function [mu,kgas,re] = reynum(t,g,d)
% evaluate dynamic viscosity, thermal conductivity, Reynolds number
% Israel Urieli, 7/22/2002 (mu units correction 2/13/2011)
% Arguments:
%   t - gas temperature [K]
%   g - mass flux [kg/m^2.s]
%   d - hydraulic diameter [m]
% Returned values: 
%   mu - gas dynamic viscosity [kg/m.s]
%   kgas - gas thermal conductivity [W/m.K]
%   re - Reynolds number

global cp % specific heat capacity at constant pressure [J/kg.K]
global mu0 % dynamic viscosity at reference temp t0 [kg.m/s]
global t0 t_suth % reference temperature [K], Sutherland constant [K]
global prandtl % Prandtl number

mu = mu0*(t0 + t_suth)/(t + t_suth)*(t/t0)^1.5;
kgas = cp*mu/prandtl;
re = abs(g)*d/mu;
if (re < 1)
      re = 1;
end

function [ht,fr]=pipefr(d,mu,re);
% evaluate heat transfer coefficient, Reynolds friction factor
% Israel Urieli, 7/22/2002 (corrected header 2/20/2011)
% Arguments:
%   d - hydraulic diameter [m]
%   mu - gas dynamic viscosity [kg.m/s]
%   re - Reynolds number
% Returned values: 
%   ht - heat transfer coefficient [W/m^2.K]
%   fr - Reynolds friction factor ( = re*fanning friction factor)

global cp % specific heat capacity at constant pressure [J/kg.K]
global prandtl % Prandtl number

% Personal communication with Allan Organ, because of oscillating
% flow, we assume that flow is always turbulent. Use the Blasius
% relation for all Reynolds numbers:
fr=0.0791*re^0.75;
% From Reynolds simple analogy:
ht=fr*mu*cp/(2*d*prandtl);

function [st,ht,fr] = foilfr(d,mu,re)
% evaluate regenerator wrapped foil stanton number, friction factor
% Israel Urieli, 7/22/2002
% Arguments:
%   d - hydraulic diameter [m]
%   mu - gas dynamic viscosity [kg.m/s]
%   re - Reynolds number
% Returned values: 
%   st - Stanton number
%   ht - heat transfer coefficient [W/m^2.K]
%   fr - Reynolds friction factor ( = re*fanning friction factor)

global cp % specific heat capacity at constant pressure [J/kg.K]
global prandtl % Prandtl number

if (re < 2000) % normally laminar flow
      fr = 24;
else
      fr = 0.0791*re^0.75;
end
% From Reynolds simple analogy:
st=fr/(2*re*prandtl);
ht=st*re*cp*mu/d;

function [st,fr] = matrixfr(re)
% evaluate regenerator mesh matrix stanton number, friction factor
% Israel Urieli, 7/22/2002
% Arguments:
%   re - Reynolds number
% Returned values: 
%   st - Stanton number
%   fr - Reynolds friction factor ( = re*fanning friction factor)

global prandtl % Prandtl number
% equations taken from Kays & London (1955 edition)
st = 0.46*re^(-0.4)/prandtl;
fr = 54 + 1.43*re^0.78;