A Model to Predict the Heat Transfer Coefficient at the Casting-Die Interface for the High Pressure Die Casting Process

A model is presented for the prediction of the heat transfer coefficient (HTC) at the casting-die interface as a function of time for the high pressure die casting process. Contact geometry and interface characteristics are included in the model through die surface roughness, the mean trapped air layer between the casting and the die, the parameters of area density and the radius of contact spots. The density and the radius of contact spots are integrated into a classical thermal flux tube theory in order to calculate HTC at the casting-die interface. The time dependence of the HTC is derived in terms of the degradation of contact between the casting and the die that occurs during solidification. The calculated HTC is found to agree well with the experimentally determined results for different casting conditions. The presented model provides a valuable tool to predict the effect of various casting process parameters, die surface roughness, casting quality and thickness on the HTC during the high pressure die casting process

Worldwide impacts of climate change on energy for heating and cooling

The energy sector is not only a major contributor to greenhouse gases, it is also vulnerable to climate change and will have to adapt to future climate conditions. The objective of this study is to analyze the impacts of changes in future temperatures on the heating and cooling services of buildings and the resulting energy and macro-economic effects at global and regional levels. For this purpose, the techno-economic TIAM-WORLD (TIMES Integrated Assessment Model) and the general equilibrium GEMINI-E3 (General Equilibrium Model of International-National Interactions between Economy, Energy and Environment) models are coupled with a climate model, PLASIM-ENTS (Planet-Simulator - Efficient Numerical Terrestrial Scheme). The key results are as follows. At the global level, the climate feedback induced by adaptation of the energy system to heating and cooling is found to be insignificant, partly because heating and cooling-induced changes compensate and partly because they represent a limited share of total final energy consumption. However, significant changes are observed at regional levels, more particularly in terms of addi- tional power capacity required to satisfy additional cooling services, resulting in increases in electricity prices. In terms of macro-economic impacts, welfare gains and losses are associated more with changes in energy exports and imports than with changes in energy consumption for heating and cooling. The rebound effect appears to be non-negligible. To conclude, the coupling of models of different nature was successful and showed that the energy and economic impacts of climate change on heating and cooling remain small at the global level, but changes in energy needs will be visible at more local scale

Applying Bayesian model averaging for uncertainty estimation of input data in energy modelling

Background Energy scenarios that are used for policy advice have ecological and social impact on society. Policy measures that are based on modelling exercises may lead to far reaching financial and ecological consequences. The purpose of this study is to raise awareness that energy modelling results are accompanied with uncertainties that should be addressed explicitly. Methods With view to existing approaches of uncertainty assessment in energy economics and climate science, relevant requirements for an uncertainty assessment are defined. An uncertainty assessment should be explicit, independent of the assessor’s expertise, applicable to different models, including subjective quantitative and statistical quantitative aspects, intuitively understandable and be reproducible. Bayesian model averaging for input variables of energy models is discussed as method that satisfies these requirements. A definition of uncertainty based on posterior model probabilities of input variables to energy models is presented. Results The main findings are that (1) expert elicitation as predominant assessment method does not satisfy all requirements, (2) Bayesian model averaging for input variable modelling meets the requirements and allows evaluating a vast amount of potentially relevant influences on input variables and (3) posterior model probabilities of input variable models can be translated in uncertainty associated with the input variable. Conclusions An uncertainty assessment of energy scenarios is relevant if policy measures are (partially) based on modelling exercises. Potential implications of these findings include that energy scenarios could be associated with uncertainty that is presently neither assessed explicitly nor communicated adequately

EXPERIMENTAL-STUDY ON THERMAL-CONDUCTIVITY OF NON-NEWTONIAN FLUIDS DURING SHEAR - APPLICATION TO CARBOPOL 940 SOLUTIONS

Polymers exhibit physical properties intermediate to those of elastic solids which follow Hook\u27s law and those of viscous fluids which behave according to Newtonian shear law, therefore, they are designated non-Newtonian fluids. Under a steady shear, non-Newtonian fluids exhibit not only the shear rate dependent viscosity but also their thermal conductivity changes with shear. It is the purpose of this paper to report on our investigation on the dependence of thermal conductivity on shear rate. Aqueous solutions of Carbopol 940 have been used as test fluids to investigate the effects of temperature and shear rate on thermal conductivity

A predictive model for the evolution of the thermal conductance at the casting–die interfaces in high pressure die casting

International audienceAn analytical model is proposed to predict the time varying thermal conductance at the casting–die interface during solidification of light alloys during High pressure Die Casting. Details of the topography of the interface between the casting and the die are included in the model through the inclusion of solid surface roughness parameters and the mean trapped air layer at the interface. The transitory phase of the interfacial thermal conductance has been related to the degradation of contact as solidification progresses through the casting thickness. The modelled time varying thermal conductance showed very good agreement with experimentally determined values for different alloy compositions and casting geometries. The analysis shows that the parameters that govern the thermal conductance are different for the first stage of contact compared to the second stage of contact when the alloy begins to solidify