Non-intrusive two-phase flow regime identification and transport characterization in microchannels subject to uniform and non-uniform heat input

Direct integration of compact microchannel heat sinks is an attractive thermal management solution for the dissipation of high heat fluxes, specifically under boiling conditions that provide high rates of heat transfer at a uniform heat sink temperature. Under two-phase flow conditions, the heat transfer and pressure drop are a function of the local flow regime. Development of sensors that detect local void fraction and flow regimes may enable better understanding of the fundamental flow phenomena. ^ The void fraction in air-water two-phase adiabatic flow in a microchannel is measured in this work using a custom-designed impedance-based sensor with electrodes on opposing walls of a single microchannel, a \u27crosswise\u27 geometry. The impedance response of the sensor is calibrated against the time-averaged void fraction determined via high-speed flow visualizations. The temporal signal is depicted as a probability density function that is used for quantitative determination of two-phase flow regimes using a Kohonen Self-Organizing Map. ^ To characterize the sensor impedance response, numerical simulations are implemented in two- and three-dimensions. Electrical simulations of the crosswise electrode geometry are performed to acquire both instantaneous and time-averaged responses. For arbitrarily defined voids, the shape and distribution has no effect on the simulated impedance; the relationship between the void fraction and impedance is found to be non-linear. Time-averaged three-dimensional impedance simulations are in good agreement with the experimental data. ^ A second set of experiments are performed using multiple electrodes placed along the flow direction of a single microchannel wall, a \u27streamwise\u27 geometry. Multiple water electrical conductivities are tested, and an optimal range between 100 and 175 μS/cm is found to provide maximum instrument sensitivity. The dependency of the impedance output on water conductivity is characterized to fit all of the data to a single calibration curve, independent of water conductivity. ^ One application where the determination of the local void fraction is important is in the case of non-uniform heating in microchannels. An experimental investigation is performed to explore flow boiling phenomena in a microchannel heat sink with hotspots, as well as non-uniform streamwise and transverse heating conditions across the entire heat sink. Local heat transfer coefficients and wall temperatures are measured while the location of boiling incipience is observed via high-speed visualizations of the flow. It is found that even though the substrate thickness beneath the microchannels is very small (200 um), significant lateral conduction occurs and must be accounted for in the calculation of the local heat flux imposed. For non-uniform heat input profiles, with peak heat fluxes along the central streamwise and transverse directions, it is found that the local flow regimes, heat transfer coefficients, and wall temperatures deviate significantly from a uniformly heated case. ^ A simple computational model is developed to predict the thermal performance of a microchannel heat sink with an imposed non-uniform heating profile. While the model underpredicts the base temperatures and overpredicts the heat transfer coefficients, the trends agree with experimental data. For the cases investigated with the model, flow non-uniformities between the channels are estimated using image analysis of high-speed videos taken during the experiments. It is observed that flow maldistribution must be taken into account in the model for heating profiles that are prone to flow maldistribution in order to improve the match to experimental data. ^ Another experimental investigation is performed to measure the critical heat flux (CHF) in a microchannel heat sink with uniform heating and various hotspot heating locations. It is found that a hotspot spanning the entire length of the heat sink in the flow direction produces the lowest CHF of all the cases investigated due to the flow maldistribution induced by boiling. A single hotspot spanning the heat sink perpendicular to the flow direction produces different CHF values based on its streamwise location. The visualizations reveal that CHF occurs when there is a sudden and unalleviated upstream expansion of vapor in one or more channels above the hotspot, causing the local wall temperature to rapidly increase. The proximity of the hotspot to the inlet manifold, which communicates between all channels and can relieve upstream vapor expansion, appears to determine the resiliency of the heat sink to CHF. ^ Non-uniform heating profiles often found in actual applications greatly affect the thermal performance of microchannel heat sinks. Measuring the void fraction and understanding how the location of hotspots affects local heat transfer allows for the creation of a computational model to aid future heat sink designs

Anti-myeloma efficacy of CAR-iNKT is enhanced with a long-acting IL-7, rhIL-7-hyFc

Multiple myeloma (MM), a malignancy of mature plasma cells, remains incurable. B-cell maturation antigen (BCMA) is the lead protein target for chimeric antigen receptor (CAR) therapy because of its high expression in most MM, with limited expression in other cell types, resulting in favorable on-target, off tumor toxicity. The response rate to autologous BCMA CAR-T therapy is high; however, it is not curative and is associated with risks of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome. Outcomes in patients treated with BCMA CAR-T cells (CAR-Ts) may improve with allogeneic CAR T-cell therapy, which offer higher cell fitness and reduced time to treatment. However, to prevent the risk of graft-versus-host disease (GVHD), allogenic BCMA CAR-Ts require genetic deletion of the T-cell receptor (TCR), which has potential for unexpected functional or phenotype changes. Invariant natural killer T cells (iNKTs) have an invariant TCR that does not cause GVHD and, as a result, can be used in an allogeneic setting without the need for TCR gene editing. We demonstrate significant anti-myeloma activity of BCMA CAR-iNKTs in a xenograft mouse model of myeloma. We found that a long-acting interleukin-7 (IL-7), rhIL-7-hyFc, significantly prolonged survival and reduced tumor burden in BCMA CAR-iNKT-treated mice in both primary and re-challenge settings. Furthermore, in CRS in vitro assays, CAR-iNKTs induced less IL-6 than CAR-Ts, suggesting a reduced likelihood of CAR-iNKT therapy to induce CRS in patients. These data suggest that BCMA CAR-iNKTs are potentially a safer, effective alternative to BCMA CAR-Ts and that BCMA CAR-iNKT efficacy is further potentiated with rhIL-7-hyFc

Electrical impedance-based void fraction measurement and flow regime identification in microchannel flows under adiabatic conditions

Electrical impedance of a two-phase mixture is a function of void fraction and phase distribution. The difference in the specific electrical conductance and permittivity of the two phases is exploited to measure electrical impedance for obtaining void fraction and flow regime characteristics. An electrical impedance meter is constructed for the measurement of void fraction in microchannel two-phase flow. The experiments are conducted in air–water two-phase flow under adiabatic conditions. A transparent acrylic test section of hydraulic diameter 780 lm is used in the experimental investigation. The impedance void meter is calibrated against the void fraction calculated using analysis of images obtained with a highspeed camera. Based on these measurements, a methodology utilizing the statistical characteristics of the void fraction signals is employed for identification of microchannel flow regimes. A self-organizing neural network is used for classification of the flow regimes

Examining effective communication in nursing practice during COVID‐19: A large‐scale qualitative study

AIM: The aim of this study was to conduct a primary examination of the qualitative communication experiences of nurses during the first wave of the COVID‐19 pandemic in the United States. BACKGROUND: Ambiguity in ever‐evolving knowledge on how to provide care during COVID‐19. Remaining safe has created a sense of urgency, which has in turn created the need for organizations to quickly alter their operational plans and protocols to support measures that increase capacity and establish a culture of safe care and clear communication. However, no known study has described communication in nursing practice during COVID‐19. METHODS: Utilizing qualitative descriptive methodology, semi‐structured interviews were conducted with 100 nurse participants from May to September 2020 and recorded for thematic analysis. The consolidated criteria for reporting qualitative studies (COREQ), a 32‐item checklist, were used to ensure detailed and comprehensive reporting of this qualitative study protocol. FINDINGS: Study participants shared descriptions of how effective communication positively impacted patient care and nursing practice experiences during the first wave of the COVID‐19 pandemic. The thematic network analyses identified the importance of effective communication across three levels: (1) organizational leadership, (2) unit leadership and (3) nurse‐to‐nurse communication. Within this structure, three organizing themes, essential to effective communication, were described including (a) presence, (b) education and (c) emotional support. CONCLUSION: Examining existing crisis communication policies and procedures across healthcare organizations is imperative to maintain highly relevant, innovative, and data‐driven policies and strategies that are fundamental to preserving quality patient care and supporting optimal nursing practice. IMPLICATIONS FOR NURSING POLICY AND HEALTH POLICY: Effective communication is critical to support nurses through extended periods of crisis. COVID‐19 represents a unique contemporary challenge to the nursing workforce given the high stress and prolonged strain it has created for both human and healthcare supply resources. There is value in nurses’ presence at local, unit level and organizational leadership levels to convey critical information that directly informs leadership decision‐making during unprecedented emergencies such as the COVID‐19 pandemic

US Nurses’ Challenges with Personal Protective Equipment during COVID-19: Interview Findings from the Frontline Workforce

This study aimed to describe nurses’ experiences with personal protective equipment while providing patient care during the first wave of the COVID-19 pandemic in the US. From May 2020 to September 2020, 100 individual interviews were conducted with nurses from diverse backgrounds and practice settings. Interviews were audio-recorded, transcribed, and verified for thematic analysis. Three key themes emerged related to personal protective equipment during COVID-19: (1) concerns with safety, (2) concerns with personal protective equipment supply, and (3) concerns with health care systems changing personal protective equipment policies. These findings support the importance of transparent and equitable institution-wide PPE standards in creating safe working environments. Clear communication around personal protective equipment policies and procedures, personal protective equipment education, and assurance of equitable access to equipment that can mitigate risk and disability while also reducing fear, confusion, and frustration among nurses. Maintaining clear and consistent personal protective equipment guidelines and communication regarding supplies and procedures enhances transparency during both routine and critical times de-escalating the inevitable strain concomitant with providing patient care during a global pandemic

US Nurses’ Challenges with Personal Protective Equipment during COVID-19: Interview Findings from the Frontline Workforce

This study aimed to describe nurses’ experiences with personal protective equipment while providing patient care during the first wave of the COVID-19 pandemic in the US. From May 2020 to September 2020, 100 individual interviews were conducted with nurses from diverse backgrounds and practice settings. Interviews were audio-recorded, transcribed, and verified for thematic analysis. Three key themes emerged related to personal protective equipment during COVID-19: (1) concerns with safety, (2) concerns with personal protective equipment supply, and (3) concerns with health care systems changing personal protective equipment policies. These findings support the importance of transparent and equitable institution-wide PPE standards in creating safe working environments. Clear communication around personal protective equipment policies and procedures, personal protective equipment education, and assurance of equitable access to equipment that can mitigate risk and disability while also reducing fear, confusion, and frustration among nurses. Maintaining clear and consistent personal protective equipment guidelines and communication regarding supplies and procedures enhances transparency during both routine and critical times de-escalating the inevitable strain concomitant with providing patient care during a global pandemic