The design of mini/micro heat exchangers: A world of opportunities and constraints

Micro heat exchangers and heat sinks broadened their use in many technological fields during the last two decades. The reduction of the dimensions of the channels allows to obtain ultra-compact heat exchangers characterized by higher surface-to-volume ratio and overall heat transfer coefficients but, in general, with large pressure losses. Many imaginative configurations have been proposed and tested, by changing the geometry of the manifolds, the position of the inlet/outlet ports, the structure of the heat transfer core, the structural materials and others more. Unfortunately, these efforts were not coordinated and a complete overview of the results accumulated up to now is not available. However, some general conclusions can be made by using the published results and the main scope of this paper is to summarize these milestones. Some shared conclusion are the following: (i) the design of micro heat exchangers can be obtained by using the classical methods developed for conventional heat exchangers even if the presence of non- negligible scaling effects (i.e. compressibility effects, conjugate wall-fluid effects, viscous dissipation) must be always verified; (ii) the performances of micro heat exchangers and heat sinks is strongly influenced by the proper distribution of the flow rate within the heat transfer core and a series of different solutions is available in order to solve this problem, as summarized in this paper; (iii) the presence of strong conjugate wall-fluid heat transfer effects can become an opportunity for the use of miniaturized heat exchangers made with inexpensive materials having low thermal conductivity values, especially in presence of counter-current flow and cross-flow configurations

DEL British Dashboard October 2020

Overall, the profile of public engagement with development has not changed significantly since June 2020. Changes in overall engagement between June and October with the 10 actions DEL tracks are small and/or insignificant

Design of a Temperature Micro-Sensor with a Gaseous Fluid Flow

Non-intrusive Liquid Crystal Thermography technique (LCT) has been proven as a powerful tool for lowtemperature application in micro-scale systems. It provides high-spatial resolution temperature maps dependent on colour response of heated thermo-chromic liquid crystal material (TLC). Different types of TLCs have been widely used in form of coated paints or water-based droplets in aqueous carrier fluid. Up to now, suitable designs of micro-devices with specific features optimized for their use in the presence of gas micro-flows has still not being proposed. Therefore, the study of a design of single channel micro-device for liquid-gas mixing is presented here. Research work has been performed experimentally and/or numerically to investigate the effect of various geometric designs of micro-devices to provide uniformly distributed TLC particles along a gas flow and to avoid their sedimentation. Beside the geometric design, material and heating systems are of high importance in order to achieve desirable observation of temperature gradients along the channel. Moreover, the flow rate and shear stress inside the channel were set to be minimal due to suspected high sensitivity of TLCs. This paper is intended to bring new insights and fresh perspectives to the development of temperature microscale sensors for practical implementation in the future

Cannula tip intravascular migration in an infant

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New Neighbours: Modelling the Growing Population of Gamma-ray Millisecond Pulsars

The Fermi Large Area Telescope, in collaboration with several groups from the radio community, have had marvellous success at uncovering new gamma-ray millisecond pulsars (MSPs). In fact, MSPs now make up a sizable fraction of the total number of known gamma-ray pulsars. The MSP population is characterized by a variety of pulse profile shapes, peak separations, and radio-to-gamma phase lags, with some members exhibiting nearly phase-aligned radio and gamma-ray light curves (LCs). The MSPs' short spin periods underline the importance of including special relativistic effects in LC calculations, even for emission originating from near the stellar surface. We present results on modelling and classification of MSP LCs using standard pulsar model geometries.Comment: 4 pages, 2 figures, proceedings of the ICREA Workshop on The High-Energy Emission from Pulsars and their Systems (HEEPS), Sant Cugat, Spai

Optimal design of multi-channel microreactor for uniform residence time distribution

Multi-channel microreactors can be used for various applications that require chemical or electrochemical reactions in either liquid, gaseous or multi phase. For an optimal control of the chemical reactions, one key parameter for the design of such microreactors is the residence time distribution of the fluid, which should be as uniform as possible in the series of microchannels that make up the core of the reactor. Based on simplifying assumptions, an analytical model is proposed for optimizing the design of the collecting and distributing channels which supply the series of rectangular microchannels of the reactor, in the case of liquid flows. The accuracy of this analytical approach is discussed after comparison with CFD simulations and hybrid analytical-CFD calculations that allow an improved refinement of the meshing in the most complex zones of the flow. The analytical model is then extended to the case of microchannels with other cross-sections (trapezoidal or circular segment) and to gaseous flows, in the continuum and slip flow regimes. In the latter case, the model is based on second-order slip flow boundary conditions, and takes into account the compressibility as well as the rarefaction of the gas flow