Numerical study on temperature response of microheater and evolution characteristics of superheated zone under fast transient heating

Abstract

The nucleate boiling process that occurs on the surface of a microheater immersed in a liquid pool under fast transient heating conditions can be regarded as homogeneous or near-homogeneous nucleation, exhibiting a significant difference when compared to boiling at conventional time scales on large and even micro spatial scales. This paper numerically investigates the boiling process at both small spatial and temporal scale by using a validated model. Results indicate a significant difference between the average microheater temperature and the maximum temperature at the boiling surface, which can reach up to 80 °C within the scope of present study. Consequently, the nucleation temperature, typically determined by the average temperature of the microheater in most references, may not precisely represent the homogeneous (or nearly homogeneous) nucleation temperature. At the initiation of nucleation, the profiles at the boundary of superheated zone are approximately circular in the z-plane and arched in the x-plane, respectively. Meanwhile, the profile of the superheated zone boundary at the onset of nucleation under direct heating mode (DHM) appears approximately trapezoidal, exhibiting a significant difference from that observed under indirect heating mode (IHM). It is also noted that the local temperature distribution in the fluid region can be considerably affected by natural convection, potentially exerting a substantial influence on the bubble dynamic behaviors during the subsequent bubble growing phase. These findings may provide valuable references for future experimental study on the mechanisms involving in microscale boiling heat transfer process under rapid heating conditions.

Keywords

• Microheater
• Temperature response
• Fast transient heating
• Superheated zone