(ORDO NEWS) — Water often boils, whether it’s a cup of tea brewed in the kitchen or a power plant generating electricity. Any improvements in the efficiency of this process will have a huge impact on the total amount of energy used for it each day.
One such improvement could be a newly developed surface treatment involved in heating and evaporating water. . The treatment improves two key parameters that determine the boiling process: heat transfer coefficient (HTC) and critical heat flux (CHF).
Most of the time, there is a trade-off between the two as one gets better, the other gets worse. After years of research, the research term behind this technique has found a way to improve both.
“Both parameters are important, but improving both parameters together is quite difficult because they have an internal trade-off,” says bioinformatics scientist Youngsap Song of Lawrence Berkeley National Laboratory in California.
“If we have a lot of bubbles on the boiling surface, that means boiling is very efficient, but if we have too many bubbles on the surface, they can coalesce together to form a vapor film over the boiling surface.”
Any vapor film between the hot surface and the water creates resistance, reducing the heat transfer efficiency and CHF value. To get around this problem, the researchers developed three different types of surface modification.
First, a number of microtubules are added. This array of tubes, 10 micrometers wide, spaced about 2 millimeters apart, controls bubble formation and keeps bubbles in cavities. This prevents the formation of a vapor film.
At the same time, it reduces the concentration of bubbles on the surface, reducing the boiling efficiency. To solve this problem, the researchers implemented even less processing as a second modification, adding bulges and protrusions as small as nanometers across the surface of the hollow tubes. This increases the available surface area and promotes evaporation rates.
Finally, microcavities were placed in the center of a series of pillars on the surface of the material. These pillars speed up the liquid withdrawal process by increasing the surface area. In combination, the efficiency of boiling is greatly increased.
Since the nanostructures also promote evaporation under the bubbles, and the columns provide a constant flow of liquid to this base of the bubbles, it is possible to maintain a layer of water between the boiling surface and the bubbles, increasing the maximum heat flux.
“Showing that we can control the surface in such a way as to get an improvement is the first step,” says the mechanical engineer. Evelyn Wang of the Massachusetts Institute of Technology. “Then the next step is to think about more scalable approaches.”
“These kinds of structures that we create are not designed to scale in their current form.”
Considering converting a small lab into something commercially viable won’t be easy, but the researchers are confident it’s possible.
One of the tasks will be the following. finding ways to create surface textures and three “tiers” of modifications. The good news is that there are different approaches to explore and the procedure should work for different types of liquids as well.
“Details like that can be changed and that could be our next step. Song says.
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