EFECTS OF SURFACE CONDITION AND WORKING FLUID ON LIQUID FILM BREAKDOWN DURING HEAT TRANSFER

Heat transfer correlations were developed for the liquid film region, in the evaporator section of closed, two-phase, gravity-assisted thermosyphons in the following regimes: (a) laminar convection, at low heat fluxes, (b) combined convection, at intermediate heat fluxes, and (c) nucleate boiling, at high heat fluxes. These correlations were based on a data set consisting of a total of 305 points for ethanol, acetone, R-11, and R-113 working fluids, wall heat fluxes of 0.99–52.62 kW/m2, working fluid filling ratios of 0.01–0.62, inner diameters of 6–37 mm, evaporator section lengths of 50–609.6 mm, and vapor temperatures of 261–352 K. The combined convention data were correlated by superimposing the correlations of laminar convention and nucleate boiling using a power law approach, to ensure smooth transition among the three heat transfer regimes. The three heat transfer correlations developed in this work are within ±15 percent of experimental data.

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Inverse-thermocapillary evaporation in a thin liquid film of self-rewetting fluid

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-05-2020-0266 ◽

2020 ◽

Vol ahead-of-print (ahead-of-print) ◽

Author(s):

Elaine Lim ◽

Tze Cheng Kueh ◽

Yew Mun Hung

Keyword(s):

Heat Transfer ◽

Surface Tension ◽

Liquid Film ◽

Temperature Region ◽

Thin Liquid Film ◽

Thermocapillary Flow ◽

Working Fluid ◽

Surface Tension Gradient ◽

Thermocapillary Effect ◽

Content Type

Purpose The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of long-chain alcohol. Design/methodology/approach A long-wave evolution model modified for self-rewetting fluids is used to study the inverse thermocapillary characteristics of an evaporating thin liquid film. The flow attributed to the inverse thermocapillary action is manifested through the streamline plots and the evaporative heat transfer characteristics are quantified and analyzed. Findings The thermocapillary flow induced by the negative surface tension gradient drives the liquid from a low-surface-tension (high temperature) region to a high-surface-tension (low temperature) region, retarding the liquid circulation and the evaporation strength. The positive surface tension gradients of self-rewetting fluids induce inverse-thermocapillary flow. The results of different working fluids, namely, water, heptanol and DAS of heptanol, are examined and compared. The thermocapillary characteristic of a working fluid is significantly affected by the sign of the surface tension gradient and the inverse effect is profound at a high excess temperature. The inverse thermocapillary effect significantly enhances evaporation rates. Originality/value The current investigation on the inverse thermocapillary effect in a self-rewetting evaporating thin film liquid has not been attempted previously. This study provides insights on the hydrodynamic and thermal characteristics of thermocapillary evaporation of self-rewetting liquid, which give rise to significant thermal enhancement of the microscale phase-change heat transfer devices.

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Orientation-Independent Atomization Heat Transfer Cell for Thermal Management of Microelectronics

2003 International Electronic Packaging Technical Conference and Exhibition, Volume 2 ◽

10.1115/ipack2003-35299 ◽

2003 ◽

Cited By ~ 3

Author(s):

Samuel N. Heffington ◽

Ari Glezer

Keyword(s):

Heat Transfer ◽

Liquid Film ◽

Heat Dissipation ◽

Heated Surface ◽

Thin Liquid Film ◽

Transfer Cell ◽

Working Fluid ◽

Small Scale ◽

Operating Characteristics ◽

Diaphragm Pump

This paper describes a new gravity-independent version of a two-phase cooling, closed heat transfer cell, similar to a thermosyphon. The cooling method is based upon a Vibration-Induced Droplet Atomization, or VIDA, process that can generate small liquid droplets inside a closed cell and propel them onto a heated surface. The VIDA technique involves the violent break-up of a liquid film into a shower of droplets by vibrating a piezoelectric actuator and accelerating the liquid film at resonant conditions. A piezoelectric diaphragm pump is used to supply a constant stream of liquid to the VIDA atomizer enabling gravity-independent operation. The atomized secondary droplets continually coat the heated surface with a thin liquid film that evaporates. The resulting vapor is condensed on internal surfaces of the heat transfer cell as well as the liquid working fluid. The condensed liquid is collected and returned to the atomizing driver by the piezoelectric diaphragm pump. A small-scale gravity independent VIDA atomizer generating spherical droplets of relatively uniform diameter and having sufficient momentum to reach the remotely located heated source has been constructed. Initial test data described in this study include the operating characteristics of the VIDA spray and heat transfer capabilities. Heat dissipation levels as high as 195 W have been measured from an evaporation surface held below 120°C at atmospheric pressure.

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Flow Visualization inside Thermosyphon for Measuring Heat Transfer Limit

Journal of Heat Transfer ◽

10.1115/1.4035581 ◽

2017 ◽

Vol 139 (2) ◽

Cited By ~ 2

Author(s):

Jungho Lee ◽

Jaebum Park ◽

Jinsub Kim ◽

Seung M. You

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Liquid Film ◽

Transfer Coefficient ◽

Heat Pipe ◽

Heat Input ◽

Nucleate Boiling ◽

Working Fluid ◽

Heat Transfer Limit ◽

Condensed Liquid

Heat pipe is a highly effective passive heat transfer device using phase change within small temperature difference. It is noted that heat pipe should be operated under heat transfer limit for practical heat pipe heat exchanger applications. The measurement in local and overall heat transfer coefficient is significant to anticipate the heat transfer limit. The wall temperatures and inner working fluid temperatures were measured to determine the heat transfer coefficient. The adiabatic part with transparent Pyrex glass was visualized to understand flow behaviors inside the thermosyphon. The dynamic behaviors of condensed working fluid were visualized for the specific tilted angle and power inputs at pseudo steady-state. At low heat input of 250W, the thin condensed liquid film is observed to be returned from condenser to evaporator. With increasing heat input of 500W, the nucleate boiling starts to occur in evaporator. More activated vapors turn to make wavy motion in free surface of the returned condensed liquid film which is thickened. In power input of 1,250W, the vigorous flow motion happens periodically and the interaction between vapor and liquid bursting reaches a maximum heat transfer which is led to the heat transfer limit in the thermosyphon. Over heat transfer limit (2,000 and 2,500W), the overall heat transfer is decreased when the degree of bursting motion between vapor and liquid is gradually reduced.

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Experimental study of thermohydraulic characteristics and irreversibility analysis of novel axial corrugated tube with spring tape inserts

The European Physical Journal Applied Physics ◽

10.1051/epjap/2020200192 ◽

2020 ◽

Vol 92 (3) ◽

pp. 30901

Author(s):

Suvanjan Bhattacharyya ◽

Debraj Sarkar ◽

Ulavathi Shettar Mahabaleshwar ◽

Manoj K. Soni ◽

M. Mohanraj

Keyword(s):

Heat Transfer ◽

Experimental Study ◽

Thermal Performance ◽

Working Fluid ◽

The Novel ◽

Heat Exchanger Tube ◽

Heat Transfer Augmentation ◽

Corrugated Tube ◽

The Impact ◽

Exchanger Tube

The current study experimentally investigates the heat transfer augmentation on the novel axial corrugated heat exchanger tube in which the spring tape is introduced. Air (Pr = 0.707) is used as a working fluid. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The experimental study is further extended by varying the important parameters like spring ratio (y = 1.5, 2.0, 2.5) and Reynolds number (Re = 10 000–52 000). The angular pitch between the two neighboring corrugations and the angle of the corrugation is kept constant through the experiments at β = 1200 and α = 600 respectively, while two different corrugations heights (h) are analyzed. While increasing the corrugation height and decreasing the spring ratio, the impact of the swirling effect improves the thermal performance of the system. The maximum thermal performance is obtained when the corrugation height is h = 0.2 and spring ratio y = 1.5. Eventually, correlations for predicting friction factor (f) and Nusselt number (Nu) are developed.

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