Specific humidity, calculation

Specific humidity used in calculations on certain types of compressors is a totally different term. It is the ratio of the weight of water vapor to the weight of dry air and is usually expressed as pounds, or grains, of moisture per pound of dry air. Where pa is the partial air pressure, specific humidity can be calculated as ... 

The meteorological input required in the Unified EMEP model are the 3D horizontal and vertical wind fields, specific humidity, potential temperature cloud cover, and precipitation. The transferred surface 2D fields for use in the chemical transport model are surface pressure, 2 m temperature, surface flux of momentum, sensible and latent heat, and surface stress. All variables are given in 3-h interval. Table 13.1 lists the variables and their main purposes in the EMEP model. Inside the model different boundary layer parameters like the stability, eddy diffusion, and mixing height are calculated based on MOST. 

Molion (1975) employed climatological data (average charts of wind and specific humidity seasonal values) and the method of Penman (1963) to estimate that about 52% of the rain falling on the region was lost through the river. Similarly Villa Nova et al. (1976) applied Penman s method adapted to forested regions by Shiau and Davar (1973) and calculated that evaporation represented 54%, and 46% of rainfall was lost to the river. 

Volumetric humidity Y Mass of vapor per unit volume of gas-vapor mixture. It is sometimes, confusingly, called the absolute humidity, but it is really a vapor concentration preferred units are kg/m or Ib/fT, but g/nV and gr/ft are also used. It is inconvenient for calculations because it depends on temperature and pressure and on the units system absolute humidity Y is always preferAle for heat and mass balances. It is proportional to the specific humidity (wet basis) Yy = Yy/pg, where pg is the humid gas density (mass of gas-vapor mixture per unit volume, wet basis). Also... 

Fig. 8-1. Zonally averaged partial pressures of water vapor for January and July calculated from specific humidities presented by Oort and Rassmusson (1971) and Newell et al (1972) for latitudes between 10°S and 75°N. Data at pressure levels of 400, 500, and 700 mbar are shown by dots, data at 850 mbar by open circles, and data at 1000 mbar by crosses.

In calculations with humid air, when the pressure is not high (usually the atmosphetic pressure of 1 bar), water vapor and dry air can be handled as an ideal gas, as we have already done in Eqs. (4.76) and (4.78). For ideal gases the specific enthalpy is just a function of tempetatute ... 

The specific heat capacity of humid air calculated per kilogram of dry air is... 

Dry air rising in the atmosphere has to expand as the pressure in the atmosphere decreases. This pV work decreases the temperature in a regular way, known as the adiabatic lapse rate, Td, which for the Earth is of order 9.8 Kkm-1. As the temperature decreases, condensable vapours begin to form and the work required for the expansion is used up in the latent heat of condensation of the vapour. In this case, the lapse rate for a condensable vapour, the saturated adiabatic lapse rate, is different. At a specific altitude the environmental lapse rate for a given parcel of air with a given humidity reaches a temperature that is the same as the saturated adiabatic lapse rate, when water condenses and clouds form Clouds in turn affect the albedo and the effective temperature of the planet. Convection of hot, wet (containing condensable vapour) air produces weather and precipitation. This initiates the water cycle in the atmosphere. Similar calculations may be performed for all gases, and cloud layers may be predicted in all atmospheres. 

Reference TDI contains an enthalpy table for ammonia at different pressures. Reference TD2 contains a series of tables in an appendix from which the specific heats of the reaction-gas mixture were calculated. Humidity charts were also useful. Reference TD3 is valuable for its steam tables, while Ref. TD4 contains both thermodynamic and chemical equilibria data for nitric acid. The final reference, Robertson and Crowe (Ref. TD5), contains formulae and tables for the sizing and choice of an air-feed compressor. 

Neglecting radiation losses, calculate the mass of dry air passing through the dryer and the humidity of the air leaving the dryer. Latent heat of water at 294 K = 2450 kJ/kg. Specific heat capacity of ammonium nitrate =1.88 kJ/kg K. Specific heat capacity of dry air = 0.99 kJ/kg K. Specific heat capacity of water vapour = 2.01 kJ/kg K. 

In a countercurrent packed column, n-butanol flows down at the rate of 0.25 kg/m2 s and is cooled from 330 to 295 K. Air at 290 K, initially free of n-butanol vapour, is passed up the column at the rate of 0.7 m3/m2 s. Calculate the required height of tower and the condition of the exit air. Data Mass transfer coefficient per unit volume, hDa = 0.1 s 1. Psychrometric ratio, (h/hDpAs) = 2.34. Heat transfer coefficients, hL = 3hG. Latent heat of vaporisation of n-butanol, A = 590 kJ/kg. Specific heat capacity of liquid n-butanol, Cl = 2.5 kJ/kg K. Humid heat of gas , s = 1.05 kJ/kg K. 

Define the dry-bulb temperature, wet-bulb temperature, and humid volume of humid air. Given values of any two of the variables plotted on the psychrometric chart (dry-buib and wet-bulb temperatures, absolute and relative humidity, dew point, humid volume), determine the remaining variable values and the specific enthalpy of the humid air. Use the psychrometric chart to carry out material and energy balance calculations on a heating, cooling, humidification, or dehumidification process involving air and water at 1 atm. 

With regard to the upper specification limit for moisture, this increase was marginal, and it was calculated that there was no risk to breach the specification limit at the relative humidity of the clean room, assuming a cumulation of worst cases. 

So far boundary conditions for gas phase calculations are taken from measurements or empirical correlation, limiting the application only to specific cases. Therefore the aim of the current project is to develop a numerical model, which predicts the conversion of the solid fuel in the packed bed. The model should take different operating parametors and main fuel properties, such as size and humidity of the fuel particles, into account. 

A dryer produces 180 kg/hr of a product containing 8% water from a feed stream that contains 1.25 g of water per gram of dry material. The air enters the dryer at 100°C dry-bulb and a wet bulb temperature of 38°C the exit air leaves at 53°C dry-bulb and 60% relative humidity. Part of the exit air is mixed with the fresh air supplied at 21°C, 52% relative humidity, as shown in Fig. P4.169. Calculate the air and heat supplied to the heater, neglecting any heat lost by radiation, used in heating the conveyor trays, and so forth. The specific heat of the product is 0.18. 

The chemical composition of the different catalysts investigated are collected in Table 1. Also the sulfur contents calculated for complete conversion to Zr(S04)2 are indicated. The experimental sulfur contents are lower than the calculated values. The reaction of the silica-supported zirconia with gaseous sulfur trioxide is therefore not complete and the reaction of zirconium hydroxide and zirconia with sulfuric acid involves only a limited fraction of the zirconia. As to be expected, the specific surface area of the catalyst prepared from zirconium hydroxide is much larger than that of the other catalysts. The catalyst based on calcined zirconia exhibited the X-ray diffraction pattern of zirconia and the catalyst based on zirconium hydroxide showed broadened reflection of zirconia. The bulk water-free zirconium sulfate did not display an X-ray diffraction pattern after exposure to ambient air (relative humidity 50 to 60%) for two weeks the sharp X-ray diffraction pattern of Zr(S04)2-4H20 appeared [1]. 

Lines are shown on Fig, 23.2 for the specific volume of dry air and the saturated volume. Both lines are plots of volume against temperature. Volumes are read on the scale at the left. Coordinates of points on these lines are calculated by use of Eq. (23.7a). Linear interpolation between the two lines, based on percentage humidity, gives the humid volume of unsaturated air. Also, the relation... 

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