Richard F Flynn wrote:
> How would one go about or What is the best way to measure the temperature drop
> across a radiator? I've seen some old Rootes reports that had such data and
> I've wondered how they did that sort of thing at speed.
>
> Its just another cooling mystery to me . . .
>
> rick
Rick,
Well, you asked!
The usual method of measuring temperature involves a temperature sensing element
in contact with the media to be measured, and a read-out device to determine the
signal output.
In the case of the radiator, one might wish to know the rise in the temperature
of
the air, or water passing through the radiator. As Bob Palmer has pointed out,
the temperature difference in the water entering and leaving a well performing
radiator will be nearly the same, but the heat removed would be significant. To
measure heat changes (as opposed to 'temperature') you need flow rates and fluid
parameters. Air, coolant are both considered 'fluids', in this discussion.
Surface temperatures are equally determinable by these techniques, as well.
The "drop in temperature" is really the result of two measurements. The
temperature of the fluid (air or water) on one side, and on the exit side. The
difference between these two readings would be the "drop", so actually two
readings need be taken at the same time, and condition. There are systems
designed to use dual sensors and read-out the difference, but two sensors in any
event.
The simplest sensor is a bi-metallic coil with one end fixed and the other
rotating a needle. These are direct reading, low accuracy, and require
simultaneous visual observation. Not very practical.
A bulb of fluid attached to a fine, evacuated capillary tube is a direct contact
device. It is usually called a 'thermometer' and can be found in Doctor's lab
jackets, and various human body orifices. Sometimes, it is a BIC pen, in which
case, you'd want a different doctor, if it weren't in his pocket!
The next step up would be a resistor of known value immersed in the fluid, a
controlled voltage source, and an electric voltmeter. The system must be
calibrated with known temperatures to make the reading accurate, and two are
required to get a differential measurement. This is the system you now have on
your car for Water Temperature.
A more accurate sensor would be a thermocouple. This consists of two fine
wires,
of dissimilar metals, that are welded together at a "sensing tip".
Iron-Constintan
and Chromel-Alumel are used, depending on the temperature range. They are
connected to a "bridge circuit" of three accurate resistors, and a calibrated
voltmeter is used to 'read' temperature. Dissimilar metals actually generate
their own voltage with temperature change, and have been used as power supplies
for small devices.
Another sensor element is a "thermistor", which is made for specific temperature
ranges, is a solid state device, and requires an electronic circuit to read the
changes. The system must be calibrated.
This is probably much more than you ever wanted to know, but your wife's oven
thermometer (bi-metalic coil) is probably not what you want.
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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