Moisture Condensation Research Articles

Calculation of Higher-Order Moments in the Atmospheric Boundary Layer

The results of analyzing a number of models to calculate the statistical fourth-order moments of turbulent fluctuations of vertical velocity and temperature, which describe diffusion processes in equations for triple correlations in RANS models, are presented. Correct calculation of higher-order moments allows adequate description of the impact of large-scale vortex structures on the vertical flow of turbulence energy, as well as the impact of chemical reactions (in the case of reactive impurities) and/or phase transitions (moisture condensation and evaporation) in the atmospheric boundary layer.Results of calculations with the use of the quasi-normality hypothesis, a number of empirical formulas. and algebraic models for fourth-order cumulants are comparedwith in situ measurements in the convective boundary layer of the atmosphere. It is shown that the secondorder- closure models, which are much more efficient in numerical implementation than the thirdorder models, predict the behavior of the higher-order moments not worse than the latter.

Експериментальні дослідження теплообміну під час глибокого охолодження продуктів згоряння газоспоживальних котлів

Викладено результати експериментальних досліджень закономірностей тепло- і масообміну в пучках поперечно оребрених труб водогрійних теплоутилізаторів відхідних газів котельних установок під час охолодження цих газів нижче від температури точки роси водяної пари. Наведено схеми експериментального стенду і досліджуваної моделі теплоутилізатора, характеристики трубних пучків та застосовуваних біметалевих труб (зі сталевою основою та алюмінієвим оребренням), описано умови проведення досліджень. Подано результати визначення експериментального значення коефіцієнта тепловіддачі з боку димових газів у таких діапазонах зміни їхніх основних параметрів: початкових температурах tвх = 140÷180 °С і вологовмісту Х = 0,09÷0,15 кг/кг с.г., кінцевої температури tвих = 50÷100 °С, а також Reг = 5000÷10000. Отримані дані узагальнено залежністю для розрахунку цього коефіцієнта, яка є функцією Reг, Х та безрозмірної температури нагріваної води q. Для підтвердження достовірності отриманих результатів проведено їх зіставлення з даними інших досліджень для режимів роботи експериментальної моделі без конденсації вологи з димових газів у пучках поперечно оребрених труб та за її наявності в пучках гладких труб. Унаслідок проведених зіставлень отримано задовільний збіг порівнюваних величин.

Study of Long Term Drift of Aluminum Oxide Thin Film Capacitive Moisture Sensor

Drift is an important phenomenon of capacitive humidity sensor, the most vital device in the commercial dew point meter. Due to drift in the output, most of the meters for critical applications require costly and time-consuming recalibration. Modeling of drift phenomenon for RH humidity sensors was reported in various literature. But to the best of our knowledge, there is no work reported so far about the drift of the sensors utilized for trace level moisture detection. This paper presents the mathematical model, the electrical equivalent circuits, and long-term drift analysis of the aged capacitive sensors for trace moisture sensing. The sensors were fabricated using porous alumina oxide thin film for detecting moisture in the range of 3 to 100 ppm. To study the long-term drift, experiments were performed under different operating conditions over a period of nearly one year. The response behaviors of the sensors were simulated with the help of the model. Comparing the model response with the experimental results, the proposed model can be used for drift analysis for an aged sensor, determination of hydration level and moisture condensation inside the pores. Experimental results showed that when a sensor was kept in drying agent, a maximum average drift of only 1.50% was observed but when a similar sensor was kept in open high humidity atmosphere, the maximum long-term drift was found to be ~11.20%.

Design of Active Modified Atmosphere and Humidity Packaging (MAHP) for ‘Wonderful’ Pomegranate Arils

Modified atmosphere packaging (MAP) systems have been shown as beneficial to prolong postharvest life of pomegranate arils. Current application of such system is limited due to a lack of appropriate packaging films which are able to control in-package moisture condensation. Therefore, the aim of this study was to design a MAP system to balance the optimum gas composition with packaging film permeability as well as optimum in-package relative humidity (RH). The following packaging materials design were used: (i) 100% cellulose-based film NatureFlex (NF), (ii) bi-axial-oriented polypropylene (BOPP)-based film PropaFilm (PF), (iii) NF-PF (66:33%) film, and (iv) PF-NF (33:66%) film. The effects of package design on quality attributes of pomegranate arils stored at 10 °C (91 ± 2% RH) for 9 days were investigated. Package design had significant (p ≤ 0.05) impact in changing the in-package RH and gas composition. The 100% cellulose-based (NF) package created the lowest RH (60–66%) with highest reduction in O2 concentration, highest total soluble solids (TSS), hardness, colour change, and high bacterial count. However, the 100% BOPP-based (PF) film resulted in highest in-package water vapour condensation and mould growth at the end of storage. The optimized packages using PF-NF and NF-PF films, respectively, maintained quality of pomegranate arils and minimized water vapour condensation. The results indicated that PF packaging film fitted with NF film window was the best to maintain the quality of pomegranate arils.

Energy analysis of a hybrid radiant cooling system under hot and humid climates: A case study at Shanghai in China

A conventional radiant panel system offers advantages in terms of energy savings; however, compared with an all-air system, it has limitations such as moisture condensation risk, slow air movement, difficult space zoning, slow air pollutants removal from a highly polluted room, and time delay in start-up of the radiant panel system. This research performs an energy consumption analysis of a hybrid radiant cooling system for buildings in summer. The hybrid radiant cooling system combines a typical radiant panel with a decentralized air convector connected in series. The hybrid radiant panel system generates additional cooling output through its air convector, dehumidifies indoor air, increases indoor air movements, and reduces the time delay in start-up and a filter in the air convector removes air pollutants. This study exhibits the energy performance of the hybrid radiant cooling system compared with an all air system and a typical radiant panel system via numerical modeling using experimental data. This hybrid radiant panel system is effective for energy-saving, because it has a higher cooling impact ratio, and larger coefficient of performance of the chiller, and because the air movement increases the offset effect of the operation indoor temperature rise by an enhanced mixed convection effect. Thus it can reduce cooling energy consumption. The hybrid radiant cooling system can be used very effectively for saving energy in the summer season.

SOME SPECIFIC FEATURES OF ENERGY CONSUMPTION IN MODERN RESIDENTIAL BUILDINGS

Over the past 20 years there have been significant changes in the customer requirements for housing in the countries of the former USSR. Besides, new materials and construction products, such as the ones for sealed windows and balcony doors have appeared in the market. The number of vacant flats with the heating off in the winter significantly increased that may cause condensation on the surfaces of interroom partitions and the formation of mold. Meanwhile, the requirements for lower energy consumption are constantly increasing, that is especially pronouncedly manifested in the growth of normative values of thermal resistance of enclosing structures of buildings and in the increased interest in the use of secondary energy resources extracted from the air and effluent wastewater. The present article describes the method to prevent moisture condensation on the fencing of adjacent premises with different temperatures containing heating systems and the use of waste heat removed from the room exhaust air. For quick emergency switching of in-house systems of heat and gas supply to outdoor mobile sources of heat and gas it is recommended to install special taps with connectors insulated in special niches in the walls or other parts of buildings considering the possibility of placing them close to the outer mobile sources of heat and gas. In the case of heating the building with the aid of a roof gas boiler or by doorto-door heaters fueled by gas, a single pipeline (collector), equipped with an additional device for the connection of emergency gas supply is being put along the wall. In order to reduce specific heat consumption for heating of buildings it is recommended to increase the net enclosure volume of buildings and to improve their form in various ways, including by combining two or more adjacent low-rise buildings in one secondary building with increasing height and with the broadening of either or each side for modernization and reconstruction. The dimensions of the reconstructed building are accepted as the maximum possible, and their proportions (in any number of merged buildings) – as providing tend of shapes to spherical or equicylindrical, or cubic – in any combination.

One-dimensional model of heat-recovery, non-recovery coke ovens Part V: Coking-bed sub-model using an inverse procedure

A one-dimensional home-made mathematical model of coke-making process in the heat-recovery (HR)/non-recovery (NR) coke oven has been developed. The model includes a series of sub-models described in associated publications (Buczynski et al., 2016 [1–4]). In this paper (Part V) a different approach for predicting the carbonization process is proposed. The coking-bed sub-model presented in Buczynski et al. (2016) [2] is based on a direct procedure (forward calculations) and the moving boundary technique. This approach is difficult to implement and calculations are time consuming. Moreover, the model is valid for one particular coal blend only. This paper describes the coking-bed sub-model based on an inverse problem formulation that adjusts itself to represent carbonization of particular charge. The new coking-bed sub-model contains completely different algorithm for predicting time-dependent processes such as: moisture evaporation and condensation, formation and condensation of tars.

Broadband Antireflection Coatings Based on Low Surface Energy/Refractive Index Silica/Fluorinated Polymer Nanocomposites

We demonstrated the fabrication of broadband antireflection coatings (ARCs) comprising low-surface energy/refractive index (RI) silica/polymer nanocomposites by silica mineralization of layer-by-layer (LbL) assembled poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2,2,3,3-tetrafluoropropyl methacrylate)/poly(L-glutamic acid) (PDMA-b-PTFP/PGA) multilayer films without any post-treatments. The introduction of the fluorinated polymer (PTFP segments) effectively lowered not only the RI of the as-fabricated coatings but also the surface energy of the constituted pore surface, which rendered the ARCs with high transmittance and durable AR performance by preventing the absorption and capillary condensation of moisture at ambient conditions. Moreover, the formation of nanosized PDMA-b-PTFP vesicles can render the ARCs exhibiting small pore size, which can improve their light transmittance. The coated substrate with an average transmittance over 97.0% was obtained at the visible wavelength region. The combina...

Wetting properties of hybrid structure with hydrophilic ridges and hydrophobic channels

In the present study, we fabricated a hybrid structure where the upper surface of the ridge is hydrophilic and the inner surface of the channel is hydrophobic. Laser-induced backside wet etching (LIBWE) process was performed to machine the hybrid structure on a Pyrex glass substrate. Wetting properties were evaluated from static contact angles (CAs) measurement in parallel and orthogonal directions. The water droplet on the hybrid structure was in the Cassie-Baxter state and showed anisotropic wetting property along groove lines. Moisture condensation studies under humid condition indicated that water droplets grew and coalesced on the ridge with hydrophilicity. Furthermore, water–oil separation was tested using a microfluidic chip with the developed hybrid structure. In case of hybrid microfluidic chip, the water could not flow into channel but the hexadecane could flow due to the capillary pressure difference.

Tritium concentration in ambient air around Kaiga Nuclear Power Plant

Tritium (3H) is one of the important long-lived radioisotopes in the gaseous effluent from nuclear power plants. In this article, we present the results of 3H monitoring in ambient air samples around the Kaiga Nuclear Power Plant, on the West Coast of India. Air samples were collected by moisture condensation method and the 3H concentration was determined by liquid scintillation spectrometry. The 3H concentration in the 2.3–15 km zone of the power plant varied in the range of <0.04–6.64 Bq m−3 with a median of 0.67 Bq m−3. The samples collected from the 2.3–5 km zone of the power plant exhibit marginally higher concentration when compared to the 5–10 km and 10–15 km zones, which is as expected. The values observed in the present study for Kaiga region are similar to those reported from other nuclear power plants, both within India and other parts of the world.

Experimental studies on the performance of dehumidifier using calcium chloride as a liquid desiccant

The performance of liquid desiccant air conditioning system (LDAS) mainly depends on dehumidifier of the system. In this study, the effects of inlet parameters on the performance of liquid desiccant dehumidifiers were studied with and without indirect evaporative cooler or intercooler (IDEC) between the dehumidifier for single stage and double stage. The results show that: i) the dehumidification effectiveness decreases by 8.6% for the all types considered here, with increase in air flow rate from 0.05 kg/s to 0.11 kg/s; ii) the dehumidifier effectiveness decreases due to decrease of moisture removal rate with increasing desiccant temperature in all stages; iii) the moisture condensation rate and dehumidifier effectiveness increases by 30% and 22.67% respectively with increase in desiccant flow rate; iv) the moisture condensation rate is increased by 13% in increasing desiccant concentration. It is concluded that double stage desiccant dehumidifier with indirect evaporative cooler performs better.

Numerical Simulation of rivulet build up via lubrication equations

A number of engineering problems involve the evolution of a thin layer of liquid over a non-wettable substrate. For example, CO2 chemical absorption is carried out in packed columns, where post-combustion CO2 flows up while liquid solvent falls down through a collection of corrugated sheets. Further application include, among others, in-flight icing simulations, moisture condensation on de-humidifier fins, fogging build up and removal. Here, we present a development of an in-house code solving numerically the 2D lubrication equation for a film flowing down an inclined plate. The disjoining pressure approach is followed, in order to model both the contact line discontinuity and the surface wettability. With respect to the original implementation, the full modeling of capillary pressure terms according to Young- Laplace relation allows to investigate contact angles close to π/2. The code is thus validated with literature numerical results, obtained by a fully 3D approach (VOF), showing satisfying agreement despite a strong reduction in terms of computational cost. Steady and unsteady wetting dynamics of a developing rivulet are investigated (and validated) under different load conditions and for different values of the contact angles.

Use of phase change materials during compressed air expansion for isothermal CAES plants

Compressed air energy storage (CAES) plants are designed to store compressed air into a vessel or in an underground cavern and to expand it in an expansion turbine when energy demand is high. An innovative CAES configuration recently proposed is the isothermal process. Several methods to implement isothermal CAES configuration are under investigation. In this framework, the present paper deals with the experimental testing of phase change materials (PCM) during compressed air expansion phase. The experimental investigation was carried out by means of an apparatus constituted by a compression section, a steel pressure vessel, to which an expansion valve is connected. The initial internal absolute pressure was equal to 5 bar to avoid moisture condensation and the experimental tests were carried out with two paraffin-based PCM amounts (0.05 kg and 0.1 kg). Results show that the temperature change during air expansion decreases with increasing the PCM amount inside the vessel. With the use of PCM during expansions an increase of the expansion work occurs. The increase is included in the range from 9.3% to 18.2%. In every test there is an approach to the isothermal values, which represent the maximum theoretical value of the obtainable expansion work.

Dependence of the Temperature of Effluent Gases of the Boilers on a Change in the Loading of Thermal Power Plants

One of the efficient methods of inexpensive modernization of thermal power plant is to reduce the temperature of effluent gases of the boilers (t exh ). The purpose of this paper was to carry out the experimental computation investigation of a degree of influence of the operation mode and performance factors (feed water flow rate and temperature, electric and thermal power) on the temperature of effluent gases of the boilers with the retention of the longevity of gas escape ducts. The attempts made to reduce the temperature of effluent gases in order to increase an efficiency factor of the boilers are restricted by the influence of (t exh ) on the longevity of heating surfaces both of the convective ducts and the entire gas-air duct (air heaters, gas-air mains, and the smoke pipe), taking into consideration the dew point (t d ) at which the combustion gas moisture condensation is possible. Based on the analysis of performance indices of the steam boilers of a ТGМP-314А type the regression equation was formed. The research data prove that the feed water temperature produces the greatest influence on the temperature of combustion gases in the entire range of variation in the electric load of the unit. The analysis of obtained data showed that the temperature of exhaust gases is increased with an increase in the electric power to 130 °С. This allows us to decrease the temperature of combustion gases on average by 20 °С taking into consideration the reliability of convective heating surfaces. Computations of the influence of t exh on q 2 showed that with the 1°С drop in the temperature of combustion gases an increase in the efficiency factor of the boiler reaches 0,035 % for the natural gas burning and 0,06 % for the fuel oil burning. Thus, we can come to a conclusion that the efficiency factor of the boiler of a ТGМP-314А type can be increased by 0,7 % with no degradation of the reliability of the heating surfaces of convective duct for the natural gas burning. The specific consumption of standard fuel will be reduced by 1,61 g.s.f. (grams of the standard fuel)/(kw∙h).

Special aspects of attic floor warming in historic buildings

This article containsreasoning of the heat transfer performance uniformity factor determination for attic floors of historic residential buildings while energy effective modifying buildings. The numeral value of this heat transfer performance uniformity factor for the wooden attic floor structure was found during investigation. It was estimated that there was no moisture condensation in the wooden attic floor structure. Energy efficiency modifying of residential historical buildings should imply the principle of highest possible preserving historical engineering structures of a building. The studied structure solution of the attic floor thermal insulation using modern efficient thermal insulation materials enables to exclude the risk of condensate formation in layers of a wooden floor being preserved.

On rehabilitation of buildings with historical façades

A basic challenge of the rehabilitation of facades is to eliminate the problems of moisture and select efficient thermal insulation. For years we have witnessed the discussions what materials and technology can be used for internal thermal insulation with exception of attics and underground. While internal insulation reduces heat loss by conduction it does not eliminate thermal bridges and opposite often increases their effect on condensation of moisture. Nevertheless, internal insulation can be a factor contributing to a high quality of internal environment and if combined with forced ventilation then also to control relative humidity inside façade. The work is now undertaken to determine how to address long-term hygrothermal performance of the whole wall assembly that is provided with additional means of heat and moisture control.

Two-phase flows in the formed tornado funnel

At present, it is obvious that the problem of the tornado is important not only for our planetЮ to determine the conditions for the formation of a tornado, it is required to take into account a number of hydrodynamic and plasma processes [1 - 6]. Along to prediction of a tornado generation conditions [1 - 3] it is necessary to evaluate the characteristics of its quasi-stationary motion in a formed funnel: the mass of the moving moist air involved in the funnel and the size and form of the funnel. For a complete description of the phenomena, it is necessary to involve numerical calculations. We note that even for numerical calculations using powerful computers, the problem is very difficult because of the need to calculate multiphase turbulent flows with free, self-organizing boundaries [1, 6]. However, “strict” numerical calculations, it is impossible to do without the use of many, often mutually exclusive, models. For example, how to choice an adequate model of turbulence (algebraic, k-ε model, etc.) or the use of additional, often not accepted, hypotheses about certain processes used in calculations (mechanisms on the nature of moisture condensation, etc.). Therefore, along with numerical calculations of such flows, modeling problems that allow an exact solution and allow to determine the most important and observed characteristics of a tornado.

Experimental Research of Drying Red Chili by Two Methods: Solar Drying and Low - Temperature System Drying

The objective of this research was to experiment of solar drying and Low-Temperature system drying (45-50%RH, 27-30°C) for drying red chili. Solar drying during daytime (greenhouse dryer) and during at night using climate control system to coordinate with air conditioner in drying. The Low-Temperature system consists the humidity control unit (ultrasonic), air-conditioner, temperature and relative humidity sensor, heating coil and microcontroller unit. For Low-Temperature drying process, climate control system controls the compressor in the air conditioner by turn on-off to control the temperature and relative humidity in the chamber. The dehumidification process by controlling the temperature of the surface evaporator coil is decreased to the dew point temperature, making water vapor in the air condensed to be water drops. The result of solar drying and Low-Temperature system takes 52h to reduce the moisture content of about 74% to 13.5% (w.b). For temperature and relative humidity of the solar drying at 50 °C and 36%RH by average, in during daylight and at night with Low-temperature drying system by the climate control system coordinate with air conditioning system in moisture reduction at 27-30°C and relative humidity at 45-50%RH for drying chili in the night. These processes were found to have average temperatures and relative humidity for drying at 27.55°C, 47.37% RH., moisture condensation rate and specific energy consumption at 2.16 kgwater/h and 0.75 MJ/kg.

Experimental study on an innovative enthalpy recovery technology based on indirect flash evaporative cooling

An indirect flash evaporative cooling enthalpy recovery technology used for building ventilation was proposed based on counter flow plate heat exchanger combing with ultrasonicatomizer. The technology is aimed at enhancing enthalpy recover efficiency and preventing contaminant transfer of heat recovery unit. The principle of the technology is to over saturate indoor exhaust air by ultrasonic atomizing humidification. The evaporation of ultrafine mists cools down indoor exhaust air to its wet-bulb temperature and makes not only sensible heat transfer but also moisture condensed in outdoor supply air to realize total heat recovery. Compared with conventional indirect evaporative cooling, the application of ultrasonicatomizing enhances cooling effect through increasing water mists evaporation area and decreasing heat transfer resistance between exhaust air and supply air. No mass permeation, carrying-over or sorption occurs in this heat exchange process which guarantees no contaminant transfer from exhaust air to supply air. A prototype unit of the proposed technology was developed and tested in climate chambers. Temperatures and humidity ratios at inlets and outlets of the heat recovery unit were measured to investigate and analyze its energy recover efficiencies. The results showed that in hot and humid climate, up to 71% of total heat recover efficiency could be achieved by the prototype unit, and more than 50% of the enthalpy recovered was contributed by moisture condensation in the outdoor supply air.

Indoor visible mold and mold odor are associated with new-onset childhood wheeze in a dose-dependent manner.

Evidence is accumulating that indoor dampness and mold are associated with the development of asthma. The underlying mechanisms remain unknown. New Zealand has high rates of both asthma and indoor mold and is ideally placed to investigate this. We conducted an incident case-control study involving 150 children with new-onset wheeze, aged between 1 and 7years, each matched to two control children with no history of wheezing. Each participant's home was assessed for moisture damage, condensation, and mold growth by researchers, an independent building assessor and parents. Repeated measures of temperature and humidity were made, and electrostatic dust cloths were used to collect airborne microbes. Cloths were analyzed using qPCR. Children were skin prick tested for aeroallergens to establish atopy. Strong positive associations were found between observations of visible mold and new-onset wheezing in children (adjusted odds ratios ranged between 1.30 and 3.56; P≤.05). Visible mold and mold odor were consistently associated with new-onset wheezing in a dose-dependent manner. Measurements of qPCR microbial levels, temperature, and humidity were not associated with new-onset wheezing. The association between mold and new-onset wheeze was not modified by atopic status, suggesting a non-allergic association.