qconv {Thermimage}

Estimates the area specific heat transfer by convection (W/m2)

Description

Estimates heat transfer by convective heat exchange, using the heat transfer coefficient estimate, surface temperature, and air temperature. Positive value = heat gain from air to object. Negative value = heat loss from object to air.

Usage

qconv(Ts = 30, Ta = 20, V = 1, L = 0.1, c = NULL, n =NULL, a=NULL, b = NULL, m = NULL, 
type = "forced", shape="hcylinder")

Arguments

Ts

Surface temperature (degrees celsius). Default value is 30.

Ta

Air temperature (degrees celsius). Default value is 20.

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 0.1.

c

coefficient used in forced convection (see Blaxter, 1986, default value is 0.24). see forcedparameters() for details.

n

coefficient used in forced convection (see Blaxter, 1986, default value is 0.6). see forcedparameters() for details.

a

coefficient used in free convection (see Gates, 2003. default value is 1). see freeparameters() for details.

b

coefficient used in free convection (0.58 upright cylinder, 0.48 flat cylinder, default value is 0.58). see freeparameters() for details.

m

coefficient used in free convection (0.25 laminar flow, default value is 0.25). see freeparameters() for details.

type

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

shape

"sphere", "hplate", "vplate", "hcylinder", "vcylinder" to denote shape and orientation. h=horizontal, v=vertical. Default shape is "hcylinder"

Details

Estimates an area specific rate of heat transfer (W/m2), where a negative value depicts heat loss from surface to air, while positive value depicts heat gain from air to surface. Uses the gradient in temperature (Ta minus Ts) multiplied by a convection coefficient to estimate heat transfer from a surface. Designed for estimating steady state heat exchange from animal surfaces using thermal images.

Author(s)

Glenn J Tattersall

References

Blaxter, 1986. Energy metabolism in animals and man. Cambridge University Press, Cambridge, UK, 340 pp.

See Also

hconv, forcedparameters, freeparameters

Examples

## The function is currently defined as
function (Ts = 30, Ta = 20, V = 1, L = 0.1, c = NULL, n = NULL, a=NULL,
    b = NULL, m = NULL, type = "forced", shape="hcylinder") 
{
    qconv <- (Ta - Ts) * hconv(Ta = 20, V = 1, L = 0.1, c = NULL, n = NULL, a=NULL,
    b = NULL, m = NULL, type = "forced", shape="hcylinder")
    qconv
  }

# Example:
Ts<-30
Ta<-20
V<-1
L<-0.1
type="forced"
shape="hcylinder"

qconv(Ts=Ts, Ta=Ta, V=V, L=L, type=type, shape=shape)

qconv(Ts=Ts, Ta=Ta, V=V, L=L, type=type, shape="sphere")

# For detailed examples and explanations, see:
# https://github.com/gtatters/Thermimage/blob/master/HeatTransferCalculations.md