Improving the efficiency of domestic ovens

Abstract

This project aimed to realise and validate a novel design of domestic oven to reduce cooking time and energy consumption compared to a traditional design of domestic oven.

The design concept was developed by Dr Mark Williamson of Cambridge Oven Innovation (COI). Initially computational models were used to predict the efficacy of the design concept. Heat transfer coefficients from literature and a computational fluid dynamics (CFD) simulation were imported into a lumped property model, which predicted that the COI design would reduce both energy consumption and cooking time. Three successive physical prototypes were constructed to develop the concept, successively improve the user experience and progress towards a mass manufacturable design. Comparative food trials were undertaken with the third prototype and a domestic fan oven of traditional design. The COI design was able to reduce energy consumption by 30% and cooking time by 60% across a wide range of thermal masses and Biot numbers.

The CFD simulation was validated using heat flux and velocity measurements taken in the first prototype. The simulation was found to predict velocity, temperature distribution and convective heat flux reasonably accurately, with a mean absolute error in the convective heat flux of 22%. The radiative heat flux was predicted less accurately, with a mean underprediction of 53.2%. This was attributed to an inaccurate prediction of the temperature of the oven walls, due to: (i) neglecting conduction through interior dividing walls of the oven, (ii) an inaccurate estimate of the overall heat transfer coefficient from the inner wall of the oven to the ambient air and, (iii) reliance on empirical wall functions to calculate heat flux on the walls of the cooking chamber.

The CFD simulation was used to investigate the possibility of applying the COI design to a 45 cm high standard kitchen unit, rather than the typical 60 cm height units. The simulation showed that this would increase the heat flux into the food at a given setpoint temperature, and therefore the efficiency and cooking time would be improved. However, the evenness of cooking would be reduced. Potential solutions, namely increasing the number of jet nozzles and changing the size of the jet nozzles, were investigated. This was found to improve evenness at the cost of energy efficiency and cooking time, although they were still less even than the 60 cm design.