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Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245
Fabric Cooling by Water Evaporation
Uwe Reischl a,, Ravindra S. Goonetilleke b
aBoise State University, 1910 University Ave., Boise, Idaho 83725, USA
bThe Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
Clothing can provide safety and comfort for persons exposed to both cold and hot thermal environments.
To assess the potential impact of clothing moisture and wetness on fabric cooling, a series of wind-tunnel
tests was conducted to quantify the evaporative cooling capacity of selected fabric samples. Single-
layer cotton, polyester, nylon and silk were evaluated. The results showed that onset and magnitude of
evaporative cooling was determined by the amount of water contained in a fabric sample. The results
also showed that an exposed “skin” exhibited more cooling when covered with a fabric than when it was
not. The information obtained helps better understand the evaporative cooling process for fabrics and
assist in the selection of garment materials that optimize worker comfort and safety.
Keywords: Evaporative Cooling; Fabrics Moisture; Protective Clothing
1 Background
Evaporation of water from the skin can provide significant cooling benefits for individuals exposed
to hot and / or dry environments. However, clothing can complicate the evaporation process by
creating a barrier to metabolic heat loss through the insulation created by the clothing itself.
This, in turn, can create a humid microclimate that reduces the evaporative cooling efficiency
of sweat from the skin [1]. Assessing the cooling effect of evaporation in clothing systems is
very complex. Sweat may evaporate directly from the skin surface or wick into the fabric where
evaporation takes place on the surface of the garment rather than on the skin surface. Both
of these processes can occur simultaneously. Furthermore, excessive sweat may roll off the skin
or remain trapped in the clothing system. It is assumed that sweat evaporated from the skin
surface can deliver more cooling than when sweat evaporates from a garment [2]. When sweat
evaporates from a garment, the location of the evaporative phase change is moved from the skin
to the outer surface of the garment where heat is extracted from the external environment rather
than from the surface of the skin. The overall cooling effects of sweat evaporation for clothed
persons has been carried out on human subjects as well as using thermal manikins [3-6]. However,
the outcomes have been difficult to related to clothing design and fabric selection because the
Corresponding author.
Email address: (Uwe Reischl).
1940–8676 / Copyright ©2016 Textile Bioengineering and Informatics Society
238 U. Reischl et al. / Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245
data are confounded by heat loss due to the latent heat of vaporization which cannot be assessed
separately [7]. The cooling generated by wet clothing, independent of body metabolic heat loss,
and the associated latent heat of vaporization, have not been separated. To address this issue,
a series of tests was carried out to measure the cooling created by evaporation not impacted by
metabolic heat production or subsequent sweating.
2 Methods and Procedures
Wind-tunnel tests were conducted on cotton, polyester, nylon and silk fabric samples to determine
the cooling generated by water evaporation from the fabric samples under controlled temperature,
humidity, and air velocity conditions. The temperature drop due to water evaporation was mea-
sured using a thermocouple temperature probe imbedded into the surface of a mounting platform.
A “control” configuration which did not include a fabric sample placed on the temperature sensor
was used as a reference. All tests were performed three times and the data averaged.
2.1 Wind Tunnel
A negative pressure laminar air flow wind-tunnel was used for this study. The wind-tunnel
measured 2.3 meters in length, 40.5 cm in height and 30.5 cm in width. Fabric samples were
placed onto a mounting platform which was positioned in the center of the wind-tunnel 1.2 meters
from the inlet. The air velocity was maintained at 1.5 m/sec. Air temperature was maintained
at 22 C (±2C) and relative humidity maintained at 15% (±5%).
2.2 Fabric Samples
Four types of fabric materials were tested. These included 100% cotton, 100% polyester, 100%
nylon, and 100% silk. Each sample was 5.0 cm×6.0 cm in size.
2.3 Mounting Platform
Fabric samples were placed onto a convex shaped mounting platform made of water impermeable
Styrofoam. Samples were placed onto the platform surface at a 45angle relative to the horizontal
and oriented into the wind-tunnel airflow. The platform allowed a fabric sample to lay smoothly
on the surface. To prevent potential displacement of the fabric sample by the air flow, each sample
was secured to the platform by four corner pins. The platform provided gravity run-off for all
excess water. A precision type K fine-wire glass insulated thermocouple was embedded into the
surface of the mounting platform which provided a temperature measurement of the underside of
the fabric sample. The digital thermometer provided an accuracy of ±0.1 C
2.4 Test Protocol
Fabric samples were spray irrigated with water 10 seconds prior to the start of each test run. The
irrigation water was maintained at room-temperature prior to application and was applied until
U. Reischl et al. / Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245 239
a fabric sample was saturated. Saturation was determined when the water was dripping freely
from the mounting platform. The fabric samples tested for the “moist” condition were initially
saturated with the irrigation water but then manually squeezed to remove all excess water. This
procedure was subjective. No water was added to any of the samples later during the tests.
The temperature drop created by each sample was measured for duration of 15 minutes. The
temperature on the surface of the platform and bottom of the fabric sample was recorded at 0.5
minute, 1.0 minute, 1.5 minutes, 2 minutes, 5 minutes, 10 minutes and 15 minutes. All fabric
samples, including the saturated and moist conditions, were tested three times.
3 Results
3.1 Control
Table 1 summarizes the evaporative cooling observed for the “control” condition in comparison
to the saturated cotton fabric sample. The temperature drop seen for the control condition was
5.1 C during the first five minutes and declined to 4.4 C afterwards. However, the temperature
drop observed for the cotton sample was 8.6 C during the first 10 minutes but showed no decline
Table 1: Temperature drop observed for the “control” condition and saturated cotton sample. Values
represent the average of three trials
Exposure Time (Minutes) “Control” Configuration (C) Cotton Sample (C)
0 0 0
0.5 3.4 4.2
1.0 4.4 6.2
1.5 4.7 7.3
2 4.8 7.9
5 5.1 8.5
10 4.5 8.6
15 4.4 8.6
3.2 Water Content
Table 2 summarizes the evaporative cooling observed for the “moist” and the “saturated” cotton
samples. During the first 1.5 minutes of exposure, cooling created by the “moist” sample was
substantially greater than by the “saturated” sample. However, after two minutes of exposure,
the “saturated” cotton sample exhibited substantially greater cooling than the “moist” cotton
3.3 Fabric Materials
Table 3 summarizes the evaporative cooling for the cotton, polyester, nylon and silk saturated
fabric samples. During the first 1.5 minutes the temperature drop measured was greater for
240 U. Reischl et al. / Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245
Table 2: Cotton sample temperature drop observed for the “moist” and “saturated” conditions. Values
represent the average of three trials
Exposure Time (Minutes) Cotton Sample (Moist) (C) Cotton Sample (Saturated) (C)
0 0 0
0.5 6.7 5.7
1.0 7.8 7.4
1.5 8.3 8.2
2 8.4 8.5
5 8.5 8.8
10 8.5 8.8
15 8.5 8.8
Table 3: Evaporative cooling observed for the saturated cotton sample, polyester sample, nylon sample,
and silk sample. Values represent the average of three trials
Exposure Time (Minutes) Cotton Sample (C) Polyester Sample (C) Nylon Sample (C) Silk Sample (C)
1.5 8.5 8.3 9.1 9.2
2 9.1 8.9 9.2 9.3
5 9.6 9.5 9.3 9.4
10 9.7 9.6 9.2 9.4
15 9.7 9.6 9.0 9.4
the Nylon and silk samples in comparison to the temperature drop measured for the cotton and
polyester samples. However, this relationship was reversed after five minutes when the cotton
and polyester cooling was observed to be greater than that for the nylon and silk samples.
4 Analysis
Comparing the temperature drop created by the cotton sample with the temperature drop created
by the “control” condition suggests that the improved cooling for the saturated cotton fabric
sample was due to the water contained in the fabric sample. Since the testing platform was made
of non-absorbing material, water applied to the platform flowed off the surface freely with only
a surface layer of water remaining due to the surface adhesion. This condition provided only a
limited amount of water for evaporation. As shown in Fig. 1, the “control” cooling decreased
over time while the cotton fabric sample exhibited no such decrease. This difference in cooling
suggests that the amount of water retained by the fabric sample determined the final cooling
capacity as well as the duration of the cooling process. The T-test applied to the equilibrium
conditions, i.e., the 2-15 minute time segments, yielded p = 0.001.
The relationship between water retention in a fabric and the evaporative cooling capacity of the
sample is illustrated in Fig. 2. The saturated (high water content) cotton sample exhibited the
greatest overall cooling than the moist sample. However, the moist sample exhibited a greater
temperature drop during the first 1.5 minutes while the saturated sample exhibited a greater
temperature drop afterwards. The dynamics of the relative cooling advantages offered over time
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00 2 4 6 8 10
Time (minutes)
12 14 16
Temperature Drop
Fig. 1: Evaporative cooling for the saturated cotton sample in comparison to the “control” over a 15
minute period
8.10 2 4 6 8 10
Time (minutes)
12 14 16
Temperature Drop
Fig. 2: Evaporative cooling observed for the saturated and the moist cotton samples. The moist sample
generated a greater temperature drop during the first 1.5 minutes while the saturated sample generated
a greater temperature drop afterwards
by each of the fabric samples is illustrated in Fig. 3. This suggests that the maximum cooling
does not always occur when the water retained in a sample is high. The T-test applied to the
equilibrium conditions, i.e., the 5-15 minute time segments, yielded p = 0.007.
A comparison of the cooling dynamics exhibited by the cotton, polyester, nylon, and silk samples
is illustrated in Fig. 4. It is seen that the cotton and polyester samples offered greater evaporative
cooling overall than the silk and nylon samples. It is important to note, however, the nylon and
silk samples initially provided greater evaporative cooling. These differences were statistically
significant. The T-test was again applied to the equilibrium conditions. The cotton/polyester
comparison yielded p = 0.05, the cotton/silk comparison yielded p = 0.001, and the cotton/nylon
comparison yielded p = 0.006 This finding again supports the concept illustrated in Fig. 2 and
Fig. 3 where the moist sample exhibited greater initial evaporative cooling than the saturated
242 U. Reischl et al. / Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245
Time (minutes)
Relative temperature difference (°C)
0 5 10 15 20
Fig. 3: Illustration of the relative evaporative cooling advantage offered by the moist sample relative to
the saturated sample during the first 1.5 minutes followed by a cooling disadvantage afterwards
Time (minutes)
Temperature drop (°C)
8.20 2 4 6 8 10 12 14 16
Fig. 4: Evaporative cooling observed for the cotton, polyester, silk and nylon fabric samples after 1.5
minutes of air flow exposure
5 Discussion
The water introduced into a fabric is dispersed and also retained in response to the interaction of
water molecule surface tension, cohesion and adhesion to the fabric fibers. These forces interact
U. Reischl et al. / Journal of Fiber Bioengineering and Informatics 9:4 (2016) 237–245 243
with the water droplets and the fabric fibers which influence the total amount of water that is
stored in the fabric and also determines the surface area over which the water can evaporate.
The ability of a fabric to capture water and distribute the water over the material will dictate
the evaporation capacity of the material. The distribution of the water over the fabric material
determines the evaporation capacity of the fabric material which will be greater than the evapo-
ration capacity of the skin where the water remains attached to the skin in the form of droplets
as illustrated in Fig. 5. Fig. 6 illustrates the mechanism by which fibers promote the spread of
water over a larger area in a fabric that increases the overall cooling capacity through evaporation.
This is illustrated in Fig. 3 showing the cooling advantage offered by wet fabrics. However, the
evaporation efficiency of water from a fabric can also be influenced by the total amount of water
that is retained within the fabric. As seen in Table 2 and Fig. 3, the cooling efficiency is optimal
at lower “wetness“ levels, i.e., moist conditions, while cooling over an extended period of time is
promoted by higher water content levels.
Fig. 5: Sweat droplets accumulating on the surface of the human skin as a result of water molecule
cohesion and adhesion. This limits the spread of water over the skin and reduces the potential of
evaporative cooling from the skin
Fabric fibers
Dry threads
Heat loss by conduction
Water exposure
capillary action
Wet threads
complete wetting
Fig. 6: Interaction of water droplets with fabric fibers that increases the available surface area for
evaporation and subsequent skin cooling
The results of this study suggest that a person wearing an appropriate garment experiences bet-
ter cooling and more comfort than a person without a garment. Such an approach is observed for
experienced athletes who wear a shirt when engaged in athletic competitions. This is illustrated
in Fig. 7.
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Fig. 7: Runner wearing a T-shirt to maximize cooling through garment sweat evaporation (Hong Kong
Sports Photography Association Photo)
6 Conclusions
Based on the results obtained in this study, the following conclusions can be reached:
Wet clothing can create cooling that is significantly greater than cooling generated by water
evaporating directly from the skin
Initial cooling by wet fabrics is greatest when a fabric contains a minimal amount of water
(moist) while cooling is optimal over a longer period of time when the fabric contains high
levels of water (saturated).
The level of cooling created by wet clothing over time is dictated by the total water content
in the fabric. The greater the amount of water, the longer the cooling effect over time.
This study also helps explain why persons frequently report improved comfort in hot environ-
ments when wearing single-layered clothing that does not absorb much sweat. The materials that
absorb little water such as nylon and silk provide immediate cooling while cotton provides better
cooling later. Application of this information can help in the design and development of future
clothing systems that create both immediate and long-term improvements in comfort and safety
for the users.
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[2] Craig FN, Moffit JJ. Efficiency of Evaportive Cooling from Wet Clothing. J Appl Physiol 1974;
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[5] McLellan TM, Pope JL, Cain JB, Cheung SS. Effects of Metabolic Rate and ambient Vapor
Pressure on Heat Strain in Protective Clothing, Eur J Appl Physiol 1996; 74: 518-527
[6] Mitchell D, Wyndham CH, Atkins AR, Vermeulen AJ, Hofmeyer HS, Strydom NB, Hodgson T.
Direct Measurement of Thermal Responses of Nude Men Resting in Dry Environments. Arch Ges
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[7] Havenith G, Brode P. Den Hartog E, Kuklane K., Homer I, Rossi RM, Richards M, Farnworth B,
Wang X. Evaporative Cooling: Effective Latent Heat of Evaporation in Relation to Evaporation
Distance from the Skin, J Appl Physiol 2013; 114: 778-785
... Reischl & Goonetilleke [4] indicated that wet fabric with minimal amount of water can provide a greater instant cooling effect than the fabric with a large amount of water. However, this behavior is not suitable to apply to this project case. ...
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This study evaluated the cooling properties of summer cooling towels of different brands by Q-max analysis. It was found all the samples could provide a cooling effect at first contact after being wetted. The samples of Perfect Fitness showed the highest cooling effect followed by the N-rit samples, whereas Street samples had the poorest cooling effect. The reason may be explained by the yarn density, fabric structure and thickness.
... Sweat evaporation is one effective way by which to cool the human body; evaporation of sweat from the skin to the environment provides effective body cooling for individuals exposed to hot/dry environments. 18 Heat from the skin converts sweat (water) to sweat vapor, and body heat can be released by sweating. In high-intensity heat, the human body loses up to 1 L of sweat per hour. ...
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The human body releases heat via four mechanisms: conduction, convection, evaporation, and radiation. The normal core temperature of the human body is around 37 °C, and metabolism may be negatively affected and enzymes/proteins may be destroyed if the core temperature rises above 45 °C. To prevent such overheating, we developed an evaporative–radiative–convective fabric which can control the personal microclimate of the human body through a cooling mechanism (evaporation of perspiration, air convection, and emission of heat radiation directly into the environment). In this work, we fabricated a thermo–moisture sensitive polyurethane/silica aerogel composite membrane which showed super evaporative and radiative effects and which can facilitate the convection process in the human body. We also fabricated a sensitive membrane-based textile which can cool down the human body by releasing body heat. The developed material possessed robust mechanical properties for the longevity of the material, high water-evaporative ability, and air permeability to provide comfort to the wearer. Microclimate-controlled clothing can release most of our body heat to the environment.
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Calculation of evaporative heat loss is essential to heat balance calculations. Despite recognition that the value for latent heat of evaporation, used in these calculations, may not always reflect the real cooling benefit to the body, only limited quantitative data on this is available which has found little use in recent literature. In this experiment a thermal manikin (MTNW, Seattle) was used to determine the effective cooling power of moisture evaporation. The manikin measures both heat loss and mass loss independently allowing a direct calculation of an effective latent heat of evaporation (λ(eff)). The location of the evaporation was varied: from the skin or from the underwear or from the outerwear. Outerwear of different permeabilities was used and different numbers of layers were used. Tests took place in 20°C, 0.5 m.s(-1) at different humidities and were performed both dry and with a wet layer allowing the breakdown of heat loss in dry and evaporative components. For evaporation from the skin λ(eff) is close to the theoretical value (2430J.g(-1)), but starts to drop when more clothing is worn, e.g. by 11% for underwear and permeable coverall. When evaporation is from the underwear, λ(eff) reduction is 28% wearing a permeable outer. When evaporation is from the outermost layer only, the reduction exceeds 62% (no base-layer) increasing towards 80% with more layers between skin and wet outerwear. In semi- and impermeable outerwear the added effect of condensation in the clothing opposes this effect. A general formula for the calculation of λ(eff) was developed.
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A condensation theory is presented that enables the calculation of the rate of vapour transfer with its associated effects on temperature and total heat transfer inside a clothing ensemble consisting of underclothing, enclosed air, and outer garment. The model is experimentally tested by three experiments: (1) impermeable garments worn by subjects with and without plastic wrap around the skin, blocking sweat evaporation underneath the clothing; (2) comparison of heat loss in impermeable and semi-permeable garments and the associated discomfort and strain; (3) subjects working in impermeable garments in cool and warm environments at two work rates, until tolerance. The measured heat exchange and temperatures are calculated with satisfying accuracy by the model (mean error = 11, SD = 10 Wm-2 for heat flows and 0.3 and 0.9 degree C for temperatures, respectively). A numerical analysis shows that for total heat loss the major determinants are vapour permeability of the outer garment, skin vapour concentration and air temperature. In the cold the condensation mechanism may completely compensate for the lack of permeability of the clothing as far as heat dissipation is concerned, but in the heat impermeable clothing is more stressful.
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Studies have shown that variations in ambient water vapour pressure from 1.7 to 3.7 kPa have little effect on heat tolerance time at a metabolic rate above 450 W while wearing protective clothing. With lighter exercise, where tolerance times exceed 60 min, variations in vapour pressure have a significant impact on evaporative heat loss and, therefore, heat tolerance. The present study has examined whether these findings extend to conditions with more extreme variations in vapour pressure. Twelve males performed light (L, 350 W) and heavy (H, 500 W) exercise at 40 degrees C in a dry (D, 1.1 kPa) and humid (H, 4.8 kPa) environment while wearing a semi-permeable nuclear, biological and chemical protective clothing ensemble (0.29 m2 x degree C-1.W-1 or 1.88 clo; Woodcock vapour permeability coefficient, im = 0.33). Partitional calorimetry was used to determine the rate of heat storage (S) with evaporative heat loss from the skin (Esk) calculated from changes in dressed mass or the physical properties of the clothing and the vapour pressure gradient between the skin and the environment. Skin vapour pressure was predicted from measurements of water vapour pressure above the skin surface and in the clothing with humidity sensors coupled with thermistors. Final mean skin temperature (Tsk) was higher for the humid trials and averaged 37.4 (0.3) degree C, 38.9 (0.4) degree C, 37.6 (0.5) degree C and 38.5 (0.4) degree C for LD, LH, HD and HH, respectively. Final rectal temperature (Tre) was higher for D with respective values for LD, LH, HD and HH of 39.0 (0.4) degree C, 38.7 (0.4) degree C, 38.8 (0.4) degree C and 38.5 (0.4) degree C. Tolerance time was significantly different among the trials and averaged 120.3 (19.3) min, 54.8 (7.3) min, 63.5 (6.9) min and 36.8 (3.1) min for LD, LH, HD and HH, respectively. Esk was overestimated and, therefore, S was underestimated when the changes in dressed mass were used to determine evaporative heat loss. When skin vapour pressure determined from the humidity sensor data was used to calculate Esk, heat storage was significantly different among the trials and averaged 15.0 (3.0), 13.0 (1.8), 14.2 (2.6) and 12.2 (1.9) for LD, LH, HD and HH, respectively. It was concluded that while wearing the protective clothing all indices of heat strain, including tolerance time, were significantly affected by the change in ambient water vapour pressure from 1.1 to 4.8 kPa during both light and heavy exercise.
Two nude resting men were exposed for two-hour periods to each of 25 dry environments, with air temperatures ranging between 12.8 C and 49.1 C and wind speeds between 0.67 m/sec and 4.94 m/sec. The mean radiant temperature of the surroundings was kept equal to the air temperature. Rates of radiant and convective heat exchange were measured directly, separately and continuously. The men had reached a thermal steady state after 105 min in the warm environments, but not in the cold environments. Graphs are presented to show the effect of ambient temperature and wind speed on the radiation and convection rates attained after 105 min, as well as on metabolic rate, sweat evaporation rate, rectal temperature and mean skin temperature. These graphs revealed some important aspects of the behaviour of man's thermal control system. In particular the physiological conductance increased with increasing ambient temperature and then saturated at an ambient temperature near 35 C. This saturation resulted in a constant difference between rectal temperature and mean skin temperature irrespective of the environmental conditions.
Two men wearing fatigue clothing walked on the treadmill and stored heat at rates from -14 to +121 W/m2. Twenty one tests were made to relate the efficiency of evaporative cooling, E/E', to the water content of the clothing, D. The heat lost from the body by evaporation, E, was obtained from the equation E = M + R + C - S, where storage was determined from changes in skin and rectal temperatures, and metabolism, radiation, and convection were estimated. The total heat of evaporation, E', was determined from the change in clothed body weight. D was the ratio of the average wet weight of the clothing to the standard dry weight; the wet weight varied during the walk with the rates of evaporation and sweating and with the amount of water added initially. As D increased there was little change in M, R and C, but E' increased more than E and the increase in E was counterbalanced by a decrease in S. The approach of E/E' to unity at minimum values of D supported the validity of the estimate of M, R and C. In 6 sets of tests under different conditions, the average data were D 1.05, E/E' 0.96, for no water added; D 1.20, E/E' 0.72, for 400 g added; and D 1.47, E/E' 0.59, for 1,000 g added. A decrease in E/E' with an increase in D was to be expected, but the extent of the decrease could not be predicted.
A theory of moisture absorption in clothing, with the associated effects of heat transfer, was developed and applied in a computer model. The model considers the body, underclothing, an outer layer, and the adjacent air layer. The theory was checked with an experiment involving four subjects. They wore heavy woollen clothing, which was either initially dry or humid, in both a warm and a cool environment. Model calculations and experimental results agree approximately upon the timing and magnitude of the effect of absorbing clothing on heat flows, temperatures and physiological reactions. Contrary to expectations the observed vapour resistance is lower in the heat than in the cold, probably due to differences in sweat distribution. It is pointed out that the usual way to determine the clothing characteristics by means of partitional calorimetry leads to considerable errors when the steady state has not been reached. In clothing that has high absorption properties the transient effects may be sustained for hours. Tests using the model show few beneficial effects of absorbing clothing on thermal sensation.
Evaporative Cooling: Effective Latent Heat of Evaporation in Relation to Evaporation Distance from the Skin
  • G Havenith
  • P Brode
  • E Den Hartog
  • K Kuklane
  • I Homer
  • R M Rossi
  • M Richards
  • B Farnworth
  • X Wang
Havenith G, Brode P. Den Hartog E, Kuklane K., Homer I, Rossi RM, Richards M, Farnworth B, Wang X. Evaporative Cooling: Effective Latent Heat of Evaporation in Relation to Evaporation Distance from the Skin, J Appl Physiol 2013; 114: 778-785