Teq {Thermimage}

Estimates equivalent temperature.

Description

Estimates equivalent black-body temperature of an object. Analagous to other measures of operative temperature

Usage

Teq(Ts = 30, Ta = 25, Tg = NULL, RH = 0.5, E = 0.96, rho = 0.1, cloud = 0, SE = 0, V = 1, 
L = 0.1, type = "forced")

Arguments

Ts

Surface temperature (degrees Celsius). Default value is 30. Not used in this calculation but kept for similar structure to other functions in package.

Ta

Air temperature (degrees Celsius). Default value is 20. Used to estimate ground temperature if Tg is unavailable.

Tg

Ground temperature (degrees Celsius). Default value is NULL, but a measured Tg can be substituted or estimated with other functions. Used in estimating long wave radiation from the ground.

RH

Relative humidity (fraction 0 to 1). Default value is 0.5. Used in call to Ld() to determine incoming radiation.

E

Emissivity (fraction 0 to 1) of the object absorbing longwave radiation. According to Kirschoff's law, emissivity = absorptivity. Absorptivity is multiplied by the average of the incoming longwave radiation to estimate absorbed radiation.

rho

Reflectivity (fraction 0 to 1) of the object absorbing solar radiation. Used to modify absorbed solar energy. Default is 0.1.

cloud

Fractional cloud cover (fraction from 0 to 1). Used in call to Ld() to determine incoming radiation. Default is 0.

SE

Solar energy (W/m2), usually measured. Default is 100.

V

Air velocity (m/s). Default value is 1.

L

Characteristic dimension (m) of object. Usually the vertical dimension (i.e. height). Default value is 1.

type

"forced" or "free" - to calculate convection coefficient for either forced or free convection. Default value is "forced"

Author(s)

Glenn J Tattersall

References

Mahoney, S.A. and King, J. R. (1977). The use of the equivalent black-body temperautre in the thermal energetics of small birds. J Thermal Biol. 2: 115-120

Examples

## The function is currently defined as
function (Ts = 30, Ta = 25, Tg = NULL, RH = 0.5, E = 0.96, rho = 0.1, 
    cloud = 0, SE = 0, V = 1, L = 0.1, type = "forced") 
{
    if (type == "forced") 
        k <- 0.7 * 310
    if (type == "free") 
        k <- 310
    rr <- airdensity(Ta) * airspecificheat(Ta)/(4 * E * StephBoltz() * 
        (Ta + 273.15)^3)
    ra <- k * (L/V)^0.5
    re <- 1/(1/ra + 1/rr)
    Rni <- qabs(Ta = Ta, Tg = Tg, RH = RH, E = E, rho = rho, 
        cloud = cloud, SE = SE) - StephBoltz() * E * (Ta + 273.15)^4
    Teq <- Ta + Rni * re/(airdensity(Ta) * airspecificheat(Ta))
    Teq
  }
  
# For detailed examples and explanations, see:
# https://github.com/gtatters/Thermimage/blob/master/HeatTransferCalculations.md