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We demonstrated a method of fabricating three-dimensional (3D) metal structures in hydrogels with good conductivity by using femtosecond laser ablation and electroplating. The hydrogel containing A g + was first ablated by a femtosecond laser to form microchannels with an entrance achieving surface and then sandwiched between the anode and cathode to operate electroplating. Silver structures were formed along the microchannel from the microchannel entrance close to the cathode due to reduction of A g + . The average resistivity of metal structures is measured to be about 4 × 10 − 7 Ω m . A tetrahedron metallic microstructure embedded in hydrogel by this method was demonstrated to show its ability of 3D micromachining.

Direct contact thermal energy storage (TES) for use in conventional air-conditioning systems is proposed to reduce the operational energy demand. Thermal performance of a novel kind of phase change material (PCM) prepared for use in conventional air-conditioning systems with the proposed direct contact TES tank, is evaluated. A 3-dimensional (3D) numerical model is built using ANSYS FLUENT to investigate dynamic characteristics of the discharging process of TES system. The model is validated by comparing the numerical with the experimental results. The effects of heat transfer fluid (HTF) flow rate, HTF inlet temperature, liquid PCM volume fraction, complete discharging time, discharging capacity of the tank, and temperature distribution in direct contact TES tank are investigated. The results indicate that increasing the HTF flow rate speeds up the discharging capacity and the discharging time of the direct contact TES system reduces. When the flow rate increases from 0.503 m 3 /h to 0.936 m 3 /h, the melting PCM increases from 63.33 vol.% to 70.74 vol.% within 600 s. The discharging capacity increases with HTF inlet temperature; however, the whole discharging capacity does not change obviously by changing HTF inlet temperature.