Heat Insulation Layer Research Articles

Встановлення ефективності вогнезахисту деревини органо-неорганічною композицією

Опис поведінки вогнезахисних засобів у момент формування теплоізоляційної структури є окремим і складним завданням, а просочення характеризується розкладом антипіренів під дією температури з поглинанням тепла та виділенням негорючих газів, гальмування окислення в газовій і конденсованій фазі та утворенням на поверхні деревини теплозахисного шару коксу. Наведено результати дослідження процесу термодеструкції деревини сосни і визначено термограми її розкладу та встановлено, що кінетика процесу розкладу деревини вогнезахисної композицією "Skela-i" зміщується у напрямку високих температур, із коксовим залишком у 4 рази більшого ніж для необробленої деревини. Експериментально встановлено, що під дією теплового потоку на вогнезахищені зразки відбувається інтенсивне виділення інертних газів та зменшення горючих, що доводить про ефективність вогнезахисту. Після випробувань виявлено, що інтенсивність утворення негорючих газів переміщується у сторону підвищеної температури з утворенням пінококсу. Газохроматографічними дослідженнями аналізу летких продуктів піролізу вогнезахищених зразків виявлено збільшення негорючих газів у 8 разів та зменшення вмісту горючих – понад 50 %. Здійснено дослідження з визначення групи горючості деревини та встановлено зменшення у 3 рази втрати маси зразків захищеної деревини, порівняно з необробленими, а температура димових газів становила менше 165°С.

The Role of Carbonized Layers for Fire Protection of Polymer Materials

The present work studies the processes occurring in pre-flame zone in the form of «candle-like flame» which is spread over the surface of epoxy polymer. As exemplified by epoxy polymer, it can be seen that the dominating mechanism of heat transfer from flame to pre-flame zone of carbonized polymers is a thermal conductivity by condensed phase (to phase). The mechanism of gasification processes in pre-flame zone is proposed. Gasification of the material in front of the flame edge is a controlling process, and when selecting flame retardants, it is necessary to register their ability to influence on kinetics and mechanism of gasification. The flame leading edge is bordered with the surface of polymer, which largely determines the nature of heat transfer in pre-flame region. Due to investigations of gas-phase composition at «candle-like» combustion of epoxy polymer it has been detected a considerable amount of oxygen (up to 10‒12%) near burning surface. Its presence facilitates the thermal oxidation of polymer, moreover the rate of thermal oxidation can significantly exceed the thermal decomposition rate of the polymer. The possibility to form the heat-insulating intumescent layer during decomposition of carbonizable polymers was used at development of flame retardant coatings ‒ complex multicomponent systems. Which in turns forms the intumescent carbonized layer with high porosity and low thermal conductivity, and protects based material or construction from premature heating up to critical temperatures.

Reduction of POME final discharge residual using activated bioadsorbent from oil palm kernel shell

Abstract A double insulated carbonisation-activation reactor was developed in order to produce activated carbon with high yield and surface area. This reactor was double insulated using low cement castable and covered around the internal space of the reactor with stainless steel plated and fibre glass jacketed heat insulation layer, which allow efficient heat transfer into the bed of material in the reactor. The carbonisation of oil palm kernel shell (OPKS) at 400 °C, followed by steam activation at 500–1000 °C continuously in the same reactor, with steam flow rate of 12.80–18.17 L/min had improved the activated carbon surface area from 305 ± 10.2 m2/g to 935 ± 36.7 m2/g and gave a high yield of 30% within 7 h retention time with a low gaseous emission. The activated carbon produced was successfully applied as bioadsorbent for the treatment of POME final discharge with the reduction of TSS, COD, colour and BOD up to 90%, 68%, 97% and 83%, respectively which met the standard set by Department of Environment Malaysia (DOE).

Research into energy efficiency of the underfloor heating system, assembled dry

The object of research is the thermal parameters of operation of a fragment of the floor heating system assembled dry, under conditions of actual application set in the lab premises. One of the most problematic issues in the course of our experimental study has turned out to be a small area of the investigated heating system, relative to the volume of the room. Considerable ambient air temperature fluctuations resulted in certain difficulties while the heating system entered the quasi-steady mode. We have established in our study the effect of thickness of a heat insulation layer under the heating circuit on a change in the density of heat flow from the floor surface to the air in a heated room. It is noted that the floor heating system, assembled dry, has small thermal inertia due to the absence of a relatively thick layer of the monolithic concrete slab (with high specific heat capacity), which is typically used for the installation of a heating system circuit. Specifically, it was established that the use of ceramic tiles as the finish coating, compared with laminate, significantly reduces the overall thermal resistance of heat transfer from a heat carrier to the air in a heated room. In this case, the presence of an aluminum heat-scattering plate, which is in direct contact with the outer surface of the pipe in a heating circuit, has a positive effect on the uniformity of distribution of thermal field in the plane of the floor. This in turn leads to a reduction in thermal stresses in the finish coating. Calculations show that the quantitative control over thermal load of such a system by changing the consumption of a heat carrier proves to be less effective than the qualitative control through changing its temperature. Experimental studies reveal that the density of a heat flow on the floor surface increases almost two-fold when using ceramic tiles, in comparison with laminate, at all other thermal system settings being almost identical. The research we conducted make it possible to construct a mathematical model for the operation of a floor heating system, assembled dry, whose application would enable the optimization calculations and improvement of the design of a given heater.

Application of monolithic foam concrete in building envelopes of a cottage, used in conditions of intermittent heating

The paper focuses upon the peculiarities of application of monolithic foam concrete as a heat-insulating layer in building envelopes of houses used in conditions of intermittent heating. The researchers analyze thermal characteristics, review literature describing the application of foam concrete in construction and demonstrate this material applicability at outer walls insulating, taking buildings and constructions with variable thermal behaviour as an example. The paper outlines main criteria that building envelopes of such structures should meet. To assess the effectiveness of monolithic foam concrete in building envelopes application, the authors carried out thermo-technical calculation of the outer walls, insulated with monolithic foam concrete. The graphs of dependence of multilayer building envelope heating time upon thickness of a heat-insulating layer and upon heat transmission resistance of the construction was obtained on the basis of these calculations. The dependence of specific energy consumption upon the heating time is also given in the paper. The study reveals the optimal range of thickness and density of monolithic foam concrete for insulating outer walls of buildings, used in in conditions of intermittent heating. This calculation also proves that the application of foam concrete as an insulant on the inside of the outer wall makes it possible to reduce the load on the building foundation.

Foam Concretes for Heat Insulation Layers of External Walls Constructed by the Method of 3D Printing

Foam Concretes for Heat Insulation Layers of External Walls Constructed by the Method of 3D Printing

Transient heat transfer analysis of laminated materials based on extended separation of variables

In general, when the one-dimensional heat conduction equation is solved by the method of separation of variables, we need to know the governing equations, two boundary conditions and initial condition. Because the thermophysical parameters in different layers of laminated materials are different, the heat conduction model cannot be expressed by the same governing equation. For each layer of laminated material, the boundary condition is unknown. That equation can-not be solved directly by the general separation variable method. In this work the separation of variable method is extended. The temperature field of laminated material's heat transfer is divided into many minute time intervals on the time axis. Based on differential conception, in a minimum time interval, the temperature at the junction of laminated materials can be considered to be proportional to time. Assume that the slope coefficient makes the boundary condition known, then for each layer of laminated materials, the general separation of variables method will be used to solve the temperature field. According to the same temperature and the energy continuity at the junction of laminated materials, one can solve the slope coefficient. The temperature field in the whole time domain can be obtained through cycling. Then the three-layer insulation materials are analyzed by the extended separation variable method. The correctness of the method is verified by comparing the calculated results with those from the finite element method. The influences of the type and thickness of heat insulation layer, heat transfer coefficient, air temperature on the heat insulation are studied. It is found that the thermal conductivity of the thermal insulation layer has a great influence on the insulation. The material with low heat conduction coefficient can enhance the heat insulation effect. The thicker the thickness of the insulation layer, the more slowly the surface temperature of the heat insulation material rises, and the lower the final temperature, the better the insulation effect is. The thicker the thickness of the insulation layer, the smaller the heat flux density of the heat insulation material shell is, and the better the heat insulation effect when the heat transfer reaches a stable state. All calculation results are consistent with physical phenomena. In this work, the analytical method is used to solve the heat transfer problem of laminated materials. Compared with the general numerical methods, the analytical method presents clear physical meaning and high efficiency of operation as well.

Энергоэффективные материалы нового поколения в строительстве

The table with a tendency to use primary energy resources (oil, gas, coal, nuclear and hydropower) is presented in the work. This statistics makes wonder about the significance of the energy saving process around the world. The reason for the importance of energy conservation is the exhaustion of energy resources and the difficulty of their extraction. This task should be taken into account in the process of design, construction and operation of facilities. One of the ways is using energy efficient materials. Heat escapes through the enclosing structures, so it is important to provide a heat-insulating layer of high-quality materials. The article discusses such innovative materials as liquid insulation, aerogels and vacuum insulation panels. These materials have many advantages in comparison with classical heaters - a very low coefficient of thermal conductivity, environmental friendliness, lightness. Such materials do not weigh down the structures and save from heat loss. Aerogels are able to withstand cyclic temperature effects. The only disadvantage of innovative materials is their expensive price, but it is a temporary phenomenon, because the number of their manufacturers is gradually expanding. In addition, new insulation materials should recoup the investment in them during operation.

The influence of the thickness of the heat-insulating layer and the bulk of the cold source on the time of its storage

The influence of the thickness of the heat-insulating layer and the bulk of the cold source on the time of its storage

Numerical Investigation of Heat-Insulating Layers in a Cold Region Tunnel, Taking into Account Airflow and Heat Transfer

In cold regions, heat-insulating layers play a crucial role in frost prevention in tunnels. This paper presents a numerical study on the anti-freezing behavior of a cold region tunnel (the Dege tunnel) with heat-insulating layers. A numerical model based on the temperature field coupling theory is firstly proposed and validated using field test data of the Dege tunnel. Subsequently, a comprehensive parametric study is carried out to investigate the influences of heat-insulating layers on the temperature characteristics of airflows inside the tunnel, the surrounding rock, and the tunnel lining. Furthermore, a numerical investigation based on the proposed numerical model is carried out to propose reasonable design parameters of heat-insulating layers for different velocities of mechanical ventilation, and different heat-insulating materials for cold region tunnels. The numerical results show that using the heat-insulating layer can effectively reduce the heat transfer between the surrounding rock and the airflow inside the tunnel. It is also found that the design parameters for the heat-insulating layer are greatly affected by the tunnel ventilation conditions and heat-insulating materials.

EVALUATION OF HEAT PROTECTION CHARACTERISTICS OF BUILDINGS WITH INTERMITTENT HEATING INSULATED WITH SANDLESS COARSE-POROUS EXPANDED CLAY CONCRETE

Mathematical modeling of process of nonstationary heat transfer through walling exploited in intermitt ent heating conditions is viewed. Analytical dependence is revealed for fi nding of maximum permissible thickness of heat insulation layer providing required heating time. Based on this procedure the results of calculation of outer walls diff erent variants are presented. Comparative analysis of heating time of walling insulated with sandless coarse-porous expanded clay concrete.

INFLUENCE OF NON-PERFORATED SCREEN LOCATION ON HEAT TRANSFER PROCESS IN BUILDING ENCLOSING PARTS

It is recommended to have a vapor-proof barrier on the internal side of heat insulation system in multi-layer building enclosing parts in order to ensure protection of a heat-insulation layer against humidification because relative humidity of internal air is generally higher than external one and diffusion of water steam is directed from premises outside. While having a barrier with high vapor permeability a part of moisture can be accumulated in the structure and heat insulation core and difference of actual and maximum possible partial pressures leads to condensate formation. In order to improve thermal properties of enclosing parts the necessity arises to create a vapor-proof protection screen. It complies with the design of a panel with a vapor-proof screen in the form of non-perforated aluminium foil. The given screen located at internal panel layer prevents penetration of water vapor from premises into enclosing part and heat insulation layer. In such a case condensation zones and, consequently, their moistening can occur in some layers of enclosing parts according to their thermal and physical characteristics. The paper contains a calculation of thermal and moisture regime of the enclosing parts with vapor-proof layer (non-perforated aluminium foil) located in enclosing part core between various layers. An analysis of thermal and moisture regime diagrams for multi-layer external enclosing part demonstrates that the part of non-perforated screen (aluminium foil) located between internal concrete layer and perforated heat insulation layer is considered the most rational one. At the same time other screens between separate layers are perforated.

Heat insulating capacity of Sm2Zr2O7 coating added with high absorptivity solids

Rare earth zirconates has the potential to be a new generation of ceramic top coat material in thermal barrier coatings (TBCs). However, the heat insulating capacity of rare earth zirconates will weaken with the temperature rising because of infrared radiation. In order to evaluate the shielding effect of the coatings for infrared radiation, single layer coatings (SLC), double layer coatings (DLC) and triple layer coatings (TLC) with pure Sm2Zr2O7 (SZO) layer and Sm2Zr2O7–15vol%NiCr2O4 (SZO-15%NCO) layer were deposited by atmospheric plasma spraying (APS). The phase, microstructure and heat insulating capacity of the coatings were investigated. The results show that the powders and coatings are only composed of spinel-type and pyrochlore type SZO. The coatings are in a well compact state. The SLC has the lowset ΔT (213℃), while the highest ΔT (225℃) is obtained in TLC. Due to high absorptivity and conductivity of NCO, both positive and negative effects on heat insulating capacity generate in the SZO-15vol%NCO layer. The DLC shows a slightly higher ΔT (216℃), which is 3℃ higher than that in SLC. Compared with SLC and DLC, ΔT in TLC increases by 12℃ and 9℃, respectively. It indicates that suitable arrangement of heat insulation layer and absorption layer can effectively obstruct radiation, which can improve effectively the insulating capacity of the coatings.

Broadband ultrasound emission from a three-layer thermo-acoustic transducer

A thermophone generates sound with temporal variation of Joule heat which leads to expansions and contractions of a small volume of air near the surface of the metallic film. Consequently, the SPL of the sound is proportional to the input power and the emitted sound is the second harmonic of the input signal.1 Here, the fundamental characteristics of a three-layer thermophone (200-nm-thick Pt film, 5-μm-thick glass heat-insulating layer, and 500-μm-thick Si heat-releasing layer) were investigated. The device (10×12 mm2, 2.32 Ω) showed a broadband frequency response up to 140 kHz, and its SPL level at 50 mm was nearly constant (61.5±3 dB) from 20 to 140 kHz at 1.8 W power consumption. The conversion efficiency was 2.68×10-5%, which is 150 times the efficiency of the authors’ previous prototype, in which the heat release was less efficient (594-μm-thick alumina layer). Furthermore, by applying both AC and DC currents to the thermophone, it emitted the fundamental and the second harmonics of a 50-20 kHz FM sound, and hence a broadband (100-20 kHz) compound signal. These results and this device’s simple manufacturing process suggest that it may be used as a high resolution ultrasound sensor. 1Shinoda et al. (1999), Nature, 400(6747), p.853

Agglomerates, smoke oxide particles, and carbon inclusions in condensed combustion products of an aluminized GAP-based propellant

In solid propellants, aluminum is widely used to improve the performance, however the condensed combustion products especially the large agglomerates generated from aluminum combustion significantly affect the combustion and internal flow inside the solid rocket motor. To clarify the properties of the condensed combustion products of aluminized propellants, a constant-pressure quench vessel was adopted to collect the combustion products. The morphology and chemical compositions of the collected products, were then studied by using scanning electron microscopy coupled with energy dispersive (SEM-EDS) method. Various structures have been observed in the condensed combustion products. Apart from the typical agglomerates or smoke oxide particles observed before, new structures including the smoke oxide clusters, irregular agglomerates and carbon-inclusions are discovered and investigated. Smoke oxide particles have the highest amount in the products. The highly dispersed oxide particle is spherical with very smooth surface and is on the order of 1–2µm, but due to the high temperature and long residence time, these small particles will aggregate into smoke oxide clusters which are much larger than the initial particles. Three types of spherical agglomerates have been found. As the ambient gas temperature is much higher than the boiling point of Al2O3, the condensation layer inside which the aluminum drop is burning would evaporate quickly, which result in the fact that few “hollow agglomerates” has been found compared to “cap agglomerates” and “solid agglomerates”. Irregular agglomerates usually larger than spherical agglomerates. The formation of irregular agglomerates likely happens by three stages: deformation of spherical aluminum drops; combination of particles with various shape; finally production of irregular agglomerates. EDS results show the ratio of O to Al on the surface of agglomerates is lower in comparison to smoke oxide particles. C and O account for most element compositions for all the carbon inclusions. The rough, spherical, strip shape and flake shape carbon-inclusions are believed to be derived from the degradation products of the binder or oxidizer, while the fiber silk is possibly the combustion product of fiber inside the heat insulation layer of the propellants. Images of products at different pressures reveal high pressure reduces the degree of agglomeration. The chemical compositions, size range and content of all the observed structures are given in this paper. Results of our study are expected to provide better insight in the working process of solid rocket motor.

Highly porous basalt-fiber-based heat insulation for steam-heated oil wells in the Far North

An experimental and theoretical justification of the efficiency of a highly porous basalt-fiber-based heat insulation capable of providing geophysical equilibrium conditions for the existence of permafrost during the operation of steam-heated oil wells in the Far North is given. A mathematical model of heat transfer in highly porous fibrous materials is proposed to describe the steady-state mode of the process, with consideration given to Stefan–Boltzmann radiation into the pores of the highly porous material, thickness of the heat insulation layer, and temperature of the hot wall. The temperature dependence of the thermal conductivity of a highly porous heat-insulating material is obtained. It is shown that the thermal conductivity of a basaltbased fibrous heat-insulating material decreases by two orders of magnitude as its temperature rises to 930°C. The analysis performed provided new information of the parameters of the pore space of fibrous material in the processes of conductive heat transfer. The proposed solution makes it possible to calculate the thickness of a heat-insulating layer and concurrently optimize the porosity of the material. The results provide a basis for selecting suitable technological solutions.

Development of a Variable Stiffness Over Tube Based on Low-Melting-Point-Alloy for Endoscopic Surgery

Instruments used in endoscopic surgery (colonoscopy surgery or natural orifice transluminal endoscopic surgery (NOTES)) are flexible to be advanced in human body. However, when the end of the instrument reaches the target, the instrument should be rigid enough to hold its shape against external forces for better surgical accuracy. In order to obtain these two properties, a variable stiffness over tube based on low-melting-point-alloy (LMPA) is proposed in this paper. The structure exploits the phase transformation property of the LMPA which enables the stiffness change of the over tube by heating and cooling. A prototype was fabricated using a special molding method, and experiments were carried out to evaluate its variable stiffness property and response characteristics. According to experimental results, it costs 17 s to make the over tube transform from rigid state to flexible state and 18 s to make the over tube transform from flexible state to rigid state. The experimental results also indicated that the over tube is very rigid in rigid state and flexible in compliant state. A heat insulation layer was assembled to prevent human tissue from thermal damage. The temperature of the outer wall of the over tube was 42.5 °C when hot water of 80 °C was pumped into the over tube continually with the help of the heat insulation layer.

Protection of electronic devices on nuclear rescue robot: Passive thermal control

Thermal control is one of the most crucial problems for electronic devices on nuclear emergency rescue robot due to the harsh operating conditions. Phase change material (PCM) based heat sink and heat insulation layers, serving as a passive thermal control system, were applied for motor driver as a case for electronics protection on nuclear rescue robot. Two types of PCM based thermal control systems for both room temperature and elevated temperature environments were proposed considering the nuclear accident condition. The anti-irradiation property of an organic commercial PCM OP44E was studied. Experiments were conducted to investigate effects of system structure and heat source power on the temperature control. Results showed that the system can greatly prolong the motor driver's safe running time for more than 1 hour without any power consumption. The best working time was almost linearly decreased with the increase of the input power. High temperature test at 100 °C indicated that the motor driver could safely operate for more than 98 min. The PCM based support frame increased 54% of the best working time.

Improving the Lining of Cars Used in Short Tunnel Furnaces

An improved design of lining has been developed for the cars of short PG-30 tunnel furnaces, which are used to fire ceramic tooling: crucibles, cores, and molds for casting products made of heat-resistant alloys. The top part of the refractory layer that is installed on the heat-insulating layer consists of two superimposed panels. All of the panels except for the top panel contain interrupted holes (a total of 44 such holes) that are arranged in staggered fashion and open onto the panels’ main surfaces. The top panel contains blind holes (totalling 22). In assembling the refractory layer, the ends of the panels are connected to one another in such a way that the holes their surfaces are coaxial. The top panel is positioned so that the surface without holes faces upward and the holes on the other surface face downward. The box-inserts that hold the ceramic products which are to be fired are placed on the top panel. Such a design of car significantly reduces its weight while also increasing its service life. Durability is improved in particular for high-speed operation of the cars, such as in the firing of foundry molds for casting nickel alloys.

EFFECT OF THE SCREENS RADIANT REFLECTANCE ON THERMAL TRANSPORT PROCESS IN THE CLADDING STRUCTURES

The article analyses variants of the heat insulating layers disposition in relation to the cladding load-carrying structures and demonstrates prime advantages and drawbacks of the three variants. The authors notice that from the heat-engineering viewpoint the variant with exterior side winterization is the most favourable. However, utilizing micromodules as heat-insulating layers screened with leafing aluminum makes it necessary to account for the screens reflecting power. It allows reducing the irradiating component in the combined value of thermal transport through the enclosure and consequently raises the structure thermal resistance or, with parity of these values, leads to lower thickness of the heat-insulating layer. The known data applied for calculating the total heat transmission helps demonstrate reduction of the general heat flux value by 1.4 times, and the heat transmission resistance by 1.76 m2 deg./W. This allows reducing thickness of the heat-insulating layer (with regard of two screens) by 0.07 m. Computations illustrate the fact that account for the radiant reflectance of screening enables lowering the rated heat flux passing through the enclosure. Which again allows decreasing the structure thermal resistance and its general thickness (by 70 mm) at the expense of small thickness of the heat insulation of micromodules. The humidity regime calculations establish good acceptability of the enclosure service conditions in winter. The period will see no real water vapour condensation. The plotted diagrams of the cladding heat-and-humidity conditions demonstrate that condensation zones do not affect the layer of thermal insulation (micromodules). And the condensation zone with reduction of the heat-insulating layer appears only during ‘severe’ outside temperature conditions of a cold month. Reduced to 230 mm thickness of the wall construction allows utilizing ‘old’ stock of forms with prefabricated panels in parallel with energy saving during thermal treatment.