Evaporation, heat loss

As mentioned previously, the other term for characterizing skin moisture is skin wettedness (w) or the size of the water film as a fraction of total skin area that is necessary to account for the observed evaporative heat loss from the skin... 

I 1.988). Dissociation of temperature-gradient and evaporative heat loss during cold gas hyptt -ventilation in cold-induced asthma. Am. Rei. Respir. Dis. 138, 540-546. 

Heat dissipation can also be achieved by increased production of sweat, because evaporation of sweat on the skin surface consumes heat (evaporative heat loss). Shivering is a mechanism to generate heat. Autonomic neural regulation of cutaneous blood flow and sweat production permit homeostatic control of body temperature (A). 

A decrease in core body temperature was observed in the offspring of Long Evans rats exposed to 1 g/kg on Gd 15 no effect on metabolic rate or evaporative heat loss was observed (Gordon et al. 

Direct evaluation of the convective heat transfer coefficient (h ) of subjects clothed in undergarments and socks (normal ventilated environment) was achieved by observing the sublimation rate of naphthalene balls uniformly positioned three centimeters from the body surface. Equations were developed for prediction of h as a function of metabolic activity and posture, calculation o average skin temperature, and estimation of maximum evaporative heat losses from the body (U2 ). In another approach, the coefficients of dry heat transfer at varying wind speeds for nude and clothed sectional mannequins were determined (U3). At air flow rates above 2 m/sec, percentage contributions of individual body sections to total heat transfer remain constant for the nude and clothed mannequin, yet increased for normally uncovered units such as the face and hands. Generally, the ratio of total heat flow for the nude to clothed mannequin increased with air flow. 

At low cirabient temperatures a greater portion of the metabolic heat production (depending upon exercise intensity and clothing) is dissipated by convection and radiation and a minor portion by evaporation of sweat and respiratory water. As ambient temperature rises, the portion of heat dissipated by convection and radiation decreases progressively in concert with a proportional increase in the rate of sweating and evaporative heat loss. The coordination of the rate of heat loss between conduction, radiation, and evaporation is so precise that, for ambient dry-bulb temperatures between 5 C and 29 C, the equilibrium level of core (rectal) temperature is related directly to the intensity of the exercise load and is independent of environmental temperature (25). 

FIG. 1. General effects of changes in ambient temperature on core and skin lemperamre and aciiviiy of autonomic ihcrmocf-fecior temperature in a homeotherm. SkBF, skin blood flow EHL evaporative heat loss MR, metabolic rate LCT, lower critical temperature UCT, upper critical temperature. 

A first patent for the technical implementation of ozonolysis of OA was claimed by Rieche [21]. According to a BASF patent filed in 1941, AA (97%) and PA (95%) are accessible by treatment of the ozonide with alkaline lye and Ag20 [22]. However, the technical manufacturing of AA succeeded first by Emery Industries in the year 1953 [23]. Their successor Emery Oleochemicals is still the worlds largest producer of AA by ozonolysis of OA with a production volume of about lOOOOt/year [9, 24]. The achievable yield of AA is 70-80% [24], based on the amount of applied OA. AA yields of more than 90% were obtained in a pilot plant [25]. The reaction is carried out in PA/water (70/30v/v) as solvent. The admixture of water reduces the formation of side products by removal of the heat of reaction via evaporative heat loss, and in addition, undesired reactive radicals are quenched by reaction with water [25, 26]. 

As the water content of the air approaches saturation, evaporative heat loss becomes less efficient. When the air can hold no more water vapor, further evaporation is impossible. When providing ventilation systems for human or animal BU, the possibility of air saturation must be taken into account because the combination of high temperature and high humidity, especially if air movement is limited, can easily be fatal. The environment inside an impermeable protective suit, inside a livestock housing facility, or inside a modem apartment building when the air conditioning shuts off can reach this lethal state. People and animals have died as a resnlt. Evaporation, of course, is not available as a heat loss mechanism to BU bathed in water. 

The combination of ambient temperature and wind speed is called windchill. Wind-chill may be used to predict the risk of freezing of the exposed skin and to predict the amount of manual dexterity decrease (Daanen, 2009). The windchill index, as an estimator of cold injury risk, is part of an ISO standard (11079, 2007). In the heat, wind has a cooling effect by enhancing convective and evaporative heat loss. 

Thermo-physiological and climate-controlling properties of the spacer-fabrics will also be discussed in this paper. These tests directly relate to the functional comfort characteristics of the spacer-fabric structures which include thermal resistance, thermal absorpitivity, water vapour permeability, and evaporative heat loss. In all of the tests undertaken, comparisons are made to results obtained for traditional compression bandages and padding bandage materials. 

Emax = maximum evaporative heat loss (kilocalories per hour)... 

Equation (18 ) helps us understand evaporative heat loss, even if it may not be accurate for all thermal conditions. Note that the two parameters involved are air speed and vapor pressure difference between the air and skin. The most important of the two is the vapor pressure difference. Also note that evaporative cooling works in one direction only, removing heat. 

In equation (1) HL denominates the overall heat loss of the subject, HL g the nonevaporative, radiate heat loss of the subject to the environment, HL the sensible heat loss of the subject (heat transfer by warmed air) and HL the latent (evaporative) heat loss (heat transfer by vaporised water. 

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