FIRE RESISTANCE CHARACTERISTICS OF MATERIALS WITH POLYMER GELS WHICH ABSORB AQUEOUS SOLUTION OF CALCIUM CHLORIDE

It is well known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of perlite-mortar and high-water-content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heat propagation in these materials. A superabsorbent polymer gel that absorbs calcium chloride solution contains much water, and it is one of these high-water-content materials. In this study, numerical simulations of fire resistance tests were conducted for materials of different mixing ratio of perlite-mortar and the super absorbent polymer gel to investigate the effect of the mixing ratio on the fire resistance characteristics. The effective thermal conductivity and the water content of the materials were measured and those values were used for computations. One of the test materials shows excellent fire resistance characteristics, and its fire resistance time at 60 mm thick is about 300 min. The relations of thermal properties and composition of the test material and the effects of mixing ratio of the gels and the perlite-mortar on the fire resistance characteristics are discussed.     

煤水混烧技术与链条炉排新材质的研究

分析了层燃锅炉煤水混烧技术的运行特点及其对炉排失效的影响,提出该技术条件下对炉排材质的要求,介绍新试验炉排的优化配方、化学成分及金相组织,试验结果表明,试验的新炉排材质从高低温机械性能到耐热性等方面均比现用炉排材质KT350-10优越。     

余热制冷用氯化钙_硅胶复合吸附剂的制备及性能研究

为了开发出利用余热进行吸附制冷的高性能吸附剂,采用浸渍法在真空下将氯化钙担载于粗孔硅胶上,制备了硅胶/氯化钙复合吸附剂,测试了复合吸附剂的吸附等温线和吸附速率,测试结果表明:浸渍法得到的复合吸附剂对水具有更大的吸附能力,在20%的湿度下,复合吸附剂在2h的吸附量为15.64 g/100 g吸附剂,是单一硅胶在相同条件下吸附量的8.06倍。用制备的复合吸附剂制作了一台小型吸附制冷机并进行了测试,当热源温度为90℃,冷却水温度为35℃时,在整个循环周期内(15 min),制冷功率为0.705kW,单位质量吸附剂的制冷功率(SCP)为70.51 W/kg,COP为0.25。     

An open heat pump process for moist gases

A heat pump process is proposed for the recovery of the latent heat of water vapour in waste heat gases. The process includes a humidifier where the moist waste gas is additionally humidified. The moist gas leaving the humidifier is pressurized in a turbocompressor. The dew point temperature of the gas is increased by the humidification and the compression. This is utilized by indirect heat exchange for the production of low pressure steam and for the required heat of vaporization in the humidifier. It should be possible to use the process for waste heat recovery from moist flue gases and from process gases such as dryer exhaust air. Performance data have been calculated for production of low pressure steam at 1.2 bar from moist air at atmospheric pressure, dry temperature 100°C and the absolute humidity 0.19 kg water vapour per kg dry air. With these data a coefficient of performance for the heat pump process has been calculated to be 2.8. 85% (m/m) of the waste heat has been recovered from the moisture content. For these calculations the pressurization in the compressor has been set to 4.0 bar. The process should be further investigated to find performance data under optimal operating conditions.     

Preparation and characterization of building mortar with lauric acid-stearic acid/expanded vermiculite composite phase change material

以改性膨胀蛭石为吸附材料,以月桂酸和硬脂酸为相变材料,通过熔融共混法与真空吸附法制备定型复合相变材料,然后将其掺入砂浆中制备得到蓄热砂浆。结果表明：复合相变材料经过1000次循环后相变焓为167.6 kJ/kg,变化率仅为3.6%,热稳定性良好,无渗漏现象,掺入30%体积含量复合相变材料的砂浆28 d强度为9.2 MPa。掺有该定型相变材料的蓄热砂浆具有优异的热力学性能,完全可以应用于建筑物围护结构来调节室内温度。     

A new approach to analysis and optimization of evaporative cooling system II: Applications

After introducing the concepts of moisture entransy, moisture entransy dissipation and thermal resistance based on moisture entransy dissipation (TRMED) in part I of this study, we further analyze several direct/indirect evaporative cooling processes based on the above concepts in this part. The nature of moisture entransy, moisture entransy dissipation and TRMED during evaporative cooling processes was reexamined. The results demonstrate that it is the moisture entransy, not the enthalpy, that represents the endothermic ability of a moist air, and reducing the entransy dissipation by both enlarging the thermal conductance of heat and mass transfer, and decreasing the temperature potential of the moist air, i.e. the difference between the dry-bulb temperature of moist air over its dew-point temperature, will result in a smaller system TRMED, and consequently a better evaporative cooling performance. Then, a minimum thermal resistance law for optimizing evaporative cooling systems is developed. For given mass flow rates of both moist air and water, with prescribed moist air and water conditions, minimizing the TRMED will actually lead to the most efficient evaporative cooling performance. Finally, the thermal conductance allocation for an indirect evaporative cooling system is optimized to illustrate the application of the proposed minimum thermal resistance law.     

考虑沸腾和缸内局部传热的缸盖流固耦合传热分析

以某商用车直列6缸柴油机作为研究对象,基于缸内传热模型获得内燃机缸盖和缸套的燃气侧局部传热边界条件;基于均相流沸腾传热模型获得水侧传热边界;实现水侧、燃气侧边界与结构温度场计算的耦合,并判断水腔内沸腾传热的状态。结果表明:缸盖温度计算值与实测值吻合,缸盖最高温度位于缸盖底面两个排气门之间;排气门之间的燃气传热系数和燃气温度均处于较高值,缸内局部传热显著;在缸盖底面中心和排气门附近水腔内的冷却水处于部分发展泡核沸腾状态。     

Vapor Convection in Gypsum Plasterboard Exposed to Fire: Numerical Simulation and Validation

This article investigates the contribution of water vapor convection to heat transfer through gypsum plasterboard exposed to fire. The vapor is generated as a product of the endothermic dehydration reaction in gypsum, and it is then expelled from the material through the pore network by its own pressure, thereby taking part in the heat transfer from the fire-exposed to the cold surface of plasterboard. The gas permeability values of plasterboard core and paper liner are obtained experimentally. The results of simulations are validated against the temperature measurement data obtained for two types of commercial plasterboard tested in the standard fire ISO 834. It is shown that vapor convection plays an essential role in heat transfer through plasterboard during the initial stage of fire. The amount of condensate developing in the pores of the material is found to be low, which allows it to be neglected in engineering calculations.     

600MW锅炉机组膜式水冷壁壁温的试验研究及理论分析

在６００ＭＷ锅炉机组水冷壁热力试验的基础上,为找到使壁温发生波动的根本原因,利用有限元分析的方法对低倍率锅炉膜式水冷壁管壁温度分布随传热工况的动态变化进行了分析。分析表明：导致水冷壁管壁温度波动最根本的原因是管内传热恶化;单面受热水冷壁在管内发生传热恶化时其向火这内外壁温差随时间的波动较小,而水冷壁周向温差则随向炎侧外壁的壁温波动而剧烈波动。     

石墨烯-PFA复合材料换热器与金属换热器的传热性能对比

氟塑料换热器以其耐腐蚀、耐磨损等优点而备受关注,但氟塑料热导率较低,换热能力差,限制了其广泛应用。石墨烯-PFA复合材料兼具石墨烯优异的导热性和可熔性聚四氟乙烯(PFA)良好的耐酸碱腐蚀性,是新一代的换热器材料。搭建了余热回收测试实验台,对石墨烯-PFA复合材料换热器和金属换热器的传热性能进行对比。研究了不同烟气流速、不同进口烟气温度以及不同石墨烯配比对复合材料传热性能的影响。结果表明:对于金属换热器和复合材料换热器,当烟气流速从2.0增加到4.0 m/s时,传热系数分别增加到原来的1.19和1.34倍;随着进口烟温的升高,两种材质的传热系数分别降低了15.6%和14.7%;随着石墨烯含量增加,复合材料的导热系数以及传热系数均增加。     

Mathematical modeling of agricultural fires beneath high voltage transmission lines

This paper presents a mathematical model for agricultural fires based on a multi-phase formulation. The model includes dehydration and pyrolysis of agricultural fuel and pyrolysis products. The model considers a homogeneous distribution of the agricultural solid fuel particles, interacting with the gas flow via source terms. These terms include: drag forces, production of water vapour and pyrolysis products, radiative and convective heat exchange. A multi-phase radiative transfer equation for absorbing-emitting medium is considered to account for the radiative heat exchange between the gas and solid phases of the fire. The main outputs of the present model are most important to study the influence of agricultural fire occurring beneath high voltage transmission lines. The agricultural fire causes a flashover due to the ambient temperature rise and soot accumulation on the insulator of these transmission lines. Numerical results of the present model are obtained for flat grassland fires to study the effects of wind velocity, solid fuel moisture content and ignition length on some selected fire outputs. These outputs include the temperature, velocity, soot volume fraction fields of the gas phase, together with fire propagation rate and flame geometry. The numerical results are compared to the available experimental work in the literature.     

Three dimensional numerical modeling of simultaneous heat and moisture transfer in a moist object subjected to convective drying

The drying behavior of a moist object subjected to convective drying is analyzed numerically by solving heat and moisture transfer equations. A 3-D numerical model is developed for the prediction of transient temperature and moisture distribution in a rectangular shaped moist object during the convective drying process. The heat transfer coefficients at the surfaces of the moist object are calculated with an in-house computational fluid dynamics (CFD) code. The mass transfer coefficients are then obtained from the analogy between the thermal and concentration boundary layer. Both these transfer coefficients are used for the convective boundary conditions while solving the simultaneous heat and mass transfer governing equations for the moist object. The finite volume method (FVM) with fully implicit scheme is used for discretization of the transient heat and moisture transfer governing equations. The coupling between the CFD and simultaneous heat and moisture transfer model is assumed to be one way. The effect of velocity and temperature of the drying air on the moist object are analyzed. The optimized drying time is predicted for different air inlet velocity, temperature and moisture content. The drying rate can be increased by increasing the air flow velocity. Approximately, 40% of drying time is saved while increasing the air temperature from 313 to 353 K. The importance of the inclusion of variable surface transfer coefficients with the heat and mass transfer model is justified.     

The numerical study of the thermal performance of a condensing gas-water heater

Abstract

Cast silicon-aluminum alloys exhibit corrosion resistance and heat transfer characteristics, and can be used as new materials in a condensing gas-water heater. A 3D mathematical model is established, and verified by the experiment, and then the flow and heat transfer characteristics are studied. It is observed the temperature misdistribution of the flue gas resulted from the condensation of water vapor. The temperature drop occurring in the high temperature zone exceeds 80%. Nusselt (Nu) empirical formulas for flue gas and water are obtained for two conditions. When inlet water gauge pressure reaches 0.02?MPa, heat transfer efficiency is the highest.     

Experimental study on the kinetics of water vapor sorption on selective water sorbents, silica gel and alumina under typical operating conditions of sorption heat pumps

A selective water sorbent (SWS) is a composite material consisting of a porous host matrix and a hygroscopic substance (commonly an inorganic salt) impregnated into its pores. This work presents an experimental investigation for the kinetics of water vapor sorption on two host materials; namely mesoporous silica gel and alumina in comparison with the two composites SWS-1L and SWS-1A formed by impregnating these two host matrices with CaCl₂. Moreover, the kinetics of water vapor sorption on microporous silica gel have been also investigated. The measurements have been carried out on 3 g samples of loose pellets on an isothermal wall under three different operating conditions of sorption heat pumps. The results obtained evidence a remarkable increase in the differential water loading of both SWS-sorbents over their host materials. However, and due to the increased diffusion resistance to water sorption resulting from the salt impregnation, the kinetics of water sorption into the host matrices is faster than that into the two SWS-composites. Moreover, SWS-1L is found to be faster than SWS-1A in sorbing water vapor. The differential water loading on microporous silica is about twice that on mesoporous silica and alumina, but the sorption kinetics are a little bit slower.     

Numerical study of the thermal–hydraulic performance of evaporative natural draft cooling towers

In this paper, the mathematical and physical models governing the flow, mass and heat energy of moist have been set up for an evaporative natural draft cooling tower. The models consider the effect of non-spherical shape of water drops on the flow, heat and mass transfer. Experimental data has been adopted to validate the numerical scheme. Average difference between the measured and the predicted outlet water temperature is 0.26°C. Distributions of the velocity components of the moist air, density, pressure, enthalpy and moisture content, the water temperature and its mass flux have been predicted. The simulation shows that some recirculation exits under the lower edge of the shell, where the air enthalpy, temperature, humidity and moisture content are higher, but the density is lower. The simulation also proves that the main transfer processes take place in the fill region where the percentage of latent heat transfer is predicted as 83%. However, about 90% of the heat energy is transferred via evaporation in the rain region although the total heat transfer rate there is very small compared to the fill region. Hourly performance of a natural draft cooling tower under the meteorological condition of Singapore has also been predicted.     

Numerical Thermal Analysis of Applying Insulation Material to Holes in Hollow Brick Walls by the Finite-Volume Method

A numerical study by self-programming three-dimensional software which can efficiently deal with complicated heat transfer is conducted to investigate the effect on the thermal performance of pasting 10 mm insulation around holes in external walls constructed from 240 × 115 × 90 mm hollow bricks. A comprehensive parametric investigation includes varying the arrangement of holes, insulation, or building materials. The results show that adopting this method can markedly reduce the equivalent thermal conductivity by between 20.3 and 61.1%, and choosing higher-thermal resistance mortar or hollow brick material achieves better insulation performance whereas the optimum configuration of hollow bricks is barely affected.     

Properties of high density polyethylene and its behaviour under ‘Galisol’ heat storage conditions

High density polyethylene (HDPE), crosslinked by electron beams in air, is presented as a latent heat storage material for energy storage applications at a temperature level of about 120°C. The study includes thermal investigations before and after the irradiation, investigations of the form stability, gel content determinations and microscopic investigations of HDPE. An electron energy of 0.4 MeV and a radiation dosage of 200 kGy were found to be the optimum conditions for the irradiation of the investigated HDPE in air. The pellets obtained were form-stable owing to the formation of a thin crosslinked surface layer (about 0.5 mm thickness). In spite of the presence of oxygen during irradiation, the melting enthalpy of the initial state was retained almost quantitatively. Apart from that, a quasicomplete irradiation of the pellets in volume in air, with a higher electron energy, is also possible. In this case about 95% of the initial melting enthalpy is obtained, providing a maximum gel content of 50%. Moreover, the paper offers a possibility of overcoming the low heat transfer power of HDPE by applying it in form of modified pellets in a ‘Galisol’ model storage unit with water as the heat transfer liquid. Owing to the large heat transfer area connected to boiling and condensation of water, excellent values of heat transfer power of 100–114 W/kg HDPE (ΔT=16 K) are obtained. These are comparable to those of salt hydrates, provided there is sufficient form stability. The significant influence of somewhat lower form stability on the heat output is shown.     

Influence of chitosan and porosity on heat and mass transfer in chitosan-treated porous fibrous material

This paper focuses on a theoretical investigation of the coupling mechanism of heat transfer and liquid moisture diffusion in chitosan-treated porous fibrous material. The porous fibrous materials made of cotton with different porosities are modified by chitosan solution with different concentrations. The moisture regain of the chitosan-treated porous fibrous material increases and the contact angle of the chitosan-treated fiber decreases significantly after modification. For comparison, the simultaneous heat and liquid moisture transfer in porous fibrous materials with different porosities modified by chitosan solution with different concentration are discussed. With specification of initial and boundary conditions, the distributions of the water vapor concentration in the void spaces, the volume fraction of the liquid water in the void spaces, the distribution of the water content in fibers and the temperature changes in chitosan-treated porous fibrous material are obtained numerically. The comparison with the experimental measurements shows the superiority of the numerical model in resolving the coupled heat and mass transfer in chitosan-treated porous fibrous material. Analysis of the computational and experimental results illustrates that the heat and mass transfer in chitosan-treated porous fibrous material is influenced by chitosan concentration and fabric porosity significantly.