Effect of Nano-Structured Surface on Meniscus Evaporation at Nanoscale

2010 ◽  
Author(s):  
Shalabh C. Maroo ◽  
J. N. Chung
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heater Surface ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Enhancing Heat Transfer ◽  
To Come

Evaporation of a nanoscale meniscus on a nano-structured heater surface is simulated using molecular dynamics. The nanostructures are evenly spaced on the surface and rectangular-shaped with a length and height of 0.41 nm and 0.96 nm respectively, and stretching throughout the width of the domain. The simulation results show that the film breaks during the early stages of evaporation due to the presence of nanostructures and no non-evaporating film forms (unlike a previous simulation performed in absence of nanostructures where non-evaporating film forms on the smooth surface). High heat transfer and evaporation rates are obtained. We conclude that heat transfer rates can be significantly increased during bubble nucleation and growth by the presence of nanostructures on the surface as it breaks the formation of non-evaporating film. This will cause additional chaos and allow the surrounding cooler liquid to come in contact with the surface enhancing heat transfer coefficients.

A Possible Role of Nanostructured Ridges on Boiling Heat Transfer Enhancement

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Shalabh C. Maroo ◽  
J. N. Chung
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Heater Surface ◽  
Transfer Enhancement ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
To Come

Evaporation of a nanoscale meniscus on a nanostructured heater surface is simulated using molecular dynamics. The nanostructures, evenly spaced on the surface, are ridges with a width and height of 0.55 nm and 0.96 nm, respectively. The simulation results show that the film breaks during the early stages of evaporation due to the presence of nanostructures and no nonevaporating film forms (unlike a previous simulation performed in the absence of nanostructures where nonevaporating film forms on the smooth surface). High heat transfer and evaporation rates are obtained. We conclude that heat transfer rates can be significantly increased during bubble nucleation and growth by the presence of nanostructure ridges on the surface as it can break the formation of nonevaporating film. This causes additional chaos and allows the surrounding cooler liquid to come in contact with the surface providing heat transfer enhancements.

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.

An Analytical Study of the Optimized Performance of an Impingement Heat Sink

2004 ◽  
Vol 126 (4) ◽  
pp. 528-534 ◽  
Author(s):  
S. B. Sathe ◽  
B. G. Sammakia
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
High Performance ◽  
Cross Flow ◽  
High Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Flow Through

The results of a study of a new and unique high-performance air-cooled impingement heat sink are presented. An extensive numerical investigation of the heat sink performance is conducted and is verified by experimental data. The study is relevant to cooling of high-power chips and modules in air-cooled environments and applies to workstations or mainframes. In the study, a rectangular jet impinges on a set of parallel fins and then turns into cross flow. The effects of the fin thickness, gap nozzle width and fin shape on the heat transfer and pressure drop are investigated. It is found that pressure drop is reduced by cutting the fins in the central impingement zone without sacrificing the heat transfer due to a reduction in the extent of the stagnant zone. A combination of fin thicknesses of the order of 0.5 mm and channel gaps of 0.8 mm with appropriate central cutout yielded heat transfer coefficients over 1500 W/m2 K at a pressure drop of less than 100 N/m2, as is typically available in high-end workstations. A detailed study of flow-through heat sinks subject to the same constraints as the impingement heat sink showed that the flow-through heat sink could not achieve the high heat transfer coefficients at a low pressure drop.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

The Thickness of the Liquid Microlayer Between a Cap-Shaped Sliding Bubble and a Heated Wall: Experimental Measurements

2006 ◽  
Vol 128 (9) ◽  
pp. 934-944 ◽  
Author(s):  
Xin Li ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
High Heat ◽  
Heated Wall ◽  
Transfer Coefficients ◽  
Data Set ◽  
Laser Probe ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Spherical Bubbles

A laser-based method has been developed to measure the thickness of the liquid microlayer between a cap-shaped sliding bubble and an inclined heated wall. Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend on the evolution of the microlayer that forms between the bubble and the surface. Past experiments have used heat transfer measurements on uniform-heat-generation surfaces to infer the microlayer thickness through an energy balance. These studies have produced measurements of 20–100 μm for refrigerants and for water, but they have yet to be confirmed by a direct measurement that does not depend on a first-law closure. The results presented here are direct measurements of the microlayer thickness made from a reflectance-based fiber-optic laser probe. Details of the construction and calibration of the probe are presented. Data for saturated FC-87 and a uniform-temperature surface inclined at 2 deg to 15 deg from the horizontal are reported. Millimeter-sized spherical bubbles of FC-87 vapor were injected near the lower end of a uniformly heated aluminum plate. The laser probe yielded microlayer thicknesses of 22–55 μm for cap-shaped bubbles. Bubble Reynolds numbers range from 600 to 4800, Froude numbers from 0.9 to 1.7, and Weber numbers from 2.6 to 47. The microlayer thickness above cap-shaped bubbles was correlated to a function of inclination angle and a bubble shape factor. The successful correlation suggests that this data set can be used to validate the results of detailed models of the microlayer dynamics.

Numerical Investigation on Forced Convection in Circular Tubes With Septa

2008 ◽  
Author(s):  
D. Corrente ◽  
O. Manca ◽  
S. Nardini ◽  
D. Ricci ◽  
G. Masullo
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Forced Convection ◽  
High Heat ◽  
Ideal Gas ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Heating And Cooling ◽  
High Heat Transfer

Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility to increase heat transfer with gas is to employ extended surfaces. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, if the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa can significantly augment pressure drops. In this paper a numerical investigation is carried out on forced convection in circular isothermal tubes. The fluid is air and ideal gas model is employed. Septa are introduced and several shapes and arrangements are analyzed. The investigation is accomplished by means of the commercial code Fluent. A turbulence model is used. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients and pressure drops. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.

Heat Transfer Analysis of Microgrooved Evaporator and Condenser Surfaces Utilized in a High Heat Flux Two-Phase Flow Loop

2007 ◽  
Author(s):  
Edvin Cetegen ◽  
Thomas Baummer ◽  
Serguei Dessiatoun ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Heat ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Microgrooved Surface

This paper investigates the heat transfer and pressure drop analysis of micro grooved surfaces utilized in evaporators and condensers of a two-phase flow cooling loop. These devices utilize the vapor-liquid phase change to transfer large amounts of heat, and they offer substantially higher heat flux performance with lower pumping power than most liquid cooling technologies. Microgrooved surfaces, combined with force-fed evaporation and condensation technology discussed in this paper yield high heat transfer coefficients with low pressure drops. Our most recent results, aiming to test the limits of the technology, demonstrated dissipation of almost 1kW/cm2 from silicon electronics using HFE 7100 as the working fluid. In a compact two phase system, the heat generated by the electronic components can be absorbed by microgrooved evaporators and rejected through the microgrooved surface condensers to liquid cooled slots with high heat transfer coefficients and low pressure drops on the refrigerant side. In the case of air-cooling, the same microgrooved surface heat exchanger can reject heat with a heat transfer coefficient of 3847 W/cm2 and a pressure drop of 4156 Pa. These heat transfer processes have the added capability of being combined and used together in a self-contained system cooled either by liquid or air.

scholarly journals Numerical Analysis of Water Forced Convection in Channels with Differently Shaped Transverse Ribs

2011 ◽  
Vol 2011 ◽  
pp. 1-25 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Daniele Ricci
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
High Heat ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
High Heat Transfer ◽  
Friction Factors ◽  
Turbulent Water

Heat transfer enhancement technology has the aim of developing more efficient systems as demanded in many applications. An available passive method is represented by the employ of rough surfaces. Transversal turbulators enhance the heat transfer rate by reducing the thermal resistance near surfaces, because of the improved local turbulence; on the other hand, higher losses are expected. In this paper, a numerical investigation is carried out on turbulent water forced convection in a ribbed channel. Its external walls are heated by a constant heat flux. Several arrangements of ribs in terms of height, width, and shape are analyzed. The aim is to find the optimal configuration in terms of high heat transfer coefficients and low losses. The maximum average Nusselt numbers are evaluated for dimensionless pitches of 6, 8, and 10 according to the shape while the maximum friction factors are in the range of pitches from 8 to 10.

scholarly journals Heat Transfer Characteristics of Swirling Impinging Jets

2010 ◽  
Author(s):  
Karl J. Brown ◽  
Tim Persoons ◽  
Darina B. Murray
Keyword(s):  
Heat Transfer ◽  
Thermal Imaging ◽  
High Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Film Sensor ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Hot Film ◽  
Hot Film Sensor

Impinging jets are well renowned for their abilities to achieve significantly high heat transfer coefficients. It has been found in previous studies that the incorporation of a swirl in the flow can enhance heat transfer but it can also decrease it. The objective of this research is to discover the defining characteristics of swirling impinging jets and to find an optimal swirl geometry for enhancing the heat transfer of the system. Using thermal imaging and hot film sensor techniques the heat transfer distribution of the swirling jet is examined in the context of the flow field; heat flux fluctuations at the impinging surface are investigated also.

The Effect of the Combustor-Turbine Slot and Midpassage Gap on Vane Endwall Heat Transfer

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Stephen P. Lynch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
High Heat ◽  
Turbine Disk ◽  
Vortical Flow ◽  
Leakage Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
The Individual

Turbine vanes are generally manufactured as single- or double-airfoil sections that are assembled into a full turbine disk. The gaps between the individual sections, as well as a gap between the turbine disk and the combustor upstream, provide leakage paths for relatively higher-pressure coolant flows. This leakage is intended to prevent ingestion of the hot combustion flow in the primary gas path. At the vane endwall, this leakage flow can interfere with the complex vortical flow present there and thus affect the heat transfer to that surface. To determine the effect of leakage flow through the gaps, heat transfer coefficients were measured along a first-stage vane endwall and inside the midpassage gap for a large-scale cascade with a simulated combustor-turbine interface slot and a midpassage gap. For increasing combustor-turbine leakage flows, endwall surface heat transfer coefficients showed a slight increase in heat transfer. The presence of the midpassage gap, however, resulted in high heat transfer near the passage throat where flow is ejected from that gap. Computational simulations indicated that a small vortex created at the gap flow ejection location contributed to the high heat transfer. The measured differences in heat transfer for the various midpassage gap flowrates tested did not appear to have a significant effect.

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