Date on Master's Thesis/Doctoral Dissertation

8-2022

Document Type

Master's Thesis

Degree Name

M.S.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, MS

Committee Chair

Brehob, Ellen

Committee Co-Chair (if applicable)

Kelecy, Andrea

Committee Member

Kelecy, Andrea

Committee Member

Roussel, Thomas

Author's Keywords

Heat transfer; heat flux; heat flux sensor; residential oven

Abstract

Thermal characterization of an oven is an important part of designing an oven. Understanding how changes in cooking algorithm, oven construction, and oven materials affect cooking performance is critical in ensuring that an oven is properly designed. Often temperature data is used to characterize oven behavior, but this neglects the mode of heat transfer used to achieve these temperatures. Several studies have compared the different modes of heat transfer and cooking performance and have shown that cooking performance in radiation dominated modes are different than in convection dominated modes. The goal of this study is to develop a heat flux sensor that can be used in a residential oven operating at 375°F, mimicking the bake conditions of sugar cookies. The sensor designed must break heat transfer into conduction, convection, and radiation. The sensor designed must have nondestructive requirements for sensor use, be usable in an array of multiple sensors, and be lower cost than its predecessor the RC01 heat flux sensor. A composite material heat flux sensor was designed that consists of a thin foil styled heat flux sensor mounted on to an aluminum mass embedded into an

insulation base. This thin foil styled heat flux sensor was used to measure convection or radiation and convection depending on its emissivity. A second aluminum mass was embedded into the bottom of the insulation to serve as a conduction path during experiments. The sensor designed provided a cost reduction of 90% when compared to the RC01 sensor This heat flux sensor was deployed in a residential oven where three distinct cooking modes were tested: traditional bake, convection bake, and the air fry mode. These modes provided a radiation dominated mode, a convection dominated mode, and a mode that is a balance of both. In these oven tests the average of six high emissivity sensors and six low emissivity sensors was used to characterize the runs. The tests are run for ten minutes to mimic cooking test procedure and are run three times in each cooking mode to measure repeatability of each sensor. The maximum coefficient of variation measured for a sensor is 6.1%, all other sensors had a coefficient of variation of less than 5%. The heat flux results from the oven tests reflected design intent for each mode in this study. A comparison of the average heat flux values for each mode can be seen below. Traditional bake is a mode reliant on the heating elements cycling and only natural convection. Convection bake multi and air fry deploy a combination of different heating elements and the convection fan to improve air flow. A pseudo energy efficiency is calculated that considers a ratio of energy stored by the sensors to energy consumed by the unit and shows that on average traditional bake, convection bake multi, and air fry had efficiency values of 12.16%, 22.37%, and 22.28% respectively. This demonstrates the effectiveness of improved air flow resulting in higher energy transfer. These results are summarized in the following table.

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