Measurement thermal environment

IS( ) EN 7726 Requirements for measuring instruments Thermal environments instruments fov measuring physical quancirie.s... 

The application of the above standards requires measurement or estimation of a number of parameters. The supporting and complementary standards described below provide information that is required for the application of standards for assessing thermal environments. They can also be used independently in ergonomics and other investigations. 

ISO EN 9886 presents the principles, methods, and interpretation of measurements of relevant human physiological responses to hot, moderate, and cold environments. The standard can be used independently or to complement other standards. Four physiological measures are considered body core temperature, skin temperature, heart rate, and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject, and cost of each of the physiological measurements. The use of ISO 9886 is mainly for extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. 

Subject scales are useful in the measurement of subjective responses of persons exposed to thermal environments. They are particularly useful in moderate environments and can be used independently or to complement the use of the objective methods (e.g., thermal indices) that were described previously. ISO EN 10551 presents the principles and methodology behind the construction and use of subjective scales and provides examples of scales that can be used to assess thermal environments. 

ESR spectroscopy can be used with adsorbed paramagnetic ions to study the liquid associated with mineral surfaces. Cu(II) and Mn(II) have been used in his type of investigation, although difficulties are encountered with observing a resonance from Mn(II) in distorted environments. Measurements of Cu(II) on silica at room temperature and above have shown that adsorbed water behaves in the same manner as bulk water, but at lower temperatures it experiences a decreased mobility (61). On freezing two types of water are found one which is freezable and undergoes crystallization and the other which is unfreezable, in which the ice structure cannot be formed because of the surface interaction. NMR, IR and differential thermal... 

Mench et al. developed a technique to embed microthermocouples in a multilayered membrane of an operating PEM fuel cell so that the membrane temperature can be measured in situ. These microthermocouples can be embedded inside two thin layers of the membrane without causing delamination or leakage. An array of up to 10 thermocouples can be instrumented into a single membrane for temperature distribution measurements. Figure 32 shows the deviation of the membrane temperature in an operating fuel cell from its open-circuit state as a function of the current density. This new data in conjunction with a parallel modeling effort of Ju et al. helped to probe the thermal environment of PEM fuel cells. 

A water-cooled sampling probe of internal diameter 1 mm and external diameter 5 mm with a 3-meter long heated line was used to measure concentrations of unburned hydrocarbon (flame ionization detector, Analysis Automation, 520) and NOj (chemiluminescence analyzer, Thermal Environment Instruments, 42) at the combustor exit on a wet basis. The former, measured to a precision of the order of 1 ppm, was used to ensure complete consumption of fuel within the duct, and the latter with a precision of around 0.2 ppm was used to quantify the effect of oscillations on NOj. emissions. 

Fig. 28. Response of gauche isomer to thermal environment. Difference spectra of gauche isomers at elevated measurement temperatures, from 1650 cm-1 to 1320 cm-1...

During this century there has been considerable interest in the application of thermoluminescence studies to the recent history of meteorites. Natural TL provides a means of exploring radiation history and thermal environment in a manner which is complementary to isotopic methods, and the measurement of natural TL is now routine for the numerous meteorites being returned each year from the Antarctic (3,4). However, induced TL measurements have also proved of considerable interest, because the measurements have implications for the earliest history of meteorites. Essentially, the induced TL properties of meteorites are determined, with a few notable exceptions, by the amount and the nature of the feldspar in them, and feldspar is very sensitive to the major processes experienced by meteorites. In the present paper, we describe our recent work on the induced TL properties of meteorites and briefly discuss how these data relate to early meteorite history. We emphasize the relationship between the TL data and mineral properties. We also present here detailed descriptions of the cathodoluminescence properties of primitive meteorites, as these provide new insights into mineralogical controls on TL properties. 

Plant respiration is a relatively constant proportion of GPP, when ecosystems are compared. Although the respiration rate of any given plant increases exponentially with ambient temperature, acclimation and adaptation counterbalance this direct temperature effect on respiration. Plants from hot environments have lower respiration rates at a given temperature than do plants from cold places (Billings et al., 1971 Billings and Mooney, 1968 Mooney and Bilhngs, 1961). The net result of these counteracting temperature effects is that plants from different thermal environments have similar respiration rates, when measured at their mean habitat temperature (Semikhatova, 2000). 

To reduce thermal pollution, measures must be taken before the heated water is released into the environment. The water can be discharged into holding lakes or canals and allowed to cool. In addition, many facilities use cooling towers to dissipate heat into the air. 

The thermal environment is sometimes very complex. Convection, radiation and conduction are the common means of heat exchange and they vary independently over time and location. The final effects on the surface heat exchange of the human body are important factors for heat balance and for perception of the thermal conditions. Assessment of the thermal environment in a modern office or a car can create difficulties due to the complex interaction of the ventilation system with the situation close to the person and the external, environmental factors (e.g. radiation, air temperature and air movements). Furthermore, measurements in reality, as well as in the laboratory, contain various methodological problems. In this chapter some important aspects of dynamic water vapour and heat transport through fabrics are discussed. 

Measurement of the temperature difference is simple, and this is why DTA is more than a century old. With modern electronics one can achieve a greatly increased sensitivity, but the extension to accurate calorimetry is far from easy because of the uncertainty of the thermal environment. Although this problem has been overcome in commercial equipment which is designed... 

This chapter summarizes many of the contributions that the recoil technique of generating excited radiotracer atoms in the presence of a thermal environment is making to the field of chemical dynamics. Specific topics discussed critically include characterization of the generation and behavior of excited molecules including fragmentation kinetics and energy transfer, measurement of thermal and hot kinetic parameters, and studies of reaction mechanisms and stereochemistry as a function of reaction energy. Distinctive features that provide unique approaches to dynamical problems are evaluated in detail and the complementarity with more conventional techniques is addressed. Prospects for future applications are also presented. 

The effects of the thermal environment about the wire were investigated at low rates of sweep, of the order of 10 kgauss/min or 16 amp/min. It has been found that at these rates of sweep, the results obtained were almost independent of the thermal environment of the wire. Measurements were carried out with parts of the wire surface exposed directly to liquid helium, with the wire (1) firmly cemented against a holder of large thermal capacity, (2) cemented in frozen glycerin, (3) cemented in Duco cement, and (4) unsupported and un-eoated in contact with liquid helium across the whole area of the hairpin tip. 

Measuring thermal parameters of Li-ion cells is crucial for optimizing the thermal design of battery systems with respect to lifetime and safety issues. The thermal parameters of interest are heat capacity, thermal conductivity, and heat exchange between the cell s surface and the environment due to radiation and convection. Traditionally, heat capacity is obtained by calorimeter measurements and thermal conductivity is obtained by heat flux or Xenon-Flash measurements [1], Disadvantages of these methods are the requirement of expensive measurement devices and the destruction of the cell for thermal conductivity measurements. 

Practical tests may be used to determine the internal and external temperatures of the package under normal conditions by simulating the heat source due to radioactive decay of the contents with electrical heaters. In this way, the heat source can be controlled and measured. Such tests should be performed in a uniform and steady thermal environment (i.e. fairly constant ambient tanperature, stiU air and minimum heat input from external sources such as sunlight). The package with its heat source should be held under test for sufficient time to allow the temperatures of interest to reach steady state. The test ambient temperature and internal heat source should be measured and used to adjust linearly all measured package temperatures to those corresponding to a 38 C ambient temperature. 

The second item of information the quantity or concentration of an agent. Measurements vary for different agents. For thermal environments, for example, there is a need to measure the dry bulb air temperature, humidity, air velocity, and radiant heat load. For non-ionizing radiation, one must know the intensity and wavelengths. For airborne chemicals, one must know the concentration of each contaminant present. 

Before determining how hazardous a thermal environment is, one must make measurements of conditions. An assessment may involve several instmments. Some measurements in... 

To obtain a correct assessment of a thermal environment, four parameters require to be measured together ... 

In addition to the individnal techniqnes cited above, there are sitnations where individnal samples are snbjected to a common atmosphere and thermal environment. This is referred to as a concurrent analysis. An example of this is the combined DTA and TGA measin-ement, where two separate measurement devices share the same oven. In some cases two or more measnrements are performed on the same sample. There is also the possibility of interfacing several techniqnes, such as TGA combined with some form of evolved gas analysis snch as gas chromatography, Mass Spectrometry (qv), or infrared spectroscopy (or some combination of these) (see Chromatography, AFPmiTY Vibrational Spectroscopy). This situation is referred to as coupling or a coupled technique. Since the possibilities for interfacing several analytical techniques are quite large, conciurent or coupled techniques will not be considered further in this presentation. 

Before embarking upon the design for a ventilation system, it is necessary to assess the extent of the problem, that is, the amount of airborne pollution to be encoimtered in a workplace, and/or the degree of discomfort or stress expected from a thermal environment. Measmement and analysis techniques need to be devised and criteria and standards applied to the environment imder consideration. Where measurement and analysis are concerned, the physics and the chemistry of the properties of the pollutant and its mode of emission need to be studied in such a way that a reliable and accmate assessment of the exposure of a worker can be made. As far as criteria and standards are concerned, medical evidence, biological research and epidemiological methods need to be applied to establish the relationship between the exposure and the long- and short-term effect upon the human body of the worker taking into account the duration of exposure and the work rate. It can be seen, therefore, that many scientific skills... 

Thermal analysis can be used in a variety of combinations. The most common combinations all share the same sample as well as thermal environment. A key distinction is made between true simultaneous methods like TGA/DTA and TGA/DSC, in which there is no time delay between the measurements, and near-simultaneous measurements like TGA/MS and TGA/ FTIR, in which the time delay is small between the mass loss and the respective gas detector. Such combined techniques not only represent a saving in time, but also they help to alleviate or minimize uncertainties in the comparison of such results. And TGA/MS and TGA/IR can be instrumental in identifying complex processes that involve mass loss. Although combined instruments are not described in this book in detail, some examples are given in the TGA chapter. 

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