Browsing by Subject "Heat--Convection"

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An experimental study of the thermal processes relevant to infrared solder reflow
(1990) Fernandes, Neil Joseph, 1967-; Bergman, T. L.
An experimental system has been built to replicate, as closely as possible, the radiative and convective conditions during the infrared solder reflow process. Experiments were performed to measure the transient thermal response of modules for different module array configurations, under combined radiative and convective conditions. Numerical predictions have been obtained to i) identify and quantify the heat transfer mechanisms responsible for the transient thermal response of a center module within different array configurations and ii) to determine the level of modeling sophistication necessary to develop a detailed numerical model that can predict the thermal response of the card assembly. A comparison of the center module's thermal response in a uniform height array and in an array with different module heights illustrates the the module's sensitivity to shading. The predictions and measurements show the general need to incorporate the radiative exchange analysis which includes module-to-module radiative interactions and detailed evaluation of view factors. The predicted heat transfer mechanisms associated with the center module's thermal response shows that, for the case considered here, radiation is the dominant mode of heat transfer and is influenced by i) shading of the module's sides from the infrared panel heaters and ii) radiative exchange with neighboring modules. The convective cooling rate, although smaller than the radiative heating rates for the results presented here, increases with Reynolds number due to increasing convection coefficients. Radiative and conductive heat transfer rates through the gap separating the module and the card are small
In vivo measurements of the heat convection coefficient on the endocardial surface
(2003) Santos, Icaro dos; Valvano, Jonathan W., 1953-
This work describes the fundamentals, calibration procedure and in vivo results of an instrument for the measurement of the heat convection coefficient between the endocardium and the circulating blood flow. The heat transfer parameters will assist calculating the proper dose for radio-frequency ablation. The probe is a thermistor mounted in a Swan-Ganz catheter, and it is driven by a constant temperature anemometer circuit. A 1-D thermal model of the sensor behavior in a convective medium, the calibration procedure, and the apparatus are explained in detail. A performance analysis of the instrument in the range tested showed that the average absolute error of full scale was 7.4 %, and its time-constant was 0.05 s. This instrument was used to measure the heat transfer on the right atrial and ventricular endocardial surfaces of two pigs in vivo. The average heat convection coefficients found were between 510 and 4800 Wm−2K−1 . It was found that the average heat convection coefficient varied significantly both spatially and temporally on the endocardium.