Experimental investigation of bubble group and temperature distribution uniformity in the direct contact boiling heat transfer process

• A new method for measuring the uniformity of bubble groups is proposed. • The relationship between temperature distribution uniformity and mixing uniformity is confirmed. • The method of measuring the uniformity of mixing by the gray value of the image is proposed. In the present study, a new method is proposed to measure the uniformity of temperature distribution and the phase distribution in direct contact boiling heat transfer. The proposed method is applied to explore the relationship between uniformity of bubble distribution and temperature distribution. Based on the uniformity theory, the relationship between temperature distribution uniformity, temperature field uniformity, two-phase mixing uniformity and volumetric heat transfer coefficient is explored. Then the uniformity of temperature distribution is obtained through thermal imaging under specific conditions. The obtained results show that the actual temperature distribution uniformity and the correlation coefficient of the uniformity through the gray value are higher than 99%. Moreover, the obtained relationship between bubble group distribution and temperature distribution reveals the essence of the uniformity of bubble group distribution in improving heat transfer. It is concluded that the temperature non-uniformity mainly originates from improper mixing of different streams with different temperatures when entering the heat exchanger, which reduces the thermal performance of a heat transfer process. This non-uniformity has a strong correlation with the flow pattern. The main objective of the present study is to provide a new method to evaluate bubble group distribution and temperature distribution in boiling heat transfer.