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  • Gao, Chuansi, et al. (författare)
  • Thermoregulatory manikins are desirable for evaluations of intelligent clothing and smart textiles
  • 2010
  • Konferensbidrag (refereegranskat)abstract
    • Thermal manikins have been used to measure thermal properties of clothing. The use of thermal manikins has made a step forward in terms of quantifying thermal properties of clothing in a 3-D manner compared with the use of hotplates for material testing. The effects of clothing properties measured on the thermal manikins under steady state (constant manikin surface temperature and constant environmental condition) have usually to be validated by human subject tests. The thermal insulation and evaporative resistance values measured in the constant conditions are also used in modeling to calculate heat balance, predict human thermal physiological responses, and thermal comfort. However, in many real life situations, clothing properties (e.g. moisture transfer), in particular the clothing properties with smart materials, e.g. phase change materials (PCMs), environmental conditions, sweating rate, skin temperatures are neither constant nor uniform. These make mathematical modeling complicated to take into account various transient, non-uniform conditions, and changeable properties of smart clothing which is becoming increasingly popular (Tang and Stylios 2006). Moreover, skin and core temperatures rather than heat loss or storage are commonly used to evaluate thermal comfort, define hypothermia and hyperthermia and evaluate heat strain. Therefore, the direct prediction of thermophysiological responses (skin and core temperatures) based on manikin measurements are valid (Psikuta and Rossi 2009), and could be considered another step forward towards direct evaluation of human-clothing-thermal environment interactions. In the case of measuring a personal cooling system, current standard specifies the measurement of the average heat removal rate from a sweating heated manikin (ASTM F2371-10). This heat removal rate is not constant for the PCMs. The objective of this study was to investigate the gap between the measured heat removal rate of smart clothing with PCMs obtained on a thermal manikin in a stable state, and clothing effects on local human skin and on core temperature, to compare the difference of the results obtained from both methods, and to highlight the need for developing intelligent thermoregulatory manikins.
  • Kuklane, Kalev, et al. (författare)
  • European manikin standards and models to calculate thermal insulation
  • 2010
  • Konferensbidrag (refereegranskat)abstract
    • ISO 9920 defines three insulation calculation methods: global, parallel and serial. It considers global method a general one that works in any situation, and parallel and serial could be used in specific cases. EN ISO 15831 is the basic manikin testing standard. It gives only two possibilities: parallel and serial. The specific requirements for equations’ use are not set as in ISO 9920, e.g. uniform heat loss or surface temperature. The parallel method is defined similarly to the global in ISO 9920. Thus, the calculation methods’ definitions in the standards differ. EN 342, EN 14058 and EN 13537 for testing cold protective clothing or equipment refer to the methods in EN ISO 15831. Calculation of insulation by any method or using the average insulation of both methods is allowed depending on the test results with reference calibration ensembles. However, several issues need to be considered when using serial method. EN 511 Protective gloves against cold gives its own equation assuming that the whole hand is just one zone. In the case of one zone the serial and the parallel model give the same result. More zones increase the insulation difference between the methods. With uniform surface temperature (required by EN ISO 15831) the parallel method provides the same insulation value with any number of zones while the serial method provides higher value with more zones compared to one zone. EN 342 (cold) and EN 14058 (cool) use the same measuring principles and the same calibration garments. In the case of evenly distributed insulation, the differences in serial and parallel methods are relatively small, and proportional. However, with more insulation layers overlapping in heavy cold protective ensembles the differences increase, and don’t follow the linear relationship any more. The calibration ensembles are selected to represent proper cold protective garments. Thus, if a garment piece does not represent a proper cold protective ensemble (faulty design, manufacturing error) the calibration does not have to be valid. Lately a study on insulation measurements with electrically heated vest was presented. The vest provided an additional 10 W totally to torso region, and turned results from serial method to impossible 83 clo. It may be argued that manikin test is not meant to measure clothing with auxiliary heating. However, what happens if components of an ensemble do employ smart textile technology? A standard should avoid allowing any unrealistic results. EN 13537 Requirements for sleeping bags utilizes the physiological model that has been developed assuming serial values to be correct. It works with properly manufactured sleeping bags. It would be a considerable work to replace the method, although, equally good models are available. Such a major change requires good will and participation from several labs including the ones outside Europe, too.
  • Kuklane, Kalev, et al. (författare)
  • Moisture and clothing layers: effect of ambient temperature on heat loss and insulation
  • 2010
  • Konferensbidrag (refereegranskat)abstract
    • During the latest years the research on the effects of moisture on clothing system has been boosted. New information has revealed phenomena, e.g. “heat pipe” effect with its condensation-evaporation cycle(s) that has not been considered earlier in prediction of physiological reactions or evaluating clothing properties. Considering the material properties, e.g. the evaporative resistance measurements, the tests at homogenous conditions with registration of mass loss would be probably the correct approach. On the other hand, until there is no clear picture where condensation occurs, role of wicking and the probability of re-evaporation in multilayer clothing at different environmental conditions measuring the real heat losses in order to evaluate human thermal responses in realistic test conditions is important. An example of such need is the selection of proper means for protection against cold in prehospital care at accident sites. In this study thermal manikin was tested with wet underwear and wrapped in 1, 2 or 7 layers of woollen rescue blankets at -15 and +10 °C. This paper discusses the issues related to possibility to improve predictions for the cases when other situations, materials or exposure temperatures are involved. A method to quantify “heat pipe” effect was proposed, and for control the calculation of dry insulation from wet tests was applied. The measured apparent insulation, i.e. insulation based on total heat loss in wet conditions, was higher at -15 °C than at + 10 °C. That could be related to higher condensation rate in materials or suppressed evaporation. However, the measured weight loss rate (higher at 15 °C) and accumulation in layers (lower at 15 °C) did not support this conclusion. Effect could partly be related to the lower water pressure gradient between wet clothing at manikin surface and ambient air at +10 (2.5 kPa) than -15 °C (3.0 kPa). In the case of 7 layers the highest accumulation occurred in the layers near body and in the outermost layer while only minimal accumulation of moisture was observed in the middle layers. The total accumulation was divided into ratios for each layer, and expected condensation heat to environment was based on insulation (7 layers, 1/7 of the first and 7/7 of the outer layer leaves the system). When this correction was applied to “heat pipe” effect then the corrected heat loss did lead to insulation values similar to dry tests. The method worked also for 1 and 2 layer systems with highest difference for 1 layer system. The method could be tested more accurately on a sweating cylinder/torso, where layers may be separated in order to avoid wicking or vice versa set to allow it. Using different number of layers, layer thickness and less hygroscopic materials than wool may improve estimation of the “heat pipe” effects.
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