Heng Ban

Dry triboelectrostatic beneficiation of fly ash

A laboratory-scale triboelectrostatic separation system in conjunction with analytical techniques was used to study fly ash beneficiation. Fly ash samples were characterized by size analysis and carbon content and then subjected to dry triboelectrostatic separation. Due to differences in the surface physical and chemical properties of the carbon and ash, particles of unburnt carbon and fly ash were triboelectrically charged to opposite polarity and then separated by passing them through a static electric field. Ash fractions deposited on the positive and negative electrodes were collected, analysed for carbon content and subjected to SEM and petrographic analyses. The results indicate that the physical and chemical properties of the ash dictate the maximum carbon-ash separation that would be possible. In addition, the potential of dry separation technology for removing unburnt carbon from coal ash was demonstrated.

Adsorption of arsenic(V) onto fly ash: a speciation-based approach.

Arsenic (As) poses a significant water quality problem and challenge for the environmental engineers and scientists in the world. The large volume of coal fly ash produced around the world is a potentially significant anthropogenic source of arsenic. Currently the leaching behavior of arsenic from fly ash is not well understood. Batch methods were used in this study to investigate arsenic leaching using a raw ash, and arsenic adsorption using a clean, washed ash. Experimental results indicated that pH had a significant effect on arsenic leaching or adsorption. Between pH 3 and 7, less arsenic was in the dissolved phase. When pH was less than 3 or greater than 7, increasing amounts of arsenic were leached or desorbed from fly ash. The leaching and adsorption behavior of arsenic was interpreted with the speciation of surface sites and arsenic. In a new approach, a speciation-based model was developed to quantify the arsenic adsorption as a function of pH and surface acidity parameters. This work is important in offering insight into the leaching mechanism of arsenic from coal fly ash, and providing a robust model based upon specific, measurable parameters to quantify arsenic adsorption by other solid media in addition to fly ash.

Particle tribocharging characteristics relating to electrostatic dry coal cleaning

Abstract The velocity, number density and size of representative coal mineral matter particles were measured using laser phase Doppler velocimetry subsequent to their triboelectrification and while flowing through a constant electric field. For 60 μm diameter silica particles, the accumulated negative charge, q, could be represented by a normal distribution having an average value which was linearly dependent on the gas velocity in the tribocharger, V, and represented by qSi = [2.6V + 4] × 10−14C. The width of the distribution increased with increasing gas velocity. Physical mixtures of similar sized silica and glassy carbon, and coal, were also subjected to electrostatic separation while being monitored by the non-intrusive laser optical technique. The purity of the carbon separated from silica was >90%, and dependent on the accumulation of either positive charge or no charge on the silica. For a high volatile A, Elswick seam, Pike County, Kentucky coal, the removal of mineral matter was comparable to that obtainable by wet processes, decreasing mineral matter content from 6.4% to 3.7% at a 72% combustible recovery.

Hydrogen bonding-assisted thermal conduction in β-sheet crystals of spider silk protein

Using atomistic simulations, we demonstrate that β-sheet, an essential component of spider silk protein, has a thermal conductivity 1-2 orders of magnitude higher than that of some other protein structures reported in the literature. In contrast to several other nanostructured materials of similar bundled/layered structures (e.g. few-layer graphene and bundled carbon nanotubes), the β-sheet is found to uniquely feature enhanced thermal conductivity with an increased number of constituting units, i.e. β-strands. Phonon analysis identifies inter-β-strand hydrogen bonding as the main contributor to the intriguing phenomenon, which prominently influences the state of phonons in both low- and high-frequency regimes. A thermal resistance model further verifies the critical role of hydrogen bonding in thermal conduction through β-sheet structures.

Maceral/microlithotype partitioning through triboelectrostatic dry coal cleaning

Abstract Three eastern Kentucky and two Illinois Basin coals were tested in a bench scale triboelectrostatic separation unit. The three eastern Kentucky samples provided a rank series of petrographically comparable coals. The Illinois Basin bituminous coals were lower rank and had high vitrinite ( ∼ 80%) and sulfur contents in comparison to the other three coals. Triboelectrostatic beneficiation provides efficient maceral and mineral partitioning in the high volatile A and B bituminous coals tested, with vitrinite, as vitrite and vitrinite-enriched microlithotypes, reporting to the clean fractions and the inertinites, liptinites, and minerals reporting to the tails. The high volatile C bituminous Springfield coal had a lower separation efficiency than the petrographically similar, but higher rank, Herrin coal. The decreased separation efficiency in the behavior of the Springfield coal may be a response to its higher moisture content. Compared to bench-scale fuel oil agglomeration of some of the same coals, triboelectrostatic separation provides clearer partitioning of mineral matter, sulfur, and macerals.

Effect of electrical double layer on electric conductivity and pressure drop in a pressure-driven microchannel flow

The effect of an electrical double layer (EDL) on microchannel flow has been studied widely, and a constant bulk electric conductivity is often used in calculations of flow rate or pressure drop. In our experimental study of pressure-driven micropipette flows, the pipette diameter is on the same order of magnitude as the Debye length. The overlapping EDL resulted in a much higher electric conductivity, lower streaming potential, and lower electroviscous effect. To elucidate the effect of overlapping EDL, this paper developed a simple model for water flow without salts or dissolved gases (such as CO(2)) inside a two-dimensional microchannel. The governing equations for the flow, the Poisson, and Nernst equations for the electric potential and ion concentrations and the charge continuity equation were solved. The effects of overlapping EDL on the electric conductivity, velocity distribution, and overall pressure drop in the microchannel were quantified. The results showed that the average electric conductivity of electrolyte inside the channel increased significantly as the EDL overlaps. With the modified mean electric conductivity, the pressure drop for the pressure-driven flow was smaller than that without the influence of the EDL on conductivity. The results of this study provide a physical explanation for the observed decrease in electroviscous effect for microchannels when the EDL layers from opposing walls overlap.

Analysis of the electrothermal technique for thermal property characterization of thin fibers

The transient electrothermal technique has been developed to measure the thermal conductivity and thermal diffusivity of electrically conductive or non-conductive nano-to-microscale fibers. In this work, a full theoretical model is developed in detail including the effects of radiation heat loss and non-constant heating as a result of sample temperature rise during measurement, and is compared to the more commonly used reduced model, which neglects these effects. Non-dimensional parameters are derived representing radiation heat loss and non-constant heating to identify the true parameter dependences on these effects. A numerical model is used to perform parametric analyses on the experimental setup providing results that were fitted with the full and reduced models to find thermal conductivity and thermal diffusivity. Additionally, the numerical model was used to investigate nonlinear radiation heat losses and spatially non-uniform heating effects resulting from uneven coating of the conductive layer on electrically non-conductive samples. As a result, these influences are shown to require careful consideration in the application of this technique. A clear linear relationship was found between the non-dimensional parameters and measurement error, which provides a measure for the proper estimation of systematic error induced by these effects. Using the reduced model for data reduction results in measurement percentage error equal to ten times the radiation and non-constant heating dimensionless parameters under the assumption of linear radiation heat losses (small sample temperature rise compared to ambient temperature).

Thermal Conductivity Profile Determination in Proton-Irradiated ZrC by Spatial and Frequency Scanning Thermal Wave Methods

Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 °C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the best resolution finding a very uniform thermal conductivity envelope in the damaged region measuring ∼52 ± 2 μm deep. Frequency-based scanning PTR provides quantification of the thermal parameters of the sample using the SThM measured profile to provide validation of a heating model. Measured irradiated and virgin thermal con...

Spatially localized measurement of thermal conductivity using a hybrid photothermal technique

A photothermal technique capable of measuring thermal conductivity with micrometer lateral resolution is presented. This technique involves measuring separately the thermal diffusivity, D, and thermal effusivity, e, to extract the thermal conductivity, k = (e2/D)1/2. To generalize this approach, sensitivity analysis is conducted for materials having a range of thermal conductivities. Application to nuclear fuel is consider by performing experimental validation using two materials (CaF2 and SiO2) having thermal properties representative of fresh and high burnup nuclear fuel. The measured conductivities compare favorably with literature values.

Wideband fluorescence-based thermometry by neural network recognition: Photothermal application with 10 ns time resolution

Neural network recognition of features of the fluorescence spectrum of a thermosensitive probe is exploited in order to achieve fluorescence-based thermometry with an accuracy of 200 mK with 100 MHz bandwidth, and with high robustness against fluctuations of the probe laser intensity used. The concept is implemented on a rhodamine B dyed mixture of copper chloride and glycerol, and the temperature dependent fluorescence is investigated in the temperature range between 234 K and 311 K. The spatial dependence of the calibrated amplitude and phase of photothermally induced temperature oscillations along the axis of the excitation laser are determined at different modulation frequencies. The spatial and frequency dependence of the extracted temperature signals is well fitted by a 1D multi-layer thermal diffusion model. In a time domain implementation of the approach, the gradual temperature rise due to the accumulation of the DC component of the heat flux supplied by repetitive laser pulses as well the immedi...