Electrohydrodynamic Enhancement of Heat Transfer and Mass Transport in Gaseous Media, Bulk Dielectric Liquids and Dielectric Thin Liquid Films

Controlling transport phenomena in liquid and gaseous media through electrostatic forces has brought new important scientific and industrial applications. Although numerous EHD applications have been explored and extensively studied so far, the fast-growing technologies, mainly in the semiconductor industry, introduce new challenges and demands. These challenges require enhancement of heat transfer and mass transport in small scales (sometimes in molecular scales) to remove highly concentrated heat fluxes from reduced size devices. Electric field induced flows, or electrohydrodynamics (EHD), have shown promise in both macro and micro-scale devices. Several existing problems in EHD heat transfer enhancements were investigated in this thesis. Enhancement of natural convection heat transfer through corona discharge from an isothermal horizontal cylindrical tube at low Rayleigh numbers was studied experimentally and numerically. Due to the lack of knowledge about local heat transfer enhancements, Mach-Zehnder Interferometer (MZI) was used for thermal boundary layer visualization. For the first time, local Nusselt numbers were extracted from the interferograms at different applied voltages by mapping the hydrodynamic and thermal field results from numerical analysis into the thermal boundary layer visualizations and local heat transfer results. A novel EHD conduction micropump with electrode separations less than 300 µm was fabricated and investigated experimentally. By scaling down the pump, the operating voltage was reduced one order of magnitude with respect to macro-scale pumps. The pumping mechanism in small-scales was explored through a numerical analysis. The measured static pressure generations at different applied voltages were predicted numerically. A new electrostatically-assisted technique for spreading of a dielectric liquid film over a metallic substrate was proposed. The mechanism of the spreading was explained through several systematic experiments and a simplified theoretical model. The theoretical model was based on an analogy between the Stefan’s problem and current problem. The spreading law was predicted by the theoretical approach and compared with the experimental results. Since the charge transport mechanism across the film depends on the thickness of the film, by continuing the corona discharge exposure, the liquid film becomes thinner and thinner and both hydrodynamic and charge transport mechanisms show a cross-over and causes different regimes of spreading. Four different regimes of spreading were identified. For the first time, an electrostatically accelerated molecular film (precursor film) was reported. The concept of spreading and interfacial pressure produced by a corona discharge was applied to control an impacting dielectric droplet on non-wetting substrate. For the first time, the retraction phase of the impact process was actively suppressed at moderate corona discharge voltages. At higher corona discharge strengths, not only was the retraction inhibited but also the spreading phase continued as if the surface was a wetting surface

Enhancing droplet deposition through in-situ precipitation

Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays

Statistical modeling of the inactivation of spoilage microorganisms during ohmic heating of sour orange juice

To reduce food pathogens, increase shelf life of fruit juices and maintaining bioactive properties preservation technologies as ohmic heating have gained interest. This study sought to investigate the effect of four ohmic resistance variables, temperature (Temp), voltage (V), current (AMP) and electric conductivity (EC), on the population of two yeasts, an ascospore and three fermentative bacteria, by inoculation into sour orange juice. The incidence of the variables was evaluated through different regression models. The results of the simple linear regression (SLR) indicated that Temp, AMP and EC had a significant negative effect on the population of all microorganisms, while V had no effect on the population of any microorganism. The results of the stepwise linear regression (SWLR) showed that, for each microorganism, the variables Temp and AMP were considered to be significant being the only ones included in the model. Temperature had the highest negative effect on the population of each microorganism, explaining more than 87% of the variability of the microorganism. A full quadratic multiple linear regression (FQMLR) model fitted to the dataset such that all significant variables and interactions between variables were considered. Diverse statistical analysis confirmed the goodness of the model.publishe

A hybrid egalitarian bargaining game-DEA and sustainable network design approach for evaluating, selecting and scheduling urban road construction projects

Selecting and scheduling urban road construction projects (URCPs) is inherently an Urban Network Design Problem (UNDP) with a complex decision making process. Recently some studies have focused on sustainable UNDP, using different mathematical methods. In this paper, first a new network data envelopment analysis (NDEA) model has been developed. Then, considering sustainability dimensions, by integrating data envelopment analysis (DEA), game theory and sustainable UNDP, a bi-level model has been proposed for selecting and scheduling URCPs. A meta-heuristic algorithm is proposed to solve the presented bi-level model. Different test instances are solved to show the acceptable performance of proposed algorithm in both solution quality and execution time. Afterwards, the proposed model is applied to study the problem of urban road construction projects selection in a real-world case study of urban transportation network of Isfahan city in Iran. The results show that by applying obtained solution the environmental and social performance of the network has been improved and the performance of the network is almost efficient in all evaluation periods

Visible light guided manipulation of liquid wettability on photoresponsive surfaces

Photoresponsive titania surfaces are of great interest due to their unique wettability change upon ultraviolet light illumination. However, their applications are often limited either by the inability to respond to visible light or the need for special treatment to recover the original wettability. Sensitizing TiO2 surfaces with visible light-absorbing materials has been utilized in photovoltaic applications. Here we demonstrate that a dye-sensitized TiO2 surface can selectively change the wettability towards contacting liquids upon visible light illumination due to a photo-induced voltage across the liquid and the underlying surface. The photo-induced wettability change of our surfaces enables external manipulation of liquid droplet motion upon illumination. We show demulsification of surfactant-stabilized brine-in-oil emulsions via coalescence of brine droplets on our dye-sensitized TiO2 surface upon visible light illumination. We anticipate that our surfaces will have a wide range of applications including microfluidic devices with customizable wettability, solar-driven oil–water clean-up and demulsification technologies

Association between obesity categories with cardiovascular disease and its related risk factors in the MASHAD cohort study population

Background Cardiovascular disease (CVD) is a significant cause of morbidity and mortality globally. Obesity is an important CVD risk factor and is increasing in prevalence. Methods In this study, 3829 men and 5720 women (35‐65 years) were enrolled as part of the MASHAD cohort study. Four categories were identified according to body mass index and waist circumference that was defined by the World Health Organization. Logistic regression analysis was used to determine the adjusted odds ratio (OR) for the occurrence of CVD, and Cox regression model was used to evaluate the association of obesity with CVD incidence. Results We found that the higher risk groups defined by categories of adiposity were significantly related to a higher prevalence of a high serum total cholesterol (TC), and triglycerides (TG), and lower high‐density lipoprotein cholesterol (HDL), and higher fasting blood glucose (FBG) in both genders and a higher low‐density lipoprotein cholesterol (LDL) in women (P < .001). Additionally, a high percentage of participants with dyslipidemia, high LDL, high TC, and low HDL and a high percentage of participants with metabolic syndrome, diabetes, hypertension, and a high serum TG were observed across obesity categories (P < .001). Moreover, women with the very high degrees of obesity had a greater risk of CVD (HR: 1.91, 95% CI: 1.06‐3.43, P = .03). Conclusion Obesity strongly predicts several CVD risk factors. Following 6 years of follow‐up, in individuals within increasing degrees of obesity, there was a corresponding significant increase in CVD events, rising to approximately a twofold higher risk of cardiovascular events in women compared with men

Complications following Bacille Calmette-Guérin Vaccination in Children under the Age of 18 Months: A Multi-center Study

Background: The BCG vaccine, used since 1921 to prevent tuberculosis (TB), considered the world's most widely used vaccine. This study aimed to investigate the frequency and the type of complications associated with Bacillus Calmette-Guérin (BCG) vaccination in Iranian children. Materials and Methods This cross-sectional study conducted for 6months among children aged up to 18 months who presented to primary health care centers in Tehran (under supervision of all three Medical Universities of Tehran) for their routine vaccinations. All children had received BCG vaccination at birth. We investigated the occurrence of BCG complications through history taking from the parents and physical examination by the study physician. Complications categorized into four major groups: local, regional, remote, and generalized and the rate of occurrence compared between the two genders. Results: Finally, 14,095 children enrolled during the study period; 574 patients (4%) had experienced at least one complication following BCG vaccination. The most common complications were local side effects observed in 304 children (2.1%); followed by lymph node involvement detected in 270 children (1.9%). Lymph node involvement was more common in males (

Evaluation of Human Papilloma Virus Infection in Patients with Esophageal Squamous Cell Carcinoma from the Caspian Sea Area, North of Iran

Introduction: HPV has been found repeatedly in esophageal squamous cell carcinoma (ESCC) tissues. However, reported detection rates of HPV DNA in these tumors have varied markedly. Differences in detection methods, sample types, and geographic regions of sample origin have been suggested as potential causes of variation. We have reported that infection of HPV DNA in ESCC tumors depends on anatomical sites of esophagus of the patients from Mazandaran, north of Iran. Materials and Methods: HPV DNA was examined in 46 upper, 69 middle and 62 lower third anatomical sites of esophageal squamous cell carcinoma specimens collected from Mazandaran province in north Iran, near the Caspian Littoral as a region with high incidence of ESCC. HPV L1 DNA was detected using Qualitative Real time PCR and MY09/MY11 primers. Results: 28.3% of upper, 29% of middle and 25.8% of lower third of ESCC samples were positive for HPV DNA. 13.6% for males and 14.1% for females were HPV positive in all samples. Conclusions: HPV infection is about one third of ESCC in this area. Findings in this study increase the possibility that HPV is involved in esophageal carcinogenesis. Further investigation with a larger sample size is necessary