Effect of ultrasound on frost formation on a cold flat surface in atmospheric air flow

2010 ◽  
Vol 34 (8) ◽  
pp. 1247-1252 ◽  
Author(s):  
Dong Li ◽  
Zhenqian Chen ◽  
Mingheng Shi
Keyword(s):  
Flat Surface ◽  
Air Flow ◽  
Frost Formation ◽  
Atmospheric Air

Observations of Early-Stage Frost Formation on a Cold Plate in Atmospheric Air Flow

2003 ◽  
Vol 125 (1) ◽  
pp. 95-102 ◽  
Author(s):  
Chin-Hsiang Cheng ◽  
Keng-Hsien Wu
Keyword(s):  
Growth Rate ◽  
Early Stage ◽  
Air Flow ◽  
Growth Period ◽  
Layer Growth ◽  
Cold Plate ◽  
Frost Formation ◽  
Atmospheric Air ◽  
Frost Layer ◽  
Frost Growth

The present study is conducted to investigate the frost formation on a cold plate in atmospheric air flow by means of experimental and theoretical methods. In order to provide observations for the early stage of the frost growth process, a microscopic image system is used to record the pattern and the thickness of the frost layer per five seconds after the onset of frost formation. In this study, a multiple-step ascending frost growth pattern caused by melting of frost crystals at the frost surface has been observed. Effects of velocity, temperature and relative humidity of air (V,Ta, and ϕ) are studied, and the surface temperature of the cold plate Tw is also varied. The considered ranges of these dominant variables are: 2⩽V⩽13 m/s, 20⩽Ta⩽35°C, 40 percent ⩽ϕ⩽80 percent, and −13⩽Tw⩽−2°C. The theoretical model presented by Cheng and Cheng [22] for predicting the frost growth rate during the frost layer growth period is verified. Results show that the predictions of frost growth rate by the model agree with the experiment data, especially for the frost layer growth period.

scholarly journals Performance of PV Panel Mounting Structure for Flat Surface and Roof-Top in UAE Climatic Conditions

2015 ◽  
Vol 07 (1) ◽  
Keyword(s):  
High Probability ◽  
Flat Surface ◽  
Air Flow ◽  
Climatic Conditions ◽  
Pv System ◽  
Flat Surfaces ◽  
Pv Panel ◽  
Short Span ◽  
Flat Roof ◽  
Surface Mounting

PV Panel mounting structure for ground, flat surface and rooftops are getting common and gaining their popularity for several reasons, with availability of vast land that can easily be turned into flat surfaces and flat roof tops of buildings, there is a high probability of such products getting common in short span of time in this region. Conventional mounting structures require ample amount of time for them to be ready for installation, such flat surface mounting structures reduces or eliminates a huge chunk of expense. The efficiency is effected due to the tilt which is obvious, but the effect on performance of the rooftop PV system due to temperature and less air flow is discussed in this paper.

scholarly journals Shortening Stabilization Time Using Pressurized Air Flow in Manufacturing Mesophase Pitch-Based Carbon Fiber

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 1911 ◽  
Author(s):  
Hiroki Shimanoe ◽  
Seunghyun Ko ◽  
Young-Pyo Jeon ◽  
Koji Nakabayashi ◽  
Jin Miyawaki ◽  
...  
Keyword(s):  
Heating Rate ◽  
Mechanical Performance ◽  
Air Flow ◽  
Mesophase Pitch ◽  
Homogeneous Distribution ◽  
Oxidation Reactions ◽  
Stabilization Time ◽  
Soaking Time ◽  
Atmospheric Air ◽  
Air Flows

Oxidation–stabilization using pressurized air flows of 0.5 and 1.0 MPa could successfully shorten the total stabilization time to less than 60 min for manufacturing mesophase pitch-based carbon fibers without deteriorating mechanical performance. Notably, the carbonized fiber heat-treated at 1000 °C for 30 min, which was oxidative–stabilized at 260 °C without soaking time with a heating rate of 2.0 °C/min using 100 mL/min of pressurized air flow of 0.5 MPa (total stabilization time: 55 min), showed excellent tensile strength and Young′s modulus of 3.4 and 177 GPa, respectively, which were higher than those of carbonized fiber oxidation–stabilized at 270 °C without soaking time with a heating rate of 0.5 °C/min using 100 mL/min of atmospheric air flow (total stabilization time: 300 min). Activation energies for oxidation reactions in stabilization using pressurized air flows were much lower than those of oxidation reactions using atmospheric air flow because of the higher oxidation diffusion from the outer surface into the center part of pitch fibers for the use of the pressurized air flows of 0.5 and 1.0 MPa than the atmospheric one. The higher oxygen diffusivities resulted in a more homogeneous distribution of oxygen weight uptake across the transverse section of mesophase pitch fibers, and allowed the improvement of the mechanical properties.

Experimental Study of Frost Formation on a Flat Surface Under Nature Convection

2003 ◽  
Author(s):  
Y. L. Hao ◽  
Y.-X. Tao ◽  
J. Iragorry ◽  
D. Castro
Keyword(s):  
Surface Temperature ◽  
Flat Surface ◽  
Microscopic Analysis ◽  
Growth Period ◽  
Surface Characteristics ◽  
Freezing Temperature ◽  
Early Growth ◽  
Cold Surface ◽  
Frost Formation ◽  
Frost Layer

A series of experiments were conducted to investigate the frost formation and characteristics on a flat surface under natural convections. The process of frost formation and structures is visibly observed and measured by using of a microscope. The temperature distribution of the air around the frost layer is measured by using of the holographic interferometry technique. The influences of the main parameters are analyzed. Especially, the microscopic analysis of frost growth on the surface characteristics on the microscopic characteristics of a frost layer during the early growth period when sub-cooled droplets are formed and changed to the ice. The thickness and mass of frost layer are measured while frost formation is visualized simultaneously. The results show that the frost surface temperatures are much lower than the freezing temperature and close to the cold surface temperature at the early growth period. After the early growth period, the frost surface temperature is dominated by the convective heat transfer between the frost surface and surrounding air.

Computation and Analysis of Frost Formation on Ground Aircraft

2012 ◽  
Vol 490-495 ◽  
pp. 166-170
Author(s):  
Li Wen Wang ◽  
Dan Dan Xu
Keyword(s):  
Water Vapor ◽  
Theoretical Model ◽  
Surface Temperature ◽  
Air Temperature ◽  
Temperature Decrease ◽  
Air Velocity ◽  
Frost Formation ◽  
Atmospheric Air ◽  
Air Speed ◽  
The Stability

Aircraft ground icing can result in decreasing the stability of the aircraft at or shortly after take off.. A theoretical model for frost formation by water vapor on aircraft in atmospheric air has been presented in this study. Frost surface temperature and frost thickness can be obtained by the model. Effects of aircraft surface temperatures and air conditions, such as aircraft surface temperature, air temperature and air velocity on the frost surface temperature and frost thickness can be evaluated by using this model. It revealed that the surface temperature increases with the surface temperature, the air speed and air temperature. The frost thickness increases with the air speed and the air temperature, decrease with the surface temperature.

Velocity Based Defrost and Frost Inhibition of Evaporator Coils of Heat Pump

2014 ◽  
Author(s):  
Kamalakkannan Muthusubramanian ◽  
Serguei V. Dessiatoun ◽  
Amir H. Shooshtari ◽  
Michael M. Ohadi
Keyword(s):  
Heat Pump ◽  
Air Flow ◽  
Working Fluid ◽  
Time Interval ◽  
Heating Cycle ◽  
Air Velocity ◽  
Frost Formation ◽  
The Past ◽  
Minute Duration ◽  
Direction Opposite

Researchers in the past have reported various methods to either retard frost formation or minimize energy expenditure during defrosting, but the methods reported in this paper is novel. Use of air flow during heating and defrosting cycles has not been studied and reported so far. The effect of using air flow during heating and defrosting cycles of heat pump were investigated experimentally. In the heating cycle, it is found that at higher air flow velocities, it is possible to retard the rate at which frost grows on the evaporator coils of the heat pump. Changing the air velocity from 0.8 m/s to 2 m/s caused a significant reduction in the frost growth rate. The ΔT of the working fluid for the 2 m/s experiment stayed at least 0.5 ∼ 1.0 °C more than the corresponding value of the 0.8 m/s experiment for the entire 90 minute duration of the heating cycle. In the defrost cycle, it is found that using air flow in the direction opposite to the normal air flow on the evaporator coil provides an energy saving opportunity by increasing the time interval between subsequent defrosting. It was seen that a reduction of 1 ∼ 2 defrost cycle was possible in 1 hour of operation, depending on the level of frost formation.

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