Problem Of Condensation Research Articles

The Influence of Building Materials on Relative Humidity of Internal Microclimate

Sustainable building covers wide range of criteria including environmental, social and economy issues. Relative humidity of the internal environment belongs to the group of social criteria dealing with the quality of indoor microclimate and is one of the important indicators. Low humidity level can cause dry skin, throats and nasal passages and can cause annoying static electric sparks. High humidity level can lead to growth of moulds and bacteria and can cause condensation problems on the cold surfaces. Appropriate level of relative humidity can be operate by building service systems which increases operating energy in buildings and is sensitive to correct set up, control and monitoring. Relative humidity can be also influenced by the choice of building structures and structural materials without any operating energy. The paper summarizes latest research on the influence of relative humidity on health hazards and influence of building structures and structural materials on the relative humidity.

Condensation for random variables conditioned by the value of their sum

We revisit the problem of condensation for independent, identically distributed random variables with a power-law tail, conditioned by the value of their sum. For large values of the sum, and for a large number of summands, a condensation transition occurs where the largest summand accommodates the excess difference between the value of the sum and its mean. This simple scenario of condensation underlies a number of studies in statistical physics, such as, e.g. in random allocation and urn models, random maps, zero-range processes and mass transport models. Much of the effort here is devoted to presenting the subject in simple terms, reproducing known results and adding some new ones. In particular we address the question of the quantitative comparison between asymptotic estimates and exact finite-size results. Simply stated, one would like to know how accurate are the asymptotic estimates of the observables of interest, compared to their exact finite-size counterparts, to the extent that they are known. This comparison, illustrated on the particular exemple of a distribution with Lévy index equal to 3/2, demonstrates the role of the contributions of the dip and large deviation regimes. Except for the last section devoted to a brief review of extremal statistics, the presentation is self-contained and uses simple analytical methods.

The effect of disjoining pressure on the shape of condensing films in a fin-groove corner

Thin film condensation is commonly present in numerous natural and artificial processes. Phase-change driven passive heat spreaders such as heat pipes, which are widely used in electronics cooling, employ a continuous condensation process at the condenser region. When the wick structure of a heat pipe is composed of grooves, the top surfaces of the walls (fins) located between consecutive grooves function as the major source of condensation and the condensate flows along the fin top into the grooves. Modeling of this condensation problem is vital for the proper estimation of condensation heat transfer, which constitutes the basis for the overall performance of a heat pipe together with the evaporation process. In the current study, a solution methodology is developed to model the condensation and associated liquid flow in a fin-groove system. Conservation of mass and momentum equations, augmented Young-Laplace equation and Kucherov-Rikenglaz equation are solved simultaneously to calculate the film thickness profile. The model proposed enables the investigation of the effect of disjoining pressure on the film profile by keeping the fin-groove corner, where the film becomes thinnest, inside the solution domain. The results show that dispersion forces become effective for near isothermal systems with sharp fin-groove corners and the film profile experiences an abrupt change, a slope break, in the close proximity of the corner. The current study is the first computational confirmation of this behavior in the literature.

The quality of air outside and inside the home: associations with emotional and behavioural problem scores in early childhood

BackgroundThis study explored the role of outdoor air pollution [nitrogen dioxide (NO2) and sulphur dioxide (SO2)] and indoor air quality (measured with damp or condensation and secondhand smoke exposures) at age 9 months in emotional, conduct and hyperactivity problems at age 3 years.MethodData from 11,625 Millennium Cohort Study children living in England and Wales were modelled using multilevel regression.ResultsAfter adjusting for a host of confounders, having a damp or condensation problem at home was related to both emotional and conduct problems. Secondhand smoke exposure was associated with all three problem types. Associations with outdoor air pollution were less consistent.ConclusionsExposures to damp or condensation and secondhand smoke in the home are likely to be risk factors for child emotional and behavioural problems. Parents should continue to be educated about the dangers of exposing their children to poor air quality at home.

Coatings Help Control Condensation

A new insulation coating solution manages condensation problems in water tanks and water treatment plants.

Experimental Evaluation of the Ability of an Auxiliary Heating Device to Reduce the Condensation Risk around Built-in Wardrobes of Apartment Buildings in Winter

Recently, there has been an increase in the condensation and mould problems of apartment buildings in Korea owing to the high insulation and high air-tightness performance of buildings, which increase energy savings. Condensation is generally found in winter on furniture back panels and adjacent surfaces of the wall, floor, and ceiling. These problems are related to the weather conditions and indoor room conditions in winter. To solve these problems, an auxiliary heating device that can be installed was developed. The purpose of this study was to evaluate condensation risk in the condensation vulnerable areas around built-in furniture of apartment buildings by installing an auxiliary heating device. The experimental results reveal that condensation risk can be reduced by comparing the thermal environment around the built-in furniture with and without installation of an auxiliary heating device in winter. Furthermore, they reveal that it is possible to increase the surface temperature of vulnerable areas around built-in wardrobe by applying an auxiliary heating device to minimize condensation problems by using a minimum device.

Simulating the boiling fluid outflow taking into account external condensation

This paper considers the axisymmetric problem of condensation at a boiling liquid outflow in a closed region filled with steam. It has been found that the unsteady condensation is due to the formation of a complex structure of lateral pressure surges, Mach disk, barrel shocks and a wall, on which the pressure exceeds the local saturation pressure.

Analytical solution for filmwise condensation in confined high-aspect ratio geometry

This study revisits the problem of free vapor condensation in the filmwise regime by constructing and solving a comprehensive transport model that describes heat and mass transport through the gas phase, interfacial and thermal resistance of the condensate film, and heat conduction through the cooled wall in a self-consistent manner. We have shown that it is possible to obtain an analytical solution of the model which describes the net condensation flux in the presence of an arbitrary amount of noncondensables. This solution demonstrates that the overall thermal resistance reduces to a sum of the thermal resistances of the wall, the condensate film, the interfacial resistance, and the diffusive resistance of the gas layer only in the limit of infinite thermal resistance of the gas layer, but generally has a more complicated form. Finally, we derived an analytical solution for the condensate film thickness profile which generalizes Nusselt’s classical free condensation solution. Both finite thermal conductivity of the wall and thermocapillary stresses were shown to play an important role, substantially altering the thickness profile.

A Stochastic Lagrangian Basis for a Probabilistic Parameterization of Moisture Condensation in Eulerian Models

Abstract In this paper, we describe the construction of an efficient probabilistic parameterization that could be used in a coarse-resolution numerical model in which the variation of moisture is not properly resolved. An Eulerian model using a coarse-grained field on a grid cannot properly resolve regions of saturation—in which condensation occurs—that are smaller than the grid boxes. Thus, in the absence of a parameterization scheme, either the grid box must become saturated or condensation will be underestimated. On the other hand, in a stochastic Lagrangian model of moisture transport, trajectories of parcels tagged with humidity variables are tracked, and small-scale moisture variability can be retained; however, explicitly implementing such a scheme in a global model would be computationally prohibitive. One way to introduce subgrid-scale saturation into an Eulerian model is to assume the humidity within a grid box has a probability distribution. To close the problem, this distribution is conventionally determined by relating the required subgrid-scale properties of the flow to the grid-scale properties using a turbulence closure. Here, instead, we determine an assumed probability distribution by using the statistical moments from a stochastic Lagrangian version of the system. The stochastic system is governed by a Fokker–Planck equation, and we use that, rather than explicitly following the moisture parcels, to determine the parameters of the assumed distribution. We are thus able to parameterize subgrid-scale condensation in an Eulerian model in a computationally efficient and theoretically well-founded way. In two idealized advection–condensation problems, we show that a coarse Eulerian model with the subgrid parameterization is well able to mimic its Lagrangian counterpart.

NUMERICAL RESEARCH OF THE MOISTURE CONDENSATION ELIMINATION IN THE CABIN OF THE UNIFIED TECHNOLOGICAL ELECTRIC TRANSPORT VEHICLE

Introduction. This article deals with the problem of moisture condensation inside the cabin of the technological electric transport vehicle. The hypothesis of using the forced air ventilation in the cabin is substantiated, by which such problem could be solved.Materials and methods. The article describes the application of the ANSYS Fluent Software Package to assess the effect of the location and shape of the ducts on the ventilation process inside the cabin. Accordingly, the key stages of air flow modeling in this program are considered.Results. The main content of the research is to analyze the modeling airflow process in the cabins with a different configuration of inlet and outlet nozzles. Therefore, basing on the analysis of the obtained airflow velocity contours, the conclusion is made about the rational arrangement of the inlet and outlet channels.Discussion and conclusions. The conclusion is made about the necessity of the further research that would refer to creating a three-dimensional model of the cabin. The results of the research as well as resolutions are taken into account.

Thermo-economic analysis and comparative study of transcritical power cycles using CO2-based mixtures as working fluids

Transcritical carbon dioxide (CO2) cycle is a promising method to utilize both low and high temperature heat sources. However, its application is restricted to lower temperature cooling source conditions since the condensing temperature must be lower than the critical temperature of CO2 (about 31.1 °C). In this study, organic fluids are selected to blend with CO2 to overcome the condensation problem by elevating the critical temperature. The effects of several key parameters on thermodynamic and exergoeconomic performances of the system are investigated for different CO2-based mixtures and pure CO2 under both low and high temperature heat source conditions. Single-objective and multi-objective optimizations are carried out to achieve the better system performances. Meanwhile, the performance comparisons between different CO2-based mixtures and pure CO2 are conducted. Results show that transcritical power cycle using CO2-based mixtures could obtain better thermodynamic and exergoeconomic performances compared with the one using pure CO2 for both low and high temperature heat source conversions. Among the CO2-based mixtures and pure CO2, CO2/R32 presents the highest exergy efficiency of 52.85% and CO2/R161 presents the lowest levelized cost per unit of exergy product of 47.909$/MWh for low temperature transcritical power cycle. For high temperature transcritical power cycle, CO2/Propane presents the lower levelized cost per unit of exergy product of 29.212$/MWh.

Case Study on the Inspection and Repair of Window Condensation Problems in a New Apartment Complex

AbstractDisputes and repairs due to window condensation problems frequently occur after the completion of apartments. However, most repairs are performed individually and confidentially by construc...

Thermodynamic and economic analysis and multi-objective optimization of a novel transcritical CO2 Rankine cycle with an ejector driven by low grade heat source

Transcritical CO2 Rankine cycle (T-CO2) is a promising technology for the utilization of low temperature heat source. The low critical temperature of CO2 (about 31 °C) leads to a restriction in the practical application of the cycle, since CO2 could hardly be condensed into liquid using higher temperature heat sink under the environment conditions. In this paper, a novel transcritical CO2 Rankine cycle with an ejector is proposed to solve the condensation problem of CO2 under the higher temperature heat sink. By establishing the mathematical model, a parametric analysis is carried out to examine the effects of five key parameters on thermodynamic and economic performances of the system. A multi-objective optimization is also conducted to obtain the optimum performance of cycle. The results indicate that increasing turbine inlet temperature and ejector back pressure could increase the exergy efficiency. In addition, lower investment cost of the system could be achieved by increasing the turbine back pressure and the valve expansion pressure. Furthermore, according to the Pareto frontier solution of multi-objective optimization, the exergy efficiency could reach a maximum of 19.33% and the investment cost of the system could reach a minimum of 657.9 × 103 USD.

Correlations of occupation numbers in the canonical ensemble and application to a Bose-Einstein condensate in a one-dimensional harmonic trap

We study statistical properties of $N$ non-interacting identical bosons or fermions in the canonical ensemble. We derive several general representations for the $p$-point correlation function of occupation numbers $\overline{n_1\cdots n_p}$. We demonstrate that it can be expressed as a ratio of two $p\times p$ determinants involving the (canonical) mean occupations $\overline{n_1}$, ..., $\overline{n_p}$, which can themselves be conveniently expressed in terms of the $k$-body partition functions (with $k\leq N$). We draw some connection with the theory of symmetric functions, and obtain an expression of the correlation function in terms of Schur functions. Our findings are illustrated by revisiting the problem of Bose-Einstein condensation in a 1D harmonic trap, for which we get analytical results. We get the moments of the occupation numbers and the correlation between ground state and excited state occupancies. In the temperature regime dominated by quantum correlations, the distribution of the ground state occupancy is shown to be a truncated Gumbel law. The Gumbel law, describing extreme value statistics, is obtained when the temperature is much smaller than the Bose-Einstein temperature.

Propagation-Based Temporal Network Summarization

Modern networks are very large in size and also evolve with time. As their sizes grow, the complexity of performing network analysis grows as well. Getting a smaller representation of a temporal network with similar properties will help in various data mining tasks. In this paper, we study the novel problem of getting a smaller diffusion-equivalent representation of a set of time-evolving networks. We first formulate a well-founded and general temporal-network condensation problem based on the so-called system-matrix of the network. We then propose NetCondense , a scalable and effective algorithm which solves this problem using careful transformations in sub-quadratic running time, and linear space complexities. Our extensive experiments show that we can reduce the size of large real temporal networks (from multiple domains such as social, co-authorship, and email) significantly without much loss of information. We also show the wide-applicability of NetCondense by leveraging it for several tasks: for example, we use it to understand, explore, and visualize the original datasets and to also speed-up algorithms for the influence-maximization and event detection problems on temporal networks.

Random matrices and condensation into multiple states.

In the present work, we employ methods from statistical mechanics of disordered systems to investigate static properties of condensation into multiple states in a general framework. We aim at showing how typical properties of random interaction matrices play a vital role in manifesting the statistics of condensate states. In particular, an analytical expression for the fraction of condensate states in the thermodynamic limit is provided that confirms the result of the mean number of coexisting species in a random tournament game. We also study the interplay between the condensation problem and zero-sum games with correlated random payoff matrices.

Assessing the airtightness performance of container houses in relation to its effect on energy efficiency

This study examines the airtightness performance of four types of commonly-used container houses (CHs) and its impact on their energy efficiency. One of the CHs was treated by sealing all junctions inside the container envelope. The airtightness levels of unsealed and sealed CHs were measured by using the fan pressurization method. The interior surfaces of building envelope were scanned by thermal imaging in order to locate the areas suffering from air leakages and thermal failures. The annual energy consumptions of unsealed and sealed CHs for their heating were predicted by energy simulation analyses. The unsealed CHs have poor airtightness features while performing in Energy Rating B category. The junctions of those houses, especially where wall, slab and roof panels come together and the edges of the openings also suffer from air leakages, thermal bridges and condensation. Sealing the interior surfaces of junctions and edges improves the airtightness level considerably while heat loss and condensation problems at the junctions still continue. An 81% improvement in airtightness performance of the CH Type B provided a reduction of 9.3% in annual energy demand which is not enough to step up its Energy Rating category. The results indicate that airtight jointing is needed at junctions while the use of thermal breaks at junction details has vital importance to eliminate thermal failures and to improve energy efficiency performance of CHs. The combined use of Blower Test Method and Infrared Thermography is useful for non-destructive assessment of airtightness features of building envelopes.

Prevention of dew condensation on the case surfaces of ceiling-cassette indoor air conditioning units

We proposed a new method for preventing dew condensation on the case surfaces of ceiling-cassette indoor air conditioning units. We investigated the dew condensation problem numerically using a diffusion boundary layer phase-change model that incorporates the effect of non-condensable gases. By installing a blocking device on the case surface, we significantly reduced the suction flow of warm, humid air and the total condensation rate on the surface. We optimized the installation location, height, and angle of the blockage in order to minimize dew condensation. When the optimized blockage device was installed, and the air conditioning unit was operated at low discharge speed, we observed that the total numerical and experimental condensation rate fell by 41 and 30%, respectively.

Modern wood windows now and trends after the year 2020

The article deals with the issues of wood windows applicable according to the expected requirements after the year 2020. It analyses the potential of the current top windows in regard to modern design, functionality, and building physical properties. By applying progressive material solutions, it is possible to create windows with proportionally variable frame solutions or even with frameless wing construction. The introduction of vacuum glass systems requires the optimization of the profile system of a wooden window. Modern quality glass systems bring the problem of condensation of water vapour on the exterior surface of the glass. Also, a new phenomenon in the emerging trend of energy-saving buildings and despite the use of quality wooden profile systems is the condensation of water vapour that occurs in the functional joint of the profile system of the wooden window. This fact is increasingly leading to mold growth in functional joints, which subsequently has a negative impact on human health.

Film condensation generated by free convection in a porous medium

In this paper, the steady process of laminar film condensation on a vertical wall with the backside cooled by free convection in a fluid-saturated porous medium is analysed as a conjugate problem. In the analysis, neither the temperature nor the heat flux at the wall sides is assumed, but they are determined from the solution like other unknown parameters. The analysis is conducted in a dimensionless way to generalize the solution. The main variables controlling the film condensation process are revealed from the analysis, which define the relative importance of interactive wall conduction, free convection and film condensation modes. The study indicates that the conjugate solution of laminar-film condensation problem is different from a Nusselt-type solution.