Which statement best describes isothermal flow through an uninsulated pipe kept at a constant temperature?

• A. Thermally insulated
• B. Adiabatic
• C. Isothermal
• D. Isobaric

Answer: (C)

Isothermal flow means the fluid temperature stays the same as it moves through the system. Here, the pipe is uninsulated but held at a constant wall temperature by the surroundings. Heat can transfer between the fluid and the wall, and if that transfer is effective and the flow is steady, the fluid temperature remains at that fixed value along the length. That makes the flow isothermal.

Thermal insulation would prevent heat transfer, which isn’t the situation described. Adiabatic implies no heat transfer across the boundary, also not true here since the wall exchanges heat with the fluid. Isobaric would require constant pressure, which isn’t the defining feature given. Therefore the best description is isothermal.