TES Project 2023

Results 1.0

5/27/2023

Here, we detail the results of our tests, including what went well, what went wrong, and our general reflections.

The results were not as accurate as we had hoped, mainly because the thermometers for the insulated test demonstrated a quicker drop in temperature than the uninsulated test. However, after analyzing the data further and constructing graphs, we quickly realized that the insulated test retained the temperature for longer at a steadier rate, compared to the uninsulated. Moreover, the insulated test was clearly far warmer, with steam rising from the device for more than an hour. Contrastingly, the uninsulated pot did not display the same level of evidence of heat.

As for future tests, we can definitely ensure that the thermocouple is first properly aligned and tested accurately by conducting placebo tests on different substances with known temperatures, then comparing to see if they are the same.

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Testing Prototype 1.0

5/11/2023

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The first iteration of our prototype is focused on the Thermal Energy Storage (TES) aspect of the product. This follows from our user and technical requirements that we want to create a cookstove that’s able to adequately replace current methods of cooking, which means that it has to be usable at all times of the day and be compatible with the region's electricity infrastructure. Concretely, from a technical standpoint, it has to be capable of operating with off-grid solar and grid infrastructure, and from a user standpoint, it has to operate at least 300 degrees Celsius. As such, our testing plan’s main objective is to determine the efficiency of the thermal energy storage prototype. Below is a testing plan we plan to use for our first major test – testing insulation. We will follow this same structure for future tests.

Comprehensive Testing Plan

Objective: To determine the efficiency of the Thermal Energy storage prototype in terms of the rate of heat loss and how much it can be minimized, how long

Materials and Equipment:

Cole Parmer Container, 304 SS, 1.25 qt, Internal Vessel
Cole Parmer Container, 304 SS, 4.5 qt, External Vessel
Fiberglass Insulation Roll
Induction Burner
Potassium Nitrate, 10 lb
Sodium Nitrate, 10 lb

Procedure: Testing Effect of Insulation:

Comparing boiling water and its rate of heat loss when placed inside insulated vessel vs regular dissipation (no vessel)
Pour 0.5 kg of water inside internal vessel, then place internal vessel into the insulated TES prototype
Place prototype on induction burner then heat vessel until water is 100 degrees celsius
Remove prototype from induction burner then test temperature using temperature probe at 15 minute intervals to determine rate of heat loss - this is the test of the insulated vessel
When the water has cooled to room temperature, stop recording
Repeat steps 1-3
Instead of keeping the internal vessel inside the insulation, remove it and place it in open air - this is the test of it with no vessel
When the water has cooled to room temperature, stop recording

Variables

Independent Variable: Insulation or No Insulation
Dependent Variable: Rate of Heat Output (kW)
Controlled Variables: Amount of water, Temperature heated to, Size of vessel, Insulation material

Data Analysis

Place plot points of temperatures to calculate heat output at each interval, then plot a graph of heat output (kJ) vs time (s). Integral of graph will be the power output (kW)

Predicted Results
Q = m x c x t = (0.5 kg) (4.18 kJ/kg x c) (100 - 17.2 degrees C) = 173 kJ heat loss total
Rate: Newton's Law of Cooling: t = -ln[ (T - Tambient) / (Tinitial - Tambient) ] / k

Expected time: 42 minutes
Expected power: 0.068 kW

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From Blueprint to Life: The Protyping Process

4/13/2023

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The Thermal Energy Storage (TES) team spent the first three weeks of the quarter working on the following tasks — identifying which technical requirements the first iteration of the prototype would target and what materials such a prototype would require.

Specifically, the TES team’s first iteration of the prototype will be a smaller scale model that employs a hot plate and stainless steel pre-made container model that tests the exchange of heat into the internal shell specifically. We chose to focus on these technical requirements because it is the most important aspect of the stove, to transfer heat to a storable shell; of course, the final prototype would scale the charging portion, cooking surface, and external shell to a larger scale: We plan on performing the following tests:

INITIAL PROTOTYPE
Heat output: after connecting the hot plate with the stainless steel container, will use a infrared thermometer to measure both the internal shell and external shell temperature
Heat retention and insulation: will test the storage component of the device and measure the length of time that heat is retained at a certain value, thus
LARGER SCALE PROTOTYPE
Discharge testing: Use TES material to heat 2 kg of water, measure temperature difference. After reaching equilibrium, place an additional 1 kg of water to determine how much residual energy remains in TES material
Charging testing: Incorporate OTP circuit system and test the length of time device works when fully charged + OTP circuit integration (failsafe for when temperature is too high)

Initially, our team struggled with scaling our high-level prototype to a smaller, more manageable, and targeted prototype. We recognized that we couldn’t perform isolated tests on our prototype because the three main components of our product — namely, charging, storage, and discharging — are inseparable from one another. After multiple group meetings and conversations with members of the teaching team, we decided that our prototype will focus on heating and insulation, as explained above.

Finalizing the design and testing concepts for the first iteration of our prototype was a difficult but important step, as it influenced our final budget which includes the materials we seek and where we ordered the materials from. Here is our breakdown of the budget:

Note that we put in an order for sheet metal; our goal is to weld this sheet metal into an internal shell. As of now, no member of the TES team has welding experience, so we plan to outsource welders — perhaps a friend who’s further down in the Mechanical Engineering track.

Our plan for the next two weeks leading up to Week 5 is to build our first prototype. The team will resume its out-of-class two-hour-meetings (held on Wednesdays from 8-10pm) to put all the materials together. As of now, we expect to have all the materials by April 26 — the hot plate comes in last. Once the materials are delivered, we will build the prototype and record a video to document the aforementioned tests we plan to perform and record our observations and results. Then, we will begin ideating for our second iteration of the prototype.

From a non-technical standpoint, last quarter we identified that a major challenge was establishing a direct point of contact with our Indigenous users. We recognize that our positionally as a group of non-Ecuadorian Stanford students inherently requires us to establish this mode of direct communication with our direct user; unfortunately, communication with our community partner, Beyond Chacay Foundation, has been rocky. In the next two weeks, we plan to engage in at least one group call and ask to talk with at least one Indigenous woman who cooks for her family.

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TES 2023

Results 1.0

Testing Prototype 1.0

From Blueprint to Life: The Protyping Process

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