Two-phase heat transfer

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Detection of liquid–vapor–solid triple contact line in two-phase heat transfer phenomena using high-speed infrared thermometry

Detection of liquid–vapor–solid triple contact line in two-phase heat transfer phenomena using high-speed infrared thermometry

 M. Bieberle, F. Fischer, E. Schleicher, D. Koch, H.-J. Menz, H.-G. Mayer, U. Hampel, 2009, “Experimental two-phase flow measurement using ultra fast limited-angle-type electron beam X-ray computed tomography”, Experiments in Fluids, v 47, n 3, p 369-378.  H. J. Chung, H. C. No, 2003, Simultaneous visualization of dry spots and bubbles for pool boiling of R-113 on a horizontal heater, International Journal of Heat and Mass Transfer 46 2239–2251.

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Modeling heat transfer in dilute two-phase flows using the Mesoscopic Eulerian Formalism

Modeling heat transfer in dilute two-phase flows using the Mesoscopic Eulerian Formalism

Abstract In dilute two-phase flows, accurate prediction of the temperature of the dis- persed phase can be of paramount importance. Indeed, processes such as evaporation or chemical reactions are strongly non-linear functions of heat transfer between the carrier and dispersed phases. This study is devoted to the validation of an Eulerian description of the dispersed phase –the Meso- scopic Eulerian Formalism (MEF)– in the case of non-isothermal flows. Di- rect numerical simulations using the MEF are compared to a reference La- grangian simulation for a two-dimensional non-isothermal turbulent jet laden with solid particles. The objectives of this paper are (1) to study the influ- ence of the thermal inertia of particles on their temperature distribution and (2) conduct an a posteriori validation of the MEF, which was recently ex- tended to non-isothermal flows. The focus is on the influence of additional terms in the MEF governing equations, namely heat fluxes arising from the
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Effect of spray cooling on heat transfer in a two-phase helium flow

Effect of spray cooling on heat transfer in a two-phase helium flow

in a thickness dependence on flux weaker than a cubic power, which we do not observe. A last possibility is that, for a given average thickness, the film drains faster than predicted by eq.6. Due to the non linear dependance of the velocity on the thickness, this is possible if the film is not uniform in the horizontal direction, which might happen if the deposited droplets fall faster than they spread. If this is the case, the lack of difference between the superfluid and normal data indicates that this is equally true in both cases. To summarize, the CHF measured by the thermal probe is about one or- der of magnitude smaller than expected for a perfect spray efficiency of 1 and the assumption of an impact velocity of order the fluctuation of the vapor axial velocity. A dedicated spray cooling experiment with a controlled inci- dent mass flux would be needed in order to directly measure the deposition efficiency, and, indirectly, to determine the impact velocity in the present case of turbulent spray deposition. On the other hand, the film thickness measured by the capacitive probe is smaller than expected for the deposited flux deduced from the CHF of the thermal probe, coupled with a simple lu- brication model for a homogeneous, one-component, viscous film. Possible explanations are that the flux deposited on a wet, cold, surface is smaller than expected from the CHF on a dry surface, or that the film is not homo- geneous, due to incomplete spreading of incident droplets. Settling between the two hypotheses is challenging, as it probably requires direct imaging of the impingement process and/or the film morphology, in both cases with a resolution of several micrometers. At any rate, our results show that neither the cooling capabilities of a given flux of droplets impinging a vertical surface, nor the draining of this surface, do strongly depend on the superfluid nature of the incoming liquid. If superfluidity modifies the spreading of droplets on the surface, it is not by a sufficient amount to affect these properties.
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Modelling of heat transfer and hydrodynamic with two kinetics approaches during supercritical water oxidation process

Modelling of heat transfer and hydrodynamic with two kinetics approaches during supercritical water oxidation process

Keywords: Supercritical water oxidation; Heat transfer; Eddy Dissipation Concept (EDC); FLUENT; Computational Fluid Dynamics (CFD); k–ω 1. Introduction Supercritical water oxidation (SCWO) is a technology of high interest to treat organic liquid wastes. The supercritical water (P > 22.1 MPa, T > 647 K) offers physicochemical proper- ties between those of gas and liquid. Thereby, waste and oxygen are highly miscible in supercritical water leading to a single homogeneous phase and hence to the main advantage of no transfer limitation. The oxidation reaction is completed within seconds. The temperature is relatively low compared to classical combustion mode, so there is no formation of gaseous SO x or
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Tube banks, single-phase heat transfer in

Tube banks, single-phase heat transfer in

simple enthalpy-conservation equation (convection-source-term equations). It is possible to devise much more sophisticated two- phase enthalpy equations, which account for bank-side mixing, 3D phenomena etc., in addition to bulk convection It is also possible to generate momentum equations to account for flow-related effects, bypassing, finite-number of rows, etc. For complex flows, the definition of U may be of limited use. Numerical methods differ from traditional methods in that there is no need to rely on the premiss that heat transfer is governed by a rate equation. The reader is referred to the articles by D.B. Spalding in the Heat Exchanger Design Handbook (1983), and elsewhere. The use of spreadsheet programs, specialised heat-exchanger-design programs and general-purpose computational fluid dynamics software should be considered prior to writing source code.
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LES of knocking in engines using dual heat transfer and two-step reduced schemes

LES of knocking in engines using dual heat transfer and two-step reduced schemes

shows the value of the total flux to the cylinder head (valves are not included) obtained from LES for 15 consecutive engine cycles with the empirical approach and reveals a significant variability. For en- gine cycles where the whole mixture is burned quickly, pressure and temperature in the cylinder are high and increase thermal exchanges at the boundaries leading to large and variable fluxes during the com- bustion phase. However, Fig. 7 also shows that the main flux from the fluid to the cylinder head occurs during the exhaust stroke when the cylinder is filled with hot gases and high velocities caused by the ex- haust valve opening. For this engine, all the fuel is consumed when the exhaust valves open, so that the temperature inside the cylinder is almost the same for all cycles. Even though the instantaneous flux to the cylinder head varies from cycle to cycle ( Fig. 7 ), its value av- eraged over each cycle exhibits much less variation ( Fig. 8 ). To eval- uate the impact of these variations on combustion, the engine cycle
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On the prediction of single-phase forced convection heat transfer in narrow rectangular channels

On the prediction of single-phase forced convection heat transfer in narrow rectangular channels

As can be seen in Fig. 2, the axial layout of the channel includes one heated and two adiabatic regions. The heated zone corresponds to the central part of the rectangular channel, where the largest part of the electrical power is transferred to the fluid. Along this zone, the heat flux is approximatively uniform. The two adiabatic zones are at the entrance and at the exit of the test section. Each of them is 70 mm long. In these zones, the power (and consequently the heat flux) is much lower compared to the heated zone (approximatively 2 % of the total electrical power). A smooth entrance in the test section was used in order to minimize the entrance effects on the measurements.
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Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer

Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer

IV. SUMMARY AND OUTLOOK A new experimental facility the Twente Mass and Heat Trans- fer Water Tunnel (TMHT) has been built. This facility has global temperature control, bubble injection, and local heat/mass injec- tion and offers the possibility to study heat and mass transfer in turbulent multiphase flow. The tunnel is made of high-grade stain- less steel permitting the use of salt solutions in excess of 15% mass fraction, besides water. The total tunnel volume is 300 l. Three inter- changeable measurement sections of 1 m height but of different cross sections (0.3 × 0.04 m 2 , 0.3 × 0.06 m 2 , and 0.3 × 0.08 m 2 ) span a Reynolds-number range from 1.5 × 10 4 to 3 × 10 5 in the case of water at room temperature. The glass vertical measurement sec- tions allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Ther- mistors mounted on a built-in traverse provide local temperature information at a few millikelvin accuracy. Combined with simulta- neous local velocity measurements, the local heat flux in single phase and two phase turbulent flow can be studied.
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Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer

Twente mass and heat transfer water tunnel: Temperature controlled turbulent multiphase channel flow with heat and mass transfer

IV. SUMMARY AND OUTLOOK A new experimental facility the Twente Mass and Heat Trans- fer Water Tunnel (TMHT) has been built. This facility has global temperature control, bubble injection, and local heat/mass injec- tion and offers the possibility to study heat and mass transfer in turbulent multiphase flow. The tunnel is made of high-grade stain- less steel permitting the use of salt solutions in excess of 15% mass fraction, besides water. The total tunnel volume is 300 l. Three inter- changeable measurement sections of 1 m height but of different cross sections (0.3 × 0.04 m 2 , 0.3 × 0.06 m 2 , and 0.3 × 0.08 m 2 ) span a Reynolds-number range from 1.5 × 10 4 to 3 × 10 5 in the case of water at room temperature. The glass vertical measurement sec- tions allow for optical access to the flow, enabling techniques such as laser Doppler anemometry, particle image velocimetry, particle tracking velocimetry, and laser-induced fluorescent imaging. Ther- mistors mounted on a built-in traverse provide local temperature information at a few millikelvin accuracy. Combined with simulta- neous local velocity measurements, the local heat flux in single phase and two phase turbulent flow can be studied.
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Direct numerical simulation of heat transfer from liquid droplet in a continuous  immiscible liquid phase

Direct numerical simulation of heat transfer from liquid droplet in a continuous immiscible liquid phase

parameters representing to hydrodynamics (Re, µ ∗ and ρ ∗ ), studies[5] [15] have shown that the density ratio effect is small in axisymmetric problems therefore we reduce our hydrodynamic parameters to the Reynolds number and the viscosity ratio, (the density ratio bring fixed to 1). Similarly the parameters that influence the physics of the transfer are the Peclet number and the thermal diffusivity ratio. To investigate these parameters we start by studying the evolution of the Nusselt number in terms of Peclet number for a given hydrodynamic configuration. Figures 5 and 6 correspond to two different flow regimes (Re = 0.1 and Re = 100). In those figures,
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Steady state heat transfer in microcracked media

Steady state heat transfer in microcracked media

and c, Fig. 1-b) with a volume fraction f c = 4 3 πdω . Here d = N a 3 is the scalar crack density as defined by Budiansky and O’Connell [10] and ω = c / a is their mean aspect ratio. Taking all this into account and considering n as the unit vector normal to the crack plane, estimated solutions for localization tensor over the crack’s phase hAi c can be determined. They depend

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Modeling heat transfer within porous multiconstituent materials

Modeling heat transfer within porous multiconstituent materials

3 Conditions Extrêmes et Matériaux : Hautes Températures et Irradiation (CEMHTI), CNRS UPR 3079, 45071 ORLÉANS, France denis.rochais@cea.fr Abstract. The purpose of our work has been to determine the effective thermal properties of materials considered heterogeneous at the microscale but which are regarded as homogenous in the macroscale environment in which they are used. We have developed a calculation code that renders it possible to simulate thermal experiments over complex multiconstituent materials from their numerical microstructural morphology obtained by volume segmentation through tomography. This modeling relies on the transient solving of the coupled conductive and radiative heat transfer in these voxelized structures.
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Steady-state heat transfer in microcracked media

Steady-state heat transfer in microcracked media

Let denote Ω the area of the 2D Representative Volume Element (RVE) of the microcracked media, ∂Ω its outer boundary and u the outward unit normal to ∂Ω ( Fig . 1 a). The macroscopic temperature gradient G (respectively heat flux Q) can be defined as the mean temperature (resp. external heat flux) on the boundary ∂Ω. Under sta- tionary thermal conditions, the macroscopic temperature gradient G (resp. heat flux Q) corresponds to the average of the corresponding microscopic quantity g (resp. q):

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Experimental study of single and two-phase adiabatic flow distribution in compact heat exchangers

Experimental study of single and two-phase adiabatic flow distribution in compact heat exchangers

4 Conclusions Flow distribution in small channels of compact heat exchanger has been experimentally studied. In single-phase flows, the distribution did not depend on the inlet mass flow rate and it was rather homogeneous in both configurations. However it was less homogeneous in the horizontal flow than in the vertical one because of gravity. In two-phase flows, for the horizontal position, the flow patterns depended on the inlet vapour quality. On the contrary, in the vertical position, the flow at the manifold inlet was always annular, whatever the inlet vapour quality. As for the distribution, it was significantly affected by the manifold orientation and the inlet vapour quality. When the inlet vapour quality increased, the phase distribution was more homogeneous.
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Finned tube heat exchanger : correlation of dry surface heat transfer data

Finned tube heat exchanger : correlation of dry surface heat transfer data

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Finned tube heat exchanger : correlation of dry surface heat transfer data.. [r]

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EFFECT OF RADIATION ON THE FLOW STRUCTURE AND HEAT TRANSFER IN A  TWO - DIMENSIONAL GRAY MEDIUM

EFFECT OF RADIATION ON THE FLOW STRUCTURE AND HEAT TRANSFER IN A TWO - DIMENSIONAL GRAY MEDIUM

7 Figure 2. Variation of fluid temperature and velocity vs time 4.1. Effect of Planck number The fixed parameters of simulation are Ra = 5.10 6 , τ = 1. However, to examine the impact of the Planck number, we consider different values of Pl number varying from 0.1 to 100. At low Planck number (Pl = 0.1), the streamlines have a two-cell shape indicating a two asymmetrical secondary flows. With increasing Pl, cells are decomposed into S-shape indicating a unicellular flow in the core of the cavity (fig. 3). The flow and temperature fields present symmetrical structure with respect to the cavity center, indicating therefore a similar behavior of the fluid when the heat transfer is governed by pure natural convection.
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Analysis and optimization of a transcritical CO2 heat pump system using a two-phase ejector

Analysis and optimization of a transcritical CO2 heat pump system using a two-phase ejector

4.6 Conclusion The new model presented in this work predicts the performance of a CO2 two-phase ejector for both single and double choking conditions. It is based on the conservation of mass, momentum and energy as well as relations to account for irreversibilities. A model has also been developed to design a two-phase ejector under given operating conditions. The dimensions of different parts of the ejector have been calculated. The performance of a CO2 two phase ejector has been predicted under different operating conditions for both on-design and off-design conditions. The results have been validated using the data available in the literature. The occurrence of a normal shock wave is assumed at the inlet of the constant area. Unlike other previous models this assumption reveals the effect of a shock wave inside a CO2 two-phase ejector. Polytropic efficiencies have also been employed to account for the pressure ratio during the acceleration and deceleration processes in the nozzle and diffuser. These have allowed evaluation of the effect of irreversibilities on the dimensions of a two-phase ejector. The newly proposed model has been investigated for different operating conditions typical for a two-phase ejector. It successfully predicts the flow properties at different cross sections of the ejector as well as the relation between entrainment ratio and pressure ratio. The results will be used to develop an optimum design of an ejector heat pump system. The present model will be incorporated into a thermodynamic model describing the whole system. A better understanding of the ejector characteristics will help to better analyse the effects of the different variables on the overall performance of the heat pump system.
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Advanced materials for enhanced condensation heat transfer

Advanced materials for enhanced condensation heat transfer

However, we find that although this mode of condensation is readily achievable when condensing working fluids with high surface tension, such as water, even re-ent[r]

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Heat transfer intensification and flow rate control in dynamic micro-heat exchanger

Heat transfer intensification and flow rate control in dynamic micro-heat exchanger

Very recently, Kumar et al., [8] extended this works and proposed a realistic 3-D geometry of dynamic corrugated heat exchanger. In their work, the average height of the channel is fixed while the minimum gap (distance between the lowest point of the deformed wall and the fixed wall) varies as a function of the relative amplitude. Numerical studies have been conducted by imposing high pressure and low pressure at the outlet and inlet sections of the channel, respectively, for an imposed frequency of 50Hz. It was observed heat transfer coefficient increases with increase in amplitude and the requirement of external pump could be completely eliminated due to self-pumping capacity of the device.
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Hydrodynamic and mass transfer study of micro-packed beds in sigle-and two-phase flow

Hydrodynamic and mass transfer study of micro-packed beds in sigle-and two-phase flow

165 6.2 Suggested future work It was shown in the introduction section that hydrodynamic studies of micro-packed beds, unlike microchannels, have received little coverage in the open literature. In case of microchannels many different aspects such as flow regimes, factors affecting flow regimes, pressure drop, phase holdup, residence time distribution have been extensively and thoroughly studied. The number of publications in the open literature focusing only on flow in micro-channels nearly exceeds 1000. In contrast, investigations on micro-packed beds are still in their infancy with only a small number of publications in the literature as mentioned throughout this thesis. Very few works that have been published indicate that there are still many gaps to be filled in this realm. Although there are many challenges that arise in studying the hydrodynamics of micro-packed beds in terms of both fabrication and operation, once they are successfully surpassed there will be a huge research gradient in this field. For example, a comprehensive set of investigations can be conducted on the subject of flow regimes and factors contributing to its transitions by getting inspirations from the pool of research available on microchannels 1-3 and use them as platform for the current studies. For
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