Counterflow Micro Research Articles

Study the hydro and thermal performance of microchannel heat exchanger with hybrid suspension of nanoparticles and MEPCM particles

This paper aims to study the flow and heat transfer of hybrid suspension in counter flow micro channel heat exchanger (CFMCHE). In order to enhance the thermal properties of micro encapsulated phase change material (MEPCM) suspension. The hybrid suspension studied in this paper consists of nanoparticles and MEPCM particles, these particles are suspended in water as abase fluid, two types of hybrid suspension are used (Cu + MEPCM suspension) and (Al2O3+ MEPCM suspension) by n-octadecane as a PCM for both of them. The hydrodynamic and thermal characteristics of thes suspensions flow in micro channels of CFMCHE is numerically investigated. From obtained results, using of hybrid suspensions as a cooling fluid lead to modify thermal performance of a CFMCHE by increase its effectiveness but it also lead to high increasing in pressure drop. The results showed considerable enhancement in cooling effectiveness of (Al2O3 + MEPCM suspension) above of the pure PCM suspension, Nanofluids, and water. While (Cu + MEPCM suspension) showed enhancement above of the pure PCM suspension and water, but was not best effectiveness than Nanofluids. Extra increase in pressure drop in both types of hybrid suspension above are leads to reduce the overall performance compared with pure PCM suspension. Therefore its use depends on the application at which this heat exchanger is employed

Effect of Dimensionless Number (KN and RE) on Performance Index of Concentric Circular Micro Channel

Overall performance of any type of heat channel is largely depends upon Knudsen number and Reynolds number [1]. In present work the outcome of dimensionless number on heat transfer properties of micro channel heat exchanger [2]are investigated. CFD analysis of counter flowmicro channel was performed for both slip and no slip flow using Fluent as CFD code. Based on results obtain, pressure drop increases with increment in Reynolds number and Knudsen number. The effectiveness reduces with increment in Reynolds number. The comparison of thermal and hydrodynamics performance between slip and no slip flow for heat exchanger is investigated. The effectiveness increases with decreasing values of Reynolds number for counter flow. For higher effectiveness of the micro channel heat exchanger, Reynolds number should be less.

Evaluation of axial conduction effects and heat losses in counter-flow microscale heat exchangers

A gas to gas counter flow micro Heat Exchanger (HE) made of an array of microchannels and fabricated using a combination of silicon and glass wafers is studied. A divergence of the experimental results from the classical heat exchanger theory is observed due to discernible axial conduction effects and heat loss to the environment. Hence, device performance is evaluated using a modified NTU approach that includes also non-negligible axial conduction effects due to the relatively thick and thermally conductive separating wall. This along with replacement of the adiabatic boundary conditions at the separating wall ends with proper temperature conditions enables to evaluate the heat losses to the environment and to reduce the average error between theoretical model and experimental data by 56%.

Comparative Study of Thermal Performance of Parallel Plate and Rectangular Microchannel Counter Flow Heat Exchangers

ABSTRACTThis paper is aimed at comprehensive investigations of the thermal performance of parallel plate and rectangular microchannel counter flow heat exchangers based on axial conduction, number of transfer units, and non-dimensional power density. The geometrical parameters of the two configurations are optimized for a given heat transfer rate, effectiveness, and pressure drop. A reduced order model of rectangular micro channel counter flow heat exchanger is developed in which it is transformed into a hydrodynamically and thermally equivalent parallel plate micro heat exchanger. To improve the accuracy of the model, correction factors obtained from detailed computational fluid dynamics model are introduced. Various factors affecting the dimensionless power density of both the counter flow micro heat exchangers are studied. It is found that the axial conduction plays an important role on the performance of rectangular channel counter flow micro heat exchanger. In the limiting case where the channel aspect ratio tends to zero, the dimensionless power density of rectangular channel is found to approach that of a parallel plate counter flow micro heat exchanger.

Design and Experimental Investigation of a Gas-to-Gas Counter-Flow Micro Heat Exchanger

In this work, a double-layered microchannel heat exchanger is designed for investigation on gas-to-gas heat transfer. The micro-device contains 133 parallel microchannels machined into a polished polyether ether ketone plate for both the hot side and cold side. The microchannels are 200 μm high, 200 μm wide, and 39.8 mm long. The design of the micro-device allows tests with partition foils in different materials and of flexible thickness. A test rig is developed with the integration of customized pressure and temperature sensors for in situ measurements. Experimental tests on the counter-flow micro heat exchanger have been carried out for five different partition foils and various mass flow rates. The experimental results, in terms of pressure drop, heat transfer coefficients, and heat exchanger effectiveness are discussed and compared with the predictions of the classic theory for conventionally sized heat exchangers.

A design method for rectangular microchannel counter flow heat exchangers

This paper presents a method for designing rectangular microchannel counter flow heat exchangers. The adopted methodology is based on two models: a one-dimensional model and a CFD model. A one-dimensional model for parallel plate micro heat exchangers is adopted to adjust the geometries of the rectangular microchannel counter flow heat exchanger. To this end a hydro-dynamically and thermally equivalent parallel plate heat exchanger is used. A more accurate CFD model serves to fit the parameters of the one-dimensional model. The related correction factors are presented for a range of pressure drops and axial conduction parameters. The present study provides quantitative data for the optimal plate dimensions and resulting maximal power density of a gas–gas rectangular channel counter flow micro heat exchanger with effectiveness varied between 0.6 and 1.

Development and analysis of a LTCC micro stagnation-point flow combustor

A micro stagnation-point flow burner was fabricated using low-temperature co-fired ceramic (LTCC) tapes. Methane/oxygen counterflow micro diffusion flames with luminous zones of less than 1 mm in length and 250 µm in width were stabilized in the reaction channel of the burner and analyzed using microscopic imaging spectroscopy. The burner was built with 25 layers of LTCC tapes which were pre-laminated into seven blocks. Integrated sapphire windows and sub-millimeter sized internal channels provide optical accessibility and reactant feeds, respectively. Spatial distributions of CH* and C*2 species were measured and compared with those obtained from multi-dimensional reacting flow calculations. Results show that the location and size of the diffusion flame may be controlled by flow velocity, or strain rate, just as in larger centimeter scale flames, and that the chemical structure of the micro flames was in agreement with those predicted by the numerical simulations. In this paper, we show that LTCC tape technology may be used to fabricate microburners for continuous flow steady-state homogeneous gaseous combustion and that integrated optical windows may be incorporated into the fabrication process for in situ optical diagnostics. The understanding and analysis of the present reacting flowfield, because of its simplicity, is important to the development of more complicated microreactors and microburners, in which mixing and variable strain rates exist.

21823 向流形マイクロ熱交換器の熱交換特性(ミニ・マイクロ・ナノスケールの流れおよび熱の現象,OS.5 ミニ・マイクロ・ナノスケールの流れおよび熱の現象)

21823 向流形マイクロ熱交換器の熱交換特性(ミニ・マイクロ・ナノスケールの流れおよび熱の現象,OS.5 ミニ・マイクロ・ナノスケールの流れおよび熱の現象)

MICROSTRUCTURE DEVICES FOR APPLICATIONS IN THERMAL AND CHEMICAL PROCESS ENGINEERING

Metallic microstructure devices have been manufactured and tested for applications in technical applications in thermal and chemical process engineering and in the laboratory. Manufacturing has been performed by micromachining of metal foils and diffusion bonding of a laminated foil stack, followed by welding of the microstructured core into a housing. Crossflow and counterflow micro heat exchangers with microchannel or microcolumn structures have been developed for throughputs up to 7 t water/h with a heat transmission power up to 200 kW. Overall heat transfer coefficients up to 54,000 W/m2 K have been determined with water as test fluid. Electrically driven microstructured heaters have been developed for fast and precise heating of sensitive liquids or gases. The heater has been used as an evaporator as well. Static micromixers have been developed for fast and complete mixing of reactands. They can be utilized with parallel reactions, for example, to decrease the yield of undesired by-products. For heterogeneously catalyzed reactions, several methods have been developed to coat fluid passages of already manufactured microstructure devices with thin catalytic layers.