Temperature dependence hquid water

AH glass capillary viscometers should be caUbrated carefully (21). The standard method is to determine the efflux time of distilled water at 20°C. Unfortunately, because of its low viscosity, water can be used only to standardize small capillary instmments. However, a caUbrated viscometer can be used to determine the viscosity of a higher viscosity Hquid, such as a mineral oil. This oil can then be used to caUbrate a viscometer with a larger capillary. Another method is to caUbrate directly with two or more certified standard oils differing in viscosity by a factor of approximately five. Such oils are useful for cahbrating virtually all types of viscometers. Because viscosity is temperature-dependent, particularly in the case of standard oils, temperature control must be extremely good for accurate caUbration. 

Liquid Third Phase. A third Hquid with coUoidal stmcture has been a known component in emulsions since the 1970s (22) for nonionic surfactants of the poly(ethylene glycol) alkylaryl ether type. It allows low energy emulsification (23) using the strong temperature dependence of the coUoidal association stmctures in the water—surfactant—hydrocarbon systems. 

Figure 2.2. Temperature dependence of the isobaric heat capacity (Cp) in liquid water. The dashed hne represents the behavior of typical hquids. Note the turnaround and divergence-Uke behavior for water at the melting temperature (Tin). The figure is reproduced Ifom the thesis of Dr. Pradeep Kumar, http //polymer.bu.edu/ hes/water/thesis-kumar.pdf...

Evaporation/condensation heat transfer between the body, the clothing and the environment can also occur through the evaporation of hquid water or the condensation of water vapour. This phase change of water is dependent on the latent heat of vaporisation, which is temperature-dependent. 

Nafion 117 in Hquid water takes up more water per sulfonic acid group than S-PEEKK of lEC values between 0.78mmol/g and 1.78mmol/g up to a certain temperature, which depends on the lEC value of the S-PEEKK. At this temperature, which is 65 °C for lEC = 1.78mmol/g, 80 °C for lEC = 1.4 mmol/g, 100 °C for lEC = 0.78 mmol/g, the water content of the S-PEEKK membranes increases tremendously. Nafion shows similar behavior only at a temperature of 140 °C. Until this temperature is reached, its molar water content is almost constant at A. = 20. The excess swelling of S-PEEKK at temperatures of 100 °C or less causes severe problems in using these materials as membranes in fuel cells. 

Viscosity. Sedimentation rate increases with decreased viscosity, )J., and viscosity is dependent on temperature. Often mineral oils, which are highly viscous at room temperature, have a viscosity that is reduced by a factor of 10 at 70—80°C. Tar, soHd at room temperature, is a low viscosity Hquid at 150—200°C and can be clarified of inorganic soHds at high flow rates. Even the viscosity of water changes significantly when the temperature changes between 10 and 35°C (10). 

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