Abstract

At present, most of the downhole electrical devices use disposable batteries or rechargeable batteries as power supplies. When the disposable batteries run out, the downhole devices have to be fished up to replace the batteries. For those tools with rechargeable batteries, chargers should be put into the downhole position close to the tools to recharge the batteries. The operations are very tedious and the normal production is interrupted. Inspired by discharging characteristic of electrophorus electricus, this paper proposes a vibration energy harvester, aiming to provide a long term power supply for downhole tools. The harvester mainly consists of bluff body, piezoelectric energy transducer, the size of designed piezoelectric beam is 52mm * 7mm * 0.82mm (Length * Width * Thickness), and a proof mass. The bluff body is cylinder and installed in front of the harvester, facing the flowing fluid. It destroys the steady flow and makes the piezoelectric energy transducer vibrating. Due to the piezoelectric effect, the vibrating of the energy transducer regularly generates electric energy. The electric energy rectified by voltage conversion circuit can be used to power the controlling system and the driving unit, or to recharge the rechargeable batteries of downhole tools. Under the laboratory condition of water flow velocity of 0.81 m/s and the Reynolds Number Re is 20000, the output peak-peak voltage of the piezoelectric energy harvester is around 44 V, which means it can directly provide the energy for rechargeable battery. This results show that the harvester can potentially offer an intriguing alternative for harvesting ambient energy from flow and provides a new method for long-term energy supply for downhole electrical tools. Futere piezoelectric energy harvester may use more efficient piezoelectric transducer and this device must be optimized to make the piezoelectric energy harvester could have a higher harvesting power.

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