scholarly journals Some observations concerning "laminarization" in heated vertical tubes

2020 ◽  
Vol 163 ◽  
pp. 120101
Author(s):  
Donald M. McEligot ◽  
Xu Chu ◽  
Joong Hun Bae ◽  
Eckart Laurien ◽  
Jung Yul Yoo
Keyword(s):  
Vertical Tubes

Boiling within vertical tubes

2017 ◽  
Author(s):  
John G. Collier ◽  
Geoffrey F. Hewitt
Keyword(s):  
Vertical Tubes

Prediction of Temperature Profiles in Fluid Bed Boilers

1978 ◽  
Vol 100 (3) ◽  
pp. 508-513 ◽  
Author(s):  
J. L. Hodges ◽  
R. C. Hoke ◽  
R. Bertrand
Keyword(s):  
Large Scale ◽  
Solid Material ◽  
Temperature Gradients ◽  
Temperature Profiles ◽  
Mixing Height ◽  
Vertical Temperature ◽  
Bed Temperature ◽  
Fluid Bed ◽  
Solids Mixing ◽  
Vertical Tubes

Data acquired in the Exxon Research and Engineering Company’s fluid bed boiler program indicate that the arrangement and orientation of internal boiler tubes has a strong effect on the measured bed temperature profile. Horizontally oriented tubes yield much steeper temperature gradients than do vertical tubes. Excessive vertical temperature gradients in coal fired fluid bed boilers can either limit coal feed rates or result in the formation of agglomerates of solid material which are destructive of bed internals. This study represents an attempt to understand the influence of orientation on vertical temperature profiles in fluid bed boilers. A back-mixing model for solids recirculation was developed and applied to the prediction of bed temperatures. Bubbling bed theory is not suitable for estimating solids circulation rates in pressurized beds of large particles with immersed tubes. However, by introducing the concept of a solids mixing height it was possible to estimate solid movement. The solids mixing height and vertical boiler tube dimensions were correlated in a manner which resulted in good agreement between theoretical and experimental bed temperature profiles. It is felt that this simple model may prove quite useful in the design of large scale commercial fluid bed boilers.

Transient rheological behavior of blood in low-shear tube flow: velocity profiles and effective viscosity

1995 ◽  
Vol 268 (1) ◽  
pp. H25-H32 ◽  
Author(s):  
C. Alonso ◽  
A. R. Pries ◽  
O. Kiesslich ◽  
D. Lerche ◽  
P. Gaehtgens
Keyword(s):  
Effective Viscosity ◽  
Velocity Profiles ◽  
Low Flow ◽  
Cross Sectional ◽  
Video Recordings ◽  
Horizontal Tubes ◽  
Rbc Aggregation ◽  
Glass Tubes ◽  
Vertical Tubes ◽  
Low Shear

Velocity profiles of human blood flowing through vertical and horizontal glass tubes (25–100 microns ID) were measured as a function of time following a sudden reduction of wall shear stress (tau w) from a high value to values ranging from 2 to 100 mPa. Cell velocities at various radial positions were determined off-line from video recordings by digital image analysis. In vertical tubes, symmetric velocity profiles were obtained that developed increasing bluntness with time, particularly at lower tau w and in smaller tubes. In horizontal tubes, velocity profiles developed strong asymmetry as a function of time. Red blood cell (RBC) sedimentation was associated with uniform low flow velocities in the concentrating cell sediment, whereas faster flow and almost parabolic profiles were observed in the supernatant plasma region. Calculations of effective blood viscosity showed a decrease with time at low tau w in vertical tubes but an increase in horizontal tubes. The differences between profile shape and effective viscosity in vertical and horizontal tubes disappeared at tau w > 50 mPa. These findings are related to the cross-sectional distribution of RBC, which depends on RBC aggregation and sedimentation.

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