A microfluidic sensor with high sensitivity and low cost was developed for detection of heavy metal ions. The sensor utilizes a novel glassy carbon/graphene composite electrode synthesized by layer-by-layer self-assembly and subsequent pyrolysis. The electrode exhibits low overpotential enabling detection of almost any heavy metal ions in aqueous solutions. The incorporation of graphene results in high sensitivity. To enhance mass transfer and sensitivity, a valveless micropump was integrated into the system, achieving two orders of magnitude higher sensitivity and a detection limit of 20 ppt for lead and 100 ppt for cadmium. The sensor was employed for simultaneous detection of lead and cadmium in water, documenting the multiple influences of the two heavy metal ions. The sensor achieved consistent results when it was applied to environmental water. Additionally, a neural network model was employed for data analysis.

A highly sensitive lead ion sensor is developed using graphene ion-sensitive field-effect transistors (G-ISFETs) in an aqueous environmental setting. The sensing channel employs monolayer graphene, while a PVC membrane, incorporating a lead ionophore, serves as the ion-sensitive membrane. The sensor utilizes an electrochemical deposition technique to preconcentrate Pb ion concentration at the solution-sensor interface to enable detection at ultra-low concentration. Notably, the integrated sensor exhibits an exceptional sensitivity of - 36.7 mV/decade and achieves an ultra-low detection limit of 5.6x10 -4 ppt, with a limit of quantitation (LOQ) set at 1.0x10 -3 ppt.

Perovskite Solar Cell (PSC) have recently emerged as exciting new candidates of Photovatics (PVs) for solar-to-electrical energy conversion. Nevertheless, one huge obstacle to its commercialization is how to improve its tolerance to operation at elevated temperatures. To address this issue, Composite Phase Change Material (CPCM) incorporated with a porous skeleton structure is proposed to integrate with PVs. In this structure, an important theoretical problem is that the temperature dependence of PV and the temperature control behavior of CPCMs interact with each other (bidirectional relationship). In this work, a pore-scale lattice Boltzmann phase change model is established to describe the dynamic thermal behavior of CPCMs and explore the roles of the bidirectional relationship between PVs and CPCMs, the change of power conversion efficiency influenced by temperature variation and glass transmissivity is discussed by comparing the overall liquid fraction of CPCMs, and the average temperature and power conversion efficiency of PVs. Furthermore, the situation of time-varying solar irradiation is discussed to mimic real application conditions. Results indicate that the neglecting temperature dependency of PVs leads to underestimation of PV surface temperatures and overestimation of power conversion efficiencies, while glass transmissivity provides reverse effects. These phenomena not only happen in constant solar irradiation but also in varying solar irradiation, calling for increasing attention to designing PV/CPCMs for varying heat flux conditions. The findings of this work establish a comprehensive manner toward integrated design of CPCMs for PV thermal control.

This work presents a new microparticle focusing technique for Impedance Flow Cytometry (IFC) affected by acoustic excitation in a microchannel with air pockets. Particle focusing is achieved by utilizing the secondary flow generated by the vibration to alter the trajectories of particles in microchannels. Different excitation frequencies are used to drive the vibration of a gas-liquid interface and two particle focusing modes are achieved under different excitation frequencies. The impedance measurement is performed downstream to verify its applicability to IFC. The results indicate that when particle focusing is present, there is a significant reduction in the standard deviation of impedance changes caused by 10 mu m microspheres, dropping from 0.0096 mV to 0.0021 mV compared to non-oscillating conditions.

This paper presents an innovative approach by integrating laser-induced graphene (LIG) as a low-power heater and a CRISPR-Cas9 sensor for efficient DNA amplification and detection. LIG, engineered using a laser-induced carbonization technique on polyimide tape, serves as a rapid heater for isothermal DNA amplification, achieving results within 30 minutes with minimal power consumption. Simultaneously, a CRISPR-Cas9 sensor detects DNA concentrations as low as 16 pM, offering cost-effective and sensitive detection. The combination of LIG heaters and CRISPR-Cas9 sensors streamlines DNA amplification and detection processes, offering substantial advantages over traditional methods in terms of power efficiency, cost effectiveness, and application simplicity. We validated our approach using lateral flow assay technology. Further, a pyrolytic glassy carbon electrode-based electrochemical sensor demonstrates specificity in DNA detection, with a detection limit of 16 pM. This integrated approach holds promise for multiple applications, particularly in nucleic acid diagnostics, showcasing a resource-efficient strategy for DNA amplification and detection in molecular biology research.

The introduction of flows within sessile droplets is highly effective for many lab-on-a-chip chemical and biomedical applications. However, generating such flows is difficult due to the typically small droplet volumes. Here, we present a simple, non-contact strategy to generate internal flows in sessile droplets for enhancing mixing and mass transport. The flows are driven by actuating a rigid substrate into oscillation with certain amplitude distributions without relying on the resonance of the droplet itself. Substrate oscillation characteristics and corresponding flow patterns are documented herein. Mixing indices and mass transfer coefficients of sessile droplets on the substrate surface are measured using optical and electrochemical methods. They demonstrate complete mixing within the droplets in 1.35 s and increases in mass transfer rates of more than seven times static values. Proof of concept was conducted with experiments of silver nanoparticle synthesis and with heavy metal ion sensing employing the sessile droplet as a microreactor for synthesis and an electrochemical cell for sensing. The degrees of enhancement of synthesis efficiency and detection sensitivity attributed to the internal flows are experimentally documented.

Professor Richard J. Goldstein was perhaps one of the "tallest" colleagues in our field with a career spanning over seven decades, and during which he contributed extensively to a gamut of heat and mass transfer topics and his work has impacted nearly all areas of thermal science. He was a pioneering innovator and his scholarship influenced the way scientists and engineers solve the world's contemporary engineering and technological challenges. This has been particularly evident in thermal science frontiers relating to novel diagnostics in temperature measurements, cooling technologies for high-performance gas turbines, innovative evaluation techniques for thermal convection, and visionary leadership on the global stage in energy engineering.

AbstractCurrent potentiometric sensing methods are limited to detecting nitrate at parts-per-billion (sub-micromolar) concentrations, and there are no existing potentiometric chemical sensors with ultralow detection limits below the parts-per-trillion (picomolar) level. To address these challenges, we integrate interdigital graphene ion-sensitive field-effect transistors (ISFETs) with a nitrate ion-sensitive membrane (ISM). The work aims to maximize nitrate ion transport through the nitrate ISM, while achieving high device transconductance by evaluating graphene layer thickness, optimizing channel width-to-length ratio (RWL), and enlarging total sensing area. The captured nitrate ions by the nitrate ISM induce surface potential changes that are transduced into electrical signals by graphene, manifested as the Dirac point shifts. The device exhibits Nernst response behavior under ultralow concentrations, achieving a sensitivity of 28 mV/decade and establishing a record low limit of detection of 0.041 ppt (4.8 × 10−13 M). Additionally, the sensor showed a wide linear detection range from 0.1 ppt (1.2 × 10−12 M) to 100 ppm (1.2 × 10−3 M). Furthermore, successful detection of nitrate in tap and snow water was demonstrated with high accuracy, indicating promising applications to drinking water safety and environmental water quality control.

This is the text of the eulogy to Prof. Richard Goldstein that was published in the International Journal of Heat and Mass Transfer and made available to this journal.

The experimental study deals with the nature of interrelated unstable equilibrium of lamella and rim of an emulsion drop based on n-dodecane and bidistilled water after its collision with a solid surface heated to 350–400 °C at Weber numbers We =160–310 and in the presence of a stable boundary vapor layer. The relationship between the delay time of the onset of emulsion lamella destabilization relative to maximum drop spreading time and the ratio of the characteristics of diffusive and convective heat transfer at unstable equilibrium of the liquid is revealed. The combined effect of We and the emulsion concentration on the critical Rayleigh and Marangoni numbers characterizing the lamella perforation is demonstrated. A mechanism is proposed where the fingering causes the lamella rupture near attachment to the rim. Liquid wettability is partially restored and the liquid periodically contacts the surface, resulting in the vapor bubbles formation and growth, as well as their collapse, which ensures the cascade of the lamella destruction and the liquid bridges formation. The proposed physical model develops ideas about the complexity and interconnectedness of the destabilization mechanisms of the emulsion drop rim and lamella, including not only rim instabilities, but also the long-wave Marangoni instability taking into account the emulsion concentration and, in some cases, Rayleigh-Benard instability.

Research results demonstrate the heat transfer effectiveness of an impinging synthetic jet toward cooling a plane normal to it. The utility of the synthetic jet lies in that the supply of coolant comes from the device itself as an alternating jetting flow that emerges from a plenum followed by a sink flow that returns to that same plenum. Experiments reported herein were conducted with the synthetic jet driven by an oscillating diaphragm powered by a rotating cam to expel fluid from the plenum out of a single hole, then return it through the same hole. The frequency of diaphragm oscillation and the distance from the synthetic jet's orifice to the surface being cooled are varied in the test program to determine their effects on cooling performance. A numerical study agrees with the results given by the experiment and flow visualization utilizing a smoke generator supports the data and numerical results. The local, time-average Nusselt numbers were measured in the experiment using the thermochromic liquid crystal technique and air as coolant. The color display of each test case was recorded with a fisheye camera. In the case of the highest frequency and shortest distance from orifice to cooled plate, a Nusselt number of nearly 40 was achieved within the central region of the cooled plate when the Reynolds number based upon jet maximum velocity and orifice diameter was 7500 and the distance from the orifice to cooled plate was 3.2 orifice diameters.

Due to the proximity of the first stage gas turbine vanes to the combustor, coolant introduced to the combustor walls interacts with the endwall film coolant and changes the vane passage flow physics. Recent results show that combustor coolant contributes significantly to cooling the endwall and vane surfaces. In this paper, the traditional combustor-turbine interface was modified to improve overall cooling performance. The performance of this new injection cooling scheme on passage fluid dynamics and surface cooling is assessed. The first of this two-part paper reports detailed experimental tests that document secondary flows and coolant transport throughout the vane passage for four combustor coolant flowrates. The experimental facility imitates combustor coolant injection and engine-level turbulence and has a modified transition duct design, called the ‘close-coupled combustor-turbine interface.’ The ‘impingement vortex’ seen in previous studies with combustor cooling appears as the dominant secondary flow. It is observed in the present study over a wide range of flowrates, confirming its tie to the combustor coolant flowrate and not the combustor-turbine interface geometry. It was found, however, that the location and size of the impingement vortex are affected by coolant flowrate. The second of this two-part paper discusses the impact of the observed secondary flows on cooling vane passage surfaces.

The two-step calcium oxide based calcination–carbonation cycle is studied for carbon dioxide capture and solar thermochemical energy storage applications. An indirectly-irradiated packed-bed solar thermochemical reactor is experimentally evaluated using simulated high-flux solar irradiation provided by a multi-source solar simulator. Experimental runs include a single calcination reaction step as well as single and multiple (up to four) consecutive calcination–carbonation cycles. The samples are characterised using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The reactor temperature peaked at 1,035°C. The average solar-to-chemical conversion efficiency, defined as the ratio of heat consumed by the reaction to radiant heat supplied to the reactor, was found to be between approximately 1.3% and 8.6% for the five performed experimental runs. The necessary advancements to the presented reactor design identified during the experimental campaign include improvements in thermomechanical characteristics of ceramic and metallic parts of the reactor to prevent fast mechanical and chemical degradation, application of more robust high-temperature reaction chamber seals, and optimisation of reactor geometry and gas flow patterns towards spatially more uniform thermal conditions and chemical reaction rates.

In this paper, we discuss the results of a measurement program initiated to describe the turbulence in a gas turbine first-stage vane passage. The flow entering the passage comes from a simulation of a low-NOx combustor within which the mainstream flow interacts with a series of crossjets to create a high-turbulence, large-turbulence-length-scale flow that passes downstream through a combustor-to-turbine transition duct and to the linear cascade that simulates a first-stage turbine. Measured mean flow, RMS velocity fluctuations, and dissipation of turbulence in the passage are compared with values computed using RANS simulation.

This paper reports, for the first time, the use of pyrolyzed KMPR photoresist to form carbon sensors for detection of trace heavy metals using anodic stripping voltammetry. Shown in this report is its integration with a valveless micropump. This sensor can be used to detect ions of almost any heavy metal in an aqueous solution due to its low overpotential, preventing production of hydrogen. It achieves continuous, real-time measurements. Bismuth ions are added, and the concentration is optimized to enhance sensitivity. The limit of detection of lead ions is 40 ppt under a steady mass flow rate of 10 mL/h. Compared with traditional heavy metal sensors, this microfluidic carbon sensor reduces the limit of detection by three orders. Use of it with a valveless micropump doubles its sensitivity. This doubling is due to fast mass transfer effected by the unsteady valveless micropump flow.

Micropumps are microelectromechanical system (MEMS) devices that pump small quantities of liquids. They are used in many applications such as electronics cooling and drug delivery. Valveless fluid diode micropumps with no moving parts have recently attracted great interest in the MEMS community. In this paper, topology optimization is used to design two-dimensional, fixed-geometry, fluidic diodes of high diodicity, which is the ratio of pressure drops of forward to reverse flows. One of the fluidic diodes, of the Tesla type, shows a diodicity of over five. Another is of the nozzle-diffuser type. Both are experimentally and computationally demonstrated herein. Then the numerical simulation was applied to simplify the structures, and the two-dimensional geometry was converted into three-dimensional model for micropumps. Three-dimensional and unsteady numerical analyses of micropump fluid flow with optimized diodes were conducted for pumps of each of the two diode designs. The micropump with the Tesla-type fluidic diode reached a measured flow rate of 34 ml/h, consistent with the computed results and 2.2 times that of the nozzle-diffuser type micropump. The performance results show a high dependence on internal channel geometry. The two types show highest flow rates with an internal channel thickness of $200 ~\mu \text{m}$ . Demonstrated good repeatability and precise flow control show positive prospects for application. [2021-0144]

Based on surface reaction technology, electrochemical sensing methods are well suitable for small-volume samples, such as droplets. However, rapid mass transfer of analytes within droplets is usually hard to achieve due to small fluid volumes and minimal convection. Here, we present a mass transfer enhancement method achieved by actuating a sessile droplet into certain vibration modes. Electrodes for electrochemical detection, each with a droplet retainer, are placed on a vertically vibrating platform. The vibrational and mass transfer properties of the sessile droplets are experimentally tested with optical and electrochemical methods. Internal flows generated by the droplet vibration are visualized to explain the enhancement in mass transport. Compared with a static case, measurements with droplet vibration in the (0, 2) mode demonstrate an increase in mass transfer rate of over five times. Finally, improvement in sensing performance of electrochemical sensors caused by vibration is experimentally verified by detecting heavy metal ions and large molecules (proteins) using a gold working electrode.

This paper presents the results of a numerical study of the effects of swirling flow in coolant jets on film cooling performance. Some combined-hole designs with swirling coolant flow entering the delivery hole are proposed and analyzed. Adiabatic film cooling effectiveness values for cases with various blowing ratios are compared. Detailed flow structures and underlying mechanisms are discussed. The results show that film cooling effectiveness is improved with jet swirl at high blowing ratios, and that swirl strength has significant influence on film cooling performance. Combined-hole designs can further improve film cooling performance using swirling jets due to mixing of coolant flows and interaction of vortices. The largest improvements of area-averaged film cooling effectiveness for a single-hole swirl case and a combined-hole swirl case over corresponding non-swirling case results are 157% and 173%, respectively.

Rapid mass transfer of analytes is essential for effective electrochemical sensing. Here, we present a vibrating air bubble as a stirrer and evaluate the optimal working frequency. A vibration system that contains a flexible piezoelectric plate coupled with a trapped bubble integrated with a gold working electrode is employed. The vibrational properties and mass transfer of the coupled system are experimentally tested with optical and electrochemical methods, respectively. Streaming flows generated by the vibrating bubble are characterized by visualization to explain the enhancement of mass transport to the working electrode. Compared with a static case, measurements with a vibrating bubble demonstrate a twelve-times enhancement in mass transfer coefficient. Enhanced sensing performance is experimentally quantified with the bubble stirrer and its integrated electrochemical metal ion sensor. This integrated system can be used for various types of electrochemical sensing applications that are limited by slow molecular diffusion.