High heat transfer efficiency is typically associated with which feature of appliances?

High heat transfer efficiency is associated with a long residence time of hot gases within the appliance. When hot gases have more time to interact with the heat exchange surfaces, they transfer more heat to the surrounding air or water, enhancing overall efficiency. This prolonged exposure allows for a more complete transfer of heat before the gases exit the system, resulting in better utilization of the heat generated by the fuel being burned.

In contrast, small exterior surfaces limit the area available for heat exchange, thus reducing the efficiency. Poor convection of air indicates that air movement is not effectively facilitating heat transfer, which can lead to lower heating efficiency. Low turbulence means that gases flow smoothly without mixing, which can prevent optimal heat transfer since the hot gases might not adequately contact the heat exchange surfaces.

By maximizing the time hot gases spend within the heat exchanger, the appliance can achieve high heat transfer efficiency, making this a crucial feature in effective design.