FREON COOLING MINISYSTEM USING CIRCULAR MICRO-CHANNELS

<p>The necessity of a higher data processing speed was crucial for the advances in computer science. There were created processors that needed increasingly more power, so that new methods were discovered and more complex systems were created in order to solve the cooling issue. In this paper, there are presented the trials performed on a mini refrigeration plant that used mechanical compression of Freon’s, designed to cool electronic components like microprocessors, microcontrollers, graphic stations, or in the case of local cooling in diverse areas such as bioengineering, optics and nanotechnologies. The refrigeration system was constructed as an experimental set-up and consists of the following: two mini heat exchangers, working both as a condenser and a vaporizer, which are made of circular micro channels, a refrigeration compressor, lamination valve which contains a circular nano channel and a micro filter. The experimental determinations have proven that, although such a system contains a small quantity of Freon, of the order of milligrams, it reaches temperatures of -44 °C.</p>

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In-Line Analysis of Diffusion Processes in Micro Channels by Long Distance Raman Photometric Measurement Technology—A Proof of Concept Study

Micromachines ◽

10.3390/mi12020116 ◽

2021 ◽

Vol 12 (2) ◽

pp. 116

Author(s):

Julian Deuerling ◽

Shaun Keck ◽

Inasya Moelyadi ◽

Jens-Uwe Repke ◽

Matthias Rädle

Keyword(s):

Numerical Aperture ◽

Spot Size ◽

Measuring System ◽

Optical Systems ◽

Measurement Technology ◽

Long Distance ◽

Measuring Point ◽

Acetone Concentration ◽

Micro Channels ◽

Set Up

This work presents a novel method for the non-invasive, in-line monitoring of mixing processes in microchannels using the Raman photometric technique. The measuring set-up distinguishes itself from other works in this field by utilizing recent state-of-the-art customized photon multiplier (CPM) detectors, bypassing the use of a spectrometer. This addresses the limiting factor of integration times by achieving measuring rates of 10 ms. The method was validated using the ternary system of toluene–water–acetone. The optical measuring system consists of two functional units: the coaxial Raman probe optimized for excitation at a laser wavelength of 532 nm and the photometric detector centered around the CPMs. The spot size of the focused laser is a defining factor of the spatial resolution of the set-up. The depth of focus is measured at approx. 85 µm with a spot size of approx. 45 µm, while still maintaining a relatively high numerical aperture of 0.42, the latter of which is also critical for coaxial detection of inelastically scattered photons. The working distance in this set-up is 20 mm. The microchannel is a T-junction mixer with a square cross section of 500 by 500 µm, a hydraulic diameter of 500 µm and 70 mm channel length. The extraction of acetone from toluene into water is tracked at an initial concentration of 25% as a function of flow rate and accordingly residence time. The investigated flow rates ranged from 0.1 mL/min to 0.006 mL/min. The residence times from the T-junction to the measuring point varies from 1.5 to 25 s. At 0.006 mL/min a constant acetone concentration of approx. 12.6% was measured, indicating that the mixing process reached the equilibrium of the system at approx. 12.5%. For prototype benchmarking, comparative measurements were carried out with a commercially available Raman spectrometer (RXN1, Kaiser Optical Systems, Ann Arbor, MI, USA). Count rates of the spectrophotometer surpassed those of the spectrometer by at least one order of magnitude at identical target concentrations and optical power output. The experimental data demonstrate the suitability and potential of the new measuring system to detect locally and time-resolved concentration profiles in moving fluids while avoiding external influence.

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Bejan’s Constructal Theory Analysis of Gas-Liquid Cooled Finned Modules

Journal of Heat Transfer ◽

10.1115/1.4003556 ◽

2011 ◽

Vol 133 (7) ◽

Cited By ~ 14

Author(s):

Giulio Lorenzini ◽

Simone Moretti

Keyword(s):

Thermal Behavior ◽

Heat Exchangers ◽

High Performance ◽

Numerical Study ◽

Constructal Theory ◽

Electronic Components ◽

Theory Analysis ◽

Pressure Losses ◽

Different Types ◽

Overall Performance

High performance heat exchangers represent nowadays the key of success to go on with the trend of miniaturizing electronic components as requested by the industry. This numerical study, based on Bejan’s Constructal theory, analyzes the thermal behavior of heat removing fin modules, comparing their performances when operating with different types of fluids. In particular, the simulations involve air and water (as representative of gases and liquids), to understand the actual benefits of employing a less heat conductive fluid involving smaller pressure losses or vice versa. The analysis parameters typical of a Constructal description (such as conductance or Overall Performance Coefficient) show that significantly improved performances may be achieved when using water, even if an unavoidable increase in pressure losses affects the liquid-refrigerated case. Considering the overall performance: if the parameter called Relevance tends to 0, air prevails; if it tends to 1, water prevails; if its value is about 0.5, water prevails in most of the case studies.

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Comparison of 30 Boiling and Condensation Correlations for Two-Phase Flows in Compact Plate-Fin Heat Exchangers

Volume 2: Heat Transfer Equipment; Heat Transfer in Multiphase Systems; Heat Transfer Under Extreme Conditions; Nanoscale Transport Phenomena; Theory and Fundamental Research in Heat Transfer; Thermophysical Properties; Transport Phenomena in Materials Processing and Manufacturing ◽

10.1115/ht2017-4907 ◽

2017 ◽

Cited By ~ 4

Author(s):

Wenhai Li ◽

Ken Alabi ◽

Foluso Ladeinde

Keyword(s):

Heat Transfer ◽

Heat Exchangers ◽

Flow Boiling ◽

Transfer Coefficients ◽

Two Phase Flows ◽

Two Phase ◽

Heat Transfer Coefficients ◽

Heat Exchanger Design ◽

Micro Channels ◽

Vertical Tubes

Over the years, empirical correlations have been developed for predicting saturated flow boiling [1–15] and condensation [16–30] heat transfer coefficients inside horizontal/vertical tubes or micro-channels. In the present work, we have examined 30 of these models, and modified many of them for use in compact plate-fin heat exchangers. However, the various correlations, which have been developed for pipes and ducts, have been modified in our work to make them applicable to extended fin surfaces. The various correlations have been used in a low-order, one-dimensional, finite-volume type numerical integration of the flow and heat transfer equations in heat exchangers. The NIST’s REFPROP database [31] is used to account for the large variations in the fluid thermo-physical properties during phase change. The numerical results are compared with Yara’s experimental data [32]. The validity of the various boiling and condensation models for a real plate-fin heat exchanger design is discussed. The results show that some of the modified boiling and condensation correlations can provide acceptable prediction of heat transfer coefficient for two-phase flows in compact plate-fin heat exchangers.

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Modelling, Analyses and Optimization for Exergy Performance of an Irreversible Intercooled Regenerated Brayton CHP Plant: Part 1 — Thermodynamic Modelling and Parametric Analyses

Volume 6: Energy ◽

10.1115/imece2017-70045 ◽

2017 ◽

Cited By ~ 2

Author(s):

Lingen Chen ◽

Bo Yang ◽

Huijun Feng ◽

Zemin Ding

Keyword(s):

Heat Exchangers ◽

Variable Temperature ◽

Pressure Ratio ◽

Exergy Efficiency ◽

Heat Reservoir ◽

Output Rate ◽

Rate Versus ◽

Optimum Heat ◽

Set Up ◽

Parametric Analyses

A variable-temperature heat reservoir irreversible intercooling regenerated Brayton combined heat and power (CHP) plant model is set up in this paper. The model considers the heat transfer losses in all the heat exchangers, the working substance pressure drop loss in the piping, and the expansion and compression losses in turbine and compressor. Exergy output rate and exergy efficiency are considered as the research targets, and their analytical formulae are obtained. The optimal performances are gotten by optimizing the intercooled pressure ratio and total pressure ratio. The influences of some important parameters on the performances are studied in detail. Besides, the relation of exergy output rate versus exergy efficiency is investigated, and the curve is loop-shaped one. The results indicate that optimum heat capacity rate matching between the heat reservoir and working substance, and optimum heat consumer required temperature exist respectively, which generate double-maximal exergy output rate and double-maximal exergy efficiency, respectively. The heat conductance allocation optimization of all the heat exchangers will be carried out in Part 2 of this paper.

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Adaptive Model for Credit Card Fraud Detection

International Journal of Interactive Mobile Technologies (iJIM) ◽

10.3991/ijim.v14i03.11763 ◽

2020 ◽

Vol 14 (03) ◽

pp. 54

Author(s):

Imane Sadgali ◽

Naoual Sael ◽

Faouzia Benabbou

Keyword(s):

Credit Card ◽

Fraud Detection ◽

Machine Learning Techniques ◽

Adaptive Model ◽

Credit Card Fraud ◽

New Methods ◽

Learning Techniques ◽

Multi Level ◽

Set Up ◽

High Level

<p>While the flow of banking transactions is increasing, the risk of credit card fraud is becoming greater particularly with the technological revolution that we know, fraudulent are improve and always find new methods to deal with the preventive measures that financial systems set up. Several studies have proposed predictive models for credit card fraud detection based on different machine learning techniques. In this paper, we present an adaptive approach to credit card fraud detection that exploits the performance of the techniques that have given high level of accuracy and consider the type of transaction and the client's profile. Our proposition is a multi-level framework, which encompasses the banking security aspect, the customer profile and the profile of the transaction itself.</p>

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Review of the achievements of project MERIT for the intercomparison of techniques for monitoring the rotation of the Earth

Symposium - International Astronomical Union ◽

10.1017/s0074180900119539 ◽

1988 ◽

Vol 128 ◽

pp. 227-232

Author(s):

G. A. Wilkins

Keyword(s):

Earth Rotation ◽

Working Group ◽

New Techniques ◽

New Methods ◽

The Earth ◽

Terrestrial Reference System ◽

Rotation Of The Earth ◽

Analyse Data ◽

Set Up ◽

International Services

It is generally recognised that the Working Group on the Rotation of the Earth that was set up after IAU Symposium No. 82 has successfully achieved its principal objectives, namely: “to make recommendations on … future international services on earth-rotation” and “to obtain and analyse data on earth-rotation by both current and new methods …”. In particular, by organising Project MERIT, it has stimulated the development and use of new techniques and it has brought together in fruitful collaboration scientists from many countries and disciplines. Other subsidiary objectives have also been achieved and the project has been extended through cooperation with the COTES Working Group on the terrestrial reference system. The possible reasons for this success are also reviewed in the expectation that the conclusions will be relevant to other future projects.

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Study on Heat Transfer and Pressure Drop Characteristics in Fin Micro Channels of Hybrid Heat Exchangers

2019 5th International Conference on Transportation Information and Safety (ICTIS) ◽

10.1109/ictis.2019.8883554 ◽

2019 ◽

Cited By ~ 1

Author(s):

Jiawei Wang ◽

Mingjian Lu ◽

Yuwei Sun ◽

Xinping Yan ◽

Jian Wang

Keyword(s):

Heat Transfer ◽

Pressure Drop ◽

Heat Exchangers ◽

Micro Channels

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Mini- and Microchannel Research in Sweden

1st International Conference on Microchannels and Minichannels ◽

10.1115/icmm2003-1004 ◽

2003 ◽

Cited By ~ 5

Author(s):

Bjo¨rn Palm

Keyword(s):

Heat Exchangers ◽

Single Phase ◽

Single Channels ◽

Phase Flow ◽

Single Phase Flow ◽

Two Phase ◽

Compact Heat Exchangers ◽

Micro Channels ◽

Parallel Channels ◽

Institute Of Technology

The purpose of the present paper is to present research and development within the area of mini- and micro channels in Sweden. A review is made of the historical development of highly compact heat exchangers within the country, starting with plate heat exchangers. The main focus is on the research performed at the Royal Institute of Technology, where mini-channel research has been going on since more than ten years. Single-phase flow as well as two-phase flow is treated, both in single channels and in full-size heat exchangers with multiple parallel channels.

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