In a process for making the mixture liquid 5 of the oil and the water circularly flow through a heat exchanger 2 to perform cooling, the oil, the water and the heat exchanger 2 are charged with electivity. 油・水の混合液5を熱交換器2経由して循環流動させ冷却する過程で、油・水ならびに熱交換器2は帯電する。 - 特許庁