Techniques based on temperature-sensitive paints (TSP) to measure time-resolved temperature and heat transfer distributions at the interface between a wall and fluid during pool and flow boiling are described. The paints are excited using ultraviolet (UV) light emitting diodes (LEDs), and changes in fluorescence intensity are used to infer local temperature differences across a thin insulator from which heat flux distribution is obtained. Advantages over infrared (IR) thermometry include the ability to use substrates that are opaque to IR (e.g., glass, plexiglass and plastic films), use of low-cost optical cameras, no self-emission from substrates to complicate data interpretation, high speed, and high spatial resolution. TSP-based methods to measure wall heat transfer distributions are validated and then demonstrated for pool and flow boiling.

No abstract

No abstract

Better understanding of phase change phenomena can be obtained through local measurements of the heat transfer process, which can’t be attained by traditional thermocouple point measurements. Infrared (IR) technology, which has been used by many researchers in the past, cannot be used under certain circumstances due to spectral transparency issues present in some materials. In the current study, Quantum Dots (QDs) are proposed as a novel tool for heat transfer measurements. QDs are nano-sized semiconductor materials which fluoresce upon excitation by blue or UV light. The light intensity emitted by QDs drops with temperature, which can be utilized to obtain the surface temperature distribution at a camera pixel resolution. If QDs are distributed on a surface of interest and optical access to that surface is available, the heat transfer processes can be examined using inexpensive equipment such as CCD/CMOS cameras and LED excitation sources. In this paper, a description of a QD based technique is given, where it is applied to visualize the heat transfer associated with ethanol droplet evaporation.

No abstract