scholarly journals Airborne infection in a fully air-conditioned hospital: III. Transport of gaseous and airborne particulate material along ventilated passageways

1975 ◽  
Vol 75 (1) ◽  
pp. 45-56 ◽  
Author(s):  
O. M. Lidwell
Keyword(s):  
Mathematical Model ◽  
Flow Velocity ◽  
Effective Diffusion ◽  
Diffusion Constant ◽  
Particulate Material ◽  
Airborne Particulate ◽  
Airborne Infection ◽  
Directional Flow ◽  
A Value

SUMMARYA mathematical model is described for the transport of gaseous or airborne particulate material between rooms along ventilated passageways.Experimental observations in three hospitals lead to a value of about 0.06m.2/sec. for the effective diffusion constant in air without any systematic directional flow. The ‘constant’ appears to increase if there is any directional flow along the passage, reaching about 0.12 m.2/sec. at a flow velocity of 0.04 m./sec.Together with previously published methods the present formulae make it possible to calculate the expected average amounts of gaseous or particulate material that will be transported from room to room in ventilated buildings in which the ventilation and exchange airflows can be calculated.The actual amounts transported in occupied buildings, however, vary greatly from time to time.

Urea gradient-associated fluid absorption with sigma urea = 1 in rat terminal collecting duct

1990 ◽  
Vol 258 (5) ◽  
pp. F1173-F1180 ◽  
Author(s):  
C. L. Chou ◽  
J. M. Sands ◽  
H. Nonoguchi ◽  
M. A. Knepper
Keyword(s):  
Mathematical Model ◽  
Absorption Rate ◽  
Collecting Duct ◽  
Null Point ◽  
Absorption Measurement ◽  
Urea Transport ◽  
Fluid Absorption ◽  
A Value ◽  
Collecting Ducts ◽  
Isolated Rat

It has been proposed that inner medullary collecting ducts (IMCDs) can absorb fluid in the absence of a transepithelial osmolality gradient if a perfusate-to-bath urea gradient is present. Such a process has been suggested to be caused by a nonunity reflection coefficient for urea (sigma urea less than 1). However, our recent measurements of sigma urea yielded values not significantly different from 1.0. The present study was done to readdress the possibility of direct coupling of water and urea transport in the rat IMCD. Isolated rat terminal IMCD segments were studied in the presence of 10(-10) M vasopressin with the osmolality of the perfusate equal to that of the peritubular bath but with a perfusate-to-bath urea gradient (bath osmolality balanced with NaCl). We measured both fluid absorption rate and urea concentration in collected fluid and calculated the osmolality of the collected fluid. We observed rapid fluid absorption associated with substantial urea absorption. The urea absorption caused a large fall in the osmolality of the collected fluid with respect to the bath. Simulations with a mathematical model of an isolated perfused tubule revealed that the transepithelial osmolality gradient generated along the length of tubule (caused by urea absorption) was large enough to account for the fluid absorption. Measurement of sigma urea with the "zero-flux" (or null point) method revealed a value of 1.00 +/- 0.02. Thus we conclude that the observed fluid absorption is the result of a transepithelial osmolality gradient generated by rapid urea absorption and does not require sigma urea less than one.

Variations in chemistry of airborne particulate material with particle size and time

1974 ◽  
Vol 8 (2) ◽  
pp. 131-135 ◽  
Author(s):  
Paul T. Cunningham ◽  
Stanley A. Johnson ◽  
Ralph T. Yang
Keyword(s):  
Particle Size ◽  
Particulate Material ◽  
Airborne Particulate

scholarly journals CO2 Adsorption–Desorption Kinetics from the Plane Sheet of Hard Coal and Associated Shrinkage of the Material

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 4013 ◽  
Author(s):  
Norbert Skoczylas ◽  
Anna Pajdak ◽  
Mariusz Młynarczuk
Keyword(s):  
Mathematical Model ◽  
Co2 Adsorption ◽  
Effective Diffusion ◽  
Hard Coal ◽  
Desorption Kinetics ◽  
Size Change ◽  
Co2 Desorption ◽  
Plane Sheet ◽  
Adsorption Desorption ◽  
Kinetics Of

The paper presents the results of studies on sorption and CO2 desorptions from coals from two Polish mines that differed in petrographic and structural properties. The tests were carried out on spherical and plane sheet samples. On the basis of the sorption tests, the effective diffusion coefficient was calculated on the plane sheet samples based on a proper model. Similar tests were performed on the spherical samples. Mathematical model results for plane sheet samples were compared with the most frequently chosen model for spherical samples. The kinetics of CO2 desorption from plane sheet samples were compared with the kinetics of sample shrinkage. In both samples, the shrinkage was about 0.35%. The size change kinetics and CO2 desorption kinetics significantly differed between the samples. In both samples, the determined shrinkage kinetics was clearly faster than CO2 kinetics.

Mathematical and Physical Simulation of the Cross-Flow Velocity Pulsation Effect on the Flame Structure during the Diffusion Mode of Methane Combustion

2020 ◽  
pp. 65-84
Author(s):  
K.Yu. Arefyev ◽  
K.V. Fedotova ◽  
A.I. Krikunova ◽  
V.A. Panov
Keyword(s):  
Mathematical Model ◽  
Flow Velocity ◽  
Stokes Equations ◽  
Flame Structure ◽  
Cross Flow ◽  
Methane Combustion ◽  
Velocity Pulsation ◽  
Diffusion Mode ◽  
Cross Flow Velocity ◽  
The Cross

The paper presents the results of calculation and experimental studies of the diffusion combustion of methane in the air cross-flow. We developed a mathematical model for describing a diffusion air-methane flame, the model being based on solving a system of averaged Navier --- Stokes equations in an unsteady setting. To calculate the combustion processes, we used the flamelet models and eddy dissipation concept (EDC) model. The mathematical model was supplemented by a detailed kinetic mechanism consisting of 325 elementary reactions involving 53 substances. Furthermore, we carried out calculations and comparative analysis of the flame characteristics using various turbulence models: k − ε, k − ω SST and Transition SST. The study introduces a diagram of the experimental setup for physical modeling of methane combustion in the air cross-flow, and presents the results of the calculation and experimental study of the cross-flow velocity pulsation effect on the flame structure, as well as the efficiency of methane combustion in the diffusion mode. We obtained data on temperature and concentration fields at pulsation frequencies of 0--100 Hz. Findings of research show that for the case under consideration, stable combustion occurs at pulsation frequencies of 0--90 Hz. The maximum observed flame lift-off is 3.2 times the diameter of the burner nozzle

scholarly journals Perturbation theory for the effective diffusion constant in a medium of random scatterers

2004 ◽  
Vol 37 (44) ◽  
pp. 10459-10477 ◽  
Author(s):  
D S Dean ◽  
I T Drummond ◽  
R R Horgan ◽  
A Lefèvre
Keyword(s):  
Perturbation Theory ◽  
Effective Diffusion ◽  
Diffusion Constant

WALKING ON RATCHETS WITH TWO BROWNIAN MOTORS

2004 ◽  
Vol 04 (01) ◽  
pp. L161-L170 ◽  
Author(s):  
JOSE L. MATEOS
Keyword(s):  
Effective Diffusion ◽  
Diffusion Constant ◽  
Brownian Motors ◽  
Coherent Transport ◽  
Dimensionless Ratio ◽  
Bistable Potential ◽  
External Time ◽  
Stable Points ◽  
White Noises ◽  
Ratchet Potential

We analyze a model for a walker moving on an asymmetric periodic ratchet potential. This model is motivated by the properties of transport of the motor protein kinesin. The walker consists of two feet represented as two particles coupled nonlinearly through a double-well bistable potential. In contrast to linear coupling, the bistable potential admits a richer dynamics where the ordering of the particles can alternate during the walking. The transitions between the two stable points on the bistable potential, correspond to a walking with alternating particles. In our model, each particle is acted upon by independent white noises, modeling thermal noise, and additionally we have an external time-dependent force that drives the system out of equilibrium, allowing directed transport. In the equilibrium case, where only white noise is present, we perform a bifurcation analysis which reveals different walking patterns. In particular, we distinguish between two main walking styles: alternating and no alternating. These two ways of walking resemble the hand-over-hand and the inchworm walking in kinesin, respectively. Numerical simulations showed the existence of current reversals and significant changes in the effective diffusion constant. We obtained an optimal coherent transport, characterized by a maximum dimensionless ratio of the current and the effective diffusion (Péclet number), when the periodicity of the ratchet potential coincides with the equilibrium distance between the two particles.

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