Result of a 3D-Printed solar receiver of honeycomb mesh shows the heat distribution through the tubes carrying the air that acts as heat transfer fluid IMAGE©OmarBehar, KAUST
A 3D-Printed solar receiver could solve some problems holding back a new technology:
High-temperature solar receivers – for solar thermochemistry and industrial heat – can be prone to uneven heat distribution. These temperature differences create thermal stress, particularly between the sun-facing front and the back of each tube carrying heat.
To solve this problem, A team of three concentrated solar thermal researchers at KAUST (King Abdullah University of Science and Technology in Saudi Arabia) propose an advanced 3D-printed metal solar receiver with a conical cavity made up of a honeycomb lattice structure designed to reduce thermal stress. They presented their paper (3D-Printed solar cavity receiver for heating pressurized air – A preliminary evaluation) and 3D-printed receiver presentation at the recent SolarPACES Conference.
The heat is circulated via pressurized air heated by concentrated sunlight through tubing that encircles the inside of the cone-shaped receiver. This tubing is embedded within a honeycomb mesh. This honeycomb design enables the heat to be distributed evenly.
Solar receivers that use a gas like air or CO2 to transfer the solar heat are capable of the super-high temperatures we need to displace fossil fuels for industrial processes or to produce solar fuels like 100% solar hydrogen or aviation fuel. Air doesn’t degrade at 1,000C.
However, the lower thermal conductivity of gases compared to a liquid like molten salts, means these gas-based solar receivers need to operate at high pressure while finding a way to even out temperature distribution to overcome thermal stress.
To solve this challenge, the KAUST team has found a way to distribute the heat more evenly. The solution is a honeycomb mesh design, and to perfect such a complex material, to 3D-printing.
Cross section of honeycomb mesh surrounding tubes in 3D-Printed solar receiver IMAGE©Omar Behar, KAUST
3D-printing has opened opportunities in engineering that didn’t exist before
“The 3D-printed technology allows us to print whatever we can imagine,” said KAUST Post Doc Fellow, Omar Behar.
“This mesh would be really difficult to manufacture using classical technology. It’s like a honeycomb, that starts big and then it decreases slowly. So this design is difficult using the classic manufacturing process. The only way to do this is to manufacture it with a printed process.”
The material they plan on using in the 3D-printer is Inconel, a metal which is favored in concentrated solar receivers for its ability to withstand stress as it goes through 24-hour heating and cooling cycles with each days’ solar radiation. Previous solar researchers working on high temperature solar thermal have used ceramic, but Behar said that ceramic will have problems in scaling up to commercial size, in part because these solar receivers require a quartz window which can create problems.
“Inconel is a very good material that can withstand temperatures up to 1000°C and it is commercial available,” he said.
“The advantage over ceramic, which is more fragile, is that a metal can be scaled up to a large scale application, so it will be possible to scale up the technology and make it commercial.”
Having first simulated the novel 3D-printed honeycomb design, they have started to try out the first testing of the manufacturing process, to see how it would work if it were to be deployed on a commercial scale.
“To understand the performance we did the simulation using Ansys,’ said Behar.
“The results were really promising. Based on the simulation, we are manufacturing the receiver in two phases. We will first manufacture a small piece, that we will test, and then, if everything goes well, we will then print the whole system.
While KAUST is situated north of Jeddah, this testing of parts of the prototype is manufactured by nami at a factory 800 km away in Riyadh. The team hoped to see if any manufacturing challenges might require rethinking. Two came up.
“The first issue that we faced was the manufacturing itself, because even the tubes need to be printed,” he explained. “The entire receiver is 3D-printed. And these tubes are just 10 mm in diameter.
They also learned that in order for this to be able to be 3D-printed that they would need to have a minimum thickness in the composition of the honeycomb for the printing machine to work. That the honeycomb needed to be simplified and no part of it could be under 1 mm thick.
The paper states: “Simulation results indicate that the receiver operates efficiently at a maximum heat flux density of 230 kW/m², corresponding to the maximum working temperature of Inconel 718 (1000°C), while maintaining a low pressure drop of approximately 170 mbar. The design allows for significant improvements in temperature distribution, particularly in gas-based receivers where thermal stress is more pronounced due to lower thermal conductivity.”
The 3D-Printed solar receiver in the lab at KAUST
Lab scale 3D-printed cone shaped solar receiver IMAGE©Omar Behar KAUST
In the lab, their solar receiver would be 3 kW, but Behar suggested that for many industrial uses, a useful commercial scale would be about a megawatt (1,000 kW).
The industry that the team is looking at in particular within the Kingdom is its cement industry, which uses heat at 800°C to 900°C to calcine limestone from local quarries. Saudi Arabia can rely on at least 340 sunny days a year – making concentrated solar to generate heat directly a good fit.
