Leping Zhou

On the Specific Heat Capacity of CuO Nanofluid

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.

Deposition pattern and tracer particle motion of evaporating multi-component sessile droplets

The understanding of near-wall motion, evaporation behavior and dry pattern of sessile nanofluid droplets is fundamental to a wide range of applications such as painting, spray drying, thin film coating, fuel injection and inkjet printing. However, a deep insight into the heat transfer, fluid flow, near-wall particle velocity and their effects on the resulting dry patterns is still much needed to take the full advantage of these nano-sized particles in the droplet. This work investigates the effect of direct absorptive silicon/silver (Si/Ag) hybrid nanofluids via two experiments. The first experiment identifies the motion of tracer particles near the triple line of a sessile nanofluid droplet on a super-hydrophilic substrate under ambient conditions by the multilayer nanoparticle image velocimetry (MnPIV) technique. The second experiment reveals the effect of light-sensitive Si/Ag composite nanoparticles on the droplet evaporation rate and subsequent drying patterns under different radiation intensities. The results show that the presence of nanoparticle in a very small proportion significantly affects the motion of tracer particles, leading to different drying patterns and evaporation rates, which can be very important for the applications such as spray coating and inkjet printing.

Subcooled Nucleate Boiling of Alumina Nanofluid With/Without n-Butanol as Surfactant

Nucleate boiling process in nanofluids is important because of its potential in enhanced heat transfer. However, it is difficult to observe the boiling phenomenon due to the indistinct image. In this investigation, stable nanofluids was prepared by α-Al2O3 nanoparticles, 30 nm in diameter, and ultrapure water. The bubble behaviors in water were observed by high-speed CCD camera. Unique bubble sweeping phenomenon, existing in the upper and/or lower part of the heated wire, emerged due to the existence of nanoparticles. The experiment shows that the bubble-top jet flow phenomenon only exists when the small bubble returned to the heated surface, which demonstrates that it was the vertical Marangoni convection along the bubble interface that induced the jet flow. Meanwhile, flocculent clustering of nanoparticles can be observed to swirl at the bubble-bottom for low-concentration nanofluid, when the heat flux was relatively small. The SEM images of the nanoparticle deposition layers indicated increased thermocapillarity, but it seemed to delay the detachment of small bubbles from the heated surface. While n-butanol was included as surfactant, it promoted the nanoparticle deposition for low heat flux condition. The bubble behaviors were consistent with those of pure fluids and no bubble circling phenomenon was observed. The boiling curves were then depicted for alumina nanofluid with or without n-butanol. The boiling heat transfer in water was enhanced with increasing nanoparticle concentration. The boiling curves shifted right when increased the surfactant concentration in the nanofluid. It appeared that the surfactant-induced inhibited bubble growth and enhanced nanoparticle clustering in the near-wall region were the main reason for the shifting.© 2013 ASME

Fluid Flow and Thin-Film Evolution near the Triple Line during Droplet Evaporation of Self-Rewetting Fluids

The microscopic region near the triple line plays an important role in the heat and mass transfer of droplets, although the mechanisms of evaporation and internal flow remain unclear. This paper describes an experimental study of fluid flow and thin-film evolution near the triple line in sessile droplets of self-rewetting fluids, aqueous solutions of alcohols with the number of carbon atoms varying from 1 to 7, to analyze the influence of various factors on the mesoscale flows. The mechanism of internal flow for self-rewetting fluid droplets was different from that of conventional fluids, and hence, a novel expression of the in-plane average velocity was fitted for them. The temporal and spatial evolution of the thin-film thickness near the triple line during droplet evaporation was obtained by using a proposed subregion method, which was developed from an evanescent-wave-based multilayer nanoparticle image velocimetry technique. The self-rewetting fluids are conducive to increase the microscopic critical contact angle and the energy barrier of the contact line, which reduces the rate of thin-film thickness variation. The inhibited impact of self-rewetting fluids on evaporation increases gradually with an increasing number of carbon atoms.

Influence of temperature on performance of all vanadium redox flow battery: analysis of ionic mass transfer

The main mass transfer processes of the ions in a vanadium redox flow battery and the temperature dependence of corresponding mass transfer properties of the ions were estimated by investigating the influences of temperature on the electrolyte properties and the single cell performance. A composition of 1.5xa0M vanadium solutions in 3.0xa0M total sulfate was selected and a range of −u200910–50xa0°C was set as the operating temperature limits. It shows that the temperature effect on the concentration polarization of reactive substances and the ionic mobility of H+ in the membrane may be the main factor affecting the performance at low temperatures, while the diffusion coefficient and the ionic mobility of vanadium ions are dominant for the performance at high temperatures. The relation between the mass transfer properties of the ions in electrolyte and the battery performance was then clarified using a route map of the temperature effects.

Heat Transfer Characteristics in an Evaporating Thin Film and Intrinsic Meniscus in a Binary Fluid Sessile Droplet

ABSTRACT The evaporation of binary droplets containing a mixture of two species with completely different physicochemical properties is important in many applications. This paper describes a numerical study of the heat transfer characteristics of a thin liquid film and an intrinsic meniscus in a sessile droplet of a binary fluid, 5.0wt% aqueous n-butanol solution, to analyze the influence of various factors on the heat transfer. The thin film was longer than for a water droplet and the heat and mass fluxes were greater. The droplet contact radius, wall superheat, contact angle, and the air in a closed environment can affect the contribution of the heat transfer in the thin film region on the overall heat transfer. The wall superheat has the greatest effect on the heat transfer followed by the droplet size, surface wettability, and non-condensable gas. These four significant effects can be efficiently combined to enhance the heat transfer in applications involving binary droplet evaporation.

Near-Wall Velocity and Temperature Measurements in the Meniscus Region for Staggered Glass Beads.

Velocity and temperature fields in the meniscus are crucial for the heat transfer mechanism in porous medium. The meniscus zone, however, is narrow so that it is difficult for observation. The velocimetry and thermometry in the near-wall region of the surface provide possible measurement methods with the development of micro/nanotechnology. Being exponentially decay in the intensity, the evanescent-wave illumination has the advantage of high spatial resolution and non-intrusion for these measurement methods. The multilayer nano-particle image velocimetry (MnPIV) uses the evanescent-wave illumination, decayed exponentially with the wall-normal distance, to obtain near-wall velocity data at different distances from the wall. The thermometry in the meniscus region could also use the evanescent-wave to illuminate the fluorescence dye, the emitted intensity of which changes with temperature. In this paper, these techniques are employed to measure the near-wall velocity and temperature between the porous media and the ITO heater, in order to explore the role of meniscus during convection of water. Near-wall velocity and temperature of the deionized water, seeded with 100 nm fluorescent colloidal tracers and flow in the staggered glass beads with diameters ranging from 2 mm to 6 mm, are obtained and discussed.