Summary
The purpose of this experiment is to understand how the speed of external convection air flow affects the speed of the transient cooling process of an object, such as food, based on the assumption of a plate in a lumped system analysis. The final temperature of the object after a constant time plotted against the uniform air flow speed should show exponential decay. Exploring this relationship requires identifying the relationship between the Reynolds number and Biot’s number at different flow velocities. Furthermore, the Reynolds number will dictate whether the flow is laminar or turbulent, and therefore which calculations to use.
This project aimed at understanding the effects of external convection air flow speed on the transient cooling process of an object, exemplified by a metal plate, which mimics the cooling process of food. A strong theoretical framework grounded on thermal convection and conduction principles was established, utilizing various equations to model heat transfer rates, Biot’s number, Reynolds number, and the Nusselt number, providing a mathematical basis for analyzing the convection cooling effect.
I designed the entire experimental setup which included a pitot tube, pressure transducer, and a heated metal block with a thermocouple. All these components were interfaced with a LabVIEW script, which I also designed, and an Arduino UNO circuit for real-time data acquisition. The metal block, made of either aluminum or copper, was heated to a specific initial temperature, following which, the airflow speed was varied using different nozzle sizes, and the cooling process was observed and recorded.
The data collected included the velocity of airflow derived from pressure measurements and the temperature variation of the metal block over time. This data was compiled and analyzed using MATLAB and Excel to derive the convective heat coefficient and understand its relationship with the airflow speed.
