Content Of Air Research Articles

Numerical Analysis and Experimental Investigation of Cavitating Flows Considering Thermal and Compressibility Effects

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical simulations were validated by means of already published experiments or compared with experiments conducted by the authors, and with good agreement.

Experimental investigation on condensation characteristics of a novel radiant terminal based on sepiolite composite humidity-conditioning coating

The problem of condensation hinders the application and popularization of the radiant cooling system. According to the characteristics of temperature and humidity independent control of the radiant cooling system, a novel humidity-conditioning radiant terminal combined with solid humidity-conditioning material is proposed which can control temperature and humidity simultaneously, and a sepiolite composite humidity-conditioning coating (SCHCC) suitable for the radiant terminal with good humidity control ability in high relative humidity environment is prepared. The humidity-conditioning coating can adsorb water vapor in the air to reduce the risk of condensation that is different from the surface condensation of traditional radiant terminals. Then, the condensation and desorption characteristics of three humidity-conditioning boards are tested which is considered scaled-down humidity-conditioning radiant terminal. The results show that SCHCC has good humidity control ability in a high relative humidity environment, the moisture adsorption capacity of SCHCC between 85% RH and 95% RH is 0.208 g/g, which is 11.43 and 22.47 times that of gypsum and diatomite. The sepiolite based humidity-conditioning board (SHCB) with the best moisture adsorption characteristics has the longest condensation time, and the condensation time increases with the decrease of undercooling. SHCB also shows better humidity control ability even for the experimental condition without condensation within 300 min. In summary, SHCB can reduce the moisture content of indoor air through its excellent hygroscopic properties, and reduce the risk of condensation at the radiant terminal. • A novel humidity-conditioning radiant terminal is proposed. • The material has good humidity control ability under high relative humidity. • The condensation and desorption behavior of the novel radiant terminal is tested. • The novel radiant terminal can effectively prolong the surface condensation time.

Numerical prediction of the influence of free surface vortex air-entrainment on pump unit performance

Free surface vortex (FSV) is a complex gas-liquid two-phase flow, which is harmful to the pump unit. In this paper, FSV in the pump sump with a double-suction centrifugal pump is numerically simulated by two-phase flow method, which is verified by experimental data and agreed well with theoretical models. The purpose of this paper is to study the influence of FSV on the performance of pump, the variation characteristics of several paramount paraments (FSV evolution process, vortex strength, air-laden content, head-drop, flow stability, pressure amplitude) was revealed for the first time. The vortex strength affects the air-laden capacity of FSV, the maximum air content in this impeller can reaches 17.1%. The air destroys the stable structure of the flow field in the impeller, affects the flow rate, and the mean head-drop by 36.8%, meanwhile inducing irregular pressure pulsation. The duration and content of suction air of FSV determine the performance-drop amplitude. The change of unit performance is proportional with the air-entrainment content and vortex strength, which shows that the larger the FSV air-entrainment is, the worse the pump performance. It is clear that the predicted results are consistent with the existing problems of the unit on site, which can provide a method to predict the influence of the FSV on the unit.

The Nuclear Magnetic Flowmeter for Monitoring the Consumption and Composition of Oil and Its Complex Mixtures in Real-Time

The necessity of increasing the efficiency of primary oil purification in a drilling station or an offshore platform has been substantiated. We consider the problems that arise during the primary processing of oil mixtures. Important conditions for increasing the efficiency of primary purification (separation) of oil mixtures include measuring the consumption and determining the content of various impurities (water, undissolved particles) and air in them, with an error of no more than 2%. We analyzed the possibilities of using various designs of flowmeters to measure the consumption of the oil mixture coming from a well. It is also necessary to use other measuring instruments to control the state of this mixture, which creates additional problems (searching for an appropriate locations to place them, providing the required operating conditions). Various designs of nuclear magnetic flowmeters–relaxometers were considered, making it possible to measure the consumption of a liquid medium and its times of longitudinal T1 and transverse T2 relaxation with one device. The measured values of T1 and T2 determine the state of the medium. The design of the industrial nuclear magnetic flowmeter–relaxometer M-Phase 5000, which is used to control the flow and quality of oil and oil products, was considered in more detail. Problems were identified that did not allow using this design of a nuclear magnetic flowmeter–relaxometer in a drilling rig or offshore platform. A new design of a nuclear magnetic flowmeter–relaxometer was developed, implementing the methods for measuring q, T1, and T2. These methods and various technical solutions make it possible to use this device at a drilling station or offshore platform. The measurement errors of the consumption q, T1, and T2 were determined. The results of various media studies are presented and compared with q, T1, and T2 measurements on other devices and measured volume (to confirm the adequacy of q measurements). The application scopes of the developed nuclear magnetic flowmeter–relaxometer were determined, in addition to the systems of primary oil processing.

The impact of oxygen content in the primary air supply on fuel burning rate and pollutant emissions in a forced-draft biomass stove

Forced-draft biomass stoves have been proposed as a substitute for traditional solid fuel stoves in rural areas. The change in the O2 content of the supply air via flue gas recirculation (FGR) significantly affects the combustion and pollutant emission performances of this household stove type, which has not been thoroughly investigated. In this study, O2 content control system was designed to accurately adjust the O2 content of the primary air supply for a typical household forced-draft biomass stove. Then, six conditions with an O2 content of 16%, 17%, 18%, 19%, 20%, and 21% were tested. The dynamic burning rate and emission rates of carbon monoxide (CO), nitrous oxides (NOx), and particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM2.5) were measured for each O2 content. The results showed that the average burning rate of the six O2 contents ranged from 9.6 to 16.9 g/min. There was a positive linear relationship between the average burning rate and the O2 content in the primary air supply. The CO and PM2.5 emission amounts exhibited the concave and convex quadratic relationships with O2 content, respectively, while trends in NOx emission amount had a negative linear relationship with the O2 content. The real-time burning rate and pollutant emission rates exhibited different trends that influenced the amount of emissions. When FGR was utilized with a constant primary airflow rate, an O2 content of 19.7% may be optimal for household biomass stoves. This study provides basic information on air supply design of household biomass stoves, which is essential for future clean stove design and improvement.

Liquid desiccant dehumidification and regeneration process: Advancing correlations for moisture and enthalpy effectiveness

The paper developed correlations for predicting moisture and enthalpy effectiveness of the liquid desiccant dehumidification and regeneration process. Experimental dehumidification and regeneration data available from the literature with different system dimensions, liquid desiccant solutions (LiBr and LiCl), geometry and size of the packing and flow configuration (counter- and cross-flow) were gathered for correlations development. The developed correlations involved the mass flow rates of air and desiccant solution, the inlet temperature of the air and the desiccant solution, the moisture content and enthalpy of the inlet air, the moisture content and enthalpy of air at an equilibrium state with the inlet desiccant solution, the geometry, dimensions and wetting of the packing and the contact time between air and desiccant solution. The comparison between the calculated and experimental effectiveness showed a good match, which had errors ranging 4.37–7.2%, and performed better when compared to other correlations available in the literature. These newly developed correlations will be useful for quick system design and performance analysis and to establish cost-effective solutions for liquid desiccant technology.

Energy and exergy analysis of an atmospheric water generator integrated with the compound parabolic collector with storage tank in various climates

The drinkable water storages shortage is one of the main obstacles that many societies are envisaged with. In addition, the water content of humid air is known as the main storage of drinkable water for the future. In this paper, the energy and exergy analysis of a solar driven atmospheric water generator which contains an absorption refrigeration cycle coupled to a compound parabolic collector is performed. The mathematical model of the proposed system is developed in MATLAB software. In the solar thermal system provided in this paper, the storage tank is employed for extending the working hours of the system leading to improvement of total water generation rate. Furthermore, the performance of the system is evaluated in various climates included arid, semi-arid and Mediterranean, and for this purpose three cities of Iran named Bandar Abbas, Ramsar and Tehran were selected. Moreover, by comparing the water production in various months during the year, the highest value of water production during the year is held by Bandar Abbas city leading to owning the lowest values of specific power consumption and specific collector area. The maximum rate of water production of proposed system is approximately 400 lit per month in tropical climates with specific energy consumption of 3 kWh/lit. Based on the results of exergy analysis of whole system, the most exergy destruction rate belongs to compound parabolic collector component, therefore, large amount of energy is wasted through compound parabolic collector which can be recovered for generation of chilled water. Moreover, the impacts of geographical and environmental parameters on the energy and exergy efficiencies of the atmospheric water generator are also assessed.

Experimental Study on Humidifier Performance in a Humidification-Dehumidification System

The characteristic of Humidification-dehumidification seawater desalination technology is flexible scale. It is suitable for dispersive fresh water demand and easy to couple with low-grade energy. In this study, an experimental platform of humidifier performance is designed to investigate the influence of spray flow, spray liquid temperature, air flow, hole diameter, pitch of holes and the number of sieve plates on moisture content of humid air at outlet and evaporation capacity. The results show that, when the spray flow and temperature increase, the moisture content of outlet air and evaporation capacity increase. The evaporation capacity increases when the extent of the air flow increasing is more than that of the moisture content decreasing. When the spray flow is 0.025kg/s, the evaporation capacity is the highest when the sieve plate with the hole diameter of 3.0mm and the holes pitch of 9.0mm is used. For other flow conditions, the evaporation rate is the highest when the sieve plate with the hole diameter of 2.5mm and the hole pitch of 7.5mm is used. The evaporation capacity with double sieve plates is higher than that with single sieve plate. The research of this paper provides guidance for practical application of the HDH seawater desalination system.

Screening of important parameters in optimal design of compressed air energy storage system using an ensemble learning method

Accurate prediction of thermophysical properties of compressed air is specifically crucial in optimal design and analyzing performance of a Compressed Air Energy Storage (CAES) system. In this regard, an advanced machine learning method, namely stochastic gradient boosting (SGBTree) technique was examined based on reported data points in the literature for estimation of specific heat ratio of air, water content of atmospheric air, water content of compressed saturated air, viscosity of compressed air as well as thermal conductivity of compressed air. The used ensemble learning method precisely functions for a wide range of temperature, pressure and relative humidity. The SGBTree models estimate the aforementioned target values well, matching to those available in the literature as the correlation coefficient (R) and Mean Relative Absolute Error (MRAE) values are greater than 0.999 and less than 0.007, respectively. Moreover, a comparison was carried out between the outputs of the SGBTree model and two intelligent models namely Artificial Neural Network (ANN) and Least Squares Support Vector Machine (LSSVM) schemes as well as a reported simple empirical correlation for estimating specific heat ratio of air. In terms of accuracy, it is found that the SGBTree model is better than other methods for estimation of specific heat ratio of air.

Diesel engine behavior using coconut oil methyl esters and its blends

Diesel engines are renowned for its reliable performance. However, it continues to be a major polluter in terms of nitrogen oxides and smoke. Many researches are working on the adaptability of vegetable oil methyl ester (biodiesel) for lowering emissions of smoke, hydrocarbons, and carbon monoxide. This may be performed by delivering more amount of oxygen available within the cylinder. Also, it is possible to do this by increasing the oxygen content of the intake air or by using oxygenated fuels (biodiesel), although certain biodiesels increase nitrogen oxide emissions. The biodiesel investigated in this study is coconut oil methyl ester (COME), and the outcomes of its blend are compared to diesel fuel operation. Transesterification was used to produce the fuel from coconut oil. COME's fatty acid composition and fuel characteristics were determined. COME is composed of around 90% saturated fatty acids. Apart from neat COME operation, the trials were carried out for various COME and diesel fuel blends of 20%, and 30%, COME in the fuel blend. The laboratory results reveal that neat COME and its blend operation resulted in decreased brake thermal efficiency, increase in NOx, and decrease in smoke and hydrocarbon emissions. However, it is concluded that COME and its blend can be used as an alternative fuel for compression ignition engines with a sacrifice of thermal efficiency.

Підвищення продуктивності процесу лиття шляхом регулювання теплового режиму кокіля на основі комп’ютерного дослідження потоку повітря в каналах стержня

The most common technology for the manufacture of aluminum parts and blanks is casting in a chill mold. To determine ways to improve casting technology, it is necessary to analyze the possibility of changing the parameters that affect the reduction of production costs (reduction of energy consumption, material consumption, increase productivity) and improve the quality of casting. The thermal regime of the metal form determines the productivity of the process, the duration of curing of the casting, its quality, durability of the chill mold. The analysis of the work of the chill mold for the manufacture of castings Pump Housing showed that when the forms are filled, the most heated new portions of metal meet on their way to the central core. That is, when pouring the mold, the central core is heated the most, especially in the lower part. This circumstance hinders the process of directed curing and can lead to shrinkage defects. In addition, the higher the temperature of the mold, the slower the casting will crystallize and the worse its structure and mechanical properties will be. Based on the analysis of structures and methods of cooling molds, the method of controlled cooling of the central core by air is substantiated. A new design of the core has been developed, which provides adjustable air cooling of the chill mold by connecting the central core through a valve to the pneumatic system of the shop. 3D-models of details and assembly drawings of the central core of a new design are developed. A computer study of the air flow in the core channels in SolidWorks Flow Simulation was performed. The results of parametric modeling of air flow in the channels of the Central core showed the maximum air flow rate during cooling 0.371 kg / s, the heat content of air when cooled 25081 J / s. Evaluation of the cooling efficiency of the developed chill mold design showed that when using air cooling of the central core with cooling air at its maximum consumption, 41% of heat is removed. Thus, the developed design of the cooled central core allows to increase the productivity of the casting process, improve the quality of casting by improving the structure and mechanical properties of the casting, as well as increase the life of the chill mold. But the obtained research results are of a recommendatory nature and require practical verification in the production environment. In addition, the simulation did not take into account the change in core temperature due to its heat exchange with the melt. Given all this, there is a need for further study of the effect of regulated air cooling on the thermal regime of the chill mold.

INFLUENCE OF THE MAGNETIC FIELD ON THE GAS CONTENT OF WATER

The conclusions drawn from previous studies, which showed that the magnetic field stimulates the formation of nanobubbles in seawater, are discussed. It was found that the air content in nanobubbles in freshwater can be neglected. Seawater contains air mainly in the form of nanobubbles, and its concentration increases with an increase in the magnetic field. The mechanism behind the influence of the magnetic field on the solubility of air in water is related to the scale reduction process during the magnetic treatment of water. The Lorentz force during the Brownian motion of charged nanobubbles decreases their electrokinetic potential and stimulates coalescence. On the one hand, this leads to the absorption of additional atmospheric air; however, on the other hand, it accelerates the rise of bubbles to the surface, reducing the total gas content of air in the water.

Elucidating the Effects of a Cryptomeria fortunei Forest Environment on Overall Health Based on Open Field Testing of Mice

In order to elucidate the impact of fortunei forest environment on overall health, the effect of the Cryptomeria fortunei forest environment on mice was examined. Using an OFT (Open Field Test), the behavior of mice in fortunei forest and in an indoor environment (used as a control) was analyzed, while minor changes in climate, oxygen, and suspended particulate matter were observed and recorded simultaneously. The results indicated that the two environments were significantly different in regard to relative humidity, wind speed, and the oxygen content of air, while there were no significant differences in temperature. Importantly, spontaneous activity behavioral indicators in mice were significantly different. Mice in the Cryptomeria fortunei environment (LS group) spent less time in the corners and near walls in comparison to mice in the indoor environment (CK group). Compared with indoor control mice, for the mice exposed to forest environments total distance traveled, central grid distance, frequency of movement through the central grid, frequency of standing, and body mass significantly increased; The number of fecal grains significantly decreased. The spontaneous activity behavioral indicators changed over time stages. In the early stages there were no differences, but after accumulation of environmental effects in the late stages, significant differences were evident. The above results showed that the Cryptomeria fortunei forest environment increased excitability and cognitive ability of mice, was able to effectively alleviate anxiety, and was able to emotionally relax and improve the appetite of the mice.

Performance analysis of 300 GHz backhaul links using historic weather data

Abstract. According to the recently published IEEE standard 802.15.3d (2017), THz links operating at 300 GHz are viable to achieve more than 100 Gbit s−1 of data rate. This feature can support a transition of the future backhaul connectivity from the underground fibre connection to the wireless, where fibre links are not available or too costly to install. The EU-Japan Horizon 2020 project “ThoR” is working towards the demonstration of such links. A detailed investigation on the influence of weather conditions will help to derive planning guidelines of 300 GHz backhaul links for forthcoming applications. This paper focuses on the dependency of the THz link on the general weather by using ray-tracing simulation. Simulation is conducted combining ITU-R propagation models for atmospheric attenuation (water vapour and oxygen content of air, droplets of rains, liquid content of clouds or fog), a wind-depending swaying model for the antenna poles, and historical measured climate data for the deployment scenarios considered in the ThoR project. As a result, this research will show the feasibility of THz link in outdoor applications under general weather conditions, defines weather-dependent outage probabilities, and allows us to derive planning guidelines of THz links at a frequency of 300 GHz.

Understanding the uncertainty of the long‐term precipitation trend under global warming through the water cycle

AbstractIt is certain that globally the troposphere has warmed since the industrial revolution because of the greenhouse gas emissions. The water vapour content of air increases as the climate warms. However, there is nonsignificant long‐term trend in global‐scale precipitation. This study aims to investigate the sources of the uncertainty of the long‐term precipitation trend under global warming through the water cycle. The data of the historical simulations (1850–2005) from 30 CMIP5 models are used in the estimate. The p‐value is utilized to indicate the significance of the long‐term trend of the water‐vapour‐related variable in the water cycle as well as the air temperature near surface and at the condensation level. For each variable, the p‐value is calculated for each of the grid points. The overall spatial distribution patterns of the p‐values are compared between two variables that linked directly, and a point‐to‐point comparison is also performed to the two fields. Results show that over the globe, the near‐surface specific humidity increases significantly at most of the grid points while the increase of the specific humidity at the condensation level is significant at some, and, however, the long‐term trend of the relative humidity at the condensation level is majorly nonsignificant. This suggests that as assessed from the global grid points, the uncertainty of the long‐term trend of the water‐vapour‐related variable enlarges substantially in the process of condensation, and modestly in the process of the transport of water vapour. Therefore, the uncertainty of the long‐term precipitation trend under global warming is mainly attributed to the condensation and slightly due to the transport of water vapour. The results obtained from the 30 models are consistent with each other, which supports the reliability of the conclusion.

Carboxylation Capacity Can Limit C3 Photosynthesis at Elevated CO2 throughout Diurnal Cycles.

The response of carbon fixation in C3 plants to elevated CO2 is relatively larger when photosynthesis is limited by carboxylation capacity (VC) than when limited by electron transport (J). Recent experiments under controlled, steady-state conditions have shown that photosynthesis at elevated CO2 may be limited by VC even at limiting PPFD. These experiments were designed to test whether this also occurs in dynamic field environments. Leaf gas exchange was recorded every 5 min using two identical instruments both attached to the same leaf. The CO2 concentration in one instrument was controlled at 400 μmol mol−1 and one at 600 μmol mol−1. Leaves were exposed to ambient sunlight outdoors, and cuvette air temperatures tracked ambient outside air temperature. The water content of air in the leaf cuvettes was kept close to that of the ambient air. These measurements were conducted on multiple, mostly clear days for each of three species, Glycine max, Lablab purpureus, and Hemerocallis fulva. The results indicated that in all species, photosynthesis was limited by VC rather than J at both ambient and elevated CO2 both at high midday PPFDs and also at limiting PPFDs in the early morning and late afternoon. During brief reductions in PPFD due to midday clouds, photosynthesis became limited by J. The net result of the apparent deactivation of Rubisco at low PPFD was that the relative stimulation of diurnal carbon fixation at elevated CO2 was larger than would be predicted when assuming limitation of photosynthesis by J at low PPFD.

A comparison of proton stopping power measured with proton CT and x-ray CT in fresh postmortem porcine structures.

Currently, calculations of proton range in proton therapy patients are based on a conversion of CT Hounsfield units of patient tissues into proton relative stopping power. Uncertainties in this conversion necessitate larger proximal and distal planned target volume margins. Proton CT can potentially reduce these uncertainties by directly measuring proton stopping power. We aim to demonstrate proton CT imaging with complex porcine samples, to analyze in detail three-dimensional regions of interest, and to compare proton stopping powers directly measured by proton CT to those determined from x-ray CT scans. We have used a prototype proton imaging system with single proton tracking to acquire proton radiography and proton CT images of a sample of porcine pectoral girdle and ribs, and a pig's head. We also acquired close in time x-ray CT scans of the same samples and compared proton stopping power measurements from the two modalities. In the case of the pig's head, we obtained x-ray CT scans from two different scanners and compared results from high-dose and low-dose settings. Comparing our reconstructed proton CT images with images derived from x-ray CT scans, we find agreement within 1% to 2% for soft tissues and discrepancies of up to 6% for compact bone. We also observed large discrepancies, up to 40%, for cavitated regions with mixed content of air, soft tissue, and bone, such as sinus cavities or tympanic bullae. Our images and findings from a clinically realistic proton CT scanner demonstrate the potential for proton CT to be used for low-dose treatment planning with reduced margins.

Experimental study on the performance of a novel hybrid indirect evaporative cooling/thermoelectric cooling system

A novel hybrid cooling system combining indirect evaporative cooling and thermoelectric cooling technologies was built and experimentally investigated. The system was mainly comprised of a cross flow regenerative indirect evaporative cooler and a water cooled thermoelectric cooler. The incoming air was firstly pre-cooled in the indirect evaporative cooler, and then further conditioned in the thermoelectric cooler to achieve desirable temperature and humidity. In particular, the thermoelectric cooler could operate under two modes of with or without spray water on the air channel surface. The performance of the proposed system under the above mentioned two operation modes was experimentally investigated and compared in detail under various operation parameters. The experimental results show that the product air temperature decreases more significantly with larger electric current and larger number of thermoelectric modules, smaller relative humidity, larger temperature and smaller velocity of inlet primary air. Under certain conditions, air condensation occurs leading to the increase of the product air temperature and the decrease of moisture content of the product air. Adding spray water in the air channel of the thermoelectric cooler would further decrease the temperature and increase the moisture content of the product air, which is more obvious under smaller electric current and number of thermoelectric modules, smaller relative humidity, smaller temperature and larger velocity of inlet primary air. The coefficient of performance of the system with spray water is smaller but the dew point effectiveness is higher compared to the system without spray water.

Effect of surface wettability on air parameters and performance of indirect evaporative cooler in the presence of primary air condensation

The surface wettability in the wet channels is an important factor affecting the performance of the indirect evaporative cooler (IEC). However, in previous studies on surface wettability, little attention has been paid to air condensation. Therefore, this paper presents a mathematical model of plate type IEC focusing on the surface wettability in the wet channels and air condensation. Besides, a test bench was built to verify the reliability of the model. The effect of surface wettability on air parameters and performance of IEC unit was intensively studied. The results show that with the increase of wettability factor from 0.3 to 1, and the outlet temperature of primary air decreases from 23.4 °C to 21.6 °C. It is worth noting that the condensation behavior of primary air at the entrance is restrained. The outlet temperature of secondary air decreases from 23.6 °C to 22.3 °C, and the outlet moisture content of secondary air increases from 13.9 g/kg to 16.86 g/kg. Moreover, when wettability factor increases from 0.2 to 1, the enlargement coefficient, wet-bulb efficiency, dehumidification rate, total heat transfer and water consumption increase by 5.9%, 61%, 68%, 81.8% and 251% respectively.

Analysis of the growth conditions of icicles during insulator icing

In this paper, the accretion processes of different icing types of insulators are analyzed, and the insulator icing types are creatively redefined into three types according to the characteristics of water film and icicle growth. Based on which, a new parametric method of wet-growth icing and icicles is proposed and a mathematical model of water film flowing on insulators is established. The method and model make it possible to simulate the uneven distribution of water film on insulator and precisely predict the insulator icing. The simulation results show that the water film on the insulator surface is mainly generated at the collision area of water droplets, the edge of insulator shed and the steel cap on the windward side. The overflowing water expands the icing area on the insulator surface and at the same time supplies water for the growth of icicles. The greater the wind velocity, the liquid water content of air and the median volume diameter of water droplets, the faster water film will overflows to insulator shed edge and the greater the probability of icicles.