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This paper reviews briefly the definition of heat capacity and clarifies the defined specific heat capacity and volumetric heat capacity. The specific heat capacity and volumetric heat capacity, with our measured experimental data for CuO nanofluids, are discussed as an illustrating example. The result indicates that the specific heat capacity of CuO nanofluid decreases gradually with increasing volume concentration of nanoparticles. The measurement and the prediction from the thermal equilibrium model exhibit good agreement. The other simple mixing model fails to predict the specific heat capacity of CuO nanofluid. The nanoparticle size effect and solid-liquid interface effect on the specific heat capacity of nanofluid are discussed.

An investigation was conducted to understand flow boiling of de-ionized water in locally heated parallel microchannels. High speed visualization technology was employed to visually observe the transient phase change process in an individual microchannel. The process at locally heated condition was different from those at entirely heated condition where vapor column(s) stayed quasi-stable for a long time without venting out. Intensive interface oscillation occurred during phase change. Thin film evaporation appeared to be the main evaporation mode at the upstream vapor column cap, whereas nucleation happened occasionally at favorable flow, heat transfer and local wall conditions. Continuous condensation at the downstream vapor column cap led the flow back to single liquid phase regime out of the microchannel. A signal analysis method was introduced to study the interfacial oscillation behavior at the evaporating cap, which showed marked impact of the evaporation mode on the characteristic frequency.Copyright © 2008 by ASME

An experimental investigation was conducted to visually observe the transitional boiling in an individual water droplet on heated solid surfaces, with temperature ranging from 120°C to 160°C. Using a high-speed video imaging system, the dynamical process of the evaporation and boiling behavior of a droplet was recorded. Infrared ray temperature measurement technique was employed to investigate the instantaneous characteristics of heat transfer as the droplet was boiled. In the transition boiling regime, the phase change behavior of a droplet displayed a cyclical process. Restricted cyclical, sole-bubble cyclical and metastable cyclical styles were observed as the surface temperature increased.Copyright © 2007 by ASME