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Search results for: COMPACT HEAT EXCHANGERS
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High-temperature heat pumps – potential technology for heat recovery and production of process heat
PublicationIn the paper, the high temperature vapour compressor based heat pump with a selection of working fluids, both perspective and ecological ones, is considered. Such system is not yet commercially available on the market and in author’s opinion it has significant potential for various applications. In the presented analysis it was assumed that the heat source has a temperature of 50oC and the temperature lift is 60, 80 and 100K respectively....
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Jeffreys heat conduction in coupled semispaces subjected to interfacial heating
PublicationA Jeffreys heat conduction problem for coupled semispaces subjected to the action of an interfacial heat source was defined. An analytical solution of the problem was derived for a polynomial specific power of the heat source using the Laplace transform approach. The asymptotic and parametric analysis was performed for different ratios of thermal conductivities , thermal diffusivities , thermal relaxation times and coefficients...
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Natural convective heat transfer from isothermalconic
PublicationTheoretical considerations on convective heat transfer from isothermal upward conicalsurfaces have been presented. The physical model of this phenomenon consists of an isothermalcone of inclination angle (φ) between the cone generating line (X) and the radius (R) of the cone base. The angle is a parameter of conical surface which varied from (φ = 0−circular horizontal plate) to (φ = π/2—vertical cylinder) . Onthe basis of Navier–Stokes...
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Selected prtoblems of heat ans mass transfer
e-Learning CoursesThew lecture presentes advanced topics in heat ans mass transfer
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Selected studies of flow maldistribution in a minichannel plate heat exchanger
PublicationAnalysis of the state of-the-art in research of minichannel heat exchangers, especially on the topic of flow maldistribution in multiple channels, has been accomplished. Studies on minichannel plate heat exchanger with 51 parallel minichannels with four hydraulic diameters, i.e., 461 μm, 574 μm, 667 μm, and 750 μm have been presented. Flow at the instance of filling the microchannel with water at low flow rates has been visualized. The...
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Modeling of Passive and Forced Convection Heat Transfer in Channels with Rib Turbulators
PublicationThe main goal of the research presented in this paper was the experimental and numerical analysis of heat enhancement and aerodynamic phenomena during air flow in a channel equipped with flow turbulators in the form of properly configured ribs. The use of ribs intensifies the heat transfer and at the same time increases not only the flow resistance but also the energy costs. Therefore, designing modern heat exchangers with optimal...
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Window frame integrable air recuperation minichannel/minigap heat exchanger
PublicationThis article describes an evaluation of mini heat exchangers operation as a decentralized mechanical ventilation system with recuperative heat recovery that can be integrated into the window frame. The relatively small yet efficient air recuperation system allows for retrofitting existing buildings by reducing the overall energy consumption and thus the CO2 emissions. The proposed design, unlike existing systems, is easy to scale...
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Evaluating the influence of radiative heat flux on convective heat transfer from a vertical plate in air using an improved heating plate
PublicationThis article examines the influence of radiative heat flux on the accuracy of the results of free convective heat transfer in air. In order to carry out these tests, based on the experience gained during the operation of a plate heated on one side, compensated by a reverse heat loss flux counter-heater, a unique double-sided heating sandwich plate was designed and built, consisting of three thin epoxy resin plates reinforced with...
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Comparison of heat transfer from single- and double-sided heated horizontal plate under free convection in air with constant heat flux condition
PublicationThis paper presents the results of an experimental and numerical study of convective heat transfer from a newly designed double-sided heated horizontal plate in air. To ensure equal heat transfer from both surfaces, the plate was equipped with two independently supplied electric heaters and resistance thermometers on each side. Minimizing the plate's thickness reduced lateral heat loss and improved measurement accuracy. The study...
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Otopy Classification of Gradient Compact Perturbations of Identity in Hilbert Space
PublicationWe prove that the inclusion of the space of gradient local maps into the space of all local maps from Hilbert space to itself induces a bijection between the sets of the respective otopy classes of these maps, where by a local map we mean a compact perturbation of identity with a compact preimage of zero.
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Slow-wave fractal-shaped compact microstrip resonant cell
PublicationA novel fractal-shaped compact microstrip resonant cell (CMRC) featuring a strong slow-wave effect has been presented. Its vital usefulness in the process of microstrip line miniaturisation has been proved and experimentally validated on the basis of a compact 3-dB branch-line coupler illustrating the possibilities of the approach. A prototype example structure has been designed to mirror the characteristics of a conventional device,...
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Lefschetz periodic point free self-maps of compact manifolds
PublicationLet f be a self-map of a compact connected manifold M. We characterize Lefschetz periodic point free continuous self-maps of M for several classes of manifolds and generalize the results of Guirao and Llibre [J.L.G. Guirao, J. Llibre, On the Lefschetz periodic point free continuous self-maps on connected compact manifolds,
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Numerical Study of Turbulent Flow and Heat Transfer of Nanofluids in Pipes
PublicationIn this work, Nusselt number and friction factor are calculated numerically for turbulent pipe flow (Reynolds number between 6000 and 12000) with constant heat flux boundary condition using nanofluids. The nanofluid is modelled with the single-phase approach and the simulation results are compared with experimental data. Ethylene glycol and water, 60:40 EG/W mass ratio, as base fluid and SiO2 nanoparticles are used as nanofluid...
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Heat transfer and pressure drop characteristics of the silicone-based plate heat exchanger
PublicationThe paper presents an experimental investigation of a silicone based heat exchanger, with passive heat transfer intensification by means of surface enhancement. The main objective of this paper was to experimentally investigate the performance of a heat exchanger module with the enhanced surface. Heat transfer in the test section has been examined and described with precise measurements of thermal and flow conditions. Reported...
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Low-Cost Automated Design of Compact Branch-Line Couplers
PublicationBranch-line couplers (BLCs) are important components of wireless communication systems. Conventional BLCs are often characterized by large footprints which make miniaturization an important prerequisite for their application in modern devices. State-of-the-art approaches to design of compact BLCs are largely based on the use of high-permittivity substrates and multi-layer topologies. Alternative methods involve replacement of transmission-line...
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Lefschetz periodic point free self-maps of compact manifolds
PublicationLet f be a self-map of a compact connected manifold M. We characterize Lefschetz periodic point free continuous self-maps of M for several classes of manifolds and generalize the results of Guirao and Llibre [J.L.G. Guirao, J. Llibre, On the Lefschetz periodic point free continuous self-maps on connected compact manifolds, Topology Appl. 158 (16) (2011) 2165-2169].
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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
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Perfect thermal contact of hyperbolic conduction semispaces with an interfacial heat source
PublicationThe problem of thermal contact between two bodies with a heat source at their interface presents great scientific and practical interest. On the time scale of a nanosecond or shorter, heat propagation should be considered in the form of thermal waves of finite speeds. This study investigated the thermal behaviour of hyperbolic conduction semispaces in perfect thermal contact subjected to the action of an interfacial heat source....
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Design of Compact and Wideband Groove Gap Waveguide-Based Directional Couplers
PublicationThis paper proposes a compact cross-shaped groove gap waveguide structure for creating wideband and compact directional couplers with different coupling levels. Groove gap waveguide technology is applied to overcome fabrication challenges of printed and hollow waveguide structures in high frequency bands. The validity of the novel concept is demonstrated through the design and evaluation of several compact broadband directional...
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Effect of Flow Normalization in Micro-Pin-Finned Heat Sink: Numerical Study
PublicationThe micro-pin-fin heat sink (MPFHS) is widely employed for the heat transfer enhancement of microchannel heat sinks. In the current paper, the effect of flow normalization on the thermohydraulic performance of micro-pin-finned heat sinks is studied numerically. Two geometries of MPFHSs, the conventional design micro-pin-fin heat sink (CD-MPFHS) with a uniform-width micro pin fin and the proposed design micro-pin-fin heat sink (PD-MPFHS)...
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Empirical Relationship Describing Total Convective and Radiative Heat Loss in Buildings
PublicationOn the basis of theoretical considerations of convective-radiative heat transfer, a relationship was developed enabling the total convective and radiative heat flux QC+R emitted from any object at tw and its surroundings at t∞ to be calculated from known values of the surface temperature of such an object, i.e., the known temperature difference Δt=tw - t∞ and average air temperature Tav. This relationship is applied to thermal...
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A simplified energy dissipation based model of heat transfer for subcooled flow boiling
PublicationIn the paper a model is presented based on energetic considerations for subcooled flow boiling heat transfer. The model is the extension of authors own model developed earlier for saturated flow boiling and condensation. In the former version of the model we used the heat transfer coefficient for the liquid single-phase as a reference level, due to the lack of the appropriate model for heat transfer coefficient for the subcooled...
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Recent advances of selected passive heat transfer intensification methods for phase change material-based latent heat energy storage units: A review
PublicationThe following article overviews recent studies regarding heat transfer enhancement methods, explicitly focusing on fins and coils utilization, in phase change material-based latent heat thermal energy storage systems. It discusses the influence of various geometrical and material parameters on the melting and solidification processes, as well as the orientation of the heat transfer surface within the storage tank. Additionally,...
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Compact Dual-Polarized Corrugated Horn Antenna for Satellite Communications
PublicationIn this paper, a structure and design procedure of a novel compact dual-polarized corrugated horn antenna with high gain and a stable phase center for satellite communication is presented. The antenna incorporates an Ortho-Mode Transducer (OMT), a mode converter, and a corrugated structure. The compact OMT section is designed to be fed by standard WR-75 waveguides. The proposed compact design utilizes only ten corrugated slots...
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Management of low-temperature heat source by ORC aided by additional heat source
PublicationIn the paper presented is a concept to utilize waste heat from the power plant with the aid of the low-temperature ORC cycle. The ORC system is heated from two heat sources, the first one being the flow rate of waste heat obtained from the exhaust gases. Subsequently, the working fluid in the cycle is additionally heated by the condensing steam from the low pressure turbine extraction points increasing in such way the level of...
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Performance‐driven modeling of compact couplers in restricted domains
PublicationFast surrogate models can play an important role in reducing the cost of EM-driven design closure of miniaturized microwave components. Unfortunately, construction of such models is challenging due to curse of dimensionality and wide range of geometry parameters that need to be included in order to make it practically useful. In this letter, a novel approach to design-oriented modeling of compact couplers is presented. Our method...
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Effect of tube bundle arrangement on performance of shell-and-tube latent heat storage system
PublicationThis work presents the results of experimental investigation on charging and discharging of latent heat storage systems (LHSS) in the form of shell-and-tube heat exchangers with a variable arrays of the tube bundles. The tests included two tube arrangements – in-line and triangular (staggered), a variable number of tubes in a bundle, two pitch ratios, and different tube positions in a bundle. Three commercial products (LTP56, RT54HC,...
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Heat transfer in plate heat exchanger channels: experimental validation of selected correlation equations
PublicationThis study is focused on experimental investigation of selected type of brazed plate heat exchanger. The Wilson approach was applied in order to estimate heat transfer coefficients for the PHEx passages. The main aim of the paper was to experimentally check ability of several correlations published in the literature to predict heat transfer coefficients by comparison experimentally obtained data with appropriate predictions. The...
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Heat transfer in plate heat exchanger channels: experimental validation of selected correlation equations
PublicationThis study is focused on experimental investigation of selected type of brazed plate heat exchanger. The Wilson approach was applied in order to estimate heat transfer coefficients for the PHEx passages. The main aim of the paper was to experimentally check ability of several correlations published in the literature to predict heat transfer coefficients by comparison experimentally obtained data with appropriate predictions. The...
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A note on compact and compact circular edge-colorings of graphs
PublicationW pracy rozważamy dwa warianty kolorowania krawędzi grafów prostych i ważonych, mianowicie kolorowania zwarte oraz zwarte cyrkularne. Rozważamy relacje pomiędzy nimi. Dowodzimy, że każdy zewnętrznie planarny graf dwudzielny posiada zwarte pokolorowanie krawędziowe oraz, że problem ten dla grafów ogólnych jest NP-zupełny. Podajemy również wielomianowy 1.5-przybliżony algorytm oraz pseudowielomianowy dokładny algorytm zwartego cyrkularnego...
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Compact City na Żernikach = Compact City in Żerniki
PublicationThe paper explores the impact of the new neighbourhood built within the framework of the European Capital of Culture 2016 in Wrocław on the future development of the city.
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Hyperbolic heat conduction at a microscopic sliding contact with account of adhesion-deformational heat generation and wear
PublicationDifferent non-Fourier models were proposed to simulate temperatures in materials subjected to extremely fast thermal disturbances, when the speed of heat propagation should be concerned. The present study investigated temperature and heat balance at a microscopic sliding contact during a single frictional interaction based on the Cattaneo-Vernotte hyperbolic heat conduction equation. Two fundamental features of friction, namely,...
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Experimental investigation on straight and u-bend double tube heat exchanger with active and passive enhancement methods
PublicationAuthors in this work want to demonstrate the possibility to increase the heat transfer efficiency by using simple wire coil inserts to create turbulent flow in the boundary layer as well as air blowing into the annulus of the pipe. In the study, Wilson plot approach was applied in order to estimate heat transfer coefficients for all heat exchanger (HX) configurations. The study focuses on experimental values of heat transfer coefficient...
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Management of low-temperature heat source by ORC aided by additional heat source
PublicationThe presented work is aimed at utilisation of waste heat in the manner to produce electricity in ORC installation. Therefore the precondition of the study was to use the waste heat available in the form of a stream of hot water at 90°C. Such low enthalpy heat source is rather insufficient to produce a good quality vapour to feed the ORC turbine. That was the incentive to search for the ways of increasing the temperature of the...
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Heat Turbomachinery
e-Learning CoursesPodstawowe informacje dotyczące obiegów cieplnych siłowni z turbinami parowymi i gazowymi. Główne elementy siłowni turbinowych. Zagadnienia przepływowe maszyn wirnikowych. Teoria stopni turbinowych. Część przepływowa turbin.
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Heat Turbomachinery
e-Learning CoursesPodstawowe informacje dotyczące obiegów cieplnych siłowni z turbinami parowymi i gazowymi. Główne elementy siłowni turbinowych. Zagadnienia przepływowe maszyn wirnikowych. Teoria stopni turbinowych. Część przepływowa turbin.
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Heat Turbomachinery
e-Learning Courses -
Heat turbomachinery
e-Learning Courses1. Steam turbine cycles. 2. Gas turbine cycles. 3. Combined gas-steam cycles. 4. Flows in nozzles. 5. Theory of turbine stages. 6. Multistage turbines. 7. Examples of turbine design.
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An Implementation of a Compact Smart Resistive Sensor Based on a Microcontroller with an Internal ADC
PublicationIn the paper a new implementation of a compact smart resistive sensor based on a microcontroller with internal ADCs is proposed and analysed. The solution is based only on a (already existing in the system) microcontroller and a simple sensor interface circuit working as a voltage divider consisting of a reference resistor and the resistive sensor connected in parallel with an interference suppression capacitor. The measurement...
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A Geometrically Simple Compact Wideband Circularly Polarized Antenna
PublicationA compact broadband wide-slot circular polarization (CP) antenna is proposed. An inverted L-shape parasitic strip at the open end of a microstrip line extension and a slot modification is applied to attain wideband CP. The advantage of this technique is simplicity which makes it readily re-designable for different frequency bands. To demonstrate the concept, three designs working at different frequencies are obtained. The redesign...
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A robust design of a numerically demanding compact rat-race coupler
PublicationA fast and accurate design procedure of a computationally expensive microwave circuit has been presented step-by-step and experimentally validated on the basis of a compact rat-race coupler (RRC) comprising slow-wave resonant structures (SWRSs). The final compact RRC solution has been obtained by means of a sequential optimization scheme exploiting the implicit space mapping (ISM) algorithm. A well-suited surrogate optimization...
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Natural convective heat transfer from isothermal cuboids
PublicationThe paper presents results of theoretical and experimental investigations of the convective heat transfer from isothermal cuboid. The analytical solution was performed taking into account complete boundary layer length and the manner of its propagation around isothermal cuboid. It arises at horizontal bottom surface and grows on vertical lateral surface of the block. After changing its direction, the boundary layer occurs above...
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Rapid surrogate-assisted statistical analysis of compact microstrip couplers
PublicationIn this paper, a technique for low-cost statistical analysis and yield estimation of compact microwave couplers has been presented. The analysis is executed at the level of a fast surrogate model representing selected characteristic points of the coupler response that are critical to determine satisfaction/violation of the prescribed design specifications. Because of less nonlinear dependence of the characteristic points on geometry...
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A simplified energy dissipation based model of heat transfer for post-dryout flow boiling
Publicationmodel for post dryout mist flow heat transfer is presented based on considerations of energy dissipation in the flow. The model is an extension of authors own model developed earlier for saturated and subcooled flow boiling. In the former version of the model the heat transfer coefficient for the liquid singlephase convection as a reference was used, due to the lack of the appropriate model for heat transfer coefficient for the...
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Experimental study and comparison with predictive methods for flow boiling heat transfer coefficient of HFE7000
PublicationThis article describes an experimental study of flow boiling of HFE7000 inside a smooth vertical channel. The investigation has been carried out in a circular stainless-steel tube with an inner diameter of 2.3 mm. The data have been collected for the applied heat fluxes q ranging from 61 to 205 kW/m2, the mass flux G ranging from 214 to 1006 kg/(m2 s), the saturation temperature Tsat ranging from 30 to 54 °C and the full range...
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Simulation-driven design of compact ultra-wideband antenna structures
PublicationPurpose–The purpose of this paper is to investigate strategies and algorithms for expedited designoptimization and explicit size reduction of compact ultra-wideband (UWB) antennas.Design/methodology/approach–Formulation of the compact antenna design problem aiming atexplicit size reduction while maintaining acceptable electrical performance is presented. Algorithmicframeworks are described suitable for handling various design situations...
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Experimental study on single phase operation of microjet augmented heat exchanger with enhanced heat transfer surface
PublicationThe article presents experimental investigations on a prototype heat exchanger. Presented research is focused on combined active and passive enhancement techniques of surface modification and microjet impingement. The results were compared to reference plate heat exchanger without microjet impingement. The Wilson plot method was applied to determine the heat transfer coefficients in the single phase operation. The heat exchanger...
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A structure and design of a novel compact UWB MIMO antenna
PublicationIn the paper, a concept and design procedure of a novel compact MIMO slot antenna is presented. In order to achieve a better filling of available space, individual antennas are constrained to a triangular shape and optimized for a reduced size. The MIMO structure is then assembled using the two of previously designed antennas in orthogonal arrangement. Surrogate-assisted numerical optimization involving variable-fidelity electromagnetic...
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Rapid design optimization of compact couplers using response features and adjoint sensitivities
PublicationA technique for rapid EM-driven design optimization of compact microwave couplers is presented. Our approach exploits response features and adjoint sensitivities and allows for low-cost design closure both in terms of performance enhancement and structure miniaturization. It is demonstrated using a compact rat-race coupler working at 1 GHz and compared to adjoint-based gradient optimization.
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Thermodynamic and geometrical characteristics of mixed convection heat transfer in the shell and coil tube heat exchanger with baffles
PublicationThe article presents passive heat transfer enhancement method in the form of baffles to increase the energy efficiency of the shell coil heat exchanger. Conducted literature review shows that, despite numer- ous studies, there is little work on the intensification of heat transfer at the shell side. Most of the work focuses on the impact of geometrical parameters of the coil itself. This article successfully proves that it is possible...