Contained in a unit mass of air m a gkg q m w m a the

This preview shows page 30 - 32 out of 41 pages.

We have textbook solutions for you!
The document you are viewing contains questions related to this textbook.
Precalculus with Limits: A Graphing Approach
The document you are viewing contains questions related to this textbook.
Chapter 3 / Exercise 109
Precalculus with Limits: A Graphing Approach
Larson
Expert Verified
) contained in a unit mass of air (Ma) [g/kg] q = Mw/MaThe saturation specific humidity (qs) is the quantity of water vapour required for saturation. The value of qs depends on temperature and pressure, as shown in Table 1. Table 1 Saturation specific humidity (qs) for various temperatures and pressures (g/kg) [Byers (1974)] T (°C) P = 1000 mb P = 900 mb P = 800 mb -30 0.317 0.353 0.397 -20 0.784 0.871 0.980 -10 1.79 1.99 2.23 0 3.80 4.23 4.76 10 7.67 8.53 9.60 20 14.7 16.3 18.4 30 26.9 29.9 33.7 Relative Humidity (RH)The ratio of the actual water vapour content of the air to that required to produce saturation (in percent): RH = q/qs x 100% The relative humidity is also given by: RH = Pv/Pvs x 100% Where;Pv is the vapor pressure Pvs is the vapor pressure at saturation for the given temperature. Dry Bulb Temperature (T)The air temperature as measured by a thermometer or thermocouple. Wet Bulb Temperature (Tw)The lowest temperature that can be achieved by evaporating water into the air. The wet bulb temperature can be measured with a standard thermometer that has a wetted wick covering the bulb.
We have textbook solutions for you!
The document you are viewing contains questions related to this textbook.
Precalculus with Limits: A Graphing Approach
The document you are viewing contains questions related to this textbook.
Chapter 3 / Exercise 109
Precalculus with Limits: A Graphing Approach
Larson
Expert Verified
28
Dew Point Temperature (Td)The temperature to which the air must be cooled, at constant pressure, so that the air becomes saturated (i.e. RH = 100 %). Td can be determined from the psychrometric chart if the dry bulb and wet bulb temperatures are known. The dew point temperature is obtained by drawing a horizontal line from the intersection of T and Tw to the saturation curve. MEASUREMENT OF AIR MOISTURE CONTENTNumerous methods are available for determining the moisture content of air. Many of these are listed in Chapter 14 of the ASHRAE Fundamentals Handbook (2001). Several of the more common methods are described below. (1)PsychrometerThis instrument has two temperature sensors, one of which is covered by a moistened wick. When air is blown over the instrument, the temperature of the moistened sensor reduces due to evaporation. The temperature of this sensor eventually reaches the wet bulb temperature Tw. The other temperature sensor indicates the dry bulb temperature, T. The values of T and Tw enable the state point of the air-vapour mixture to be fixed on a psychrometric chart. Various types of psychrometer are available. A sling psychrometer is rotated rapidly to produce airflow over the wicked thermometer. An aspirated psychrometer has a blower that produces air flow over a stationary sensor. (2)Dew Point HygrometerThis apparatus consists of a cooling plate, a light source, a light sensor, a thermocouple and a control circuit. The unit operates by sensing the amount of light reflected from the cooling plate. When the cooling plate reaches the dew point temperature (Td), condensation on the plate causes the amount of light reflected to change. The plate is then allowed to warm until the condensation disappears and

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture