Contact: Rajneesh Bhardwaj
The objective of this project is to produce significant advances in the understanding of interfacial heat transfer during microdroplet deposition on a flat substrate. A combined numerical and experimental study is performed as follows: A finite-element model is developed to simulate the transient fluid dynamics and heat transfer during the process, considering wetting and the Laplace forces on the liquid-gas boundary. The high-resolution Lagrangian scheme that allows a very precise tracking of the free surface motion. A novel laser thermoreflectance technique (Figure 1) allows to probe temperatures at a solid-liquid interface with temporal and spatial resolution of 1 microsecond and 20 micrometer respectively. High-speed visualization (up to 1 million frame/second) is also used. Combining these experimental and numerical tools offers a novel, high-resolution approach to measure and understand interfacial heat transfer. Non-intuitive results such as in Figure 2 show that the temperature at the interface between a cooling drop and a solid surface oscillates because of the strong coupling between bulk fluid dynamics, free surface oscillations and heat transfer. Also, once the parameters controlling heat transfer have been identified, the next step will be to engineer surfaces and the deposition process to enhance heat transfer. Applications of this project include spray cooling, micro-manufacturing and coating processes, and electronics packaging.
Figure 1: Principle of the temperature measurement system. A focused laser beam is reflected at the solid-liquid interface. The change of reflected intensity is related to the change of temperature at the interface.
Figure 2: Time evolution of the temperature at the interface between a warm water drop and a cold solid surface, during the early stages of the impact. The simulations results (red curve, with images of temperature contours and streamlines) show oscillations of the interfacial temperature due to the complex interplay of heat transfer and fluid dynamics. The high-resolution interfacial temperature measurement (blue) agrees well with these results.
Funding: NSF grant Coupling the High Resolution of Laser Measurements and Finite-Element Simulations to Understand Transport Phenomena during Microdroplet Deposition
Publications: