Characteristic length and cooling circle
Modular design, outsourcing and open innovation create a complex network of possible end product embodiments in product design for the consumer market. Analyzing each and every possibility in detail is out of the question as resources are limited and module details are often proprietary information. To meet this challenge the thermal engineer needs a feeling about what will and what will not work out, without getting bogged down in too much detail. This paper presents the concepts of characteristic length and cooling circle as an approximate measure for the extent of heat spreading in beam and in flat thin plate geometries. Beam and flat thin plate geometries are widely used by mechanical designers, and being able to assess how much of the geometry is actually thermally affected by a heat source is of great value in thermal decision making and communication. For both geometries an application is discussed and compared to CFD simulations to assess the validity of the approach.
Time constant spectra based fitting of thermal model parameters
This paper discusses the problem offitting parameters of a detailed circuit thermal model when the complete data on problem geometry or material properties are not available. The problem is illustrated based on a practical example of a test hybrid circuit. Unknown model parameter values are determined here from dynamic temperature measurement results which were processed employing the Network Identification by Deconvolution method. The thermal model is solved using the numerical finite element method and the analytical Green's function method. Then, the simulated heating curves are compared with the measured ones.
Prediction of a representative point for rail temperature measurement by considering longitudinal deformation
Monitoring rail temperature is very important for determining the safe running speed of trains and to prevent buckling. In general, the maximum variation of the internal rail temperature can be >7 ℃ depending on the point of measurement. However, there is as yet no sufficient information about how to predict the measurement point to represent the thermal deformation due to temperature distribution. In this study, the authors report a new point, called the representative measurement point, at which the rail temperature can be measured. This point considers the average deformation of the rail through structural analysis by adopting experimental and actual rail temperature data. The authors designed and installed a measurement system similar to an actual rail environment. Using the system, various data were acquired (internal/surface rail temperature and weather data) for 10 months. On the basis of these data, an analysis was done to calculate the average deformation point through thermal analysis. Finally, the representative measurement point was proposed as the position at which the average deformation point converges regardless of weather or seasons. The authors believe that the method described herein is advantageous in that it could be used in a high-accuracy temperature-monitoring system and for predicting thermal deformation and buckling.