A heat transfer system has a heat source that generates heat, a heat dissipator that dissipates heat, and a flow controller (hat controls a flow of a heat medium in a heat medium passage (n which the heat medium in a liquid state flows. The heat from the heat source is transferred to the heat dissipator through the heat medium. The heat medium is a solution that includes a solvent and at least one solute. The at least one solute is configured by a molecule. The molecule has (i) a first portion that selectively approaches a solid-liquid interface of the solvent when a temperature of the heat medium becomes lower than or equal to a predetermined base temperature and (ii) a second portion that is lyophobic and coupled with the first portion.