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In this paper, a 3D mathematical model is proposed to investigate the physical transport phenomena in weld pool and vapour plume during the stationary vacuum electron beam welding on 2219 aluminium alloy plate. Three beam current cases are employed to investigate the heat transfer, fluid flow, keyholing, keyhole backfilling and collapsing processes, and the resulting spiking defect and residual crater. In the model, a keyhole-tracing heat source is adopted to simulate the energy interactions between electron beam and material with the help of VOF technique. Results indicate that the beam profile and heat flux distribution decreases the growing speed of keyhole dimensions. The increase of beam current raises the evaporation intensity, keyhole wall temperature, keyholing depth and keyhole instability. On the premise of same heating time, a larger beam current produces a spiking defect in partially-penetrated weld. Finally, all the simulation results are validated against experiments. [ABSTRACT FROM AUTHOR]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [ABSTRACT FROM AUTHOR]