Chapter 9
on a chart for standard conditions, humidity ratio 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
a grain is the unit of measure that equals ___ lb
1/7000
relative humidity is ___% at the saturation line
100%
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
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 94 F
75
enthalpy is expressed in ____
BTU per lb
____ air is the mixture of dry air, moisture, and particles
atmospheric
if the dry bulb volume temperature decreases, the specific volume will ____
decrease
___ air does not contain moisture or particles
dry
wet bulb depression is the difference between wet bulb and ___ 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
false
a change in one property of air has no effect on the other properties
false
a change in the dry bulb temperature of air does not change the relative humidity of the air
false
a psychrometer measures the enthalpy of the air
false
any psychrometric chart may be used to find the properties of air at all atmospheric conditions and air pressures
false
as the humidity ratio decreases, the latent heat content of the air increases
false
dew point is the temperature above which moisture in the air begins to condense
false
horizontal lines on a psychometric chart indicate the dry bulb temperature of the air
false
on a chart for standard conditions, the scale begins at about 30 F and increases to about 100 F
false
the final condition of air during a mixing process cannot be determined using a psychrometric chart
false
the volume of air increase as air cools
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 a ___ change in humidity
no
humidity ratio is expressed in grains per pound or ___ of moisture per pound of dry air
pounds
humidity can e measured with a ____
psychrometer or hygrometer
a ___ is a chart that defines the condition of air at various properties
psychrometric
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
a ___ is an instrument used for measuring humidity that consists fo a wet bulb and a dry bulb thermometer mounted on a base
sling psychrometer
___ 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 certain quantity of heat is required to change water (liquid) into water vapor (gas)
true
a change in the wet bulb temperature of air indicates a change in the moisture content
true
a change in wet bulb temperature changes the humidity ratio and relative humidity of the air
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
true
if any two properties are known in a psychrometric chart, the others can be found by locating the point defined by those properties
true
if two properties of air are known, the others can be found on a psychometric chart
true
on a psychrometric chart, the vertical lines identify the dry bulb temperature of the air at a given point
true
the hygrometer senses the amount of electricity conducted and gives a reading based on that amount
true
the two properties used most often for identifying specific conditions of the air are temperature and humidity
true
____ is the amount of space occupied by a three-dimensional figure
volume
____ directly relates to the amount of moisture in the air
wet bulb temperature humidity ratio relative humidity
