Mechanisms of Heat Transfer

By Dez Duran-Lamanilao

Heat transfer plays a huge role in the application of the First Law of Thermodynamics, which refers to the application of the conservation of energy principle to heat and thermodynamic processes. The first law is used extensively in the discussion of heat engines. A heat engine converts heat or thermal energy, as well as chemical energy, to mechanical energy. Examples that make use of heat engine are refrigerators, diesel engines, and heat pumps. Heat pumps are used to provide compact heating and hot water solution to marine vessels.

The basic principles of heat transfer involve temperature and the flow of heat. It can be grouped into three main categories:

1. Conduction – transfers heat via direct molecular division. When air in contact with the ocean is at different temperature than the sea surface, conduction takes place.

2. Convection – when a fluid is heated and travels away from the source, carrying the thermal energy along. Convection currents in the ocean are a result of differences in the density of ocean water.

3. Radiation – the transfer of energy by means of photons in electromagnetic waves. The largest source of radiation in the ocean comes from naturally occurring substances such as potassium and uranium.

The image below (source: NASA) shows how all three heat-transfer methods work in the same environment:

Hydraulic systems can make use of heat exchangers to avoid excess heat, which can break down oil, damage seals and bearing, and increase wear on pumps and other components. There are various things to consider when determining the key configurations of a heat exchanger:

  • • Oval tubes vs. round tubes – What are your flow rate level and pressure drop requirements?
  • • Materials: brass, aluminum or steel – What are your structural needs?
  • • Fin types: flat plate, humped or louvered – Do you prefer faster turbulent flow over cleanability or vice versa?

Gulf Coast Air & Hydraulics is an expert in hydraulic systems and manufactures heat transfer products for the industrial and marine industry. Custom packages are designed and manufactured according to customer’s specifications.