Convective heat coefficient (W/m2/oC)

Description

Calculates the convective heat coefficient for an object of known dimensions, and given various physical parameters.

Usage

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hconv(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). Required for free convection function call. 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 Gates, 2003). Default value is NULL, typical values is 0.24)

n

coefficient used in forced convection (see Gates, 2003). Default value is NULL, typical value is 0.6)

a

coefficient used in forced convection (see Gates, 2003). Default value is NULL, typical value is 1.

b

coefficient used in free convection (see Gates, 2003). Default value is NULL, typical value is 0.58 for upright cylinder, 0.48 for horizontal cylinder.

m

coefficient used in free convection. Default is NULL. For laminar flow, m=0.25

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

Calculates the convection coefficient for heat transfer estimation. Used in conjunction with known temperature differences in order to estimate heat transfer via convection. Bates advises to use "forced" convection coefficients down to 0.1 m/s as appropriate for very low air flow rates, rather than distinguishing between "free" and "forced" convection.

Value

A value corresponding to the convection coefficient, units: W/m/oC.

Author(s)

Glenn J Tattersall

References

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

Gates, DM. 2003. Biophysical Ecology. Dover Publications, Mineola, New York, 611 pp.

See Also

qconv

Examples

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## 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") 
{
    if (V == 0) 
        type <- "free"
    if (type == "forced" | type == "Forced") 
        Nu <- Nusseltforced(c = c, n = n, V = V, L = L, Ta = Ta, shape="hcylinder")
    if (type == "free" | type == "Free") 
        Nu <- Nusseltfree(a = a, b = b, m = m, L = L, Ts = Ts, Ta = Ta, shape="hcylinder")
    k <- airtconductivity(Ta)
    hconv <- Nu * k/L
    hconv
  }
  

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