Thermal Homogenization in Spherical Reservoir by Electrohydrodynamic Conduction Phenomenon

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Miad Yazdani ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Temperature Distribution ◽  
Body Force ◽  
Mixing Time ◽  
Electric Conduction ◽  
Nonuniform Temperature ◽  
Dimensionless Numbers ◽  
Steady State Condition ◽  
Resultant Velocity ◽  
Final Steady State ◽  
Spherical Reservoir

Effect of electric conduction phenomenon on the mixing mechanism is studied numerically to thermally homogenize a dielectric liquid with an initial nonuniform temperature distribution. The fluid is stored in a spherical reservoir, and the electrodes are embedded on the reservoir surface such that the resultant local electric body forces mix the fluid. The electric field and electric body force distributions along with the resultant velocity field at the final steady-state condition are presented. The mixing mechanism is illustrated by the time evolution of temperature distribution inside the reservoir. The effects of primary dimensionless numbers on the mixing time are studied.

Thermal Homogenization in Spherical Reservoir by EHD Conduction Phenomenon

2008 ◽  
Author(s):  
Miad Yazdani ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Electric Field ◽  
Body Force ◽  
Mixing Time ◽  
Dielectric Fluid ◽  
Dimensionless Numbers ◽  
Fluid Medium ◽  
Two Fluids ◽  
Resultant Velocity ◽  
Higher Temperature ◽  
Spherical Reservoir

Electrohydrodynamic (EHD) conduction phenomenon involves the interaction of electric field and flow field in a dielectric fluid medium via the process of dissociation and recombination of free charges. This paper numerically studies the effect of electric conduction phenomenon on the mixing mechanism of two fluids with identical physical properties but separated due to the non-homogeneity of the temperature field. The fluid is designated to be restored in a spherical reservoir and it is not spontaneously mixed since the reservoir is predicted to be located in non-gravity environment. The electrodes are embedded on the reservoir surface such that the resultant electric body force causes the fluid with higher temperature mixes with the colder fluid and vice versa. The electric field and electric body force distribution and the resultant velocity field are presented. The results are illustrated in the form of time evolution of temperature distribution inside the reservoir. The effects of primary dimensionless numbers on the mixing time are studied.

Direct and Indirect Methods for Calculating Thermal Emission From Layered Structures With Nonuniform Temperatures

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
L. P. Wang ◽  
S. Basu ◽  
Z. M. Zhang
Keyword(s):  
Temperature Distribution ◽  
Thermal Emission ◽  
Local Density ◽  
Direct Method ◽  
Direct Methods ◽  
Layered Structures ◽  
Nonuniform Temperature ◽  
Indirect Methods ◽  
Nonuniform Temperature Distribution ◽  
Direct And Indirect Methods

The determination of emissivity of layered structures is critical in many applications, such as radiation thermometry, microelectronics, radiative cooling, and energy harvesting. Two different approaches, i.e., the “indirect” and “direct” methods, are commonly used for computing the emissivity of an object. For an opaque surface at a uniform temperature, the indirect method involves calculating the spectral directional-hemispherical reflectance to deduce the spectral directional emissivity based on Kirchhoff’s law. On the other hand, a few studies have used a combination of Maxwell’s equations with the fluctuation-dissipation theorem to directly calculate the emissivity. The present study aims at unifying the direct and indirect methods for calculating the far-field thermal emission from layered structures with a nonuniform temperature distribution. Formulations for both methods are given to illustrate the equivalence between the indirect and the direct methods. Thermal emission from an asymmetric Fabry–Pérot resonance cavity with a nonuniform temperature distribution is taken as an example to show how to predict the intensity, emissivity, and the brightness temperature. The local density of states, however, can only be calculated using the direct method.

Axial Temperature Distribution for a Nuclear Reactor With Sinusoidal Space and Exponential Time-Varying Power Generation

1961 ◽  
Vol 83 (4) ◽  
pp. 423-431 ◽  
Author(s):  
W. O. Doggett ◽  
E. L. Arnold
Keyword(s):  
Temperature Distribution ◽  
Nuclear Reactor ◽  
Response Times ◽  
Characteristic Temperature ◽  
Temperature Response ◽  
Time Varying ◽  
Exponential Time ◽  
Temperature Distributions ◽  
Axial Temperature ◽  
Final Steady State

Analytic temperature distributions are obtained for the fuel and coolant regions of a heterogeneous, convection-cooled reactor with axial power variation ewt sin (πz/H). The fundamental assumption in the governing differential equations is that the temperature distribution in the fuel region does not vary in the direction transverse to the coolant flow. The solutions involve two and three-parameter integrals encountered and numerically evaluated previously which are integrated herein and arranged in a form suitable for desk calculations. Closed-form expressions are developed for the final steady-state axial distributions which are applicable at times long in comparison with the characteristic temperature-response times.

Heat Transfer Augmentation of Parallel Flows by Means of Electric Conduction Phenomenon in Macro- and Micro-Scale

2009 ◽  
Author(s):  
Miad Yazdani ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Channel Wall ◽  
External Pressure ◽  
Operating Conditions ◽  
Electric Conduction ◽  
Micro Scale ◽  
Heat Transfer Augmentation ◽  
Parallel Flows ◽  
Resultant Velocity

Electrohydrodynamic (EHD) conduction phenomenon takes advantage of the electrical Coulomb force exerted on a dielectric liquid generated by externally applied electric field. The conduction phenomenon can be applied to enhance or control mass transport and heat transfer in both terrestrial and microgravity environments with advantages of simplicity and no degradation of fluid properties for isothermal as well as non-isothermal liquids. This paper numerically studies the heat transfer augmentation of externally driven macro- and micro-scale parallel flows by means of electric conduction phenomenon. The electric conduction is generated via electrode pairs embedded against the channel wall to solely enhance the heat transfer; it is not utilized to pump the liquid. Two cases of Poiseuille and Couette parallel flows are considered where for the former, a constant external pressure gradient is applied along the channel and for the latter, the channel wall moves with a constant velocity. The electric field and electric body force distributions along with the resultant velocity fields are presented. The heat transfer enhancements are illustrated under various operating conditions for both scales.

An Empirical Model for the Prediction of Hemodialysis System Performance

2011 ◽  
Author(s):  
Jane Kang ◽  
Amit Jariwala ◽  
David W. Rosen
Keyword(s):  
Steady State ◽  
Time Constant ◽  
Empirical Model ◽  
Prediction Method ◽  
Fixed Time ◽  
State Behavior ◽  
Steady State Condition ◽  
Inverse Simulation ◽  
Optimal Inputs ◽  
Final Steady State

The examination of steady state behavior of hemodialysis treatment using the analytical model created by Olson et al. revealed that for each set of hemodialysis conditions, a fixed time constant exists that dictates how quickly the patient’s waste level cycle reaches a steady state condition. They also revealed that initial waste level does not affect the final steady state waste level. In this study, an empirical model for the time constant and the final steady state maximum waste level were found that lumps hemodialysis inputs such as flow rates, dialyzer properties, and patient waste generation by conducting a parametric study on a previous hemodialysis model from Olson et al. [1] The empirical model is validated by comparing the curve that predicts how the peak waste level of each cycle changes over time with the analytical model’s results. For all the tested input values which cover most of practical hemodialysis treatments, the curve closely matched the numerical model’s results with R2 value higher than .9973. The empirical model created in this study provides a much simpler prediction method without the use of complex numerical simulations. In addition, the Olson model cannot be used to run an inverse simulation to determine optimal inputs for desired outputs. This limitation is overcome by our empirical model, which further allows much easier and more extended exploration of different therapies (dose length and schedule) for both doctors and renal replacement system designers.

Ratcheting due to Thermal Stratification

2019 ◽  
Author(s):  
R. Adibi-Asl ◽  
D. O’Kane ◽  
E. Chen
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Temperature Distribution ◽  
Thermal Stratification ◽  
Fluid Flows ◽  
Uniform Temperature ◽  
Element Analysis ◽  
Steady State Condition ◽  
Thermal Ratcheting ◽  
The Finite Element Analysis

Abstract Thermal ratcheting is required to be checked by most of the piping design codes, specifically the ASME B&PV Code. For cases where the variation of temperature distribution is not uniform, the existing ratchet check methodology for piping is inadequate and therefore the finite element analysis (FEA) is often used to perform ratchet checks. Thermal stratification, in which cold and hot fluid flows are layered in a relatively steady state condition, is a good example of non-linear/non-uniform temperature distribution across the pipe. This paper develops straightforward equations to address thermal stratification in piping. Finite element analysis is used to benchmark the results.

scholarly journals Mixing Performance Analysis of Orbitally Shaken Bioreactors

2020 ◽  
Vol 10 (16) ◽  
pp. 5597
Author(s):  
Angus Shiue ◽  
Shih-Chieh Chen ◽  
Jyh-Cheng Jeng ◽  
Likuan Zhu ◽  
Graham Leggett
Keyword(s):  
Mixing Time ◽  
Power Input ◽  
Energy Dissipation Rate ◽  
Mixing Efficiency ◽  
Thermal Method ◽  
Turbulent Regime ◽  
Mixing Process ◽  
Dimensionless Numbers ◽  
Filling Volume ◽  
Input Variables

This study investigated the efficacy of a novel correlation of power input, energy dissipation rate and mixing time as a potential route to identify the orbitally shaken bioreactor (OSB) system. The Buckingham’s π-theorem was used to designate and transform dimensionless Newton numbers with five relevant power input variables. These variables were empirically varied to evaluate the correlation among the dimensionless numbers. The Newton number decreases with the increased shaking frequency and filling volume. Previous work has focused on optimizing the mixing process by evaluating different shaking and agitation mixing methods. We establish a new mixing process and assessable measurement of the mixing time in the OSB. An innovative explanation of mixing time for the thermal method is proposed. The optimal mixing time is independent of the temperature of filled liquid. The dimensionless mixing number remained constant in the turbulent regime and increasing with the increased liquid viscosity and filling volume. Our findings revealed that the observed correlation is a practical tool to figure the power consumption and mixing efficiency as cell cultivation in all OSB scales and is fully validated when scaling–up system.

scholarly journals Quantitative Evaluation of the Thermal Heterogeneity on the Surface of Cryotherapy Cooling Pads

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Sepideh Khoshnevis ◽  
Jennifer E. Nordhauser ◽  
Natalie K. Craik ◽  
Kenneth R. Diller
Keyword(s):  
Image Analysis ◽  
Temperature Distribution ◽  
Distribution Patterns ◽  
Temperature Fields ◽  
Spatial Gradient ◽  
Temperature Profiles ◽  
Operating Characteristics ◽  
Nonuniform Temperature ◽  
Quantitative Examination ◽  
Thermal Heterogeneity

We have investigated thermal operating characteristics of 13 commercially available cryotherapy units (CTUs) and their associated cooling pads using IR imaging. Quantitative examination of the temperature profiles from pad IR images shows diverse, nonuniform temperature distribution patterns. The extent of heterogeneity of the temperature fields was quantified via standard image analysis methods, including thresholding, spatial gradient diagrams, and frequency histogram distributions. A primary conclusion of this study is that it is a misnomer to characterize the thermal performance of a CTU and cooling pad combination in terms of a single therapeutic temperature.

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