Convection Heat Transfer in the Presence of Apparent Slip.
Lam, Lisa.
2015
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Abstract: Structured
surfaces, e.g., superhydrophobic surfaces or superoleophobic surfaces are a class of
surfaces engineered on the micro- and nano-scale that resist wetting and decrease
hydrodynamic drag. The capacity to design these surfaces with a variety of textures and
coatings continues to develop and they are being considered for a wide variety of
application areas ranging from retarding ... read morefrost formation on airplane wings to drag
reduction in microchannel flows. This dissertation addresses four problems related to
heat transfer to flows over structured surfaces. We first investigate the problem of
heat transfer in a thermally developing, steady, laminar Couette flow in the presence of
hydrodynamic and thermal slip. Fluid temperature at the inlet to a parallel plate
channel is prescribed, as are various combinations of isothermal and adiabatic boundary
conditions along its surfaces. Analytical expressions incorporating arbitrary slip are
developed for temperature profiles, and developing and fully developed Nusselt numbers.
Representative results show the presence of thermal slip lowers the Nusselt number
relative to the no-slip value. The second problem we consider is liquid cooling in a
microgap lined with microscale ridges oriented parallel to the flow. Using available
expressions for Nusselt number and Poiseuille number as a function of hydrodynamic and
thermal slip length, thermal resistance expressions for a Poiseuille flow in a parallel
plate channel are developed in order at assess the relative contributions of convection
and caloric heat transfer. Water and a liquid metal, galinstan, are considered as the
working fluids. Notably heat transfer is enhanced with the use of structured surfaces in
the selected geometry. We develop a dimensionless expression to evaluate the tradeoff
between the pressure stability of a liquid-solid-gas system and hydrodynamic slip.
Finally, we consider entrance effects and the temperature dependence of thermophysical
properties and quantify their the effect on thermal resistance. The third problem we
consider is evaporation and condensation across menisci between ridge structures. We
assume that the gaps between ridges, where the vapor phase resides, are closed systems;
therefore, the net rate of heat transfer across menisci is zero. The reduction in
apparent thermal slip length due to evaporation and condensation relative to the
limiting case of an adiabatic meniscus is quantified. Results suggest that interfacial
evaporation and condensation need be considered in the design of microchannels lined
with structured surfaces for direct liquid cooling of electronics applications. A
quantitative means to do so is elucidated. The final problem we consider is the effect
of meniscus curvature on thermal slip length. Perturbation theory is used to develop
expressions that account for the change to temperature that occurs in the limit of small
deflections to an adiabatic meniscus. Constant heat flux boundary conditions are
considered at the tips of the ridges. Results show that slip length is sensitive to
meniscus protrusion angle at low solid fractions. When liquid pressure is higher than
that of the gas, a negative protrusion angle exists and heat transfer is enhanced.
Conversely, the presence of bubble mattresses formed because the pressure in the gas is
higher than that of the liquid reduces heat transfer to the liquid at low protrusion
angles.
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Marc Hodes.
Committee: Scott MacLachlan, Ryan Enright, Vincent Manno, Jeffrey Guasto, and Nikhil Nair.
Keyword: Mechanical engineering.read less - ID:
- j9602b562
- Component ID:
- tufts:21465
- To Cite:
- TARC Citation Guide EndNote
