HKDSE Physics Core
Chapter 3: Transfer Processes | 熱轉移過程
Billy Sir’s Smart Notes: Master Conduction, Convection, Radiation, and Real-life Applications.
由中大物理系碩士 Billy Sir 編寫，助你極速掌握傳導、對流、輻射及生活應用。
1. The Three Heat Transfer Processes | 三種熱轉移過程
Heat always flows from a region of higher temperature to a region of lower temperature. This occurs via three main processes: 熱量總是從高溫區域流向低溫區域。這主要透過三種過程發生：
| Process (過程) | Mechanism (機制) | Medium Required? (需要介質？) |
|---|---|---|
| Conduction 傳導 |
Energy is transferred through particle collisions and free electrons (in metals). (能量透過粒子碰撞及金屬中的自由電子轉移) | Yes (Mainly Solids) (是，主要在固體) |
| Convection 對流 |
Hot fluid expands, becomes less dense, and rises. Cold fluid sinks to replace it. (熱流體膨脹、密度降低並上升。冷流體下沉補充) | Yes (Liquids & Gases) (是，液體及氣體) |
| Radiation 輻射 |
Energy is transferred via infrared electromagnetic waves. (能量透過紅外線電磁波轉移) | No (Can travel in a vacuum) (否，可在真空中傳播) |
2. Real-Life Applications & Examples | 生活應用與例子
☕ Vacuum Flask (Thermos) | 真空保溫瓶
A vacuum flask is designed to minimize heat transfer by all three processes to keep drinks hot or cold: (真空保溫瓶的設計旨在減少所有三種熱轉移過程，以保持飲料的冷熱：)
- Vacuum between double glass walls: Prevents heat loss by conduction and convection because both require a medium. (雙層玻璃壁之間的真空：防止熱量透過傳導和對流流失，因為兩者都需要介質。)
- Silvered inner walls: Shiny surfaces are poor emitters and good reflectors of infrared radiation, reflecting heat back into the liquid. (鍍銀內壁：光亮表面是紅外輻射的不良發射體和良好反射體，將熱量反射回液體中。)
- Plastic/Cork stopper: Plastic is a poor conductor, reducing heat loss by conduction. It also seals the flask to stop hot air from escaping via convection and evaporation. (塑膠/軟木塞：塑膠是絕緣體，減少傳導熱流失。它也密封瓶口，防止熱空氣透過對流和蒸發逃逸。)
🏕️ Survival Blanket | 救生毯
Used by marathon runners or in emergencies to prevent hypothermia: (馬拉松跑手或緊急情況下使用，以防止體溫過低：)
- Shiny silver surface: Reflects the body’s thermal radiation back to the person. (光亮的銀色表面：將身體的熱輻射反射回人體。)
- Trapping air: When wrapped around the body, it traps a layer of still air. Air is a poor conductor, significantly reducing heat loss by conduction and convection. (困住空氣：包裹身體時，會困住一層靜止的空氣。空氣是熱的不良導體，大幅減少傳導和對流造成的熱流失。)
❄️ Cooling Coils (e.g., Back of a Refrigerator) | 黑色冷卻盤管
The cooling coils at the back of refrigerators or air conditioners are deliberately painted dull black: (雪櫃或冷氣機背面的冷卻盤管特意塗成暗黑色：)
- Dull black surfaces are the best emitters of radiation. This helps the appliance dissipate unwanted heat to the surroundings as quickly as possible. (暗黑表面是最佳的輻射發射體。這有助於電器盡快將多餘的熱量散發到周圍環境中。)
🥚 How to Keep an Egg Warm? | 如何為雞蛋保暖？
If you need to design a container to keep a boiled egg warm, you must tackle all three heat transfer methods: (如果你需要設計一個容器來為熟蛋保溫，你必須應對所有三種熱轉移方法：)
- Wrap it in cotton wool or bubble wrap: These materials trap pockets of still air. Air is an excellent insulator, minimizing heat loss by conduction. (用脫脂棉或氣泡布包裹：這些物料能困住靜止的空氣。空氣是極佳的絕緣體，能將傳導熱流失減至最低。)
- Wrap it in aluminum foil: The shiny surface reflects thermal radiation back to the egg. (用鋁箔包裹：光亮的表面會將熱輻射反射回雞蛋。)
- Put it in a closed container: A lid prevents hot air from rising and escaping, stopping heat loss by convection. (放入密封容器：蓋子防止熱空氣上升逃逸，阻止對流造成的熱流失。)
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