A pressure drop occurs at the ONB regardless of the conditions with the pressure drop appearing earlier at higher heating currents and liquid temperatures and lower flow rates.ĭespite that mechanistic and accurate correlations predicting the Onset of Nucleate Boiling (ONB) for pool boiling are widely presented in the literature, models for forced convective boiling remain few. The effects of the operating conditions on the Onset of Nucleate Boiling (ONB) were analyzed qualitatively by correlating the pressure fluctuation signals with visual images obtained from the experiments. Higher heating currents, lower liquid temperatures and lower flow rates result in wider frequency distributions and larger pressure fluctuation amplitudes in the time domain and wider frequency distributions and higher PSD of the pressure fluctuations in the frequency domain.
Peristaltic pump controller minitube pdf#
The CDF and PSD methods were more effective than the PDF and FFT methods for the time-frequency analyses of the pressure fluctuations. The experimental conditions were heating currents to a high frequency induction heater of 200–720 A, liquid temperatures of 50–85☌, and flow rates of 0–290 L/h. Time and frequency analyses methods including PDF (Probability Density Function), CDF (Cumulative Probability Function), FFT (Fast Fourier Transform) and PSD (Power Spectral Density) were used to investigate the pressure fluctuation characteristics during subcooled nucleate flow boiling and the effects of various parameters. Comparisons of experimental heat transfer coefficient in the subcooled boiling regime with the existing correlations are also presented. Predictive models for ONB were evaluated and Kandlikar's ONB model was found to agree well with the present data. During ONB, pressure drop and the fluctuations of fluid outlet temperature are observed near the exit of the test section. Based on sudden oscillations of the pressure drop and wall temperature, onset of nucleate boiling (ONB) is identified in the tube. The variation in wall temperature and pressure drop gives an indication of the different boiling regions along the axis of the horizontal tube. The test section is a horizontal AISI 316 stainless-steel minitube with internal diameter of 1.13 mm with uniform heated length of 250 mm and the tube is heated by AC electric current. The experiments were conducted with high surface tension liquid (water), which clearly indicates that inertial effects are important for both momentum and thermal transport in minichannels. The present work presents experimental results of subcooled flow boiling heat transfer phenomena in minichannels.
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