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Monde, M.; Wang, X.
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Critical heat flux (CHF) has been measured in saturated forced convective boiling with a wall jet on a rectangular heated surface of 40 and 80 mm in length and 20 mm in width. The jet velocity is varied from 3 to 15 m/s, and the system pressure is 0.1, 0.2, and 0.4 MPa for R113. It is found that the existing correlation for saturation condition can be applied to the CHF at high and low ρ_{l}/ρ_{g} values (e.g. water and R22), but hardly to the CHF at medium ρ_{l}/ρ_{g} values (e.g. R113 at 0.2 and 0.4 MPa). A revised correlation is proposed to predict most of the CHF data within an accuracy of ±25%.
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Tan, F. L.
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2 Citations
This paper presents experimental findings on the phenomenon of solidification of a binary alloy in a finned enclosure using aqueous ammonium chloride solution. Solidification experiments are carried out over a wide range of initial composition of binary alloy solution from hypoeutectic to hypereutectic concentration ranging from 8, 16 and 24% of ammonium chloride are discussed. An interesting “snowing” phenomenon is observed for the hypereutectic concentration in a finned enclosure.
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Baouab, I. Bhouri; Mahjoub Saïd, N.; Mhiri, H.; Bournot, Ph.; Palec, G.
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The present work consists in an experimental investigation of the flow issuing from a bent chimney over a downstream obstacle. Our purpose is to explore the resulting flow field and its different characterizing features. These features were captured by means of the Particle Image Velocimetry technique. A numerical simulation of the problem has also been carried out and validated after comparison of the corresponding results to the experimental data. A good level of agreement was achieved between the experiments and the calculations. Then, we tried to upgrade our model by adopting large (real) scale dimensions. Our purpose consisted mainly in the observation and evaluation of the behavior of the incoming flow in presence of a double tandem obstacle. In a second step, we proposed to increase the number of the placed obstacles to four. The results given by the threedimensional model are likely to highlight the dynamic features of the established field as well as the resulting mass transfer. Finally, we tried to evaluate the effect of further parameters on the characterizing features of the resulting flow filed such as the velocity ratio, the obstacles’ gap, the arrangement of the obstacles and the obstacles’ geometry.
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El Omari, Kamal; Le Guer, Yves
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3 Citations
In a recent paper we have investigated mixing and heat transfer enhancement in a mixer composed of two circular rods maintained vertically in a cylindrical tank. The rods and tank can rotate around their revolution axes while their surfaces were maintained at a constant temperature. In the present study we investigate the differences in the thermal mixing process arising from the utilization of a constant heat flux as a boundary condition. The study concerns a highly viscous fluid with a high Prandtl number for which this chaotic mixer is suitable. By solving numerically the flow and energy equations, and using different statistical tools we characterize the evolution of the fluid temperature and its homogenization. Fundamental differences are reported between these two modes of heating or cooling: while the mixing with an imposed temperature results in a homogeneous temperature field, with a fixed heat flux we observe a constant difference between the maximal and minimal temperatures that establish in the fluid; the extent of this difference is governed by the efficiency of the mixing protocol.
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Huai, Xiulan; Wang, Guoxiang; Jin, Renxi; Yin, Tienan; Zou, Yu
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6 Citations
This paper presents an experimental study of microscopic explosive boiling introduced by a pulsed laser. The violent explosive boiling was observed in the liquid film, and the vapor bubbles together with liquid droplets were expelled from the platinum film. It is found that the apparent bubble nucleation temperature is a strong function of the heating rate. The pressure signal appears as continuous oscillation and is intensified as laser power density increases.
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Subudhi, Sudhakar; Sreenivas, K. R.; Arakeri, Jaywant H.
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This work is concerned with the removal of unwanted fluid through the source–sink pair. The source consists of fluid issuing out of a nozzle in the form of a jet and the sink is a pipe that is kept some distance from the source pipe. Of concern is the percentage of source fluid sucked through the sink. The experiments have been carried in a large glass water tank. The source nozzle diameter is 6 mm and the sink pipe diameter is either 10 or 20 mm. The horizontal and vertical separations and angles between these source and sink pipes are adjustable. The flow was visualized using KMnO_{4} dye, planer laser induced fluorescence and particle streak photographs. To obtain the effectiveness (that is percentage of source fluid entering the sink pipe), titration method is used. The velocity profiles with and without the sink were obtained using particle image velocimetry. The sink flow rate to obtain a certain effectiveness increase dramatically with lateral separation. The sink diameter and the angle between source and the sink axes don’t influence effectiveness as much as the lateral separation.
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By
Atashafrooz, M.; Gandjalikhan Nassab, S. A.; Lari, K.
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2 Citations
In the present work, the interaction between nongray radiation and forced convection in a laminar radiating gas flow over a recess including two backward and forward facing steps in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum (50 cm^{−1} < η < 20,000 cm^{−1}) are obtained from the HITRAN2008 database. The fullspectrum kdistribution method is used to account for nongray radiation properties, while the gray radiation calculations are carried out using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation is solved by the discrete ordinates method. The effects of radiation–conduction parameter, wall emissivity, scattering coefficient and recess length on heat transfer behaviors of the convection–radiation system are investigated for both gray and nongray mediums. In addition, the results of gray medium are compared with nongray results in order to judge if the differences between these two approaches are significant enough to justify the usage of nongray models. Results show that for air mixture with 10 % CO_{2} and 20 % H_{2}O, use of gray model for the radiative properties may cause significant errors and should be avoided.
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By
Suri, Amar Raj Singh; Kumar, Anil; Maithani, Rajesh
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2 Citations
The present work deals with experimental investigation of heat transfer and fluid flow characteristics of multiple square perforated twisted tape with wing inserts in a heat exchanger tube. The range of selected geometrical parameters are, perforation width ratio (a/W_{T}) of 0.083–0.333, twist ratio (T_{L}/W_{T}) of 2.0–3.5, wing depth ratio (W_{d}/W_{T}) of 0.042–0.167 and number of twisted tapes (T_{P}) of 4. The Reynolds number (Re_{n}) selected for experimentation ranges from 5000 to 27,000. The maximum heat transfer and friction factor enhancement was found to be 6.96 and 8.34 times that of plane tube, respectively. The maximum heat transfer enhancement is observed at a a/W_{T} of 0.250, T_{L}/W_{T} of 2.5, and W_{d}/W_{T} of 0.167.
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By
Muria, Michela; Lamberti, Gaetano; Titomanlio, Giuseppe
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10 Citations
The pharmacokinetic (PK) models predict the hematic concentration of drugs after the administration. In compartment modeling, the body is described by a set of interconnected “vessels” or “compartments”; the modeling consisting of transient mass balances. Usually the orally administered drugs were considered as immediately available: this cannot describe the administration of extendedrelease systems. In this work we added to the traditional compartment models the ability to account for a delay in administration, relating this delay to in vitro data. Firstly, the method was validated, applying the model to the dosage of nicotine by chewinggum; the model was tuned by in vitro/in vivo data of drugs (divalproexsodium and diltiazem) with mediumrate release kinetics, then it was applied in describing in vivo evolutions due to the assumption of fast and slowrelease systems. The model reveals itself predictive, the same of a Level A in vitro/in vivo correlation, but being physically based, it is preferable to a purely statistical method.
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By
Karlsson, Linn; Ljung, AnnaLena; Lundström, T. Staffan
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The flow within freezing water droplets is here numerically modelled assuming fixed shape throughout freezing. Three droplets are studied with equal volume but different contact angles and two cases are considered, one including internal natural convection and one where it is excluded, i.e. a case where the effects of density differences is not considered. The shape of the freezing front is similar to experimental observations in the literature and the freezing time is well predicted for colder substrate temperatures. The latter is found to be clearly dependent on the plate temperature and contact angle. Including density differences has only a minor influence on the freezing time, but it has a considerable effect on the dynamics of the internal flow. To exemplify, in the vicinity of the density maximum for water (4 ^{∘}C) the velocities are about 100 times higher when internal natural convection is considered for as compared to when it is not.
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