have you taken thermodynamics and heat transfer classes?
for one, the faster the fluid flows the higher the rate of convective heat transfer so that's probably why it is preferable to have a high flow rate, this is called forced convection.
also the pressure being 5 bar prevents the water from boiling at 100C, in fact it can reach 151C before boiling which is preferable since the vapor has a half the specific heat capacity (see previous post)
Temperature (T) 151.9 C
Pressure (P) 5.0000 bar
personally, (although i have not done alot of heat exchanger problems yet) i do not think the problem is with the water not being able to transfer heat, but rather exchange that heat with the outside air.
- convective heat transfer from the water to the inside radiator surface
- conduction through the inside radiator surface to the outside surface
- convective heat transfer from the outside radiator surface to the outside air
i'm pretty sure that the limiting value is the heat transfer to the outside air, lets see:
the equations:
dQ/dt = rate of heat tranfer
h = convective heat transfer coefficient
A = area
L = material thickness
DT = temperature difference
- convection (inside): dQ/dt = h*A*DT
obviously, water is ideal here because of it's specific heat capacity,
* h_Water - 500 to 10 000 W/m2K
- conduction: dQ/dt = k*A*DT/L
*k_silver = 429 W/m*K
*k_copper = 401 W/m*K
*k_aluminum 221 W/m*K
thin silver tubing is ideal, but probably has bad mechanical properties at high temperatures and pressures (not sure though)
- convection (outside): dQ/dt = h*A*DT
* h_Air - 10 to 100 W/m2K
Yup, definitely looks like convection to the outside air is the bottleneck here, depending on flow conditions it's between 100-1000 times worse than water at transferring heat.
I love to love Senna.
