Computational and Experimental Study of the Flow in Evaporative Crystallizers

2005 ◽  
Author(s):  
Luiz F. Echeverri ◽  
Sumanta Acharya ◽  
Peter W. Rein
Keyword(s):  
Complex Geometry ◽  
Natural Circulation ◽  
Frictional Resistance ◽  
Product Yield ◽  
Circulation Rate ◽  
Physical Parameters ◽  
Two Phase ◽  
Convective Boiling ◽  
Void Fractions ◽  
The Individual

Various evaporative-crystallization systems rely on the natural circulation generated by boiling as the only driving force for the fluid flow. The circulation resulting from the balance between the buoyancy forces of the vapor bubbles and the frictional resistance plays an important role in the convective-boiling heat transfer, and it is desired that this circulation be as high as practically possible to maximize the capacity of the equipment and to lead to high-quality product yield. Although the basic mechanisms that govern the individual processes of boiling, buoyancy, and two-phase interactions have been extensively studied in simpler geometries, their combined behavior in the complex geometry of evaporative-crystallizers and the interaction of numerous physical and chemical variables make it difficult to understand and optimize the key parameters leading to improved product yield. In the present study measurements and computations have been reported both in a lab-scale test rig and in a full-scale crystallizer in order to obtain a better understanding of the physical processes. It is observed that one of the key physical parameters that influence the circulation rate is the drag coefficient, and that, existing correlations have to be corrected for flow contamination and high void fractions to obtain reasonable agreement with measurements.

Paper 7: Mass Flow Prediction in Natural Circulation Boilers

1969 ◽  
Vol 184 (7) ◽  
pp. 6-15
Author(s):  
A. S. T. Thomson ◽  
A. W. Scott ◽  
D. H. Rooney ◽  
A. M. Bradford
Keyword(s):  
Void Fraction ◽  
Flow Model ◽  
Natural Circulation ◽  
Circulation Rate ◽  
Two Phase ◽  
Flow Prediction ◽  
Friction Pressure ◽  
Type Flow ◽  
Friction Pressure Drop ◽  
Theoretical Results

This paper presents results from a programme of steady-state natural circulation tests carried out on a two-tube experimental boiler. The circuit was constructed using normal commercial tubes and the tests covered the following range of variables: During the tests, measurements were taken of pressure, pressure difference, circulation rate, and density or void fraction at the top of the riser tube. The void fraction data are presented for use. A theoretical analysis was carried out using an annular type flow model in the riser tube with a simple two-phase friction pressure drop expression which required only void fraction data. A comparison was made between the theoretical results and the experimental data and the comparison was extended to include ( a) homogeneous flow, ( b) Martinelli–Nelson correlation, and ( c) Thom correlation. The results indicate that the analysis used, which requires only void fraction data, gave the best correlation over the range of natural circulation conditions covered.

Steady-State Performance of a Rectangular Natural Circulation Loop With Differentially Heated Parallel Channels

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Shubhankar Chakraborty ◽  
Prasanta Kr. Das
Keyword(s):  
Steady State ◽  
Phase Change ◽  
Energy Transport ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Circulation Rate ◽  
Working Fluid ◽  
Two Phase ◽  
State Behavior ◽  
Natural Circulation Loop

Natural circulation loop (NCL) transfers thermal energy without using any external power. As with phase change, one can expect a higher rate of heat transfer and a greater change in density, NCL with a phase change of the circulating fluid is a more effective energy transfer device. Though in many of the practical NCLs there are multiple heating risers, the characteristics of NCLs with parallel boiling risers have not been investigated in detail. In the present work, the steady-state behavior of a two-phase NCL with two parallel boiling risers for water as the working fluid has been investigated. Emphasis has been given to the performance of the loop when the risers are differentially heated. Effect of different parameters on the loop circulation rate and energy transport for both equally and differentially heated conditions has been thoroughly examined and compared to the performance of a single-riser loop under equivalent working condition.

Experimental study on saturated boiling of two phase natural circulation under low pressure in narrow rectangular channels

Kerntechnik ◽  
2017 ◽  
Vol 82 (6) ◽  
pp. 631-636
Author(s):  
Li Zi-chao ◽  
Qi Shi ◽  
Zhou Tao ◽  
Li Bing ◽  
Muhammad Ali Shahzad ◽  
...  
Keyword(s):  
Experimental Study ◽  
Natural Circulation ◽  
Low Pressure ◽  
Two Phase ◽  
Rectangular Channels ◽  
Saturated Boiling

A Statistical Approach to Improve Wafer Fabrication Yield

2002 ◽  
Author(s):  
Nael Barakat ◽  
Hesham Enshasy
Keyword(s):  
Statistical Approach ◽  
Product Yield ◽  
Wafer Fabrication ◽  
Statistical Process ◽  
Control Approach ◽  
Yield Increase ◽  
Cost Cutting ◽  
Knowing That ◽  
The Individual ◽  
Industrial Problem

In spite of the recent advancements in wafer fabrication techniques, devices are still being individually checked and modified. This is due to the fact that the general manufacturing processes involved in wafer production have their inherent inconsistencies. As a consequence, individual devices show differences in characteristics that would render a big group of them operating out of the range of the pre-set spec limits. Therefore they would require types of modifications specific to the individual device. Knowing that the resources spent on checking and eliminating out-of-spec devices before they reach the customer are very significant, the manufacturing operation becomes hardly profitable. These wafers normally carry devices in the range of a thousand or so, making a statistical approach very attractive. In this paper, an actual industrial problem in wafer fabrication to the desired specifications is presented. The problem shows in passive filters built using Surface Acoustic Wave (SAW) theory. A solution considering a statistical process control approach to the population of devices on the wafer is proposed. The results of applying this solution are realized in significant product yield increase, huge cost cutting, and automation promotion and application.

Two-Phase Friction Factor Obtained From Various Void Fraction Models During Condensation of R134A in Vertical Downward Flow at High Mass Flux

2008 ◽  
Author(s):  
Ahmet Selim Dalkilic ◽  
Suriyan Laohalertdecha ◽  
Somchai Wongwises
Keyword(s):  
Void Fraction ◽  
Annular Flow ◽  
Smooth Tube ◽  
High Mass ◽  
Two Phase ◽  
Void Fractions ◽  
Mass Fluxes ◽  
Friction Factors ◽  
Flow Void ◽  
Fraction Models

Void fractions are determined in vertical downward annular two-phase flow of R134a inside 8.1 mm i.d. smooth tube. The experiments are done at average saturated condensing temperatures of 40 and 50°C. The average qualities are between 0.84–0.94. The mass fluxes are around 515 kg m−2s−1. The experimental setup is explained elaborately. Comparisons between the void fraction determined from 35 void fraction correlations are done. According to the use of various horizontal and vertical annular flow void fraction models together with the present experimental condensation heat transfer data, similar void fraction results were obtained mostly for the smooth tube. The experimental friction factors obtained from void fraction correlations are compared with the friction factors determined from graphical information provided by Bergelin et. al. Effect of void fraction alteration on the momentum pressure drop is also presented.

On the Natural Lubrication of Synovial Joints: Normal and Degenerate

1977 ◽  
Vol 99 (2) ◽  
pp. 163-172 ◽  
Author(s):  
Joseph M. Mansour ◽  
Van C. Mow
Keyword(s):  
Articular Cartilage ◽  
Solid Phase ◽  
Articular Surface ◽  
Moving Load ◽  
Frictional Resistance ◽  
Elastic Solid ◽  
Surface Load ◽  
Two Phase ◽  
Tissue Properties ◽  
Synovial Joints

Fluid flow and mass transport mechanisms associated with articular cartilage function are important biomechanical processes of normal and pathological synovial joints. A three-layer permeable, two-phase medium of an incompressible fluid and a linear elastic solid are used to model the flow and deformational behavior of articular cartilage. The frictional resistance of the relative motion of the fluid phase with respect to the solid phase is given by a linear diffusive dissipation term. The subchondral bony substrate is represented by an elastic solid. The three-layer model of articular cartilage is chosen because of the known histological, ultrastructural, and biomechanical variations of the tissue properties. The calculated flow field shows that for material properties of normal healthy articular cartilage the tissue creates a naturally lubricated surface. The movement of the interstitial fluid at the surface is circulatory in manner, being exuded in front and near the leading half of the moving surface load and imbibed behind and near the trailing half of the moving load. The flow fields of healthy tissues are capable of sustaining a film of fluid at the articular surface whereas pathological tissues cannot.

Prediction of Pump Performance Under Air-Water Two-Phase Flow Based on a Bubbly Flow Model

1993 ◽  
Vol 115 (4) ◽  
pp. 781-783 ◽  
Author(s):  
Kiyoshi Minemura ◽  
Tomomi Uchiyama
Keyword(s):  
Two Phase Flow ◽  
Bubbly Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Flow Conditions ◽  
Two Phase ◽  
Performance Change ◽  
Void Fractions ◽  
Two Phases

This paper is concerned with the determination of the performance change in centrifugal pumps operating under two-phase flow conditions using the velocities and void fractions calculated under the assumption of an inviscid bubbly flow with slippage between the two phases. The estimated changes in the theoretical head are confirmed with experiments within the range of bubbly flow regime.

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