Thermal analysis of a building brick containing phase change material

This paper presents the thermal analysis of a building brick containing phase change material (PCM) to be used in hot climates. The objective of using the PCM is to utilize its high latent heat of fusion to reduce the heat gain by absorbing the heat in the bricks through the melting process before it reaches the indoor space. The considered model consists of bricks with cylindrical holes filled with PCM. The problem is solved in a two-dimensional space using the finite element method. The thermal effectiveness of the proposed brick-PCM system is evaluated by comparing the heat flux at the indoor surface to a wall without the PCM during typical working hours. A paramedic study is conducted to assess the effect of different design parameters, such as the PCM's quantity, type, and location in the brick. The results indicate that the heat gain is significantly reduced when the PCM is incorporated into the brick, and increasing the quantity of the PCM has a positive effect. PCM cylinders located at the centerline of the bricks shows the best performance.     

Steady state theoretical model of fired clay hollow bricks for enhanced external wall thermal insulation

This paper proposes a theoretical model to study the steady state thermal behavior of fired clay hollow bricks for enhanced external wall thermal insulation. The study aims at the development of new materials and structural components with good thermal material properties, with respect to energy saving and ecological design. Thermal insulation capacity of two external walls of different thicknesses, constructed of locally produced bricks, is studied. The basic brick units used for the investigation are small-size bricks with eight equal cavities or recesses and big-size bricks with twelve equal recesses. Their recesses configuration has been varied to perform the assessment. The insulation materials injected within brick recesses during the assessment are granulated cork and expanded polystyrene. The improvement in the thermal performance of the walls will be the result of optimization among the various factors such as brick cavity configurations, integration of insulation within brick recesses and the cavity surface emissivities. So emphasis is given to the study of the impact of these factors singly or in combination on the overall thermal resistance of walls in order to find out the best design solutions to maximize their thermal insulation capacity. Computer modeling and calculations performed, for steady state conditions, show that the increase in hollow brick cavity height contributes to the improvement of the overall thermal resistance of the order of 18–20%. The improvement could significantly increase to the range of 88.64% and 93.33%, if the bricks used are injected with the insulating material. If the cavity surface emissivities are lowered to 0.3, the improvement will be 72.73–78.33%. The results have also shown that replacing the cork by expanded polystyrene (EPS), having lower thermal conductivity, would not improve significantly the overall thermal resistance. This improvement is 9.08% for a wall of small-size bricks having configuration BS2CV and 8.34% for a wall of big-size bricks having configuration BB3CV.     

夹心保温砌体房屋振动台试验研究

黏土砖是我国北方地区广泛使用的主要建筑材料。通过水平灰缝和竖向灰缝连接成整体砖墙,承受竖向荷载和水平荷载。传统的砌体墙热工性能差,在我国最寒冷的地区其厚度可达半米,过大的厚度,一方面使建筑自重过大,抗震能力较差,另一方面也占用较大的居住面积。为解决这一矛盾,文中研究的夹心保温砌体砖墙黏土夹层砖墙是通过在钢筋网连接的两层较薄的砖墙之间插入隔热层,形成夹心保温砌体房屋。为研究其抗震性能,对一个1/2比例的4层黏土夹层砖墙结构进行不同地震烈度下的振动台试验,对其抗震性能进行试验评估,包括动力特性和响应、破坏模式、荷载和变形能力以及损伤演化等。试验结果表明：由于水平拉结钢筋网和构造柱的约束,外墙、保温层和内墙能较好地协同工作;黏土夹芯砖墙结构能满足我国《建筑抗震设计规范》(GB 50011—2010)规定的7度抗震设防的要求。     

Analysis of coupled natural convection–conduction effects on the heat transport through hollow building blocks

In the present study, the coupled convective and conduction heat transport mode in a common hollow building brick is studied. Heat transfer rate through building bricks is examined in order to asses the suitable brick insulation configuration. Three different configurations for building bricks are considered. The first is a typical brick of three identical hollow cells (air cavities), the second is obtained by filling these cells with ordinary polystyrene bars and the third is obtained by using hollow polystyrene bars. The geometry of the first and third configurations considered in this study is simply a solid closed frame surrounding square cavities filled with air. The second configuration is a solid composite slab. Solving Navier–Stocks equations assuming Boussinesq approximation, using the commercial Fluent software, showed that the cellular air motion inside blocks’ cavities contributes significantly to the heat loads. Insertion of polystyrene bars reduced the heat rate by a maximum of 36%. Using a hollow polystyrene bars reduces the heat rate by 6% only due to the air motion inside cells. In order to estimate the heat rate during a day, the air temperature and solar insolation data of a typical summer day for the city of Jeddah, Saudi Arab, are used. A quazi-steady state approach is implemented to estimate an equivalent facade surface temperature, which is then used as boundary for solving the simulation model. Such an approach showed that the effective overall daily heat rate reduction using polystyrene filled bricks to be 25%.     

Internal baffles to reduce the natural convection in the voids of hollow blocks

Hollow bricks are widely used to build facades of light weight and high thermal resistance. The air filled voids within the brick configuration elevates the block’s thermal resistance. Disturbing the natural flow patterns developed inside the voids affects the blocks overall thermal resistance. This paper presents a numerical study for a section of a masonry brick represented by a baffled squared cavity surrounded by a conductive wall of finite thickness. The baffles are attached to the top and bottom sides dividing the void into three regions. The thermal resistance of the partitioned voids depends on baffles length and location. Short baffle develops a stratified region in the central gap and generates two circulation zones near the upper left and lower right corners. Long baffles, on the other hand, splits the flow into three different convection circulation cells, a cell near each side of the cavity and a third in the central gap. Increasing the baffle height increases the thermal resistance of the partitioned cavity for all gap widths. The highest increase in thermal resistance is 53% over the non baffled voids and is achieved with long baffles when located to divide the cavity into three regions of equal widths.     

Thermal response of brick wall filled with phase change materials (PCM) under fluctuating outdoor temperatures

Based on the enthalpy-porosity technique, a model of thermal conduction accompanied with solidification and melting processes is developed and numerically analyzed to investigate the thermal response of the brick wall filled with phase change materials (PCM). The thermal response, which is represented by indoor wall surface temperature response, of brick wall filled with PCM is evaluated and compared with that of solid brick wall. The effects of PCM filling and its filling amount on thermal response of brick wall are investigated and discussed. It is indicated that, compared to the common solid brick wall, the thermal storage of brick wall filled with PCM is elevated by the alternate process of melting and solidification under fluctuating outdoor temperatures. The use of PCM in the brick walls is beneficial for the thermal insulation, temperature hysteresis and thermal comfort for occupancy. In addition, with the increasing filling amount of PCM, the fluctuation of indoor wall surface temperature is significantly smoothed. Correspondingly, the hysteresis in response to the outdoor temperature fluctuation is enhanced. Moreover, the present model is verified by experimental data available in the literature.     

Transfer function coefficients for time varying coupled heat transfers in vertically heated hollow concrete bricks

This paper describes a two step numerical procedure to determinate empirical transfer function coefficients (TFCs) for vertically heated hollow concrete bricks. For such systems TFCs cannot be generated using the analytical techniques available in the literature such as the z-transfer function method or the space state representation method because of the nonlinear local character of the heat transfer by natural convection and radiation in the air cells of the hollow concrete bricks. The first step of the procedure consists in predicting coupled heat transfer by conduction, convection, and radiation in realistic time varying conditions using a detailed numerical simulation. In the second step, the results of the simulation (the time-varying heat fluxes at the hollow brick surfaces) are used to obtain empirical transfer function coefficients using an identification technique. Transfer function coefficients are generated for three different types of hollow concrete bricks mostly used in practice. It is shown that the empirical transfer function coefficients permit fast and accurate prediction of heat transfer for thermal excitations that differ markedly from those used to generate these coefficients without solving the complex system of equations governing the coupled heat transfer mechanisms.     

烧结砖石灰爆裂检验和消除方法探讨

我国年产墙体材料8500亿块,其中烧结墙体材料占80％,一直在墙体材料中居主导地位。在烧结墙体材料中页岩烧结砖发展很快,但由于页岩分布广,形成的地质条件不同,矿物组成和化学组成不同,因而不同的页岩对制品有着不同的影响,砖会产生石灰爆裂。有许多页岩砖厂因石灰爆裂造成了巨大的经济损失。石灰爆裂对砖砌体影响较大,轻者影响外观,重者将使砖砌体强度降低直至破坏,砖中石灰质颗粒越大,含量越多,则对砖砌体强度影响越大。在检验过程中要正确识别爆裂点对样品直接影响的评定。因此,烧结砖石灰爆裂检验研究是消除石灰爆裂．提高烧结砖的质量的一种重要手段。     

Untersuchung der thermisch‐hygrischen Eigenschaften von Ziegeln mit Hohlraumfüllung aus Recyclingmaterial

Investigation on the thermal‐hygral behaniour of bricks with canity filling by recycling meterials. In the investigation project was examined whether bricks with simple cavity structure have a higher heat resistance by use of a heat insulation material filling in the cavities. The insulation material is a recycled product made of polystyrene and wood covered and bonded with cement. The influence of the configuration and thickness of the perforated bricks with vertical perforations and the geometry of the cavities of the brick on the thermal moisture states was evaluated. For investigation of the thermal resistance and the heat transmission coefficients were used the simulation program THERM, that considered the heat transportation through conduction in the brick fragments and the transport mechanisms conduction, convection and radiation in the airfilled cavities. The software package WUFI 2D was employed for the investigation of moisture transfer in the bricks. The investigations showed that the composite brick insulation stone has a thermal resistance twice as high as the initial brick. The moisture states can be partially in the brick more than 80 % humidity. This load is estimated as uncritical because the wooden particles are covered with cement slime.     

Structural behaviour of ferrocement–brick composite floor slab panel

This study introduces a semi-fabricated system for the construction of floor slab. The slab panel consists of two layers joined together using truss type shear connectors. The first layer is a precast ferrocement layer which acts initially as a formwork, while the second layer consists of bricks and mortar. Continuous truss shear connectors are used to connect the two layers. The paper experimentally investigates the structural response of ferrocement–brick composite panel under flexural load. Four full scale specimens were cast and tested under two-line loads. The study highlights the effect of shear connectors and brick layout on the overall structural response of the slab. The results in terms of load–deflection, crack pattern, strain distribution and failure loads indicate that the response of the composite slab to the flexural loading is satisfactory and can be used as a floor slab in construction sector.     

Experimental unsteady characterization of heat transfer in a multi-layer wall including air layers—Application to vertically perforated bricks

Vertically perforated bricks were developed with a view to building environmentally friendly houses since they make insulating materials unnecessary. By an experimental approach, this study proposes to analyze the propagation of a temperature signal in this kind of brick, in order to characterize the thermal inertia of the brick. The steady-state knowledge is completed by the determination of properties like influence functions or characteristic depth concerned by a surface temperature variation. This allows to validate a simple unsteady surface model to be validated for this heterogeneous material which is classified as an insulating structural material. Furthermore, this study supplements the steady-state knowledge in local heat transfer through the air layers of the brick. Indeed, it is verified that convection heat transfer can be ignored in an unsteady heat transfer in this kind of brick, even in extreme conditions such as a sudden temperature fall.     

Strength and thermal conductivity in lightweight building materials

Pumice can be used in bricks and concrete to produce lightweight building materials with high porosity, high thermal insulation and resistance to earthquake motion. The paper presents ongoing research to design a structural lightweight concrete and brick using Nevşehir pumice. The testing of four different brick types is reported. The density, thermal conductivity, compressive and tensile strengths and Young’s elastic modulus indicated that these lightweight materials had significant advantages as a construction material in earthquake-prone areas.      

填充墙对框架结构抗侧刚度的影响分析

建立12个带填充墙的10层框架结构有限元模型,研究不同地震波作用下填充墙的材料、空间布置、各层墙数量等因素对结构抗侧刚度的影响。分析表明:填充墙分别采用标准砖、空心砖、加气混凝土砌块时,"薄弱层"刚度突变的影响逐渐减小,但不宜忽略不计;某层填充墙截面面积与其相邻上层填充墙截面面积之比γw≤45%时,应将该层视为薄弱层,实际设计过程中建议γw最小取60%;在数值分析基础上,提出了考虑填充墙影响的框架结构层间抗侧刚度计算模型。     

再生碎砖混凝土墙梁抗弯性能分析

以废弃碎砖块为再生骨料制成的再生碎砖混凝土作为墙体材料,制作了一种新型墙梁,并与普通砖墙梁进行了试验对比分析,结果表明:再生碎砖混凝土墙梁的承载力大于普通砖墙梁的承载力,且延性更好。     

Numerical simulation by the FVM of coupled heat transfers by conduction, natural convection and radiation in honeycomb’s hollow bricks

This paper presents a detailed numerical study, in steady state regime, of the interaction between two dimensional heat transfers by conduction, natural convection and radiation in double hollow bricks formed by two honeycomb walls separated by an air layer. The air motion in all cavities of the system is laminar. The left and right vertical sides of the hollow bricks are considered isothermal and maintained at different constant temperatures. The top and bottom horizontal sides are assumed to be adiabatic. The governing equations are solved using the finite volume method (FVM) and the SIMPLE algorithm. The impact of the thickness of the air layer on the global heat flux through the structure is discussed. The simulation results show that the variation of the overall heat flux through each hollow brick as a function of the temperature difference ΔT between the vertical sides of the system is almost linear for the different types of double hollow bricks considered. This linear thermal behaviour allowed the generation of appropriate overall heat exchange coefficients that permit fast and accurate prediction of heat transfers through the hollow bricks without solving the complex system of equations governing the coupled heat transfers. Comparison of the performance of different types of double hollow bricks is made.     

Experimental and numerical investigation of a hollow brick filled with perlite insulation

The present study is focused on the investigation of the effective thermal properties of a modern vertically perforated masonry unit filled with perlite insulation. Based on measurements and numerical calculations, the thermal performance of the new hollow brick was determined. The authors suggest to use the following parameters for this building material: equivalent heat capacity equal to 855.1 J/kg K, equivalent heat conductivity equal to 0.09 W/mK and equivalent density equal to 653.15 kg/m³. The dependence of the equivalent thermal resistance of the whole wall made of this brick and mortar, is shown for different mortar joint thicknesses. All results, presented in this paper, can be used in energy balance calculations for buildings made of masonry unit.     

再生混凝土多孔砖砌体抗压强度试验研究

通过24个用再生混凝土多孔砖砌筑的试件的抗压试验，讨论了再生混凝土多孔砖砌体的裂缝发展特点和变形规律：根据抗压试验结果，建立了抗压强度计算公式和再生混凝土多孔砖砌体的抗压强度设计值的建议取值。结果表明，再生混凝土多孔砖是脆性材料，在正常的使用状态下，不会出现裂缝，可以成为替代黏土砖的一种新型墙体材料。     

再生骨料混凝土多孔砖砌体抗压强度试验研究

通过24个用再生混凝土多孔砖砌筑的试件的抗压试验,讨论了再生混凝土多孔砖砌体的裂缝发展特点和变形规律;根据抗压试验结果,建立了抗压强度计算公式和再生混凝土多孔砖砌体的抗压强度设计值的建议取值。结果表明,再生混凝土多孔砖是脆性材料,在正常的使用状态下,不会出现裂缝,可以成为替代黏土砖的一种新型墙体材料。     

The behaviour of masonry walls subjected to fire: Modelling and parametrical studies in the case of hollow burnt-clay bricks

A thermo-mechanical model is adopted in order to investigate the fire behaviour of clay masonry walls. In this analysis, conductive, convective and radiative thermal transfers are considered together with local energy consumption due to phase changes. These latter are essentially initiated by both the vaporisation of adsorbed water and the chemical transformation of clay under rising temperatures. Therefore, experimental tests at both the material scale and the brick scale are performed in order to identify the parameters that characterise the thermo-hygral behaviour of clay. For this purpose, numerical simulations are carried out on the experimentally tested hollow bricks in order to determine by back analysis these material parameters. The thermal model being validated, the thermo-mechanical behaviour of a masonry wall subjected to fire, is thereafter investigated by adopting a full three-dimensional finite-element analysis. Numerical simulations results are compared to the experimentally measured ones in terms of both temperature and out-of plane displacement fields. In this analysis, it is shown that a non-linear elastic behaviour for bricks and mortar with temperature-dependent mechanical parameters is sufficient to retrieve the overall behaviour of thin masonry walls. Finally, a parametric study provides the influence of each material parameter on the fire behaviour of the partition walls.     

Reuse of waste bricks in the production line

The main objective of this research was to investigate the addition of waste-brick material in brick production. The effects of recycling of waste brick material on the durability and mechanical properties of the bricks were analysed. Fired waste bricks cause considerable harm to the environment. During production, especially in the firing, transportation and construction procedures, large amounts of bricks are broken and have to be dumped in landfills or used as a filling material. For this purpose, the chemical and mineralogical structures of waste bricks from the orum region in West-Anatolia, Turkey, were investigated. After pulverizing, the samples were divided into two categories: A passing through a 4.75 mm sieve (coarse) and B passing a 600 μm sieve (fine). In order to obtain comparable test results, ratios of the waste (0, 10, 20 and 30% by mass) were added to the raw-brick clay. Standard test methods were used to determine the mechanical properties of the bricks at different firing temperatures. The results show that at a mass of 30% fine-waste material additive, fired at 900°C, the test sample has an adequate strength. The reuse of this material in the industry would contribute to the protection of farmland and the environment.