餵食系統：4C楊尚餘 恒溫系統：4C趙心怡 過濾系統： 4C張喆熙 4D鍾卓林 生物化學： 4C黃逸朗 4C張喆熙 外觀設計： 5B鄧凱兒
構思計劃 2019.10-11月 焊製底架 2019.12月-2020.1月 訂造魚缸 2020.1月 安裝喉管及過濾系統 2020.2月-4月 恒溫系統 2020.3月-4月 餵食系統 2020.3月-4月 ............... 完成 希望在7月完成
共有兩個設計方案，兩者皆用stepper motor推動餵食裝置，由Arduino UNO控制。
設計的靈感來自輸送帶。類似輸送帶的設計，利用齒條搭配 stepper motor以推動擋板餵食魚糧。在指定時間，程式會先倒出一定份量糧食，然後啟動stepper motor配合齒條推動食物。
Nichrome wires are used for the heating element of our fish tank. Nichrome(Cr20Ni80) is commonly used for making heating elements of electrical appliances because 1) nichrome has a high melting point, which prevents it from melting from the heat produced and 2) nichrome has a high resistivity and therefore a high resistance, which leads to faster generation of heat.
In order to maintain the water temperature of the fish tank, we need to compensate for heat loss into the surroundings by supplying an equivalent amount of heat to the water.
Heat loss is due to the difference between the temperature of the inner surface of glass (water temperature) and that of the outer surface of the glass (room temperature). It is calculated with the formula Q=U*A*ΔT. Q is the heat loss per second. U is thermal transmittance, which is the rate of heat transfer through matter. A is the size of the area in which heat loss occurs. ΔT is the temperature difference.
Since the optimal water temperature for fish is 24-27°C, we set the upper limit of water temperature as 27°C. And since the lowest temperature in Hong Kong is around 10°C, we set the lower limit of water temperature as 10°C. Therefore, the maximum temperature difference ΔT is 17°C.
U of glass= 4W/m2°C
U of plastic= 0.2W/m2°C
The 4 sides and the bottom of the tank are glass, while the top is covered by a plastic sheet.
Height of the tank=42cm
Area of the 4 sides and the bottom(glass)
= 0.42×0.35×2 + 2.14×0.42×2 + 2.14×0.35m2
Area of the top(plastic)
= 2.14×0.35 = 0.749m2
Maximum heat loss through glass
= 4×2.84×17W = 193W
Maximum heat loss through the plastic sheet
= 0.2×0.749×17W = 2.55W
Total maximum heat loss
= 193+2.55W = 195.55W
Since there will be further heat loss into the glass and heat loss due to the water circulatory system, extra energy needs to be supplied in order to fully compensate for heat loss. Therefore, taking the design of commercial products as reference, we decided to supply a total of 216W through 12 sets of nichrome heating wires each of diameter 0.5mm.
The resistance of each wire can be calculated with the formula R=ρL/A, where R is resistance, ρ is resistivity, L is the length of the wire and A is the cross-sectional area.
ρ of nichrome = 1.09×10-6Ωm
L of the wire = 1.5m
A of the wire = (0.0005/2)2π = 1.96×10-7m
Therefore, R= 8.32Ω
By measuring the resistance of the 1.5m nichrome wire with an ohmmeter, we obtained a result of 8Ω.
The power of each wire can be calculated with the formula P=V2/R, where P is power, V is voltage and R is resistance.
For 12 sets of wires, total P =18×12= 216W
The nichrome wires are each contained within a 1.5m long glass tube. However, the glass tube is in danger of cracking if the wire is heated to a great extent in a short time. Therefore, to ensure the safety of the heating system, we carried out an experiment in which a single 1.5 m nichrome wire of 0.5 mm diameter is heated, with a voltage of 12V. The wire was simply placed on a table under room temperature and pressure. Throughout the experiment, there were no abnormal signs and the surface of the glass was warm to the touch. The positive result shows that there is no danger of glass cracking and the system is safe to use.
The heating system makes use of proportional control. Proportional control is a control system technology based on a response in proportion to the difference between what is set as a desired process variable and the current value of the variable, which means that the greater the difference, the greater the response and the smaller the difference, the smaller the response. In our case, the power supplied to the heating element decreases as the water temperature approaches the desired temperature. This helps maintain a stable water temperature and ensure rapid response, which enhances accuracy. When the temperature of water exceeds the appropriate temperature, the system will be turned off to prevent overheating.
水泵一：HAILEA海利HX8860 130W 5800L/h 揚程4.1m
水泵二： HAILEA海利HX8830 45W 2900L/h 揚程2.3m
過濾箱四(底層，右):打氣石(HAILEA ACO-9610 4出口 10Lit/min 0.015Mpa)，水位監察器，水泵
Diameter of holes: found by doing experiments to test the flow rate against the density and diameters of the holes. Some adjustments were made to optimize the results. Acceptable result is obtained using 3.5mm drills to make the holes.
No. of holes: determined by calculating the surface area of the pipe opening and the diameter of each hole.
Distribution of holes: to make water flow in a certain rate and to clear suspended particles in all heights.
Function of overflow tube: to let excess water flow out and to control the amount of water in tank.