Feminicidio

A CAD model of our initial design is pictured in Figure 17. Both an exploded view and a cross-sectional view of our model are shown. Our initial design consisted of a foam cooler, fiberglass insulation, a lid, and the concentric pot subassembly.

The diode chain subassembly and erythritol are contained within the concentric pot subassembly and are shown in the cross-sectional view. These major subsystems and components will be discussed in detail in the following sections.

(a) Exploded View of the Full ISEC Assembly

(b) Cross-Sectional View of the Full ISEC Assembly

Figure 17. The Full ISEC assembly of the first prototype with labeled major components and subassemblies

The ultimate goal of this design is to store thermal energy for the cooker and to increase heat transfer rate to the food for faster cooking. This was accomplished using a phase change thermal

26 storage medium. The cooker is powered by a 100 Watt solar panel connected to the diode chain.

The diode chain is submerged in the erythritol and heats the PCM directly. Throughout the day, the diode chain melts the PCM and stores thermal energy, which is kept in the system with insulation. Once ready, the user can put food into the internal pot and the hot PCM will transfer heat to the colder food at a faster rate than the diode chain could provide alone.

5.1.1 Concentric Pot Subassembly

The first major subsystem is the concentric pot subassembly which is shown in Figure 18. This subassembly includes the internal and external pots, the PCM contained between them, the diode chain subassembly, and a flange extension. This subsystem is directly responsible for containing the erythritol and food. These pots are made of aluminum.

Figure 18. Concentric pot assembly exploded view with labeled components 5.1.2 Flange Extension

The flange extension in the concentric pot subassembly, shown in Figure 19 was the most complex component of our design from a manufacturing standpoint. This flange extension, made from sheet metal, separates and lifts the internal pot away from the external pot while covering the erythritol filled cavity between them as shown in Figure 18. The inner diameter of the flange extension had to be larger than the outer diameter of the internal pot walls but could not exceed the outer diameter of the internal pot flange. Meanwhile, the outer diameter of the flange extension needed to be larger than the inner diameter of the external pot walls in order to bridge the gap between the two concentric pots. Holes for the diode chain leads and thermocouples also needed to be cut into the

27 flange extension above the PCM cavity so that power could be supplied to the heating element and the temperature of the PCM could be monitored.

Figure 19. Flange Extension between the Internal and External Pot

There are several methods for cutting straight line geometry in sheet metal but the methods for cutting precise curves into sheet metal, like the concentric circles that needed to be cut into this flange extension, are more restrictive. These curve cutting techniques are further limited by the fact that we wanted a continuous, solid ring. This means the inner circle cut could not start from the outer circle. For these reasons, the team elected to use a water jet cutter to manufacture this component. We recognize that water jet cutters are not the most accessible technology, especially in the developing communities we ultimately wish to help. This is an instance where our proof of concept project goal allows us to deviate from designing for the end customer. Ultimately, the flange extension should be eliminated through an iterative design approach. In order to begin that iterative process, the concept of phase change materials as a thermal storage system must be proven as something worth iterating. The earlier the team can validate this concept, the earlier the process of redesigning our project for the end user can begin. As a result, we believe that utilizing the water jet cutter helped accomplish this goal.

5.1.3 Diode Chain Subassembly

The second major subsystem is the diode chain. This subsystem is the heating element of our cooker and is responsible for utilizing the power from the solar panel to melt the erythritol and ultimately cook the food. As a result, the diode chain is the most critical subsystem of our design.

The diode chain was constructed using 22 diodes, a bi-metallic switch, and wire leads. A 100 Watt photovoltaic panel provides power to the diode chain which in turn provides heat to the PCM. The bi-metallic switch was submerged in the PCM and will open the circuit if the temperature exceeds 150 °C. The circuit diagram for the diode chain can be seen in Figure 20 and a completed diode chain is also shown in Figure 21.

28 Figure 20. Circuit diagram drawing of the ISEC with thermal storage prototype 1 diode chain

Figure 21. Completed diode chain with 22 diodes, bi-metallic switch, and wire leads.

29 5.1.4 Housing and Insulation

The remaining major components of this design are the housing and insulation. This includes the foam cooler, fiberglass insulation, and pot lid. The pot lid is placed on top of the concentric pot subassembly to seal the cooking pot. The concentric pot subassembly with lid is designed to be placed in the center of the foam cooler with fiberglass insulation stuffed all around.