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PSYCHROMETRICS

PSYCHROMETRICS. 1. The study of air and it’s properties A. Is called psychrometrics Air A. Has weight B. Occupies space 1) 1 ft 3 of air weighs a) 0.075 lb i. At standard atmospheric conditions. 3. Air offers resistance to movement

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PSYCHROMETRICS

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  1. PSYCHROMETRICS 1. The study of air and it’s properties A. Is called psychrometrics Air A. Has weight B. Occupies space 1) 1 ft3 of air weighs a) 0.075 lb i. At standard atmospheric conditions

  2. 3. Air offers resistance to movement A. Like a large piece of cardboard waved in the air 1. The larger the piece of cardboard the more resistance the air offers 4. Air has moisture in it A. Called humidity 1) Large amounts of moisture in air can be seen i. Clouds ii. Fog

  3. Psychrometric Chart • Used to plot the condition of air A. Relative Humidity B. Heat Content C. Wet-Bulb D. Dry-Bulb

  4. HUMIDITY • Humidity is measured by weight A. Expressed in pounds or grains 1) 7000 grains per pound B. 100% humid air at 29.92 in. hg. @ 70ºF 1) Can hold 110.5 gr. of moisture a. 0.01578 lb. per pound of air

  5. RELATIVE HUMIDITY • Based on the weight of water vapor in one pound of air A. Compared to the weight of water vapor a pound of air could hold if it were 100% saturated 1) 100% saturated air @ 70ºF holds 110.5 grains of moisture per pound a. 50 % saturated air will hold 55.25 grains @ the same temperature

  6. MOISTURE CONTENT • Checked by using a combination of temperatures A. Dry Bulb 1) The sensible – heat level of the air a. Taken with an ordinary thermometer B. Wet Bulb 1) Takes into account the moisture content in air a. Uses a wick on the sensing bulb i. Soaked with distilled water b. Can never be higher than the dry bulb temp c. Due to the evaporation of the distilled water

  7. USING THE CHART • Obtain wet-bulb and dry-bulb readings with a sling psychrometer • Plot the readings on the chart A. From these readings we can plot: 1) Dew Point 2) Total Heat Content of 1 lb of air 3) Moisture Content of 1 lb of air 4) Relative Humidity 5) Specific Volume of air

  8. 3. Using your book (Refrigeration Technology) A. Page 835 illustrates a psychrometric chart B. Page 836 illustrates a breakdown of the chart 1) Notice the directions the lines go for different conditions being plotted 4. Using the chart A. Locate 75ºF dry-bulb B. Locate 65ºF wet-bulb 1) Determine relative humidity 2) Determine grains of moisture

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