Droplet evaporation and de-pinning in rectangular microchannels

Experimental and numerical studies are presented for evaporation of micro-droplets of deionised (DI) water and toluene on lead zirconate titanate (PZT) substrates. The microchannels are fabricated with SU-8 2025 and 2075. The effects of channel width and depth on the evaporation and de-pinning rates of embedded micro-droplets are presented and compared for both fluids. The study reveals a partially hydrophobic nature of SU-8/PZT microchannel to DI water and a complete wetting when toluene is used as the droplet. The rate of evaporation of toluene is about double the rate of evaporation of DI water. Comparisons of the rates of evaporation and de-pinning show that the channel width has a larger effect on evaporation than the depth of the channel. The equivalent contact angle of the pinned film and bulk fluid compensated for the evaporation of the droplet. Surface roughness was also shown to have a significant effect on the pinned film in the rectangular microchannels

Calcium oxide/steam chemical heat pump for upgrading waste heat in thermochemical hydrogen production

This paper presents a numerical study of a chemical heat pump (CHP) for upgrading waste heat from a cement plant for thermochemical hydrogen production. A calcium oxide/steam CHP is investigated as a potential system to upgrade waste heat from industrial processes for thermochemical hydrogen production. The heat produced by the CHP drives the decomposition of copper oxychloride (CuO·CuCl2) in a copper–chlorine (Cu–Cl) thermochemical cycle. A transient analysis of the temperature distribution in each sub process in the combined CHP/Cu–Cl cycle is presented in this study. The numerical results of hydration temperature distribution are compared with experimental results to validate the predictive model. A maximum hydrogen production of 12.28 mol/kg Ca(OH)2 can be achieved from the combined system analyzed in this study. The effect of heating load and oxygen decomposition supply temperature is reported for the hydration, dehydration, condenser and evaporator heat transfer processes

Transient response of thermocapillary pumping of a droplet in a micro heat engine

A new analytical model is developed to predict the transient velocity and voltage generated due to thermocapillary pumping in a micro heat engine (MHE). Modeling, fabrication, and experimental studies of the MHE are presented in this paper. The fabrication technique uses lead zirconate titanate (PZT) as a substrate for the MHE. Analytical and experimental results are reported for Ti-W microheaters that transfer heat to the thermocapillary motion. The effect of surface roughness on thermocapillary motion of the droplet in the MHE is examined. The results show that a higher bulk droplet velocity reduces the effect of surface roughness on the displacement of the droplet. The analytical model of the efficiency of the system considers the electromechanical coupling factor and frictional irreversibilities to yield about 1.6% efficiency with a maximum voltage of 1.25 mV for the range of displacement considered in this study

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl2) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant

Integrated fossil fuel and solar thermal systems for hydrogen production and CO2 mitigation

In most current fossil-based hydrogen production methods, the thermal energy required by the endothermic processes of hydrogen production cycles is supplied by the combustion of a portion of the same fossil fuel feedstock. This increases the fossil fuel consumption and greenhouse gas emissions. This paper analyzes the thermodynamics of several typical fossil fuel-based hydrogen production methods such as steam methane reforming, coal gasification, methane dissociation, and off-gas reforming, to quantify the potential savings of fossil fuels and CO2 emissions associated with the thermal energy requirement. Then matching the heat quality and quantity by solar thermal energy for different processes is examined. It is concluded that steam generation and superheating by solar energy for the supply of gaseous reactants to the hydrogen production cycles is particularly attractive due to the engineering maturity and simplicity. It is also concluded that steam-methane reforming may have fewer engineering challenges because of its single-phase reaction, if the endothermic reaction enthalpy of syngas production step (CO and H2) of coal gasification and steam methane reforming is provided by solar thermal energy. Various solar thermal energy based reactors are discussed for different types of production cycles as well

Particle morphology of CuCl2 droplets in evaporative spray drying of aqueous slurries by laser diffraction and microscopy

New empirical correlations that predict the evaporative spray drying behavior of slurries are developed in this paper. The analysis examines a single droplet of CuCl2 solution in a continuum drying media. The results indicate a combination of convection and spray drying modes could improve the drying process. Validation of the experimental results involves comparisons based on non-dimensional analysis. The Ohnesorge number has a greater effect on the particle diameter than the Nusselt numbers. Analytical models of heat and mass Spalding numbers are developed for the aqueous solution, subject to various drying conditions. Also, the effect of temperature on the atomization flow rate is reported. The Log-normal distribution provides the most accurate fit for the measured data. Particle size diameters are predicted and compared with experimental results using SEM and laser diffraction. The results indicate the average particle size is about 229.5 μm

Matrix Diagonalization as a Board Game: Teaching an Eigensolver the Fastest Path to Solution

Matrix diagonalization is at the cornerstone of numerous fields of scientific computing. Diagonalizing a matrix to solve an eigenvalue problem requires a sequential path of iterations that eventually reaches a sufficiently converged and accurate solution for all the eigenvalues and eigenvectors. This typically translates into a high computational cost. Here we demonstrate how reinforcement learning, using the AlphaZero framework, can accelerate Jacobi matrix diagonalizations by viewing the selection of the fastest path to solution as a board game. To demonstrate the viability of our approach we apply the Jacobi diagonalization algorithm to symmetric Hamiltonian matrices that appear in quantum chemistry calculations. We find that a significant acceleration can often be achieved. Our findings highlight the opportunity to use machine learning as a promising tool to improve the performance of numerical linear algebra.Comment: 14 page

Training and Development Practices and Employees’ Performance in Selected Manufacturing Companies in Nigeria

Managing workforce diversity in manufacturing organisations has been a problem all over the world including Nigeria. Manufacturing organisations in Nigeria continue to experience occasional drop in performance due to employees’ apathy and non-challant attitudes as a result of high level of dissatisfaction caused by inadequate attention to training and development practices. This study assessed the relationships between training and development practices and employees’ performance in selected manufacturing companies in Nigeria. A cross sectional survey research design was employed, and out of the 1,568 copies of questionnaire that were administered proportionally in the selected manufacturing companies, 1,153 copies were retrieved and found useful. Data were analysed using descriptive statistics and the hypotheses were tested using Analysis of Variance (ANOVA). The results of the findings show f-statistics of 223.717 and so, there is a significant relationship between training and development practices and employees’ performance among Nigerians working in the selected manufacturing companies. Also, f-statistics of 244.391 shows a significant relationship between training and development practices and employees’ performance among other nationals in the selected MNCs. The study concluded that there are significant relationships between training and development practices and employees’ performance in selected manufacturing MNCs in Nigeria

Evaluation of climate variability impact on sources of water supply

Climate is a key factor in water availability and accessibility on both the earth surface and below the earth surface. The study evaluated climate variability impact on sources of water supply in Offa, Kwara State, Nigeria. The study utilized both primary and secondary source of data. Household proximity to water sources was computed using the percentages of household that falls within the basic indicator for measuring water access by World Health Organization. Correlation and multiple regression analyses were used to determine the relationship between the climatic variables and water supply; and groundwater level in the study area. Pearson Product Moment Correlation was employed to establish the association between climate and water supply; and groundwater level. Multiple regression analysis was used to examine the relationship between water supply and the selected climatic variables. Trend analysis was used to determine the trend of the selected climatic variables in the study area. The result revealed that rainfall amount, minimum and maximum temperature, and evaporation exhibit an upward trend which are not statistically significant. The fluctuating trend in these climatic variables, though not statistically significant are probably related to the already established changes in climatic parameters in Nigeria. The result also showed that the spatial distributions of public boreholes in the study area are heterogeneous in nature. The study recommended that the clustering of water sources, especially the shallow wells should be discouraged to avoid over abstraction of groundwater in the study area

Heat and mass transfer in a copper oxy-chloride spray reactor for thermochemical hydrogen production

A new predictive model is developed in this paper to analyze the height of the reactor for continuous production of copper oxy-chloride in the thermochemical Cu–Cl cycle for hydrogen production. The volumetric phase fraction is used to develop an energy balance and integrated spatially to determine the inlet temperature of nitrogen and steam mixtures for continuous production of copper oxy-chloride. The effects of the ratio of mixing power to mass of the suspended particle, the ratio of interfacial surface area of the gas film to the volume of liquid, and diameter of the steam/nitrogen bubble in the reactor, on the height of the reactor are reported for a production capacity of 3 kg of hydrogen per day. Results indicate that a smaller ratio of interfacial surface area to volume of liquid significantly reduces the height of the reactor