An Integrated Modeling Approach for Predicting Process Maps of Residual Stress and Distortion in a Laser Weld: A Combined CFD–FE Methodology

Laser welding has become an important joining methodology within a number of industries for the structural joining of metallic parts. It offers a high power density welding capability which is desirable for deep weld sections, but is equally suited to performing thinner welded joints with sensible amendments to key process variables. However, as with any welding process, the introduction of severe thermal gradients at the weld line will inevitably lead to process-induced residual stress formation and distortions. Finite element (FE) predictions for weld simulation have been made within academia and industrial research for a number of years, although given the fluid nature of the molten weld pool, FE methodologies have limited capabilities. An improvement upon this established method would be to incorporate a computational fluid dynamics (CFD) model formulation prior to the FE model, to predict the weld pool shape and fluid flow, such that details can be fed into FE from CFD as a starting condition. The key outputs of residual stress and distortions predicted by the FE model can then be monitored against the process variables input to the model. Further, a link between the thermal results and the microstructural properties is of interest. Therefore, an empirical relationship between lamellar spacing and the cooling rate was developed and used to make predictions about the lamellar spacing for welds of different process parameters. Processing parameter combinations that lead to regions of high residual stress formation and high distortion have been determined, and the impact of processing parameters upon the predicted lamellar spacing has been presented

Computational design of a Massive Solar-Thermal Collector enhanced with Phase Change Materials

A cement-based device that can meet, partially or completely, the heating loads of a building by absorbing the solar radiation and converting it into thermal energy can be defined as a Massive Solar-Thermal Collector. The absorbing material for the incoming radiation is made of a cementitious composite, generally concrete, and flowing water inside tubes acts as a heat transfer medium. For an optimized performance, during periods of solar radiation, the device has to efficiently conduct the heat flow from the absorbing surface of the collector and transfer this heat energy to the water. Then, when the radiation is reduced or became null, the device should retain as much as possible the heat energy, reducing the heat that is escaping the collector and consequently the losses to the surrounding environment. In this work, by performing a parametric analysis, different absorbing materials are tested with the objective of finding the best configuration that maximizes the energy efficiency of the collector. Cementitious materials, in combination with Phase Change Materials with distinct melting (and solidification) temperatures, are selected as candidate absorbing materials. The weather variables of an entire year and for two different locations are considered to evaluate the behavior of these devices in opposite climates. After numerical simulations, in where an enthalpy-based finite element formulation is used to solve the physical problem, the obtained results allow to conclude that the inclusion of Phase Change Materials within the absorber material of the collectors, if it is done in a correct way, can improve the energy performance of these devices. In this study, 34 °C and 53 °C are chosen as the most appropriated melting temperatures, which conduct to considerable improvements in the achieved performances, and in both warm and cold climates