			Home About us Contact

Mean Temperature Difference (mean + temperature_difference)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

URANS computations for an oscillatory non-isothermal triple-jet using the k,, and second moment closure turbulence models

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2003
M. Nishimura
Abstract Low Reynolds number turbulence stress and heat flux equation models (LRSFM) have been developed to enhance predictive capabilities. A new method is proposed for providing the wall boundary condition for dissipation rate of turbulent kinetic energy, ,, to improve the model capability upon application of coarse meshes for practical use. The proposed method shows good agreement with accepted correlations and experimental data for flows with various Reynolds and Prandtl numbers including transitional regimes. Also, a mesh width about 5 times or larger than that used in existing models is applicable by using the present boundary condition. The present method thus enhanced computational efficiency in applying the complex turbulence model, LRSFM, to predictions of complicated flows. Unsteady Reynolds averaged Navier,Stokes (URANS) computations are conducted for an oscillatory non-isothermal quasi-planar triple-jet. Comparisons are made between an experiment and predictions with the LRSFM and the standard k,, model. A water test facility with three vertical jets, the cold in between two hot jets, simulates temperature fluctuations anticipated at the outlet of a liquid metal fast reactor core. The LRSFM shows good agreement with the experiment, with respect to mean profiles and the oscillatory motion of the flow, while the k,, model under-predicts the mixing due to the oscillation, such that a transverse mean temperature difference remains far downstream. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Study on carbon dioxide gas cooler heat transfer process under supercritical pressures

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2002
Jianfeng Wang
Abstract In carbon dioxide transcritical air-conditioning and heat pump systems, the high-pressure-side heat exchanger operating at supercritical pressures is usually called as gas cooler. The carbon dioxide gas cooler displays much difference from the traditional heat exchangers employing constant property fluids. The commonly used logarithmic mean temperature difference (LMTD) and effectiveness,heat transfer unit (,-NTU) fail for the gas cooler design calculation as the carbon dioxide properties change sharply near the critical or pseudo-critical point in the heat transfer processes. The new effective heat transfer temperature difference expression for variable fluid property derived by the authors is verified by numeric simulation of the carbon dioxide gas cooler. Moreover, the available correlated models for the cooled carbon dioxide supercritical heat transfer are used to simulate the gas cooler. Detail analysis is made for the deviations among the different models, and for the distributions of local convective coefficient, heat flux, and local temperature of carbon dioxide along the flow path in the gas cooler. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Temperature measurement: comparison of non-invasive methods used in adult critical care

JOURNAL OF CLINICAL NURSING, Issue 5 2005
Sarah Farnell BSc
Aims and objectives., To assess accuracy and reliability of two non-invasive methods, the chemical (Tempa.DOTTM) and tympanic thermometer (GeniusTM First Temp M3000A), against the gold standard pulmonary artery catheter, and to determine the clinical significance of any temperature discrepancy using an expert panel. Background., There is continued debate surrounding the use of tympanic thermometry in clinical practice. Design., Prospective study. Methods., A total of 160 temperature sets were obtained from 25 adult intensive care patients over a 6-month period. Results., About 75.2% (n = 115) of chemical and 50.9% (n = 78) of tympanic readings were within a ±0.0,0.4 °C range of the pulmonary artery catheter. Both the chemical and tympanic thermometers were significantly correlated with temperatures derived from the pulmonary artery catheter (r = 0.81, P < 0.0001 and r = 0.59, P < 0.0001) and limits of agreement were ,0.5,0.9 °C and ,1.2,1.2 °C respectively. The chemical thermometer was associated with a mean temperature difference of 0.2 °C, which increased 0.4 °C when used in conjunction with a warming blanket. With regard to clinical significance 15.3% (n = 26) of chemical and 21.1% (n = 35) of tympanic readings might have resulted in patients receiving delayed interventions. Conversely 28.8% (n = 44) of chemical and 37.8% (n = 58) of tympanic readings might have resulted in patients receiving unnecessary interventions. Conclusions., The chemical thermometer was more accurate, reliable and associated with fewer clinically significant temperature differences compared with the tympanic thermometer. However, compared with the pulmonary artery catheter both methods were associated with erroneous readings. In the light of these findings and previous research evidence, it is becoming increasingly difficult to defend the continued use of tympanic thermometry in clinical practice. However, as chemical thermometers are not without their limitations, further research needs to be undertaken to evaluate the accuracy and reliability of other non-invasive methods. Relevance to clinical practice., Chemical and tympanic thermometers are used in both adults and children in a wide variety of settings ranging from community to intensive care. As such these findings have significant implications for patients, users and budget holders. [source]

Experimental investigation of the energy balance for the metering zone of a twin screw extruder

POLYMER ENGINEERING & SCIENCE, Issue 2 2000
Stephan Tenge
The object of this study is to investigate experimentally the mechanical power transported from the screws to the polymer melt, the heat dissipated in the polymer melt, and the heat transferred to the barrel of the metering zone of a co-rotating twin screw extruder. For the experimental investigations, different screw elements, mixing elements, and kneading discs are used. The experimental results for the dissipation show good agreement with known calculation models. For the calculation of the heat transfer, a new equation is used to calculate the mean temperature difference under consideration of the dissipation. The Nusselt-number can be calculated in good agreement with the experimental results as a function of the Brinkmann-number. [source]