Arterial pulsations drive oscillatory flow of CSF but not directional pumping

The brain lacks a traditional lymphatic system for metabolite clearance. The existence a “glymphatic system” where metabolites are removed from the brain’s extracellular space by convective exchange between interstitial fluid (ISF) and cerebrospinal fluid (CSF) along the paravascular spaces (PVS) around cerebral blood vessels has been controversial for nearly a decade. While recent work has shown clear evidence of directional flow of CSF in the PVS in anesthetized mice, the driving force for the observed fluid flow remains elusive. The heartbeat-driven peristaltic pulsation of arteries has been proposed as a probable driver of directed CSF flow. In this study, we use rigorous fluid dynamic simulations to provide a physical interpretation for peristaltic pumping of fluids. Our simulations match the experimental results and show that arterial pulsations only drive oscillatory motion of CSF in the PVS. The observed directional CSF flow can be explained by naturally occurring and/or experimenter-generated pressure differences.

Analysis of Reactive Flow of Third-grade Exothermi Chemical Reaction with Variable Viscosity and Convective Cooling

The study examines incomprssible laminar Poiseuille flow of a non-Newtonian fluid and heat transfer in a cooling convective fixed wall. The third-grade exothermic reactive fluid is stimulated by heat generation, gradient pressure and thermal buoyancy force. The convective exchange of temperature with the ambient takes after Newtons cooling law. Transilation of the formulated equations to the non-dimensional form is done using relevance quantities and solutions to the nonlinear equations are provided by employing Weighted residual techniques. The obtained solutions for the flow rate, energy, flow wall friction and temperature gradient are graphically plotted for the reactive flow system. Numerical validation of results in comparison with the presented method of solution is carried out. The results revealed that some parameters which are strong heat generation or source should be consciously guided to avoid reactive solution blow up in the exothermic system.

The Effect of Photovoltaic Panels on the Rooftop Temperature in the EnergyPlus Simulation Environment

In this paper, the effects that photovoltaic (PV) panels have on the rooftop temperature in the EnergyPlus simulation environment were investigated for the following cases: with and without PV panels, with and without exposure to sunlight, and using roof materials with different thermal conductivities and for different climatic zones. The results demonstrate that heat transfer by convection, radiation, and conduction in the air gaps between PV panels and the building envelope can be simulated in the EnergyPlus environment when these air gaps are in the “air conditioning zone.” Nevertheless, in most cases, particularly on the rooftop, the air gaps between the PV panels and the building envelope cannot be set as the “air conditioning zone.” Therefore, in this case, none of the EnergyPlus models are appropriate to simulate the effect that PV panels have on the rooftop temperature. However, all the terms of the Heat Balance Model, including the absorbed direct and diffuse solar radiation, net long-wave radiation with the air and surroundings, convective exchange with the outside air, and conduction flux in or out of the surface, can still be used to calculate the temperature and heat flux within the BIPV’s air gap.

Approaches to the Moisture Content Monitoring Intimber Elements: Development of a Resistive Method

The scope of this work is based on the use of resistive method to quantify the water content in timber elements. For an in-depth mapping, we adapted a multiplexed technique derived from geophysics based on a maximum crossing of current lines to obtain topography of measures sweeping the space boundary conditions being defined by the sample. The calibration of these measures is completed by a gammadensimetry laboratory method which allows access to water profiles along a preferred direction. Nevertheless, the resistive method is penalized by logarithmic laws linking moisture and resistivity. So, we develop a hybrid method for coupling the data obtained to diffusion models: it will provide complementary information where resistivity and gammadensimetry are no longer effective. The developed experimental protocol allows employing the selected method and optimizing the diffusion properties (diffusion coefficient and convective exchange coefficient) injected into a characterization algorithm (Nelder-Mead’s simplex inversion method) based on a finite difference method for the Fick’s diffusion law determination integrating orthotropic and non- linear properties. Overlap between electric field and density measurements and the numerical simulation tool are possible.

Methods for Characterizing Convective Cryoprobe Heat Transfer in Ultrasound Gel Phantoms

While cryosurgery has proven capable in treating of a variety of conditions, it has met with some resistance among physicians, in part due to shortcomings in the ability to predict treatment outcomes. Here we attempt to address several key issues related to predictive modeling by demonstrating methods for accurately characterizing heat transfer from cryoprobes, report temperature dependent thermal properties for ultrasound gel (a convenient tissue phantom) down to cryogenic temperatures, and demonstrate the ability of convective exchange heat transfer boundary conditions to accurately describe freezing in the case of single and multiple interacting cryoprobe(s). Temperature dependent changes in the specific heat and thermal conductivity for ultrasound gel are reported down to −150 °C for the first time here and these data were used to accurately describe freezing in ultrasound gel in subsequent modeling. Freezing around a single and two interacting cryoprobe(s) was characterized in the ultrasound gel phantom by mapping the temperature in and around the “iceball” with carefully placed thermocouple arrays. These experimental data were fit with finite-element modeling in COMSOL Multiphysics, which was used to investigate the sensitivity and effectiveness of convective boundary conditions in describing heat transfer from the cryoprobes. Heat transfer at the probe tip was described in terms of a convective coefficient and the cryogen temperature. While model accuracy depended strongly on spatial (i.e., along the exchange surface) variation in the convective coefficient, it was much less sensitive to spatial and transient variations in the cryogen temperature parameter. The optimized fit, convective exchange conditions for the single-probe case also provided close agreement with the experimental data for the case of two interacting cryoprobes, suggesting that this basic characterization and modeling approach can be extended to accurately describe more complicated, multiprobe freezing geometries. Accurately characterizing cryoprobe behavior in phantoms requires detailed knowledge of the freezing medium's properties throughout the range of expected temperatures and an appropriate description of the heat transfer across the probe's exchange surfaces. Here we demonstrate that convective exchange boundary conditions provide an accurate and versatile description of heat transfer from cryoprobes, offering potential advantages over the traditional constant surface heat flux and constant surface temperature descriptions. In addition, although this study was conducted on Joule–Thomson type cryoprobes, the general methodologies should extend to any probe that is based on convective exchange with a cryogenic fluid.

An Improved Cryosurgical Probe Testbed Based on Convective Exchange Boundary Conditions

Cryosurgery has demonstrated significant capabilities as a minimally invasive technique for treating cancer and other conditions [1], but has been limited by the ability to accurately predict treatment outcome and damage to surrounding tissues. Contributing to this problem has been the accuracy of predictive modeling and translating this to effective pretreatment planning. The two key factors in accurately modeling cryosurgical freezing are the temperature-dependent thermal properties of the freezing medium and cryoprobe boundary conditions. Both of these issues are considered in this study.

Martensite Fraction Determination Using Cooling Curve Analysis

This work presents a method of calculating the martensite fraction of an Fe-alloy, usingcooling curve analysis (CCA). It is based on a differential heat balance equation which takes intoaccount only convective exchange with the surroundings. By measuring a T(t) curve of an Fe-alloyand solving numerically the differential heat balance equation the martensite fraction can be calcu-lated. It is found that calculated martensite fraction using this methodology is comparable with resultsobtained using electron backscattering diffraction (EBDS).