Heat is transferred through a metal radiator primarily through a combination of conduction through the metal itself and then released into the surrounding environment via convection and radiation.
When hot water or steam flows through a central heating radiator, the heat energy from the fluid is transferred to the metal of the radiator. This initial transfer occurs mainly through convection from the fluid to the inner surface and conduction from the inner surface into the metal.
The Journey of Heat Through the Metal
Once the heat energy reaches the metal, it travels through the solid material by conduction.
- Conduction: Metal is a good conductor of heat. The heat energy causes the atoms and electrons within the metal lattice to vibrate more vigorously. These vibrations are passed from atom to atom throughout the structure of the radiator's fins and panels, spreading the heat across the entire surface.
Releasing Heat to the Room
From the hot surface of the metal radiator, heat is then transferred into the room via two main mechanisms: convection and radiation.
Convection
Convection is often the most significant way a standard radiator heats a room, involving the movement of air. As described in the reference:
- A convection current from a radiator: Air close to the radiator is heated. It expands, becomes less dense and rises. It is replaced by the cooler, denser air which surrounds it. This air is in turn heated, expands becomes less dense and rises. This continuous cycle of rising warm air and sinking cool air creates a convection current that circulates warm air throughout the room.
This process effectively distributes the heat energy away from the radiator and into the living space.
Radiation
Radiators also transfer heat through radiation.
- Radiation: The hot surface of the radiator emits infrared electromagnetic waves. These waves travel directly through the air and are absorbed by objects and surfaces they encounter, such as walls, furniture, and people, heating them directly. While convection heats the air, radiation heats surfaces.
Practical Insights
- Radiator Design: Radiators are often designed with fins or multiple panels to increase their surface area. A larger surface area allows for more efficient heat transfer through both convection and radiation, warming the room faster.
- Placement: Placing radiators under windows helps to counteract the downdraught of cold air from the window surface, drawing it into the radiator's convection current to be heated.
In summary, heat moves into the metal radiator from the hot fluid (convection/conduction), through the metal itself (conduction), and out from the metal surface into the room (convection and radiation).
