# UnitSimplify returns unexpected non-SI unit combination

I am trying to get units working in mathematica in the following expression for diffusion:

$D = {K_B T}/{3 \pi \eta L}$

My code is as follows:

KB = Quantity[1.380650*10^-23, ("Meters")^2*"Kilograms"*("Seconds")^-2*("Kelvins")^-1];
T = Quantity[20 + 273.15, "Kelvins"];
eta0 = Quantity[8.9*10^-4, "Pascals"*"Seconds"];
L = Quantity[200*10^-9, "Meters"];

D = (KB*T)/(3*Pi*eta0*L)


This evaluates to:

$2.41258\times10^{-12}\,\text{kg}\, \text{m}\text{/(}\text{s}^3\text{Pa})$

Which under UnitSimplify reduces to:

$2.41258\times10^{-12}\,\text{V}/\text{T}\,\, ... \,\,(volts\,per\,tesla??)$

for diffusion coefficients I am expecting units of $meters^{2}/second$.

Can anyone see whats gone wrong?

Thanks

UnitSimplify simplifies the units it doesn't guarantee it'll give you the units in SI. Just use UnitConvert, it gives you the answer in SI units.
UnitConvert[(KB T)/(3 Pi eta0 L)]