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Pure argon metal inert gas (MIG) welding is expected to offer the possibility to obtain high toughness weld joints. However, due to its arc instability and low wettability, it is difficult to apply pure argon MIG to a practical welding structure. In order to solve these problems, an improved MIG welding process with a duplex current feeding (DCF-MIG) mechanism was developed. In the DCF-MIG process, the welding current and the wire feeding speed are independently controlled by an additionally feeding secondary current from a secondary power source. Thereby, DCF-MIG can supply a large current compared to conventional MIG under the same deposition rate. In this study, to consider the influence of the secondary current feeding position of DCF-MIG on droplet heat quantity, droplet heat quantity was measured by calorimetry. As a result, the droplet heat quantity was found to be increased significantly with the increase of the distance between the primary current feeding point and secondary current feeding point. The increase of the droplet heat quantity in the DCF-MIG process had a strong effect on improving bead shape and penetration. The droplet heat quantity with the effective current value of DCF-MIG was derived from the simplified calculation and the results roughly agreed with the experimental data.

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A simulation model, using a mass transfer coefficient which has as its driving force a humidity difference and a heat transfer coefficient which has as its driving force an enthalpy difference, is developed for investigating the operating characteristics of membrane distillation. Optimum conditions are calculated by the model and the calculated results are proved by actual experiments. Simulated results show that the higher the feed input temperature and the cooling water input temperature, the smaller are the recycling rate, membrane area, and heat energy. For a system which has a 0.216‐m2 membrane and heat exchange area, optimum conditions of feed input and cooling water input temperature and recycling rate are 90 °C, 50 °C, and 18.5 kg/h, respectively. Furthermore, an actual experiment was performed and its permeate rate and heat input were 1 kg/h and 0.21 kW h. From the work, the latent heat recovery is seen as about 66 percent and the simulation model reliability is verified. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res 25(3): 135–150, 1996