Effect of Pressure and Heat Flux on Bubble Departure Diameters and BubbleEmission Frequency

摘要

The bubble departure diameters and bubble emission frequency have been calculatedfor the nucleate pool boiling data of Engelhom for many refrigerants over a wide range of heat flux and pressure. The pressure ranged from 0.019 bar to 10.55 bar and the heat flux ranged from 102,000 W/m2 to 1,000 W/m2. The bubble departure diameters were calculated using Laplace Equation and the bubble emission frequency were calculated using the equations of Sharma et al. The study reveals that the bubble departure diameter increases as the pressure decreases. The bubble emission frequency is the strong function of heat flux. The frequency also increases with increase in pressure, however, not as strong as it increases with heat flux. An increase in the size of the bubble makes the heat transfer process sluggish. An increase in the bubble emission frequency leads to higher heat transfer rates due to enhanced turbulence in the process. Therefore, the heat transfer coefficients are lower at lower pressures and higher at higher pressures and heat fluxes.