Inside Enclosure Research Articles

A Numerical Analysis on MHD Mixed Convective Hybrid Nanofluid Flow Inside Enclosure with Heat Sources

The MHD mixed convection inside a lid driven enclosure having heat sources filled with hybrid nanofluid is investigated numerically. This study aims to analyze the impact of Richardson number (0.01 ≤ Ri ≤ 100), Hartmann number (0 ≤ Ha ≤ 100) and different combination of hybrid nanoparticles (Ag–MgO, Ag–TiO2 and Ag–CuO) on fluid flow and heat transfer inside the enclosure. The finite volume method was used to solve the governing equations. The values of Ri, Ha, Re were found to have a great influence on thermal transport of hybrid nanofluids concerned in this investigation. Furthermore, at Ri = 100, the heat transfer rate is maximum for all values of Hartmann number. Increasing values of Richardson number strongly enhances the heat transfer rate whereas Hartmann number attenuates the aggrandization of heat transfer. It has been concluded that the rate of heat transfer of Ag–CuO/water hybrid nanofluid is higher than Ag–TiO2/water and Ag–MgO/water.

Numerical Modelling of Moisture Transport Between Two Enclosures Connected by a Tube

The electronics is protected using plastic or metallic enclosures. Although, the electronics is protected by the enclosures from the surrounding environment, the moisture can still enter the enclosure via gasket, plastic enclosure walls, cable feedthroughs. The moisture existing inside enclosure may condense on PCBA or components due to a temperature changes or different temperature levels and can lead to a moisture-related failures. The temperature in the enclosure is also very dependent on the location and the heating of electronic components. Furthermore, the electronics can be mounted nearby to other heating or cooling components in the complex mechanical systems, such as water pump or water meter. The paper concerns the complex transient heat and mass transfer processes between two connected enclosures with one being warm and another cold. The objective of the paper is to develop an in-house code based on the RC approach for predicting and studying the temperature and moisture behaviour inside two connected enclosures. The developed RC model combines one-dimensional description and lumped analysis for heat and mass transport. The modelling of temperature and moisture response is carried out under non-isothermal B3 STANAG ambient conditions. Moreover, the effect of different material of warm enclosure and the heating are considered.

Архитектура каменных сооружений эпохи бронзы в окрестностях Бурабая

The article deals with the materials of the study of ancient religious buildings of the Bronze Age at the Kyzyltobe burial ground. The architecture of buildings, the funeral rite, and the accompanying inventory are described, the technological methods used in the extraction of materials used in construction are considered. As a result of the work carried out, four fences were excavated at the burial ground: No. 9, 13, 29, 50. The burial, located in enclosure No. 9, was made in a dirt pit with a dromos designed in the form of a tambour, which obliquely enters the eastern wall of the grave pit under the stone ring of the tomb enclosure. The ashes of a cremated person were located on a flat wooden dish, located in a stone box in fence No. 13. Inside enclosure No. 29, two burials were found, made according to the rite of inhumation: an adult — in the main enclosure, a children's — in an extension. In enclosure number 50, a monumental stone box without a burial was fixed and examined, in the center of which a granite stone lay at the bottom. The box is covered with large slabs, in the center of which there is a round opening. A petroglyph of a deer was found on one of the side walls of the box. Soil burial pits, stone cists, burials according to the rite of cremation and accompanying inventory in the form of ornamented ceramic vessels, located in fenced areas, studied at the Kyzyltobe burial ground, find analogies in the burial grounds of Borovoye, Buyrekkol and Obali. These monuments are located in the vicinity of Burabay and belong to the Fedorov archaeological culture. The new fixed elements of the burial structures are the dromos and the stone box with an opening in the ceiling. The image of a deer on the wall of the box is a remarkable fact in itself; the image of a deer is one of the motifs of animal-style art. Perhaps this is an echo of totemism. According to radiocarbon analysis of bone material from fence No. 29, the Kyzyltobe burial site dates back to the 18th–17th centuries BC.

Heat Transport Exploration of Free Convection Flow inside Enclosure Having Vertical Wavy Walls

This paper expresses a numerical study of flow features and heat transport inside enclosure. Governing equations will be discretized by finite-element process with a collected variable arrangement. The assumptions of the Grashof number (103 - 106), aspect ratio (1.0 – 2.0), wave ratio (0.0 - 0.40) concerning a fluid with Pr = 0.71. Streamlines and isotherm lines are utilized to show the corresponding flow and thermal field inside a cavity. Global and local distributions Nusselt numbers are displayed for the before configuration. Finally, velocity and temperature profiles are displayed for some selected positions inside an enclosure for a better perception of the flow and thermal field.

Numerical Study on the Effect of Angle of Inclination on Magnetoconvection Inside Enclosure with Heat Generating Solid Body

Convective ow and heat transfer of uid inside a square en- closure having heat generating solid body, with various thermal boundary conditions is investigated numerically. The top wall of the enclosure is adiabatic, both the bottom and right walls are kept at constant temper- ature, while the left wall is heated using sin function. Numerical simu- lations is carried out by solving the governing equations using SIMPLE algorithm by means of the nite-volume method with power-law scheme. The important parameters focused are angle of inclination of the enclo- sure, area ratio of solid-enclosure, Hartmann number and temperature dierence ratio of solid- uid, which are ranges 0 o - 90 o , 0:0625 - 0:5625, 0 - 100 and 0 - 50, respectively. Thermal conductivity ratio of solid- uid is xed as 5 and Rayleigh number as 10 5 .

Experimental Heat Transfer From Heating Source Subjected to Rigorous Natural Convection Inside Enclosure and Cooled by Forced Nanofluid Flow

Mixed convection heat transfer characteristics from heat source located symmetrically inside square enclosure and cooled by Al2O3/water-based nanofluid flow was experimentally investigated. The configuration was subjected to high levels of natural convection and low rates of nanofluid flow. The nanofluid thermophysical properties were characterized using the available correlations in the literatures except the viscosity which was measured and correlated in terms of the nanoparticles loading ratios. Comparative analysis indicated that the application of nanofluid could not guarantee heat transfer enhancement in configurations dominated by natural convection. Exception heat transfer enhancement was only found when very low nanoparticles loading ratio was applied. Instead, heat transfer degradation was found especially in the cases of highest nanoparticles loading ratios. Alternatively, heat transfer enhancement was observed when the forced convection effect was substantial at the highest nanofluid flow rate. The present conclusions were justified and correlated to the findings reported in the literature.

Heat transfer by natural convection of Fe3O4-water nanofluid in an annulus between a wavy circular cylinder and a rhombus

Researchers in modern science always attempt to find new techniques to optimize the performance of energy devices through heat transfer enhancement. It comes to the knowledge that such enhancement can be done with the help of nanofluids. Therefore, the present study is aimed to investigate the role of natural convection and thermal radiation on thermo-hydrodynamics of nanofluid heat transfer in an annulus between a wavy circular cylinder and a rhombus enclosure subject to a uniform magnetic field. A new model for viscosity called magnetic field dependent (MFD) viscosity is used. Mathematical formulation of the current physical model is based on the continuity, momentum and energy equations. Numerical simulation of the reduced problem is done with the help of Control Volume based Finite Element Method (CVFEM). The impacts of controlling physical parameters, for instance, Rayleigh number, radiation parameter, Hartmann number, aspect ratio, shape factor of nanoparticles and solid volume fraction of nanoparticles on thermo-hydrodynamics of flow are studied. The quantities of physical interest are graphically presented and discussed in detail. From the present study it becomes apparent that the local heat transfer rate decreases with an increase in aspect ratio in the absence of Hartmann number. In addition, for decreasing values of aspect ratio, the space for fluid flow inside enclosure becomes wider.

Natural convective heat transfer of Ag-water nanofluid flow inside enclosure with center heater and bottom heat source

A numerical study on natural convective heat transfer inside an enclosure with center heater using nanofluid has been carried out. The effect of different length of center heater on the flow and temperature fields is analysed for different Rayleigh numbers. Results are displayed in terms of streamlines, isotherms, mid height velocity profile and average Nusselt number. The numerical results reveal heat transfer increases with increasing heater length at both vertical and horizontal positions for increasing values of Rayleigh numbers. In particular, a higher increase in heat transfer is obtained with heater situated with vertical position of maximum length. Also it is obtained that enhancement of heat transfer is high for Ag - water nanofluid than CuO -water and Al2O3 -water nanofluids.

Dynamic response of a modified water tank exposed to concentrated solar energy

Power generation by using concentrated solar thermal energy on liquid enclosures is one of the most promising renewable energy technologies. In this work, a developed liquid enclosure fitted with various number and configurations of horizontal metal rings have been analyzed, fabricated and tested. The influence of adding metal rings arrangement is investigated for its potential to enhance radial heat conduction to the center-line of the enclosure from the side-walls. Experiments were carried out for fluid in both static and dynamic modes of operation inside the enclosure that subjected to high heat flux. A developed two-dimensional CFD model to predict the transient flow and thermal fields within liquid enclosure subjected to heat flux has been developed and tested. The developed numerical model takes into consideration energy transport between the liquid inside enclosure and the solid material of the enclosure. The numerical simulations have been compared with experimental measurement. The computational code has been found in a good level of agreement with the experimental data except for liquid at the peak part of the enclosure. The results indicate that adding metal rings produce significant impact on the transient temperature difference inside enclosure during both static and dynamic modes. The six-ring model is found to be more effective for enhancing radial heat transfer than other three models that have been tested. The in-line arrangement is found to provide better thermal effect as compared to the staggered rings. Two new correlations for natural heat transfer inside liquid enclosures subjected to high heat flux have been formulated (one for no-ring model and the other for six-ring model). The natural Nusselt number is found to be around a constant value for Rayleigh number less than (5 X 108). The recommended use of metal rings inside liquid enclosures subjected to heat flux, and the predicted Nusselt number correlation, will add to local knowledge a significant mean to gain more heat in large scale concentrated solar power plants. Two new correlations for natural heat transfer inside liquid enclosures subjected to high heat flux have been formulated (one for no-ring model and the other for six-ring model). The natural Nusselt number is found to be around a constant value for Rayleigh number less than (5 X 108). The recommended use of metal rings inside liquid enclosures subjected to heat flux, and the predicted Nusselt number correlation, will add to local knowledge a significant mean to gain more heat in large scale concentrated solar power plants.

Patterns of Behaviour, Group Structure and Reproductive Status Predict Levels of Glucocorticoid Metabolites in Zoo-Housed Ring-Tailed Lemurs, Lemur catta

In ring-tailed lemurs, Lemur catta, the factors modulating hypothalamic-pituitary-adrenal (HPA) activity differ between wild and semi-free-ranging populations. Here we assess factors modulating HPA activity in ring-tailed lemurs housed in a third environment: the zoo. First we validate an enzyme immunoassay to quantify levels of glucocorticoid (GC) metabolites in the faeces of L. catta. We determine the nature of the female-female dominance hierarchies within each group by computing David's scores and examining these in relation to faecal GC (fGC). Relationships between female age and fGC are assessed to evaluate potential age-related confounds. The associations between fGC, numbers of males in a group and reproductive status are explored. Finally, we investigate the value of 7 behaviours in predicting levels of fGC. The study revealed stable linear dominance hierarchies in females within each group. The number of males in a social group together with reproductive status, but not age, influenced fGC. The 7 behavioural variables accounted for 68% of the variance in fGC. The amounts of time an animal spent locomoting and in the inside enclosure were both negative predictors of fGC. The study highlights the flexibility and adaptability of the HPA system in ring-tailed lemurs.

Effect of Adding Horizontal Rings on the Thermal Behavior of Cylindrical Liquid Enclosure Exposed to High Heat Flux

Power generation by using concentrated solar thermal energy on liquid enclosures is one of the most promising renewable energy technologies. In this work, a developed liquid enclosure fitted with various number and configurations of horizontal metal rings have been analyzed, fabricated and tested. The influence of adding metal rings arrangement is investigated for its potential to enhance radial heat conduction to the center-line of the enclosure from the side-walls. Experiments were carried out for fluid in both static and dynamic modes of operation inside the enclosure that subjected to high heat flux.A developed two-dimensional CFD model to predict the transient flow and thermal fields within liquid enclosure subjected to heat flux has been developed and tested. The developed numerical model takes into consideration energy transport between the liquid inside enclosure and the solid material of the enclosure. The numerical simulations have been compared with experimental measurement. The computational code has been found in a good level of agreement with the experimental data except for liquid at the peak part of the enclosure. The results indicate that adding metal rings produce significant impact on the transient temperature difference inside enclosure during both static and dynamic modes. The six-ring model is found to be more effective for enhancing radial heat transfer than other three models that have been tested. The in-line arrangement is found to provide better thermal effect as compared to the staggered rings.Two new correlations for natural heat transfer inside liquid enclosures subjected to high heat flux have been formulated (one for no-ring model and the other for six-ring model). The natural Nusselt number is found to be around a constant value for Rayleigh number less than (5 x 108). The recommended use of metal rings inside liquid enclosures subjected to heat flux, and the predicted Nusselt number correlation, will add to local knowledge a significant mean to gain more heat in large scale concentrated solar power plants.

Numerical and experimental investigation of infrared radiation characteristics of a turbofan engine exhaust system with film cooling central body

A new concept of film cooling central body for the exhaust system of turbofan engine was brought out to suppress the infrared radiation of engine in this paper. The ability of infrared suppression was estimated by experiments and numerical calculations. The numerical method, which use forward–backward ray tracing and narrow band model, had been validated by the experimental results. The aerodynamic characteristics and infrared radiation distribution of exhaust system with/without film cooling central body were investigated for several different configurations. The experimental results reveal that the bypass flow can be used to cooling the central body and suppress the infrared radiation at the rear aspect of the engine. The inlet area of lugs in the bypass passage determined the mass flow rate into the central body. To obtain the effects of the film cooling holes configuration on the surface temperature and infrared radiation intensity of the exhaust system, a series of computations on full scale exhaust system have been performed. The numerical simulation results indicate that the film cooling central body can suppress the infrared radiation of the inside enclosure by 40–70% comparing to the central body without the film cooling at zero degree aspect (normal to nozzle outlet). The film cooling central body for exhaust system of turbofan engine has remarkable ability to suppress the infrared radiation from the inside enclosure of nozzle.

Numerical Simulation of Acoustic Streaming for Nonlinear Standing Ultrasonic Wave in Water Inside Axisymmetric Enclosure

In this paper, acoustic streaming generated by standing waves in a cylindrical enclosure filled with water is simulated. The effects of geometry, vibrating amplitude and frequency on formation of streaming structures are numerically investigated. The vibrating source is located at the central region of the lower plate. This source generates a plane wave at the bottom of the cylinder. The complete Navier-Stokes equations are considered and an explicit finite-difference method is used to track the acoustic waves. Water in this simulation is assumed to be a Newtonian rotational compressible single-phase liquid with an accurate equation of state. Equations are derived in Lagrangian cylindrical coordinates, using the condition of axial symmetry. The variation of acoustic pressure demonstrates a periodic modulation. The shape of the mean flow field in a period of the modulation does not differ significantly from the second period and there is a steady state condition for all periods. Results showed stronger acoustic streaming because of a decrease in enclosure height and decrease in frequencies.In addition, the increase in the enclosure radius or radius of the vibrating plate and the increase in the maximum displacement of the vibrating plate caused higher acoustic streaming velocities.

Fecal Glucocorticoid Measurements and Their Relation to Rearing, Behavior, and Environmental Factors in the Population of Pileated Gibbons (Hylobates pileatus) Held in European Zoos

Pileated gibbons (Hylobates pileatus) are rated as endangered according to the International Union of Conservation of Nature (IUCN) Red List. The captive population suffers from poor breeding success and is threatened to become overaged. Although several factors are likely to contribute to the poor breeding success, one in particular may be chronic stress associated with prolonged periods of high glucocorticoid (GC) output. We investigated fecal GC levels of pileated gibbons (Hylobates pileatus) and their relationship to specific life-history variables and environmental factors. After validation of an enzyme immunoassay for the measurement of 5-reduced 3α,11β-dihydroxy cortisol metabolites to assess GC output reliably in pileated gibbons, we collected fecal samples over several days from all 36 European adult pileated gibbons located in 11 institutions and compared GC levels to intrinsic individual parameters, husbandry, behavior, and breeding history. Age, sex, and origin (wild vs. captive born) had no effect on GC levels. However, unnaturally reared gibbons had higher GC levels and showed more behavioral abnormalities than parent-reared individuals. Further, nonreproducing gibbons living in a pair without infants had higher GC concentrations than gibbons living in a family, bachelor group, or as singletons. With respect to environmental factors, a large size of the inside enclosure and the existence of visual protection from visitors was associated with lower fecal GC output. The data indicate that rearing and housing conditions appear to correlate to GC levels in pileated gibbons housed under captive conditions. It is hoped this knowledge will support the future management of the species in captivity and thus lead to a more successful breeding of this endangered primate.

Numerical investigation of flow mixture enhancement and infrared radiation shield by lobed forced mixer

For the exhaust system of turbo-fan engine, the numerical calculation is used to investigate the different mixer configurations. The method using forward–backward ray-tracing and narrow-band model to predict the radiation from engine exhaust has been developed. The scheme has been validated in accuracy for spectral radiation intensity predictions, and some useful results of practical importance have been obtained to establish its ability for infrared signature analysis of exhaust system. A series of computations on exhaust system model have been conducted to obtain the effects of mixer configuration on the aerodynamic performances and infrared radiation intensity. The results indicate that the lobed forced mixer can increase the mixing efficiency by 65%, decrease the thrust coefficient by 3% only, but the infrared radiation of plum can reduce about 40% relative to confluent mixer at zero degree aspect (normal to nozzle outlet), especially. That means the lobed forced mixer has the remarkable ability to shelter the infrared radiation from the inside enclosure of nozzle.

Ecological restoration engineering in Lake Wuli, Lake Taihu:a large enclosure experiment

五里湖是太湖北部富营养化程度最为严重的-湖湾.从2004年1月起,为了改善水质,重建五里湖生态环境,在五里湖南岸建立了一个面积为10×10⁴m²示范工程试验区,采用多技术措施集成应用,开展湖泊生态重建技术研究.经过近2年的生态重建研究与实践,在示范工程试验区内建立了挺水植物、浮叶植物和沉水植物群丛23个,水生植物种类从生态重建前的零上升至15科、22属、32种,水生植物的多样性指数(Shannon-Wieher index)达到2.33,覆盖度达到40%-55%.水质监测结果表明,示范工程区内水体的TN、TP、NH₄-N、NO₃-N、NO₂-N及PO₄-P的平均值分别比示范工程区外下降了20.7%、23.8%、35.2%、21.1%、45.6%和54.0%,TN、TP分别下降至2.50mg/L、0.080mg/L以下,水质得到明显改善,达到或低于“浅水湖泊稳态转换理论”指出的向“稳定清水态”转换的临界值,水体透明度(SD)平均值也有较大幅度提高,平均从0.39m提高至0.70m;初步实现湖泊水体从藻类占优势浊水态向大型水生植物占优势的清水态转变.因此重建与恢复湖泊生态系统要从沿岸带着手,首先重建湖滨带结构与功能,通过湖滨带水生生物-系列反馈机制, 逐步改善湖泊水质,最终实现沉水植被恢复;湖泊敞水区应主要采用生物操纵技术措施来实现湖泊生态恢复.;Lake Wuli is a hyper-eutrophic, shallow-lake in China, situated near the Wuxi city in Jiangsu Province. It is a northern bay of Lake Taihu, which has a mean depth of 1.6 m, a maximum depth of 2.6 m and a surface area of 6.4 km². For improving water quality, from January 2004 a large-scale ecological restoration experiment (10x10⁴ m) has been carried out in southwestern Lake Wuli. Main measures applied include setting-up a large enclosure for facilitating growth of submerged macrophytes, sediment dredging, fish removal, rehabilitating sediment, stocking piscivorous fish, planting aquatic macrophytes, stocking benthic animals and so on. The results showed that 23 aquatic macrophyte associations had been set up, including 15 family, 22 genus and 32 species. The coverage of aquatic macrophytes increased from 0 to 40%-55%.Water quality has been markedly improved inside enclosure. The mean concentrations of TN, TP, NH4-N, NO3-N, NO2-N and PO4-P from August 2004 to July 2005 inside enclosure were 20.7%, 23.8%, 35.2%, 21.1%, 45.6% and 54.0% lower than those of outside enclosure. The mean concentrations of TN and TP were lower than 2.50 mg/L and 0.080 mg/L, respectively. Secchi depth was increased significantly from 0.39m to 0.70m. According to the results of this study, it is important and a first step to rehabilitate ecological structure and function in littoral of lakes, and to improve water quality gradually, and to establish submerged macrophytes at length. Biomanipulation could he applied to increasing secchi depth, reducing algal biomass and improving water quality in open area for whole lake restoration.

THE INFLUENCE OF NATURAL CONVECTION ON THERMAL PROPERTIES OF BUILDING ENCLOSURE WITH POLYSTYRENE BOARDS/PUTŲ POLISTIRENO PLOKŠTĖMIS IZOLIUOTŲ PASTATŲ SIENŲ ŠILUMINIŲ SAVYBIŲ PRIKLAUSOMYBĖ NUO NATŪRALIOS KONVEKCIJOS

Building insulating materials with good insulation properties usually are porous, because they contain large amounts of air or other gas inside. The pore system can be closed, as in many cellular plastics, or open as in fibre materials. The mechanisms of heat transfer in porous material are: conduction in solid phase, radiation within material and conduction due to the gas confined in the insulation. In an open-pore material, like lightweight mineral wool, the transportation of heat can be further increased by air movement (convection) through the permeable material. Convection is impossible in a closed porous materials like polystyrene (EPS, XPS) boards. But heat losses can be increased by air movement if there are cracks between boards and other building envelope structures. The airflow velocity and direction may vary strongly due to the changing boundary condition. However, at the present time in Lithuania convection in insulating materials is considered as non-existent, when calculating heat transmission and designing building structures. Because of the lack of knowledge concerning air movement in external building structures, and how it is affecting the heat transfer, this investigation has been carried out. For research an equipment (Fig 2) was made, assigned for exploring both vertical and horizontal structures (height 2100 mm, width 1100 mm and thickness up to 300 mm). For reducing heat losses through the sides up to minimum, an equipment was built from slabs (thickness 150 mm). As the hot side of equipment gypsum board was applied to the surface of which 8 heat flow sensors and 9 thermocouples were attached. For maintaining constant and isothermal temperature of the surface of this partition (Θi, =+20°C), heating elements and ventilators were mounted inside the equipment. The cold surface of the equipment was of the same construction as the warm one only with the regulated slide valve with an area of 0,02 m2. It allows exploring the so-called not-ventilated structures. During the test, temperature was measured at different places and depths. The research was performed on the foam polystyrene plates of 3×50 mm of thickness with 3–5 mm air gaps. Measurements were conducted in the following sequence: Two basic measurements of closed structure were performed for constant values of temperatures Θe=0°C and Θe=10°C. In this case the structure was held horizontally and heat flow was directed from top to bottom. Therefore it could be assumed that heat was transferred by conduction and radiation. Measurements of the closed structure were performed on the equipment being in vertical position and for external temperature Θe=0°C and Θe=10°C. Measurements of the opened structure. The measurement carried out for the same external environment conditions, the ventilating orifice being opened. The results of laboratory experiments allowed to assess the heat losses of the enclosure being arranged in the form of wall with air gaps applying foam polystyrene slabs. Different types of structures being investigated are shown in Fig 1. The Nu numbers for closed and ventilated structures are presented in Figs 8 and 9. The research results could be applied to enclosures with hard type insulation too. Although the natural convection does not occur inside the ideal material, but it takes place inside enclosure with air gaps. Thus, actual U-value depends on structural solutions and air tightness on building envelope. If wind barrier is permeable, then air filtration through the structure may cause even critical values for heat losses.

The Early and Current English Business Letters

Updated English business correspondence requires a modern and unsophisticated method of expression ranging from the layout to the contents of the letter. It has to be accurate, concise, neat and easy to read. To the reader, the most significance of the contents has to be understandable. The out-of-date style of writing in the 20(superscript th) century is full of long wordiness and too much courteousness. Sometimes it is too vague, ambiguous, and hard to understand. There are a lot of expressions to which the writer should pay attention besides the said obsolete expressions, e.g., the use of inside address, salutation, complimentary close, signature block, initials, carbon (circulated) copy, enclosure, postscript, and layout.

THE INFLUENCE OF NATURAL CONVECTION ON THERMAL PROPERTIES OF BUILDING ENCLOSURE WITH POLYSTYRENE BOARDS

Summary Building insulating materials with good insulation properties usually are porous, because they contain large amounts of air or other gas inside. The pore system can be closed, as in many cellular plastics, or open as in fibre materials. The mechanisms of heat transfer in porous material are: conduction in solid phase, radiation within material and conduction due to the gas confined in the insulation. In an open-pore material, like lightweight mineral wool, the transportation of heat can be further increased by air movement (convection) through the permeable material. Convection is impossible in a closed porous materials like polystyrene (EPS, XPS) boards. But heat losses can be increased by air movement if there are cracks between boards and other building envelope structures. The airflow velocity and direction may vary strongly due to the changing boundary condition. However, at the present time in Lithuania convection in insulating materials is considered as non-existent, when calculating heat transmission and designing building structures. Because of the lack of knowledge concerning air movement in external building structures, and how it is affecting the heat transfer, this investigation has been carried out. For research an equipment (Fig 2) was made, assigned for exploring both vertical and horizontal structures (height 2100 mm, width 1100 mm and thickness up to 300 mm). For reducing heat losses through the sides up to minimum, an equipment was built from slabs (thickness 150 mm). As the hot side of equipment gypsum board was applied to the surface of which 8 heat flow sensors and 9 thermocouples were attached. For maintaining constant and isothermal temperature of the surface of this partition (Θi, =+20°C), heating elements and ventilators were mounted inside the equipment. The cold surface of the equipment was of the same construction as the warm one only with the regulated slide valve with an area of 0,02 m2. It allows exploring the so-called not-ventilated structures. During the test, temperature was measured at different places and depths. The research was performed on the foam polystyrene plates of 3×50 mm of thickness with 3–5 mm air gaps. Measurements were conducted in the following sequence: 1. Two basic measurements of closed structure were performed for constant values of temperatures Θe=0°C and Θe=10°C. In this case the structure was held horizontally and heat flow was directed from top to bottom. Therefore it could be assumed that heat was transferred by conduction and radiation.2. Measurements of the closed structure were performed on the equipment being in vertical position and for external temperature Θe=0°C and Θe=10°C.3. Measurements of the opened structure. The measurement carried out for the same external environment conditions, the ventilating orifice being opened. The results of laboratory experiments allowed to assess the heat losses of the enclosure being arranged in the form of wall with air gaps applying foam polystyrene slabs. Different types of structures being investigated are shown in Fig 1. The Nu numbers for closed and ventilated structures are presented in Figs 8 and 9. The research results could be applied to enclosures with hard type insulation too. Although the natural convection does not occur inside the ideal material, but it takes place inside enclosure with air gaps. Thus, actual U-value depends on structural solutions and air tightness on building envelope. If wind barrier is permeable, then air filtration through the structure may cause even critical values for heat losses.

Plutonium aerosol characterization inside safety enclosures at a demonstration mixed-oxide fuel fabrication facility.

Plutonium aerosol characterization inside safety enclosures at a demonstration mixed-oxide fuel fabrication facility.