Final answer:
In a cryotainer, an operator can control the convection type of heat transfer, which involves the macroscopic movement of a fluid.
Step-by-step explanation:
The type of heat transfer that an operator can control in a cryotainer is convection. This is different from conduction, which is the heat transfer through stationary matter by physical contact, and radiation, which is heat transfer that occurs when electromagnetic radiation is emitted or absorbed. In convection, the heat transfer involves the macroscopic movement of a fluid, and this process can generally be controlled by adjusting the flow or movement of that fluid, which is something an operator can manage.