Xuan Gao

• Ph.D.
• Professor (Associate) at Beihang University

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 an...

Spray cooling exhibits outstanding cooling performances compared to other liquid cooling techniques, which offers robust thermal management for numerous applications facing high heat flux challenges. In spray cooling, coolant droplets generated from a spray nozzle continuously impinge onto a hot surface at high flow rates. The interaction between t...

This study aims to develop a reliable numerical model for predicting the supercritical heat transfer of aviation kerosene RP-3 in a tube under heating conditions, thereby providing a reference for revealing the mechanism behind the experimental phenomena. Based on validation studies between seven turbulence models and experiments, a numerical metho...

The unpredictable spray characterization caused by different manufacturing standards still limits the implementation of spray cooling. To obtain a predictable spray, a droplet generator was in-house designed and fabricated, which can generate predictable monodisperse droplets or multiple droplet trains at a certain droplet generation frequency (fG)...

In pool boiling on a horizontal surface, the flow of vapor is mainly the departure of vapor bubbles from the boiling surface. If the surface is composed of specially laid-out areas with varied wettabilities, vapor can move on the surface and out of the boiling region. In the present work, a silicon surface with such a function is fabricated using l...

A highly efficient thermal management is imperative to overcome the main challenges associated with heat extraction requirements in electronics. In this study, the flow and heat transfer characteristics of microchannels with various types of fins were numerically analyzed for Re = 0–500 (Re: Reynolds number). Investigation of the aspect ratio, inci...

Droplet impact affects water collection, which is the key to investigating the icing process on an aero-engine spinner. Different from a stationary spinner, droplet impact is affected by Coriolis acceleration and centrifugal acceleration on rotating aero-engine spinners, showing different impact dynamics. Based on the Eulerian method, using the rot...

Smooth and laser-ablated silicon surfaces with wettability ranging from SHI (super-hydrophilic) to SHO (super-hydrophobic) are tested in subcooled pool boiling of water. The experiment focuses on the observation of bubble phenomena using a high-speed camera and the measurement of surface temperature using an infrared camera. The formation and depar...

We experimentally investigate the transient flow boiling that takes place when a stream of ethanol droplets starts impinging on a heated copper plate. If the initial surface temperature is sufficiently high, the flow boiling develops from film boiling, to transition boiling and then nucleate boiling, while the flow behavior development shows repell...

The existence of the hot spot area in the impact center of spray cooling indicates that the temperature is not uniform on a relative large spray-covered surface. In this study, the temperature distribution on a large spray-cooled surface is experimentally studied, and cooling non-uniformity (CNU) is defined to quantify the global and local temperat...

The convection heat transfer of transient flow usually involves transient temperature and transient heat flux at the flow-wall interface. For experimental studies on this type of convection heat transfer problems, it is difficult to take measurement at the flow-wall interface, particularly for liquid flow. A substrate with small thickness can be us...

Different from a fully developed continuous flow in an annular pipe, a liquid plug moving in an annular pipe generates two toroidal vortexes, which cause radial transport that enhances heat transfer. The fully developed heat transfer of the concentric plug is studied for three types of thermal wall conditions: inner-flux, outer-flux, and isothermal...

The cooling of a surface can be achieved by the impingement of spray, which is a free surface flow of droplets ejected from a spray nozzle. Spray cooling can provide uniform cooling and handle high heat fluxes in both single phase and two phases. In this chapter, spray cooling is reviewed from two aspects: the entire spray (spray level) and droplet...

To better understand the drop impact on film flow in spray cooling, we study the impact of a drop burst flow on a film flow that is cooling a hot surface. Focus is put on the cooling enhancement by the drop burst flow. The drop burst flow is generated by periodically interrupting a drop train flow (formed by the breakup of a capillary jet) into a f...

The effects of nozzle positioning on spray cooling is experimentally studied using water sprays generated by a full-cone nozzle to cool a sputter-coated thin-film heater on a silicon wafer. Infrared camera is used to measure surface temperature with high spatial resolution. The nozzle positioning can be adjusted by moving the nozzle toward or away...

A water drop impacts a thin heated wafer which is being cooled by a film flow generated from water jet impingement. The drop impact breaks the steady-state cooling and causes the local temperature around the drop landing location to change. This transient heat transfer process is experimentally investigated using an IR camera to record the surface...

The heat transfer of boiling flows in helically-coiled tubes has significant relation with the bubble dynamics in the curved flows. To understand the bubble dynamics in curved flows, we experimentally study air bubbles in water flows in a coiled tube, which is approximately considered as a toroidal tube. The torus is perpendicular to the ground. Ai...

The impact of a single liquid drop on a flowing liquid film is experimentally and theoretically studied. The drop impact produces a crownlike rising liquid sheet, which radially expands. Small droplets can be formed from the crown sheet, resulting in splash. The present study results in three major contributions. (1) A theoretical model is develope...

The impact of water droplets on solid surfaces is studied experimentally and theoretically. Theoretical equations based on energy conservation are developed. In our theoretical study, the droplet is modeled as a ring-like shape, which matches the dynamic shape of droplets observed from our experimental tests. In the analysis of energy conservation,...