Spectral Characteristics of Water-Soluble Rhodamine Derivatives for Laser-Induced Fluorescence

Journal of Fluorescence · 2024-07-02 · 4 citations

Spectral Characteristics of Water-Soluble Rhodamine Derivatives for Laser- Induced Fluorescence

Research Square · 2024-05-02 · 1 citations

<title>Abstract</title> We present a comprehensive fluorescence characterization of seven water-soluble rhodamine derivatives for applications in laser-induced fluorescence techniques (LIF). Absorption and emission spectra for these dyes are presented over the visible spectrum of wavelengths (400 to 700 nm). Their fluorescence properties were also investigated as a function of temperature for LIF thermometry applications. Rhodamine 110 depicted the least fluorescence emission sensitivity to temperature at -0.11%/°C, while rhodamine B depicted the most with a -1.55%/°C. We found that the absorption spectra of these molecules are independent of temperature, supporting the notion that the temperature sensitivity of their emission only comes from changes in quantum yield with temperature. Conversely, these rhodamine fluorophores showed no change in emission intensities with pH variations and are, therefore, not suitable tracers for pH measurements. Similarly, fluorescent lifetime, which is also a property sensitive to local environmental changes in temperature, pH, and ion concentration, measurements were conducted for these fluorophores. It was found that Rhodamine B and Kiton Red 620 have shorter fluorescence timescales compared to those of the other five rhodamine dyes, making them least suitable for applications where temporal changes in emission are monitored. Lastly, we conducted experiments to assess the physicochemical absorption characteristics of these dyes’ molecules into PDMS, the most common material for microfluidic devices. Rhodamine B showed the highest diffusion into PDMS substrates as compared to the other derivative dyes.

Hydrodynamic Characteristics of Textured Microchannel Flow

Journal of Fluids Engineering · 2023 · 6 citations

• Mechanics
• Materials science
• Physics

Abstract Microchannel flow is of great interest across many disciplines and applications, from biochemical diagnostics to thermal management systems. Nonetheless, such flow requires large pumping power due to its small cross-sectional length scale. Textured surfaces have shown encouraging results in terms of drag reduction in external flows and at larger scales (turbulent regime). However, there have been some discrepancies in the literature regarding the possibility of drag/friction reduction in microscale internal flows (laminar regime), which is believed to be due to the absence of a proper definition for the reference baseline. The main goal of this paper is to determine whether the (rectangular) textures lead to drag/friction reduction while comparing their results with the correct reference. The rectangular trenches have been introduced on the side walls of the microchannels/microgaps to understand the underlying frictional physics by conducting numerical simulations and experiments. The effect of geometrical parameters of the rectangular trenches as well as the Reynolds number has been investigated on characteristics of the flow. A thorough analysis has been performed using a neural network (NN) to evaluate the potential drag reduction in textured microchannels. The results showed that using the correct reference baseline, no drag reduction was observed in textured microchannels with rectangular trenches. Moreover, the width-to-depth aspect ratio of the trenches and roughness (texture size to mean microchannel dimension) are introduced to be critical parameters in the flow behavior inside textured microchannels.

Effect of Wetted Microtexturing on Friction in Microchannel Flow

2021-07-16

Study of drag reduction potential in textured microchannels

Bulletin of the American Physical Society · 2021-11-21

Investigating the Potential Drag Reduction and Thermal Transport Improvement in Textured Microchannels

2021-08-10 · 1 citations

Abstract Over the past few decades, microscale duct flow has been the key element for many applications, such as drug delivery and microelectronics cooling. To enhance the performance of such systems and to save more energy, looking for new ways to control the hydrodynamic and thermal characteristics of the microchannel flow has been of great interest lately. The aim of this research is to gain a better understanding of the flow physics within microchannels with microtextured walls. Therefore, a set of numerical study has been conducted on the combined effect of flow and heat transfer for spanwise rectangular trenches. The surface microstructures increase the wetting surface area, which is supposed to increase friction (skin drag). Recirculation produced inside the grooves, on the other hand, aids in increasing main flow slippage and lowering pressure drop along the microchannel. It is also worth noting that recirculation creates a negative pressure difference in the opposite direction of the flow (pressure drag). The geometrical parameters of the trenches have a significant impact on the trade-off between the drag reducing and drag increasing factors in textured microchannel flow, which is addressed in this research. Furthermore, the textures disrupt the thermal boundary layer, which can boost thermal transport through recirculation mixing. However, the stagnant fluid trapped within the grooves has weak convective heat transfer. So far, the results have been promising and a drag reduction of about 25% has been reported for wide trenches at low Reynolds numbers. Thermal transport enhancement is also possible for some tested geometries when the flow has not achieved the thermally fully development.

Effect of Wetted Microtexturing on Friction in Microchannel Flow

2021

• Mechanics
• Materials science
• Composite material

Effect of Wetted Microtexturing on Hydrodynamic and Thermal Characteristics in Microchannel Flow

Bulletin of the American Physical Society · 2020-11-24

Effect of Wetted Microtexturing on Friction in Microchannel Flow

2020-07-13

Abstract Microchannel flows are widely used in applications where small diffusion length scales are important. However, their inherent dimensional constrain also translates into high pumping power requirements. Inspired by nature, one possible method to reduce the large viscous pressure losses is to introduce textures in a microchannel. Depending on the interaction between the textured surface and the liquid, the microstructures can either be wetted or nonwetted. Less adhesion between solid and liquid in nonwetted state has made it popular in most of the friction reduction studies. However, in the nonwetted state, preventing liquid from penetrating into the grooves under pressurized conditions and the gas-liquid interface acting like a solid boundary open space to consider the wetted state for friction reduction as well. When dealing with the wetted state we should be aware that penetration of the flow inside the grooves can induce the pressure drag alongside the skin drag. Therefore, the wetted state will lead to a trade-off between skin and pressure drag. The aim of this work is to understand how different microtextures affect the total drag in a laminar microchannel flow. Textured microchannels with width-to-depth aspect ratios of 1, 10 and 50 and different width of the land region have been tested. In order to perform correct comparisons, the textured and baseline microchannels are designed to have the same volume. The results show that increasing the aspect ratio of the trenches introduces an extermum point in the hydraulic resistance of the microchannels. The optimum aspect ratio for the tested microchannels is 10, in which the trenches are not wide enough for streamlines to bend inside the trenches and increase the skin drag and they are not highly dense along the microchannel to reveal the negative effect of the pressure drag. On the whole, the hydraulic resistance of the textured channels is higher than the equivalent baseline for all the tested geometries.