Assessment of cold stress in terms of required clothing insulation—IREQ

A heat exchange model has been developed, by which the thermal stress associated with work in cold environments can be evaluated. Based on measurements of air temperature, mean radiant temperature, humidity and air velocity and measurements or estimates of activity level (energy metabolism) the model calculates a clothing insulation (IREQ) required to maintain body heat balance. IREQ may be regarded as an index of cold stress, and the value for IREQ specifies the insulation to be provided by clothing under given conditions, in addition to the insulation of the boundary air layer. IREQ, hence, may serve as a guideline for selection of appropriate clothing in cold environments. Basic insulation values of clothing (I_cI) measured with thermal manikins can be used for this purpose, but need to be corrected to account for the effect of body motion, posture, wind penetration and moisture absorption before a comparison is made with IREQ.     

Finite element stress analysis of a reinforced high-strength concrete column in severe fires

The objective of this study is to quantify the development of thermal stress states that account for the occurrence of moisture-induced explosive spalling of reinforced high-strength concrete structures under rapid heating conditions. Obtained from finite difference models of simulating coupled heat and mass transport phenomena in heated reinforced concrete elements, transient temperature profiles are used as prescribed boundary conditions for subsequent finite element thermo-elastic stress analysis. A computational methodology using the theory of mixtures (volume averaging) is presented to compute thermally induced effective stresses that are potentially associated with thermal spalling of high-strength concrete.     

Determining temperature ratings for children's cold weather clothing

This study examined the physical and physiological differences between children and adults that affect body heat generation and losses and then developed a heat loss model for determining the temperature ratings of cold weather clothing designed for use by children of various ages. The thermal insulation values of selected jackets were measured using a heated manikin dressed in two base ensembles, and the temperature ratings were calculated using the model. The results indicated that the type of garments used in the base ensemble had a major effect on jacket ensemble insulation and the predicted comfort temperature. For a given level of insulation, the temperature rating decreased as the wearer's age and activity level increased. This is probably because children have a higher surface area per unit mass ratio than adults, and they lose heat faster. However, this effect is partially offset by their higher metabolic rates.     

Simulation analysis of thermal stress of RCC dams using 3-D finite element relocating mesh method

The 3-D finite element relocating mesh method is developed for simulation analysis of temperature and thermal stress distribution in a roller compacted concrete dam during the construction period. According to the relation between specific properties and age of concrete, some meshes are merged into a larger mesh or a few larger meshes when the age of the concrete is appropriate. Using this method, the total number of elements and nodes were remarkably reduced when the dam height was increased. When the change in elastic modulus, creeps and hydration heat is within the limits permitted by design criteria, the relocating of mesh will start. Using this method, a 3 D simulation analysis of thermal stress in a roller compacted concrete (RCC) high dam can be realized by microcomputer and appeared at the construction site. On the basis of real factors during the construction period, an engineer can predict the distribution of temperature and thermal stress in the RCC dam. Therefore, engineers can take appropriate measures to control the concrete temperature to reduce the thermal stress and avoid crack development within the dam.     

Wearer related performance standards for conditioned clothing

Abstract

Estimates, based on American experience of work in the heat, indicate that in the UK, half a million workers or more may be working in thermally uncomfortable and stressfully hot environments. In addition, many will be experiencing cold working conditions and associated discomfort. The role of protective clothing as one of the factors involved in imposing thermal stress is emphasized.

One method of thermal stress control is to provide conditioned garments which warm or cool the wearer as required. The use of ‘air supplied’ garments for cooling is specifically dealt with and the methods of defining their performance reviewed. The application of the concept of ‘per cent wetted skin surface area’ is discussed as one method of defining the performance of air ventilated garments if thermal comfort cannot be achieved. The use of low pressure air for ventilating garments is proposed. The performance of such a system employing a small battery powered blower is defined in terms of the wearers work rate and supply air temperature and volume using the wetted surface area concept. The necessary steps to be taken by manufacturers if they are to develop the market for such conditioned garments are outlined.     

发电列车车下燃油箱保温性能CFD仿真

基于CFD理论,应用STAR-CCM+仿真某发电列车车下燃油箱在给定高寒工况下的保温性能.在考虑列车运行时车外流场影响的基础上,耦合分析箱体、保温材料和燃油等的温度分布特性,找出燃油可能发生结蜡的区域.给出相关分析结论和改进建议,为保证燃油箱拥有稳定的工作性能提供可靠的设计参考.     

Optimal structure for heat and cold protection under transient heat conduction

A suitable combination of materials for sheltering a system from a sudden change of environmental temperature has been theoretically studied. The protective composite wall consists of two materials. An insulating material is placed on the outer surface, while, for the inner surface, materials that have good heat storage properties but negligible heat transfer resistance are chosen. The results show that by replacing some of the insulation material with a heat storage material, the temperature of the protected system can be maintained at a considerably lower level. Although the optimal thickness ratio X depends on the Biot number, Fourier number, and on the heat capacity ratio K _C, for a large number of thermal protection cases, the approximation X = 0.45 yields practically the minimum progress of the transient. If the Biot number is sufficiently small, it is better to replace all of the insulation material with a good heat storage material.     

The effect of added fullness and ventilation holes in T-shirt design on thermal comfort

This paper reports on an experimental investigation on the effect of added fullness and ventilation holes in T-shirt design on clothing comfort measured in terms of thermal insulation and moisture vapour resistance. Four T-shirts in four different sizes (S, M, L, XL) were cut under the traditional sizing method while another (F-1) was cut with specially added fullness to create a 'flared' drape. A thermal manikin 'Walter' was used to measure the thermal insulation and moisture vapour resistance of the T-shirts in a chamber with controlled temperature, relative humidity and air velocity. The tests included four conditions: manikin standing still in the no-wind and windy conditions and walking in the no-wind and windy condition. It was found that adding fullness in the T-shirt design (F-1) to create the 'flared' drape can significantly reduce the T-shirt's thermal insulation and moisture vapour resistance under walking or windy conditions. Heat and moisture transmission through the T-shirt can be further enhanced by creating small apertures on the front and back of the T-shirt with specially added fullness. STATEMENT OF RELEVANCE: The thermal comfort of the human body is one of the key issues in the study of ergonomics. When doing exercise, a human body will generate heat, which will eventually result in sweating. If heat and moisture are not released effectively from the body, heat stress may occur and the person's performance will be negatively affected. Therefore, contemporary athletic T-shirts are designed to improve the heat and moisture transfer from the wearer. Through special cutting, such athletic T-shirts can be designed to improve the ventilation of the wearer.     

Interactions of the surface heat and moisture transfer from the human body under varying climatic conditions and walking speeds

The surface heat and moisture transfer from the human body are normally characterized by the thermal insulation and moisture vapor resistance, which are important parameters in environmental engineering. In the past, due to the limitation of measurement technology, simultaneous measurement of these two parameters was not possible and hence there is a lack of clear understanding on the interaction of surface heat and moisture transfer. In this paper, through the experimental measurements on a newly developed sweating/non-sweating fabric manikin (named WALTER) under varying climatic conditions and "walking" speeds, we show that the surface thermal insulation is little affected by moisture transfer. The surface moisture vapor resistances measured under isothermal conditions tend to be greater than those measured under non-isothermal conditions, especially when the wind velocity is less than 2.0m/s. The Lewis Relation holds under non-isothermal conditions, but should be corrected under isothermal condition when the wind velocity is small.     

Isothermal phase change model for freezing and thawing soils I: Development

A model of phase change in freezing and thawing soils is developed for cold regions engineering problems which require two-dimensional analysis of the thermal regime of soils. Such problems include complex boundary conditions such as atmosphere-ground surface thermal interaction and snowpack-insulation. Other concerns include complex soil conditions such as the presence of a peaty muskeg or tundra-like soil which may provide thermal insulation for underlying ice-rich mineral soil. Although several models have been developed to predict temperatures in freezing and thawing soils, oftentimes the key question is simply whether or not the soil is frozen since soil structural properties are significantly influenced by the soil-water state of phase. In this paper, a simple two-dimensional model is developed for use in cold regions engineering studies.     

Development of finite element computer code for thermal analysis of roller compacted concrete dams

Thermal analysis of roller compacted concrete (RCC) dams plays an important role in their design and construction. This paper deals with the development of a finite element based computer code for the determination of temperatures within the dam body. The finite element code is then applied to the real full-scale problem to determine the impact of the placement schedule on the thermal response of roller compacted concrete dam. Based on the results obtained, it could be concluded that for a given roller compacted concrete dam, changing the placing schedule can optimize the locations of maximum temperature zones.     

Pumping effects on thermal insulation of clothing worn by human subjects

This study was undertaken in order to analyse the importance of the pumping effect on clothing's thermal insulation. To enhance differences in heat exchanges due to the pumping effect, two sets of condition were fixed, minimizing either the convective or the radiative heat transfers. The results showed that: (i) the clothing insulation determined on a manikin, even if he is moving, is larger than the resultant clothing insulation for living subjects; (ii) the insulation is not the same for radiant heat or cold as for convective heat or cold;(iii) the pumping effect can increase or decrease the resultant clothing insulation; (iv) the clothing insulation is smaller in warmer conditions thanin cooler ones; (v) it becomes necessary to make a definite distinction between several kinds of clothing insulation; intrinsic or basic insulation against radiation and convection; effective insulation against radiation and convection taking into account only the heat flowing through the clothing fabric; resultant insulation taking into account the magnitude of the pumping effect when clothing is worn by living subjects     

Comparison between required clothing insulation and that actually worn by workers exposed to artificial cold

Required Clothing Insulation (IREQ) is a new thermal index submitted to the International Organisation for Standardisation (ISO) for discussion. It is designed to prevent general body cooling and is based on an analysis of heat exchanges. The thermal clothing insulation actually worn (lcl) is estimated using a new method, also submitted to ISO.

IREQ of 54 workers exposed to artificial cold (air temperature between −30° C and +10° C) was compared with lcl actually worn by these workers. The results of the present study show that, on average, the workers choose accurately lcl they need if their IREQ is below and up to 1·5 clo. Moreover, these workers prefer to wear garments which provide them with thermal comfort. If IREQ of workers is higher than 1·5–2 clo (i e, workers exposed to −20° C), it is difficult for them to increase their thermal insulation with additional garments. Although their lcl is not sufficient, there is no risk of gradual body cooling because of their continuous time exposure (CTE) which is shorter than the calculated Duration Limited Exposure (DLE). On the other hand, Wind Chill Index (WCI), which is proposed to prevent local cooling, is better adapted to prevent cold injuries than physiological thermal strain; for example, impairment of manual dexterity cannot be prevented with this index.     

Comparative analysis of urban reflectance and surface temperature

Urban environmental conditions are strongly dependent on the biophysical properties and radiant thermal field of the land cover elements in the urban mosaic. Observations of urban reflectance and surface temperature provide valuable constraints on the physical properties that are determinants of mass and energy fluxes in the urban environment. Consistencies in the covariation of surface temperature with reflectance properties can be parameterized to represent characteristics of the surface energy flux associated with different land covers and physical conditions. Linear mixture models can accurately represent Landsat ETM+ reflectances as fractions of generic spectral endmembers that correspond to land surface materials with distinct physical properties. Modeling heterogeneous land cover as mixtures of rock and/or soil Substrate, Vegetation and non-reflective Dark surface (SVD) generic endmembers makes it possible to quantify the dependence of aggregate surface temperature on the relative abundance of each physical component of the land cover, thereby distinguishing the effects of vegetation abundance, soil exposure, albedo and shadowing. Comparing these covariations in a wide variety of urban settings and physical environments provides a more robust indication of the global variability in these parameter spaces than could be inferred from a single study area. A comparative analysis of 24 urban areas and their non-urban peripheries illustrates the variability in the urban thermal fields and its dependence on biophysical land surface components. Contrary to expectation, moderate resolution intra-urban variations in surface temperature are generally as large as regional surface heat island signatures in these urban areas. Many of the non-temperate urban areas did not have surface heat island signatures at all. However, the multivariate distributions of surface temperature and generic endmember fractions reveal consistent patterns of thermal fraction covariation resulting from land cover characteristics. The Thermal-Vegetation (TV) fraction space illustrates the considerable variability in the well-known inverse correlation between surface temperature and vegetation fraction at moderate (< 100 m) spatial resolutions. The Thermal-Substrate (TS) fraction space reveals energetic thresholds where competing effects of albedo, illumination and soil moisture determine the covariation of maximum and minimum temperature with illuminated substrate fraction. The dark surface endmember fraction represents a fundamental ambiguity in the radiance signal because it can correspond to either absorptive (e.g. low albedo asphalt), transmissive (e.g. deep clear water) or shadowed (e.g. tree canopy shadow) surfaces. However, in areas where dark surface composition can be inferred from spatial context, the different responses of these surfaces may still allow them to be distinguished in the thermal fraction space.     

单搭接接头温度场与热应力分布的研究

为了对胶接接头承受热载荷时的温度场和热应力分布进行数值模拟,利用有限元法对单搭接接头的被粘物外表而承受不同温度、速度气流时的温度分布情况进行了分析.在考虑接头变形为几何非线性的前提下,研究了约束方式、胶层厚度及搭接长度对接头热应力分布的不同影响.结果表明,峰值热应力出现在搭接区边缘;当约束方式使胶层发生较大转动时,胶层处于高应力水平;随胶层厚度的增加,热应力降低且在胶层中分布更趋于均匀;搭接长度对热应力的影响因接头所受约束方式的不同,呈现不同的规律.     

某柴油机缸盖强度计算

以某4缸轿车用柴油机铝合金缸盖为研究对象,用某CFD软件计算得到水套表面的温度和对流换热系数,用Abaqus计算缸盖稳态温度场、装配载荷下冷机的应力分布、装配状态下的热机应力分布和各缸爆发时刻缸盖的应力分布,结果表明缸盖强度低于材料屈服极限.基于应力结果计算缸盖的高周疲劳安全因数和低周循环次数,结果表明缸盖疲劳安全因数满足使用要求.     

Thermal effects of steel toe caps in footgear

This study investigated cold weather safety footwear and the possible thermal effects of steel toe caps in footwear. Two models of boots were used. Both models were manufactured in two variants – with and without steel toe cap. The boot insulation was measured with an artificial, heated foot (AHF). One model was used in experiment with subjects (n=6). Cold exposure consisted of sitting for 60 min at −10°C. There were no differences between insulation levels of boots with and without steel cap for one boot model, but the differences were statistically significant for the second model showing slightly higher insulation values for the boot without steel cap. No significant differences due to insulation dissimilarities could be found from the measurements on subjects. Statistically significant differences were found for both models regarding the rate of change of heat loss from AHF when its location was changed from warm to cold and back to warm. The rise and decrease of heat loss from AHF depended on the rate of temperature change of the boots. The results showed that a faster change in heat loss from AHF occurred for boots without steel toe caps. Data from subjects seemed to confirm this by a somewhat faster, though not significant, rise in toe skin temperatures after cold exposure in boots without steel toe caps. The effect may be attributed to the higher mass and heat contents of the boots with steel toe cap.

Relevance to industry

Many jobs need additional protection of the toes or shins. The steel toe cap and its alleged cooling effect have been a frequent subject of complaints. This study discusses reasons that could explain the complaints, and presents a standard method for evaluating thermal properties of footwear.     

A method for dynamic measurement of the resistance to dry heat exchange by footwear

Five different types of cold protective footwear have been tested with regard to their resistance to dry heat loss (i.e. the insulation) with a new electrically heated foot model. The model is able to simulate ‘walking’ movements in order to provide a more realistic simulation of wear conditions. Thermal insulation of shoes with and without a steel toe cap was the same. The insulating properties during simulated walking movements were 10–25% lower compared with static conditions. For two of the shoe models a significantly lower insulation value for the sole area was obtained when adding a weight of 30 kg. A significant difference could also be found between the insulation values of two different sizes of one of the models. Measurements with the standard method (EN 344) correlated well with the local insulation value of the sole part of the thermal foot. Correlation with the insulation value for the whole shoe was much less, variation was bigger and ranking in terms of cold protection differed between methods. The electrically heated foot model appears to provide a reproducible, accurate and more realistic method for measuring the insulation properties of shoes than EN 344.     

Evaporative resistance and sustainable work under heat stress conditions for two cloth anticontamination ensembles

When a work scenario in protective clothing is a nominal two hours of work followed by a short break, the level of heat stress must be limited to conditions of thermal equilibrium. By comparing changes in maximum sustainable work rate in a fixed environment, differences due to different protective clothing ensembles can be determined. To illustrate this principle, two protective clothing ensembles were examined. The Basic Ensemble was a cotton blend coverall over gym shorts with hard hat, gloves and full face mask respirator. The Enhanced Ensemble added a light weight, surgical scrub suit under the coveralls, plus a hood worn under the hard hat. Five young, acclimated males were the test subjects. Environmental conditions were fixed at T_db=32°C and T_pwb=26°C. After a physiological steady state was established at a low rate of work, treadmill speed was increased by 0.04 m/s every 5 min. The trial continued until thermal equilibrium was clearly lost. A critical treadmill speed was noted at the point thermal equilibrium was lost for each ensemble and subject. The drop in treadmill speed from the basic to enhanced ensemble was 11%. Based on measured values of average skin temperature and metabolic rate at the critical work rate and estimated values of clothing insulation, the average evaporative resistances for the basic and enhanced ensembles were 0.018 and 0.026 kPa m²/W, respectively.

Relevance to industry

Protective clothing decisions are based on the need to reduce the risk of skin contact with chemical or physical hazards. Sometimes over-protection of the skin results in a hazard secondary to the skin, such as heat stress. With or without over-protection, protective clothing decisions may affect the level of heat stress and result in lower rates of sustainable work. This paper illustrates the affects of a relatively small change in protective clothing requirements on the ability to work in the heat.     

Effects of Landscape Pattern on Annual Variation of Thermal Environment in Hangzhou

Taking the Hangzhou city as an example,this paper retrieves the urban land surface temperature (LST) using 4 Landsat ETM+/OLI_TIRS images and investigates the effects of landscape pattern on the urban thermal environment change.The hot spot analysis was used to identify both the urban heat island and cold island.Landscape pattern indices were adopted to analyze the relationship between the change of the thermal environment and the landscape pattern.Analysis results show that：(1) The proportions of area in urban heat island and cold island in Hangzhou increase first and then decrease with the alternating four seasons;The urban heat island of Hangzhou is the most significant in summer,and the urban cold island effect is more dominant in autumn;(2) Throughout the year,all kinds of landscape has the highest average land surface temperature in summer and the lowest in winter;As for a variety of landscapes,the construction land has the highest average land surface temperature,while,the water body and forest have the relatively low average land surface temperature;(3)On the landscape level,the selected landscape pattern indices are significantly correlated with average land surface temperature in four seasons,the strength of correlation fluctuates with alternating four seasons and the enlargement of analysis window;On the class level,landscape pattern indices of construction land,water body and forest are significantly and highly correlated with average land surface temperature in different seasons.The research in our paper could help to lay out construction land rationally and execute planning and design on urban green space and waters to effectively alleviate the urban heat island effect of Hangzhou.