Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Latent Heat Flow

Latent heat is the heat when supplied to or removed from air results in a change in moisture content - the temperature of the air is not changed.

Latent Heat Flow - English (Imperial) units

The latent heat flow due to moisture in air can be expressed in English (Imperial) units as

Q l = 60 h we ρ q Δx                                   (1)

where

Q l = latent heat flow (Btu/hr)

h we = 1060 - latent heat of vaporization of water (Btu/lb)

ρ = 0.075 - air density at standard conditions (lb/ft 3 )

q = measured air flow (ft 3 /min)

Δx = difference in humidity ratio (lb h2o /lb dry_air )

Latent Heat Flow - SI-Units

The latent heat flow due to moisture in air can be expressed in SI-units (metric) as

Q l = h we ρ q Δx / 3600                                  (2)

where

Q l = latent heat flow (kW)

h we = latent heat of vaporization of water ( 2454 kJ/kg - in air at atmospheric pressure and 20 o C)

ρ = air density at standard conditions ( 1.202* kg/m 3 )

q = air flow (m 3 /hr)

Δx = difference in humidity ratio ( kg h2o /kg dry_air )

*Note that properties of air changes with temperature. Interpolate values if necessary.

Example - Latent Heat Flow

A ventilation system transports 10000 m 3 /h of air through a building.

The state of the make-up (supply) air is 0 o C and 100% relative humidity. From the Mollier diagram the humidity ratio - x - can be estimated to 0.0037 ( kg h2o /kg dry_air ) .

The state of the room air is 20 o C and 40% relative humidity. From the Mollier diagram the humidity ratio can be estimated to 0.0057 ( kg h2o /kg dry_air ) .

The latent heat flow can be calculated as

Q l = (2465.56 kJ/kg) (1.202 kg/m 3 ) (10000 m 3 /h) (( 0.0057 (kg h2o /kg dry_air ) ) - ( 0.0037 ( kg h2o /kg dry_air ) )) / 3600

= 16.5 kW

Related Topics

• Air Psychrometrics

Moist and humid air - psychrometric charts, Mollier diagrams, air-condition temperatures and absolute and relative humidity and moisture content.

Related Documents

• Air - Density, Specific Weight and Thermal Expansion Coefficient vs. Temperature and Pressure

Online calculator, figures and tables showing density, specific weight and thermal expansion coefficients of air at temperatures ranging -100 to 1600 °C (-140 to 2900 °F) at atmospheric and higher pressure - Imperial and SI Units.
• Air - Humidity Ratio

The mass of water vapor present in moist air - to the mass of dry air.
• Air Heating Systems

Air heating buildings - heat supply vs. air flow and temperature.
• Cooling and Heating Equations

Latent and sensible cooling and heating equations - imperial units.
• Cooling Load - Latent and Sensible Heat

Latent and sensible cooling loads to consider when designing HVAC systems.
• Great Sensible Heat Factor - GSHF

The Great Sensible Heat Factor is the ratio sensible to total heat in a cooling coil.
• Heat Recovery Efficiency

Classification of heat recovery efficiencies - temperature efficiency, moisture efficiency and enthalpy efficiency - online heat exchanger efficiency calculator.
• Humid Air - Heating

Enthalpy change and temperature rise when heating humid air without adding moisture.
• Liquids - Latent Heat of Evaporation

Latent heat of vaporization for fluids like alcohol, ether, nitrogen, water and more.
• Melting and Boiling Temperatures - Evaporation and Melting Heats common Materials

Melting and boiling point temperatures, latent heat of evaporation, and melting heat of common substances like copper, gold, lead and more - SI units.
• Moist Air - Enthalpy

Sensible and latent heat of moist air.
• Propane - Latent Heat of Vaporization vs. Temperature

Latent heat with vaporized propane.
• Removing Heat with Air

Calculating heat removed with air by measuring the wet bulb temperature.
• Room Sensible Heat Factor - RSHF

Room Sensible Heat Factor - RSHF - is defined as the sensible heat load divided by the total heat load in a room
• Saturated Steam - Properties - Imperial Units

Steam table with sensible, latent and total heat, and specific volume at different gauge pressures and temperatures.
• Saturated Steam - Properties for Pressure in Bar

Saturated Steam Table with properties like boiling point, specific volume, density, specific enthalpy, specific heat and latent heat of vaporization.
• Sensible Heat Flow

Sensible heat is dry heat causing change in temperature but not in moisture content
• Sensible Heat Ratio - SHR

The ratio Sensible Heat (or Cooling) Load to the Total Heat (or Cooling) Load.
• Steam and Vapor Enthalpy

Vapor and steam enthalpy, specific enthalpy of saturated liquid, saturated vapor and superheated vapor.
• Water - Thermophysical Properties

Thermal properties of water at different temperatures like density, freezing temperature, boiling temperature, latent heat of melting, latent heat of evaporation, critical temperature and more.

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

We don't collect information from our users. More about

Citation

• The Engineering ToolBox (2004). Latent Heat Flow. [online] Available at: https://www.engineeringtoolbox.com/latent-heat-flow-d_703.html [Accessed Day Month Year].

Modify the access date according your visit.

12.8.9