scholarly journals On the motion of a fluid heated from below

1938 ◽  
Vol 165 (921) ◽  
pp. 216-228 ◽  
Author(s):  
R. J. Schmidt ◽  
O. A. Saunders ◽  
Sydney Chapman
Keyword(s):  
Heat Transfer ◽  
Experimental Error ◽  
Temperature Gradients ◽  
Lower Plate ◽  
Theoretical Formula ◽  
Optical Refraction ◽  
Higher Temperature ◽  
The Difference ◽  
Horizontal Temperature Gradients ◽  
Moving Fluid

In some previous experiments (Schmidt and Milverton 1935) a layer of water between two horizontal plates was slowly heated from below. The critical temperature difference at which the water began to move was found from a change in the slope of the curve relating the difference of temperature between the plates and the rate of supply of heat to the lower plate. An optical refraction (Saunders and Fishenden 1935) method was also used for finding the critical condition, and the results found by the two methods agreed and conformed to a theoretical formula of Jeffreys (1928) within the limits of experimental error. The present experiments were undertaken to find whether any change in the type of motion occurs at higher temperature differences, and also to study further the vertical and horizontal temperature gradients in the moving fluid using the optical method. It was also thought of interest to perform experiments with air instead of water. An improved apparatus was used, in which the downward heat loss from the lower plate could be measured, so that the actual heat transfer between the plates could be found.

PRECISION OF HEAT TRANSFER MEASUREMENTS WITH THERMOCOUPLES—INSULATION ERROR

1948 ◽  
Vol 26f (12) ◽  
pp. 565-583 ◽  
Author(s):  
W. A. Mohun
Keyword(s):  
Heat Transfer ◽  
Temperature Variation ◽  
Experimental Error ◽  
Specific Conductivity ◽  
Small Diameter ◽  
Critical Distance ◽  
Simple Method ◽  
The Difference

A method has been developed for calculating the temperature variation in insulated thermocouple lead wires that do not follow an isothermal path. The difference between the temperature of the junction and that of the surrounding material that it purports to measure has been called "insulation error." It has been shown that insulation error is determined by variations in the temperature of the path followed by the lead wires only over a limited distance from the junction, which has been called the "critical distance." Hence, to eliminate insulation error the path of the wires need be isothermal only for the critical distance. A simple method has been developed for calculating the critical distance and the insulation error. When the path of the wires cannot be made isothermal the conditions for minimum experimental error are shown to be small diameter wires of low specific conductivity with a minimum of insulation.

scholarly journals Measured Horizontal Temperature Gradients Constrain Heat Transfer Mechanisms in Greenland Ice

2017 ◽  
Vol 44 (19) ◽  
pp. 9778-9785 ◽  
Author(s):  
Benjamin H. Hills ◽  
Joel T. Harper ◽  
Neil F. Humphrey ◽  
Toby W. Meierbachtol
Keyword(s):  
Heat Transfer ◽  
Temperature Gradients ◽  
Horizontal Temperature Gradients ◽  
Transfer Mechanisms

Buildings

2017 ◽  
Author(s):  
Peter Rez
Keyword(s):  
Heat Transfer ◽  
Heat Pump ◽  
Energy Efficient ◽  
Energy Use ◽  
Fossil Fuel ◽  
Local Climate ◽  
Heating And Cooling ◽  
The Difference ◽  
As If

Most of the energy used by buildings goes into heating and cooling. For small buildings, such as houses, heat transfer by conduction through the sides is as much as, if not greater than, the heat transfer from air exchanges with the outside. For large buildings, such as offices and factories, the greater volume-to-surface ratio means that air exchanges are more significant. Lights, people and equipment can make significant contributions. Since the energy used depends on the difference in temperature between the inside and the outside, local climate is the most important factor that determines energy use. If heating is required, it is usually more efficient to use a heat pump than to directly burn a fossil fuel. Using diffuse daylight is always more energy efficient than lighting up a room with artificial lights, although this will set a limit on the size of buildings.

scholarly journals Comparison of Building Simulation Methods for Modeling Apartment Balconies

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3955
Author(s):  
Yonghan Ahn ◽  
Hanbyeol Jang ◽  
Junghyon Mun
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Parameter Analysis ◽  
Interior Space ◽  
Heating And Cooling ◽  
Significant Difference ◽  
Calculation Results ◽  
Infiltration Parameter ◽  
The Difference ◽  
Heating And Cooling Load

The purpose of this study is to compare the load calculation results by a model using the air changes per hour (ACH) method and a model using an airflow network (AFN) and to ascertain what causes the difference between the two models. In the basic case study, the difference in the heat transfer distribution of the model in the interior space was investigated. The most significant difference between the two models is the heat transfer that results from infiltration. Parameter analysis was performed to investigate the relationship between the difference and the environmental variables. The result shows that the greater the difference is between the air temperature inside the balcony and the outdoor air temperature, and the greater the air flows from the balcony to the residential area, and the greater the heating and cooling load difference occurs. The analysis using the actual weather files of five domestic cities in South Korea rather than a virtual case shows that the differences are not so obvious when the wind blows at a constant speed throughout the year, but are dominant when the wind does not blow during the night and is stronger alongside the occurrence of sunlight during the day.

scholarly journals Hyperfine structure in the arc spectrum of cæsium and nuclear rotation

1928 ◽  
Vol 121 (787) ◽  
pp. 432-447 ◽  
Keyword(s):  
Hyperfine Structure ◽  
Nuclear Spin ◽  
High Frequency ◽  
Principal Series ◽  
Very High Frequency ◽  
Nuclear Rotation ◽  
Higher Temperature ◽  
The Difference ◽  
Mechanical Moment ◽  
Very High

The arc spectrum of cæsium was investigated with the object of finding whether any of its lines possessed hyperfine structure, resulting from a nuclear magnetic moment, due to a quantised nuclear spin. The lines belonging to the principal series should, owing to the greater degree of penetration of the electron in the (1 s or 6 1 ) orbit, and the correspondingly greater interaction, show the greatest effect. The lines of the principal series are very easily broadened if the vapour pressure of the metal becomes high, so that great care had to be used in obtaining the spectrum of cæsium at a sufficiently low temperature. The most satisfactory method of excitation was found to be the application by means of external electrodes of a very high frequency alternating current to a tube filled with helium at about 2 mm. pressure containing a small quantity of cæsium. The tube required slight heating to bring out the cæsium lines; without this the helium spectrum was very much stronger than the metallic spectrum. At a very low vapour pressures of cæsium the discharge was blue in colour. Under these conditions the lines of the principal series showed no broadening greater than that due to thermal agitation, but at a slightly higher temperature the colour of the discharge became purple and the lines broadened. The lines belonging to the principal series were found to be very close doublets with very nearly constant frequencies differences. A theory is worked out which explains the origin of these doublets, assuming a nuclear spin of one half quantum; by correlating the difference in the separation of the hyperfine structure doublets in the 1 s — m 2 p 3/2 lines and the 1 s — m 2 p 1/2 lines, it is shown that a ratio of the magnetic to the mechanical moment of the nucleus about twice as great as the corresponding ratio for the electron would account for the observed frequency differences. The spectral notation used throughout is that of Hund. The results are compared with those found for the hyperfine structure of some of the bismuth lines by Back and Goudsmid, and are found to be in satisfactory agreement. A selection principle is found which applies both to the bismuth and the cæsium spectrum.

A Numerical Study on Heat Transfer and Lubricant Depletion on an Anisotropic Multilayer Hard Disk

2012 ◽  
Vol 232 ◽  
pp. 770-774
Author(s):  
Yan Zeng ◽  
Xiao Yang Huang ◽  
Wei Dong Zhou ◽  
Sheng Kai Yu
Keyword(s):  
Heat Transfer ◽  
Laser Power ◽  
Numerical Study ◽  
Disk Surface ◽  
Lubricant Film ◽  
Multilayer Structures ◽  
Lubricant Depletion ◽  
Thermal Anisotropy ◽  
Anisotropy Effect ◽  
Higher Temperature

This paper presents a numerical investigation on the effect of thermal anisotropy of the top layer alloy on heat transfer and lubricant depletion on the disk surface in a heat-assisted magnetic recording (HAMR) system. The disk consists of multilayer structures and a thin layer of lubricant on the top surface. Cases under different laser powers and initial lubricant film thicknesses are examined. The top-layer alloy thermal anisotropy does show non-negligible effect on the heat transfer and lubricant depletion. With the top-layer alloy being more anisotropic, higher temperature increase and lager lubricant depletion can be observed on the disk surface. The results also show that the thermal anisotropy effect is more significant under a lower laser power but nearly keeps no much difference under different initial lubricant film thicknesses. Thus it is of importance to include the thermal anisotropy effect of the top-layer Co-alloy when simulating the heat transfer and lubricant depletion in practical multilayer HMAR systems, especially for the cases under the condition of lower laser power, as the effect cannot be neglected under such conditions.

Combined Experimental and CFD Study of a HP Blade Multi-Pass Cooling System

2009 ◽  
Author(s):  
D. Jackson ◽  
P. Ireland ◽  
B. Cheong
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Cooling System ◽  
Detailed Comparison ◽  
Bulk Temperature ◽  
Internal Cooling ◽  
3 Dimensional ◽  
Turbine Cooling ◽  
Cooling Hole ◽  
The Difference

Progress in the computing power available for CFD predictions now means that full geometry, 3 dimensional predictions are now routinely used in internal cooling system design. This paper reports recent work at Rolls-Royce which has compared the flow and htc predictions in a modern HP turbine cooling system to experiments. The triple pass cooling system includes film cooling vents and inclined ribs. The high resolution heat transfer experiments show that different cooling performance features are predicted with different levels of fidelity by the CFD. The research also revealed the sensitivity of the prediction to accurate modelling of the film cooling hole discharge coefficients and a detailed comparison of the authors’ computer predictions to data available in the literature is reported. Mixed bulk temperature is frequently used in the determination of heat transfer coefficient from experimental data. The current CFD data is used to compare the mixed bulk temperature to the duct centreline temperature. The latter is measured experimentally and the effect of the difference between mixed bulk and centreline temperature is considered in detail.

Fluid Flow and Heat Transfer of Liquid Sodium in Small-Scale Heat Sinks With Different Geometries

2021 ◽  
Author(s):  
Mahyar Pourghasemi ◽  
Nima Fathi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Sections ◽  
Heat Sink ◽  
Volume Ratio ◽  
Heat Sinks ◽  
Liquid Sodium ◽  
Small Scale ◽  
Nusselt Numbers ◽  
The Difference

Abstract 3-D numerical simulations are performed to investigate liquid sodium (Na) flow and the heat transfer within miniature heat sinks with different geometries and hydraulic diameters of less than 5 mm. Two different straight small-scale heat sinks with rectangular and triangular cross-sections are studied in the laminar flow with the Reynolds number up to 1900. The local and average Nusselt numbers are obtained and compared against eachother. At the same surface area to volume ratio, rectangular minichannel heat sink leads to almost 280% higher convective heat transfer rate in comparison with triangular heat sink. It is observed that the difference between thermal efficiencies of rectangular and triangular minichannel heat sinks was independent of flow Reynolds number.

Temperature Distribution in a Cylindrical Rod Moving From a Chamber at One Temperature to a Chamber at Another Temperature

1964 ◽  
Vol 86 (2) ◽  
pp. 265-270 ◽  
Author(s):  
G. Horvay ◽  
M. Dacosta
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Arbitrary Constant ◽  
Families Of Curves ◽  
Special Cases ◽  
Method Of Solution ◽  
Lower Chamber ◽  
Higher Temperature ◽  
Hopf Method ◽  
The Heat Transfer Coefficient

When an infinitely long cylindrical rod travels from a chamber at one temperature ϑa to a chamber (insulated from the first) at a higher temperature ϑf, then heat will leak out along the rod from the second chamber to the first, whose amount decreases as the speed of the rod increases. Using the Wiener-Hopf method of solution, we determine the temperature distribution in the rod for the case where in the second chamber the heat-transfer coefficient h+ is infinite, while in the first chamber it has an arbitrary constant value h. Families of curves illustrate the temperature distribution in the two special cases where h = ∞ (isothermal boundary conditions in lower chamber) and where h = 0 (rod is insulated in lower chamber).

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