Blog 4 Capstone Project Update

Howdy fellow Houstonians!

Well, this concludes our work for this semester's capstone project. We found ourselves pulling our hair out more than we were crying. Nonetheless, it has been a pleasure working alongside future engineers. Below we have an update on our project and what we intend to do for the upcoming semester. 

Work Completed

For the work period from April 14th to April 27th, the team accomplished several major tasks. The first task was a detailed engineering analysis. This analysis was required to help the group identify specific components based on our device's requirements. Through the analysis, we determined the thickness of materials, heating time, fan capabilities, heating pad needs, and insulation requirements, which allowed the team to select specific components. A detailed CAD drawing was created to represent the geometries of the selected components. The final budget was also completed after component selection was complete. Error analysis is still ongoing and is expected to be finished by the end of next week. The summer break will be used to refine the group's Python code for the Arduino. Below is a list of completed and uncompleted tasks for this period:

Tasks Completed:

-          Perform Detailed Engineering Analysis

-          Select Components Based on Analysis

-          Create Detailed CAD Drawing

-          Finalized Budget

-          Perform Analysis of Selected Components

Tasks Remaining:

-          Complete Error Analysis

-          Refine Python/Arduino Code and Prepare for Capstone II

Description of the Team’s Final Design

With comprehensive heat transfer analysis completed and confidence in our findings, the team is ready to proceed with our design. Following careful consideration and feedback from stakeholders and our instructor, our final design includes key features such as a variable-speed fan, a heat sink, heat-dissipating material, and insulation. Heat will be applied to the bottom of our device, where layers of heat-dissipating material will transfer the heat upwards through a "sandwich" configuration. This analogy involves high-conductivity material acting as the "bread" and low-conductivity material serving as the "filling" between layers. Thermistors will be utilized to measure the heat transfer between these layers by obtaining temperature readings. To dissipate the transferred heat effectively within the time limit, an attached heat sink and a variable-speed fan will be employed. Concerns were raised about potential heat recirculation within the enclosure and heat storage. In response, openings have been incorporated into the side and top of the heat-dissipating enclosure to facilitate airflow and ensure heat is carried away in an axial path upwards from the device. High-conductivity material will encase our components, with insulation encapsulating the device to enable controlled heat movement solely by our components. The team has achieved significant progress through design analysis, providing a comprehensive visual representation of our heat rejection device.

Key Analytical Results

Thus far, we’ve conducted various analyses on what is necessary for the major components of our device, which are as follows:

• Dissipating Heat Material Analysis - to allow the device to heat up and cool down like we want it to within our time constraint of 5 minutes, we analyzed what the maximum thickness of the heat-dissipating material needs to be. Using aluminum as the material, it was calculated the maximum thickness of the material has to be 0.30 inches, which yielded a time to heat up of 251 seconds, and a time to cool down of 46 seconds, totaling 297 seconds, just under our 5-minute time constraint.

• Fan Capability Analysis - Based on the heatsink we chose to reject the heat from the heating pad, and eventually the benchtop surface, the manufacturer of the heatsink specified two axial fans to mate with the heatsink, one with speed control and one without. As controlling the fan speed is crucial for our design, we chose that model, and the maximum capabilities of that particular fan are 60.8 CFM. It was calculated that the fan had maximum heat rejective capabilities of 1879.15 Watts, which is significantly more than our required heat rejective wattage of 5-100 Watts, indicating this fan is more than capable of doing what we need it to do.

• Maximum and Minimum Operating Temperature of the Heating Pad - As part of our validation process, a heating pad was deemed necessary to test the design functionality of our device, until we can get to the benchtop surface in the laboratory environment at NASA to properly test the device. It was calculated that the heating pad would need a minimum temperature of 32.25 Celsius, and a maximum temperature of 105.7 Celsius, to be able to properly meet the specified minimum temperature of 30 Celsius and maximum temperature of 90 Celsius.

• Insulating Material Analysis - To minimize heat loss through the walls of our device before it is rejected through the fan, extensive research of various insulating materials that fit within our budget was conducted. We settled on ceramic fiber insulation from McMaster-Carr, with an R-value of 0.4 and a thickness of ¼ of an inch. Further analysis based on the characteristics of the insulation yields a heat loss through the walls of 0.0434 Watts, indicating this insulation material significantly reduces the heat lost through the walls of the device.

These analyses demonstrate the components we analyzed fall within the necessary specifications for our design as dictated by NASA.

Preparations Completed 

• “Sandwich” design analysis for optimum thickness of heat-dissipating material 

• Error analysis on thermistors 

• Optimization of Arduino code 

• Power supply and heater pad compatibility assured. 

• Design modifications for increased air intake of heatsink

To this day we are still identifying aspects of our project that we can modify and improve to better prepare ourselves for Capstone II. The most prominent one is the design optimization of the heat-dissipating material. We decided to make a design change of a single layer of heat-dissipating material to a three-layer heat-dissipating material for an increase in temperature difference. This will give us more accurate results on our project. 

Next, we have an error analysis of thermistors. Taking into account factors like temperature, thickness, and thermal conductivity will allow us to create an error analysis in case we run into problems like inaccuracies in temperature readings. The Arduino is the brain of this prototype. Making sure that it can process information imputed by the thermistors to control the heat sink fan is crucial for our project's success. Making sure the power supply and the heating pad may sound like a simple task but it is an important one. Having 100W of power passing heat through our device will allow us to hit the numbers we need for our data. Previously, we had a design that did not allow air circulation inside the device. We have been advised to have openings on the side so that air can circulate and properly cool the heatsink. 

Figure 1: Prototype CA

Figure 2: Arduino Diagram Display

Figure 3: The “Sandwich” Design for Prototype