Correlation between small‐scale temperature gradients and acoustic scatterers

1978 ◽  
Vol 64 (S1) ◽  
pp. S165-S165
Author(s):  
G. T. Kaye
Keyword(s):  
Temperature Gradients ◽  
Small Scale ◽  
Scale Temperature

scholarly journals Flow Field Study of a Top Heated Immiscible Liquid Layer Adjacent to Ice

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Hamed Farmahini Farahani ◽  
Tatsunori Hayashi ◽  
Hirotaka Sakaue ◽  
Ali S. Rangwala
Keyword(s):  
Free Surface ◽  
Flow Field ◽  
Immiscible Liquid ◽  
Surface Flow ◽  
Temperature Gradients ◽  
Small Scale ◽  
Density Gradients ◽  
Ice Surface ◽  
Scale Temperature ◽  
Horizontal Temperature Gradients

A series of experiments were conducted to investigate the flow field of a top-heated liquid fuel adjacent to an ice block. The experimental setup consisted of a borosilicate container containing an ice wall and a layer of n-heptane heated from above. Particle Image Velocimetry (PIV) and Background Oriented Schlieren (BOS) measurements were conducted on the liquid -phase. PIV measurements showed a surface flow toward the ice caused by surface -tension forces, which is driven by the horizontal temperature gradients on the liquid surface. A recirculation zone was observed under the free surface and near the ice. The combination of the two flow patterns caused lateral intrusion in the ice, instead of a uniform melting across ice surface. BOS measurements indicated presence of density gradients below the free surface of n-heptane and in regions near the ice block. These density gradients were created by local small-scale temperature gradients. The current experiments were conducted to explore the processes that influence the ice melting by immiscible liquid layers.

The Origin of High Ice Crystal Number Densities in Cirrus Clouds

2005 ◽  
Vol 62 (7) ◽  
pp. 2568-2579 ◽  
Author(s):  
C. R. Hoyle ◽  
B. P. Luo ◽  
T. Peter
Keyword(s):  
Cirrus Clouds ◽  
Small Scale ◽  
Ice Crystal ◽  
Cooling Rates ◽  
Density Distributions ◽  
In Situ Forming ◽  
Independent Particle ◽  
Scale Temperature ◽  
High Cooling Rates ◽  
Homogeneous Freezing

Abstract Recent measurements with four independent particle instruments in cirrus clouds, which formed without convective or orographic influence, report high number densities of ice particles (as high as nice = 50 cm−3) embedded in broad density distributions (nice = 0.1–50 cm−3). It is shown here that small-scale temperature fluctuations related to gravity waves, mechanical turbulence, or other small-scale air motions are required to explain these observations. These waves have typical peak-to-peak amplitudes of 1–2 K and frequencies of up to 10 h−1, corresponding to instantaneous cooling rates of up to 60 K h−1. Such waves remain unresolved in even the most advanced state-of-the-art global atmospheric models. Given the ubiquitous nature of these fluctuations, it is suggested that the character of young in situ forming cirrus clouds is mostly determined by homogeneous freezing of ice in solution droplets, driven by a broad range of small-scale fluctuations (period ∼a few minutes) with moderate to high cooling rates (1–100 K h−1).

Micro-Scale Thermal Sensor Manufacturing for Semiconductor Furnace Chamber

2012 ◽  
Author(s):  
Hongcheon Yang ◽  
Jun Young Kim ◽  
Kwang-Sun Kim
Keyword(s):  
Semiconductor Device ◽  
Furnace Chamber ◽  
Small Scale ◽  
Thermal Sensor ◽  
Micro Scale ◽  
Thermoelectric Voltage ◽  
Scale Temperature ◽  
Pattern Size ◽  
Different Temperatures ◽  
Analog Voltage

As the demand of complex and small scale semiconductor devices has been increased, the measurement technologies were developed to meet the accurate requirement in semiconductor manufacturing process. The uniform temperature requirement on the wafer is the major factor related to the semiconductor device yield. It is normally acquired from the thermocouples following the inner wall of the chamber. However, since the temperature difference between the wall of equipment and the surface of wafer is existed, the actual wafer temperature is commonly measured by a thermocouple wafer to calibrate the temperature measurement accuracy of the equipment. However, as the diameter of the commercial thermocouple wires is larger than the recently demanded pattern size, the TC wafer has not been able to measure the micro scale temperature differences on the micro patterned wafer. We, therefore, designed a micro-scale thermal sensor. The developed sensor has 37 sets of the measurement points on a 4-inch silicon wafer. The size of the measurement point is approximate to 16 um2. Two alloys, chromel and alumel which are as same as the materials of the K-type thermocouple are used to generate the thermoelectric voltage. The sensor has the temperature range of −200°C to 1300°C. The commercial K-type thermocouple extension wires are connected to the pads of the sensor array and they transfer the analog voltage data to a data acquisition device (DAQ). The sensor was calibrated by comparing the EMF voltage at different temperatures to the standard thermocouple EMF voltage. With the developed micro-scale thermal sensor system, the temperature distribution of the wafer in the furnace chamber is obtained.

Small-Scale Temperature Fluctuations in Perfused Tissue During Local Hyperthermia

1986 ◽  
Vol 108 (3) ◽  
pp. 246-250 ◽  
Author(s):  
J. W. Baish ◽  
P. S. Ayyaswamy ◽  
K. R. Foster
Keyword(s):  
Scaling Laws ◽  
Temperature Fluctuations ◽  
Small Scale ◽  
Adjacent Tissue ◽  
Local Hyperthermia ◽  
Thermal Equilibration ◽  
Scale Temperature ◽  
Tissue Region ◽  
Significant Temperature ◽  
Analytical Expressions

We develop analytical expressions (scaling laws) for the local temperature fluctuations near isolated and countercurrent blood vessels during hyperthermia. These scaling laws relate the magnitude of such fluctuations to the size of the heated region and to the thermal equilibration length of the vessels. A new equilibration length is identified for countercurrent vessels. Significant temperature differences are predicted between the vessels and the immediately adjacent tissue when the equilibration length is comparable to or longer than the size of the heated tissue region. Countercurrent vessels are shown to have shorter equilibration lengths and produce smaller temperature fluctuations than isolated vessels of the same size.

scholarly journals Balloon-borne match measurements of mid-latitude cirrus clouds

2013 ◽  
Vol 13 (10) ◽  
pp. 25417-25479 ◽  
Author(s):  
A. Cirisan ◽  
B. P. Luo ◽  
I. Engel ◽  
F. G. Wienhold ◽  
U. K. Krieger ◽  
...  
Keyword(s):  
Temperature Fluctuations ◽  
Cloud Microphysics ◽  
Cirrus Clouds ◽  
Climate Feedback ◽  
Small Scale ◽  
Model Parameters ◽  
Air Mass ◽  
Upper Troposphere ◽  
Weather Model ◽  
Scale Temperature

Abstract. Observations of persistent high supersaturations with respect to ice inside cirrus clouds are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. Single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information of the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer "SnowWhite" and a particle backscatter detector "COBALD" (Compact Optical Backscatter Aerosol Detector). Extensive trajectory calculations based on regional weather model COSMO forecasts are performed for flight planning and COSMO analyses are used as basis for comprehensive microphysical box modeling (with grid scale 2 km and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2–15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the small-scale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear sky or cloudy sky conditions, highlighting the importance of a proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30% in-cloud supersaturation measured in a massive, 4-km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or – much more likely – by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrometers under the extreme humidity conditions in the upper troposphere.

scholarly journals A Unique Small Gas Turbine Test Facility for Low-Cost Investigations of Ceramic Rotor Materials and Thermal Barrier Coatings

1998 ◽  
Author(s):  
Björn Schenk ◽  
Torsten Eggert ◽  
Helmut Pucher
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Low Cost ◽  
Temperature Gradients ◽  
Test Facility ◽  
Small Scale ◽  
Transient Temperature ◽  
Turbine Inlet ◽  
Turbine Rotors

The paper describes a test facility for small-scale gas turbines, which basically has been designed and assembled at the Institute of Combustion Engines of the Technical University Berlin. The facility exposes ceramic rotor components to the most significant loads that occur during real gas turbine operation in a clearly predefined manner (high circumferential velocities and highest turbine inlet temperatures). The test facility allows the investigation of bladed radial inflow turbine rotors, as well as — in a preceding step — geometrically simplified ceramic or coated metallic rotors. A newly designed, ceramically lined, variable geometry combustion chamber allows turbine inlet temperatures up to 1450°C (2640 F). A fast thermal shock unit (switching time of about 1s), which is integrated into the test facility between the combustion chamber and the turbine scroll, can be used to create, for example, severe transient temperature gradients within the rotor components to simulate gas turbine trip conditions. In order to generate steady state temperature gradients, especially during disk testing, the rotor components can be subjected to an impingement cooling of the rotor back face (uncoated in case of TBC-testing). The test facility is additionally equipped with a non-contact transient temperature measurement system (turbine radiation pyrometry) to determine the test rotor surface temperature distribution during operation. Apart from the possibilities of basic rotor material investigations, the test facility can also be used to automatically generate compressor and turbine performance characteristics maps. The latter might be used to assess the aerodynamic performance of bladed ceramic radial inflow or mixed flow turbine rotors with respect to manufacturing tolerances due to near-net-shape forming processes (e.g., gelcasting or injection molding).

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