Numerical Analysis on Flow Characteristics of Anti-Gravity Flow

2011 ◽  
Author(s):  
Yan Li ◽  
Shuchao Zhang ◽  
Ning Mei
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Flow Characteristics ◽  
Gravity Flow ◽  
Radius Of Curvature ◽  
Micro Channel ◽  
Subcooled Boiling ◽  
Evaporation Heat ◽  
Micro Channels

Fluid flow phenomena in micro channels received wide attention due to its high heat transfer coefficient. As a new technique in the field of micro channel phase-change heat transfer, anti-gravity flow can drive fluid flow by capillary force and create enhanced evaporation heat transfer conditions by promoting the formation of an extended meniscus in the three-phase contact-line region. Resulting from the circumferential discrepancy of degree of superheat, the radius of curvature of intrinsic meniscus decreases rapidly as liquid rising up, leading to the formation of capillary pressure gradient. With the increase of heat flux, subcooled boiling occurs and micro-bubble appears at the bottom of the fluted tube. Under the action of buoyancy and drag force, the bubble rises along the channel and at the same time grows continually for the presence of superheat until its break. This paper focuses on the numerical study of flow characteristics of anti-gravity flow in the micro channel and the influence of bubble under the subcooled boiling circumstance. The results shows that bubble plays a positive role in the formation of anti-gravity flow and the analytical expressions are presented for the rising velocity of liquid, the contact angle and the curvature of the intrinsic meniscus, which are all influenced by heat flux, superheat temperature and the geometric parameters of the channel.

Optimization of Micro Channel Morphology

2006 ◽  
Author(s):  
Aleksander Vadnjal ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Cross Section ◽  
Channel Morphology ◽  
Channel Cross Section ◽  
Micro Channel ◽  
Parallel Plates ◽  
Conservation Of Energy ◽  
Micro Channels

An increasing demand for a higher heat flux removal capability within a smaller volume for high power electronics led us to focus on micro channels in contrast to the classical heat fin design. A micro channel can have various shapes to enhance heat transfer, but the shape that will lead to a higher heat flux removal with a moderate pumping power needs to be determined. The standard micro-channel terminology is usually used for channels with a simple cross section, e.g. square, round, triangle, etc., but here the micro channel cross section is going to be expanded to describe more complicated and interconnected micro scale channel cross sections. The micro channel geometries explored are pin fins (in-line and staggered), parallel plates and sintered porous micro channels (see Fig.1). The problem solved here is a conjugate problem involving two heat transfer mechanisms; 1) porous media effective conductivity and 2) internal convective heat transfer coefficient. Volume averaging theory (VAT) is used to rigorously cast the point wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the micro channel (porous media) morphology. Using the resulting VAT based field equations, optimization of a micro channel heated from one side is used to determine the optimum micro channel morphology. A small square of 1 cm 2 is chosen as an example and the thermal resistance, 0C/W, and pressure drop are shown as a function of Reynolds number.

scholarly journals Influence of fluid flow characteristics and heat transfer in a tube heat exchanger using H-shape inserts with circular ring

2021 ◽  
Author(s):  
Satyendra Singh ◽  
◽  
Tarun Joshi ◽  
Himanshi Kharkwal ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Flow Characteristics ◽  
Circular Ring ◽  
Main Section ◽  
Tube Heat Exchanger ◽  
Fluid Flow Characteristics

The heat transfer and fluid flow characteristics in a tube heat exchanger using H-shape inserts with circular ring (CRWHS) has been done by computationally and experimentally. In this investigation parameters like ratio of the diameters and pitches are considered. The value of diameter and pitch ratios are (DR=0.8, 0.9), (PR=3, 4) respectively. The main section in which investigation was done is 1.5m long and the hydraulic diameter of the tube is 68.1mm. 1000 W/m2 heat flux was provided in the main section. Heat flux was constant throughout the investigation. Air is used as a working medium in which 6000 to 21000 Reynolds number was used for the investigation. The observation revealed that the increment in heat transfer rate is 4.56 times as compare to smooth tube for the circular ring with H-shape inserts. In case of DR=0.8 and PR=3, maximum thermal performance factor was obtain which is 3.24. In GIT the deviation in Nusselt number & friction factor is limited to ±0.4% & ±0.1% respectively. CFD analysis result comparisons with experimental one are presented in which the maximum deviations for thermal performance factor are limited to ±3.6%.

Boiling in micro-channels

2010 ◽  
Vol 58 (1) ◽  
pp. 155-163 ◽  
Author(s):  
G. Hetsroni
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Mass Flux ◽  
Flow Boiling ◽  
Flow Regimes ◽  
Channel Cross Section ◽  
Micro Channel ◽  
Vapour Bubble ◽  
Micro Channels

Boiling in micro-channelsBoiling heat transfer in micro-channels is a subject of intense academic and practical interest. Though many heat transfer correlations have been proposed, most were empirically formulated from experimental data. However, hydrodynamic and thermal aspects of boiling in micro-channels are not well understood. Moreover, there are only a few theoretical models that link the heat transfer mechanism with flow regimes in micro-channels. Also, there are discrepancies between different sets of published results, and heat transfer coefficients have either well exceeded, or fallen far below, those predicted for conventional channels. Here we consider these problems with regard to micro-channels with hydraulic diameters ranging roughly from 5 μm to 500 μm, to gain a better understanding of the distinct properties of the measurement techniques and uncertainties, the conditions under which the experimental results should be compared to analytical or numerical predictions, boiling phenomenon, as well as different types of micro-channel heat sinks. Two-phase flow maps and heat transfer prediction methods for vaporization in macro-channels are not applicable in micro-channels, because surface tension dominates the phenomena, rather than gravity forces. The models of convection boiling should correlate the frequencies, sizes and velocities of the bubbles and the coalescence processes, which control the flow pattern transitions, together with the heat flux and the mass flux. Therefore, the vapour bubble size distribution must be taken into account. The flow pattern in parallel micro-channels is quite different from that in a single micro-channel. At same values of heat and mass flux, different, time dependent, flow regimes occur in a given micro-channel. At low vapour quality, heat flux causes a sudden release of energy into the vapour bubble, which grows rapidly and occupies the entire channel cross section. The rapid bubble growth pushes the liquid-vapour interface on both caps of the vapour bubble, at the upstream and the downstream ends, and leads to a reverse flow. We term this phenomenon as explosive boiling. One of the limiting operating conditions with flow boiling is the critical heat flux (CHF). The CHF phenomenon is different from that observed in conventional size channels.

Numerical study on significance of wave amplitude, wavelength and aspect ratio on heat transfer and fluid flow characteristics in circular wavy MC heat sink design

2021 ◽  
pp. 095440622198937
Author(s):  
Valaparla Ranjith Kumar ◽  
Karthik Balasubramanian ◽  
K Kiran Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fluid Flow ◽  
Aspect Ratio ◽  
Wave Amplitude ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Uniform Heat Flux ◽  
Uniform Heat ◽  
Fluid Flow Characteristics

In this study, hydrothermal characteristics in a circular wavy microchannel (CWMC) design under laminar flow conditions with uniform heat flux is numerically studied. Parametric studies in an innovative CWMC design were carried out at various wave amplitudes, wavelengths and aspect ratios. Three dimensional numerical study was performed in the Reynolds number (Re) range from 100 to 300 with uniform heat flux (50 W/cm2) applied at bottom of the channel, treating copper as channel material and water as working fluid. The obtained results were compared to sinusoidal wavy microchannel (SWMC).The results showed that heat transfer and fluid flow characteristics were significantly influenced by wave amplitude, wavelength and aspect ratio. Velocity vectors and contours were presented to understand the heat transfer and fluid flow characteristics. Stream-wise local Nusselt number, overall performance factor, span-wise velocity and temperature variation are also presented. It is concluded that CWMC with higher wave amplitude, smaller wave length and smaller aspect ratio gives higher heat transfer augmentation with corresponding pressure drop penalty.

scholarly journals COMPARISON OF HEAT TRANSFER & FLUID FLOW IN THE MICRO-CHANNEL WITH RECTANGULAR AND HEXAGONAL CROSS SECTION

2020 ◽  
Vol 1 (21) ◽  
Author(s):  
Emami Sajjad ◽  
Hosein Dibaei Bonab Mohammad ◽  
Mohammadiun Mohammad ◽  
Mohammadiun Hamid ◽  
Sadi Maisam
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Heat Transfer Fluid ◽  
Navier Stokes ◽  
Micro Channel ◽  
Rectangular Microchannel ◽  
Micro Channels

Due to the shrinking of the industrial equipment, the heat transfer and cooling of these devices are ofparticular importance. Therefore, this paper studies fluid flow and heat transfer in a micro-channel. Inthis study three-dimensional laminar numerical simulations, based on the Navier–Stokes equations andenergy equation, are obtained for pressure drop and heat transfer in these micro-channel heat sinksunder the same conditions. In this article, the first step is to investigate the effect of channel shape andgeometry on the heat transfer and pressure drop in micro-channels. In, the second step, the effect ofundefined heat flux and distinct input condition is investigated, and third step, the effect of increasingthe number of channels is checked to do an ideal form of heat transfer in a micro-channel. According tothe results, heat transfer using a hexagonal micro-channel is improved 20% on the rectangular microchannel(with equal hydraulic diameter).

scholarly journals Prospects for using two-phase micro-size systems for high heat flux removal

2021 ◽  
Vol 2057 (1) ◽  
pp. 012058
Author(s):  
V V Kuznetsov ◽  
A S Shamirzaev ◽  
A S Mordovskoy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Micro Channel ◽  
Copper Target ◽  
Jet Cooling ◽  
Micro Channels

Abstract Heat transfer in active systems for high heat removal based on the micro-channels and hybrid micro-channel/micro-jet is considered. The application of these systems allows significantly increasing the critical heat flux for a dense arrangement of the heat stressed equipment. The characteristics of heat transfer and critical heat flux during subcooled flow boiling of water in the micro-channel heat sink and during micro-jet impingement in narrow channel are obtained. The experiments are performed for the horizontal segmented microchannels with a cross section of 340×2000 μm2 made on the top of copper target and for impingement micro-jet cooling of the copper target in the gap of 1000 μm. It has been found that, compared with impingement micro-jet cooling in similar condition, the micro-channel cooling is more effective for high heat flux removal although it creates the considerably high wall temperature.

Porous Media Thermal Modeling of an Electronic Chip With Non-Uniform Power Distribution and Cooled by Micro-Channels

2013 ◽  
Author(s):  
Yubai Li ◽  
Yu Zhang ◽  
Shi-Chune Yao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Power Distribution ◽  
Micro Channel ◽  
Entrance Effect ◽  
Micro Channels ◽  
The Heat Transfer Coefficient

Micro-channels are used for the cooling of electronic chips. However, the 3D-CFD modeling of the large number of channels in a full chip requires huge number of meshes and computation time. Although porous media modeling of micro-channels can significantly reduce the effort of simulation, most porous media models are based upon the assumption that the surface heat flux or temperature is uniform on the chip. In reality, the heat flux on the chip is usually highly non-uniform. As a result, the heat transfer coefficient along the micro-channel is not uniform. In the present study, the porous media model considers the simultaneously developing entrance effect at the micro-channel inlet, and the thermally developing entrance effect due to the severe heat flux variation along the channel. Duhamel integral is used to determine the heat transfer coefficient variation corresponding to the heat flux distribution along the channels, and comparisons are made with the rigorous conjugate conduction-convection modeling. The computing cost of this modeling method is only about 1% (including one time of iteration) of 3D-CFD simulation. To demonstrate this approach, a full scale electronic chip with realistic power distribution on the surface is modeled, and the temperature map on the chip’s heating surface is provided.

scholarly journals EFFECT OF ARTIFICIAL CAVITIES ON HEAT TRANSFER AND FLOW CHARACTERISTICS MICROCHANNEL

2019 ◽  
Vol 20 (3) ◽  
pp. 180-192
Author(s):  
Suha A. Mohammed ◽  
Ekhlas M. Fayyadh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Friction Factor ◽  
Single Phase ◽  
Flow Characteristics ◽  
Channel Length ◽  
Bottom Surface ◽  
Inlet Temperature ◽  
Micro Channel

An experimental investigation was conducted to study single-phase fluid flow and heat transfer in a copper micro channel. To investigate the effect of artificial cavities on fluid flow and single phase heat transfer in micro channel heat sink, two model of straight micro channel recognized as two models (model -1and model -2) were designed and manufactured ,where model-1 have smooth bottom surface while Model-2 have 47 artificial cavities distributed uniformly at the bottom surface along the micro channel length. The two models having the same nominal dimension of 300?m height and 300?m depth while the real dimension value are 367 ?m for width and 296 ?m for depth .De-ionized water was used as the working fluids. Experimental test was conducted at 30?C inlet temperature with Reynolds numbers range from 700 to 2200 covering laminar flow conditions. The experiments were conducted with horizontal micro channel under both adiabatic (for friction factor calculation) and diabatic (for Nusselt number calculation) conditions. The results indicated that the experimental Darcy friction factor can be predicted well with conventional scale fanning friction factor correlations for developing flow in laminar region by shah and London (1978) correlation for two models. Also, the experimental Nusselt number Agree well with each correlation of shah and London (1978) and Mirmanto correlation in laminar region.

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