Simon Annaheim

Real evaporative cooling efficiency of one‐layer tight‐fitting sportswear in a hot environment

Real evaporative cooling efficiency, the ratio of real evaporative heat loss to evaporative cooling potential, is an important parameter to characterize the real cooling benefit for the human body. Previous studies on protective clothing showed that the cooling efficiency decreases with increasing distance between the evaporation locations and the human skin. However, it is still unclear how evaporative cooling efficiency decreases as the moisture is transported from the skin to the clothing layer. In this study, we performed experiments with a sweating torso manikin to mimic three different phases of moisture absorption in one‐layer tight‐fitting sportswear. Clothing materials Coolmax® (CM; INVISTA, Wichita, Kansas, USA; 100%, profiled cross‐section polyester fiber), merino wool (MW; 100%), sports wool (SW; 50% wool, 50% polyester), and cotton (CO; 100%) were selected for the study. The results demonstrated that, for the sportswear materials tested, the real evaporative cooling efficiency linearly decreases with the increasing ratio of moisture being transported away from skin surface to clothing layer (adjusted R2 >0.97). In addition, clothing fabric thickness has a negative effect on the real evaporative cooling efficiency. Clothing CM and SW showed a good ability in maintaining evaporative cooling efficiency. In contrast, clothing MW made from thicker fabric had the worst performance in maintaining evaporative cooling efficiency. It is thus suggested that thin fabric materials such as CM and SW should be used to manufacture one‐layer tight‐fitting sportswear.

Materials used to simulate physical properties of human skin

For many applications in research, material development and testing, physical skin models are preferable to the use of human skin, because more reliable and reproducible results can be obtained.

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.

A new method to assess the influence of textiles properties on human thermophysiology. Part I

Purpose – The purpose of this paper is to determine the validity and inter-/intra-laboratory repeatability of the first part of a novel, three-phase experimental procedure using a sweating Torso device. Design/methodology/approach – Results from a method comparison study (comparison with the industry-standard sweating guarded hotplate method) and an inter-laboratory comparison study are presented. Findings – A high correlation was observed for thermal resistance in the method comparison study (r=0.97, p<0.01) as well as in the inter-laboratory comparison study (r=0.99, p<0.01). Research limitations/implications – The authors conclude that the first phase of the standardised procedure for the sweating Torso provides reliable data for the determination of the dry thermal resistance of single and multi-layer textiles, and is therefore suitable as standard method to be used by different laboratories with this type of device. Further work is required to validate the applicability of the method for textiles wit...

Mechanical Predictors of Discomfort during Load Carriage.

Discomfort during load carriage is a major issue for activities using backpacks (e.g. infantry maneuvers, children carrying school supplies, or outdoor sports). It is currently unclear which mechanical parameters are responsible for subjectively perceived discomfort. The aim of this study was to identify objectively measured mechanical predictors of discomfort during load carriage. We compared twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt. The pressure distribution under the hip belt and the shoulder strap, as well as the tensile force in the strap and the relative motion of the backpack were measured. Multiple linear regression analyses were conducted to investigate possible predictors of discomfort. The results demonstrate that static peak pressure, or alternatively, static strap force is a significant (p<0.001) predictor of discomfort during load carriage in the shoulder and hip region, accounting for 85% or more of the variation in discomfort. As an additional finding, we discovered that the regression coefficients of these predictors are significantly smaller for the hip than for the shoulder region. As static peak pressure is measured directly on the body, it is less dependent on the type of load carriage system than static strap force. Therefore, static peak pressure is well suited as a generally applicable, objective mechanical parameter for the optimization of load carriage system design. Alternatively, when limited to load carriage systems of the type backpack with hip belt, static strap force is the most valuable predictor of discomfort. The regionally differing regression coefficients of both predictors imply that the hip region is significantly more tolerant than the shoulder region. In order to minimize discomfort, users should be encouraged to shift load from the shoulders to the hip region wherever possible, at the same time likely decreasing the risk of low back pain or injury.

A systematic approach to the development and validation of adaptive manikins

Recent advances in computation technologies have facilitated computer simulation of human physiological regulation mechanisms at high spatial and temporal resolution. Improvements in manufacturing techniques and control strategies have resulted in the development of advanced thermal manikins. However, the broader acceptance of human thermophysiological simulation via modelling and measurement tools is limited by the scarce public domain resources and availability of validation data supporting such tools [1]. In this study a systematic approach to the development and validation of thermophysiology models and adaptive manikins was developed. This approach is based on both the evaluation of manikin responsiveness - to be able to follow the course of human physiological responses, and the adequate validation of an adaptive manikin against human experiments representing groups with increasing complexity of exposure.

Validation of a physiological model for controlling a thermal head simulator

The head plays an important role in human thermoregulation. Helmets typically provide additional thermal insulation that impairs heat dissipation, reducing comfort and user acceptance [1]. Thermal head manikins allow analysis of the local heat transfer properties of headgear, but they usually do not provide information about human thermal response. Physiological models allow simulation of local physiological reactions and the thermal effect at the skin surface. However, they cannot account for complex heat and mass exchange processes at the skin surface when protective equipment is worn. We aim at controlling a thermal head manikin with a physiological model to develop a novel advanced method for headgear evaluation. This work presents the validation of the aforementioned physiological model by Fiala [2,4] (FPC model version 5.3, Ergonsim, Germany) for prediction of global and local temperatures at the head-site, specially needed for the coupling with body part manikins, and is going to be used as a reference for validation of the coupled thermal head simulator.

Comparison of fabric skins for the simulation of sweating on thermal manikins

Sweating is an important thermoregulatory process helping to dissipate heat and, thus, to prevent overheating of the human body. Simulations of human thermo-physiological responses in hot conditions or during exercising are helpful for assessing heat stress; however, realistic sweating simulation and evaporative cooling is needed. To this end, thermal manikins dressed with a tight fabric skin can be used, and the properties of this skin should help human-like sweat evaporation simulation. Four fabrics, i.e., cotton with elastane, polyester, polyamide with elastane, and a skin provided by a manikin manufacturer (Thermetrics) were compared in this study. The moisture management properties of the fabrics have been investigated in basic tests with regard to all phases of sweating relevant for simulating human thermo-physiological responses, namely, onset of sweating, fully developed sweating, and drying. The suitability of the fabrics for standard tests, such as clothing evaporative resistance measurements, was evaluated based on tests corresponding to the middle phase of sweating. Simulations with a head manikin coupled to a thermo-physiological model were performed to evaluate the overall performance of the skins. The results of the study showed that three out of four evaluated fabrics have adequate moisture management properties with regard to the simulation of sweating, which was confirmed in the coupled simulation with the head manikin. The presented tests are helpful for comparing the efficiency of different fabrics to simulate sweat-induced evaporative cooling on thermal manikins.

Numerical simulation of the transport phenomena in tilted clothing microclimates

Humans depend on clothing protection to minimize the thermal burden imposed on the body by the surrounding environments to which they may be exposed ([1]). The ability of clothing to offer protection depends on multiple factors, from properties of its materials to geometrical aspects influencing the shape of the clothing elements and the way they fit the body. The latter is particularly relevant for the case of loose garments (e.g. CBRN), where relatively thick microclimates exist between the skin and the clothing, which may originate internal buoyancy-driven flows (i.e. natural convection) and substantially alter the way heat is transported to/from the body. Recent literature ([2-4]) report relevant changes in the local heat transport along the skin, in horizontal clothing microclimates, stressing the need for analyses of other geometrical arrangements occurring within clothing.

Thermal effects of headgear: state-of-the-art and way forward

Headgear is widely used in both work and leisure. Much research attention has been spent on optimizing impact properties of helmets [1], [2]. However, thermal comfort of headgear is suboptimal in neutral and warm environments. In fact, thermal discomfort is often given as a reason to not wear protective headgear [3], [4]. Enhanced thermal comfort of headgear is likely to improve the willingness to wear protective headgear, and motivated an increasing number of studies, of which most were published in the last decade. The available body of literature allows for a valuable first review on the thermal effects of headgear.