Facile Fabrication of Nanostructured Microchannels for Flow Boiling Heat Transfer Enhancement (original) (raw)
Related papers
Enhancement of flow boiling heat transfer in microchannels by nano- and micro-surface treatments
Mécanique & Industries, 2011
Ce papier présente nos études sur le transfert thermique en ébullition convective dans les microcanaux dont l'objectif est de développer des systèmes de refroidissement compacts qui peuvent s'adapter aux composants de puissance miniaturisés. Les nano-et micro-structurations de surface ont été utilisées comme des techniques innovantes permettant d'améliorer la performance de transfert thermique et de retarder le phénomène d'assèchement intermittent. It a été observé que les surfaces contenant des microstructures ont de meilleurs coefficients de transfert thermique par rapport aux surfaces lisses (jusqu'à 85% d'amélioration). En particulier, en rendant cette surface structurée plus mouillante, l'assèchement intermittent a significativement retardé.
Enhanced flow boiling in a microchannel with integration of nanowires
Convective heat transfer performance of a micro-channel with copper nanowires (CuNWs) coatings has been investigated experimentally. Experimental studies were carried out on a bottom surface heated single micro-channel of 672 mm hydraulic diameter using de-ionized (DI) water as coolant. Nanowires were directly grown on the bottom surface of the micro-channel using electrochemical deposition technique. Both single-phase and two-phase convective heat transfer experiments were performed at different mass flux and different degree of sub-cooling. The results from microchannel with bare surface are used as the baseline data. CuNWs coatings have been found to enhance single-phase heat transfer rate by up to w25%, whereas in the flow boiling regime, the enhancement was up to w56% with a pressure drop increase by w20% in the single-phase regime. The obvious change of pressure drop in the fully developed boiling regime was not observed.
This study experimentally investigates single phase heat transfer and pressure drop characteristics of a shallow rectangular microchannel heat sink whose surface is enhanced with copper nanowires (CuNWs). The hydraulic diameter of the channel is 672 μm and the bottom wall is coated with Cu nanowires (CuNWs) of 200 nm in diameter and 50 μm in length. CuNWs are grown on the Cu heat sink by electrochemical synthesis technique which is inexpensive and readily scalable. The heat transfer and pressure drop results of CuNWs enhanced heat sink are compared with that of bare copper surface heat sink using deionized (DI) water as the working fluid at Reynolds Number (Re) ranging from 106-636. The experimental results indicate an enhancement in Nusselt Number (Nu) at all Re with a maximum enhancement of 24% at Re = 106. An increase in pressure drop is also observed in all test cases due to enhanced roughness. The enhanced thermal performance is attributed to the enhanced wettability and the increased heat transfer surface area due to the addition of CuNWs arrays. The surface morphology of the heat sink has also been studied before and after heat transfer experiments through SEM to determine the effect of fluid flow on CuNWs arrays. The SEM results demonstrate no notable changes in surface morphology for the Re range in which experiments have been conducted and for single phase flow.
Scientific Reports, 2017
Performance enhancement of the two-phase flow boiling heat transfer process in microchannels through implementation of surface micro- and nanostructures has gained substantial interest in recent years. However, the reported results range widely from a decline to improvements in performance depending on the test conditions and fluid properties, without a consensus on the physical mechanisms responsible for the observed behavior. This gap in knowledge stems from a lack of understanding of the physics of surface structures interactions with microscale heat and mass transfer events involved in the microchannel flow boiling process. Here, using a novel measurement technique, the heat and mass transfer process is analyzed within surface structures with unprecedented detail. The local heat flux and dryout time scale are measured as the liquid wicks through surface structures and evaporates. The physics governing heat transfer enhancement on textured surfaces is explained by a deterministic...
Flow boiling with deionized water in silicon (Si) microchannels was drastically enhanced in a single annular flow boiling regime enabled by superhydrophilic Si nanowire inner walls. Part I of this study focuses on characterizing enhanced flow boiling heat transfer. Part II focuses on revealing mechanisms in governing pressure drop and critical heat flux (CHF). Compared to flow boiling in plain-wall microchannels without using inlet restrictors (IRs), the average heat transfer coefficient (HTC) and CHF were enhanced by up to 326% and 317% at a mass flux of 389 kg/m 2 s, respectively. Additionally, compared with flow boiling in microchannels with IRs, HTC of flow boiling in the single annular flow was enhanced by up to 248%; while CHF in the new flow boiling regime was 6.4-25.8% lower. The maximum HTC reached 125.4 kW/m 2 K at a mass flux of 404 kg/m 2 s near the exits of microchannels. The significantly promoted nucleate boiling, induced liquid film renewal, and enhanced thin-film evaporation in the self-stabilized and single flow boiling regime are the primary reasons behind the significant heat transfer enhancements during flow boiling.
Methods and preliminary results on enhanced boiling heat transfer in second generation microchannels
Microfluidics and Nanofluidics, 2006
This paper reviews literature on conventional scale boiling enhancement techniques by means of reentrant cavities and discusses various avenues the knowledge obtained from that research can be used to enhance boiling in microchannels. Fabrication techniques developed by the Micro Thermal-Fluids Laboratory at Rensselaer Polytechnic Institute together with the Advanced Microsystems Materials Laboratory at McGill University are discussed and preliminary data are given. These results demonstrate the potential for improving boiling heat transfer characteristics in microchannels and introduce next generation microchannel heat transfer technology.
C-2006 Forced convection boiling in microchannels for improved heat transfer.pdf
This paper presents experimental results from research investigating the heat transfer capabilities of microchannel surfaces using a novel force-fed boiling and evaporation technique. The evaporative surfaces being investigated consist of a series of parallel, high-aspect ratio, open topped microchannels. The different sample surfaces vary in channel density, channel aspect ratio, and channel width and have heat transfer surface areas up to ten times their nominal surface areas. Liquid enters the channels of the evaporative surface from above through a developed system of feed channels. This method organizes a liquid-vapor circulation at the boiling surface that results in dissipation of very high heat fluxes in the boiling/thin film evaporation mode. By using the force-fed boiling technique, nominal area heat transfer rates of 100,000 W/m 2 -K have been achieved with HFE-7100 as the working fluid [1]. In force-fed boiling, the many very short microchannels are working in parallel; therefore the feed pressure and pumping power are very low. This technique may prove valuable to a wide range of heat transfer applications, particularly for heat removal at high heat flux surfaces.
In a microchannel system, a higher mass velocity can lead to enhanced flow boiling performances, but at a cost of two-phase pressure drop. It is highly desirable to achieve a high heat transfer rate and critical heat flux (CHF) exceeding 1 kW/cm 2 without elevating the pressure drop, particularly, at a reduced mass velocity. In this study, we developed a microchannel configuration that enables more efficient utilization of the coolant through integrating multiple microscale nozzles connected to auxiliary channels as well as microscale reentry cavities on sidewalls of main microchannels. We achieved a CHF of 1016 W/cm 2 with a 50% less mass velocity, i.e., 680 kg/m 2 s, compared to the two-nozzle configuration developed in our previous studies. Two primary enhancement mechanisms are: (a) the enhanced global liquid supply by four evenly distributed micronozzles, particularly near the outlet region and (b) the effective management of local dryout by the capillary flow-induced sustainable thin liquid film resulting from an array of microscale cavities. A significantly improved heat transfer coefficient of 131 kW/m 2 K at a mass velocity of 680 kg/m 2 s is attributed to the enhanced nucleate boiling, the established capillary/ thin film evaporation, and the induced advection from the present microchannel configuration. All these significant enhancements have been achieved with a $55% lower two-phase pressure drop. Published by AIP Publishing. [http://dx.
Experimental Investigation of Single-Phase Heat Transfer on Scalable Nanostructured Microchannels
Proceedings of the 3rd World Congress on Mechanical, Chemical, and Material Engineering, 2018
In this paper, the thermal performance of nanostructured (CuO nanostructures) copper multiple parallel microchannels for single-phase flow is studied. The test section consists of 6 parallel channels and each channel is 350 µm wide and 605 µm deep with an aspect ratio of 1.729. Microchannels are covered on the top surface with an acrylic sheet. A cartridge heater is inserted at the bottom of the microchannels for supplying the desired heat flux and the position of the heater is determined numerically. Deionized water (DI) is used as the working fluid in the experiment. Single-phase pressure drop and heat transfer coefficient in multiple nanostructured microchannels are measured. A maximum enhancement of ~21% in Nusselt number is reported without any observable increase in pressure drop upon the incorporation of nanostructured in microchannels. The current study could provide a suitable low-cost framework for investigating the potential of nanostructures in further enhancement of single phase heat transfer coefficients in microchannel geometry.
International Journal of Heat and Mass Transfer, 2018
Saturated flow boiling experiments were conducted to investigate the influence of surface wettability on the hydraulic and thermal transport performance in a large width-to-height aspect ratio, one-sided heated rectangular microchannel with deionized water as the working fluid. The contact angles of the bare silicon wafer surface and superhydrophilic surface after deposited by a thin film of 100-nmthickness silicon dioxide were 65°± 3°and less than 5°respectively, both of which were utilized as heated surfaces of the microchannel. Parametric experimental studies were carried out with the inlet vapor quality varied from 0.03 to 0.1 and the wall heat fluxes spanned from 4 W/cm 2 to 20 W/cm 2 , at various mass fluxes ranging from 120 to 360 kg/m 2 s. High speed flow visualizations were conducted coupled with instrumental measurements to illustrate the effects of heat flux, mass flux and two phase inlet quality on the local heat transfer coefficient, averaged heat transfer performance, two phase flow structure and pressure drop characteristics for surfaces with distinct surface wettability characteristics in the microchannel. Experimental results showed that the local heat transfer coefficient decreased first until approaching a minimum value and then increased towards the exit along the flow direction. Severe heat transfer deterioration was obtained for the bared silicon wafer surface with increased inlet vapor quality and heat flux, resulting from the local dryout phenomenon as can be verified by the flow visualization. While the heat transfer performance of the superhydrophilic surface was relatively constant due to continuous and uniform distribution of the thin liquid film on the heated surface during annular flow dominance and subsequent delay to partial dryout occurrence, which outperformed the untreated hydrophilic surface without additional pressure drop penalty.