Thread: fluid flow through two pipes

Simple really. Viscosity and velocity in a flowing fluid cause pressure differences between different points of the circuit therefore flow happens in that circuit. If water had no viscosity you would have perpetual motion. In the case of your heater circuit the heater core sets up a pressure difference between the two tees and the extra hoses simply allow more flow from the higher pressure to the lower. As soon as your water pump stops turning all flow stops as there is no longer any water velocity. That is why a loss of fan belt causes converters to ice up in short order and sometimes prevent an engine melt down.

soooo--
if the new hose has less pressure, will more water flow through it than the heater?

Originally Posted by Pedro_The_Swift

soooo--
if the new hose has less pressure, will more water flow through it than the heater?

I don't think you know what "pressure" means. The new pipes don't "have less pressure", they may or may not have a lower or higher pressure drop at a given flow rate. If you tested the pressure drop* as say 0.2 psi at 2 litres per second through the heater core and its pipes after the tee, and say 0.3 psi at 2 litres a second across the converter and its pipes from the tee, you would say that when connected together (ie the same pressure drop) it's likely that the converter circuit would flow less coolant than the heater. So your pressure drop in a pair of parallel circuits depends on the length of the hoses, the size of the passages in the converter or heater and any other obstruction in the hoses.

Practically, if your converter hose circuit is 6 inches long expect more coolant to flow through the converter, if it's 6 feet long expect the heater to get more. And as I mentioned a few posts ago, I once converted a P38 and had to add a restrictor to the converter circuit as it was mounted on the drivers side right next to the heater hoses. Yours is on the opposite side and the hoses are considerably longer than those to the heater.

I just found the picture I posted up way back in 2009



The converter on that one is just in front of the brake unit and has short hoses.

* To test pressure drop you could get a calibrated bucket, a garden tap and a pressure gauge at the inlet to the circuit. You'd assume zero pressure at the bucket. Nobody does so in the real world of course, this is just a thought experiment for the kiddies.

Hi
Why not put the convertor hoses in series with the heater hoses?
reasons for and against?
My gas convertor is in serires with the heater and I have never had a problem in 20 odd years with 2 Rangies and my daughters disco 1.
Rangie classic with flapper and omvl convertor
Brad

I had that brainstorm too Brad
but the man said it put too much coolant throught the reg,, would leave deposits or something?

I would, (now!) weigh that up against having 8 more joins in my cooling system!

Originally Posted by Bradtot

Hi
Why not put the convertor hoses in series with the heater hoses?
reasons for and against?
My gas convertor is in serires with the heater and I have never had a problem in 20 odd years with 2 Rangies and my daughters disco 1.
Rangie classic with flapper and omvl convertor
Brad

This is how i did my 2 rrc's , this makes it less likely to get an airlock and more likely to get a good flow of hot coolant thru the converter.

Sent from my GT-I9300 using AULRO mobile app

theres no simple answer to your question....

the implied answer is run the 2 heat exhcangers in series. the sequence depends on what you're trying to achieve.

if your heat echangers add heat to the cooling system then you put them in so the exhanger that adds the lesser amount is first in flow. IF you put it in the other way around then you may find the added heat from the first exhanger heats the coolant up to the point where the second exchanger doesnt get any heat transfer.

IF your taking heat out I recommend putting the one in the engine bay in last as you'll pick up some heat on the exhcanger from the heat radiating off of the engine.

if you're doing one addative and one subtractive... take your best guess. I generally route them up whichever way makes the hoses flow better.

The correct place to place the supply "T" to the converter is between the water pump and the heater core regulating valve.
If you connect the converter and heater core in series, when you (or the climate control) restricts hot water flow to the heater core, hot water flow to the heater converter is also restricted. This is not neccessarily what you want to achieve.