Determination of humidity air by using Dry bulb and wet bulb temperature

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#Determination of humidity air by using Dry bulb and wet bulb temperature • #Aim: Determination of humidity of air by using wet and dry bulb temperatures or Psychrometer. • #Requirements: • Thermometer, Beaker, Absorbent cotton, Water, Ice, Stand, Humidity chart, Sling Psychrometer. • #Principle: • The wet-bulb temperature is the lowest temperature which may be achieved by • evaporative cooling of a water-wetted (or even ice-covered), ventilated surface. Suppose we have a thermometer and it is wrapped in a cloth moistened with water that time the faster the water will evaporate. The faster the water evaporates, lower the thermometer will be relative to air temperature. If the relative humidity is 100%, no water will evaporate, and the thermometer will read the same as an unwrapped thermometer. This principle is why we feel cooler in dry air. The sweat evaporates quicker cooling down the skin in dry air. For air at a known pressure and dry-bulb temperature, the thermodynamic wet-bulb temperature corresponds to unique values of the relative humidity and the dew point temperature. It therefore may be used for the practical determination of these values. The relationships between these values are illustrated in a psychometric chart. • #Theory: • The wet bulb temperature of air is measured by the ordinary thermometer, but the only difference is that the bulb of the thermometer is covered by the wet cloth. Temperature of the ordinary air measured by the thermometer when it is covered by wet cloth or wick is called as the wet bulb temperature, commonly referred to as WBT. When the air comes in contact with the wet cloth it absorbs some moisture and gives up some heat, due to which the temperature of the air reduces. This reduced temperature measured by the thermometer is called as the wet bulb temperature. If the moisture content of the air is very low, it will give up more heat to the cloth and the wet bulb temperature of air will also be comparatively lower. On the other hand, if the moisture content of air is high it will lose lesser heat to the • air and wet bulb temperature will be higher. The more is the moisture or water vapor content of the air more is the wet bulb temperature. Thus, the wet bulb temperature indirectly indicates the moisture content present in the air or we can say that it is affected by the • relative humidity of the air. A widely used device for measuring wet and dry bulb • temperature is a sling psychrometer • Sling Thermometer: • Sling Thermometer: • The DBT and WBT of the air are measured by a special thermometer called sling thermometer. • #Procedure: • 1.Note down the atmospheric temperature by using thermometer and record it as dry bulb temperature. • 2. Take 100 ml beaker which is half filled with water. • 3.Tie absorbent cotton around the bulb of thermometer and keep in a beaker in such a way that only cotton dips in water and not the bulb of thermometer • 4.Allow saturation to achieve and note down minimum temperature observed denoted as the wet bulb temperature. • 5. Calculate various parameters using humidity chart. • #Observation: • Dry bulb temperature=T1= .......°C..... °F(F=32+1.8°C) • Wet bulb temperature=T2= .......°C..... °F(F=32+1.8°C) • From humidity chart • Humidity (H)=____lb water vapour/ lb dry air • % RH..........% • #Calculation: • 1. Partial vapour pressure of water in air (Pa) • H=18 Pa/[29 (P-Pa)] • H is humidity value obtained from humidity chart • P=1 atm = 14.7 lbf /in2 • Calculate value of Pa by putting value of H and P • Pa=......Ibf /in2 • 2. Percentage humidity • %H 100 x Pa /Ps x (P-Ps) / (P-Pa) • P=1 atm= 14.7 lbf/ in2 • Use Pa value obtained from above calculation • Ps is partial pressure of water vapour in Saturation obtained using steam table by considering aiy • bulb temperature. • %H=............% • 3. Relative Humidity (HR) • HR=100 X Pa /Ps=........ % • Method :2 • Use of Dew point method • 1. Take a clean beaker. • 2.Fill it with water upto half of its volume • 3. Add crushed ice to water and stir it • 4.Note down the temperature as dew point when fogginess appeared outside the beaker. • 5. Calculate humidity by using humidity chart. • Observation and calculation • Dew point temperature=........°F • From humidity chart data • Humidity (H)=........Ib water vapour/lb dry air • #Result:........... • • You guys are amazing😍 • Keep Learning 📚 • Keep Growing 📈 • Stay Happy ☺ • Stay Blessed 😇 • Thank you so much for watching this video🙏 • #Makranipharmaacademy

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