We have performed a series of experiments to characterize the different regimes observed in drop impacts during evaporative cooling of heated surfaces. We found four regimes which were named splashing, fizzing, flat film, and marbling based on the dynamic properties of the drop impact. We found that the emergence of these regimes is primarily controlled by the Jacob number, a dimensionless group describing the ratio of sensible to latent energy absorbed during liquid-vapor phase change. Using our classification scheme, we can predict a range of useful Jacob numbers to use in the cooling of electronic components. From these Jacob numbers, we can extract the material properties of a fluid required to cool a given system.

Techniques of infrared thermography were used to conduct an experimental study of the evaporative cooling of a hot, low thermal conductivity, non-metallic surface heated by radiation and subject to a random array of impinging water droplets. A droplet generating and distributing apparatus and a data acquisition system employing digital image analysis devices were also developed and implemented. Real time infrared images of the heated surface were recorded and digitized using computer resident frame grabbing hardware and analyzed on a pixel by pixel basis, giving a high degree of thermal and spatial resolution. From these analyses, the instantaneous surface temperature distribution and transient surface temperature profile were obtained for a range of initial temperatures and impinging mass fluxes. The surface temperature was found to decay exponentially with time to a steady state value for the fluxes used. Three dimensional plots of the temperature distribution on the surface also showed the significant lowering of the average surface temperature, and provided a qualitative description of the cooling phenomena at various stages during the transient. Results obtained will be used in the future validation of a computer model of the phenomena.

This thesis examines the behavior of water droplets as they impact a heated surface, namely, the droplets' spreading and contracting processes. This data is being used currently in a variety of industrial applications, for example, the automotive industries use this data in the design of fuel injectors in an IC engine. This data is also relevant in the disciplines of nuclear technology, cooling of electronic devices, and steam engines.

This report describes the research performed during the period July 1989 - July 1990 under a joint research program between the Mechanical Engineering Department of the University of Maryland and the Center for Fire Research of the National Institute of Standards and Technology. The research is conducted by Graduate Research Assistants of the ME Department under the joint supervision of Dr. di Marzo (UMCP) and of Dr. Evans (CFR - NIST). A new experimental set-up for the study of dropwise evaporation in a radiant heat transfer field has been designed, constructed and tested. The various issues of concern such as: steady state solid temperature distribution, radiant heater design and configuration, infrared background noise and post test data manipulation are outlined. The formulation of a model for the prediction of the cooling induced by an evaporating droplet impinging a semi-infinite solid is the subject of this report. The thermal interactions during the evaporation of a liquid droplet deposited on a low conductivity semi-infinite solid are complex because the evaporative process is coupled to the solid intense local cooling. A combined Boundary Element Method (BEM) and Control Volume Method (CVM) has been used to solve this complex numerical problem. The results for both high and low thermal conductivity materials are in excellent agreement with the experimental findings. Detailed comparison of the surface temperature distributions on solid Macor detected with infrared thermography are also performed to demonstrate the accuracy of the computational method.

This report describes the research performed during the period March 1987 - July 1988 under a joint research program between the Mechanical Engineering Department of the University of Maryland and the Center for Fire Research of the National Bureau of Standards. The research is conducted in the laboratories of the CFR by a Graduate Research Assistant of the ME Department under the joint supervision of Dr. Marino di Marzo (ME Dept.- UMCP) and of Dr. David D. Evans (CFR - NBS). The formulation of a model for the prediction of the cooling induced by an evaporating droplet impinging a semi-infinite solid is the subject of this report. The thermal interactions during the evaporation of a liquid droplet deposited on a low conductivity semi-infinite solid are complex because the evaporative process is coupled to the solid intense local cooling. Numerical techniques based on finite difference methods have failed to provide meaningful results. This is due to the sharp temperature gradients in the proximity of the droplet edge which cause instabilities in the solution for reasonable time steps due to the explicit coupling of the liquid-vapor regions. An integral method was proposed by Dr. Baum (CFR - NBS) in order to overcome these difficulties. The methodology and its application to this specific problem is described in detail. Preliminary result will also illustrate its validity. A brief note on the convective heat transfer coefficient measured in the previous experiments on aluminum and Macor is also included in this report.