Session: 10-01: Heat and Mass Transfer in Small Scale

Paper Number: 129836

129836 - Study on Heat Transfer Characteristics of Successive Droplet Trains Impacting on Silicon Surface. 

Abstract: 

Abstract:

With the development of electronic devices towards multifunctionality and miniaturization, spray cooling is still a highly effective cooling method in high heat flux thermal management. Important parameters of spray such as droplet diameter, quantity and velocity etc. are unpredictable due to the considerable variation in manufacturing standards and working conditions. To achieve a predictable spray, a droplet generator was in-house designed and fabricated. It can produce a large number of predictable monodisperse controlled droplets depending on the frequency setting  f_G , while it can be classified into the controlled sparse spray and dense spray based on the droplet flux. The experiments used deionized water as the cooling fluid. The droplets generated by the droplet generator is captured by a high-speed camera, which ensures that the droplets are uniformly broken up according to the Rayleigh-Plateau instability. The heating element is based on a silicon base, deposited with chromium and platinum by physical vapor deposition (PVD), and then combined through gold wire bonding. In the cooling area, the temperature field was investigated by IR thermal imaging techniques through a reflective path. 

Based on the new type of droplet generator, compared with the traditional jet array, the boiling curve of array droplet trains is above that of the jet array. The heat transfer characteristics of droplet trains were experimentally conducted from single-phase to two-phase. The number of droplet trains is from a single droplet train to a 10*10 array of droplet trains corresponding to droplet flux range is from N=3640 1/cm^₂  to N=74*10⁴ 1/cm^₂. There are two factors affecting the heat transfer performance, one is the relative spacing (the ratio of the distance between neighbor droplet trains and the droplet diameter) and the other is the droplet flux. The smaller relative spacing of the droplet trains, the higher the heat transfer coefficient. Compared to sparse spray (droplet flux is relatively low), heat transfer studies revealed that dense spray has significantly higher heat transfer coefficients and higher CHF values. The empirical relation is given between the heat flux and the dependent parameters in the two-phase state. The equation is well-fitted because its all key parameters are predictable. Compared with the large prediction error of spray cooling, the controllable successive droplet trains have obvious advantages. This study is based on the hydrodynamic and thermodynamic analysis of controlled successive droplet trains which is beneficial for the further application of controlled spraying.

Key words: Spray cooling, Droplet generator, Controlled droplet trains, single-phase, two-phase

Presenting Author: Yuhang Li Beihang University

Presenting Author Biography: Yuhang Li:
PHD at Beihang University, Beijing, China
Primary Research Direction:
the study of heat transfer on successive microdroplet trains impacts

Authors:

Yuhang Li Beihang University
Xu Gao Beihang University
Wenhao Deng Beihang University
Yakang Xia Beihang University
Haiwang Li Beihang University
Xuan Gao Beihang University