Gary Rosengarten

Nanofluid-based direct absorption solar collector

Solar energy is one of the best sources of renewable energy with minimal environmental impact. Direct absorption solar collectors have been proposed for a variety of applications such as water heating; however the efficiency of these collectors is limited by the absorption properties of the working fluid, which is very poor for typical fluids used in solar collectors. It has been shown that mixing nanoparticles in a liquid (nanofluid) has a dramatic effect on the liquid thermophysical properties such as thermal conductivity. Nanoparticles also offer the potential of improving the radiative properties of liquids, leading to an increase in the efficiency of direct absorption solar collectors. Here we report on the experimental results on solar collectors based on nanofluids made from a variety of nanoparticles (carbon nanotubes, graphite, and silver). We demonstrate efficiency improvements of up to 5% in solar thermal collectors by utilizing nanofluids as the absorption mechanism. In addition the experiment...

Computational fluid dynamics for the assessment of upper airway response to oral appliance treatment in obstructive sleep apnea

Mandibular advancement splints (MAS), which protrude the lower jaw during sleep, are recognized as an effective treatment for obstructive sleep apnea (OSA) through their action of enlarging the airway space and preventing upper airway collapse. However a clinical challenge remains in preselecting patients who will respond to this form of therapy. We aimed to use computational fluid dynamics (CFD) in conjunction with patient upper airway scans to understand the upper airway response to treatment. Seven OSA patients were selected based on their varied treatment response (assessed by the apnea-hypopnoea index (AHI) on overnight polysomnography). Anatomically-accurate upper airway computational models were reconstructed from magnetic resonance images with and without MAS. CFD simulations of airflow were performed at the maximum flow rate during inspiration. A physical airway model of one patient was fabricated and the CFD method was validated against the pressure profile on the physical model. The CFD analysis clearly demonstrated effects of MAS treatment on the patients UA airflow patterns. The CFD results indicated the lowest pressure often occurs close to the soft palate and the base of the tongue. Percentage change in the square root of airway pressure gradient with MAS (Δsqrt(ΔP(Max))%) was found to have the strongest relationship with treatment response (ΔAHI%) in correlation analysis (r=0.976, p=0.000167). Changes in upper airway geometry alone did not significantly correlate with treatment response. We provide further support of CFD as a potential tool for prediction of treatment outcome with MAS in OSA patients without requiring patient specific flow rates.

Analysis of horizontal mantle heat exchangers in solar water heating systems

Abstract The characteristics of horizontal mantle heat exchangers are investigated for application in thermosyphon solar water heaters. An experimental model of a horizontal mantle heat exchanger was used to evaluate the flow patterns in the annular passageways and the heat transfer into the inner tank. Flow visualisation was used to investigate the flow structure, and the heat transfer was measured for isothermal inner tank conditions. A numerical model of the flow and heat transfer in the annular passageway was developed and used to evaluate the heat flux distribution over the surface of the inner tank. The numerical results indicate that configurations of mantle heat exchangers used in current solar water heater applications degrade thermal stratification in the inner tank. The effects of inlet flow rate, temperature and connecting port location are quantified.

Simulation of upper airway occlusion without and with mandibular advancement in obstructive sleep apnea using fluid-structure interaction.

Obstructive Sleep Apnea (OSA) is a common sleep disorder characterized by repetitive collapse of the upper airway (UA). One treatment option is a mandibular advancement splint (MAS) which protrudes the lower jaw, stabilizing the airway. However not all patients respond to MAS therapy and individual effects are not well understood. Simulations of airway behavior may represent a non-invasive means to understand OSA and individual treatment responses. Our aims were (1) to analyze UA occlusion and flow dynamics in OSA using the fluid structure interaction (FSI) method, and (2) to observe changes with MAS. Magnetic resonance imaging (MRI) scans were obtained at baseline and with MAS in a known treatment responder. Computational models of the patients UA geometry were reconstructed for both conditions. The FSI model demonstrated full collapse of the UA (maximum 5.83mm) pre-treatment (without MAS). The UA collapse was located at the oropharynx with low oropharyngeal pressure (-51.18Pa to -39.08Pa) induced by velopharyngeal jet flow (maximum 10.0m/s). By comparison, simulation results from the UA with MAS, showed smaller deformation (maximum 2.03mm), matching the known clinical response. Our FSI modeling method was validated by physical experiment on a 1:1 flexible UA model fabricated using 3D steriolithography. This is the first study of airflow dynamics in a deformable UA structure and inspiratory flow. These results expand on previous UA models using computational fluid dynamics (CFD), and lay a platform for application of computational models to study biomechanical properties of the UA in the pathogenesis and treatment of OSA.

Planar microfluidic chamber for generation of stable and steep chemoattractant gradients.

The extracellular availability of growth factors, hormones, chemokines, and neurotransmitters under gradient conditions is required for directional cellular responses such as migration, axonal pathfinding, and tissue patterning. These responses are, in turn, important in disease and developmental processes. This article addresses critical barriers toward devising a chemotaxis assay that is broadly applicable for different kinds of cancer cells through the design of a microfluidic chamber that produces a steep gradient of chemoattractant. Photolithography was used to create microchannels for chemoattractant delivery, flow diversion barriers/conduits, and small outlets in the form of apertures. The 1-microm apertures were made at the active surface by uncapping a thin (1.5 microm) layer of AZ1518. This process also created a vertical conduit that diverted the flow such that it occurred perpendicularly to the active, experimental surface where the gradients were measured. The other side of the vertical conduit opened to underlying 20-microm deep channels that carried microfluidic flows of tracer dyes/growth factors. Modeled data using computational fluid dynamics produced gradients that were steep along the horizontal, active surface. This simulation mirrors empirically derived gradients obtained from the flow analyses of fluorescent compounds. The open chamber contains a large buffer volume, which prevents chemoattractant saturation and permits easy cell and compound manipulation. The technique obviates the use of membranes or laminar flow that may hinder imaging, rinsing steps, cell seeding, and treatment. The utility of the chamber in the study of cell protrusion, an early step during chemotaxis, was demonstrated by growing cancer cells in the chamber, inducing a chemoattractant gradient using compressed air at 0.7 bar, and performing time-lapse microscopy. Breast cancer cells responded to the rapidly developed and stable gradient of epidermal growth factor by directing centroid positions toward the gradient and by forming a leading edge at a speed of 0.45 microm/min.

Microwell perfusion array for high-throughput, long-term imaging of clonal growth

Continuous cell tracking by time-lapse microscopy has led to detailed study of cell differentiation pathways using single cell fate maps. There are a multitude of cell fate outcomes, so hundreds of clonal division histories are required to measure these stochastic branching processes. This study examines the principle of condensing cell imaging information into a relatively small region to maximize live cell imaging throughput. High throughput clonal analysis of non-adherent cells by continuous live cell tracking was possible using a microwell perfusion array with an internal volume of 16u2009μl and 600 microwells at the base. This study includes examination of biocompatibility of buffer systems, connecting tubing, cell culture substrates, and media degradation. An intermittent perfusion protocol was selected for long-term time-lapse imaging of KG1a cells in the microwell array; 1500 clones were simultaneously cultured and scanned every 3u2009min at 100u2009×u2009magnifications for 6 days. The advantages of perfusion microwell culture are continuous long-term cell tracking, higher cell imaging throughput, and greater control over cell microenvironment. Microwell devices facilitate high throughput analysis of cell lineage development and measurement of the probability distribution for cell life events such as mitosis.

Mantle heat exchangers for horizontal tank thermosyphon solar water heaters

This paper describes the characteristics of horizontal mantle heat exchangers for application in thermosyphon solar water heaters. A new correlation for heat transfer in horizontal mantle heat exchangers with bottom entry and exit ports was used to predict the overall heat transfer and stratification conditions in horizontal tanks with mantle heat exchangers. The model of a mantle heat exchanger tank was combined with the thermosyphon solar collector loop model in TRNSYS to develop a model of a thermosyphon solar water heater with collector loop heat exchanger. Predictions of stratification conditions in a horizontal mantle tank are compared with transient charging tests in a laboratory test rig. Predictions of daily energy gain in solar preheaters and in systems with in-tank auxiliary boosters are compared with extensive outdoor measurements and the model is found to give reliable results for both daily and long-term performance analysis.

CRITICAL REVIEW OF THE NOVEL APPLICATIONS AND USES OF NANOFLUIDS

Nanofluids — one simple product of the emerging world nanotechnology — where nanoparticles (nominally 1–100 nm in size) are mixed with conventional base fluids (water, oils, glycols, etc.). Nanofluids have seen enormous growth in popularity since they were proposed by Choi in 1995 [1]. In the year 2010 alone there were nearly 500 research articles where the term nanofluid was used in the title, showing rapid growth from 2000 (12) and 2005 (78). Much of the first decade of nanofluid research was focused on measuring and modeling fundamental thermophysical properties of nanofluids (thermal conductivity, density, viscosity, convection coefficients). Recent research, however, has started to highlight how nanofluids might perform in a wide variety of other applications. These applications range from their use in nanomedicine [2] to their use as solar energy harvesting media [3]. By analyzing the available body of research to date, this article presents trends of where nanofluid research is headed and suggests which applications may benefit the most from employing nanofluids. Overall, this review summarizes the novel applications and uses of nanofluids while setting the stage for future nanofluid use in industry.Copyright

Structural and hydrodynamic simulation of an acute stenosis-dependent thrombosis model in mice

Platelet activation under blood flow is thought to be critically dependent on the autologous secretion of soluble platelet agonists (chemical activators) such as ADP and thromboxane. However, recent evidence challenging this model suggests that platelet activation can occur independent of soluble agonist signalling, in response to the mechanical effects of micro-scale shear gradients. A key experimental tool utilized to define the effect of shear gradients on platelet aggregation is the murine intravital microscopy model of platelet thrombosis under conditions of acute controlled arteriolar stenosis. This paper presents a computational structural and hydrodynamic simulation of acute stenotic blood flow in the small bowel mesenteric vessels of mice. Using a homogeneous fluid at low Reynolds number (0.45) we investigated the relationship between the local hydrodynamic strain-rates and the severity of arteriolar stensosis. We conclude that the critical rates of blood flow acceleration and deceleration at sites of artificially induced stenosis (vessel side-wall compression or ligation) are a function of tissue elasticity. By implementing a structural simulation of arteriolar side wall compression, we present a mechanistic model that provides accurate simulations of stenosis in vivo and allows for predictions of the effects on local haemodynamics in the murine small bowel mesenteric thrombosis model.

Some aspects concerning modelling the flow and heat transfer in horizontal mantle heat exchangers in solar water heaters

An experimental and numerical investigation has been undertaken to study the heat transfer process in horizontal mantle heat exchangers used in solar water heaters. A rectangular cavity has been used as a simplified geometry. With the aid of particle image velocimetry (PIV) the flow field in the centre-plane of the rectangular cavity has been visualized. Three-dimensional flow simulations were performed using a commercial CFD package. The impinging jet formed by the inlet flow directed towards the opposite wall was found to produce localised turbulence in the cavity, with an inlet Reynolds number as low as 360. This turbulence was found to effect the flow field and heat transfer in the cavity when the inlet Reynolds number was above 1200. It is shown that, with the boundary conditions used in this study, most of the heat transferred was in the bottom half of the cavity. This is not the ideal situation for optimization of solar water heating systems. Copyright