MEP Chapter 9
A grain is the unit measure that equals ______ lb.
1/7000
___ air does not contain moisture or particles.
Dry
Enthalpy is expressed in ____.
Heat
A certain quantity of heat is required to change water (liquid) into water vapor (gas). T or F?
True
On a chart for standard conditions, humidity ration begins at 0 lb of moisture per pound of dry air and increases to about ____ lb of moisture per pound of dry air.
0.03
One pound of dry air and its associated moisture at standard conditions has a pressure of _____ Hg.
29.92
Air at a relative humidity of 46% holds __% of the moisture it can hold at the same temperature if it were saturated.
46
Relative humidity is __% at the saturation line.
55
Air enters a furnace at a dry bulb temperature of ___F and 50% relative humidity and leaves the furnace at a dry bulb temperature of 94F.
75
___ __ ___ _____ directly relates to the amount of moisture in the air.
All of the above
___________ air is the mixture of dry air, moisture, and particles.
Atmospheric
If the dry bulb volume temperature decreases, the specific volume will _________.
Decrease
Wet bulb depression is the difference between wet bulb ___ ____ temperature readings.
Dry bulb
___ ____ ___________ is the measurement of sensible heat.
Dry bulb temperature
A change in both dry bulb and wet bulb temperatures affects ________.
Enthalpy
A change in dry bulb temperature indicates a change in latent heat. T or F?
False
A change in one property of air has no effect on the other properties. T or F?
False
A change in the dry bulb temperature of air does not change the relative humidity of the air. T or F?
False
A psychrometer measures the enthalpy of the air. T or F?
False
Any psychrometric chart may be used to find the properties of air at all atmospheric conditions and air pressures. T or F?
False
As the humidity ratio decreases, the latent heat content of the air increases. T or F?
False
Dew point is the temperature above which moisture in the air begins to condense. T or F?
False
Horizontal lines on a psychrometric chart indicate the dry bulb temperature of the air. T or F?
False
On a chart for standard conditions, the scale begins at about 30 degrees F and increases to about 100 degrees F. T or F?
False
The final condition of air during a mixing process cannot be determined using a psychrometric chart. T or F?
False
The volume of air increases as air cools. T or F?
False
The properties of cool air are found by locating the _____ __________ ___ _______ _________ of air on the chart and identifying the appropriate properties of the air at each point.
Final condition and initial condition
_______ ________ is the point that represents the properties of air before it goes through a process.
Initial condition
______ heat is identified by the amount of water vapor in the air.
Latent
_______ heat is identified by a change of state and no temperature change.
Latent
Wet bulb temperature readings indicate the amount of ________ __ ___ ___.
Moisture in the air
When moist air is heated, sensible heat is added and there is __ change in humidity.
No
Humidity ratio is expressed in grains per pound or ______ of moisture per pound of dry air.
Pounds
A ____________ is an instrument used for measuring humidity that consists of a wet bulb and a dry bulb thermometer mounted at a base.
Psychrometer
Humidity can be measure with a ____________ __ __________.
Psychrometer or hygrometer
A ____________ _____ is a chart that defines the condition of air at various properties.
Psychrometric chart
Engineers and air conditioning technicians use _____________ ______ to define properties of moist air during processes that change the properties of air.
Psychrometric charts
Humidity is expressed as _________ _________ __ ________ ______.
Relative humidity or humidity ratio
Enthalpy is the sum of latent and ________ heat.
Sensible
________ ______ is the volume of a substance per unit of the substance.
Specific volume
_________ __________ are values used for comparing properties of air at different elevations and pressures.
Standard conditions
A change in the wet bulb temperature of air indicates a change in the moisture content. T or F?
True
A change in wet bulb temperature changes the humidity ratio and relative humidity of the air. T or F?
True
A psychrometric chart can be used to determine the amount of water that should be added to the air in a building to increase the relative humidity of the air. T or F?
True
If any two properties are known in a psychrometric chart, the others can be found by locating the point defined by those properties. T or F?
True
If two properties of air are known, the others can be found on a psychrometric chart. T or F?
True
On a psychrometric chart, the vertical lines identify the dry bulb temperature of the air at a given point. T or F?
True
The hygrometer senses the amount of electricity conducted and gives a reading based on that amount. T or F?
True
The two properties used most often for identifying specific conditions of the air are temperature and humidity. T or F?
True
______ is the amount of space occupied by a three dimensional figure.
Volume
