receiver part of solar parabolic trough collectors

In this study, CFD analysis for thermal performance of absorber tube with inner helical axial fins which is used in solar PTC collector is considered and compared. Three-dimensional numerical model simulations were performed using flow and heat transfer interfaces in COMSOL Multiphysics software. Water is used as heat transfer fluid and copper was chosen as receiver tube material. Sun's radiation is considered as constant at around (Io=1000 W/m2) and concentration ratio is C=60. Inlet velocity of heat transfer fluid is changed from 0.2ms to 0.2 4 ms in order to define its magnitude with the length of absorber tube. Electrical analog method is utilized for mathematical modeling to evaluate heat losses through the absorber tube. Variations of surface and fluid temperature are determined to investigate the receiver which shows better performance in the given boundary conditions. In the discussion section of the article, temperature variation of the receiver tube and HTF during this process is presented.

Study on a direct-coupling thermoacoustic refrigerator using time-domain acoustic-electrical analogy method

Thermoacoustic refrigeration is a clean cooling technology with high reliability. In this study, a time-domain acoustic–electrical analogy (TDAEA) method is proposed and improved, then applied to explore the performance of a high-efficiency 2-stage looped direct-coupling heat-driven thermoacoustic refrigerator. The effectiveness of the method is verified by experiments. Transient evolutions of oscillating pressure and volume flow rate are first presented. System performance under different working gases is explored, and helium is chosen due to its much larger cooling power. The influences of cooling and ambient temperatures and cavity parameters on system performance are then investigated. The results show that a rise in ambient temperature leads to a dramatic decline in cooling power. Moreover, the influences of cavity parameters are complicated. When the diameter and length of the cavity are respectively 95 mm and 440 mm, the cooling power achieves a maximum of 3.65 kW with COP of 0.76; while with diameter and length reaching 90 mm and 360 mm, respectively, a peak COP of 0.82 with cooling power of 1.47 kW is obtained. Furthermore, a comparison between the presented direct-coupling system and a series-connection system is performed. The results show better performance of the direct-coupling system, which achieves a cooling power of 5.08 kW under air-conditioning case, 22.4 % higher than that of the series-connection system, implying its superiority in air-conditioning field for larger cooling capacity and more compact configuration. This study provides a new perspective for understanding ofthermoacoustic refrigerators.

Vibro-acoustic coupling characteristics of the microperforated panel with local resonators

This paper provides a unified approach to evaluate the sound absorption performance of the metamaterial microperforated panel (MMPP) with additional local resonators under elastic boundaries. The elastic boundary conditions can be realized by setting the stiffness of restrained spring at the edges as a specific value. The vibration equations of the metamaterial panel (MP) are derived by combining the Spectral Geometry method with the Rayleigh Ritz method, and the acoustic electrical analogy method is used to solve the absorption coefficient considering the vibro-acoustic coupling. The program developed by these methods can be used to study the vibro-acoustic coupling model of the MMPP with various parameters under various boundaries. To validate the accuracy of the present method, a structure-acoustic simulation model is established, and a good agreement is achieved between the theoretical method and the finite element method. A comprehensive parametric analysis is performed to obtain the optimum suppression performance of sound absorption and the variation of the absorption coefficients has been explained justifiably in detail. The results demonstrate that additional local resonators can improve the absorption performance of the microperforated panel, and the absorption band can be appropriately broadened by reducing the spring stiffness or increasing mass ratio. This paper provides a better sound absorption prediction for the practical application of MMPP under complex conditions.

Исследование фильтрации из оросительного канала методом электрогидродинамических аналогий

Purpose: simulation of the filtration process from an irrigation canal made in an earthen channel. Materials and methods. One of the most common methods in the waterworks construction and operation is the filtration process modeling. In practice, the use of mathematical modeling based on the use of mathematical analogies of various physical processes, which are described by the same differential equations, is widespread. The electric analogy method (EGDA) is based on the analogy between the groundwater velocity and the electrical current flow and allows solving various filtration problems on models of electrically conductive materials. The purpose of modeling the groundwater velocity using the EGDA method is to develop a model similar to a full-scale object, for studying the ongoing filtration processes with its help. Results. A flow net and a filtration velocity profile which were used to study free filtration from a canal in an earthen channel were constructed. As a result of the study, the specific filtration flow rate, filtration rate were determined and a comparison with the values obtained by calculation was made. Comparison of the results obtained from the flow net with the calculation formula showed that their values coincide with an error of 1.26 %. The specific flow rate determined by the calculation method coincides with the flow net value for the selected belt of equal pressure with an error of 2.8 %. Conclusions: the EGDA method allows determine effectively the seepage water losses from the canal, however, when quantifying the seepage flow, it gives more significant errors due to the complexity of complete recording when modeling the real conditions of the object under consideration.

Analysis of the sound absorption characteristics of the curved microperforated panel with elastically restrained edges

This paper describes the analytical and experimental study on the sound absorption characteristics of the curved microperforated panel (CMPP) with elastically restrained edges backed by an air cavity. The arbitrary boundary conditions are realized by setting the restrained spring at the edges to zero or infinite. The acoustic impedance formula of the CMPP is derived based on the modal superposition method. The acoustic electrical analogy method is used to obtain the sound absorption coefficient of the CMPP, in which the effects of the structural parameters on the sound absorption coefficient such as aspect ratio, radius of curvature, perforation rates, micro holes diameters and panel thicknesses are also studied. To validate the accuracy of the present method, the impedance tube test system is designed to measure the sound absorption coefficient under different micro holes diameters and panel thicknesses. The results derived by the analytical method and the test one match well with each. This paper provides a new kind of sound absorption structures which could be used in the health environment.

An Explicit Finite Element Method for Thermal Simulations of Buildings with Phase Change Materials

The thermal performance of building envelopes is essential for building thermal comfort and the reduction of building energy requirements. Phase change materials (PCMs) implemented in building envelopes can improve thermal performance. An explicit finite element method (ex-FEM) has been developed based on a previous study to investigate the heat transfer performance through building walls with installed PCMs. For verification, we introduce an electrical circuit analogy (ECA) method. For model validation, at first, COMSOL is used. For comparison, data were collected from experiments using a small hotbox, part of the sides are covered by PCMs with different configurations. This work shows how the ex-FEM model can predict the wall’s temperature profile with and without incorporated PCM. With the implementation of PCMs, the work problematizes unpredictable influences for modeling. In addition, the study introduces results from simulations of sequencing of PCM layers in wall construction.

Investigation of a double-degree-of-freedom wave energy converter

Wave energy is a large-volume renewable, clean and pollution-free new energy source, which is of great significance in solving energy crisis and environmental degradation. Based on the similarity principle between mechanical and electrical system, the equivalent circuit model of the heave-surge double-degree-of-freedom wave energy converter (DDOF-WEC) is established by using the electrical analogue method in this paper. The sufficient condition of the system stability is analyzed using the Routh–Hurwitz criterion. It is verified that the DDOF-WEC has higher wave energy capture capability than the single-degree-of-freedom wave energy converter (SDOF-WEC).

A simulation-based analysis of photovoltaic thermal hybrid solar collectors with a new TRNSYS type model

Nowadays buildings are responsible of 36% of CO2 emissions and space heating and cooling alone accounts for 40% of the final energy consumption at European level. In this context, solar-assisted systems represent an important solution to support the decarbonisation pathways in residential sector. In this work, a novel lumped parameter simulation model for photovoltaic thermal hybrid solar collectors developed by Authors as a type of Transient System Simulation (TRNSYS) software is used to carry out computer simulations in different climatic conditions. The model is based on the electrical analogy method to solve the transient heat transfer problem and considers the effect of the thermal capacitances of the elements composing the photovoltaic thermal collector. The simulation tool was also validated with the experimental data in terms of both electrical and thermal power. In this work, a simulation-based analysis is carried out considering three climatic zones in order to evaluate the thermal performance of photovoltaic thermal hybrid solar collectors under different operating conditions.

Design Applicable 3D Microfluidic Functional Units Using 2D Topology Optimization with Length Scale Constraints.

Due to the limits of computational time and computer memory, topology optimization problems involving fluidic flow frequently use simplified 2D models. Extruded versions of the 2D optimized results typically comprise the 3D designs to be fabricated. In practice, the depth of the fabricated flow channels is finite; the limited flow depth together with the no-slip condition potentially make the fluidic performance of the 3D model very different from that of the simplified 2D model. This discrepancy significantly limits the usefulness of performing topology optimization involving fluidic flow in 2D—at least if special care is not taken. Inspired by the electric circuit analogy method, we limit the widths of the microchannels in the 2D optimization process. To reduce the difference of fluidic performance between the 2D model and its 3D counterpart, we propose an applicable 2D optimization model, and ensure the manufacturability of the obtained layout, combinations of several morphology-mimicking filters impose maximum or minimum length scales on the solid phase or the fluidic phase. Two typical Lab-on-chip functional units, Tesla valve and fluidic channel splitter, are used to illustrate the validity of the proposed application of length scale control.

The prediction of nonlinear resistance and distortion for a miniature loudspeaker with vented cavities.

The nonlinear resistance and its influence on the total harmonic distortion of a miniature loudspeaker with vented cavities are investigated. A method for the prediction of nonlinear resistance is described. In the model, the nonlinear resistance caused by the magnetic gap and the orifices in the back cover of the miniature loudspeaker is taken into account. The nonlinear acoustic resistance is estimated through the electric analogy method, and then it is transformed into the equivalent nonlinear resistance of the vibrating diaphragm. The estimated nonlinear resistance is verified through the Klippel Analyzer measurement. The influence of the nonlinear resistance, mechanical stiffness and force factor on the total harmonic distortion is calculated and compared with the measurements.

Numerical Model of HTS Cable and Its Electric-Thermal Properties

High-temperature superconducting (HTS) cables have significant advantages in large-capacity and long-distance transmission. In order to analyze the operation characteristics of HTS cables in ac power system, this paper develops a numerical model to research its electric and thermal properties in transient process. Different from the model built by finite-element method in COMSOL, this model is built in MATLAB/SIMULINK for faster calculation and simpler modeling process. Besides, it is compatible with the power system simulation. Based on the structure of HTS cables, the model is built by an equivalent circuit and an electrical-analog method. The author tested the model by comparing it with a model built in COMSOL, to verify the effectiveness and advantages. The simulation result illustrates that the proposed model helps analyze the electric and thermal property of cables during transient process in power system quickly and efficiently.

Short Overview of Early Developments of the Hardy Cross Type Methods for Computation of Flow Distribution in Pipe Networks

Hardy Cross originally proposed a method for analysis of flow in networks of conduits or conductors in 1936. His method was the first really useful engineering method in the field of pipe network calculation. Only electrical analogs of hydraulic networks were used before the Hardy Cross method. A problem with flow resistance versus electrical resistance makes these electrical analog methods obsolete. The method by Hardy Cross is taught extensively at faculties, and it remains an important tool for the analysis of looped pipe systems. Engineers today mostly use a modified Hardy Cross method that considers the whole looped network of pipes simultaneously (use of these methods without computers is practically impossible). A method from a Russian practice published during the 1930s, which is similar to the Hardy Cross method, is described, too. Some notes from the work of Hardy Cross are also presented. Finally, an improved version of the Hardy Cross method, which significantly reduces the number of iterations, is presented and discussed. We also tested multi-point iterative methods, which can be used as a substitution for the Newton–Raphson approach used by Hardy Cross, but in this case this approach did not reduce the number of iterations. Although many new models have been developed since the time of Hardy Cross, the main purpose of this paper is to illustrate the very beginning of modeling of gas and water pipe networks and ventilation systems. As a novelty, a new multi-point iterative solver is introduced and compared with the standard Newton–Raphson iterative method.

The validation of a novel lumped parameter model for photovoltaic thermal hybrid solar collectors: a new TRNSYS type

Decarbonisation is one of the most important challenges facing researchers, and solar-assisted systems represent an important solution to reduce the energy consumption at the household-scale. The current work contributes to existing research by proposing and validating a novel lumped parameter simulation model for photovoltaic thermal hybrid solar collectors using field measurements carried out at an experimental facility. The modelling approach, which also considers the effect of the thermal capacitances of the elements composing the photovoltaic thermal collector, used an electrical analogy method to solve the transient heat transfer problem. The results of the simulations were compared with the experimental data collected during different weather conditions; the effects of the thermal capacitances of the collector were also investigated. The results were compared in terms of both average daily performance and instantaneous values of the variables characterizing the system. Although the differences were negligible, the results of the simulation analyses matched the measurements more precisely when the thermal capacitances were taken into consideration. Finally, the simulation model was implemented as a TYPE of Transient System Simulation (TRNSYS) software, and it is made freely available to facilitate future integrated computer simulations.

Comparison Analysis and Optimization of Composite Micro-perforated Absorbers in Sound Absorption Bandwidth

Micro-perforated panel (MPP) absorber with a single uniform air cavity is regarded as a promising sound-absorbing structure; however, MPP absorption performance remains unfortunately limited due to the Helmholtz resonance mechanism, which results in more and more attention being placed on composite MPP absorbers. This study focuses on acoustic properties of different composite MPP absorbers, including three types of composite MPP absorbers which are coupled in serial, parallel and serial–parallel modes. Their mathematical models of the normal absorption coefficient are established by utilizing the acoustic electric analogy method. The single-cavity MPP absorber and three composite MPP absorbers are preliminarily designed to verify the equivalent circuit models and perform a pilot analysis of their sound absorption characteristics. Moreover, the particle swarm optimization algorithm is selected to optimize the absorbers so that optimal combination of structure parameters within a prescribed frequency range can be obtained. In addition, the absorbers are made based on the optimized parameters for experimental investigation. The results show that a wider absorption bandwidth may be achieved by composite MPP absorbers through introducing additional absorption peaks with reference to that for the conventional single-cavity MPP absorber, and there are more absorption peaks for the serial–parallel-coupled MPP absorber rather than the simply serial- or parallel-coupled MPP absorber so that better sound absorption effect may be achieved.

A Study of the Dynamic Processes of a Starter-Generator by the Electrical Analogy Method

The dynamics of a single-machine starter-generator unit, where the oscillatory regime occurs with the moment variation, is studied. The dynamic process calculation is performed with the use of differential equations. The mathematics analysis is presented. The basic relationships, used in the calculations of the static moments, forces and inertia moments, are considered. The present system motion equation is derived with the use of d`Alembert`s principle. The system of the equilibrium equation and the angular coordinate dependent differential equation is composed for the «starter-generator – crank shaft» calculation system. The electrical analogy method is used for deriving the equation of the torques applied to the same shaft. The angular frequency of revolution is determined by the equivalent circuit of the single-mass mechanical unit and the mechanical chain equivalent circuit in terms of the moment of rotation and the complex mechanical resistance, specified for the four-mass system. Then the process of the system transformation to the two-mass system is considered. The analytical expression for the resonance frequency is determined. The time variation of the parameters in the starter regime is considered in the Simulink program of the MATLAB software package.

Low frequency band gap characteristics of double-split Helmholtz locally resonant periodic structures

A double-split Helmholtz periodic structure with the characteristic of local resonance is designed and constructed in this paper. The double-split periodic structural cell which can be divided into internal and external cavities is adopted in structure. In such a kind of structure, the resonating area is remarkably expanded while the inner cavity is continuously enlarged. Thus, a satisfactory feature of low frequency resonance can be obtained. At the same time, the adjustability of band gap is achieved by the designed adjustment of the arc length of the inner cavity, therefore, the effect of sound insulation in a specific low frequency band can be achieved. In the analyses of the mechanism and factors of the generation of low frequency band gap, the mathematical model of the upper and lower limits of the band gap is established by using the electric circuit analogy. And some comparative analyses between the methods of electric circuit analogy and finite element method are carried out. The result suggests that a satisfactory feature of low frequency band gap is presented, and the first band-gap ranges from 86.9 Hz to 138.2 Hz. The low frequency band gap can be influenced by the arc length of inner cavity, the space between inner and outer cavities, and the interaction of the structural cells in the periodic arrangement. The longer the arc length of the inner cavity, the lower the low frequency band gap will be; the longer the distance between inner and outer cavities, and the higher the frequency of band gap, the worse the low frequency effect will be; the lower limit of low frequency band gap cannot be influenced by reducing the space between individual structures, on the contrary, the width of low frequency band gap can be sharply increased. Plenty of practical and theoretical support in the field of low frequency noise reduction is offered in the research.

Improving low-frequency sound absorption of micro-perforated panel absorbers by using mechanical impedance plate combined with Helmholtz resonators

The traditional Micro-perforated plate (MPP) is a kind of clean and non-polluting absorption structure in the middle and high frequency and has been widely used in the field of noise control. However, the sound absorption performance is dissatisfied at low frequencies when the air-cavity depth is restricted. In this paper, a mechanical impedance plate (MIP) is introduced into the traditional MPP structure and a Helmholtz resonator is attached to the MIP. Mechanical impedance plate (MIP) provides a good absorption at low frequency by using mechanism of mechanical resonance and the acoustic energy is dissipated in the form of heat with viscoelastic material. Helmholtz resonator can fill in the defect of the poor absorption effect between the Micro-perforated plate (MPP) and the mechanical impedance plate (MIP). The acoustic impedance of the proposed sound absorber is investigated by using acoustic electric analogy method and impedance transfer method. The influence of the tube’s length of Helmholtz resonator and the number of Helmholtz resonator on the sound absorption is studied. The corresponding results are in agreement with the theoretical calculation and prove that the composite structure has the characteristics of improving the low frequency sound absorption property.

English

From the literature, it is found that two different criteria were followed for the prediction of transverse thermal conductivity (K2) of fiber reinforced plastic (FRP) composites. In the first criterion, the internal anisotropy of the lamina is assumed negligible and K2 is estimated using simple Fourier’s law of 1-D heat conduction applied to representative volume element (RVE). Whereas in the second approach, an electrical analogy method is followed. To estimate the effect of internal anisotropy, through thickness thermal conductivity (K3) of an FRP lamina is determined by both the approaches through finite element method for an RVE in the auxiliary plane. The problem is modeled in ANSYS 15 software. In the present paper studies are made for various volume fractions (0.1-0.75) and for various angles (20°-90°) made by the section plane with the fiber axis. It is observed that the through thickness thermal conductivity is consistent in the second approach, whereas in the first approach there is considerable variation (max 8.7%) with the orientation of the unit cell.    Key words: Through thickness thermal conductivity, finite element method (FEM), unit cell orientation.

Consistency in Electrical Analogy Approach with Respect to Thermal Conductivity Mismatch in FRP Composites

From the literature it is found that, two different approaches were followed for the prediction of transverse thermal conductivity (K2) of FRP composites. In the first approach, the internal anisotropy of the lamina is assumed negligible and K2 is estimated using simple Fourier's law of 1-D heat conduction applied to Representative Volume Element (RVE). Whereas in the second approach, electrical analogy method is followed. To estimate the effect of internal anisotropy, through thickness thermal conductivity (K3) of an FRP lamina is determined by both the approaches using the Finite Element method for an RVE in the auxiliary plane. The problem is modelled in ANSYS 15 software. In the present paper studies are made for various Kf/Km values (1-50) and for various angles (200-900) made by the section plane with the fiber axis. It is observed that the through thickness thermal conductivity is consistent in the second approach, whereas in the first approach there is considerable variation (max. 8.6%) with the orientation of the unit cell.