📚 Pre-U CIE Engineering Case Study: Practical Exercise | Pre-U CIE 工程：案例分析实战演练
This case study walks you through a typical Pre-U CIE Engineering design and analysis project. You will follow a structured approach to develop a portable solar-powered water purification unit for emergency relief. The goal is to produce at least 1000 litres of safe drinking water per day in a refugee camp setting, using locally available resources and a budget of under $500 per unit. The exercise covers problem definition, stakeholder analysis, specification writing, concept generation, detailed calculations, materials selection, prototyping, cost analysis, sustainability and safety compliance. Each stage is paired with Chinese explanations to reinforce bilingual technical communication.
本案例带您经历一个典型的 Pre-U CIE 工程设计分析项目。您将遵循结构化方法，为紧急救援开发一个便携式太阳能净水装置。目标是在难民营环境中每天生产至少 1000 升安全饮用水，利用当地可用资源，且每台成本低于 500 美元。练习涵盖问题定义、利益相关者分析、规格编写、概念生成、详细计算、材料选择、原型制作、成本分析、可持续性与安全合规。每一阶段都配有中文解释，以强化双语技术交流。
1. Understanding the Case Background and Problem Definition | 理解案例背景与问题定义
The scenario places you in a post-earthquake humanitarian crisis where clean water sources have been destroyed. The aid agency requests a deployable water purification system that can be transported by a small truck, set up by two people in less than two hours, and operate fully on solar energy. The system must remove bacteria, viruses and suspended solids, delivering water that meets WHO guidelines. The core problem statement is: "Design a portable, low-maintenance, solar-powered unit capable of producing 1000 L/day of potable water without any grid electricity or fossil fuels." Constraints include a weight limit of 50 kg, modular construction for repair, and a target service life of five years.
场景设定为灾后人道主义危机，清洁水源遭破坏。援助机构要求设计一个可部署的净水系统，能用小卡车运输，两人在两小时内完成搭建，并完全依靠太阳能运行。系统必须去除细菌、病毒和悬浮物，出水符合世界卫生组织指南。核心问题陈述为：“设计一个便携、低维护、太阳能驱动的装置，每天生产 1000 升饮用水，不依赖电网或化石燃料。”约束条件包括重量不超过 50 kg、模块化结构以便维修、目标使用寿命五年。
A well-defined problem leads to measurable success criteria. These include flow rate, water quality parameters (turbidity < 1 NTU, E. coli 0 CFU/100 mL), total daily yield, energy autonomy for at least one cloudy day, and capital cost below the budget. The engineering team must balance conflicting demands, such as high flow rate versus low power consumption, and lightweight portability versus durability.
清晰的问题定义带来可衡量的成功标准。这些包括流速、水质参数（浊度 < 1 NTU，大肠杆菌 0 CFU/100 mL）、日总产量、至少一个阴天的能源自给能力，以及低于预算的资本成本。工程团队必须平衡相互冲突的需求，例如高流速与低功耗、轻便性与耐用性。
2. Stakeholder Analysis and Need Identification | 利益相关者分析与需求识别
Identifying all stakeholders ensures the design meets real, rather than assumed, needs. Primary stakeholders include the refugees who will consume the water, the local health workers who will monitor quality, and the aid logisticians who will transport and install units. Secondary stakeholders are the donors who fund the project, the local government that must approve technology, and the maintenance teams who will repair filters and pumps. Each group has distinct priorities: end users want simplicity and safety; logistics officers want stacking and mobility; donors want low cost per litre.
识别所有利益相关者可确保设计满足真实需求，而非臆想。主要利益相关者包括饮用该水的难民、监测水质的地方卫生人员以及运输安装设备的援助物流人员。次要利益相关者包括资助项目的捐赠者、必须批准技术的当地政府以及维修过滤器和泵的维护团队。每个群体都有不同的优先事项：最终用户要求简便与安全；物流人员注重可叠放与可移动性；捐赠者则关注每升水的低成本。
Needs are then categorised using a MoSCoW matrix. "Must have" includes absolute filtration of pathogens, < 50 kg total weight, and 1000 L/day output. "Should have" includes a battery for overnight operation and a backwash cleaning mechanism. "Could have" covers remote monitoring via IoT, while "Won't have" for this version includes desalination capability. This structured prioritisation prevents scope creep and focuses resources on critical functions.
随后用 MoSCoW 矩阵对需求进行分类。“必须项”包括绝对滤除病原体、总重 < 50 kg、日产 1000 L。“应该项”包括用于夜间运行的蓄电池和反冲洗清洁机制。“可选项”涵盖物联网远程监控，而“不包含项”指该版本的海水淡化功能。这种结构化优先级划分可防止范围蔓延，并将资源集中在关键功能上。
3. Developing Design Specifications and Constraints | 制定设计规格与约束条件
lar resource is assumed to be 5.5 kWh/m²/day peak sun hours, which informs panel sizing. Filtration must achieve a log-4 reduction for viruses and log-6 for bacteria. The unit must fit within a footprint of 1.2 m × 0.8 m × 1.5 m when packed. Noise levels should be below 50 dB at 1 m, as the unit may be placed near sleeping areas. All materials in contact with water must be food-grade and compliant with NSF/ANSI 61.
根据需求与约束，衍生出精确的设计规格。目标流速至少为 42 升/时，以便在 24 小时内达到 1000 升。假定太阳能资源为峰值日照小时 5.5 kWh/m²/天，用于确定面板尺寸。过滤须实现病毒 log-4 去除率、细菌 log-6 去除率。设备包装后须置于 1.2 m × 0.8 m × 1.5 m 的占地面积内。由于可能放置在睡眠区附近，1 m 处噪音应低于 50 dB。所有涉水材料必须为食品级，并符合 NSF/ANSI 61 标准。
Constraints include a maximum production cost of $350 to leave margin for distribution and support. Only low-voltage DC (12 V or 24 V) is permitted for safety and compatibility with solar panels. No proprietary parts may be used, ensuring that spares can be sourced globally. The design must also consider operations in temperatures ranging from 5 °C to 45 °C and tolerate dusty, humid environments.
约束条件包括最高生产成本 350 美元，以便为分发与支持留出余量。出于安全并与太阳能电池板兼容，仅允许使用低压直流电（12 V 或 24 V）。不得使用专利部件，确保全球可采购备件。设计还须考虑在 5 °C 至 45 °C 的温度范围内运行，并能耐受多尘潮湿环境。
4. Concept Design and Idea Generation | 概念设计与方案生成
Three distinct concepts were generated through brainstorming and morphological analysis. Concept A combines a sediment pre-filter, an ultrafiltration (UF) membrane and a UV-C LED disinfection chamber, all powered by a 200 Wp foldable solar panel with a 100 Ah lithium battery. Concept B uses a gravity-fed ceramic filter with a small solar pump to maintain head, but lacks chemical-free virus removal. Concept C is a solar still that evaporates and condenses water, which is extremely simple but yields only about 4 L/m²/day, requiring huge area and being vulnerable to contamination. Each concept was sketched and its working principle described with functional block diagrams.
通过头脑风暴与形态分析，产生了三种不同的概念。概念 A 组合了沉淀预过滤器、超滤膜和 UV-C LED 消毒腔，全部由一个 200 Wp 可折叠太阳能电池板与 100 Ah 锂电池供电。概念 B 使用重力式陶瓷过滤器，配以小型太阳能泵维持水头，但缺乏无化学品的病毒去除能力。概念 C 是太阳能蒸馏器，通过蒸发冷凝获取水，虽极其简单但日产量仅约 4 L/m²，需要巨大面积且易受污染。每个概念都绘制了草图，并用功能框图描述了工作原理。
Morphological chart helped systematically combine sub-solutions. For filtration, options were screen, disc, UF, RO; for disinfection, options were chlorination, UV, ozone, boiling. UF + UV offered the best balance of pathogen removal, energy efficiency, and maintenance simplicity. The team decided to develop Concept A further because it promises the highest throughput per unit volume and can be made modular.
形态分析图有助于系统组合子方案。过滤方式可选格网、叠片、超滤、反渗透；消毒方式可选氯化、紫外线、臭氧、煮沸。超滤 + 紫外线在去除病原体、能效和维护简便性方面取得了最佳平衡。团队决定进一步发展概念 A，因为它有望实现单位体积最高产水量，并可制成模块化。
5. Feasibility Assessment and Option Selection | 可行性评估与方案选择
A weighted decision matrix was applied to select the most feasible concept. The criteria and weights were: cost (0.25), microbial effectiveness (0.35), ease of maintenance (0.20), weight and portability (0.10), and durability (0.10). Each concept was scored on a 1-10 scale. The results are shown in the table below.
采用加权决策矩阵选择最可行概念。标准与权重为：成本 (0.25)、微生物效能 (0.35)、维护便捷性 (0.20)、重量与便携性 (0.10)、耐久性 (0.10)。每个概念按 1-10 分评分。结果如下表所示。
| Criterion | Weight | Concept A UF+UV |
Concept B Ceramic |
Concept C Solar Still |
|---|---|---|---|---|
| Cost | 0.25 | 8 | 9 | 4 |
| Microbial effectiveness | 0.35 | 9 | 6 | 7 |
| Ease of maintenance | 0.20 | 8 | 7 | 8 |
| Weight/portability | 0.10 | 7 | 6 | 9 |
| Durability | 0.10 | 8 | 5 | 7 |
| Weighted Total | 1.00 | 8.30 | 6.70 | 6.65 |
Concept A achieved the highest weighted score of 8.30, driven by its superior pathogen removal and reasonable cost. Ceramic filter (6.70) is cheap but lacks virus removal and has fragile components. Solar still (6.65) fails on throughput and cost-effectiveness. Thus the team selected UF+UV as the chosen concept to proceed into detailed design, with a plan to mitigate its higher power demand through efficient battery management.
概念 A 获得最高加权分 8.30，得益于优异的病原体去除能力与合理的成本。陶瓷过滤器 (6.70) 虽便宜但缺乏病毒去除能力且部件易碎。太阳能蒸馏器 (6.65) 在产水量和成本效益上不达标。因此团队选择超滤+紫外作为进入详细设计的概念，并计划通过高效电池管理来缓解其较高功率需求的问题。
6. Detailed Design and Engineering Calculations | 详细设计与工程计算
The core variables were calculated to size components. Daily energy requirement was determined first. The UV LED module consumes 20 W, the lift pump 10 W, and the control electronics 5 W, totalling 35 W. With 24-hour operation for continuous production, daily energy demand is:
首先计算核心变量以确定部件尺寸。确定了每日能源需求。UV LED 模块耗电 20 W，提升泵 10 W，控制电子 5 W，合计 35 W。为连续生产而 24 小时运行，日能耗为：
Edaily = Ptotal × t = 35 W × 24 h = 840 Wh
energy is 840 Wh × 1.5 = 1260 Wh. Using a 12 V system, the required battery capacity C is:
为提供一个阴天的自给能力，储能需覆盖 1.5 天，因此所需电池能量为 840 Wh × 1.5 = 1260 Wh。使用 12 V 系统，所需电池容量 C 为：
C = E_storage ÷ V = 1260 Wh ÷ 12 V = 105 Ah
A 110 Ah deep-cycle LiFePO₄ battery is selected, with depth of discharge 80%. Solar panel must recharge the battery while running daytime load. Assuming 5.5 peak sun hours, required panel power Ppv = (Edaily ize = 840 Wh ÷ 5.5 h ≈ 153 Wp. A 200 Wp foldable panel provides margin for soiling and temperature derating.
选用 110 Ah 深循环磷酸铁锂电池，放电深度 80%。太阳能电池板须在运行日间负载的同时为电池充电。假设 5.5 峰值日照小时，所需面板功率 Ppv = (日能耗 + 夜间补给) ÷ 日照小时。夜间部分为 35 W × 16 h = 560 Wh；日间负载 35 W × 8 h = 280 Wh，总发电量 = 560 Wh + 280 Wh = 840 Wh。因此面板大小 = 840 Wh ÷ 5.5 h ≈ 153 Wp。选用 200 Wp 可折叠面板为污染和温度衰减留出余量。
diameter is sized to keep water velocity around 1 m/s to prevent biofilm. Using continuity equation Q = A × v, with A = π × d² ÷ 4, we find d = √(4Q ÷ (π × v)). For Q = 1.16 × 10⁻⁵ m³/s (41.7 L/h), d ≈ 3.8 mm. A 6 mm ID food-grade silicone tube is chosen for safety and availability.
流量选型确保日产 1000 升。目标流量 Q = 1000 L ÷ 24 h ≈ 41.7 L/h。超滤膜组件可处理高达 60 L/h。管道内径按水流速约 1 m/s 设计以防生物膜。使用连续性方程 Q = A × v，其中 A = π × d² ÷ 4，求得 d = √(4Q ÷ (π × v))。对于 Q = 1.16 × 10⁻⁵ m³/s (41.7 L/h)，d ≈ 3.8 mm。选择内径 6 mm 的食品级硅胶管以确保安全与可得性。
7. Materials Selection and Manufacturing Processes | 材料选择与制造工艺
Materials are chosen for compatibility, weight and local sourcing. The main housing is rotationally moulded from recycled HDPE, which is impact-resistant, UV-stabilised and food-safe. The UV chamber uses 304 stainless steel for its corrosion resistance and reflectivity. The ultrafiltration membrane is made of hydrophilic PVDF with a pore size of 0.02 μm, providing a barrier to bacteria and viruses. Gaskets are EPDM rubber. Fasteners are standard stainless steel M6 bolts to allow repair with basic tools.
材料选择基于兼容性、重量与当地采购。主外壳采用滚塑再生 HDPE，具有抗冲击、抗紫外线且食品级。UV 腔体使用 304 不锈钢，以其耐腐蚀性与反射率。超滤膜由亲水性 PVDF
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