High-Efficiency Gas Fryer

 

The restaurant industry is invested in saving energy. A typical fryer found in a fast-food restaurant is less than 65% efficient when boiling water and just over 50% when cooking. Higher efficiency translates to lower operating cost for the restaurant and higher profits.

Gas fryers are far less efficient than electric fryers because the heat energy from the flame must first pass through a metal wall to get to the cooking oil. Electric fryers have heating elements submerged directly in the cooking oil so all of the electrical energy released in the heater element is directly transferred to the oil with no losses.

This project focused on a tube-type fryer where individual gas burners fire into oval tubes that are welded inside the fry pot. Combustion gases flowing through the tubes transfer heat to the tube wall and thus into the oil. Heat transfer enhancement inside the tubes leads to higher efficiency, but with a penalty of higher pressure drop and flow losses. Typical tube-type fryer combustion systems do not have a forced or induced flow system for providing combustion air, so it is critical that flow losses be minimized.

Exceptional enhancement of heat transfer leads to another problem with these fryers where excessive wall temperatures are created and the oil is scorched. Also, high heat transfer rates to the metal wall and any fins attached to it can result in excessive metal temperature and shortened life.

An analytical model of the heat transfer characteristics within the fryer tubes and through the tube wall into the cooking oil was developed to study the temperature profile in the metal parts, metal temperature in contact with the shortening, pressure drop through the flow system and combustion characteristics.

A prototype was constructed and tested to validate the model and fine tune the design. Engineering documentation was prepared and supplied to the manufacturer. This fryer entered production and is a leading product in its market.