Initial Experiment Design:

The initial idea for this experiment design was to 3D print several test samples, each one printed using a different infill pattern, and create an apparatus to test each sample for its thermal resistivity and compare these values with the tested value recorded using a completely solid 3D printed sample. The selected infill patterns, in addition to a solid control sample, were 3D Honeycomb, Gyroid, and Hilbert Curve.

Experiment Objective:

By employing a method akin to the guarded hot plate technique, the study aims to elucidate how various infill patterns affect thermal conductivity in additive manufacturing, thereby contributing to the understanding and optimization of material properties for specific applications.

Theory and Equations:

Eq.1) Calculating Thermal Conductivity using Fourier’s Law

k = (Qt)/(A∙ΔT) in (Wm∙K)

Eq. 2) Calculating Thermal Resistivity

r = 1/k = (Qt)/(A∙ΔT) in (Wm∙K)

where Q = Heat Flow

t = Specimen thickness

A = Cross−Sectional Area of the Heating Plate

ΔT=Temperature Difference Over the Sample

Eq. 3) Calculating Thermal Resistance (R-Value)

R = r∙t in (m^2∙K/W)

Materials:

Delta Heat Silicone Heater w/ Center Thermistor (40 W)
K-Flex NBR/PVC ½" Adhesive Backed Insulation

Aluminized Fiberglass Insulation

70 mm Tube Axial Fan

t-Global Technology Graphite Heat Spreader (0.055 mm thick)

100 mm Square Heatsink (10 mm thick)

Amphenol Thermometrics Adhesive Mount NTC Thermistor (K-Type) (1kΩ)

ColorFabb N-Gen Flex 3D Printer Filament [Dark Grey] (4 Printed Specimen)

Raspberry Pi 4 Model B (4 GB Ram)

Duet 3 Main Board 6XD

7" Capacitive Touchscreen

AVNTKER Thermal Double Sided Adhesive Tape

Mean Well LRS-75-24 Power Supply (75 W, 24 V)

Canakit AC/DC Convertor (US Plugin Outlet Input to USB-C Output) (5.1 V, 3.5 A) (Model: DCAR-RSP-3A5C)

Procedure:

3D Model then 3D print test samples of ColorFabb N-Gen Flex 3D Printer Filament in (dimensions) rectangular prisms, to match the dimensions of the apparatus, and using the following infill patterns: Hilbert Curve, 3D Honeycomb, Gyroid, and Solid Fill.
Attach the Amphenol Thermometrics Adhesive Mount NTC Thermistor to the Solid Fill control sample, then cover the thermistor and the entire top surface of the sample with the t-Global Technology Graphite Heat Spreader and then the AVNTKER Thermal Double Sided Adhesive Tape.
Fix the 70 mm tube axial Fan to the Square Heatsink by fastening M3 35mm screws into each of the four corners.
Assemble the apparatus by layering, from bottom to top, the Delta Heat Silicone Heater with Center Thermistor, the 3D printed test sample with the thermistor and taped side facing up, then the heatsink and fan components with the fan on top. (Figure 2)
Adhere the K-Flex NBR/PVC ½" Adhesive Backed Insulation around the apparatus, enclosing all components beneath the fan and heatsink. (Figure 1)
Connect the Duet 3 Main Board to the raspberry pi and the power supply.
Connect the raspberry pi to the 7" Capacitive Touchscreen and the AC/DC Converter via USB-C.
Connect the silicone heater, hot side thermistor, cold side thermistor, and fan to the Duet 3 using ports out 2, temp 1, temp 2, and out 7 respectively.
Once all connecting cables have been attached, and the SD card with necessary code has been inserted into the raspberry pi, run the program, and set the CMS temperature to 70°C and press Start.
Wait for the system to reach a steady state, then record the value for the Outside Temperature, and press stop. Data will be saved automatically, and all electronics will be cut off.
Disconnect 24V power supply powering the Duet 3, disassemble the apparatus, and replace the control sample with one of the three infill pattern test samples.
Repeat steps 2-11 for three trials, one trial for each of the infill pattern test samples.
Calculate the thermal resistivity of the control sample and each of the test samples and compare the results.

Results and Analysis:

Table 1. Measured, Given, and Calculated Constants

Table 2. Experimental Data and Calculated Values

Plot 1. Thermal Resistivity (m∙K/W) of Varying Infill Patterns

Results and Analysis:

The experiment aimed to ascertain the thermal resistivity of various 3D printed infill patterns akin to the guarded hot plate method. The specimens included a solid control, 3D Honeycomb infill, Gyroid infill, and Hilbert Curve infill. Through meticulous experimentation and analysis, it was deduced that the 3D Honeycomb infill exhibited the highest thermal resistivity among the tested patterns. Remarkably, the Hilbert Curve demonstrated a notable 17.14% increase in resistivity, closely followed by the Gyroid at 18.86%, while the 3D Honeycomb displayed the most substantial boost at 21.14%, when contrasted with the control specimen.

The significance of these findings extends beyond the scope of mere thermal conductivity; they illuminate the potential applications and optimization of 3D printing processes for specific thermal performance requirements. For instance, in industries where thermal insulation or heat dissipation is crucial, such as electronics or aerospace, selecting the appropriate infill pattern can be pivotal in achieving desired outcomes. The considerable variation in resistivity observed between different infill patterns underscores the importance of deliberate design choices in additive manufacturing for tailored material properties.

However, it's essential to acknowledge potential sources of error that could have impacted the accuracy of the results. One notable limitation was the reliance on a fastening method using double-sided tape, which occasionally proved insufficient to securely hold the apparatus together. This inconsistency may have introduced variability in the experimental setup, affecting the reliability of the measurements. Additionally, the observed warping of the 3D printed specimens during printing poses another challenge. Uneven surfaces resulting from warping could have compromised thermal contact with the heater or heatsink, thereby influencing the measured thermal resistivity values.

Thermal Resistivity Experiment for Different 3D Printed Infill Patterns