Human blood plasma carries blood components like ions, proteins, and gases. When a concentration gradient of these components exists, Fickian diffusion occurs. Although essential for health, the mass diffusion of these components, in human blood plasma, remains largely unstudied. Multiple factors contribute to this, the main two being the complex and viscous nature of human blood plasma. Here, we developed a shearing-cell configuration, along with an interferometric setup, that allows the measurement of mass diffusion coefficients of various solutes in viscous solutions. The diffusion coefficients of sodium chloride and sucrose at different viscosities and concentrations were measured using the setup and compared against those reported in the literature. Results show a good agreement with literature values, validating the proposed measurement method of diffusion coefficient measurement. Further measurements of the mass diffusion coefficient of sodium chloride in blood plasma were conducted, under a normal and an elevated mean sodium concentration that represent healthy and pathological conditions. The difference between sodium mass diffusion in aqueous solution and blood plasma at normal sodium level shows a minor and insignificant reduction (−6
Studies into the use of mechanically or aerodynamically generated swirl jet cooling from small impingement distances (two nozzle diameters, or less, downstream) are very limited. This study uses aerodynamically generated swirl jets at a Reynolds number 35,000 for three different swirl numbers S = 0 (non-swirling), S = 0.45 (moderate swirling), and S = 1.05 (highly swirling). Non-intrusive spatially- and time-resolved planar heat transfer measurements are undertaken using infrared thermography at two different image acquisition rates (30 and 60 Hz). Results show that an improved cooling uniformity on the impingement surface is achieved in non-swirling and weakly swirling flow conditions, but a more intense cooling is found to occur at highly swirling conditions. The findings are applicable to process applications, such as heating and cooling where localized cooling or spatial uniformity of temperature is important. Unlike the outcomes of other studies at large impingement distances (> two nozzle diameters), the present research shows double peaks in the radial temperature distributions in non-swirling (S = 0) and moderate swirl (S = 0.45) flows at close impingement. The convective heat transfer coefficient at close impingement distances is found to have larger value and more uniformity at S = 1.05 and S = 0.45, respectively compared to the results at large impingement distances. While two relatively weak peaks are seen for non-swirl-to-moderate swirl numbers, a very strong peak at a radial distance of r/D ≈ 0.75 is observed at S = 1.05.
The development of high-powered electronics has imposed a significant need for cooling mechanisms for design engineers. Effective heat dissipation solutions are essential to preventing decreased performance and breakdown of electronic components, which has led to a focused area of research on heat transfer capabilities with synthetic (or pulsed) jets. A synthetic jet is formed by the movement of an actuator in a cavity that first draws a fluid in and then discharges it through an orifice. Continuous oscillation of the actuator generates vortex rings, which periodically disturb the thermal and hydrodynamic boundary layers at the jet impinging surface, promoting heat dissipation to the fluid. In this study, a Helmholtz resonator is designed and assembled, comprising two speakers actuated by a signal generator and an amplifier. The experimental investigation analysed the reduction in temperature at a heated surface plate of known heat flux due to the influence of synthetic jet impingement. The operating parameters included the signal waveform, amplitude, frequency, orifice diameter, and impingement distance. The individual effects of each of these parameters were investigated, and the corresponding radial temperature distributions were examined. All cases showed a single hump profile for the surface heat transfer, with its greatest magnitude occurring at the jet impingement location while gradually decreasing symmetrically over larger radial distances. At an impingement distance of 5 mm, the sinusoidal waveform operating at the diaphragm resonance frequency and amplitude of 0.35 Vrms had an effectiveness of 20.2
A direct numerical simulation has been performed for a spatially developing natural convection boundary layer (NCBL) along a heated vertical surface with Prandtl number Pr=6 . Using an incompressible formulation, the buoyancy effect is modelled by the Oberbeck–Boussinesq approximation. The laminar–turbulent transition is triggered by a broadband perturbation on the isothermal wall near the leading edge. Numerical results show that the global heat transfer follows Nu∝ Ra_x^m , where m=1/3 for Ra_x>5× 10^10 , consistent with observations of Tsuji and Kajitani (Int Heat Transf 13, 2006). The profiles of mean velocity, mean temperature, Reynolds shear stress, temperature fluctuations and turbulent heat flux have also been compared with existing measurements in the laminar, transitional and turbulent regimes. With an increasing Rayleigh number, peak-value locations of first-order statistics and temperature fluctuations are shown to shift closer to the heated surface.
