Description of Problem
The insulation in the solar box cookers plays a vital role in performance. The current insulation technique involves using wood shavings in the airspace in the wall and in the bottom of the box cooker. This is done to reduce the convective heat transfer in the walls and floor of the oven. While this is the currently practiced technique for insulation, based on the experiences of the women in the Nicaraguan communities, the box ovens perform better during their first year of operation than in the years after. One of the theories associated with the diminished performance of the ovens over time is that the constant heat flow through the walls causes the insulation to settle to the bottom, and at that point the insulation would no longer be preventing convective heat transfer in the upper regions of the wall. And with an expected life of 10-12 years, diminished operation after the first year is something that needs to be analyzed. The objectives for this project are to essentially prove or disprove theories on the insulation in the box cookers and to improve the design in the most effective and economical way possible.
Task for Semester
1. Finalize the experimental design.
- In the previous semester, the team devised a preliminary scheme for testing the insulation. The basic concept of the scheme was to isolate one wall of a solar oven. This would be done by essentially insulating five faces of the solar oven far more than the sixth face (the experimental wall). Therefore, the vast majority of temperature change inside of the oven could be associated with the less insulated experimental wall.
- The plan is for the oven to be heated by some controllable heat source that would turn on and off based on desired commands. Temperatures would be monitored throughout each heating cycle to obtain relevant information that could lead to further insight on the quality of certain types of insulation materials.
- However, the details of the experimental procedure, locations of temperature sensors, and the exact type of heat source that would be used have not been determined. It will be the task of this semester's team to finalize the experimental design and obtain a consistent and effective experimental procedure.
2. Acquire the necessary materials
- The materials will hinge upon the finalized design from the first task and communication with the local community in Nicaragua.
- The methods for acquiring these materials will mainly involve communication with advisor Timothy Bond.
- Currently, the team would like to conduct experiments on wood shavings, rice hulls, and fiberglass as insulation materials. These are materials that the women of Nicaragua have expressed interest in and are attainable and relatively inexpensive.
3. Complete the construction of the experimental unit
- In the spring semester of 2010, the team began construction on an oven that can be used for testing insulation. This device consists of an old solar oven surrounded by an insulated box. This box was intended to cover 5 faces of the solar oven while leaving one face open for testing different insulations.
- The insulated box consists of pieces of plywood attached to one another by metal brackets. The insides of the insulated box are lined with mineral wool at a thickness that gives the insulated walls approximately ten times the thermal resistance of one inch of air. Inside of the mineral wool, lies the old solar oven that was previously decommissioned by the team. This solar oven is constructed just like the ovens that are currently used, with walls filled with wood shavings.
- Tasks for completion of this unit will be to finish the outer framework, constructing the experimental wall, developing a system for the heat source, positioning thermocouples, and programming the experimental procedure.
4. Experimentation
- After the completion of the design, material acquisition, and construction, we can proceed to the task of experimentation. This is where we conduct the planned experiments, and develop new ideas for experimentation.
- Since the main concern for the insulation is in the longevity of the insulation materials, our experiments are planned to mimic long term use of the ovens. For our experiments, we will assume that the solar ovens are used, on average, once per day by the women. Using this assumption, we will equate one heating cycle of the oven to one day of use. After determining the amount of time and the exact criteria for a single heating cycle, we will determine the ideal amount of heating cycles to run for each insulation material. This will allow us to monitor the changes in the performance of each insulation material over roughly the same amount of time they are used in Nicaragua.
- Currently, we believe (based on time constraints) that we will be able to simulate half a year's worth of oven use for the different types of insulation before the semester's end. We hope that this amount of time will be adequate for giving us insight into the deterioration of the performance of each insulation material.
- If necessary, these experiments can be repeated to simulate a year's worth of heating in future semesters when more time is available.
5. The final task will be write-up all our results and compile them into a final report for ease of communication with future team members and with the local community in Nicaragua.
Criteria
Technical:
Technically, in order to suggest a new material for the insulation, the material must perform equal to or superior to the current material used, wood shavings.
Social:
Socially, if a superior insulation material is found, the team must effectively explain the benefits of using the new material to the Nicaraguan women. The current material used for the insulation was discovered by the Nicaraguan women and therefore the team would like the women to understand the benefits of using the new material instead of the wood shavings. In order for us to be successful, the materials must be accepted by the women.
Economic:
Economically, the materials used for the insulation must be both inexpensive and readily available in Nicaragua.
Environmental:
Environmentally, the team will strive to ensure that all material and energy inputs and outputs are as inherently nonhazardous as possible. We will attempt to design products, processes and systems that include integration and interconnectivity with available energy and material flows.
Items Specifically Outside of Scope
If the results of the testing suggest that the reason the solar ovens are less efficient after a year of use is caused by the settling of the wood shavings that are currently used for the insulation, another solution could be to redesign the oven such that it was easy to change the insulation. However this semester's Solar Oven Team has decided to take an alternative approach and test the efficiency of using alternative materials for the insulation instead. Therefore it is out of the scope of the project this semester to attempt to redesign the solar oven so one is able to access and change the insulation.
Anticipated Critical Theory Issues and Challenges
Aside from the scientific aspect of the project, it will be important to evaluate the impact and acceptance of any new changes that we will attempt to implement based on the results of the research project. Since the study deals with the insulation of the solar ovens and possibly attempting to change materials used to build the ovens, it is first important to develop a method for presenting and explaining the research well enough so that it can be understood and accepted by the community in Nicaragua.
If the results of the study suggest that a different material should be used for insulation, it will be important to determine how using and acquiring this material would affect the community. The current material used for insulation is a byproduct of the work that is already done at the solar center; the need for another material that would perhaps have to be obtained from an outside source could cause many issues that must be addressed.
It will be of upmost importance to keep a constant line of communication with the Nicaraguan community throughout the duration of project in order to determine whether or not the research being conducted in this project will be beneficial to the people.
Gantt Chart Timeline
Financial Requirements
1. Rice Hulls $17
2. Wood $20
3. Aluminum $12
4. Fiber board $5
5. Sheet metal $15
6. Fiber glass $25
7. Wood shavings $5
8. Other required materials (nails, silicone, wood glue, etc.) $30