A question regarding power generation in MHD method

[T C]

TL;DR

If ionized flow is used to generate power/electricity by MHD method, will there be in any difference in power output if the flow is confined inside a tube made of metal instead of a free flow.

First, I want to put forward an imaginary scenario where an ionized flow is being used to generate power/electricity by MHD power generation method. The temperature of the ionized flow is the same as the surrounding atmosphere. Power/electricity is generated as the flow is ionized. Now, if the flow passes through a tube made up of metal instead of flowing in open, I want to know whether there will be any difference in power output in such a case or it will be the same?