The correction of hot-wire readings for proximity to a solid boundary

1962 ◽  
Vol 12 (3) ◽  
pp. 388-396 ◽  
Author(s):  
J. A. B. Wills
Keyword(s):  
Velocity Profile ◽  
Heat Loss ◽  
Turbulent Flows ◽  
Solid Boundary ◽  
Two Dimensional ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Air Velocity ◽  
The Wire

When using a hot wire for velocity measurements close to a solid boundary, errors may be introduced if the effect of the boundary on the rate of heat loss from the wire is ignored. An experimental determination of the effect is described, in which a hot wire was mounted at various distances from a metal surface forming one wall of a two-dimensional channel. The rate of heat loss was determined electrically, and the air velocity at the wire found from the known laminar velocity profile. The application of the results to turbulent flows is discussed briefly.

Shear Effects in Hot-Wire Measurements

1976 ◽  
Vol 98 (4) ◽  
pp. 771-773 ◽  
Author(s):  
Ronald M. C. So
Keyword(s):  
Lift Force ◽  
Viscous Sublayer ◽  
Diameter Ratio ◽  
Two Dimensional ◽  
Wire Length ◽  
Hot Wire ◽  
True Position ◽  
Shear Gradient ◽  
Shear Effects ◽  
The Wire

When a circular cylinder is placed in a two-dimensional shear flow, a lift force is experienced by the cylinder. In the case of hot-wire measurements in the viscous sublayer, this will give rise to a displacement of the wire from its true position. The resultant measurements are found to be in error if the wire length to diameter ratio is > 300 and the shear gradient of the flow is large.

Self-Aligning Hot-Wire Probe

1967 ◽  
Vol 71 (681) ◽  
pp. 657-658 ◽  
Author(s):  
A. D. Bond ◽  
A. M. Porter
Keyword(s):  
Constant Temperature ◽  
Two Dimensional ◽  
Servo Motor ◽  
Hot Wire ◽  
Turbulence Measurements ◽  
Wire Probe ◽  
Two Dimensional Flow ◽  
The Wire ◽  
Single Constant ◽  
Stream Direction

Summary:—This note describes how a single constant temperature hot wire may be used for measurements of direction, velocity and turbulence in a two-dimensional flow. The wire probe is rotated by a servo motor which automatically sets the wire with its axis either in the stream direction or normal to the flow. The accuracy of setting the wire in the direction of the stream is about , and across the stream is about 1°. If the higher accuracy is demanded the velocity and turbulence measurements require a second setting of the probe, at 90° to the previous one. When less precision is acceptable, the angle, velocity and turbulence measurements may be taken at the single setting, normal to the stream.

The thermal accommodation coefficients of gases. I. An investigation of the effect of flashing

1950 ◽  
Vol 201 (1066) ◽  
pp. 305-320 ◽  
Keyword(s):  
Heat Loss ◽  
Thermal Effects ◽  
Accommodation Coefficient ◽  
Hot Wire ◽  
Thermal Accommodation ◽  
Adsorbed Gas ◽  
Accommodation Coefficients ◽  
Wire Method ◽  
The Wire ◽  
Abnormal Temperature

Modifications to the hot-wire method of Knudsen (1911) for determining accommodation coefficients have been introduced by various workers in recent years. These methods have in common the flashing of the wire in the gas (Roberts 1930; Mann 1934) or in vacuo (Mann & Newell 1937) immediately before heat-loss measurements are begun. This treatment was originally suggested by Roberts (1930) and was assumed to give a ‘clean’ surface by removing adsorbed gas films. The heat loss from the wire was reduced by flashing, and this was ascribed to a reduction in the accommodation coefficient. The fall in heat loss after flashing has been confirmed, but it is accounted for, not by a reduction in the accommodation coefficient, but by the persistence of the thermal effects of flashing. Thus the effect of flashing is accentuated by working with silvered and platinized vessels; it is reproduced by flashing an adjacent wire and is particularly evident when working in vacuo . Abnormal temperature rises can also be observed when pipette methods are used to introduce the gas to an evacuated vessel (Mann & Newell 1937; Raines 1939; Rolf 1944). The results obtained in similar experiments were shown to be due mainly to the slowness of the diffusion process.

scholarly journals On the convection of heat from small cylinders in a stream of fluid: Determination of the convection constants of small platinum wires, with applications to hot-wire anemometry

1914 ◽  
Vol 90 (622) ◽  
pp. 563-570 ◽  
Keyword(s):  
Unit Volume ◽  
Unit Length ◽  
Stream Line ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Hot Wire ◽  
Stream Lines ◽  
Hydrodynamical Problem ◽  
Uniform Stream

Sections 1 and 2.- Until comparatively recently, the problem of solving the equations of heat conduction in the case of a solid cooled by a stream of fluid had received little attention, although the general problem was formulated by Fourier himself as long ago as 1820. In 1901 the problem was taken up by Boussinesq, and many cases were dealt with in his memoir of 1905. By means of an extremely elegant transformation Boussinesq was able to express the general equation for the two-dimensional problem in a linear form: by transforming the equation to the set of orthogonal curvilinear co-ordinates determined by the stream-lines and equipotentials of the hydrodynamical problem of the flow of a uniform stream of velocity V past the cylindrical obstacle, the equation for the temperature θ at any point of the fluid takes the form ∂ 2 θ /∂ α 2 + ∂ 2 θ /∂ β 2 = 2 n ∂ θ / ∂β , (1) where the curves α = constant represent the stream-lines and β = constant the equipotentials. The constant n is given by the relation 2 n = c V/ k = s σV/ k , where c is the specific heat of the fluid per unit volume, s that per unit mass, σ its density, and k its thermal conductivity. If the surface of the cylinder be the particular stream-line α = 0, and the critical equipotentials be the curves β =o and β = β 0 , the heat-flux per unit length of the cylinder is given by H = -∫ β 0 0 k ∂ θ /∂ α 0 dβ . (2) where the integral is taken to include the two branches of the stream-lines α = 0.

Two-dimensional determination of thermosensitive sites within the goat's hypothalamus

1976 ◽  
Vol 40 (4) ◽  
pp. 514-520 ◽  
Author(s):  
C. Jessen
Keyword(s):  
Heat Loss ◽  
Heat Production ◽  
Anterior Hypothalamus ◽  
Evaporative Heat Loss ◽  
Two Dimensional

In two conscious goats with chronically implanted multithermodes the distribution of thermosensitive sites within the anterior hypothalamus was determined. Changes in heat production at Ta=+5 degrees C and changes in respiratory evaporative heat loss at Ta=+33 degrees C in response to discrete temperature stimuli were measured and the magnitude of the responses was correlated with the histologically assessed position of the probes transmitting the stimuli. In both animals the array of probes was centered close to the center of the thermosensitive area. The density of thermosensitive structures increased toward the center of the area covered by the probes. The most sensitive points were situated close to either side of the midline in those frontal planes which contained the nuclei supraoptici and paraventriculares. No difference was found between cold- and warm-sensitive sites.

The Use of a Hot-Wire Anemometer in Turbulent Flow

1967 ◽  
Vol 71 (679) ◽  
pp. 511-513 ◽  
Author(s):  
B. J. Hoole ◽  
J. R. Calvert
Keyword(s):  
Turbulent Flow ◽  
Flow Direction ◽  
Unsteady Flows ◽  
Wire Length ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Local Flow ◽  
The Wire ◽  
Stream Direction

The hot-wire anemometer is one of the few instruments which can be used to make velocity measurements in turbulent and unsteady flows. However, the probe supporting the wire inevitably interferes with the local flow and it has been found that the effect of this interference on the reading of the anemometer varies considerably as the orientation of the probe to the flow direction is changed (the wire itself being maintained in the same direction). This leads to errors in any measurements taken where the instantaneous local flow direction differs significantly at any time from the direction for which the anemometer was calibrated. Such errors are quite separate from, and in addition to, errors due to finite wire length, incidence of the wire to the local stream direction, etc.

scholarly journals A Numerical Study on the Interpretation of Data from Open Atmospheric Balloon Soundings

2005 ◽  
Vol 44 (3) ◽  
pp. 357-366
Author(s):  
P. Alexander
Keyword(s):  
Gravity Waves ◽  
Numerical Study ◽  
Tracking System ◽  
Numerical Code ◽  
Horizontal Wind ◽  
Velocity Measurements ◽  
Atmospheric Measurements ◽  
Air Velocity ◽  
Flight Simulations

Abstract Wrong information may be extracted from balloon soundings if neither appropriate interpretation and processing nor evaluations of certain inevitable distortions or artifacts on atmospheric measurements are performed. A numerical code that finds solutions to the dynamical and thermal equations describing an open balloon in the atmosphere is used to develop flight simulations under diverse conditions. The results are then employed to point out that a valid determination of values for diverse variables is intrinsically difficult. It is shown that the distance between the balloon and gondola may be chosen to optimize the information to be obtained from observations obtained during ascent and descent, so that even without an accurate balloon-tracking system, it may be possible to reconstruct horizontal wind fluctuations from the measurements. Vertical air oscillations may be only grossly inferred in some cases. The propagation direction of gravity waves detected during a sounding may be inferred and vertical wavelengths may typically be determined with a 10% accuracy. Air velocity measurements performed during flotation may be used to find shears.

An Experimental Study of the Secondary Flow in a Curved Rectangular Channel

1980 ◽  
Vol 102 (1) ◽  
pp. 92-96 ◽  
Author(s):  
M. D. Kelleher ◽  
D. L. Flentie ◽  
R. J. McKee
Keyword(s):  
Secondary Flow ◽  
Rectangular Channel ◽  
Wave Number ◽  
Two Dimensional ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Dean Number ◽  
Wire Probe ◽  
Vortex Pattern ◽  
Secondary Motion

The Taylor-Gortler vortex pattern in a curved rectangular channel of high aspect ratio has been examined using hot wire anemometry. Using a two dimensional traversing mechanism, velocity surveys have been made at several radial locations across the channel for several values of Dean number. The velocity measurements show that the periodic secondary motion undergoes a phase shift as the hot wire probe crosses the midplane between the concave and convex walls. The measurements also indicate that the secondary flow wave number is constant over the range of Dean numbers examined. Complementary flow visualization photographs of the secondary motion have also been obtained.

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