This study examined the factors affecting the bubble generation of a motor driven bubble generator to develop a heating unit using hydrodynamic cavitation. This study also investigated the heat production and thermal efficiency by changing operating conditions. Bubble generation using the 25 ℓ-capacity motor is driven bubble generator was confirmed visually in various experimental conditions: three levels of motor powers(1, 3, 5 HP), two levels of revolutions(1800, 3200 rpm), and two levels of internal pressures of the bubble generator(the atmospheric pressure, pressurized air). After constructing the heating unit, heat production, and thermal efficiency were measured in the following experimental conditions: two levels of motor powers(3, 5 HP) and three levels of water quantities(102, 152, 230 kg). And then specifically temperature increasing rate and specific consumed energy required for the heating unit design were calculated. Bubbles were generated stably at 1,800 rpm and pressure from 0~0.8 bar. When heating water around 30℃, specific temperature increasing rate was maximized at 0.247℃/min and 0.002422℃/min-kg. Thermal efficiencies were 121% with only motor driving power as input energy and 98% with both motors driving power and water circulating pump driving power as input energy. This showed that the heating unit using hydrodynamic cavitation had higher thermal efficiency than the existing combustion boiler. Maximum specific consumed energy was 0.0270 KJ/min-kg-℃. This study confirmed that water can be heated with the heat caused by the explosion of the bubbles generated by hydrodynamic cavitation. And the results of this study could be utilized for commercial use because it showed much higher thermal efficiency than the existing combustion boiler.

Introduction
 Materials and Methods
  1 Cavitation generator
  2 Heating unit
  3 Cavitation generator experiment
  4 Heating unit experiment
 Results and Discussion
  1 Cavitation generator experiment
  2 Heating unit experiment
 References

• Dae Bin Song(Department of Bio-Industrial Machinery Engineering, Gyeongsang National University(Institute of Agric. & Life Sci.)) Corresponding author
• Byeong Gyu Kang(Hankuk Magneto Co., Ltd.)