Natural convection in an enclosure under low pressure

2002 ◽  
Vol 2002 (0) ◽  
pp. 207-208
Author(s):  
Hiroyuki HIRANO ◽  
Hiroykui OZOE ◽  
Naotaka OKAMOTO ◽  
Takahiro MASUDA
Keyword(s):  
Natural Convection ◽  
Low Pressure

scholarly journals Investigation of the Flow and Heat Transfer in a Low Pressure Turbine Interdisc Cavity With Skewed Radial Jetflow

1996 ◽  
Author(s):  
Alexander V. Mirzamoghadam
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Low Pressure ◽  
Front Face ◽  
Convection Heat ◽  
Rotating Speed ◽  
Low Pressure Turbine ◽  
Forced Convection Heat Transfer

Heat transfer in the low pressure turbine interdisc cavity of an aero gas turbine engine with a closed rotating outer-rim and forced radially outward jetflow directed along the downstream disc-cob front face was partially investigated by experiment and theory as part of an advanced cooling design concept study. Within the interdisc cavity, several metal temperature transient and steady state measurements in the circumferential direction as well as the 2-D axisymmetric plane at rotating speeds of 1500 rpm and 7000 rpm were made. The results are based on matching the measured metal and air temperature at both speed levels as well as the transient behavior between the two speed levels to those predicted by the 2-D axisymmetric transient thermal model. A qualitative description of the 3-D nature of the flow field is given with the aid of CFD studies. The results indicate that the skewed forced jetflow produces a stronger variation to the level of heat transfer at high rotating speed. The jetflow partially penetrates outward through the cavity providing enhanced free-disc forced convection heat transfer (approximately 25%) at high rotating speed to about 70% of the downstream disc radial length only. Toward the rim subcavities, the level of heat transfer drops considerably compared to that of a free-disc and heat transfer along the hot rotating rim and colder flange surfaces are described by flat plate natural convection. The jetflow exits the cavity at the bore of the upstream disc by turning forward within the cavity, substantially reducing the level of heat transfer along the diaphragm of this disc, and providing forced convection heat transfer on the cob whose level is higher than the rest of the upstream disc represented by natural convection. At low rotating speed, a dominating mixed convection mechanism is evident throughout the interdisc cavity with significantly lesser variation in heat transfer. A critical Gr/Re2 value of 0.02 was established as the minimum where both natural and forced convection are important. The resulting behavior in local heat transfer coefficient and Nusselt number along the hot bolted rim and the discs are compared with those of previous investigators looking at heat transfer in a rotating cavity.

Practical considerations for low pressure solar water heaters in South Africa

2014 ◽  
Vol 25 (3) ◽  
pp. 36-45
Author(s):  
Oelof De Meyer ◽  
Richard Okou ◽  
Adoniya Benaya Sebitosi ◽  
Pragasen Pillay
Keyword(s):  
South Africa ◽  
Natural Convection ◽  
Vertical Wall ◽  
Low Pressure ◽  
Heat Transfer Process ◽  
Design Parameters ◽  
Constant Wall Temperature ◽  
Solar Water ◽  
Water Heaters ◽  
Solar Water Heaters

This paper presents the results of the design parameters that affect natural convection of Low Pressure (LP) Solar Water Heaters (SWH) in South Africa. Fluid flow plays an important role in the heat transfer process associated with natural convection. Three partial differential governing equations were considered. These equations are non-dimensionalized and a similarity solution was applied to obtain two coupled non-linear ordinary differential equations which are solved in MATLAB. Two scenarios were considered for the simulation, a vertical wall with a constant wall temperature and a vertical wall with a constant heat flux. The temperature and velocity profiles were obtained for both scenarios and compared. The effect of the length, diameter and tilt angle of the tube in relation to the amount of heat transferred to the water was investigated specifically for Cape Town. These results are used to discuss design and installation considerations for LP SWHs and are presented in the paper.

Effects of Electrical Discharges in Low Pressure Gases on the Morphology of Polyethylene Crystals

1974 ◽  
Vol 32 ◽  
pp. 544-545
Author(s):  
L.H. Bolz ◽  
D.H. Reneker
Keyword(s):  
Power Distribution ◽  
Electrical Discharge ◽  
Dielectric Breakdown ◽  
Ionic Species ◽  
Low Pressure ◽  
Polymer Surfaces ◽  
Electrical Discharges ◽  
Adhesive Bonds ◽  
Power Distribution Lines ◽  
Modification Of The Surface

The attack, on the surface of a polymer, by the atomic, molecular and ionic species that are created in a low pressure electrical discharge in a gas is interesting because: 1) significant interior morphological features may be revealed, 2) dielectric breakdown of polymeric insulation on high voltage power distribution lines involves the attack on the polymer of such species created in a corona discharge, 3) adhesive bonds formed between polymer surfaces subjected to such SDecies are much stronger than bonds between untreated surfaces, 4) the chemical modification of the surface creates a reactive surface to which a thin layer of another polymer may be bonded by glow discharge polymerization.

Field ion microscopy

1988 ◽  
Vol 46 ◽  
pp. 434-435
Author(s):  
Gert Ehrlich
Keyword(s):  
Low Temperature ◽  
Sample Surface ◽  
Low Pressure ◽  
Radius Of Curvature ◽  
Field Ion Microscopy ◽  
Phosphor Screen ◽  
Ion Microscopy ◽  
Field Ion Microscope

The field ion microscope, devised by Erwin Muller in the 1950's, was the first instrument to depict the structure of surfaces in atomic detail. An FIM image of a (111) plane of tungsten (Fig.l) is typical of what can be done by this microscope: for this small plane, every atom, at a separation of 4.48Å from its neighbors in the plane, is revealed. The image of the plane is highly enlarged, as it is projected on a phosphor screen with a radius of curvature more than a million times that of the sample. Müller achieved the resolution necessary to reveal individual atoms by imaging with ions, accommodated to the object at a low temperature. The ions are created at the sample surface by ionization of an inert image gas (usually helium), present at a low pressure (< 1 mTorr). at fields on the order of 4V/Å.

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