Thermal Effects of Two Immiscible Fluids in a Circular Tube with Nano Particles

2017 ◽  
Vol 6 (1) ◽  
pp. 105-119 ◽  
Author(s):  
K. Maruthi Prasad ◽  
N. Subadra ◽  
M. A. S. Srinivas
Keyword(s):  
Thermal Effects ◽  
Circular Tube ◽  
Immiscible Fluids ◽  
Nano Particles

Core–annular flow in a periodically constricted circular tube. Part 2. Nonlinear dynamics

2002 ◽  
Vol 470 ◽  
pp. 181-222 ◽  
Author(s):  
CHARALAMPOS KOURIS ◽  
JOHN TSAMOPOULOS
Keyword(s):  
Nonlinear Dynamics ◽  
Flow Rate ◽  
Annular Flow ◽  
Circular Tube ◽  
Applied Pressure ◽  
Immiscible Fluids ◽  
Variable Cross ◽  
Computational Domain ◽  
Experimental Conditions ◽  
Time Periodic

Nonlinear dynamics of the concentric, two-phase flow of two immiscible fluids in a circular tube of variable cross-section is studied for parameter values where the steady core–annular flow (CAF) is linearly unstable. The simulations are based on a pseudo-spectral numerical method. They are carried out assuming axial symmetry, that the total flow rate remains constant and that all dependent variables are periodic in the axial direction, which includes the minimum necessary number of repeated units so that the obtained solution is independent of this number. The time integration originates with the numerically computed steady CAF or the steady CAF seeded with either the most unstable mode or random small disturbances. Only a limited number of the most interesting cases are presented. For the most part, the values of the majority of the dimensionless parameters are such that oil flows in the centre of the tube driven by an applied pressure gradient against gravity, whereas water is flowing in the annulus. It is shown that, whereas the steady (unstable) solution may indicate that the heavier water flows countercurrently with respect to the oil, the time periodic (observable) solution may indicate the same, albeit at a much smaller core flow rate or that concurrent flow occurs. This is due to the water being trapped between the large-amplitude interfacial waves that are generated and being convected by the oil. It is also shown that increasing the inverse Weber number increases the wave amplitude to the point that the flow of the core fluid may become discontinuous with a mechanism that depends on the viscosity ratio between the two fluids. Increasing the amplitude of the sinusoidal variation of the tube leads to a combination of travelling and standing waves, which interact to produce a time periodic solution with a long period associated with the time it takes the travelling wave to travel through the computational domain and a second much shorter period that is related to their interaction time. Qualitative agreement has been obtained upon comparing our numerical simulations with limited experimental reports, even though the experimental conditions were not identical to those in our model.

Starting Poiseuille Flow in a Circular Tube With Two Immiscible Fluids

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Chiu-On Ng ◽  
C. Y. Wang
Keyword(s):  
Circular Tube ◽  
Slip Length ◽  
Finite Thickness ◽  
Applied Pressure ◽  
Immiscible Fluids ◽  
Circular Duct ◽  
Two Fluids ◽  
Plasma Skimming ◽  
Start Up ◽  
Starting Flow

Starting flow due to a suddenly applied pressure gradient in a circular tube containing two immiscible fluids is solved using eigenfunction expansions. The orthogonality of the eigenfunctions is developed for the first time for circular composite regions. The problem, which is pertinent to flow lubricated by a less viscous near-wall fluid, depends on the ratio of the radius of the core region to that of the tube, and the ratios of dynamic and kinematic viscosities of the two fluids. In general, a higher lubricating effect will lead to a longer time for the starting transient to die out. The time development of velocity profile and slip length are examined for the starting flows of whole blood enveloped by plasma and water enveloped by air in a circular duct. Owing to a sharp contrast in viscosity, the starting transient duration for water/air flow can be ten times longer than that of blood/plasma flow. Also, the slip length exhibits a singularity in the course of the start-up. For blood with a thin plasma skimming layer, the singularity occurs very early, and hence for the most part of the start-up, the slip length is nearly a constant. For water lubricated by air of finite thickness, the singularity may occur at a time that is comparable to the transient duration of the start-up, and hence, an unsteady slip length has to be considered in this case.

scholarly journals Augmented thermal performance in a non-uniform heat flux circular tube with twisted tape insert using hybrid nanofluid

2021 ◽  
Vol 321 ◽  
pp. 04009
Author(s):  
Arvind Kumar ◽  
Kunal Dey ◽  
Suvanjan Bhattacharyya ◽  
Akshoy Ranjan Paul ◽  
Ali Cemal Benim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Volume Fraction ◽  
Circular Tube ◽  
Nano Particles ◽  
Hybrid Nanofluid ◽  
Twisted Tape ◽  
Uniform Heat

The influence of non-uniform heat transfer on a circular tube with a twisted tape insert using nanofluid (NF) is examined. The circular tube had an inner diameter 20 mm, with 0.5 mm thickness and 2 m of length. Wall heat flux conditions were examined for Reynolds number ranging from 5 000 to 25 000. Heat flux distribution included partial heating at different circumferential positions. Water was used as a base fluid, while single and multi-nano particles are used for simple and hybrid nanofluids (HNF). The goal of this study is to augment the thermal performance by incorporating non-uniform heating, using a twisted tape insert and by using nanoparticle of different volume fraction. NF act as a fluid additive and twisted tape act as a turbulence promoter and they enhance the heat transfer rate. However, major disadvantage in this investigation is the pressure drop incurred due to the twisted tape and NFs. Hence, a series of simulation are carried out to find out the optimum configuration of the set-up for which heat transfer will be enhanced with minimum pressure drop.

Heating Effects of the Magnetic-Nanoparticle Enhanced Hyperthermia Targeting Tumors Underneath the Ribs

2013 ◽  
Author(s):  
Chao Jin ◽  
Zhi Zhu He ◽  
Jing Liu
Keyword(s):  
Liver Tumor ◽  
Thermal Effects ◽  
Bone Structure ◽  
Nano Particles ◽  
Tumor Treatment ◽  
Heating Effects ◽  
Parametric Studies ◽  
Em Field ◽  
Electromagnetic Hyperthermia ◽  
Magnetic Nano Particles

Aiming at providing a detailed disclosure on the thermal effects of EM (electromagnetic) hyperthermia on the liver tumor underneath the ribs, this paper has numerically provided comprehensive interpretations on the heating effects of magnetic nano-particles induced hyperthermia for target tumor treatment. The results revealed the following factors: (1) The existing of bone structure, i.e. ribs has an inevitable effect on the distribution of EM field; specifically, due to its lower dielectric property, the bone structure seemingly acts as a barrier to attenuate the access of EM energy into the tissue, especially the tumor in the deep body. (2) Using higher dosage or bigger size magnetic nano-particles have greatly enhanced the temperature elevation of targeted tumor tissue and thereby obtain good performance of hyperthermia. (3) Further parametric studies indicated that a worse heating effect would be obtained when utilizing external EM field with a higher frequency of 10MHz; while higher strength of EM field would evidently enhance the heating effects of such EM hyperthermia. The present study would promote the understandings of thermal effects on the specific organs in EM hyperthermia, and the findings are expected to provide valuable guidance for planning an accurate dosage in clinical liver tumor thermal ablation.

Theoretical Evaluation on the Thermal Effects of Extracellular Hyperthermia and Intracellular Hyperthermia

2007 ◽  
Author(s):  
Zhong-Shan Deng ◽  
Jing Liu
Keyword(s):  
Heat Transfer ◽  
Thermal Effects ◽  
Nano Particles ◽  
Whole Body ◽  
Cell Diameter ◽  
Target Tissue ◽  
Time Varying ◽  
Extracellular Medium ◽  
Theoretical Evaluation ◽  
Magnetic Nano Particles

Although not currently a routine cancer treatment therapy, hyperthermia is developing rather rapidly as an alternative way as part of conventional treatment for some cancers. This treatment takes advantage of the high sensitivity of tumor cell to heat. Up to now, a variety of heating methods have been established to induce temperature rises either locally in target tissue region, or over the whole body. Among them, magnetic nano-particles offer some attractive possibilities in tumor hyperthermia, which have controllable sizes ranging from a few nanometers up to tens of nanometers. The magnetic nano-particles can be made to resonantly respond to a time-varying electromagnetic (EM) field, with advantageous results related to the transfer of energy from the exciting field to the nano-particles. This heat then efficiently conducts into the surrounding diseased cells and tissues. A major concern involved in magnetic nano-hyperthermia is about the controversy that whether intracellular hyperthermia is superior to extracellular hyperthermia [1]. The potential of time-varying EM heating effects in a scale length smaller than the biological cell diameter was first addressed by Gordon et al. and termed as “intracellular hyperthermia” [2]. Since experimental validation of the thermal effects of intracellular hyperthermia is still not feasible with the current experimental technique, this problem has been studied theoretically. However, different researchers have suggested different results, and the controversy still goes on [1–3]. In order to understand the exact micro-mechanisms of EM heating involved in intracellular hyperthermia and extracellular hyperthermia, an energy analysis is presented in this study to simulate the corresponding heat transfer problems thus involved. Different from intracellular hyperthermia, the main characteristic of the extracellular hyperthermia is to heat up the target tissue by EM energy absorption only in the extracellular medium. A series of numerical calculations for both intracellular hyperthermia and extracellular hyperthermia are performed. The results will answer the question from the heat transfer mechanism whether intracellular hyperthermia is superior to extracellular hyperthermia in the thermal sense.

Thermal Considerations in Lens Regulator Systems

1970 ◽  
Vol 28 ◽  
pp. 358-359
Author(s):  
K.C. Newton
Keyword(s):  
Electron Microscope ◽  
Thermal Effects ◽  
Environmental Control ◽  
Reference Networks ◽  
Better Than

Thermal effects in lens regulator systems have become a major problem with the extension of electron microscope resolution capabilities below 5 Angstrom units. Larger columns with immersion lenses and increased accelerating potentials have made solutions more difficult by increasing the power being handled. Environmental control, component choice, and wiring design provide answers, however. Figure 1 indicates with broken lines where thermal problems develop in regulator systemsExtensive environmental control is required in the sampling and reference networks. In each case, stability better than I ppm/min. is required. Components with thermal coefficients satisfactory for these applications without environmental control are either not available or priced prohibitively.

Electron holography of catalysts

1995 ◽  
Vol 53 ◽  
pp. 416-417
Author(s):  
A. K. Datye ◽  
D. S. Kalakkad ◽  
L. F. Allard ◽  
E. Völkl
Keyword(s):  
Heterogeneous Catalysts ◽  
High Surface ◽  
High Surface Area ◽  
Atomic Scale ◽  
Nano Particles ◽  
Phase Image ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Information ◽  
Particle Structure

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.

Direct measurement of electron-diffraction-pattern intensities using an energy loss spectrometer

1989 ◽  
Vol 47 ◽  
pp. 668-669
Author(s):  
A. G. Jackson ◽  
M. Rowe
Keyword(s):  
Thermal Effects ◽  
Dynamic Range ◽  
Scattering Amplitude ◽  
Dynamical Theory ◽  
Site Symmetry ◽  
Proof Of Concept ◽  
Parallel Acquisition ◽  
Kinematic Approximation ◽  
Speed Up ◽  
Structure Calculations

Diffraction intensities from intermetallic compounds are, in the kinematic approximation, proportional to the scattering amplitude from the element doing the scattering. More detailed calculations have shown that site symmetry and occupation by various atom species also affects the intensity in a diffracted beam. [1] Hence, by measuring the intensities of beams, or their ratios, the occupancy can be estimated. Measurement of the intensity values also allows structure calculations to be made to determine the spatial distribution of the potentials doing the scattering. Thermal effects are also present as a background contribution. Inelastic effects such as loss or absorption/excitation complicate the intensity behavior, and dynamical theory is required to estimate the intensity value.The dynamic range of currents in diffracted beams can be 104or 105:1. Hence, detection of such information requires a means for collecting the intensity over a signal-to-noise range beyond that obtainable with a single film plate, which has a S/N of about 103:1. Although such a collection system is not available currently, a simple system consisting of instrumentation on an existing STEM can be used as a proof of concept which has a S/N of about 255:1, limited by the 8 bit pixel attributes used in the electronics. Use of 24 bit pixel attributes would easily allowthe desired noise range to be attained in the processing instrumentation. The S/N of the scintillator used by the photoelectron sensor is about 106 to 1, well beyond the S/N goal. The trade-off that must be made is the time for acquiring the signal, since the pattern can be obtained in seconds using film plates, compared to 10 to 20 minutes for a pattern to be acquired using the digital scan. Parallel acquisition would, of course, speed up this process immensely.

Coherent electron nanodiffraction from clean silver nano particles in a UHV STEM

1993 ◽  
Vol 51 ◽  
pp. 1058-1059
Author(s):  
J. Liu ◽  
M. Pan ◽  
G. E. Spinnler
Keyword(s):  
Supported Catalysts ◽  
Imaging Techniques ◽  
Nano Particles ◽  
Metal Particles ◽  
Shape Structure ◽  
Dynamical Simulations ◽  
Small Metal Particles ◽  
Extract Information

Small metal particles have peculiar chemical and physical properties as compared to bulk materials. They are especially important in catalysis since metal particles are common constituents of supported catalysts. The structural characterization of small particles is of primary importance for the understanding of structure-catalytic activity relationships. The shape and size of metal particles larger than approximately 5 nm in diameter can be determined by several imaging techniques. It is difficult, however, to deduce the shape of smaller metal particles. Coherent electron nanodiffraction (CEND) patterns from nano particles contain information about the particle size, shape, structure and defects etc. As part of an on-going program of STEM characterization of supported catalysts we report some preliminary results of CEND study of Ag nano particles, deposited in situ in a UHV STEM instrument, and compare the experimental results with full dynamical simulations in order to extract information about the shape of Ag nano particles.

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