Unit 27 - Chapter 125 Flashcards
Dalton’s law of partial pressure states that
In a mixture of two or more gases each will exert a partial pressure which is equal to the pressure that it would exert if it filled that space alone
Air is what composition by volume?
79% nitrogen and 21% oxygen
Relative humidity is
The ratio if water vapour in the air compared to the total amount water vapour the air could contain at a given temperature
The dew point is the
Temperature below which water vapour will start to condense out of the air
The volume of standard air is
0.833 kg/cubic meters of dry air
The heat content of air is called the
Enthalpy of the air
Psychrometry is
The study of behaviour of mixtures of air and water
The composition of pure dry air is
23.2% oxygen and 76.8% nitrogen by weight
Air conditioning involves
The control of the air temperature, the control of humidity, air circulation, an the removal of contaminants
The term relative humidity applies to
The percentage of moisture in the air compared to the amount of moisture the air can hold at a specific temperature
A device for measuring relative humidity is called
A psychrometer
The difference between the wet and dry bulb readings is called the
Wet bulb depression
Which law describes the existence of moisture in the air in vapour or evaporated state?
Dalton’s law of partial pressure
Absolute or specific humidity is
The actual mass of moisture present in a specific amount of air
Relative humidity is
The ratio of the mass of moisture contained in a specific amount of air to the maximum amount of moisture this specific amount of air can contain
Dew point can best be described as
The temperature at which air, upon cooling, becomes saturated and will begin to condense out water vapour below this temperature
Dry bulb temp is
The temp of air measured with an ordinary thermometer
Wet bulb temp is
The temperature indicated by a thermometer having its bulb covered by a water wetted wick or cloth and the wet bulb is exposed to a rapidly moving stream of air
What is wet bulb depression?
Difference between dry bulb and wet bulb temperature
Psychrometers are
Instruments used to determine relative humidity of air
Which of the following instruments use a battery operated fan to draw air over the thermometer bulbs?
Aspiring psychrometer
The specific volume of air is
The volume of 1 kg of air at atmospheric pressure expressed in cubic meters
Standard air is
The volume of 1 kg of dry air at 21 degrees and at atmospheric pressure
Enthalpy of air depends on
Pressure, temp, and relative humidity of air
To find various properties of air
Use a psychrometric chart
Enthalpy of air is measured in
KJ/kg of dry air
The dry bulb temp scale is read in a psychrometric chart
Along the horizontal axis on the bottom of the chart
The wet bulb temp scale is read in a psychrometric chart
Along the saturation line and slope downward to the right
The dewpoint temp scale is read in a psychrometric chart
Along the horizontal line, same scale as wet bulb temperature but plotted along horizontal lines
Relative humidity is read in a psychrometric chart
On lines curved upwards from the lower left to the right side of the chart
Specific humidity is
The actual moisture content of air expressed as kg of moisture per kg of dry air
Specific humidity scale is read in a psychrometric chart
Along the vertical axis of the chart and right side of chart
Specific volume is read in a psychrometric chart
Has its lines originate on the volume scale along the horizontal axis and they slope steeply upwards to the left of the chart
Enthalpy values are found on a psychrometric chart by
Plotting a line through the required point on the chart parallel to the lines of the two Enthalpy scales scales, one on the left side and one on the right side of the chart
