#' Calculate the convective heat tranfer coefficient for flow around a sphere.
#'
#' Calculate the convective heat tranfer coefficient for flow around a sphere.
#'
#' @param diam.globe diameter of the sphere in m.
#' @inheritParams h_cylinder_in_air
#'
#' @return Convective heat tranfer coefficient for flow around a sphere, W/(m2 K).
#'
#' @author Ana Casanueva (05.01.2017).
#' @details Reference: Bird, Stewart, and Lightfoot (BSL), page 409.
h_sphere_in_air <- function(Tk, Pair, speed, min.speed, diam.globe){
# Constants
m.air <- 28.97
r.gas <- 8314.34
r.air <- r.gas / m.air
cp <- 1003.5 # heat capaticy at constant pressure of dry air
Pr <- cp / (cp + 1.25 * r.air)
# Calculate the thermal conductivity of air, W/(m K)
therm.con <- thermal_cond(Tk)
# Density of the air
density <- Pair * 100 / (r.air * Tk)
if(speed < min.speed) speed <- min.speed
# Reynolds number
Re <- speed * density * diam.globe / viscosity(Tk)
# Nusselt number
Nu <- 2 + 0.6 * Re ^ 0.5 * Pr ^ 0.3333
# Convective heat tranfer coefficient for flow around a sphere, W/(m2 K)
h_sphere_in_air <- Nu * therm.con / diam.globe
return(h_sphere_in_air)
}
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