Agnes Psikuta

Validation of the Fiala multi-node thermophysiological model for UTCI application.

The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index (UTCI) was its capability of accurate simulation of human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing the temporal variation of outdoor conditions. In the first part of this study, available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over a wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response, as shown by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was subjected to extensive validation using the results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-mean-square deviations of 1.35 ± 1.00°C and 0.32 ± 0.20°C, respectively.

Quantitative Evaluation of air gap Thickness and Contact Area Between Body and Garment

The thermal, evaporative and wicking properties of clothing depend not only on the properties of the fabric but also on the thickness of air layers and the magnitude of the contact area and their variation. The aim of this study was to accurately determine the contact area and the air gap thickness between clothing and the human body in detail. These parameters were measured for a range of typical patterns of garments (tight- and loose fitting) covering either the upper or lower body and made of various types of fabrics (knitted and woven). The method consisted of imposing three-dimensional scans of the nude and dressed manikin and determining the distance between their surfaces by advanced three-dimensional scan post-processing. Due to this method the distribution of the air gap thickness and the contact area over body parts was obtained and this knowledge can be applied in models of heat and mass transfer in the clothing.

Transplanar and in-plane wicking effects in sock materials under pressure:

The moisture transfer and absorption properties of fabrics play an important role in the evaluation of the overall wear comfort of the textile. The location of moisture in the textile influences the skin wetness as well as the skin/textile friction process. In this study, we used X-ray tomography to analyze the transplanar and in-plane water transport in different sock materials when two defined pressures were applied to the inner side by means of an adjustable screw. The materials used were polyamide, polypropylene and wool, and had very distinct hydrophilic/hydrophobic and hygroscopic properties. The in-plane wicking effect showed a clear time dependency for the polyamide and wool samples, while the spreading of the polypropylene samples was very scattered. This effect was generally larger in the outer side of the sock than in the inner side, showing a clear tendency of these socks to wick the moisture away from the skin. Applying a pressure generally increased the in-plane water transport, but it affected the water distribution throughout the thickness of the sock for the wool samples, as more water remained in the inner half. The transplanar wicking effect was the most efficient with the polypropylene sock under the high pressure condition, but with the low pressure, this sock was not able to absorb all the moisture and a small quantity of water remained at its inner surface. X-ray tomography was shown to be a powerful tool to analyze not only the water distribution in static conditions, but also the transient 3-dimensional water transport.

Prediction of the physiological response of humans wearing protective clothing using a thermophysiological human simulator.

Most standards and devices for determining clothing properties ignore the physiological state of the wearer and are inadequate to evaluate the transient thermal properties of clothing ensembles. This study evaluated the physiological burden of different types of protective clothing and environmental conditions using the recently developed single-sector thermo-physiological human simulator and compared its performance with a thermal cylinder (without the physiological control model) and with an advanced physiological model (with a simple clothing model). A single-sector physiological simulator developed to simulate the dynamic thermal and perceptual behavior of humans over a wide range of environmental and personal conditions was successfully validated in this study through tests with clothed individuals exposed to hot and cold conditions. In comparative tests on water vapor permeable and impermeable clothing samples, the simulator provided a much more complete picture of actual clothing performance, for example, in terms of moisture retention within the clothing and the additional cooling due to the “heat pipe” effect in impermeable clothing.

Effect of ambient temperature and attachment method on surface temperature measurements

Accurate measurement of skin surface temperature is essential in both thermo-physiological and clinical applications. However, a literature review of the last two decades of physiological or clinical research revealed an inconsistency or a lack of information on how temperature sensors were attached to the skin surface. The purpose of this study was to systematically compare and quantify the performance of different commercially available temperature sensors and their typical attachment methods, and, secondly, to provide a time-efficient and reliable method for testing any sensor-tape combination. In conclusion, both the sensor type and the attachment method influenced the results of temperature measurements (both its absolute and relative dimensions). The sensor shape and the contact of its sensing area to the surface, as well as the conductance of the tape were the most important parameters to minimise the influence of environmental conditions on surface temperature measurement. These results suggest that temperature sensors and attachment methods for human subject and manikin trials should be selected carefully, with a systematic evaluation of the sensor-tape system under conditions of use, and emphasise the need to report these parameters in publications.

Air gap thickness and contact area in undershirts with various moisture contents: influence of garment fit, fabric structure and fiber composition

The heat and water vapor transport in clothing results from fabric properties, air layers enclosed in the garment and environmental conditions. Accumulation of moisture in clothing layers intensifies this transport because of the change in thermal properties of wet fabrics and the size of air gap thickness and the contact area. This paper presents distribution of air gaps and contact areas in relation to various moisture contents in typical undershirts confectioned from fabrics with contrasting affinity to moisture. The effect of the undershirt fit, body region, fabric structure and fiber type is also discussed. The air gap thickness and the contact area were determined using three-dimensional scanning and the post-processing technique. The results show that the influence of the moisture content on the sought parameters noticeably varied among body regions and was related to the regional fit of the clothing. This variation was larger in cotton than polyester undershirts or those containing spandex, but the direct relevance of the fabric structure was not clear. Although influence of the moisture content was found, the magnitude of the air gap thickness and the contact area resulted mainly from the garment fit.

Effect of garment properties on air gap thickness and the contact area distribution

The heat and mass transfer in clothing is affected by the distribution of the air gap thickness and the contact area and this, in turn, results from the interaction between the geometrically complex shape of the human body, garment design, and fabric mechanical properties. In this study, the distribution of the air gap thickness and the contact area in typical shirts and undershirts were investigated using the three-dimensional scanning technique in relation to the garment style and fit, fabric properties, and body regions. This study showed that at the upper trunk the air gap thickness was unaffected by both the garment style and the fit, whereas the shape of the contact area was changed only by the fit. At the lower body the air gap thickness and the contact area changed proportionally with the increase of the ease allowances in the garments. As expected, larger air gaps were formed in shirts but larger contact areas were observed in undershirts. Consequently, results indicated the possibility of modeling the size of air layers in clothing by proper selection of the fabric type and ease allowances in clothing for a given body shape.

Opportunities and constraints of presently used thermal manikins for thermo-physiological simulation of the human body

Combining the strengths of an advanced mathematical model of human physiology and a thermal manikin is a new paradigm for simulating thermal behaviour of humans. However, the forerunners of such adaptive manikins showed some substantial limitations. This project aimed to determine the opportunities and constraints of the existing thermal manikins when dynamically controlled by a mathematical model of human thermal physiology. Four thermal manikins were selected and evaluated for their heat flux measurement uncertainty including lateral heat flows between manikin body parts and the response of each sector to the frequent change of the set-point temperature typical when using a physiological model for control. In general, all evaluated manikins are suitable for coupling with a physiological model with some recommendations for further improvement of manikin dynamic performance. The proposed methodology is useful to improve the performance of the adaptive manikins and help to provide a reliable and versatile tool for the broad research and development domain of clothing, automotive and building engineering.

The effect of body postures on the distribution of air gap thickness and contact area.

The heat and mass transfer in clothing is predominantly dependent on the thickness of air layer and the magnitude of contact area between the body and the garment. The air gap thickness and magnitude of the contact area can be affected by the posture of the human body. Therefore, in this study, the distribution of the air gap and the contact area were investigated for different body postures of a flexible manikin. In addition, the effect of the garment fit (regular and loose) and style (t-shirts, sweatpants, jacket and trousers) were analysed for the interaction between the body postures and the garment properties. A flexible manikin was scanned using a three-dimensional (3D) body scanning technique, and the scans were post-processed in dedicated software. The body posture had a strong effect on the air gap thickness and the contact area for regions where the garment had a certain distance from the body. Furthermore, a mathematical model was proposed to estimate the possible heat transfer coefficient for the observed air layers and their change with posture. The outcome of this study can be used to improve the design of the protective and functional garments and predict their effect on the human body.

Heat flux measurements for use in physiological and clothing research

Scientists use passive heat flow meters to measure body heat exchanges with the environment. In recent years, several such sensors have been developed and concerns about their proper calibration have been addressed. However, calibration methods have differed in the geometry of the heated device as well as in the heat transfer mechanism. Therefore, a comparison of calibration methods is needed in order to understand the obtained differences in calibration lines. We chose three commercially available heat flux sensors and placed them on four different heated devices: a hot plate, double hot plate, nude cylinder and a cylinder covered with a spacer material. We found differences between the calibration line of the manufacturer and our own measurements, especially when forced convection was involved as the main heat transfer mechanism. The results showed clearly that the calibration method should be chosen according to the intended purpose of use. In addition, we recommend use a thin, light heat flux sensor with good thermal conduction in human subject studies.