Humidity measurements

The gravimetric method is accepted as the most accurate humidity-measuring technique. In this method a known quantity of gas is passed over a moisture-absorbing chemical such as phosphorus pent-oxide, and the increase in weight is determined. 

An evaluation of the HVAC system may include limited measurements of temperature, humidity, air flow, as well as smoke tube observations. Complex investigations may require more extensive or sophisticated measurements of the same variables (e.g., repeated COj measurements taken at the same location under different operating conditions, continuous temperature and relative humidity measurements recorded with a data logger). 

Wexi.ER, A. In Humidity and Moisture. Measurements and Control in Science and Industry. Volume 1 Principles and Methods of Humidity Measurement in Gases, (Ed. R. E. Ruskin) (Reinhold. New York,... 

For gaseous sterilization procedures, elevated temperatures are monitored for each sterilization cycle by temperature probes, and routine leak tests are performed to ensure gas-tight seals. Pressure and humidity measurements are recorded. Gas concentration is measured independently of pressure rise, often by reference to weight of gas used. 

Bedoya M., Orellana G., Moreno-Bondi M.C., Fluorescent optosensor for humidity measurements in air, Helv. Chim. Acta 2001 84 (9) 2628-2639. 

Tan, K. M. Tay, C. M. Tjin, S. C. Chan, C. C. Rahardjo H., High relative humidity measurements using gelatin coated long period grating sensors, Sens. Actuators B 2005, 110, 335 341... 

However, attention must be paid to the sampling procedures in processes involving high temperatures and high degrees of humidity. Measurements indicate that such conditions may influence on ED50 values to some extent. 

Koloutsou-Vakakis, S., and M. J. Rood, The (NH4)2S04-Na2S04-H20 System Comparison of Deliquescence Humidities Measured in the Field and Estimated from Laboratory Measurements and Thermodynamic Modeling, Tel-lus, 46B, 1-15 (1994). 

Sherer Environmental Chambers models CEL-512-37 and CEL-34-14 were freshly outfitted with incandescent (93W) and cool white VHO fluorescent bulbs. Eleven plants from each of the three sources were divided between the two chambers. Plant-top light-intensity varied from 2,800-3,300 ft-c, depending on plant height and the chamber involved. Controls were set for maximum relative humidity (measurements varied between 50 and 100%). Temperature was set at 22°C day (16H) and 17°C night (8 H). Plants were grown under these conditions for 12 wk. Beginning 24 Jan 1980, daylength was decreased from 16 to 11 h over a 4 wk period. 

Unless one is routinely working with humidity measurements, there is a tendency to overlook the fact that humidity is water gas. behaving in accordance with Ihe ideal gas laws. One of the easiest ways to pul humidity in its proper perspective is through application of Dalton s law of partial pressures Io the most commonly encountered gas-cur,... 

Therefore, the partial pressure of water v tiptir in air is directly related Io the measurement of humidity This vapor pressure varies horn 1.22 x 10 mb imillihan of mercury (0.122 Pascal) at the -7 C frost point of "hone dry" arctic or industrial dry air—to 1.013 x I01 mb ol mercury 10.1013 x IO1 Pasculi at ihe IIX) C dew poini of saturated hot air in a product drier This is a change of almost a million to one over the span of interest in industrial humidity measurement,... 

The ideal humidity instrument would he n linear, wide-range pressure gage, specific to water vapor and employing a primary or fundamental measuring method. Such an instrument, although physically possible, would be cumbersome. Most humidity measurements arc made hy some secondary instrument which is responsive io humidity-related phenomena. 

Saturated Salt Dew Point Sensors. The saturated sail (lithium chloride) dew point sensor is widely used because of its inherent simplicity, ruggedness, and low cost. Both the United Slates and Canadian government weather services use this type of sensor lor must official groundbused humidity measurements. However, some of these are being converted to the more accurate condensation hygrometers... 

Descriptive of a substance, the physical characteristics of which arc appreciably altered by effects of water vapor. The hygroscopicity of certain materials has been advantageously utilized ill humidity measurement and control devices for example, the hair clement of a hair hygrometer. 

Snavely, M.J., Price, J.C., and Jun, H.W. 1990. A comparison of three equilibrium relative humidity measuring devices. Drug Dev. Industrial Pharm. 16 1399-1409. 

Wiederhold, P. 1987. Humidity measurements. In Handbook of Industrial Drying (A.S. Mujumdar, ed.). Marcel Dekker, New York. 

Relative humidity measures the saturation of water in air. One way to calculate relative humidity is to divide the amount of water in the air by the solubility of water in the air. 

Dew point is detected by either lithium chloride or, if high precision is required, by the cooled mirror-type sensors, discussed in Section 3.2.13. For relative humidity measurements, the elongation and contraction of hygroscopic elements are used. 

Figure 8.12 Spectral percent transmission of an atmosphere at several relative humidities. Measurements were taken over a path length of 1.83 m at a temperature of 26.67°C [19].

The physical condition of the tomb indicates that the primary physicochemical processes of the tomb are intimately connected to its internal climatic conditions (28). In an initial study in December 1977, a set of humidity measurements taken in the closed tomb for 1 week with an unattended clockwork hygrothermograph showed a remarkably stable internal temperature of 27 1 °C the internal relative humidity (RH) was 31 2%. Small increases in humidity that were correlated with entry were also reported (28, 31). 

As a first step toward data collection with little human interference, an automatic hygrothermograph interfaced with a minicomputer was developed in our laboratory to study the internal climate of the tomb. This instrument can take temperature and humidity measurements every 33 min for 1 year and store the data in a computer memory. Its sensitivity to humidity fluctuation exceeds that of conventional chart hygrothermographs by a factor of 5. Therefore, the instrument has an important advantage over a clockwork hygrothermograph because it provides information on long-term climatic fluctuations in the tomb. 

Figure 7 is a plot of individual temperature and humidity measurements for March 1981. The average temperature for this month was 28.2 0.3 °C,... 

P. J. Dickerman (ed.). Optical Spectroscopic Measurements of High Temperatures, reprint ed.. Books on Demand, Ann Arbor, MI (1961) R. E. Bentley (ed.). Temperature and Humidity Measurement, Springer, New York (1998). 

Figure 12.4. Hardening of dry beans stored at 32°C and at different relative humidity measured as the penetration force after standard cooking. Curves show relative hardness (i.e., force at time 0 divided by force at any time after storage) as a function of storage time. Inset Light micrographs of cotyledons of hard (upper) and soft beans (lower). Notice separation of cells in...

Measurements of 0 and D in rain and river waters have indeed made it possible to confirm (Dall Olio et al., 1979 Salati et al., 1979) the importance of re-evaporated water for the water balance throughout the Basin, and in particular to establish a model indicating the relationship with the new oceanic water. There is a predominant zonal flow from east to west (Newell et al., 1972) and vapour influx from the Atlantic Ocean was estimated from the wind and humidity measurements by radiosonde at Belem. The central east to west region of the Basin between 0° and 5° of the latitude was considered to be subdivided into eight 3° segments between Belem (48° 30 ) and just west of Benjamin Constant (72° 30 ). 

A humidity measurement shows that the mole fraction of H2O in the stack gas is 0.0700. Calculate the stack gas composition on a wet basis. 

Method (iv) is used to find the humidity and (Jew point from a relative humidity measurement at a given temperature. 

Electric hygrometers have been the fastest-growing form of humidity measurement in recent years. They measure the electrical resistance, capacitance, or impedance of a film of moistureabsorbing materials exposed to the gas. A wide variety of sensing... 

Humidity The simplest method is sometimes the best. Wet- and dry-bulb temperature measurement to get air humidity is simple and works well for the occasional gas humidity measurement. The problem... 

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