Project: Dorm-Fridge

Author: LIU-Yinyi
Date: 2019-12-08
Version: 2.0.0 [ ReForge ]
Abstract: An individual project which helped my dorm mates build up a simple fridge for ice-drink.

1. Background & Brief

This is a project done when I was a sophomore-level student. It was a burning hot summer and my dorm mates wanted some ice-drink but nothing could be used as a cooler and there was no room for a normal size refrigerator in our dorm. It just so happended that our physics class introduced Peltier Semiconductor to us as a heat transfer device. As a result, I took attempts to make one based on this theory.

This project has been re-forged and contains three parts: Simulation, Mechanics and McuCodes. The Simulation directory covers a simulink project to mimic the heat transfer procedure between dorm-fridge and ambient enviroment as well as a simple PID controller for Microprocessor Central Unit. The result helps us test the temperature-control algorithm and estimate the timespan of cooling-process. Objects Matrices as Solidworks format type are saved in the Mechanics part. Corresponding source codes for MCU are comprised in the McuCodes directory.

2. Overview & Figure

System Design in Simulink:

Simulation Result in Data-Inspector: (Ambient: $25^\circ C$ , TargetPoint: $5/10/15^\circ C$ )

Object Model in Solidworks:

Object Render in Solidworks: (No Videocard in my Mac so it might be coarse)

3. Theoretical Narrative

Firstly the box of fridge was devised at a size of 180mm x 270mm x 190mm. The volume is $9.234 \times 10^{-6}~m^3$ . Here we suppose that the average density of the air is so the mass of air is $1.194 \times 10^{-5}~kg$ . The specific heat capacity of air that could be found from books is $1004.5~J/(kg\cdot ^\circ C)$ .

Secondly the convection heat flow was simplified into a dissipation constant, which described as an equation: $P_{d} = \kappa \cdot \Delta T$ , where $\Delta T$ is the difference between fridge temperature and ambient temperature. Note here $\kappa$ unit is $W/^\circ C$ .

Thirdly the temperature controller could vary power ratio as $\eta$ to control the cooling process. The real-time power is ratio $\eta$ multiply maximum power $P_{m}$ . The equation could be defined as: $P_{tc} = \eta \cdot P_{m}$ .

For fridge simulation, heat transfer followed the equation: $\int [\kappa \cdot (T_{f} - T_{a}) - \eta \cdot P_{m}]~dt = c \cdot m ~\Delta T$ , where $T_{f}$ and $T_{a}$ indicates the fridge and ambient temperature respectively. Fridge absorbs the heat as a result of negative symbol.

4. References

[1] Mathworks, Inc. (August, 2019). Simulink Tutorials and Documents. Retrieve from: https://ww2.mathworks.cn/help/index.html?s_tid=CRUX_lftnav

[2] Picard, Alain, et al. "Revised formula for the density of moist air (CIPM-2007)." Metrologia 45.2 (2008): 149.

LIU-Yinyi/Dorm-Fridge

Project: Dorm-Fridge

1. Background & Brief

2. Overview & Figure

3. Theoretical Narrative

4. References