Thicker versus thinner radiator core 4

[JoshMalks]

The issue is the radiator in an antique automobile (1936 Cord). The size of the core is restricted by the grille shape, and air inflow is restricted by the hood shape. The original engineers opted for a 4" thick core to try to provide sufficient cooling capacity.

The car runs fine in 90% of use. Long hills or very slow traffic on hot days test its limits. A query by a member of our club to Harrison Radiator (GM) in the 1950s brought the response that the 4" core was needed to provide cooling at high speeds, but that its thickness reduced air flow thru it at lower speeds. They said that a 3" core would solve the cooling problem at low and medium speeds, but might be marginal at high speeds (over 70 mph).

Does this agree with current thought? Thanks. (And while we still drive our cars at highway speeds, we rarely exceed 70 )

 

[JoshMalks]

Thanks, Des. I knew they were thinner, but not that thin!

Since I'm told that turbulence in the tubes is important to optimum heat transfer, what do you folks think of dimpled radiator tubes to increase turbulence?

Thanks again.

 

[RossABQ]

The simplest thing to try would be to install a more agressive (mechanical) fan, possibly with a thermal clutch (depends on room available). Don't use a flex-fan. Get one for a Ford truck, early '50's, they move a bunch of air.

 

[daubery]

JoshMalks wrote:
Since I'm told that turbulence in the tubes is important to optimum heat transfer, what do you folks think of dimpled radiator tubes to increase turbulence?

desA replies:
For a US/Euro radiator (horizontal tubes), the fluid velocity in the tubes is generally designed to have turbulent flow.

The Japanese split the fluid flow over many more tubes (vertical tubes). They also use fairly small water pumps. This means that the water flow velocity inside each tube is low-enough to end up with laminar flow conditions within the tubes. Dimpled tubes are then often used (or turbulators) to mechanically mix the internal fluid & push up the effective heat transfer.

Using dimpled tubes in typical US/Euro design will - already turbulent, in general, not provide much advantage - if any.

In most radiators, the airside heat-transfer coefficient dominates heat transfer (80%) & so any change to the water-side only contributes a very small advantage, if any.



Des Aubery...
(adTherm Technology)

 

[JoshMalks]

Des Aubery wrote:
"In most radiators, the airside heat-transfer coefficient dominates heat transfer (80%) & so any change to the water-side only contributes a very small advantage, if any."

I'll work on the airflow issues, and thank you for the input. (Are louvered fins useful?)

But in addition. . . my car is a 70-year old American one with vertcal tubes. Might it not suffer from laminar flow which could be helped by dimpled tubes?

Thanks.

 

[daubery]

That is a strong possibility. The current water volume flow range for a radiator is typically 40 - 80 litre/min for Japanese vehicles. If you know that number of tubes in your radiator, you could work out the tubeside velocity.

Reynolds number: Re = density*velocity*Dh/viscosity

where: Dh = 4*Ac/P = hydraulic diameter

Ac = tube cross-sectional area
P = tube wetted perimeter

If Re < 2350, then you have laminar flow.

If you do have a laminar flow situation, then dimpled tubes could very likely be of use. Give the calculations a whirl & feed back on what Reynolds number you find. Use the lower accepted water flowrate of 40 l/min as a benchmark.



Des Aubery...
(adTherm Technology)