As the temperature difference increases, the rate of heat flow____

• A. Remains constant
• B. Decreases
• C. Increases
• D. Oscillates

Answer: (C)

The driving force for heat transfer is the temperature difference between the two sides. With the material properties, area, and transfer mode held constant, the heat flow rate scales with that difference. In conduction, this is shown by Fourier’s law, and in convection by Newton’s cooling law—both formulas have the temperature difference as a multiplier. So when you increase the temperature difference, the rate at which heat moves through the system increases, roughly in direct proportion. If you double the ΔT under the same conditions, you’ll double the heat flow rate. It wouldn’t stay constant or decrease or oscillate unless some other factor changed.