Italy: Experimenting with Coffee in 3D Printed Collectors for Better Solar Absorption

3D printing can be performed in countless ways; in fact, the choices are as infinite as the ability to innovate using this technology with an expanding force of hardware, software, and materials. Many different types of objects can be made that were not previously possible also, along with allowing for self-sustainability in creating items in the lab that can further a variety of studies. This was the case during a recent examination of thermal-physical properties by Italian researchers, explained in their recently published paper, ‘Coffee-based colloids for direct solar absorption.’

The researchers used 3D printing to create ‘collectors’ for their experiments for solar absorption, seeking an alternative to the usual carbon-based nanocolloids. To avoid the disadvantages of carbon—including cytotoxicity and harm to the environment—the authors leaned toward a much more natural mixture of:

• Arabica coffee
• Distilled water
• Glycerol
• Copper sulphate

The study revolved around the creation of a better surface absorber overall, functioning via sunlight and its energy being passed to a carrier fluid. That carrier must possess suitable thermal and optical properties, however. Because coffee is so dark, it is more conducive to soaking up sunlight, and resulting heat—harkening back to previous studies with black India ink. That research was encouraging, and in considering it, the authors have combined their experiments to try and include nanocolloids—but without the toxicity.

“Different nanoparticle types have been investigated, such as single- and multi-walled nanotubes, graphite, nano-horns, or carbon powder in water. However, the increasing use of carbon nanoparticles may lead to major environmental concerns and biological risks, because of their (cyto)toxicity. In this sense, biocompatible (nano)colloids may represent a more sustainable and safe-by-design alternative to carbon-based nanosuspensions,” stated the researchers.

Synthesis of the coffee-based colloids. (a) Coffee pot moka used for the coffee preparation (top-left); size distributions of the suspended coffee particles (top-right); Scanning Electron Microscopy (SEM) images of the coffee particles (bottom). (b) Colloids with different G30 concentration (from right to left): pure G30 fluid (56.17 g/l of suspended particles); G30w10 fluid (10% dilution); G30w1 fluid (1% dilution in water); pure water.

Coffee is much more complex than you may imagine (which may be the secret to the magic it bestows upon so many of us each morning), and available in a wide range of different compositions. For this experiment, the researchers used a stovetop aluminum coffee maker, with 100 cm³ maximum capacity, a 35 cm³ capacity filter, and a topper pot. Proposed colloids were then explored regarding extinction coefficient and stored energy fraction, while photo-thermal performance was compared with a selective surface absorber using the customized, 3D printed solar collectors. Three different flow rates were examined during the experiment.

Optical properties of the coffee-based colloids (1%, 10% and 100% dilutions in water). (a) Comparison of the spectral extinction coefficient of the coffee-based colloids at different dilutions and a 0.05 g/l suspension of carbon nanohorns in water27. The G30 preparation (100% dilution) is coffee with 2 ppm of copper sulphate and 30% wt. glycerol; G30w1, G30w10 are respectively 1% and 10% volume fractions of G30 in distilled water. (b) Stored energy fraction (EF) as a function of the path length for the three considered coffee-based colloids. Solid lines correspond to the energy fraction obtained with Planck’s black body distribution, while dashed lines that obtained with the AM1.5 standard spectrum. The curves for a 0.05 g/l suspension of carbon nanohorns in water27 are also reported for comparison.

“Experimental tests are carried out in the same conditions for direct and indirect absorption, and the efficiency of the collectors compared,” stated the researchers in their paper.

Regarding the performance of the 3D printed collectors, the researchers explained that a balance between absorption and reflection at the bottom of the channel was critical. Thermal conductivity was promoted via ‘tuning’ of the geometry channel.

“Field tests, in good agreement with numerical models, have demonstrated that these fluids can provide similar performance to the traditional indirect absorption based on selective surfaces,” concluded the researchers.

“These results may pave the way to a new, unconventional family of biocompatible, environmentally sustainable and inexpensive colloids for solar applications, for example suited for vapor formation, seawater desalination, domestic hot water production, or sustainable solar cooling.

As further advances are made in technology today, the options for materials in 3D printing continue to grow; however, this is not without concern for what types of energy we are using, along with how we are impacting the environment. Studies regarding materials and emissions, toxicity, and various methods for recycling continue to emerge also, along with different ways to harness solar energy in the actual exercise of 3D printing. Find out more about colloids and solar absorption here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Set-up for the solar absorption tests. (a) Flow chart of the solar collectors design and manufacturing: from CAD model, to 3D-printed collector, to final assembly. During field tests, the performance of the direct solar absorber is compared with that of the traditional flat-plate collector. (b) Scheme of the experimental set-up used for testing the efficiency of the coffee-based colloids for the direct solar thermal energy absorption. Solid lines represent hydraulic pipes for the colloidal flow; dashed lines electric wires for data acquisition.