A Comparative Analysis of the Tumor Pathology and the Metabolic Heat Generation of Growing Malignant Tumors

Cancer is one of the most debilitating diseases in the world, affecting over 9.6 million people worldwide every year. Breast cancer remains the second largest cause of death in women. Despite major advances in treatment, over 40,920 women died of breast cancer in 2018 in the United States alone. Early detection of abnormal masses can be crucial for diagnosis and dramatically increase survival. Current screening techniques have varying accuracy and perform poorly when used on heterogeneously and extremely dense breast tissue. Infrared imaging has the potential to detect growing tumors within the breast based on thermal signatures on the breast surface by imaging temperature gradients induced by blood perfusion and tumor metabolic activity. Using clinical patient images, previous methods to estimate tumor properties involve an iterative algorithm to estimate the tumor position and diameter. The details from the MRI are used in estimating the volumetric heat generation rate. This is compared with the published values and the reasons for differences are investigated. The tumor pathology is used in estimating the expected growth rate and compared with the predicted values. The correlation between the tumor characteristics and heat generation rate is fundamental information that is needed in accurately predicting the tumor size and location.

Flow Boiling on Heterogeneous Wetting Surface in a Vertical Narrow Microchannel

The micro structured surfaces have significant impact on the flow patterns and heat transfer mechanisms during the flow boiling process. The hydrophobic surface promotes bubble nucleation while the hydrophilic surface supplies liquid to a heating surface, thus there is a trade-off between a hydrophobic and a hydrophilic surface. To examine the effect of heterogeneous wetting surface on flow boiling process, an experimental investigation of flow boiling in a rectangular vertical narrow microchannel with the heterogeneous wetting surface was conducted with deionized water as the working fluid. The heat transfer characteristics of flow boiling in the microchannel was studied and the flow pattern was photographed with a high-speed camera. The onset of flow boiling and heat transfer coefficient were discussed with the variation of heatfluxes and mass fluxes, the trends of which were analyzed along with the flow patterns. During the boiling process, the dominated heat transfer mechanism was nucleate boiling, with numerous nucleate sites between the hydrophilic/hydrophobic stripes and on the hydrophobic ones. In the meantime, after the merged bubbles were constrained by the channel walls, it would be difficult for them to expand towards upstream since they were restricted by the contact line between hydrophilic/hydrophobic stripes, thereby reduce the flow instability and achieve remarkable heat transfer performance.

Heat Transfer and Fouling Performance During Falling Film Evaporation in Vertical Porous Tubes

An experimental investigation was conducted on falling film evaporation along two porous tubes, which were sintered by stainless-steel powder with a diameter of 0.45 and 1 um, respectively. The test section is a 2 m long sintered tube with an outer diameter of 25 mm and a wall thickness of 2 mm. During the experiment, the pressure inside the tube was maintained at 1 atm, the inlet temperature was 373 K, and mass flux ranged from 0.51 to 1.36 kg/ (m s). Conditions of the steam outside the pipe, which was the heat source, were fixed, while the fouling tests were carried out at a constant mass flow of 0.74 kg/ (m s) using high-concentration brine as work fluid. The overall heat transfer coefficient under different working conditions was tested and compared with the stainless steel smooth tube of the same dimensions. The heat transfer coefficient of the two porous stainless tubes are about 35% and 20% lower than that of the smooth one, showing an inferior effect because the steam in the pores of the pipe wall during the infiltration process will reduce the heat conductivity. The heat transfer coefficient of the smooth tube deteriorated severely due to the deposition of calcium carbonate, which had little effect on the sintered tubes. Besides, the fouling weight of porous tubes is 2.01 g and 0 g compared with 5.52 g of the smooth tube.

Active High-Throughput Micromixer Using Injected Magnetic Mixture Underneath Microfluidic Channel

Microfluidics has a lot of applications in fields ranging from pharmaceutical to energy, and one of the major applications is micromixers. A challenge faced by most micromixers is the difficulty in mixing within micro-size fluidic channels because of the domination of laminar flow in a small channel. Hence, magnetic field generated by permanent magnets and electromagnets have been widely used to mix ferrofluids with other sample fluids on a micro level. However, permanent magnets are bulky, and electromagnets produce harmful heat to biological samples; both properties are detrimental to a microfluidic chip’s performance. Taking these into consideration, this study proposes rapid mixing of ferrofluid using a two-layer microfluidic device with microfabricated magnet. Two microfluidic chips that consist of microchannels and micromagnets respectively are fabricated using a simple and low-cost soft lithography method. The custom-designed microscale magnet consists of an array of stripes and is bonded below the plane of the microchannel. The combination of the planar location and angle of the array of magnets allow the migration of ferrofluids, hence mixing it with buffer flow. Parametric studies are performed to ensure comprehensive understanding, including the angle of micro-scale magnets with respect to the fluidic channels, total flow rate and density of the array of magnets. The result from this study can be applied in chemical synthesis and pre-processing, sample dilution, or inducing reactions between samples and reagent.

Effects of Taper Configurations on Heat Transfer and Pressure Drop in Single-Phase Flows in Microgaps

This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created on a plain heated copper surface with a polysulfone cover that was either uniform or tapered with an angle of 3.4°. The average gap height was 400 microns and the length and width dimensions were 10 mm × 10 mm, resulting in an average hydraulic diameter of approximately 800 microns for all configurations. Experiments were conducted at atmospheric pressure and the inlet temperature was set to 30 °C. Heat transfer and pressure drop data were acquired for flow rates varying from 57 to 485 ml/min and the surface temperature was monitored not to exceed 90 °C to avoid bubble nucleation, so the heat flux varied from 35 to 153 W/cm2 depending on the flow rate. The uniform configuration resulted in the lowest pressure drop, and the diverging one showed slightly higher pressure drop values than the converging configuration, possibly because the flow is most constrained at the inlet section, where the fluid is colder and presents higher viscosity. In addition, a minor dependence of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in converging gaps, which compensates the decrease in temperature difference between the fluid and the surface due to fluid heating along the gap. Overall, the comparison between the three configurations shows that converging microgaps have better performance than uniform or diverging ones for single-phase flows, and such effect is more pronounced at lower flow rates, when the fluid experiences higher temperature changes.

Contact Line Pinning and Depinning Prior to Rupture of an Evaporating Droplet in a Simulated Soil Pore

Altering soil wettability by inclusion of hydrophobicity could be an effective way to restrict evaporation from soil, thereby conserving water resources. In this study, 4-μL sessile water droplets were evaporated from an artificial soil millipore comprised of three glass (i.e. hydrophilic) and Teflon (i.e. hydrophobic) 2.38-mm-diameter beads. The distance between the beads were kept constant (i.e. center-to-center spacing of 3.1 mm). Experiments were conducted in an environmental chamber at an air temperature of 20°C and 30% and 75% relative humidity (RH). Evaporation rates were faster (i.e. ∼19 minutes and ∼49 minutes at 30% and 75% RH) from hydrophilic pores than the Teflon one (i.e. ∼24 minutes and ∼52 minutes at 30% and 75% RH) due in part to greater air-water contact area. Rupture of liquid droplets during evaporation was analyzed and predictions were made on rupture based on contact line pinning and depinning, projected surface area just before rupture, and pressure difference across liquid-vapor interface. It was observed that, in hydrophilic pore, the liquid droplet was pinned on one bead and the contact line on the other beads continuously decreased by deforming the liquid-vapor interface, though all three gas-liquid-solid contact lines decreased at a marginal rate in hydrophobic pore. For hydrophilic and hydrophobic pores, approximately 1.7 mm2 and 1.8–2 mm2 projected area of the droplet was predicted at 30% and 75% RH just before rupture occurs. Associated pressure difference responsible for rupture was estimated based on the deformation of curvature of liquid-vapor interface.

Slip in the Presence of Semi-Circular Menisci Between Parallel Ridges

Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties in applications such as electronics cooling and lab-on-chip. Here, an expression is developed to characterize the hydrodynamic slip in a laminar flow which occurs near the surface for the case when positive meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered shear free. The no slip condition exists at the tips of the ridges. Conformal maps from the literature are used to derive an expression which is a function of cavity fraction of the surface. The positive protrusion angle is 90 degrees. Cavity fractions range from 0 to 75%.

Insight to Innovation: An Overview of Research Journey of Dr. Satish Kandlikar

Professor Satish G. Kandlikar has been an outstanding researcher in the field of heat transfer having published some of the most widely cited publications over the last 30 years. Through the years he has co-authored 212 journal paper in various areas of heat transfer. The present paper provides a compressive look at Professor Kandlikar’s research work over the years. The research work has been broadly categorized into 1) flow boiling correlations, 2) fluid flow and heat transfer in microchannels, 3) roughness effect at microscale, 4) pool boiling heat transfer and CHF modeling, 5) surface enhancements for pool boiling, 6) numerical modeling of bubble growth in boiling, 7) modeling liquid-vapor and liquid-liquid interfaces, 8) water transport in PEM fuel cells and 9) infrared imaging to detect breast cancer. The research conducted in each of these areas has produced some landmark findings, some of the most widely used theoretical models and an abundance of high quality experimental data. The focus of this paper is to collate major finding and highlights some of the common themes that guided the research in Professor Kandlikar’s group. This will help the readers gain a comprehensive understanding of each of the areas of study in Professor Kandlikar’s group and place the findings of the paper in a larger context.

Review of Enhancement Techniques With Vapor Extraction During Flow Boiling in Microchannels

Flow boiling heat transfer in microchannels can remove high heat loads from restricted spaces with high heat transfer coefficients and minimum temperature gradients. However, many works still report problems with instabilities, high pressure drop and early critical heat flux, which hinder its possible applications as thermal management solutions. Much comprehension on the phenomena concerning flow boiling heat transfer is still missing, therefore many investigations rely on empirical methods and parametric studies to develop novel configurations of more efficient heat sinks. Nevertheless, investigations involving vapor extraction have successfully addressed all these previously reported issues while also increasing the heat transfer of heat sinks employing flow boiling in microchannels. In this sense, the objective of this review is to identify the main techniques employed for vapor extraction in microchannels-based heat sinks and analyze the physical mechanisms underneath the observed improvements during flow boiling, such that some design guidelines can be drawn. Three main strategies can be identified: passive vapor extraction, active vapor extraction, and membrane-based vapor extraction. All these strategies were able to dissipate heatfluxes higher than 1 kW/cm2, with the best performance achieved by a membrane-based heat sink, followed by active and passive designs. According to the present experimental and numerical data available in the literature, there is still room for improvement.

Fully-Developed Convective Heat Transfer and Pressure Drop in a Square Duct With Baffle Inserts Using CFD Analysis

The scope of this project is to investigate how the geometry of baffles affect heat transfer and pressure loss of a fluid flow at Re = 1000 through a square duct. For this purpose, Large Eddy Simulations are performed to investigate the effect of baffle height and baffle width. Focus is on the fully-developed flow that repeats itself at streamwise stations. The flow field predicted by Computational Fluid Dynamics simulations was validated using Particle Image Velocimetry. The different designs are evaluated in terms of Nusselt number, Nu and a loss coefficient, f, which are normalised using a reference geometry consisting of a square duct without baffles. The two parameters are additionally combined into a performance parameter eta η = (Nu/Nu0)/(f / f0)(1/3). It was found that adding baffles can result in a quadrupling of η. Reducing the height of baffles decreases heat transfer, while significantly reducing pressure loss and ultimately leading to a higher η. Reducing baffle height was also found to increase the temperature gradient at the upper wall and reduce it at the lower wall. Reducing baffle width resulted in the largest temperature gradient, but lead to poor heat transfer within the fluid.