Let's apply the energy balance equation between the upstream and downstream of the throttling valve.
Q + h1= W + h2 + d(KE) + d(PE)
Q = 0
Reason: There is not enough time and surface area available for heat transfer
W = 0
Reason: There is no lifting of any weight (no thermodynamic work)
d(PE) = 0
Reason: There is no potential head difference
d(KE) =~ 0
Reason: there may be an increase in velocity at the outlet compared to the inlet but in many cases the change in kinetic energy is insignificant.
Hence we remain with