Malay K. Mazumder

Effects of Electrostatic Charging on Pharmaceutical Powder Blending Homogeneity

During the pharmaceutical powder blending process, electrostatic charges generate and accumulate unavoidably due to particle-particle and particle-wall collision. The effect of electrostatic charging on pharmaceutical powder blending homogeneity was investigated on two binary blending systems: (1) lactose as an excipient with caffeine as an Active Pharmaceutical Ingredient (API) and (2) Micro-crystalline Cellulose (MCC) with caffeine. Three different blending procedures were conducted: (1) conventional blending without any charge control, (2) blending with simultaneous charge neutralization, and (3) blending combined with a corona charging process. It was found that the average API concentration variation increases with the increase of charge-to-mass ratio of final blend samples. In other words, the presence of uncontrolled electrostatic charges has an adverse effect on powder blend uniformity. Elimination or minimization of electrostatic charges also appears to have a negative impact on powder blend uniformity. In contrast, blending of positively charged excipient material and negatively charged API material leads to a better blend uniformity. The controlled electrostatic charging opens an opportunity for improving uniformity of the pharmaceutical blending process.

Characterization of Electrodynamic Screen Performance for Dust Removal from Solar Panels and Solar Hydrogen Generators

The direct solar energy conversion in gigawatt scales by photovoltaic, photothermal, and photoelectrochemical processes is of national and global importance in meeting energy needs. Dust depositions on solar panels and solar concentrators cause efficiency loss from 10% to 30% depending upon the surface mass concentration of dust requiring manual cleaning with water. Such a cleaning process is expensive for large-scale installations where water is scarce. Transparent electrodynamic screens, consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film, can be used for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated by phased voltage, the dust particles on the surface of the film become electrostatically charged and are removed by the traveling wave generated by applied electric field. Over 90% of deposited dust is removed within 2 min, using a very small fraction of the energy produced by the panels. No water or mechanical movement is involved. An analysis of the electrodynamic removal mechanisms based on electrostatic and dielectrophoretic forces opposed by the adhesion forces due to van der Waals and image forces is presented.

Characterization of electrodynamic screen performance for dust removal from solar panels and solar hydrogen generators

The direct solar energy conversion in gigawatt scales by photovoltaic, photothermal, and photoelectrochemical processes is of national and global importance in meeting energy needs. Dust depositions on solar panels and solar concentrators cause efficiency loss from 10% to 30% depending upon the surface mass concentration of dust requiring manual cleaning with water. Such a cleaning process is expensive for large-scale installations where water is scarce. Transparent electrodynamic screens, consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film, can be used for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated by phased voltage, the dust particles on the surface of the film become electrostatically charged and are removed by the traveling wave generated by applied electric field. Over 90% of deposited dust is removed within 2 min, using a very small fraction of the energy produced by the panels. No water or mechanical movement is involved. An analysis of the electrodynamic removal mechanisms based on electrostatic and dielectrophoretic forces opposed by the adhesion forces due to van der Waals and image forces is presented.

Mitigation of soiling losses in concentrating solar collectors

The adverse impact of soiling (dust deposition) on solar collectors, and the mitigation of the related energy yield losses, are the main scopes of this paper. While soiling related losses have been studied more extensively for flat-plate photovoltaic (PV) panels, this study focuses primarily on the impact of dust accumulation on concentrated photovoltaic (CPV) and concentrated solar power (CSP) systems. We report on different methods used for cleaning solar collectors: (i) natural cleaning by rain and snowfall, (ii) manual cleaning by water and detergent, and (iii) an emerging method of dust removal by electrodynamic screens (EDS). Development of EDS technology as an automated, low-cost dust removal method which does not require any water or manual labor is presented.

Development of Self-Cleaning Solar Collectors for Minimizing Energy Yield Loss Caused by Dust Deposition

Concentrated Solar Power (CSP) systems used for photothermal conversion of solar energy to electricity are capable of meeting a large fraction of the global energy requirements. CSP plants are inherently robust with respect to the availability of materials, technology, and energy storage. However, dust depositions on solar collectors cause energy yield loss annually, ranging from 10 to 50% depending upon their location in the semi-arid and desert lands. Mitigation of energy loss requires manual cleaning of solar mirrors with water. A brief review of the soiling related losses in energy yield of the CSP plants is presented, which shows that cleaning of the CSP mirrors and receivers using water and detergent is an expensive and time-consuming process at best and is often impractical for large-scale installations where water is scarce. We report here our research effort in developing an electrodynamic dust removal technology that can be used for keeping the solar collectors clean continuously without requiring water and manual labor. Transparent electrodynamic screens (EDS), consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film can be integrated on the front surface of the mirrors and on the receivers for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated, over 90% of the deposited dust is removed. A summary of the current state of prototype development and evaluation of EDS integrated solar mirrors and experimental data on the removal of desert dust samples are presented. A brief analysis of cost-to-benefit ratio of EDS implementation for automated dust removal from large-scale solar collectors is included.Copyright

Modeling of Trajectories in an Electrodynamic Screen for Obtaining Maximum Particle Removal Efficiency

An electrostatic self-cleaning panel for solar collectors is described. An electrodynamic screen (EDS) is formed by interdigitated transparent surface electrodes energized by three-phase low-frequency ac voltages in the range of 5-200 Hz and 500-1000 V. The resulting electrostatic field wave exerts force on the particles and sweeps them laterally across the panel. Particle trajectories are simulated to help ascertain parameters for maximum dust-removal efficiency. The electric field of the EDS is found by a Fourier expansion of Laplaces equation solutions for a surface potential that is periodic in space and time. Trajectories are found for particles of various sizes and charges and for different electrode spacings and excitations. Computed trajectories are compared qualitatively to experimental observations. One unexpected result is the chaotic behavior of larger particles which jump sporadically back and forth and only slowly migrate in the direction of the imposed electrostatic surface wave.

Modeling of trajectories in an electrodynamic screen for obtaining maximum particle removal efficiency

An electrostatic self-cleaning panel for solar collectors is described. An electrodynamic screen (EDS) is formed by interdigitated transparent surface electrodes energized by three-phase low-frequency ac voltages in the range of 5-200 Hz and 500-1000 V. The resulting electrostatic field wave exerts force on the particles and sweeps them laterally across the panel. Particle trajectories are simulated to help ascertain parameters for maximum dust-removal efficiency. The electric field of the EDS is found by a Fourier expansion of Laplaces equation solutions for a surface potential that is periodic in space and time. Trajectories are found for particles of various sizes and charges and for different electrode spacings and excitations. Computed trajectories are compared qualitatively to experimental observations. One unexpected result is the chaotic behavior of larger particles which jump sporadically back and forth and only slowly migrate in the direction of the imposed electrostatic surface wave.

Performance Analysis of Electrodynamic Screens Based on Residual Particle Size Distribution

Dust accumulation on the optical surfaces of solar collectors causes significant losses in their energy yield. Fine dust particles, compared with coarse ones, contribute significantly more in the performance loss, assuming identical surface mass concentration. This study examines the performance of different electrodynamic screen (EDS) prototypes, operated under different conditions, in removing fine dust particles in the laboratory environment. After going through several cycles of dust deposition and cleaning using EDS, the dust residue left on each EDS prototype is collected and analyzed using a Horiba particle size distribution (PSD) analyzer. The PSD analyses determine which EDS design has performed superior in removing a given size range and in which operational condition. The results are advantageous in the optimization procedure of EDS to attain maximum dust removal efficiency and minimum optical interference.

Electrodynamic removal of dust from solar mirrors and its applications in concentrated solar power (CSP) plants

Concentrating Solar Power (CSP) systems based on parabolic trough and power tower technologies provide inherent advantage of energy storage and high efficiency for utility-scale solar plants. The specular reflectance efficiency of the solar mirrors plays a critical role in the efficiency of electric power generation. The deposition of atmospheric dust on the surface of the mirrors reduces its reflectance efficiency and requires frequent cleaning to avoid energy-yield loss. Electrodynamic screen (EDS) can provide an efficient method for maintaining the specular reflectivity above 90% by removing the deposited dust particles. In this paper, we briefly review (1) electrostatic charging mechanisms involved in EDS, (2) optimization of EDS for high dust removal efficiency, and (3) minimization of cleaning cost and water consumption. Prototype EDS-integrated solar mirrors were produced and tested in an environmental test chambers simulating desert atmospheres. The test results show that frequent removal of dust layer can maintain the specular reflectivity of the mirrors above 90% subjected to dust deposition ranging from 0 to 10 g/m2.

Environmental degradation of the optical surface of PV modules and solar mirrors by soiling and high RH and mitigation methods for minimizing energy yield losses

Utility-sale solar plants are mostly installed in semi-arid and desert lands and are subjected to high dust deposition rate. Dust layer build up on solar collectors causes major energy-yield loss. Maintaining designed plant capacities requires more than 90% efficiency of light transmission or specular reflection for PV modules and CSP mirrors, respectively. The combinations of high relative humidity (RH), high surface temperature, and long residence time of the dust on the optical surface degrades the solar collectors over time. A tenacious mud like coating is formed, which strongly adheres to the PV modules and concentrating mirrors and requires scrub cleaning. If the global solar-power output is to increase from current GW levels to the TW level, as is envisioned, the water cleaning process would result in an unsustainable demand for water. This paper provide a brief review of the application of an emerging technology of transparent electrodynamic screen (EDS) for removing dust, as frequently as needed, from the solar collectors without water. Power output efficiency is maintained greater than 90% compared to that of the panel under clean conditions. Dust removal efficiency (DRE) is more than 90% with test dust samples obtained from different arid zones and energy consumption for EDS operation is less than 0.03 Wh/m2/cleaning cycle. The method is water-free and provides easy retrofitting onto existing panels and has a high potential for a cost-effective large-scale roll-to-roll production, commercial application, and a significant reduction of operation and maintenance costs.