Phase change heat transfer from nano and micro size droplets on a non-flat substrate

Date

2019

Author

Rezaeimoghaddam, Mohamma

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

261
views

0
downloads

Heat transfer via condensation/evaporation is a major contributor to heat removal in numerous engineering applications. When the dimensions of a liquid droplet or film reaches the order of micrometers the shape of the liquid-vapor interface is dominated by the capillary forces and the effect of gravity subsides. As the dimensions of the phase change liquid approaches nanometer size, the interface shape is strongly affected by dispersion effects, predominantly in the neighborhood of the contact line. At the close proximity of the contact line, continuum mechanics breaks down due to the extreme thin liquid films, requiring the use of molecular dynamics to assess the micro contact angle at the intersection of the solid-liquid-vapor boundary. The rate of phase change is a strong function of the temperature and pressure difference at the interface as well as the liquid film thickness. In heat pipe applications, the majority of heat transfer is due to latent heat and understanding the dynamics of phase change is crucial to improving the performance of heat pipes. Thin film evaporation and condensation, droplet condensation and evaporation, unsteady growth and coalescence of condensing droplets and films are phenomena encountered in grooved heat pipes. In this thesis a methodology for solving the augmented Young-Laplace equation to determine the shape of the liquid interface during evaporation and condensation phase change is developed, the results of which are extrapolated to the limit of continuum to match the contact angle predicted by molecular dynamics simulations. This approach is also used to simulate the growth and coalescence of liquid droplets using a quasisteady assumption, the results of which can be applied to the condensation on the fin top of grooved heat pipes. Finally, the effects of surface waviness and roughness on the shape and phase change rate of liquid films are investigated for surfaces generated using manufacturing techniques in common use.

Subject Keywords

Heat, Heat Transmission, Heat Transmission Research, Thin films, disjoining pressure, droplet coalescence, phase change, surface waviness.

URI

http://etd.lib.metu.edu.tr/upload/12623397/index.pdf
https://hdl.handle.net/11511/43675

Collections

Graduate School of Natural and Applied Sciences, Thesis

Suggestions

OpenMETU
Core

Performance analysis of grooved heat pipes using 3-D multi-channel thermal resistance network Sezmen, Ramazan Aykut; Dursunkaya, Zafer; Çetin, Barbaros; Department of Mechanical Engineering (2021-9) Heat pipes are phase change heat transfer devices that transfer high amounts of heat with low temperature differences compared to conventional cooling techniques due to their high thermal conductivity. Since heat pipes do not require any external power supply and not involve any moving parts, they are preferred for high reliability applications and in wide range of industrial applications from thermal management of electronics to space applications. Essentially, heat pipes use the advantage of occurring pha...
PERFORMANCE ASSESSMENT OF COMMERCIAL HEAT PIPES WITH SINTERED AND GROOVED WICKS UNDER NATURAL CONVECTION Atay, Atakan; Sariarslan, Busra; Kuscu, Yigit F.; Saygan, Samet; Akkus, Yigit; Gurer, A. Turker; Cetin, Barbaros; Dursunkaya, Zafer (2019-01-01) Heat pipes are widely used in thermal management of high heat flux devices due to their ability of removing high heat loads with small temperature differences. While the thermal conductivity of standard metal coolers is approximately 100-500 W/m.K, effective thermal conductivities of heat pipes, which utilize phase-change heat transfer, can reach up to 50,000 W/m.K. In industrial applications, commercially available heat pipes are commonly preferred by thermal engineers due to their low cost and versatility...
Numerical analysis of laminar forced convection with temperature-dependent thermal conductivity of nanofluids and thermal dispersion Özerinç, Sezer; Kakac, S. (2012-12-01) Nanofluids are promising heat transfer fluids due to their high thermal conductivity. In order to utilize nanofluids in practical applications, accurate prediction of forced convection heat transfer of nanofluids is necessary. In the first part of the present study, we consider the application of some classical correlations of forced convection heat transfer developed for the flow of pure fluids to the case of nanofluids by the use of nanofluid thermophysical properties. The results are compared with experi...
Modeling of multidimensional heat transfer in a rectangular grooved heat pipe / Odabaşı, Gülnihal; Dursunkaya, Zafer; Department of Mechanical Engineering (2014) Heat pipes are generally preferred for electronics cooling application due to large heat transfer capacity in spite of small size. Micro heat pipes use small channels, whose dimension is on the order of micrometers, to generate necessary capillary action maintaining fluid flow for heat pipe operation. In the present study a flat micro heat pipe with rectangular cross section is analyzed numerically. A simplified axial fluid flow model is utilized to find liquid-vapor interface shape variation along the heat...
Modeling guided heat pipe design methodology and experimental validation for flat grooved heat pipes Saygan, Samet; Dursunkaya, Zafer; Çetin, Barbaros; Department of Mechanical Engineering (2021-2-24) Heat pipes are commonly preferred thermal management devices due to their rapid heat transfer characteristics, small size and reliability. It is crucial to design heat pipes that accurately match the requirements of the system to be thermally managed. In the present study, a numerical design and diagnosis simulation tool for heat pipes is developed and verified for grooved heat pipes. A modular heat pipe experimental setup is designed and manufactured. In order to decide on the geometric parameters of the h...

Citation Formats

M. Rezaeimoghaddam, “Phase change heat transfer from nano and micro size droplets on a non-flat substrate,” Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Mechanical Engineering., Middle East Technical University, 2019.