Papers by Mojtaba Edalatpour
Advanced Functional Materials, 2020
Phase-change thermal diodes effectively transport heat unidirectionally, but are currently constr... more Phase-change thermal diodes effectively transport heat unidirectionally, but are currently constrained by either a gravitational dependence, a 1D configuration, or poor durability. Here, a novel bridging-droplet thermal diode which uniquely bypasses all of these existing constraints is developed. The diode is comprised of two opposing copper plates separated by an insulating gasket of micrometric thickness; one plate contains a superhydrophilic wick structure while the other is smooth and hydrophobic. In the forward mode of operation, water evaporates from the heated wicked plate and condenses on the hydrophobic plate. The large contact angle of the dropwise condensate enables bridging across the gap to replenish the wicked evaporator, providing sustained phase-change heat transfer. Conversely, in the reverse mode, the heat source is now on the hydrophobic plate, resulting in dryout and excellent thermal insulation across the gap. An orientation-independent heat transfer ratio (i.e., diodicity) as high as 85 was measured.
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Langmuir, 2019
The application of external uniform magnetic fields to ferrofluid droplets affects their magnetic... more The application of external uniform magnetic fields to ferrofluid droplets affects their magnetic order at the nanoscale as well as their shape at the macroscale, thus changing their magneto-viscosity and contact angle with the surface. In this work, the effects of external uniform magnetic fields on the contact angles between different oil-based ferrofluid droplets and a handful of horizontal surfaces of varying wettability were studied. The contact angle is no longer constant around the ferrofluid droplet, rather it varies in a rich, yet predictable way. Droplets dispensed in the presence of the magnetic field on oleophobic surfaces adjust such that the contact angle increases at the front and back ends and decreases at the two perpendicular positions. The opposite behavior is reported for ferrofluid droplets on oleophilic surfaces. These direction-dependent changes in contact angle can have a significant impact on the behavior of ferrofluid droplets on gradient surfaces, where they can either diminish or enhance the surface tension gradient. Our work is fundamentally relevant to potential applications involving the controlled movement of ferrofluid droplets on surfaces like lab-on-a-chip under the combined effects of a magnetic field and either a surface tension gradient or an electric field (i.e. electro-wetting). It is important to understand how the two effects interact for the optimal utilization of these effects in future applications.
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Reviewer's Recognition, 2019
The Editor and Editorial Board of the ASME Journal of Solar Energy Engineering would like to than... more The Editor and Editorial Board of the ASME Journal of Solar Energy Engineering would like to thank all of the reviewers for volunteering their expertise and time reviewing manuscripts in 2018. We are grateful to all of our reviewers for contributing. Below is a complete list of reviewer's for 2018 ...
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A B S T R A C T Most materials of practical interest are neither completely wetting nor completel... more A B S T R A C T Most materials of practical interest are neither completely wetting nor completely non-wetting. " Surface wett-ability " then refers to the degree that a surface is hydrophilic (i.e. water-loving) or hydrophobic (i.e. water-fearing). Through careful design, it is possible to alter the natural wettability of a surface to be more water-loving or water-fearing. This is principally achieved by modifying the surface chemistry and/or surface roughness. In some cases, modifying the surface may bring operational benefit or advantage. For example, aluminum and copper (which are used in the construction of heat exchangers) tend to retain water in application , which can degrade performance. Modifying the surface however to be superhydrophilic can help to spread out the condensate, reduce the air-side pressure drop, and facilitate drainage. Moreover, by creating a wettability pattern or gradient, it is possible to predetermine the initiating sites for condensation on a surface as well as facilitate droplet motion and/or control the water droplet movement path. In the first part of this review, the current state of the art of surface wettability modification and control techniques are presented, which includes topographical manipulation, chemical modification, as well as methods for creating gradient surfaces and patterned wettability. In the second part of this review, possible applications and the potential impact of these methodologies in energy systems are discussed with a special focus on heating, ventilation, air conditioning , and refrigeration (HVAC&R) systems and components.
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In this research, an inclined three-dimensional nanofluid-based tube-on-sheet flat plate solar co... more In this research, an inclined three-dimensional nanofluid-based tube-on-sheet flat plate solar collector (FPSC) working under laminar conjugated mixed convection heat transfer is numerically modeled. The working fluid is selected to be alumina/water (Al 2 O 3 /water) and results from heat transfer, entropy generation, and pressure drop points of view are being presented for various prominent parameters, namely volume fraction, nanopar-ticles diameter, Richardson and Reynolds numbers. According to the simulations, Nusselt number decreases as the Richardson number or volume fraction of the nanofluid rises, whereas heat transfer coefficient experiences an augmentation when volume concentration and the Richardson number surge. Also, data reveal that total entropy generation rate of the system declines when the alumina/water nanofluid is utilized inside the system as the volume fraction or the Richardson number increases. Additionally, it is found that increasing the nanoparticle volume concentration or the Richardson number diminishes the pressure drop considerably, whereas friction factor substantially proliferates as the Richardson number or volume fraction rises. Eventually, employment of larger alumina nanoparticles mean diameter eventuates in providing lower Nusselt number and apparent friction factor while it increases the pressure drop and heat transfer coefficient. Finally, comparing the efficiency of the presented FPSC design with those available in the literature shows a superior performance by the present design with its maximum occurring at 2 vol %.
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Flat plate solar collector (FPSC) is one of the most popular equipment among solar energy systems... more Flat plate solar collector (FPSC) is one of the most popular equipment among solar energy systems which can be utilized for heating of domestic or public buildings where the demands for hot water are quite indispensable. Although they have a number of benefits such as no need for sun tracking and low maintenance cost, their low thermal performance is considered as a hindrance in their extensive development. In this paper, a three-dimensional inclined tube-on-sheet flat plate solar collector is numerically modeled. The FPSC system is deemed to work under conjugated laminar mixed convection heat transfer mechanism while the operational fluid is selected to be Al 2 O 3 /water nanofluid. The influence of several parameters on the performance of the present FPSC, namely inlet alumina/water nanofluid temperature, and volume concentration, heat flux absorbed by the absorber plate, dimen-sionless numbers consist of Reynolds (Re), Grashof (Gr), Prandtl (Pr), and Richardson (Ri) are discussed on the heat transfer, fluid flow, and entropy generation. Furthermore, the effects of friction factor inside the riser as well as the pressure drop are taken into the account in this research. Results revealed that increasing the volume fraction of nanofluid at a fixed Reynolds number declines the outlet temperature whereas lowering the Reynolds number at a same volume fraction gives rise to higher outlet temperature. From heat transfer standpoint, it is observed that in a constant Reynolds number by increasing nanoparticle volume fraction, the Nusselt number falls while the heat transfer coefficient rises. In addition, rising the Reynolds number eventuates in friction factor reduction while the pressure drop augments. Moreover, from the obtained outcomes, it is figured out that generally using alumina/water nanofluid provides lower total entropy generation, in comparison with the water. Simulation data reveal that alteration in the heat flux does not have any sensible effects on the friction factor.
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Solar Energy, 2016
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Heat Transfer-Asian Research, 2016
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Journal of Renewable and Sustainable Energy, 2016
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ABSTRACT
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ABSTRACT
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International Communications in Heat and Mass Transfer, 2015
ABSTRACT
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Applied Thermal Engineering, 2016
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Thesis Chapters by Mojtaba Edalatpour
Most materials of practical interest are neither completely wetting nor completely non-wetting. T... more Most materials of practical interest are neither completely wetting nor completely non-wetting. Through careful design, it is possible to alter the natural wettability of a surface to be more omniphilic or omniphobic. This is principally realized by modifying the physics and/or the chemistry of the surface. In this work, the effects of external uniform magnetic fields on the behavior of the static contact angle of different oil-based ferrofluid droplets were examined for a handful of horizontal surfaces of varying wettability. Experimental results show that the static contact angle of ferrofluid droplets in a magnetic field is not constant around the periphery of the droplet on a horizontal surface, rather it varies in a rich, yet predictable way with the azimuthal angle and magnetic field strength. In addition, the spontaneous motion of two oil-based ferrofluid droplets on a wedge-shaped surface tension gradient was studied for two distinct surface tension gradient orientations in the presence of different external uniform magnetic fields (0-250G). Various wedge angles from 10° to 17° were studied. It was observed that for a given ferrofluid droplet size, larger wedge angles generally produced larger overall surface tension driving forces. As a result, higher droplet velocities were generally achieved in this case, but also shorter overall travel distances. Eventually, for each ferrofluid that was studied, a magnetic field was found above which the droplet was "pinned" on the surface, and droplet movement was stopped despite the underlying presence of the surface tension gradient force.
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Papers by Mojtaba Edalatpour
Thesis Chapters by Mojtaba Edalatpour