A throttling process is a process that is isenthalpic. Thus, [tex] h_1 = h_2 [/tex]. This means that the following is also true, [tex] u_1 + P_1 v_1 = u_2 + P_2 v_2 [/tex]. So if you drop pressure in a throttling value, you increase the internal energy, and vise versa.
The Joule -thomson- effect deals with the fact that as you expand a gas it looses temperature. Note that for hydrogen; however, it gains temperaturee as it expands. This makes hyrdogen particularly dagnerous.