Filtry
wszystkich: 426
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Wyniki wyszukiwania dla: FORCED CONVECTIVE HEAT TRANSFER
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EXPERIMENTAL INVESTIGATION OF FREE CONVECTION OF GLYCOL-Al2O3 NANOFLUID FROM HORIZONTAL TUBE
PublikacjaNanofluids came to be seen as a new generation of coolants, both in single- and two phase systems. Furthermore, nanofluids or nanocomposites may be used as a media in a thermal energy storage (TES) in such systems as sensible heat storage (SHS) and phase change materials (PCM). In the SHS systems the dominating mechanism of the heat transfer is natural convection. However, in the literature only a few investigations of free convection...
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A pore-scale thermo–hydro-mechanical model for particulate systems
PublikacjaA pore scale numerical method dedicated to the simulation of heat transfer and associated thermo–hydro-mechanical couplings in granular media is described. The proposed thermo–hydro-mechanical approach builds on an existing hydromechanical model that employs the discrete element method for simulating the mechanical behavior of dense sphere packings and combines it with the finite volume method for simulating pore space fluid flow...
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Experimental validation of pressure drop models during flow boiling of R134a – effect of flow acceleration and entrainment
PublikacjaA crucial step to assure proficient work of power and process apparatus is their proper design. A wide array of those devices operates within boiling or condensation of the working fluid to benefit from high heat transfer rates. Two-phase flows are associated with high heat transfer coefficients because of the latent heat of evaporation and high turbulence level between the liquid and the solid surface. Predicting heat transfer...
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Mechanism of Solute and Thermal Characteristics in a Casson Hybrid Nanofluid Based with Ethylene Glycol Influenced by Soret and Dufour Effects
PublikacjaThis article models a system of partial differential equations (PDEs) for the thermal and solute characteristics under gradients (concentration and temperature) in the magnetohydrodynamic flow of Casson liquid in a Darcy porous medium. The modelled problems are highly non-linear with convective boundary conditions. These problems are solved numerically with a finite element approach under a tolerance of 10−8. A numerical algorithm...
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Forced vibrations in a dynamic system that is damped by a mechanism that trans-pass through its singular position
PublikacjaIn the paper, vibrations of a hybrid multibody-continuous system are investigated. For all the mechanical devices, effective damping methods are crucial in the design process. To obtain it, installation of viscous dampers or elasto-viscous elements is dominant. In the paper, an alternative method is investigated. It is based on modal disparity. To describe the method briefly, when structural damping is present in continuous systems,...
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Multi-nodal PWR reactor model — Methodology proposition for power distribution coefficients calculation
PublikacjaIn the paper the multi-nodal Pressurized Water Reactor (PWR) model called Mann’s model is presented. This models is used for modelling purposes of the heat transfer from fuel to coolant in reactor core. The authors expand widely used in literature approach by defining additional coefficients for the heat transfer model. These parameters approximate the power generation distribution in the PWR reactor core according to the to the...
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Thermal Energy Storage with PCMs in Shell-and-Tube Units: A Review
PublikacjaThe paper presents a survey of the experimental and numerical studies of shell-and-tube systems in which phase change material (PCM) is used. Due to the multitude of design solutions for shell-and-tube systems, the emphasis is placed on double-tube (DT), triplex-tube (TT), and multitube (MT) units. Additionally, only single-pass systems are considered. Particular attention is paid to the method of heat transfer intensification....
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A Comparison of Empirical Correlations of Viscosity and Thermal Conductivity of Water-Ethylene Glycol-Al2O3 Nanofluids
PublikacjaBecause of their superb thermal conductivity, nanofluids are seen as new generation of cooling mediums in many engineering applications. It is well established that even a small amount of nanoparticles mixed with a base fluid may result in distinct thermal conductivity enhancement. On the other hand, addition of nanoparticles to the base fluid results in its substantial viscosity increase. Therefore, it is very dicult to evaluate...
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Możliwości ograniczenia zużycia energii napędowej urządzeń przez optymalizację doboru wymienników ciepła, właściwą konfigurację i kontrolę przepływu płynów roboczych
PublikacjaArtykuł poświęcony możliwości ograniczenia zużycia energii napędowej urządzeń na drodze optymalizacji doboru wymienników ciepła, właściwej konfiguracji i kontroli przepływu płynów roboczych. Przedstawiono w nim ocenę zużycia energii w systemach energetycznych o największej energochłonności w realiach Polski. Zwrócono uwagę na możliwość wykorzystania wymienników ciepła o wysokiej efektywności dla zmniejszenia oporu przenoszenia...
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New trends in development of micro heat exchangers for ORC's
PublikacjaIn the paper, new trends in development of micro heat exchangers for CHP are presented. Main attention is concentrated on the question, how channels size and thermal development lenght affect the heat transfer. New types of micro heat exchangers developed at the Institute of Fluid-Flow Machinery PAS and the methoda of their design are presented. The new experimental testing methods of the micro-channel heat exchangers, new algorithms...
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Thermal and Hydrodynamic Phenomena in the Stagnation Zone — Impact of the Inlet Turbulence Characteristics on the Numerical Analyses
PublikacjaOne of the methods of heat transfer enhancement is utilization of the turbulent impinging jets, which were recently applied, for example, in the heat exchangers. Their positive impact on the heat transfer performance was proven, but many questions related to the origin of this impact are still unanswered. In general, the wall-jet interaction and the near-wall turbulence are supposed to be its main reason, but their accurate numerical...
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Experimental investigation of two-phase thermosyphon heat exchanger charged with acetone
PublikacjaThis paper presents thermal characteristics of prototype of a two-phase thermosyphon heat exchanger (TPTHEx) charged with acetone as a working fluid. The TPTHEx consists of two horizontal cylindrical vessels connected by two risers and a downcomer. Tube bundles placed in the lower and upper cylinders work as an evaporator and a condenser, respectively. The tested TPTHEx operates in a vacuum. Therefore, the working liquid is boiled...
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Turbulence models impact on the flow and thermal analyses of jet impingement
PublikacjaAccurate numerical reconstruction of heat and mass transfer processes in particular applications, such a jet impingement, is difficult to obtain even with the use of modern computational methods. In the proposed paper, the flow and thermal phenomena occurring during single minijet impingement on the flat, concave and convex, heated surfaces were considered. Problem of impingement on non-flat surface, still not common and purely...
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An advanced thermal-FSI approach of an evaporation of air heat pump
PublikacjaThe paper presents selected problems of numerical modeling of an advanced thermal-FSI approach of evaporator of air heat pomp. The example of a fin-tube evaporator has been studied, focusing on obtaining of heat exchanger characteristics applying two-phase flow model for the in-tube refrigerant flow. Special attention is given to heat transfer between separated medium for different air velocity and changed refrigerant mass flow...
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Galerkin Finite Element Process for Entropy Production and Thermal Evaluation of Third-Grade Fluid Flow: A Thermal Case Study
Publikacja: A fluid’s moving class improves its heat transmission capability, as well as its rigidity, owing to multivariate molecule suspension. In this way, nanofluids are superior to common fluids. In this study, we evaluated the features of ease and heat transfer. Furthermore, we investigated permeable media, heat source, variable heat conductivity, and warm irradiation results. A mathematical technique known as the Galerkin finite element...
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A new construction of shell-and-tube heat exchanger with impinging jets and minichannels technologies for heat recovery from gases – experimental analysis
PublikacjaA dynamic development of technologies allowing waste heat utilization is observed in a correspondence with a pro-ecological approach of the zero waste idea. Such approach becomes the most demanding in the area of low-temperature was heat sources, especially gaseous media. Till now, they were usually not utilized due to unfavorable thermal conditions and high costs. Therefore, the zero waste approach directs research on techniques...
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Performance of a plate heat exchanger operated with water-Al2O3 nanofluid
PublikacjaThis study is focused on experimental investigation of a selected type of brazed plate heat exchanger (PHEx). The main aim of the paper was to experimentally check the ability of nanofluids to enhance the performance of PHEx. A typical water-Al2O3 nanofluid was tested and compared to that of the base fluid, i.e. water. Nanoparticles were tested at the concentration of 0.1% and 1% by weight. Impact of the 1 day and 3 days break...
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Performance of a plate heat exchanger operated with water-Al2O3 nanofluid
PublikacjaThis study is focused on experimental investigation of a selected type of brazed plate heat exchanger (PHEx). The main aim of the paper was to experimentally check the ability of nanofluids to enhance the performance of PHEx. A typical water-Al2O3 nanofluid was tested and compared to that of the base fluid, i.e. water. Nanoparticles were tested at the concentration of 0.1% and 1% by weight. Impact of the 1 day and 3 days break...
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Performance of a plate heat exchanger operated with water-Al2O3 nanofluid
PublikacjaThis study is focused on experimental investigation of a selected type of brazed plate heat exchanger (PHEx). The main aim of the paper was to experimentally check the ability of nanofluids to enhance the performance of PHEx. A typical water-Al2O3 nanofluid was tested and compared to that of the base fluid, i.e. water. Nanoparticles were tested at the concentration of 0.1% and 1% by weight. Impact of the 1 day and 3 days break...
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Experimental investigations on condensation in flow of HFE-7100 in small diameter channels
PublikacjaIn the paper the authors present investigations of flow condensation with the use of the HFE-7100 as a working fluid. The original and new approach to removing the heat from the channel was applied. The research was carried out using a wide-range real time observations, e.g. using infrared camera and stroboscope microphotography. This paper presents the details of experiment as well as the influence of heat and flow parameters...
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The Use of Liquid Crystal Thermography in Selected Technical and Medical Applications—Recent Development
PublikacjaThermochromic liquid crystals (TLC) and true-colour digital image processing have been successfully used in non-intrusive technical, industrial and biomedical studies and applications. Thin coatings of TLC at surfaces are utilized to obtain detailed temperature distributions and heat transfer rates for steady or transient processes. Liquid crystals also can be used to make the temperature and velocity fields in liquids visible...
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Pool boiling of nanofluids on rough and porous coated tubes: experimental and correlation
PublikacjaThe paper deals with pool boiling of water-Al2O3 and water- Cu nanofluids on rough and porous coated horizontal tubes. Commercially available stainless steel tubes having 10 mm outside diameter and 0.6 mm wall thickness were used to fabricate the test heater. The tube surface was roughed with emery paper 360 or polished with abrasive compound. Aluminium porous coatings of 0.15 mm thick with porosity of about 40% were produced by...
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Experimental investigations of natural convection from circular plates at variable inclination
PublikacjaW pracy przedstawiono wyniki badań eksperymentalnych oraz bezwymiarową korelację liczb kryterialnych dla konwekcyjnej wymiany ciepła od izotermicznej płyty kołowej skierowanej ku górze dla różnych kątów pochylenia (od poziomej do pionowej) w szerokim zakresie wartości liczb Rayleigha. Badania przeprowadzono w wodzie dla płyty kołowej o średnicy 0,07 m. Celem pracy było określenie wpływu kąta pochylenia płyty na wartość liczby Nusselta.
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Structural optimization of microjet array cooling system
PublikacjaThe single phase heat transfer from an upward facing, horizontal copper surface to arrays of impinging water jets was experimentally investigated. Experimental configuration allows for a free-surface unconfined jets flow. Square nozzles 50 × 100 μm arranged in four different geometries were used. Additionally, for the set of two jets array geometry was varied by adjusting the nozzle to nozzle distance. The area averaged heat transfer...
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Assessment of the impact of jet impingement technique on the energy efficiency of air-cooled BIPV/T roof tile
PublikacjaThe paper concerns a numerical analysis of cooling of the hybrid photovoltaic (PV) modules dedicated to Building-Integrated Photovoltaic/Thermal (BIPV/T) systems. Attention was focused on the photovoltaic roof tiles, using a jet impingement technique, in which the intensification of heat transfer is ensured by streams of air hitting the heat exchange partition. A series of numerical simulations were carried out to assess an influence...
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Numerical analysis of high temperature minichannels heat exchanger performance
PublikacjaNowadays, the most difficult technological challenge in energy sector is connected with the gas micro-CHP units, dedicated to the distributed power generation. They are expected to be of high efficiency and at the same time of compact in size. Regarding the first reason, significant increase in microturbine efficiency can only be achieved by increase in the engine operating temperature. Therefore, one of the critical elements in...
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High-quality Experiment Dedicated to microGravity Exploration, Heat Flow and Oscillation Measurement from Gdańsk
PublikacjaIn this paper we propose HEDGEHOG (High-quality Experiment Dedicated to microGravity Exploration, Heat flow and Oscillation measurement from Gdańsk) REXUS experiment to investigate vibrational and heat flow phenomena during the whole (ascent, microgravity phase, descent and recovery) flight of a sounding rocket. First, a proposed system of cantilever beams is discussed to study dynamic behaviour of dummy payload. Dimensioning has...
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Comparative study of flow condensation in conventional and small diameter tubes
PublikacjaIn the paper a method developed earlier by the first author is applied to calculations of heat transfer coefficient for inside tube condensation. The method has been verified using experimental data from literature on several fluids in different microchannels and compared to three well established correlations.
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Comparative study of a bottoming SRC and ORC for Joule–Brayton cycle cooling modular HTR exergy losses, fluid-flow machinery main dimensions, and partial loads
PublikacjaEnergy conversion efficiency increase in power plants with high-temperature gas-cooled reactors via implementation of the bottoming cycle was investigated under nominal and minimal thermal load of a high-temperature reactor (HTR). Heat transfer surface area and turbine outlet volumetric flow rate in bottoming cycles was also investigated. Water and two low-boiling point working fluids (ammonia and ethanol) were analyzed. Analyzed...
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Curved Surface Minijet Impingement Phenomena Analysed with ζ-f Turbulence Model
PublikacjaThe jet impingement phenomenon plays an important role among the heat transfer intensification methods. Very often its application and analyses refer to simple flat surfaces, while there is a lack of information in the literature for cases addressing curved surfaces. In the present work, the single jet impingement on the non-flat (concave and convex) surface is studied for a wide range of geometries, which originate from the mini-jet...
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Recent Advances in Loop Heat Pipes with Flat Evaporator
PublikacjaThe focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle)...
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High-efficiency mini and micro heat exchangers for dispersed power generation
PublikacjaTaking into account the dispersed systems technologies and their development, the ORC systems seem to be promising technology amongst various micro-CHP domestic units (electrical power production below 10 kWe), however practical realization of the ORC cycle in a micro-scale is technically challenging. The system consists in devices such as the vapour generation unit (boiler), expansion device and heat exchangers. Each of them should...
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Investigation of the thermal effects in water-lubricated journal bearings with axial grooves
PublikacjaWater-lubricated hydrodynamic journal bearings are frequently applied as stern tube bearings due to their advantages over other bearing types. They are environmentally friendly, can operate without sealings and in conditions of low friction losses. The most popular are bearings with open axial grooves, which require, for proper operation, forced axial flow of the lubricating water. Correctly designed and operated stern tube bearings...
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Thermal analysis of Magnetohydrodynamics (MHD) Casson fluid with suspended Iron (II, III) oxide-aluminum oxide-titanium dioxide ternary-hybrid nanostructures
PublikacjaThis study is carried out to enhance and analyze the thermal performance of non-Newtonian Casson fluid by immersing Ternary hybrid nanoparticles Fe3O4-Al2O3-TiO2 uniformly. To model the behaviour of such complex phenomena mathematically, a system of complex transport differential equations is developed by utilizing a non-Fourier heat transfer model for energy transport. The non-dimensional system of transport equations involving...
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Comprehensive thermodynamic analysis of the CAES system coupled with the underground thermal energy storage taking into account global, central and local level of energy conversion
PublikacjaA key aspect of CAES is the optimal configuration of the thermodynamic cycle. In this paper, the situation of cooperation between the current conventional power plants and wind farms is analyzed, and then, based on thermodynamic models, the process of storing thermal and electrical energy in the CAES system coupled with a heat storage and recovery is developed. Therefore, three levels can be distinguished, namely: the global level...
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Numeryczna analiza możliwości zwiększenia efektywności grzewczej pompy ciepła, poprzez modyfikację skraplacza
PublikacjaW niniejszej pracy określono charakterystykę prostego modelu wymiennika ciepła bazującego na skraplaczu powietrznej pompy ciepła. Jest to helikoidalny rekuperator typu rura w rurze. Zaproponowano i poddano analizie numerycznej dwie metody intensyfikacji wymiany ciepła i zestawiono wyniki z modelem porównawczym. Zastosowane rozwiązania zwiększające strumień wymienianego ciepła spowodowały wzrost odbieranego przez wodę strumienia...
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Influence of the thermal modernization of window on transmission heat losses
PublikacjaThe article presents the results of calculations of the heat transfer coefficient for the state before and after renovation for the historic windows. The aim of the analysis was to obtain the values of thermal insulation parameters demanded by the regulations, while not losing the historical value of the window. The described example of the renovation of the existing window consisted in installing an additional window panel from...
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Numerical analysis by FEM and analytical study of the dynamic thermal behavior of hollow bricks with different cavity concentration
PublikacjaThis paper presents the investigation results on the influence of the cavity concentration in hollow bricks on static and dynamic thermal parameters: a time lag, a decrement factor, an equivalent thermal diffusivity (ETD) and an equivalent thermal conductivity (ETC). The dynamic thermal behavior of hollow bricks is studied with an optimized cavity shape to reduce the intensity of radiation and convective heat exchange. The thermal...
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Numerical analysis by FEM and analytical study of the dynamic thermal behavior of hollow bricks with different cavity concentration
PublikacjaThis paper presents the investigation results on the influence of the cavity concentration in hollow bricks on static and dynamic thermal parameters: a time lag, a decrement factor, an equivalent thermal diffusivity (ETD) and an equivalent thermal conductivity (ETC). The dynamic thermal behavior of hollow bricks is studied with an optimized cavity shape to reduce the intensity of radiation and convective heat exchange. The thermal...
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Free convection of water-Al2O3 nanofluid from horizontal porous coated tube
PublikacjaThe main aim of the present study was to investigate the influence of nanoparticles on heat transfer coefficients during free convection of water-Al2O3 nanofluid from horizontal porous coated tube under atmospheric pressure for nanoparticle concentration of 0.01% by weight. Contrary to published data present study concerns on free convection of nanofluids in extensive, quiescent fluid.
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The effect of laser on metal surfaces for multidisciplinary usage in material and thermal engineering
PublikacjaThe subject of heat transfer and cooling systems is still a matter of contention in many different fields of science and industry. Infrigidation is much more difficult than warming, and so, much more needed in more and more different devices, starting from massive industrial machinery and air conditioning in commercial buildings, up to micro and nano-surgery tools. In fact, the size of many cooling systems is still a problem. It...
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Modeling of heat and fluid flow in granular layers using high-order compact schemes and volume penalization method
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A New Approach for the Mitigating of Flow Maldistribution in Parallel Microchannel Heat Sink
PublikacjaThe problem of flow maldistribution is very critical in microchannel heat sinks (MCHS). It induces temperature nonuniformity, which may ultimately lead to the breakdown of associated system. In the present communication, a novel approach for the mitigation of flow maldistribution problem in parallel MCHS has been proposed using variable width microchannels. Numerical simulation of copper made parallel MCHS consisting of 25 channels...
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A simple model of circular hydraulic pump
PublikacjaRozpatrzono warunki powstawania osiowosymetrycznego uskoku hydraulicznego. Przedstawiono model, w którym rozpatrzono obecność dodatkowych strat w równaniu Bernoulliego. Przyczyniają się one do powstawania dodatkowego wiru w miejscu uskoku. Porównanie z wynikami badań eksperymentalnych potwierdza słuszność przyjętych tez.
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Thermal and solutal performance of Cu/CuO nanoparticles on a non-linear radially stretching surface with heat source/sink and varying chemical reaction effects
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Towards enhanced heat and mass exchange in adsorption systems: The role of AutoML and fluidized bed innovations
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The new concept of capillary forces aided evaporator for application in domestic organic rankine cycle
PublikacjaThis paper presents studies on the possibility of applying capillary forces induced in the porous structure to a modern design of evaporator. The potential application of such heat exchanger is for example an evaporator of the domestic micro combined heat and power (CHP) unit. One of the problems in the micro-CHP is excessive demand for pumping power. The proposed design helps in overcoming that issue. In the evaporator outlined...
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A model of liquid film breakdown formed due to impingement of a two-phase jet on a horizontal surface
PublikacjaThe present work aims to provide an explanation to the phenomenon of breakdown of the thin liquid film created by impinging two-phase, liquid-gas jet. Existing in the literature models describe merely thebreakdown of single phase liquid films. The model presented here is based on examination of mass and energy equations under the applied criterion of the minimum of total energy. That allows to determinethe minimum thickness of...
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Modeling of natural convection with Smoothed Particle Hydrodynamics: Non-Boussinesq formulation
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Double-diffusive natural convection energy transfer in magnetically influenced Casson fluid flow in trapezoidal enclosure with fillets
PublikacjaThe prime motive of this disquisition is to deal with mathematical analysis of natural convection energy transport driven by combined buoyancy effects of thermal and solutal diffusion in a trapezoidal enclosure. Casson fluid rheological constitutive model depicting attributes of viscoelastic liquids is envisioned. The influence of the inclined magnetic field governed by Lorentz field law is also considered. To raise the essence...