Use of biodegradable colloids and carbon black nanofluids for solar energy applications

Abstract

The conversion of solar energy to heat can be performed in direct absorption solar collectors, where the radiation from the sun is absorbed by a fluid. There are various types of fluids that can be used, and recently, nanofluids (i.e., liquids with immersed nanoparticles) have been investigated by researchers. Nevertheless, nanofluids have inherent drawbacks such as cost, toxicity, and clogging. This paper considers the use of fluids that are inexpensive and neutral to the environment, namely, coffee colloids. These types of fluids have already been tested for solar energy applications, but they have not yet been compared with nanofluids. In this research, we conducted a series of simple experiments where both coffee colloids and carbon black nanofluids were analyzed under the same conditions. According to our results, the thermal efficiency of coffee colloid and the nanofluid systems is, respectively, 12% and 16% greater than that of pure water. In addition to the experiments, we developed a mathematical model that is based on the Beer–Lambert law and a heat balance equation. Despite its simplicity, the model predicts the results relatively well.

Photothermal conversion of biodegradable fluids and carbon black nanofluids

“…Different concentrations of the nanofluids were considered, and they were compared with the coffee colloids. This part of the paper resembles our previous paper 11 , but this time we show that the change of the set-up geometry has a significant influence on the conclusions.…”

“…We produced three different weight concentrations of CB nanofluid: 0.25%, 0.50%, 1.0%. Thus, this research differed from our previous paper 11 , where the focus was on higher concentrations.

Figure 1 Scanning electron microscopy image of the carbon black nanoparticles investigated in this research.

…”

“…Afterwards, a beaker with the suspension was placed in an ultrasonic bath of the type Branson 3510. The duration of the sonication was 1 h. It must be noted that a similar procedure was used in our previous works 9 – 11 , 13 , as well as by other researchers 19 – 22 .…”

“…Some examples are the following systems: copper-water 3 , 4 , aluminium oxide-water 5 – 7 , , , CuO, or carbon nanotubes in water and in oil 8 . In our previous research, we studied carbon black (CB) nanoparticles 9 – 11 and iron oxide nanoparticles 12 , 13 in water.…”

“…Moreover, they function without other drawbacks inherent to metallic nanofluids such as potential erosion 14 – 16 or nanoparticle deposition/clogging. Nevertheless, this topic has only been discussed in a few papers 11 , 17 , 18 . Therefore, they are the objective of this research.…”