Advanced thermal models for improved design of counter flow microchannel heat exchangers

Theoretical models of counter flow microchannel heat exchangers subjected to scaling and secondary effects are developed in this dissertation. The scaling effects studied include axial heat conduction and viscous dissipation, while the secondary effects considered in this dissertation is that of external heat transfer via heat flux and temperature. The theoretical models developed are one-dimensional and consist primarily of ordinary governing equations that describe the axial variation of hot and cold fluid. For the case of axial heat conduction, the axial variation of wall temperature is also modeled. The models are dependent on various factors, such as Reynolds number, Prandtl number, microchannel hydraulic diameter, microchannel length, microchannel profile, substrate spacing, thermal conductivities of the fluids and wall, and fluid inlet temperature difference. The individual effect of all these parameters with respect to each of the scaling and secondary effects is studied using each model. The governing equations are solved using numerical method, specifically finite difference method. Studies are done for Reynolds number between 1 and 1500 for thermal models on axial heat conduction, and external heat transfer. On the other hand, the Reynolds number for the model studying viscous dissipation is varied between 1 and 1000. The effect of Prandtl number on the models is analyzed using air, ethylene glycol and water. The influence of profile on the thermal performance of microchannel heat exchanger is studied using rectangular, trapezoidal and triangular microchannels. The aspect ratio of rectangular microchannels is varied between 1 and 0.125, while that of trapezoidal microchannels considered are 0.5, 0.25 and 0.125. Only one aspect ratio for triangular microchannels is considered in this study due to the manufacturing constraints on silicon based microchannel heat exchangers. It is 1.414. The effect of microchannel hydraulic diameter is studied for hydraulic diameter of 100µm, 200µm and 300µm for all models except that for viscous dissipation. For the model analyzing viscous dissipation, the influence of hydraulic diameter is studied using microchannels with hydraulic diameter of 200µm, 300µm and 400µm. The effect of substrate spacing for all models is analyzed by varying this parameter is between 100µm and 300µm in increments of 100µm. The length is varied between 2.54cm to 5.08cm to 7.62cm in order to study the effect of length on the thermal performance of microchannel heat exchangers of each model. The effect of difference between the inlet temperatures of the fluids on the model is also studied primarily for temperature differences of 25°C, 50°C, and 75°C. All these effects except viscous dissipation are prominent at low Reynolds numbers; at high Reynolds numbers these effects have little influence on the effectiveness of the fluids. Viscous dissipation, is influential at high Reynolds numbers rather than at low Reynolds numbers. In addition it is observed from the solutions of the models that all these effects have the strongest influence on gases rather than on liquids. Based on the analysis of solutions, it can be generalized that square microchannels have the best performance between rectangular, trapezoidal and triangular microchannels under similar operating conditions

Wax Deposition in Crude Oil Transport Lines and Wax Estimation Methods

Petroleum industry is one of the major industries serving the energy demands. Flow assurance is essential for providing continuous fuel supply. Wax deposition is the main issue that affects flow assurance or reduces the efficiency of transporting crude oil. As the maintenance cost of repairing and troubleshooting is very high, addressing issues related to flow assurance becomes critical in the petroleum industry. This chapter will explore methods used for reducing, cleaning, and monitoring deposition of wax. Wax dissolved in the crude oil gets crystallized causing accumulation across the pipe walls once the bulk temperature of the crude oil gets lower than wax appearance temperature (WAT). Mechanical, thermal, chemical, and microbial methods highlighting general practice in the industry are discussed in this chapter. Next, the direct techniques providing information about the numerical wax deposition models used along with scientific measurement techniques are emphasized. Later, the indirect measurement techniques are discussed providing information about the external probing and nondestructive techniques to obtain information about wax layer deposition inside the pipe. The role of artificial intelligence and use of fuzzy logic for effective wax prediction or in developing the existing wax numerical models are emphasized in the last section

Solar Desalination

There is an increasing demand for advancing conventional desalination technologies and developing novel solar powered desalination processes. In this chapter, the use of solar powered thermal desalination will be discussed comprehensively. The different existing methods of solar energy utilization for seawater desalination will be discussed, which includes solar stills, solar powered humidification-dehumidification (HDH) desalination, solar diffusion driven desalination, solar membrane distillation, concentrated solar power (CSP) based desalination, and solar pond distillation. The advantages and limitations of these thermal desalination technology will be discussed. In addition, the environmental impacts of solar desalination will be discussed due to its importance for adoption

Tracheal suctioning improves gas exchange but not hemodynamics in asphyxiated lambs with meconium aspiration.

BackgroundCurrent neonatal resuscitation guidelines recommend tracheal suctioning of nonvigorous neonates born through meconium-stained amniotic fluid.MethodsWe evaluated the effect of tracheal suctioning at birth in 29 lambs with asphyxia induced by cord occlusion and meconium aspiration during gasping.ResultsTracheal suctioning at birth (n = 15) decreased amount of meconium in distal airways (53 ± 29 particles/mm(2) lung area) compared to no suction (499 ± 109 particles/mm(2); n = 14; P < 0.001). Three lambs in the suction group had cardiac arrest during suctioning, requiring chest compressions and epinephrine. Onset of ventilation was delayed in the suction group (146 ± 11 vs. 47 ± 3 s in no-suction group; P = 0.005). There was no difference in pulmonary blood flow, carotid blood flow, and pulmonary or systemic blood pressure between the two groups. Left atrial pressure was significantly higher in the suction group. Tracheal suctioning resulted in higher Pao2/FiO2 levels (122 ± 21 vs. 78 ± 10 mm Hg) and ventilator efficiency index (0.3 ± 0.05 vs.0.16 ± 0.03). Two lambs in the no-suction group required inhaled nitric oxide. Lung 3-nitrotyrosine levels were higher in the suction group (0.65 ± 0.03 ng/µg protein) compared with the no-suction group (0.47 ± 0.06).ConclusionTracheal suctioning improves oxygenation and ventilation. Suctioning does not improve pulmonary/systemic hemodynamics or oxidative stress in an ovine model of acute meconium aspiration with asphyxia

The Mere Forecasting Effect: How Focusing on the Future Influences Current Attitudes

The present research seeks to demonstrate that future experience, elicited by anticipating one's future affective experience with a product, can influence current product attitudes. Our claim is that the mere act of forecasting one's future affective experience can alter current evaluations of a product, often irrespective of the future attitude itself. We provide evidence that forecasting can influence current attitudes through two separate routes. First, focusing on the future increases the salience of distal information. As a result, this information is disproportionately weighted when participants consider their current attitudes. Second, even if one's anticipated future attitude is non-diagnostic (no different than the current attitude), we find evidence that the process or act of contemplating one's future experience with a product can impact current judgments through a meta-cognitive route. [to cite]

Rickettsial Seroepidemiology among Farm Workers, Tianjin, People’s Republic of China

High seroprevalence rates for Anaplasma phagocytophilum (8.8%), Coxiella burnetii (6.4%), Bartonella henselae (9.6%), and Rickettsia typhi (4.1%) in 365 farm workers near Tianjin, People’s Republic of China, suggest that human infections with these zoonotic bacteria are frequent and largely unrecognized. Demographic features of seropositive persons suggest distinct epidemiology, ecology, and risks

The Influence Of Maternal Infections On Congenital Heart Defect

ABSTRACT Congenital heart defects (CHDs) contribute significantly to heightened infant mortality rates. This review explores the intricate link between maternal infections and CHDs, emphasizing diverse factors influencing fetal development, such as bacterial, fungal, protozoan and viral agents. These infections pose reproductive health risks, potentially leading to complications like prematurity, stillbirth and heart defect to the fetus. The TORCH acronym (Toxoplasma, Other infections, Rubella, Cytomegalovirus, Herpes simplex) identifies infectious teratogens related to congenital issues, emphasizing vertical transmission through the placenta or ascending from the vagina. Rubella and Cytomegalovirus play a significant role in heart defects, particularly when maternal infections amplify CHD risk during pregnancy. Specific scrutiny is placed on Rubella and Cytomegalovirus for their impact on pregnancy outcomes and potential links to congenital heart defects, with preventive strategies discussed, including vaccination and antiviral therapy. The timing and severity of these infections are pivotal in determining their impact on fetal heart development. Environmental exposures and maternal nutrition are critical factors influencing fetal development. Maternal undernutrition in low- and middle-income countries associates with adverse pregnancy outcomes, including congenital heart defects. Emphasizing the importance of maintaining a nutritious maternal diet, rich in essential nutrients, is crucial for improved fetal health and successful pregnancy outcomes. This review offers insights into preventive measures and underscores the need for continued research to enhance prenatal care strategies

Nature and mental health: An ecosystem service perspective

A growing body of empirical evidence is revealing the value of nature experience for mental health. With rapid urbanization and declines in human contact with nature globally, crucial decisions must be made about how to preserve and enhance opportunities for nature experience. Here, we first provide points of consensus across the natural, social, and health sciences on the impacts of nature experience on cognitive functioning, emotional well-being, and other dimensions of mental health. We then show how ecosystem service assessments can be expanded to include mental health, and provide a heuristic, conceptual model for doing so