scholarly journals Numerical investigation of the effect of insulation on heat transfer of thermal bridges with different types

2016 ◽  
Vol 20 (1) ◽  
pp. 185-195 ◽  
Author(s):  
Koray Karabulut ◽  
Ertan Buyruk ◽  
Ahmet Fertelli
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
High Heat ◽  
Transfer Rates ◽  
Optimum Configuration ◽  
Building Models ◽  
High Heat Transfer ◽  
Different Types ◽  
Package Program ◽  
Thermal Bridges

In the present study, the effects of different types thermal bridges formed by beams for floor-wall junctions in reinforced concrete structures, with and without balconies, and the optimum configuration of the insulation layers to avoid heat loss were investigated as numerically. Both insulation between the walls and internal insulation was selected for floor-wall junctions and internal insulation was used for floor-wall junctions with balcony. Fluent package program was used to solve the temperature domain numerically. Results showed that high heat transfer rates were obtained in the region of thermal bridges for all building models. It was also obviously obtained that heat transfer rate decreased with making insulation on the beam surfaces.

Comparison of Heat Transfer Rates Around Moving and Stationary Bubbles During Nucleate Boiling

2005 ◽  
Author(s):  
David M. Christopher ◽  
Hao Wang ◽  
Xiaofeng Peng
Keyword(s):  
Heat Transfer ◽  
Numerical Analysis ◽  
Nucleate Boiling ◽  
High Heat ◽  
Marangoni Flow ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Nucleate Boiling Heat Transfer ◽  
Bubble Movement ◽  
Transfer Mechanisms

Nucleate boiling is known to be a very efficient method for generating high heat transfer rates from solid surfaces into liquids; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. This paper describes a numerical analysis of the heat transfer mechanisms around stationary and moving bubbles on a very thin microwire. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model was then used to study the heat transfer mechanisms around the bubbles. The analysis shows that the primary heat transfer mechanism is not the direct heat transfer to the bubble, but rather the large amount of convection around the outside of the bubble induced by the Marangoni flow that transfers at least twice as much energy from the wire than the heat transfer directly under the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles.

An Investigation of Thermal and Velocity Fields for a Confined Jet Over the RE Range of 1,000-24,000

2008 ◽  
Author(s):  
N. Jeffers ◽  
J. Punch ◽  
E. Walsh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Heat Fluxes ◽  
Hydrodynamic Characteristics ◽  
Plate Spacing ◽  
High Heat Transfer

Contemporary electronic systems currently generate high heat fluxes at component level. Impingement cooling is an effective way to generate high heat transfer coefficients in order to meet thermal constraints. This paper investigates the heat transfer and hydrodynamic characteristics of a confined impinging liquid jet with a nozzle-to-plate spacing (H/D) ratio of 0.5. A custom measurement facility was created to infer local heat transfer rates from infra-red images of a jet impinging on a 12.5μm thick stainless steel foil configured to generate uniform heat flux. Particle-Image Velocimetry (PIV) was performed in order to obtain quantitative velocity data within the jet. A series of experiments were run for Reynolds numbers (Re) in the range of 1,000–24,000 for a jet of 8 mm diameter (D). For Re > 4,000, the local heat transfer rate — in terms of Nusselt number (Nu) as a function of dimensionless radius (r/D) — had a plateau section between 0 < r/D < 0.6 followed by a peak at r/D ∼ 1.35. For higher Re the Nu peak exceeds that of the plateau section. For Re < 4,000, a plateau section exists between 0 < r/D < 0.4 followed by a shoulder located between 1 < r/D < 1.4. The PIV data for Re > 4,000 showed a strong vortex in the area of the secondary peak in Nu which was not present in the lower Re range. This phenomenon — the local peaks of heat transfer rate — has been previously reported in the literature with a degree of uncertainty as to the related fluid mechanics. This paper contributes to an understanding of the fluidic phenomenon responsible for the distribution of heat transfer rate in confined jets.

Natural Convection Heat Transfer From a Cylinder With High Conductivity Permeable Fins

2003 ◽  
Vol 125 (2) ◽  
pp. 282-288 ◽  
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Convection Heat Transfer ◽  
High Heat ◽  
Horizontal Cylinder ◽  
High Conductivity ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Wide Range

The problem of laminar natural convection from a horizontal cylinder with multiple equally spaced high conductivity permeable fins on its outer surface was investigated numerically. The effect of several combinations of number of fins and fin height on the average Nusselt number was studied over a wide range of Rayleigh number. Permeable fins provided much higher heat transfer rates compared to the more traditional solid fins for a similar cylinder configuration. The ratio between the permeable to solid Nusselt numbers increased with Rayleigh number, number of fins, and fin height. This ratio was as high as 8.4 at Rayleigh number of 106, non-dimensional fin height of 2.0, and with 11 equally spaced fins. The use of permeable fins is very advantageous when high heat transfer rates are needed such as in today’s high power density electronic components.

A Transducer for Measuring High Heat Transfer Rates

1970 ◽  
Vol 41 (12) ◽  
pp. 1732-1740 ◽  
Author(s):  
E. H. Schulte ◽  
R. F. Kohl
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Transfer Rates ◽  
High Heat Transfer

scholarly journals Properties of Kerosene-Aluminium Nanofluid used to Estimate the Overall Heat Transfer Rates during Regenerative/Film Cooling of Thrust Chambers

2019 ◽  
Vol 9 (1S3) ◽  
pp. 165-169
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Space Station ◽  
High Heat ◽  
Nano Particles ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Rocket Propulsion ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Large heat transfer rates are always desired for rocket propulsion applications as high heat loads are associated at the nozzle exit. Different strategies have been employed in order to have high heat transfer coefficients including use of liquid nitrogen, spray cooling etc. ISRO has planned to use aluminium based nano-particles with kerosene in order to cool launching vehicles including GSLV Mk III as it is the heaviest rocket that can carry large payloads. Recently, ISRO has announced to install its own International Space Station (ISS) in future and in such applications larger payloads are to be carried by the rocket. In this work, an analytical study on the thermodynamic properties of the aluminium nano-particles based kerosene nanofluid has been done and an attempt has also been made to develop a temperature and pressure dependent correlation that can be used in computational analysis of thrust chambers while film/regenerative cooling.

Study on Condensation Behavior in Two-Phase Flow Through a Microchannel

2008 ◽  
Author(s):  
Genki Takeuchi ◽  
Akiko Fujiwara ◽  
Yutaka Abe ◽  
Yutaka Suzuki
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Capillary Tube ◽  
High Heat ◽  
Flow Patterns ◽  
Rate Condition ◽  
High Heat Transfer

It is requested to develop a small and high performance heat exchanger for small size energy equipments such as fuel cells and CO2 heat pumps, et.al... In author’s previous studies, a high pressure resistant microchannel layers stacked heat exchanger has been developed. The heat exchanger is manufactured by diffusion bond technique. It can be used under high pressure condition larger than 15 MPa. Due to the high pressure resistance, the device can be applied for high flow rate condition with boiling and condensation. The objectives of the present study are to estimate the heat transfer performance of the heat exchanger and to investigate the thermal hydraulic behavior in the microchannel. The flow pattern in a glass capillary tube is observed by fabricating visualization system. As the results, it is measured that the present device attained high heat transfer quantity of approximately 7000 W on steam condensation despite the weight is only 230 g. The measurement results clarified that the device achieves very high heat transfer rate of hundreds times larger than that of the existing heat exchanger. Furthermore, visualization experiment with single glass pipe is conducted to clarify the flow condensation behavior in the microchannel. In the experiment, the microchannel of Pyrex glass is surrounded by the subcooling water. The flow patterns can visualized from the side of the microchannel. Flow patterns observations are conducted for various inlet pressure and temperatures of the subcooling water. It is observed that the continuous flow transition from annular and injection flow to slug-bubble flow in the microchannel. The reason of large heat transfer rate per unit volume is discussed as relating to narrow interval of each microchannels and small thermal resistance.

Rapid Boiling of Droplets in an Ambient Liquid at Partial Superheat

2007 ◽  
Author(s):  
Herman D. Haustein ◽  
Alon Gany
Keyword(s):  
Heat Transfer ◽  
Initial Conditions ◽  
High Heat ◽  
Heat Fluxes ◽  
Liquid Environment ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
High Superheat ◽  
Film Collapse ◽  
Critical Times

This work deals with the dynamics of rapid-boiling of a droplet, at medium-high superheat, rising in a host liquid environment. It considers the heat transfer, the superheat consumption and the hydrodynamics of the droplet as it boils. In the course of the research water-column experiments were conducted, and results are shown. Superheating was implemented by the sudden depressurization of the ambient liquid. Boiling was very rapid, concluding within several milliseconds, and high heat fluxes across the interface were obtained. Additionally, certain critical times in the boiling process were predicted and defined, and a novel criterion for the end of rapid boiling (liquid film collapse), is proposed. These defined critical times agree well with measured points of change in the boiling dynamics. From these results and analysis a deeper understanding of the three-fluid rapid boiling at medium-high superheat has been established, for the first time. In addition, various initial conditions were tested and their effect established qualitatively. This form of boiling, though being very rapid and sustaining high heat transfer rates, is non-explosive in nature, and therefore more designable and widely applicable.

Rapid Boiling of a Two-Phase Droplet in an Immiscible Liquid at High Superheat

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Herman D. Haustein ◽  
Alon Gany ◽  
Ezra Elias
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Immiscible Liquid ◽  
Two Phase ◽  
Liquid Environment ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Boiling Process ◽  
High Superheat ◽  
Transient Boiling

This work studies experimentally the rapid boiling of a droplet rising in a host liquid environment, within a range of superheats (0.2<Ja∗<0.5) not previously investigated. The direct-contact rapid-boiling process has many advantages in the fields of heat exchange and multiphase flow. By taking into account the superheat, heat transfer, and hydrodynamics of the multiphase-droplet the aim of this study is to create greater insight into the character of this transient-boiling process, for the first time. The sudden depressurization of a water column led to the rapid boiling of liquid propane droplets rising by buoyancy. During this millisecond boiling distinct stages were identified. Appropriate critical times for the transition between stages were defined by a simplified model, among these a novel criterion for the sudden pause in boiling caused by the engulfing liquid-film's collapse. Good agreement was found between these predicted time-points and measured changes in the boiling profile. This form of boiling, though being very rapid and sustaining high heat transfer rates, is still calm in nature, therefore, more predictable and widely applicable. Understanding this form of boiling suggests that the “design” of the boiling curve may be possible by setting the initial parameters.

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