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.

MC Simulation of Radiative Heat Transfer Between Planar Semi-Infinite Media and Nano-Spheres With Near Field Effect

2004 ◽  
Author(s):  
Yong Huang ◽  
Xin-Gang Liang
Keyword(s):  
Heat Transfer ◽  
Radiative Heat Transfer ◽  
Field Effect ◽  
Radiative Heat ◽  
Near Field ◽  
Emissive Power ◽  
Simple Method ◽  
The Difference ◽  
Near Field Effect ◽  
Infinite Media

Based on the principle of electric dipole radiation and the Planck’s spectral distribution of emissive power, the enhancement of thermal radiation between two planar semi-infinite media or two nano-spheres was studied in this paper by the Monte Carlo method. By this simple method, some parameter’s influence on the radiative heat transfer was investigated, such as the distance between two semi-infinite media, the particle’s radius, the distance between two particles and the difference in temperature between two particles, and so on. This solution is not rigorous but simple. The results show that heat transfer can be enhanced by several orders of magnitude for the near field effect. And the radiative heat transfer is decreasing sharply with the increasing of the distance.

Numerical and Experimental Investigation of Boiling Heat Transfer for Subcooled Water Flowing in a Small-Diameter Tube

2019 ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Koichi Hata ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Flux ◽  
Exponential Function ◽  
Boiling Heat Transfer ◽  
Small Diameter ◽  
Uniform Heat Flux ◽  
Inlet Temperature ◽  
Simple Method ◽  
Subcooled Water

Abstract Numerical simulation of boiling heat transfer for subcooled water flowing in a small-diameter tube was conducted using the commercial computational fluid dynamics (CFD) code, PHOENICS ver. 2013. A small-diameter tube (d = 1.0–2.0 mm) was modeled in the simulation. A uniform heat flux with an exponential function was given at the inner tube wall as the boundary conditions. The inner wall boundary condition was set to a non-slip. The inlet temperature ranged from 302 to 312 K. The flow velocities of d = 1.0 mm and d = 2.0 mm are 9.29 m/s and 2.34 m/s, respectively. The transient analysis was carried out from the non-boiling region since the heat flux increased with time in the author’s experiments. The governing equations including the energy equation were discretized using the finite volume method in the PHOENICS code. The SIMPLE method was applied for the numerical simulation. For modeling boiling phenomena in the tube, the Eulerian-Eulerian two-fluid model was adopted using the interphase slip algorithm of PHOENICS code. In the experiment, a platinum tube was used as the experimental tube (d = 1.0–2.0 mm) to conduct joule heating by direct current. The distilled and deionized water was pressured by the pressurizer. The heat generation rate of the tube was controlled with the exponential function to obtain the transient heat transfer characteristics from the non-boiling region. The surface superheat increased as the heat flux increased in the experiment. The numerical simulation predicted the experimental data well. When the heat flux of the experiment was reached to the CHF point, the predicted value of heat transfer coefficient was approximately 3.5 % lower than that of the experiment.

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.

Experimental and Numerical Investigations of Subcooled Boiling Heat Transfer in a Small-Diameter Tube

2020 ◽  
Vol 12 (6) ◽  
Author(s):  
Makoto Shibahara ◽  
Qiusheng Liu ◽  
Koichi Hata ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Fluid Model ◽  
Three Dimensional ◽  
Small Diameter ◽  
Inlet Temperature ◽  
Simple Method ◽  
Subcooled Water

Abstract The boiling heat transfer for subcooled water flowing in a small-diameter tube was investigated experimentally and numerically. In the experiment, a platinum tube was used as an experimental tube (d = 1.0–2.0 mm) to conduct joule heating by direct current. The heat generation rate of the tube was controlled with an exponential function. The numerical simulation of boiling heat transfer for subcooled water flowing in the small-diameter tube was conducted using the commercial computational fluid dynamics (CFD) code, phoenics ver. 2013. The small-diameter tube was modeled in the simulation. As the boundary condition, the measured heat flux was given at the inner wall. The inlet temperature ranged from 302 to 312 K. The flow velocities of d = 1.0 mm and d = 2.0 mm were 9.29 m/s and 2.34 m/s, respectively. The three-dimensional analysis was carried out from non-boiling to the critical heat flux (CHF). Governing equations were discretized using the finite volume method in the phoenics. The semi-implicit method for pressure linked equation (SIMPLE) method was applied in the numerical simulation. For modeling boiling phenomena in the tube, the Eulerian–Eulerian two-fluid model was adopted using the interphase slip algorithm of phoenics. The surface temperature difference increased as the heat flux increased in the experiment. The numerical simulation predicted the experimental data well. When the heat flux of the experiment reached the CHF point, the predicted value of the heat transfer coefficient was approximately 3.5% lower than that of the experiment.

scholarly journals An Improved Comprehensive Model of Pyrolysis of Large Coal Particles to Predict Temperature Variation and Volatile Component Yields

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 884
Author(s):  
Wenning Zhou ◽  
Hailong Huo ◽  
Qinye Li ◽  
Ruifeng Dou ◽  
Xunliang Liu
Keyword(s):  
Heat Transfer ◽  
Temperature Variation ◽  
Volatile Component ◽  
Apparent Temperature ◽  
Transfer Model ◽  
Comprehensive Model ◽  
Volatile Yield ◽  
Coal Particles ◽  
Volatile Release ◽  
The Difference

In this work, an improved comprehensive model was developed for large coal particles to predict temperature variation and volatile component yields. The kinetics model of volatile component yields, where the volatile matters were assumed to comprise nine species, was combined with heat transfer model. The interaction between volatile yield and heat transfer during pyrolysis of large Maltby coal particles was investigated. An apparent temperature difference has been observed between the surface and core of particles at the initial heating stage. The non-uniform temperature distribution inside coal particles causes non-simultaneous volatile yields release from the surface and core area. The volatile release occurs after the coal temperature rises higher than 350 °C, and its yield steeply increases within the temperature range of 450–520 °C. The peak of volatile release rate corresponds to about 485 °C due to the rapid release of tar and H2O. The tar is almost completely released at around 550 °C. With the increasing particle size, the difference in temperature and volatile yield between the surface and core increases at the end of heating. The results are expected to provide insights into the interaction between heat transfer and volatile yields during pyrolysis of large coal particles.

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.

Pump Performance Improvement by Restraining Back Flow in Screw-Type Centrifugal Pump

2005 ◽  
Vol 127 (4) ◽  
pp. 755-762 ◽  
Author(s):  
Yasushi Tatebayashi ◽  
Kazuhiro Tanaka ◽  
Toshio Kobayashi
Keyword(s):  
Pressure Fluctuations ◽  
Centrifugal Pumps ◽  
Two Phase ◽  
Simple Method ◽  
Back Flow ◽  
Pump Performance ◽  
Impeller Outlet ◽  
Pump Head ◽  
The Difference ◽  
Set Up

The authors have been investigating the various characteristics of screw-type centrifugal pumps, such as pressure fluctuations in impellers, flow patterns in volute casings, and pump performance in air-water two-phase flow conditions. During these investigations, numerical results of our investigations made it clear that three back flow regions existed in this type of pump. Among these, the back flow from the volute casing toward the impeller outlet was the most influential on the pump performance. Thus the most important factor to achieve higher pump performance was to reduce the influence of this back flow. One simple method was proposed to obtain the restraint of back flow and so as to improve the pump performance. This method was to set up a ringlike wall at the suction cover casing between the impeller outlet and the volute casing. Its effects on the flow pattern and the pump performance have been discussed and clarified to compare the calculated results with experimental results done under two conditions, namely, one with and one without this ring-type wall. The influence of wall’s height on the pump head was investigated by numerical simulations. In addition, the difference due to the wall’s effect was clarified to compare its effects on two kinds of volute casing. From the results obtained it can be said that restraining the back flow of such pumps was very important to achieve higher pump performance. Furthermore, another method was suggested to restrain back flow effectively. This method was to attach a wall at the trailing edge of impeller. This method was very useful for avoiding the congestion of solids because this wall was smaller than that used in the first method. The influence of these factors on the pump performance was also discussed by comparing simulated calculations with actual experiments.

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