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Factors influencing thermal resistance of a down sleeping bag
Abstract
Purpose
To have a better understanding of the heat transfer mechanisms in a sleeping bag and to investigate the factors influencing thermal resistance of a down sleeping bag.
Design/methodology/approach
The mechanism of heat transfer in a sleeping bag was discussed in this paper. The thermal resistances of 24 samples were investigated. Besides, the relation between fill weight and thermal resistance, and that between the air permeability of fabric and thermal resistance, as well as that between down filling rate and thermal resistance were analyzed.
Findings
The results showed that thermal resistances of samples varied from 0.35 to 0.8 m ² K/W. The fill weight was the most important factor of thermal resistance of sleeping bag and the relation between fill weight and thermal resistance matched well with cubic function. A multiple regression formula was proposed, which with thermal resistance as a dependent variable and with air permeability of fabric, down filling rate, fill weight as independent variables.
Originality/value
Thermal properties of a sleeping bag were analyzed through simplified basic unit under simplified environment conditions, which was necessary for building the first stage of systematic study of thermal performance of a sleeping bag.
... There are three ways in which heat can be exchanged between the body and the environment: conduction (C), radiation (R) and convection (K). 18 The heat transfer process of clothes in water is a mixture of these three ways: heat passed by the fibers, heat radiated between the fibers and the water and heat transferred through the convection of the water. 19 Forced convection can be ignored because this study investigated thermal resistance under hydrostatic conditions. ...
... When clothes become partially or completely wet, thermal insulation is an important physical characteristic to quantify their thermal comfort. 18 In the case of a victim falling into water, heat transfer occurs primarily in the part of the body in contact with the surface of the clothing. Since the clothes isolate direct heat transfer between the human body and the surrounding environment, the clothes act as an intermediate medium to prevent direct heat transfer from the surface of the human skin. ...
Life jackets are essential life-saving devices, and also play an important role in the thermal protection of drowning victims in cold water. To better understand the thermal performance of the combinations of suits and life jackets in water, a thermal manikin named “Walter” in a water tank was used to simulate the environment surrounding the drowning person. Three sets of suits and three sets of life jackets form a total of 12 test combinations to simulate the clothes worn by drowning people. The thermal resistance of 12 combinations in water were measured according to ISO 15831 and heat transfer coefficients for the chest, back, upper arm, arm, thigh and leg of the 12 test combinations were calculated and compared. Results showed that the combinations of the clothes and life jacket efficiently lowered conduction and convective heat transfer coefficients in the water. The total thermal resistance of the 12 test combinations ranged from 0.011 to 0.054°C · m ² /W. The post-hoc analysis revealed that the conductive thermal resistances of the clothing combinations with life jackets were all elevated compared to those of the clothing combinations without life jackets ( p < 0.001), showing that life jackets provide better thermal insulation. The linear regression indicated that the conductive thermal resistance of the test combination had a considerable impact on the convective heat transfer coefficient. This study helps to establish the systematic study of the thermal protection performance of life jackets.
... [9][10][11][12] An et al., focusing on nonwoven assemblies in sleeping bags, found that lower fill weight creates larger air channels, promoting heat loss through convection. 13 However, their controlled lab setting does not account for real-world compression of the material nor the wind velocity, which can significantly impact air gaps and thermal performance. Moving on to wind speed's influence, Zemzem et al. conducted an experimental study on three synthetic textile assemblies. ...
Numerous workers across various industries, from construction and transportation to agriculture and emergency response, face harsh working environments characterized by cold temperatures and intense winds. These conditions present serious health and safety risks, which may result in hypothermia. Although established standards, such as ISO 11092, are crucial in measuring the thermal resistance of textile assemblies, an essential factor is often overlooked: the influence of wind speed and direction. In this context, this article aimed to address this gap in current knowledge by investigating the effects of wind on the thermal resistance of nonwoven textile assemblies, to develop a more effective protective clothing system for harsh environments. This study investigated the effect of horizontal and vertical wind speeds on the thermal resistance of a technical bio-based nonwoven assembly, composed of milkweed, kapok and polylactic acid, aiming to understand how forced convection influences heat transfer in real-world conditions. Three samples (A, B, and C) were tested under wind speeds ranging from 0 to 4 m·s⁻¹, and their thermal resistance was measured in both horizontal and vertical wind directions. Results showed that increasing wind speed consistently decreased thermal resistance for all samples. Vertical wind demonstrated a more pronounced effect, with reductions in thermal resistance reaching 81% for Sample C compared to 51% under horizontal wind. Comparison of experimental and theoretically predicted thermal resistance values using the models presented in the ISO 9920 standard, indicated significant discrepancies.
... Dai et al. 19 studied the influence of quilting form and number on the thermal insulation performance of down products. Yuying et al. 20 reported that the filling amount is the most important factor affecting thermal resistance. Huiying and Ranju 21 stated that the thermal performance of down will gradually increase up to a constant value by increasing the filling density, but the thermal performance will be affected if the space partitioning is too large or too small. ...
This work investigates the thermal insulation performances of clothing based on down and a quilting method. The effect of several parameters was studied, including the amount of down, quilting number, and their geometry. An experimental study was combined with a geometrical model to confirm that a regular hexagonal geometry is the best to maximize the heat insulation properties. For the overall tiling, the best thermal resistance was obtained by using 8.67 g of down, and the thermal conductivity is the lowest when the filling was 5.14 g down. The heat resistance was also found to increase by decreasing the quilting number, but the effect is less significant as the number increases. Also, a lower amount of down in each quilting place resulted in higher heat loss. So, improving the filling down quality helped to increase heat retention. The correct space division and filling quality lead to improved warmth retention of cold protection down products.
Aerogel fibers utilized in thermal protective apparel exhibit exceptional heat insulation capabilities; however, concerns arise regarding potential degradation due to the detachment of aerogel particles during repeated washing. Accurate prediction of aerogel fiber thermal resistance is critical for assessing hydrothermal aging in aerogel textiles, yet the precision of such predictions is significantly hindered by limited sample data and numerous uncertainties constrained by testing time and expenses. The present study endeavors to ascertain the optimal parameters dictating aerogel fabric thermal resistance post-washing and establish a prediction model based on these variables using small-sample data. Four aerogel fabric candidates were selected and subjected to multiple washing cycles (0, 1, 5, 10, 15, and 20 cycles). Gray relational analysis (GRA) was initially employed to prioritize the primary thermal resistance parameters, thereby identifying the interrelations among various factors and circumventing the unreasonable equal treatment of samples in conventional gray predictions. Subsequently, a discrete gray linear regression (DGLR) algorithm was proposed and validated to estimate thermal resistance using input from four principal fabric parameters: the fabric weight, thickness, air permeability, and surface temperature distribution coefficient. The findings revealed that the GRA-DGLR model achieved relatively high accuracy, closely aligning with the experimental results. Following repeated washing, aerogel fabric thermal resistance diminished, with the air permeability, weight, thickness, and surface temperature distribution coefficient ranked in descending order of significance. This investigation highlights the considerable impact of repeated washing on aerogel fabric thermal resistance and the efficacy of the GRA-DGLR model in estimating this parameter.
We examined variation in five microscopic plumulaceous (downy) feather characters of eighteen species of dabbling (Anatini) and diving (Aythyini, Mergini) ducks to quantify the differences between these tribes, and to explain how the plumulaceous feather ultrastructure in ducks may be influenced by different ecological requirements. Over 75% of the variation in feather characters among these ducks was explained by the first two components of a principal components analysis (PCA). Component 1 explained 51% of the variation and was positively correlated with the characters that quantified the number of barbules with expanded nodes and the number of expanded nodes on barbules. The microscopic feather characters of dabbling ducks (Anatini) have triangular-shaped, expanded nodes on most proximal barbules, whereas diving ducks (Aythyini and Mergini) lack expanded nodes on some barbules. Anatini also have a greater density of expanded nodes per barbule, wider nodes, shorter distance between expanded nodes, and longer barbule length. Further analysis of node density across all taxa showed that as dive depths increase, the number of expanded nodes per barbule decreases, and in the deepest divers many of the barbules completely lack expanded nodes. The significantly greater density of expanded nodes in dabbling ducks suggests that the downy nodes may function to trap more air. Diving species have fewer expanded nodes, less buoyant plumage, and are more efficient at foraging in deeper water than dabbling ducks.
To investigate the effect of fabric architectures and weaving parameters on thermal conductivities of three-dimensional woven composites, the 2.5D angle-interlock woven composites, 2.5D angle-interlock (with warp reinforcement) woven composites, and 3D orthogonal woven composites were prepared. The thermal conductivities of these woven composites were measured by using transient hot-wire method in this study. It was indicated that the thermal conductivities of three-dimensional woven composites showed significant differences due to the distribution of continuous fibers in three-dimensional woven composites with different structures, which could influence the sum fiber content on the cross section of heat flow. More importantly, compared with 2.5D angle-interlock woven composites and 2.5D angle-interlock (with warp reinforcement) woven composites, 3D orthogonal woven composites exhibited better performance in thermal conductivity. Overall, it was concluded that the thermal conductivities of three-dimensional woven composites were influenced by the fabric architectures and weaving parameters, such as the volume fraction, density, and types of fibers. Furthermore, the volume fraction of fibers on the cross section of heat flow was the dominant factor for thermal conductivities of different woven composites.
Goose down has superior thermal insulating properties as a filler material used widely as an insulator in textile products. Its particular "tree" structure is expected to attribute greatly to this insulating property. In this paper, fractal structures of the down "tree" are observed using scanning electron microscopy (SEM), and the configuration characteristics of goose down are described quantitatively by local fractal dimensions. From two expects, the local fractal dimensions were calculated both theoretically and experimentally, revealing its value to be very close to the golden mean, 1.618. This near-optimal fractal dimension may be attributable to the excellent thermal insulation of goose down assembly, and the potential applications of such a fractal structure are also discussed.
Down fiber assemblies are used widely in thermal products in winter because of their excellent heat-insulating abilities. These consist of down fibers and air, and belong to a typical kind of porous material. The internal microstructures involved fiber arrangement and pore distribution affects assembly heat conduction greatly. In this article, the micro computer tomography as a nondestructive observing technique to assembly microstructure is introduced, and the mathematical method of "local fractal" is applied to forecast and characterize the fractal characteristics of the down fiber assembly microstructure. The parameter "local fractal dimension" quantifies the geometric complexity of both the fiber arrangement and the pore distribution in the assemblies.
The heat transmission through a fabric during the measurement of thermal resistance was simulated by a novel heterogeneous model that was constructed according to the structure of ThermolabII Tester KES-F7. In this model, the heat transmissions along the longitudinal and transverse directions of yarn were treated independently. The material constants of fabrics, such as mass density, specific heat, thermal conductivity and thickness, were used as parameters for simulation in this fabric model. The validity of this model was then confirmed by the high consistency between the heat flux obtained from experiment and simulation, with the average difference ratio lower than 5%. The simulation results suggested that the guard area could effectively reduce the horizontal heat leakage from the test plate when the experimental fabric was thin. Only less than 8% of heat leaked in the one-layer case, while the leakage was significantly aggravated when more layers of fabric were stacked, resulting in the considerably lower thermal insulation achieved in both experiment and simulation compared with that in real fabrics. The temperature distribution in the model also implied that the longitudinal and transverse thermal conductivity of yarn exerted great effect on the heat leakage during the measurement. Moreover, for multilayers consisting of different fabrics, the laying sequence could obviously influence the heat leakage and, consequently, change the obtained thermal resistance.
Purpose
The purpose of this paper is to investigate if the fibers obtained from chicken feathers have a possibility to be used or not used in Winter outerwears as a filling material in terms of thermal insulation parameters.
Design/methodology/approach
In the study, thermal properties of the heat-resistant interlining samples produced from the chicken feathers fibers were analyzed in comparison with the samples produced from the industrial filling materials.
Findings
In the study, it was revealed that the use of chicken feathers fibers as filling material in Winter outerwears was possible.
Practical implications
The use of chicken feather fibers in Winter outerwears as a filling material will be an extremely low-cost alternative to pile flies of water birds which are sufficiently expensive filling materials.
Social implications
A significant portion of the chicken feather, which is released as a by-product in the production of chicken meat, is destroyed as industrial waste by digging or burning. Some of this product is used in the production of such cheap products as poultry feed. In the case of the production of fibers from the chicken feather, the use of these fibers as a filler in Winter clothing along with environmental protection will allow the use of this product for the production of products of higher cost.
Originality/value
The use of feathers’ material as a filling material in Winter outerwears has been known since ancient times. Due to the rough structure and low elasticity of chicken feathers, chicken feathers are not the best raw material for this purpose. This study revealed that it is possible to use chicken feathers as a filling material in terms of heat protection. The study is original in this respect.
The paper investigates the influence of fabric structure variations and finishing on the thermal properties of woven fabrics for a tailored garment. Four distinctive pairs of fabrics were investigated, where the weft density, weft yarn count or type and finishing were varied within the fabrics in each pair. Several thermal properties such as conductivity, diffusivity, absorptivity, resistance, the ratio of maximal and stationary heat flow density and the stationary heat flow density were measured using an Alambeta device. The results obtained showed that variation of the weft yarn count and finishing have a significant effect on several thermal properties. Increasing the weft count increased the thermal conductivity, absorptivity, resistance and the ratio of maximal and stationary heat flow density. The application of oilproof and waterproof finishing affected thermal diffusivity, thermal absorptivity and thermal resistance. Milled finishing contributed to increasing the thermal resistance.
Convective heat transfer plays a very important role in thermal resistance of textiles due to its porous structure, and the thermal resistance of textiles will be quite different when they are investigated under different testing standards and conditions. Nowadays, however, there is still no commercial instrument for evaluating the thermal resistance of textiles under convective heat transfer. Besides, there is no report about the influence of pore structure (pore size and the ratio of a pore’s cross-sectional area to the total cross-sectional area of fabric) on thermal resistance of textiles. Therefore, in this work, one newly designed device has been developed for evaluating the thermal resistance of textiles with different parameters in terms of porosity, pore size and pore cross-sectional area under heat convection. The results showed that with the increase of the pore size and the ratio of pore area to total area of fabric, the air permeability increases and the thermal resistance of fabric decreases; the pore size and the ratio of pore area have more significant influence compared to the influence of porosity; and the thermal resistance decreases with the increase of air permeability.
In fibrous material different types of heat transfer are present: conduction in solid phase constituting the insulation, radiation in the material, and heat transfer in the gas confined in the insulation. In this report the mechanisms of heat transfer are calculated theoretically. These calculations are verified experimentally by measurements on a glass fiber insulation in a specially constructed guarded hot plate apparatus. It is shown that the theories give a complete and consistent explanation of the influence of the mechanisms of heat transfer on the effective thermal conductivity of fibrous material.
A mathematical model based on the principles of heat transfer to predict the thermal resistance of fabrics has been presented in this paper. The woven fabric is considered as a system of porous yarns, interlacements between warp and weft yarns and air pores and all the basic weaves can be depicted by this system. The conduction and radiation heat transfer together, was calculated based on the construction parameters of the fabric. The thermal insulation, which is equivalent to the thermal resistance, was predicted with the help of these parameters. The total heat transfer by conduction through each part was calculated using Fourier’s equation. Radiation heat transfer through the air pore was calculated with the help of net radiation method. Linear anisotropic scattering was used to model the radiation heat transfer through fibrous media. The total thermal resistance obtained was validated with actual values obtained from a standard thermal resistance measuring instrument.
The effect of the fluffiness of the surface of nonwoven material on its heat transfer is manifested by a small range of the
difference in the surface and ambient temperatures (∼20°), in which the heat-shielding properties of clothing are used. When
the difference in the temperature of the surface of the material and the ambient temperature is greater than 30°, the effect
of the fluffiness on the surface heat transfer coefficient can not be considered. The thermophysical constants of the material
can be determined in this temperature region with the cooling curve.
For testing the thermal insulation of sleeping bags, standard test methods and procedures using heated manikins are provided in ASTM F1720-06 and EN 13537:2002. However, with regard to the evaporative resistance of sleeping bags, no instrument or test method has so far been established to give a direct measurement. In this paper, we report on a novel supine sweating fabric manikin system for directly measuring the evaporative resistance of sleeping bags. Eleven sleeping bags were tested using the manikin under the isothermal condition, namely, both the mean skin temperature of the manikin and that of the environment were controlled to be the same at 35 °C, with the wind speed and ambient relative humidity at 0.3 m s−1 and 50%, respectively. The results showed that the novel supine sweating fabric manikin is reproducible and accurate in directly measuring the evaporative resistance of sleeping bags, and the measured evaporative resistance can be combined with thermal insulation to calculate the moisture permeability index of sleeping bags.
Penguins live in the extremely cold Antarctic. Understanding the thermal radiative properties of penguin down may help us to develop super insulating materials. In this study, Fourier transform infrared spectroscopy (FTIR) was applied to measure the thermal radiative properties of penguin down and compare them with those of other fibrous materials. It was found that penguin and duck down are superior to other fibrous materials, such as polyester, Thinsulate and wool, at the same fibre volume fraction, in shielding the radiative heat transmission, largely due to their fine fibre diameter. There is an optimum fibre diameter at which the fibrous materials are at their best in blocking thermal radiation. The fibre diameter of penguin down is very close to this optimum value. The study further found that the relationship between the effective thermal radiative conductivity and fibre fineness may be better fitted with a quadratic curve.
This paper presents a new algorithm to simulate 2D transient heat and moisture transport behavior through fabric. We established a 3D geometric fiber model first, and the fibers are anisotropic. The new model is deduced by the mass and energy conservation, capillary phenomenon. We use finite-difference time-domain to solve the partial differential equations. It describes the physical mechanisms of heat and moisture transfer in fabric, providing detailed information of the transferring process in fibrous media. The simulation results demonstrate that the new method is relatively accurate and easily implemented.