56,767 research outputs found
Exceptional Anti-Icing Performance of Self-Impregnating Slippery Surfaces
A heat exchange interface at subzero temperature in a water vapor
environment, exhibits high probability of frost formation due to freezing
condensation, a factor that markedly decreases the heat transfer efficacy due
to the considerable thermal resistance of ice. Here we report a novel strategy
to delay ice nucleation on these types of solid-water vapor interfaces. With a
process-driven mechanism, a self-generated liquid intervening layer immiscible
to water, is deposited on a textured superhydrophobic surface and acts as a
barrier between the water vapor and the solid substrate. This liquid layer
imparts remarkable slippery conditions resulting in high mobility of condensing
water droplets. A large increase of the ensuing ice coverage time is shown
compared to the cases of standard smooth hydrophilic or textured
superhydrophobic surfaces. During deicing of these self-impregnating surfaces
we show an impressive tendency of ice fragments to skate expediting defrosting.
Robustness of such surfaces is also demonstrated by operating them under
subcooling for at least 490hr without a marked degradation. This is attributed
to the presence of the liquid intervening layer, which protects the substrate
from hydrolyzation enhancing longevity and sustaining heat transfer efficiency.Comment: This document is the Accepted Manuscript version of a Published Work
that appeared in final form in ACS Applied Materials & Interfaces, copyright
(c) American Chemical Society after peer review and technical editing by the
publisher. To access the final edited and published work see
pubs.acs.org/doi/abs/10.1021/acsami.7b0018
Drying air-induced disturbances in multi-layer coating systems
A range of new experimental techniques is developed to quantify drying-air induced disturbances on low viscosity
single and multi-layer coating systems. Experiments on prototype slide-bead coating systems show that the surface
disturbances take the form of a wavelike pattern and quantify precisely how its amplitude increases rapidly with wet
thickness and decreases with viscosity. Heat transfer measurements show that the redistribution of water to form an
additional lower viscosity carrier layer while increasing the solids concentration of the upper layer or layers enables
the maximum drying rate, for which drying-air induced surface disturbances are acceptably small, to be increased
with significant commercial benefits
Understanding and Design of an Arduino-based PID Controller
This thesis presents research and design of a Proportional, Integral, and Derivative (PID) controller that uses a microcontroller (Arduino) platform. The research part discusses the structure of a PID algorithm with some motivating work already performed with the Arduino-based PID controller from various fields. An inexpensive Arduino-based PID controller designed in the laboratory to control the temperature, consists of hardware parts: Arduino UNO, thermoelectric cooler, and electronic components while the software portion includes C/C++ programming. The PID parameters for a particular controller are found manually. The role of different PID parameters is discussed with the subsequent comparison between different modes of PID controllers. The designed system can effectively measure the temperature with an error of ± 0.6℃ while a stable temperature control with only slight deviation from the desired value (setpoint) is achieved. The designed system and concepts learned from the control system serve in pursuing inexpensive and precise ways to control physical parameters within a desired range in our laboratory
An experimental investigation of natural convection with solidification in a differentially heated cavity
This paper introduces an experimental rig used to produce data for the validation of computational models of natural convection within water in an enclosed cavity. The rig consisted of a rectangular cavity with the two long sides maintained at constant temperature. All other surfaces were insulated and adiabatic except for the top surface which was a free surface with an air gap between the free surface and the insulation. Experimental data in the form of velocity, ice growth rate and profiles are presented at 30 min time steps with a cold wall temperature of −10 °C and hot wall temperature of 5 °C. The data produced has systematic and random errors of ±0.4% and ±0.5%, respectively
New devices for flow measurements: Hot film and burial wire sensors, infrared imagery, liquid crystal, and piezo-electric model
An experimental program aimed at identifying areas in low speed aerodynamic research where infrared imaging systems can make significant contributions is discussed. Implementing a new technique, a long electrically heated wire was placed across a laminar flow. By measuring the temperature distribution along the wire with the IR imaging camera, the flow behavior was identified
Three-dimensional scanning of specular and diffuse metallic surfaces using an infrared technique
For the past two decades, the need for three-dimensional (3-D) scanning of industrial objects has increased significantly and many experimental techniques and commercial solutions have been proposed. However, difficulties remain for the acquisition of optically non-cooperative surfaces, such as transparent or specular surfaces. To address highly reflective metallic surfaces, we propose the extension of a technique that was originally dedicated to glass objects. In contrast to conventional active triangulation techniques that measure the reflection of visible radiation, we measure the thermal emission of a surface, which is locally heated by a laser source. Considering the thermophysical properties of metals, we present a simulation model of heat exchanges that are induced by the process, helping to demonstrate its feasibility on specular metallic surfaces and predicting the settings of the system. With our experimental device, we have validated the theoretical modeling and computed some 3-D point clouds from specular surfaces of various geometries. Furthermore, a comparison of our results with those of a conventional system on specular and diffuse parts will highlight that the accuracy of the measurement no longer depends on the roughness of the surface
Investigation of surface water behavior during glaze ice accretion
A series of experimental investigations that focused on isolating the primary factors that control the behavior of unfrozen surface water during glaze ice accretion were conducted. Detailed microvideo observations were made of glaze ice accretions on 2.54 cm diam cylinders in a closed-loop refrigerated wind tunnel. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film, a rough zone where surface tension effects caused coalescence of surface water into stationary beads, and a zone where surface water ran back as rivulets. The location of the transition from the smooth to the rough zone was found to migrate towards the stagnation point with time. Comparative tests were conducted to study the effect of the substrate thermal and roughness properties on ice accretion. The importance of surface water behavior was evaluated by the addition of a surface tension reducing agent to the icing tunnel water supply, which significantly altered the accreted glaze ice shape. Measurements were made to determine the contact angle behavior of water droplets on ice. A simple multizone modification to current glaze ice accretion models was proposed to include the observed surface roughness behavior
Heat Transfer and Pressure Drop in a Developing Channel Flow with Streamwise Vortices
Experiments to assess the heat transfer and pressure-drop effects of delta-wing
vortex generators placed at the entrance of developing channel flows are reported in
this study. The experimental geometry simulates common heat exchanger
configurations and tests are conducted over a velocity range important to heating, air
conditioning and refrigeration. An innovative liquid-crystal thermography technique
is used to determine the local and average Nusselt numbers for an isoflux channel
wall, and conventional methods are used to determine the Fanning friction factor.
Vortex generators with aspect ratios of A = 2 and A = 4 are studied at attack angles
of a. = 20?? to 45????. The results indicate that the streamwise vortices generated by a
delta wing can enhance local Nusselt numbers by more than 200% in a developing
channel flow. Under some conditions, the spatially average Nusselt number nearly
doubled for a heat transfer area that was 37 to 63 times the wing area. The Fanning
friction factor increased by a few percent to nearly 60%, depending on the Reynolds
number.Air Conditioning and Refrigeration Project 4
Visualization techniques to experimentally model flow and heat transfer in turbine and aircraft flow passages
Increased attention to fuel economy and increased thrust requirements have increased the demand for higher aircraft gas turbine engine efficiency through the use of higher turbine inlet temperatures. These higher temperatures increase the importance of understanding the heat transfer patterns which occur throughout the turbine passages. It is often necessary to use a special coating or some form of cooling to maintain metal temperatures at a level which the metal can withstand for long periods of time. Effective cooling schemes can result in significant fuel savings through higher allowable turbine inlet temperatures and can increase engine life. Before proceeding with the development of any new turbine it is economically desirable to create both mathematical and experimental models to study and predict flow characteristics and temperature distributions. Some of the methods are described used to physically model heat transfer patterns, cooling schemes, and other complex flow patterns associated with turbine and aircraft passages
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