Nusseltfree {Thermimage}

Nusselt number for free convection.

Description

Nusselt number for free convection. Used in calculating heat loss by convection.

Usage

Nusseltfree(a=NULL, b = NULL, m = NULL, L = 0.1, Ts = 25, Ta = 20, shape="hcylinder")

Arguments

a

Coefficient used in calculating Nu. a is normally 1, except for turbulent flow.

b

Coefficient used in calculating Nu. b is 0.58 for upright cylinders, 0.48 for horizontal cylinders.

m

Coefficient used in calculating Nu. m=0.25 for laminar flow.

L

Characteristic dimension in metres.

Ts

Surface temperature in degrees celsius. Used in call to Grashof() function.

Ta

Air temperature in degrees celsius. Used in call to Grashof() function.

shape

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

Author(s)

Glenn J Tattersall

References

Blaxter, K. 1989. Energy Metabolism in Animals and Man Gates, DM. 2003. Biophysical Ecology. Dover Publications, Mineola, New York, 611 pp.

Examples

## The function is currently defined as
function (a=NULL, b = NULL, m = NULL, L = 0.1, Ts = 20, Ta = 20) 
{
    Nu <- b * (Grashof(L, Ts, Ta)*Prandtl(Ta)^a)^m
    Nu
  }

# Nusselt number for free convection
# Example calculation:

a<-1
b<-0.58
m<-0.25
L<-1
Ts<-30
Ta<-20
Nusseltfree(a,b,m,L,Ts,Ta)


# Free convection is higher when surface temperatures are elevated.  This is the effect
# that free convection predicts: greater molecular energy of air surrounding a warmer surface
# leading to air currents over top of a warm surface.

Ts<-40
Nusseltfree(a,b,m,L,Ts,Ta)