Frost-Air Interface Characterization Under Natural Convection

2005 ◽  
Vol 127 (10) ◽  
pp. 1174-1180 ◽  
Author(s):  
Y. L. Hao ◽  
J. Iragorry ◽  
Y.-X. Tao
Keyword(s):  
Natural Convection ◽  
Freezing Point ◽  
Early Stage ◽  
Critical Time ◽  
Microscopic Analysis ◽  
Interface Temperature ◽  
Effective Parameters ◽  
Steady Growth ◽  
Air Interface ◽  
Video Microscope

Surface frosting from atmospheric humidity under natural convection is encountered in conventional refrigeration systems, cryogenic surgery, and cryogenic stress relief of die casting metal forming applications. To advance the predictability of frost initiation and formation processes, this study reports a microscopic analysis of frost growth on a flat surface during the onset period of freezing when subcooled droplets are formed and changed to the ice phase. The onset of freezing is quantified by the mean droplet size and ice particle fractions at a critical time (when water droplet freezing point is reached) with the aid of a video microscope. An early-stage frost formation model with effective parameters is demonstrated to provide the important information for the transition to the steady-growth model. The model results are compared with the measured air-frost surface temperatures at different cooling and ambient boundary conditions, using holographic interferometry. The comparison between the model prediction and experimental results demonstrates the sensitivity of effective parameters in simulating the frost thickness and air-frost interface temperature.

Microscopic Characterization of Frost Surface During Liquid-Ice Phase Change Period

2002 ◽  
Author(s):  
Y. L. Hao ◽  
J. Iragorry ◽  
D. Castro ◽  
Y.-X. Tao ◽  
S. Jia
Keyword(s):  
Surface Characterization ◽  
Microscopic Analysis ◽  
Growth Period ◽  
Interface Temperature ◽  
Test Technique ◽  
Video Microscope ◽  
The Mean ◽  
Change Period ◽  
Frost Layer

In response to the need for developing a better model to predict frost formation and defrosting processes in freezer and evaporator applications, a microscopic analysis of frost growth on a flat surface is conducted to determine the microscopic characteristics of a frost layer during the early growth period when sub-cooled droplets are formed and changed to the ice. The surface characterization is performed by employing the holographic interferometry technique to determine the air-frost interface temperature, and the video microscope to determine the mean droplet size and ice particle fractions. Typical experimental results are presented to demonstrate the test technique. Preliminary experimentally determined frost thickness and air-frost interface temperature are compared with simulation results.

scholarly journals Cording Mycobacterium tuberculosis Bacilli Have a Key Role in the Progression towards Active Tuberculosis, Which is Stopped by Previous Immune Response

2020 ◽  
Vol 8 (2) ◽  
pp. 228 ◽  
Author(s):  
Lilibeth Arias ◽  
Paula Cardona ◽  
Martí Català ◽  
Víctor Campo-Pérez ◽  
Clara Prats ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Early Stage ◽  
Microscopic Analysis ◽  
Neutrophil Infiltration ◽  
Active Tuberculosis ◽  
Bcg Vaccination ◽  
H37rv Strain ◽  
First Time

Cording was the first virulence factor identified in Mycobacterium tuberculosis (Mtb). We aimed to ascertain its role in the induction of active tuberculosis (TB) in the mouse strain C3HeB/FeJ by testing the immunopathogenic capacity of the H37Rv strain. We have obtained two batches of the same strain by stopping their growth in Proskauer Beck liquid medium once the mid-log phase was reached, in the noncording Mtb (NCMtb) batch, and two days later in the cording Mtb (CMtb) batch, when cording could be detected by microscopic analysis. Mice were challenged with each batch intravenously and followed-up for 24 days. CMtb caused a significant increase in the bacillary load at an early stage post-challenge (day 17), when a granulomatous response started, generating exudative lesions characterized by neutrophilic infiltration, which promoted extracellular bacillary growth together with cording formation, as shown for the first time in vivo. In contrast, NCMtb experienced slight or no bacillary growth and lesions could barely be detected. Previous Bacillus Calmette-Guérin (BCG) vaccination or low dose aerosol (LDA) Mtb infection were able to delay the progression towards active TB after CMtb challenge. While BCG vaccination also reduced bacillary load when NCMtb was challenged, LDA did not, and its proliferative lesions experienced neutrophil infiltration. Analysis of lung cytokine and chemokine profiles points to their capacity to block the production of CXCL-1 and further amplification of IL-1β, IL-17 and neutrophilic extracellular trap formation, all of which are essential for TB progression. These data highlight the key role of cording formation in the induction of active TB.

scholarly journals A Review on the Control Parameters of Natural Convection in Different Shaped Cavities with and without Nanofluid

Processes ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1011 ◽  
Author(s):  
Sara Rostami ◽  
Saeed Aghakhani ◽  
Ahmad Hajatzadeh Pordanjani ◽  
Masoud Afrand ◽  
Goshtasp Cheraghian ◽  
...  
Keyword(s):  
Porous Media ◽  
Natural Convection ◽  
Free Convection ◽  
Forced Convection ◽  
Opposite Effect ◽  
Fluid Velocity ◽  
Experimental Studies ◽  
Effective Parameters ◽  
Magnetic Forces ◽  
Numerical Studies

Natural convection in cavities is an interesting subject for many researchers. Especially, in recent years, the number of articles written in this regard has grown enormously. This work provides a review of recent natural convection studies. At first, experimental studies were reviewed and, then, numerical studies were examined. Then, the articles were classified based on effective parameters. In each section, numerical studies were examined the parameters added to the cavity such as magnetic forces, fin, porous media and cavity angles. Moreover, studies on non-rectangular cavities were investigated. Free convection in enclosures depends more on the fluid velocity relative to the forced convection, leading to the opposite effect of some parameters that should essentially enhance rate of heat transfer. Nanoparticle addition, magnetic fields, fins, and porous media may increase forced convection. However, they can reduce free convection due to the reduction in fluid velocity. Thus, these parameters need more precision and sometimes need the optimization of effective parameters.

Natural Convection Heat Transfer of Water Within a Horizontal Cylindrical Annulus With Density Inversion Effects

1983 ◽  
Vol 105 (1) ◽  
pp. 117-123 ◽  
Author(s):  
P. Vasseur ◽  
L. Robillard ◽  
B. Chandra Shekar
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Cold Water ◽  
Freezing Point ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Density Inversion ◽  
Cylindrical Annulus

The effect of density inversion on steady natural convection heat transfer of cold water, between two horizontal concentric cylinders of gap width, L, is studied numerically. Water near its freezing point is characterized by a density maximum at 4°C. Numerical solutions are obtained for cylinders with nonlinear Rayleigh numbers RA ranging from 2 × 103 to 7.6 × 104, a radius ratio 1.75 ≤ ra ≤ 2.6 and an inversion parameter γ, relating the temperature for maximum density with the cavity wall temperatures, between −2 and 2. The results obtained are presented graphically in the form of streamline and isotherm contour plots. The heat transfer characteristics, velocity profiles, and local and overall Nusselt numbers are studied. The results of the present study were found qualitatively valid when compared with an experimental investigation carried out in the past.

scholarly journals Characterization of a nucleopolyhedrovirus with a deletion of the baculovirus core gene Bm67

2008 ◽  
Vol 89 (3) ◽  
pp. 766-774 ◽  
Author(s):  
Jun-Qing Ge ◽  
Zhang-Nv Yang ◽  
Xu-Dong Tang ◽  
Hai-Jun Xu ◽  
Jian Hong ◽  
...  
Keyword(s):  
Early Stage ◽  
Microscopic Analysis ◽  
Core Gene ◽  
Pcr Analysis ◽  
Electron Microscopic ◽  
Reading Frame ◽  
Native Promoter ◽  
Budded Virus ◽  
The Stability ◽  
Conserved Gene

Open reading frame (ORF) 67 (Bm67) of the Bombyx mori nucleopolyhedrovirus (BmNPV) is a highly conserved gene that is found in all completely sequenced baculoviruses; its function is unknown. In the present study, a Bm67-knockout virus was generated for studying the role of Bm67 in the BmNPV infection cycle. Furthermore, a Bm67-repair bacmid was constructed by transposing the Bm67 native promoter-promoted Bm67 ORF into the polyhedrin locus of the Bm67-knockout bacmid. After these recombinant bacmids were transfected into BmN cells, the Bm67-knockout bacmid caused defects in the production of infectious budded viruses. However, the Bm67-repair bacmid could rescue the defect, and budded virus titres reached wild-type levels. Quantitative real-time PCR analysis indicated that Bm67 is required for normal levels of DNA synthesis or for the stability of nascent viral DNA at the early stage. Electron microscopic analysis revealed that the formation of normal-appearing nucleocapsids is reduced in Bm67-knockout bacmid-transfected cells, and nucleocapsids are rarely found in the cytoplasm. The presence of ‘enveloped’ nucleocapsids at the nucleoplasm bilayer indicated that they are enveloped abnormally. These results indicated that Bm67 is required for the production of infectious budded viruses and for assembly of envelope and nucleocapsids.

Different Approaches for Mass Transfer Studies on Potato Cylinders and Slices during Solar Drying

2011 ◽  
Vol 7 (1) ◽  
Author(s):  
P. P. Tripathy ◽  
Subodh Kumar
Keyword(s):  
Mass Transfer ◽  
Natural Convection ◽  
Mixed Mode ◽  
Indirect Method ◽  
Direct Method ◽  
Moisture Loss ◽  
Solar Drying ◽  
Sample Geometry ◽  
Air Interface ◽  
Drying Conditions

In this paper, the influence of sample geometry and different solar drying conditions on mass transfer evaluation at food-air interface, hm obtained from different approaches is experimentally investigated. Two different approaches of hm estimation used in the analysis are based on the measurement of moisture loss rate data (direct method) and graphically computed values of drying parameters and moisture diffusion coefficient (indirect method). Drying experiments were performed with potato cylinders and slices of same thickness of 0.01 m with their respective length and diameter of 0.05 m using natural convection mixed-mode solar dryer and open air sun drying conditions. Results of analysis reveal that for each method of estimation, the cylinders vis-à-vis slices produce higher values of hm for both the solar drying conditions. It is also found that the mixed-mode solar drying enhances moisture transfer at food-air interface for each of the sample geometry as expected. Out of the two approaches investigated for hm estimation, the indirect method exhibits lower values of hm and these values are found to be more close to the results reported in the literature. The present analysis also indicates that Chilton-Colburn analogy for heat-mass convection does not hold well in the natural convection air drying of food product.

scholarly journals AtKATANIN1 Modulates Microtubule Depolymerization and Reorganization in Response to Salt Stress in Arabidopsis

2019 ◽  
Vol 21 (1) ◽  
pp. 138
Author(s):  
Jie Yang ◽  
Bang An ◽  
Hongli Luo ◽  
Chaozu He ◽  
Qiannan Wang
Keyword(s):  
Salt Stress ◽  
Salt Tolerance ◽  
Early Stage ◽  
Microscopic Analysis ◽  
Microtubule Depolymerization ◽  
Phenotypic Analysis ◽  
Microtubule Organization ◽  
Knock Out ◽  
Microtubule Disruption ◽  
Mutant Cells

The microtubule cytoskeleton is a dynamic system that plays vital roles in fundamental cellular processes and in responses to environmental stumili. Salt stress induced depolymerization and reorganization of microtubules are believed to function in the promotion of survival in Arabidopsis. Microtubule-severing enzyme ATKATANIN1 (AtKTN1) is recognized as a MAP that help to maintain organized microtubule structure. To date, whether AtKTN1 is involved in response to salt stress in Arabidopsis remains unknown. Here, our phenotypic analysis showed that the overexpression of AtKTN1 decreased tolerance to salt stress, whereas the knock-out of AtKTN1 increased salt tolerance in the early stage but decreased salt tolerance in the later stage. Microscopic analysis revealed that microtubule organization and dynamics are distorted in both overexpression and mutant cells which, in turn, resulted in an abnormal disassembly and reorganization under salt stress. Moreover, qRT analysis revealed that stress-responsive genes were down-regulated in overexpression and mutant cells compared to WT cells under salt stress. Taken together, our results indicated roles of AtKTN1 in modulating microtubule organization, salt-stress induced microtubule disruption and recovery, and its involvement in stress-related signaling pathways.

Natural Convection at the Interface Between a Vertical Porous Layer and an Open Space

1983 ◽  
Vol 105 (1) ◽  
pp. 124-129 ◽  
Author(s):  
A. Bejan ◽  
R. Anderson
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Open Space ◽  
Saturated Porous Medium ◽  
Temperature Fields ◽  
Interface Temperature ◽  
Fluid Systems ◽  
Two Fluid ◽  
Fluid Reservoir

This paper examines the interaction by natural convection between a fluid-saturated porous medium and a fluid reservoir separated by a vertical impermeable partition. The two fluid systems are maintained at different temperatures. The analysis is simplified by assuming Pr > > 1 in the fluid reservoir. It is shown analytically that the flow and temperature fields in the boundary layer regime consist of two fluid layers in counterflow. The interface temperature is shown to increase monotonically with altitude. The important dimensionless group which governs the fluid mechanics is B = (kRaK1/2) / (k′Ra1/4), where k, k′, RaK and Ra are, respectively, the porous medium conductivity, reservoir fluid conductivity, Darcy-modified Rayleigh number based on partition height, and the reservoir Rayleigh number based on partition height. The effect of parameter, B, on the flow, temperature, and heat transfer is documented in the range 0 < B < ∞.

EARLY-STAGE NATURAL CONVECTION IN A VERTICAL CHANNEL

2018 ◽  
Author(s):  
Yiqin Li ◽  
Hervé Pabiou ◽  
Christophe Menezo
Keyword(s):  
Natural Convection ◽  
Early Stage ◽  
Vertical Channel
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