Module 4: Psychrometry Flashcards
the study of the properties of mixtures of air and water vapor
psychrometry
air and water vapor at diff conditions affects the product during drying and storage operations
true or false
true
it is a binary mixture of dry-air and low-pressure water vapor
moist air
components of dry-air
- nitrogen
- oxygen
- argon
- carbon dioxide
- rare gases
for pure substances, two properties are sufficient, while for binary mixtures, three properties are needed to completely define their state
true or false
true
the major physical properties of air that affect the drying rate of grains are
- RH or humidity ratio
- dry-bulb & wet-bulb temperature
- specific volume
- enthalpy
- dew point temp
physical properties of air that affect the drying rate of grains
measured by the ordinary thermometer
dry bulb temp
physical properties of air that affect the drying rate of grains
dry bulb temp is the horizontal lines in the chart
true or false
false; it’s the vertical lines
physical properties of air that affect the drying rate of grains
air temp measured by an ordinary thermometer whose glass bulb is covered by a wet cloth or gauze
wet bulb temp
physical properties of air that affect the drying rate of grains
air temp at which moisture condenses at the surface
dewpoint temp
physical properties of air that affect the drying rate of grains
scale is the same as the wet bulb scale which is on the face of the shoe
dewpoint temp
physical properties of air that affect the drying rate of grains
dewpoint temp are lines parallel to the x axis
true or false
true
physical properties of air that affect the drying rate of grains
amount of water vapor per unit dry air
absolute humidity
physical properties of air that affect the drying rate of grains
y-axis or the ordinate (the back of the shoe)
absolute humidity (or HR)
physical properties of air that affect the drying rate of grains
relative humidity and dew points are at the same lines
true or false
false; dew point temp are the horizontal lines while RH are the lines sloping upwards
physical properties of air that affect the drying rate of grains
lines are the same as the dew point temp lines
absolute humidity
physical properties of air that affect the drying rate of grains
ratio of partial pressure of water vapor to the saturation pressure of pure water at the same temperature
relative humidity
physical properties of air that affect the drying rate of grains
face of the shoe
relative humidity
physical properties of air that affect the drying rate of grains
defined as the volume occupied by a kilogram of dry air
specific volume
physical properties of air that affect the drying rate of grains
these are the diagonal lines having a higher slope compared to wet bulb lines
specific volume
physical properties of air that affect the drying rate of grains
heat content of the air (denoted by h)
enthalpy
physical properties of air that affect the drying rate of grains
it is essential in the calculation of the energy requirement of any process involving air a the medium
enthalpy
_______ ______: cubic meter/kg dry air
enthalpy : ___________
specific volume: cubic meter/kg dry air
enthalpy : kilo Joules/kg
psychrometric processes
- sensible heating or cooling
- humidification
a. adiabatic humidification
b. non adiabatic humidification - cooling and dehumidification
a. moisture condensation
psychrometric processes
involves the increase or decrease in the air temp without changing its humidity ratio
sensible heating or cooling
psychrometric processes
sensible heating or cooling is a process that’s depicted as a horizontal line in the chart extended to the _______ for sensible heating and to the _______ for cooling
right; left
psychrometric processes
process of adding water to the air
humidification
psychrometric processes
on heat exchange with surroundings, constant wet bulb temperature, dry bulb temperature decreases
adiabatic humidification
psychrometric processes
heat is added, net heat added is positive, dry bulb temperature can increase along with moisture content
non adiabatic humidification
psychrometric processes
decrease in dry bulb temp and HR
cooling and dehumidification
psychrometric processes
cooling and dehumidification, the total heat removed is equal to the total heat removed in the ________ ____
cooling coil
this principles is referred as the refrigeration capacity
psychrometric processes
occurs when moist air is cooled to a temperature below its initial dew point
moisture condensation
is the process where ambient air is heated to a desired drying temperature at a constant humidity and vapor pressure
heating
process where the temperature of the heated air decreases during drying, approaching 100% RH and constant wet bulb temp
cooling
where are psychrometric principles applied?
- load calculations
- air-conditioning systems
- cooling and dehumidifying coils
- cooking towers
- evaporative condensers
component of moisture air consisting of composition of gases
dry-air
component of moisture air which is a very low-pressure steam, the amount of which could vary from zero to a mac value for a given pressure and temp
water-vapor
major physical properties of air that affect the drying rate of grains
- RH
- dry-bulb temp
- specific volume
- enthalpy
refers to the mole fraction of water vapor in moist air to the mole fraction of water vapor in saturated air at the same temperature and pressure
relative humidity
process by which the wet-bulb thermometer cools due to water evaporation
evaporative cooling
knowing both the dry-bulb and wet-bulb temperatures allows you to determine the ______ _______ of the air using a psychrometric chart
relative humidity
________ ______ of the drying air affect the power required by the fan
specific volume
enthalpy of the mixture of dry air and water vapour is the sum of the enthalpy of the dry air and the enthalpy of the water vapour
true or false
true
the zero value of the water vapour is saturated liquid water at __ degree Celsius, this is the same reference point used for steam
0
