Heat and mass transfer model

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An efficient 1D numerical model adapted to the study of transient convecto-diffusive heat and mass transfer in directional solidification

An efficient 1D numerical model adapted to the study of transient convecto-diffusive heat and mass transfer in directional solidification

Bi [23]. However, as mentioned earlier, due to the significant variability of with the Bi content, we will allow the values of the thermoelectric coefficient to be taken as variable in the optimization procedure. Finally, the issue of the initial condition, i.e. the state at the end of the steady solidification regime for our present re-homogenization problem, also needs to be discussed. Regarding the solutal problem, we first have to know if the initial transient leading to the steady regime is really completed. An analytical solution for the extent of this initial transient in purely diffusive solute transport conditions had been given long ago by Smith et al. [36]. We can then estimate the characteristic length of the initial transient using this analytical solution and compare it with the length solidified before the re-homogenization process. For 7D, 8B and 11C2 experiments in the USMP3 campaign, the solidified length is respectively about 5.5 times, 3.5 times and 4.5 times the characteristic length of the initial transient. Moreover, in convecto-diffusive solute transport conditions, numerical simulations and order of magnitude arguments show that the initial transient should be shorter, since the boundary layer ahead of the interface is reduced [37]. In this respect, we can reasonably think that for 8B and 11C2 experiments, the experimental initial transient is shorter than the one estimated with the analytical solution, corresponding to a still more favorable situation. Thus, we can consider that the initial transient is fully completed and that the steady-state solute profile can be safely taken as the initial condition for the simulations. We have also to take into account the fact that the initial state may be affected by residual convection for the thermal problem. Nevertheless, as Sn-Bi is a good thermal conductor, the temperature profile can be considered as diffusive with linear profiles in each phase (with the constant gradients and defined previously), taking as reference the interface temperature . can then be
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Application of the theory of Markov chains to model heat and mass transfer between stochastically moving particulate and gas flows

Application of the theory of Markov chains to model heat and mass transfer between stochastically moving particulate and gas flows

S over the cells. The problem of reliability of determination of the tran- sition probabilities arises here. It can be checked by the possibility to correspond the experimental and calculated RTD curves using only one adjusting parameter D. If the correspondence cannot be reached, it means that the one- dimensional chain of perfectly mixed cells does not fit the real flow structure, and it is necessary to employ a multi- dimensional array of the cells describing the non- homogeneous flow in the crosswise direction. This is also can be done on the basis of the theory of Markov chains but such complication of the model is beyond the present study. 2.3 Flows between chains and internal sources
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Modelling Heat and Mass Transfer in Porous Material during Pyrolysis using Operator Splitting and Dimensionless Analysis

Modelling Heat and Mass Transfer in Porous Material during Pyrolysis using Operator Splitting and Dimensionless Analysis

4 Total CSTJF, Avenue Larribau, 64000 Pau, France ABSTRACT Dimensionless analysis is used to improve the computational performance when using operator splitting meth- ods to model the heat and mass transfer during pyrolysis. The specific examples investigated are thermal de- composition of polymer composite when used as heat shields during space-craft re-entry or for rocket nozzle’s protection, and the In-Situ Upgrading (ISU) of solid oil shale by subsurface pyrolysis to form liquid oil and gas. ISU is a very challenging process to model numerically because a large number of components need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Inspectional Analysis is used to determine the minimum number of dimensionless groups that can be used to describe the process. This set of dimensionless numbers is then reduced to those that are key to describing the system behaviour. This is achieved by performing a sensitivity study using Experimental Design to rank the numbers in terms of their impact on system behaviour. The numbers are then sub-divided into those of primary im- portance, secondary importance and those which are insignificant based on the t-value of their effect, which is compared to the Bonferroni corrected t-limit and Lenth’s margin of error. Finally we use the sub-set of the most significant numbers to improve the stability and performance when numerically modelling this pro- cess. A range of operator splitting techniques is evaluated including the Sequential Split Operator (SSO), the Iterative Split Operator (ISO) and the Alternating Split Operator (ASO).
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Computational study of heat and mass transfer issues in solid oxide fuel cells

Computational study of heat and mass transfer issues in solid oxide fuel cells

The numerical model was implemented as a steady- state OpenFOAM ® solver . A useful feature of OpenFOAM is the provision of a full set of implicit finite volume discretisation operators and associated linear system solver classes, allowing transparent representation of partial differential equations in the code. Another useful feature is that the discretisation schemes (eg Gaussian integration, upwind interpolation) used by the operators can be selected at run time, allowing the user free choice of schemes without any recoding or recompiling. The selection of linear solvers and their parameters are also chosen at run time. For the experiments reported here, symmetric linear systems were solved using conjugate gradient with incomplete Cholesky pre-conditioning (ICCG) [32] and asymmetric systems using bi-conjugate gradient schemes, BiCG [33], Bi-CGSTAB [34].
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Numerical simulation of heat and mass transfer in bidispersed capillary structures: Application to the evaporator of a loop heat pipe

Numerical simulation of heat and mass transfer in bidispersed capillary structures: Application to the evaporator of a loop heat pipe

model permits to explain their behaviour based on the liquid– vapour phase distribution within the wick. The vapour mass flow rate was also investigated. The presence of a two-phase zone, i.e. the coexistence of liquid and vapour in the same zone under the casing is positively corre- lated with the best evaporator thermal performance and prevents the overheating of the casing. At low heat flux, the vaporisation of the bidispersed wick takes place at the wick-groove interface only and the thermal performance is lower than for the monoporous wick which is already invaded by vapour, i.e. the vaporisation also takes place within the wick. For a higher heat load, the bidis- persed wick reaches better thermal performance than the monodispersed wick. The first row of pores under the casing is almost full of vapour for the monoporous capillary structure, inducing an additional thermal resistance and a significant increase in the casing overheating. On the contrary, the large pores network in the bidispersed wick creates preferential paths for the vapour and keeps a two-phase zone under the casing for a large range of heat load. This phase distribution induces a slow rise of the casing overheating.
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Numerical simulation of heat and mass transfer in bidispersed capillary structures: Application to the evaporator of a loop heat pipe

Numerical simulation of heat and mass transfer in bidispersed capillary structures: Application to the evaporator of a loop heat pipe

model permits to explain their behaviour based on the liquid– vapour phase distribution within the wick. The vapour mass flow rate was also investigated. The presence of a two-phase zone, i.e. the coexistence of liquid and vapour in the same zone under the casing is positively corre- lated with the best evaporator thermal performance and prevents the overheating of the casing. At low heat flux, the vaporisation of the bidispersed wick takes place at the wick-groove interface only and the thermal performance is lower than for the monoporous wick which is already invaded by vapour, i.e. the vaporisation also takes place within the wick. For a higher heat load, the bidis- persed wick reaches better thermal performance than the monodispersed wick. The first row of pores under the casing is almost full of vapour for the monoporous capillary structure, inducing an additional thermal resistance and a significant increase in the casing overheating. On the contrary, the large pores network in the bidispersed wick creates preferential paths for the vapour and keeps a two-phase zone under the casing for a large range of heat load. This phase distribution induces a slow rise of the casing overheating.
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Heat and mass transfer in fry drying of wood

Heat and mass transfer in fry drying of wood

into the wood when the water content falls below a critical value (0.4 to 0.7 kg=kg). The higher the oil temperature, the lower the critical value. At 120 ! C, the oil starts to penetrate into the wood at 0.7 kg=kg, while at 180 ! C the penetration starts at 0.4 kg=kg. Beyond this critical value, oil penetra- tion increases progressively to an asymptotic value. For the same amount of water removed during frying, the lower the oil temperature, the higher the oil impregnation. Once 0.8 kg of water has been removed from an initial 2.2 kg of wet wood (i.e., 1.0 kg of dry matter), 0.12 kg of oil has penetrated into the wood at 120 ! C, 0.05 kg at 150 ! C, and 0.025 kg at 180 ! C. The wood is simultaneously dried and impregnated with oil, and the rate increases as the drying progresses. The impregnated oil can amount to 20% of the mass of the removed water. Throughout the impreg- nation, the wood is at an overpressure relative to the press- ure of the oil bath. The direction of the oil flux is therefore opposite to the total pressure gradient, so spontaneous impregnation can only occur if the wood is able to absorb the oil. This hypothesis is partially confirmed by the exist- ence of a saturation threshold beyond which the oil does not penetrate into the wood. However, this threshold depends on oil temperature; the higher the oil temperature, the higher the internal pressure and the lower the threshold water content. Oil impregnation can be caused by two mechanisms: it can result from spontaneous absorption or it can be vapor driven. The first mechanism does not require interaction with the vapor transfers. It develops spontaneously, with the threshold water content effects, if the wood has stronger affinity to oil than to water. For the second mechanism to operate, the capillary forces between the oil and the wood must be overcome by a posi- tive pressure gradient in the wood as the water vapor and the oil move in opposite directions. The above description is similar to the vapor drive described by the Buckley- Leverett model. [22] Observation of the samples during
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Numerical Simulation Of Heat And Mass Transfer During The Absorption Of Hydrogen In A Magnesium Hydride

Numerical Simulation Of Heat And Mass Transfer During The Absorption Of Hydrogen In A Magnesium Hydride

• In order to develop an efficient cooling, it is foreseeable that the cylindrical axisymmetric geometry, although simple, could prevent from an intense cooling. Probably the well known plate heat exchanger technology will be of interest. • The knowledge of the physical properties of the materials will need additional researches. For example, the thermal conductivity of a powder bed will have to be investigated in more details. Along the same line, the effect of dilatation (compaction) of the powder bed during the absorption (desorption) should be taken into account.

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Domain decomposition methods to model heat exchanges between a well and a rock mass

Domain decomposition methods to model heat exchanges between a well and a rock mass

1 Introduction Gas underground storage in salt caverns is a mature technique, which ensures flexi- bility on the gas network and supplies security during the winter season. These caverns built by leaching behave as pressure vessels and may deliver high flow rates on demand. Natural gas is injected during summer and withdrawn during winter. Evolution of the gas market in the last few years, however, has changed the way the caverns were operated. They are now used more often with shorter cycles lasting a month, a week or less. In this context, it becomes very important to know and predict the thermodynamic state of gas at the wellhead and in the cavern. Modelling is used, on one hand, to predict the storage performance and improve its exploitation (to determine gas volume, hydrate risk, etc...) and on the other hand, to design surface facilities [18, 3, 17] during preliminary development studies. This last point also concerns storage of other gas such as H 2 , that
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A Mass transfer model for simulating VOC sorption on building materials

A Mass transfer model for simulating VOC sorption on building materials

concentrations during the sorption phase and higher concentrations during the desorption phase. The dodecane behaves just the opposite, and the model tends to underestimate the strength of sorption. The discrepancies between the predicted and measured concentrations may be due to two different reasons. First, An et al. (1999) found that the chamber walls themselves also had a considerable sink effect, especially for compounds with low vapor pressure. This may partly explain the discrepancy between the predicted and measured results for dodecane, but not for ethylbenzene and benzaldehyde. The discrepancies for the latter compounds may be primarily due to the possible inaccurate values used for the D m and K ma , which actually determine the sorption. For example, a much better agreement for benzaldehyde can be achieved by using D m = 2 × 10 -12 m 2 /s and K ma = 3000, as illustrated in Figure 6. It is clear that an accurate method to obtain D m and K ma is essential for the further validation of the sorption model.
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Mass transfer in plane and square ducts

Mass transfer in plane and square ducts

where g * is the value of g as _m 00 ! 0. In the present work, mass transfer in ducts is ana- lysed using a numerical integration scheme. The scope of the problem is confined to Fickean diffusion, for lam- inar flow with constant properties, negligible dissipation, and Lewis number of unity. Soret (and Dufour) thermo- diffusion effects are neglected. Most theoretical hydrody- namic analyses are for plane ducts, Fig. 1 (a). Berman [2]

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Semi-empirical model of heat transfer in dry mineral fiber insulations

Semi-empirical model of heat transfer in dry mineral fiber insulations

Semi-empirical model of heat transfer in dry mineral fiber insulations Bomberg, M. T.; Klarsfeld, S. https://publications-cnrc.canada.ca/fra/droits L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

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Numerama study on heat-transfer characteristics of loop heat pipe evaporator using three-dimensional pore network model

Numerama study on heat-transfer characteristics of loop heat pipe evaporator using three-dimensional pore network model

An important consideration while designing the shape of a capillary evaporator is the phase distribution in the wick. However, the distribution depends on the working fluids and porous materials. This study investigates the heat-transfer characteristics of a loop heat pipe (LHP) evaporator by using a three- dimensional pore network model with a dispersed pore size wick. The simulation considers saturated and unsaturated wicks. A stainless steel (SS)-ammonia, polytetrafluoroethylene (PTFE)-ammonia, and copper-water LHP are simulated. The copper-water LHP has the highest transition heat flux to the unsat- urated wick. When the optimum evaporator shape of the copper-water LHP is designed, it is reasonable to assume that the phase state is saturated. On the other hand, for the ammonia LHP design, the state is assumed to be unsaturated. Simulation results show the heat-transfer structure in the evaporator and indicate that the applied heat flux concentrates on the three-phase contact line (TPCL) within the case, wick, and grooves. An evaporator configuration with circumferential and axial grooves is simulated to investigate the effect of the TPCL length. Results indicate that the optimum shape can be realized by vary- ing the TPCL length. The proposed method is expected to serve as a simple approach to design an evaporator.
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A model comparison to predict heat transfer during spot GTA welding

A model comparison to predict heat transfer during spot GTA welding

e The bias generated by the sensor itself. Indeed, the thermal diffusion is affected by the hole drilled to insert the thermo- couple. The heat flux cannot go through the air and an accu- mulation is observed near the sensor. Thus, the measured temperature is higher than the actual one (up to 80  C [1] ). Here, the correction is more complex. A tri-dimensional simulation is developed to take the sensor geometry into ac- count. A comparison between the temperature inside the thermocouple and the temperature on an unaffected zone leads to a maximal error. This error is then directly corrected on measured temperatures, and the criterion is automatically reduced (standard deviation z 30  C). The resolution of the
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Heat transfer measurements in furnaces and fires

Heat transfer measurements in furnaces and fires

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous. https://doi.org/10.4224/40001184 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

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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

natural and forced convection. 15,18–22 In systems of natural convection with bubble injection, mix- ing is provided by large scale circulations driven by density dif- ferences in the liquid and bubbles. Within such a system, studies have shown that the bubble size has a major effect on the over- all heat transfer. 10 However, there have been only a few studies on forced convective heat transfer in bubbly flows, 15,19,23 where, in addi- tion to buoyancy driven circulation, bubble wakes and their inter- play provide an additional mixing mechanism. In systems of forced convection, experiments and numerical simulations have primar- ily focused on understanding the influence of bubble accumulation and deformability on the global mixing properties. Experimental setups (e.g., Ref. 23 ) are generally limited by the Reynolds number [O(10 2 )]. Industrial systems involving heat and mass transfer with forced convection, i.e., mean liquid velocity (for e.g., heat exchang- ers), reach much higher Reynolds numbers O(10 3 –10 5 ) and beyond. Fundamental studies on the interaction between the turbulence in the carrier fluid, heat transfer, and the dispersed bubbles at such high Reynolds numbers are currently lacking. The objective of our work is to fill this gap. In this paper, we will describe a facility which is built to tackle various unresolved questions related to heat transfer in turbulent bubbly flow. The Twente Mass and Heat Transfer Water Tunnel (TMHT) will be used to (i) quantitatively characterize the global heat transfer of a turbulent flow with and without gas bub- ble injection, (ii) correlate and understand the local heat flux with the local liquid velocity and temperature fluctuations in the bub- bly turbulent flow, and (iii) explore and understand the dependence of the heat transfer on the control parameters, such as the gas con- centration, the bubble size, and the Taylor–Reynolds number of the flow.
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Heat transfer at building surfaces

Heat transfer at building surfaces

The inside surface of a wall or window exchanges heat by convection with the air in the room and by radiation with all the other surfaces that together enclose the room. It is often convenient to allow for the two independent heat transfer processes by using an inside surface conductance that is the sum of hc and hr. just as is done for an air space. This is quite all right so long as the surfaces that can be seen from the wall or window are close to the same temperature as the air in the room. This is usually the case for floors, ceilings and partitions that separate rooms at about the same temperature. It is not true, however, for a corner room, which has two outside walls; nor is it true for a room with a radiant heating system or a high level of artificial lighting. In these cases the radiation and convection can be combined by the use of a fictitious air temperature similar to the sol-air temperature for the outside surface. If the window considered in the first example were part of the outer wall of a room with a radian heating panel in the ceiling, the temperature of the inside surface would be about 4 degrees warmer and the total heat flow through the window would be about 9 per cent greater than that indicated by the simple calculation.
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Condensation heat transfer on superhydrophobic surfaces

Condensation heat transfer on superhydrophobic surfaces

supersaturations. Summary and Future Outlook Superhydrophobic surfaces for enhanced condensation requires the careful control of surface structure length scale and geometry, nucleation density, droplet morphology, and departure dynamics. Currently, metal oxides are one of the most promising methods to create these superhydrophobic surfaces in a scalable manner due to their ability to form PW droplets, relatively large thermal conductivities, reduced structure length scales, and low droplet adhesion for stable droplet jumping. In addition, jumping condensation has the potential to enhance heat transfer in the presence of NCGs 102-104 via boundary layer mixing, in addition to the 30% enhancement already observed in pure vapor environments. However, these surfaces remain limited due to flooding for applications with low supersaturations. In the future, control of nucleation density through the creation of coatings and deposition methods for the inclusion of well-defined defects at the molecular scale, and minimization of the structure length scale are promising pathways to extend the operating limits. Furthermore, significant efforts should be placed on creating robust hydrophobic coatings at high temperatures. As in classical dropwise condensation, the degradation of the hydrophobic coating poses significant challenges for industrial implementation. One idea showing promise is the study and formation of naturally occurring hydrophobic materials, such as rare-earth oxide ceramics 105 .
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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

Figure 8. –Left: View of the top box containing the 3 actuators (cover removed). The membrane is glued on the bottom of the actuators. –Right: View of the heat exchanger bottom wall, made of copper. The two grooves constitute the manifolds. Figure 9 shows the configuration of the hydraulic system: adjusting the vertical position of the two constant level tanks imposes the pressure at the inlet and the outlet of the channel. These heights are adjustable and may be changed as required for a given experiment. The mass flow rate is measured thanks to a precision balance, with an uncertainty less than 1% for all experiments. The pump P2 is used to fill the loop prior to each experiment.
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Heat, air and moisture transfer terminology: parameters and concepts

Heat, air and moisture transfer terminology: parameters and concepts

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Heat, air and moisture transfer terminology: parameters and concepts Radu, Adrian; Barreira, Eva; Saber, Hamed; Hens, Hugo; Vinha, Juha; Vasilache, Maricica; Bomberg, Mark; Koronthalyova, Olga; Matiasovsky, Peter; Becker, Rachel; Kalamees, Targo; Peixoto de Freitas, Vasco; Maref, Wahid
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