The flow of mass, heat energy and charge
Comparison of the equations for
the transfer of mass, heat energy and charge show that they are all of basically the same form,
that is:
The flow rate is proportional to:
[the pressure causing flow]/[the resistance to flow]
The three specific
equations are:
(a) Mass flow rate = [p
pr
4]/8
hL = Δp/R
M
where R
M is a constant containing the viscosity, which is the resistance to the
flow of the fluid.
(b) Heat flow rate = [ - kA(θ
1-θ
2)]/x = Δθ/R
H
where R
H is a constant containing the inverse of thermal conductivity,
which is the resistance to the flow of heat energy.
(c) Charge flow rate = [V
2
– V
1]/ R
Ewhere R
E is the electrical resistance of the
conductor.
Viscosity and temperature
Student
investigation
The variation of viscosity with temperature may be studied by the
following experiment.
The ease with which a liquid may be stirred at a given rate depends on
the viscosity of the liquid and therefore the difficulty of stirring treacle will vary with
temperature.
Set up the apparatus as shown in Figure 1 and record the power that
must be applied to the motor to maintain a steady stirring rate as the treacle is slowly
heated.
Plot a graph of power against temperature. If possible suggest a form for the
equation of the variation of power with temperature.
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