Moisture Permeability Index Research Articles

Case study comparing Fiala-based thermophysiological model and PHS Index with experimental data to predict heat strain in normal and protective clothing

The use of protective clothing under extreme conditions leads to heat stress with undesired consequences on human physiology. As a prevention measure, thermal indices and thermophysiological models have been developed. Based on these models and indices, it is possible to estimate the time limits for staying under risky conditions, e.g., by the predicted rectal temperature whose value is one of the most important parameters used for assessing the heat stress. This article is focused on the comparison of rectal and mean skin temperature prediction realized by the Fiala-based thermophysiological model (FMTK) and Predicted heat strain (PHS) index with results from the real experiment for normal and protective clothing. Three types of ensembles were tested and simulated as follows: Klimatex underwear, air-permeable military NBC suit M2000 (FOP), and impermeable chemical protective clothing Tychem-F. The real experiments of thermal strain were performed with one male participant (80 kg, 1.75 m) walking on the treadmill located in the climate chamber. The temperature range for neutral and hot tests was set from 25 °C to 40 °C. The rectal temperature, skin temperatures, and heart rate were measured. The results showed that PHS index is well usable for normal clothing (Klimatex underwear) and air-permeable protective clothing (FOP) under various ambient temperatures, and it is able to give results similar to FMTK model and experiment, the mean absolute error MAE for rectal temperature prediction was for all ambient temperatures lower than 0.5 °C. FMTK model demonstrated good predictability for impermeable protective clothing Tychem-F, the maximum value of MAE 0.69 °C. Whereas PHS index showed several times larger error, the maximum value higher than 1.8 °C, in the prediction for this type of clothing. The performed simulations showed that the accuracy of the prediction by the PHS index is not so strongly dependent on the value of the overall clothing resistance, but it depends on the value of the moisture permeability index (permeable vs impermeable clothing) which is connected with the water vapor partial pressure under the clothing.

Effect of non-uniform skin of “Walter” on the evaporative resistance and thermal insulation of clothing

PurposeThe purpose of this paper is to compare the evaporative resistance and thermal insulation of clothing measured by thermal manikin “Walter” using uniform and non-uniform skin.Design/methodology/approachThe non-uniform skin with different perspiration rates was made by laminating a silicone layer on the inner side of a uniform skin. The thermal manikin was then covered with prepared non-uniform skin as well as uniform one. Four types of clothing ensembles were tested.FindingsThe relative intensity of perspiration rate was realized in different part of “Walter” skin, which was close to the perspiration rate of human being. There was a strong correlation between uniform skin and non-uniform skin. The thermal insulation and evaporative resistance of clothing measured on the non-uniform skin were higher than the ones determined on the uniform skin. However, their moisture permeability index showed the reversed tendency.Research limitations/implicationsThe implication of the research is to investigate the differences between uniform skin and non-uniform skin for manikin “Walter.” This is possibly useful in correcting and predicting more accurate thermal insulation and evaporative resistance of clothing measured by “Walter” with a uniform skin in future.Originality/valueIt was more accurate using non-uniform skin in evaluating thermal and wet comfort comparing to uniform skin.

Study of moisture and thermal transfer properties as a function of the fiber material variation

The properties of moisture transfer and the comfort of mesh-structured fabrics with various knit compositions and properties were investigated. The comfort effects of the double knitted fabrics combined with different cross-shaped fibers composed of dyeable-polypropylene (PPd) and regular polyester (PET) double-knitted fabrics were studied. A series of PET, PPd, Coolmax® (Cm) with single knitted fabrics and PPd/Cm with double knitted fabrics were evaluated to determine the physical properties and wearing performance for comfortable clothing. To compare the structural properties involving the vapor transfer of 4 types of fabrics with different fiber compositions, fiber types, weights, and thicknesses, the surface structure and pore characteristics were evaluated by scanning electron microscopy and a capillary flow porometer. The properties of moisture transfer were tested using vertical wicking and gravimetric absorbent testing system (GATS). In addition, the comfort performance measured by the thermal insulation value (Rt) and moisture permeability index (im) with a thermal manikin in a conditioned walk-in environmental test chamber was predicted. The result showed that the PPd/Cm sample has potential applications as good comfort fabric materials.

Novel ventilation design of combining spacer and mesh structure in sports T-shirt significantly improves thermal comfort

This paper reports on novel ventilation design in sports T-shirt, which combines spacer and mesh structure, and experimental evidence on the advantages of design in improving thermal comfort. Evaporative resistance (Re) and thermal insulation (Rc) of T-shirts were measured using a sweating thermal manikin under three different air velocities. Moisture permeability index (im) was calculated to compare the different designed T-shirts. The T-shirts of new and conventional designs were also compared by wearer trials, which were comprised of 30 min treadmill running followed by 10 min rest. Skin temperature, skin relative humidity, heart rate, oxygen inhalation and energy expenditure were monitored, and subjective sensations were asked. Results demonstrated that novel T-shirt has 11.1% significant lower im than control sample under windy condition. The novel T-shirt contributes to reduce the variation of skin temperature and relative humidity up to 37% and 32%, as well as decrease 3.3% energy consumption during exercise.

Cold protective clothing with reflective nano-fibrous interlayers for improved comfort

Purpose – The purpose of this paper is to develop multilayer clothing assemblies consisting of fibrous battings and reflective nano-fibrous thin layers for cold protective clothing for improved thermal insulation. Design/methodology/approach – Thermal insulation values of totally 20 assemblies made of varying layers of a thick polyester batting and four different types of thin interlayers were measured using a guarded hot-plate to investigate the effect of the properties of thin interlayers and construction of multilayer assemblies on thermal insulation. Cold protective jackets filled with polyester battings sandwiched with or without interlayers were also made and tested on the sweating fabric manikin-Walter. Findings – Results show that the Rosseland mean extinction coefficients of the thin interlayer and the associated radiative thermal conductivity of the interlayers have significant influence on thermal insulation of the assembly when more than one reflective nano-fibrous interlayers are sandwiched in the assembly. The cold protective jacket filled with multilayer polyester battings and reflective nano-fibrous interlayers have better thermal insulation and moisture permeability index (im) than those filled with the same multilayer polyester battings, but with non-reflective nonwoven interlayers or without interlayers. Originality/value – This paper clearly demonstrates the advantages of reflective nano-fibrous thin material for interlayers in the cold projective jacket.

A comparative study of regenerated bamboo, cotton and viscose rayon fabrics. Part 1: selected comfort properties

Regenerated bamboo, also known as bamboo viscose, is a man-made cellulose fibre that has recently appeared on the market as an apparel and home-furnishing textile. The products are marketed as having exceptional properties such as superior comfort and hand, as well as antimicrobial properties. Apart from the claimed “cool feeling”, the comfort properties referred to in the promotion of bamboo viscose fabrics can generally be ascribed to most cellulose fibres or fabrics. The purpose of this study was to investigate whether the moisture management and thermo-physiological properties of regenerated bamboo fabrics differ significantly from those of cotton and viscose rayon fabrics. A knitted regenerated bamboo fabric was compared to cotton and viscose rayon fabrics of comparable construction by using the results of objective measurements. Test apparatus used included the WALTERTM sweating manikin to measure thermal resistance, water vapour permeability, water absorbency and the moisture permeability index, the ALAMBETA instrument to measure thermal resistance and absorption and the PERMETEST instrument to measure water vapour permeability. To compare the structure of the regenerated bamboo fibre with that of cotton and viscose rayon fibres, the longitudinal character and cross-section of fibres were studied using scanning electron microscopy (SEM). Results confirmed that regenerated bamboo fibre fabrics have excellent moisture and temperature management properties. Contrary to the expectations created, however, no empirical evidence was found in this study, when properties pertaining to comfort were compared, to confirm that regenerated bamboo fibre fabrics are superior to those made of cotton and viscose rayon.

Measuring the thermal insulation and evaporative resistance of sleeping bags using a supine sweating fabric manikin

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.

Evaluating the Effects of Material Component and Design Feature on Heat Transfer in Firefighter Turnout Clothing by a Sweating Manikin

With a sweating manikin, the heat exchange efficiency through firefighter turnout clothing system from the wearer to the environment and the effects of material component and design feature on heat transfer were evaluated in a climatic chamber. Material component and design feature were varied to measure thermal insulation ( It — in clo units) and moisture permeability index ( im — dimensionless) of firefighter turnout clothing under two circumstances, with openings at the neck, wrists, waist and ankles sealed or not. Two new indices CIt and Cim were proposed to evaluate heat and moisture transfer capabilities of firefighter turnout clothing, which were defined as the changing rates of It and im from conditions of the clothing dressed in a regular way with openings unsealed to the openings sealed. The results showed that CIt indicated the effects of clothing design differences on heat transfer through firefighter turnout clothing, while Cim was dependent greatly on material properties (moisture permeability).

The Limitations of Woodcock's "Moisture Permeability Index"

The limitations of Woodcock's "Moisture Permeability Index, im," are discussed together with his suggested method of measuring im. The general expression is derived for im. from which it is clear that the Moisture Permeability Index is not a dimensionless index but depends upon the values of the convective and radiative heat losses from the outer surface of the clothing assembly. It is pointed out that Woodcock's test method using an unheated sweating cylinder is liable to give an underestimate of the heat loss from a clothed, perspiring body, first because in actual wear the clothing may become wetted in which "liquid assisted heat and vapor transfer" will take place, and second, because evaporation tends to increase the convective heat transfer from the outer surface of the clothing.

Effect of Laundering and Starching on Insulation and Vapor Permeability of Standard Fatigues

An electrically heated copper manikin with a wettable "skin" has been used to assess the effect of laundering and starching on the insulating value and evaporative heat transfer characteristics of a new, unused U. S. Army fatigue uniform. Except for small changes attributable to shrinkage of the clothing items, machine washing with detergents or commercial laundering with soap, followed by medium heavy starching and pressing, had no effect on the insulation value or moisture permeability index of the uniform. The effect of starching and pressing was also studied on volunteer subjects performing a rest-walk-rest routine in a hot humid environment. Based on body heat storage during the period, heat stress was unaffected by starching the uniform. This study, which included three other types of uniforms, also provided evidence that the level of heat stress in a given uniform is directly related with the ratio of the permeability index to the insulating value for the uniform as measured on the "sweating" copper manikin.

Moisture Transfer Through Impermeable Foam Insulations

The biophysical characteristics of perforated foam systems are presented in terms of experimentally determined values of insulation and moisture vapor permeance (MVP). The effect of windbreak motion on the moisture vapor transfer through such systems is discussed. A theoretical comparison among systems is given in terms of environmental range using the concept of moisture permeability index.

Moisture Transfer in Textile Systems, Part II

While the moisture permeability index and insulation value define the heat transfer characteristics of fabric systems under equilibrium conditions, such conditions do not always occur. Moisture may accttmulate in clothing during periods of activity due to unevaporated sweat or sweat which has evaporated from the skin and recondensed in cooler layers of clothing, or to moisture which is absorbed by the textile fibers. Upon cessation of activity and sweating, this moisture accumulated in the clothing will evap orate and produce undesired cooling or "after-exercise chill." A special thermostated hot plate is described which is used to measure rates of heat transfer through fabrics before, during, and after periods of simulated sweating. Typical curves are given for absorptive and nonabsorptive systems measured under conditions in which no excess moisture secretion or recondensation takes place. An interpretation of these curves is suggested. It is shown that with an absorptive textile the after-exercise chill is large and persists for about two hours but with a nonabsorptive type it is negligible.

Moisture Transfer in Textile Systems, Part I

From theoretical considerations a new clothing parameter, the moisture permeability index, has been developed, which describes the efficiency of fabrics or fabric systems in transferring moisture and its associated latent heat. This index extends the existing "clo" formula, which related dry or nonsweating heat loss to clothing insulation and ambient temperature, to include the heat losses from sweat evaporation. Using this index, it is possible to predict the environmental range over which man may maintain thermal balance with a given heat production or, alternatively, the range of activity and associated heat dissipation for any given environment. It thus supplies not only the missing parameter for quantitatively describing the effect of clothing in hot weather but also permits the same theory to be applied in hot, temperature, or cold environments. The experimental method of determining this index is outlined, and typical results are given.