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In order to decrease the energy consumptions in energy conversion devices, boiling heat transfer augmentation is one of the important research activities for the scientific community. In present study, the pool boiling heat transfer characteristics of Cu–TiO 2 composite coating on copper surfaces are reported. A two-step electrodeposition technique is employed to develop the nanocomposite coatings on copper surfaces, where higher current densities are applied for a short period and then the deposition is continued with lower current density for longer period in the second step of electrochemical deposition. The layer deposited during the first step is fragile, which is stabilized during the second step of electrodeposition at lower current density for longer duration. The surface morphology properties like porosity, wettability, coating layer thickness are easily controlled by managing the electrodeposition parameters like electrolyte composition, deposition time and current density. The pool boiling experiments are performed on bare and composite-coated surfaces at atmospheric pressure with saturated DI water. The boiling performance of coated surfaces is compared with the bare (uncoated) surface. The maximum boiling heat transfer coefficient and critical heat flux on coated surfaces are achieved to be 151 kW m −2  K −1 and 1988 kW m −2 , which are 185% and 86% higher than the bare copper surface, respectively. The enhancement in boiling performance is associated with several parameters like increase in porosity, presence of high-density nucleation sites, and improvement in surface wettability.

Open microchannels and micro/nanoporous coatings by nanofluid boiling have been used separately by earlier researchers to improve heat transfer during pool boiling. The combined impact of these factors is examined in this work by novel ZnO-coated Cu (Cu@ZnO) hybrid nanofluid boiling on the apex of microchannels’ fins, resulting in development of micro/nanoporous coatings on the apex of microchannels’ fins. The Cu@ZnO hybrid nanoparticles were prepared by optimal spark discharging in liquid nitrogen. The next phase involves dispersing the developed nanoparticles in DI water as the base fluid to achieve stable nanofluids. This article reports on the impact of microchannel geometry on the efficiency of heat transmission for water and hybrid nanofluid boiling on copper chips. A higher concentration of nanofluid with microchannel configuration enhanced the CHF and HTC throughout the pool boiling experiment. The highest increases in HTC and CHF were reported to be 287.57% and 123.60%, respectively, for 0.1% hybrid nanofluid on 300-µm microchannel. The mechanisms of bubble formation and heat transport are changed when nucleation occurs mostly on the fin tops. The present study’s theory is founded on the improved rewetting routes offered by microchannels and the extra nucleation spots offered by porous layers, both of which operate in concert to improve boiling behaviour. A microconvective process wherein highly localized liquid circulating currents are created in the microchannels by bubbles emerging from the tops of the fins. Additionally, a conceptual framework based on liquid microcirculation is suggested.

The effective disposal of plastic waste has been a key global research issue. In this regard, the pyrolysis of plastic wastes seems to be an effective technique as this process is capable of producing fuel-grade oils. In the present work, the thermal decomposition of polyethylene (PE), polystyrene (PS), and their mixture (PS/PE) was investigated with an aim to enhance yields of liquid fractions with fuel-grade quality. The effect of operating parameters on the end products was studied. The obtained maximum liquid yields for polyethylene (PE) and polystyrene (PS) samples were 96.3 wt.% at 380 °C and 88.1 wt.% at 415 °C, respectively. For the PS/PE (50/50%) sample, the maximum conversion was 93.2 wt.% at 420 °C. Char yield was observed negligible (1–3 wt.%) at low reaction temperatures (350–420 °C). PE samples showcased a sharp initial decrease from 1.8 wt.% at 350 °C to 0.7 wt.% at 415 °C. PS also presented a similar trend; whereas, PS/PE sample was observed with 3.1 wt.% char at 350 °C that decreased to 1.4 wt.% at 420 °C. PE oil samples showed the presence of 1-alkenes and n-alkanes compounds in abundance, with carbon numbers in the range of C7 to C28. PS oil fractions comprised of toluene, ethylbenzene, and styrene in higher proportions of around 42%. On the other hand, PS/PE oil fractions mostly constituted the aliphatic hydrocarbons embracing both alkanes and alkenes with carbon numbers C12 to C22. Comparative assessment reveals that for PE oil fractions from the autoclave reactor are 44.4% and 90.2% higher than the same with fluidized bed and microwave-assisted reactors, whereas for PS oil fractions the values were marginally higher.

The rapid latent heat transfer in boiling heat transfer directs its potential use in a variety of heat transfer devices. A new four-step electrodeposition technique is recommended for the development of the micro–nanostructured surface of Cu–Al 2 O 3 nanoparticles (higher thermal conductive) to increase pool boiling heat transfer performance. The nanoparticles deposited at lower current density have increased the nucleation density and the two-step sintering has improved the physical properties of deposited nanoparticles. Thus, apart from cost effectiveness, reliability, and simplicity, the electrodeposition method is able to provide more stable micro–nanostructured surface. Therefore, the method offered in this work is a proficient method for the development of micro–nanostructured surfaces. After carrying out the surface characterization of structured surfaces, the boiling heat transfer performance is studied through experimentations. The influence of different parameters on pool boiling heat transfer (PBHT) enhancement is also analyzed. Based on the study of the achieved results, it is inferred that the fabricated micro–nanostructured surfaces are uniform in structure, achieve higher critical heat flux (92 %), and PBHT coefficient (6.1 times). Thus, the proposed heating surfaces may be considered as a prospective candidate for the cooling of microelectronics devices.

Numerous energy systems, including distillation, power production, air conditioning, cooling, and purification, use evaporation and flow boiling in minichannels. In this study, we show noticeably higher heat transfer coefficients and critical heat flux of 182% and 114% during DI water flow boiling in ZnO-nano-thin-film nanostructured (∼110–423 nm), industrial-scale-heated copper bottom surface. By using a combination of the sol–gel spin coating and annealing methods, we produce durable and highly conformal nanostructured surfaces that enable scale nano-manufacturing. Flow boiling experiments were carried out in 1.5 mm height bottom surface-heated minichannel using DI water as the working fluid. In order to measure the effectiveness of present method and clarify how the structural length scale affects it, the present study ZnO-nano-thin-film structured surfaces are compared with previously published micro/nano-scale fabricated surfaces, demonstrating the necessity and importance of the nanoscale properties of ZnO-nano-thin films for improvement. The surfaces of the nano-thin film were subjected to durability testing utilizing a seven-day continuous flow boiling experiment, which revealed minor deterioration. The higher boiling performance is achieved on ZnO-TF-423 is due to the proper bonding between polished copper bare surface (BS) and deposited ZnO thin films. Additionally, the rough surface on BS allows the copper and ZnO thin films to bind properly. It can be concluded that surfaces made using an efficient sol–gel spin coating process possesses superior boiling heat transfer capabilities at comparatively lower surface temperatures, suggesting a smaller chance of damaging the surface from rising temperatures.

The present study aims to examine the effects of varying concentrations of the unique Cu@ZnO hybrid nanofluid on the pool boiling heat transfer coefficient ( HTC ) and critical heat flux ( CHF ). A four-step process was used to create the Cu@ZnO hybrid nanofluids by discharging in liquid nitrogen. Copper nanoparticles ( Cu-NPs ) are created by initially running discharges between two copper electrodes. In the same liquid where Cu-NPs , generated during the previous stage, are present, fresh discharges are then conducted between two zinc electrodes. At first, Cu@Zn core–shell nanoparticles are produced, followed by copper nanoparticles coated in zinc. The oxidation of the synthesised core–shell nanoparticles takes place in the last stage after liquid nitrogen has evaporated, exposing the metals to air and causing them to change into oxides. The fourth phase involves dispersing the created nanoparticles in DI water as the base fluid. By dispersing the hybrid nanoparticles by an ultrasonication procedure at four distinct volume concentrations: 0.025 %, 0.050 %, 0.075 %, and 0.1 %, stable nanofluids were achieved. The heated surface was a 10-mm-diameter cylindrical copper test piece. When compared to DI water, the hybrid Cu@ZnO water nanofluids thermal conductivity was established to be 31 % greater at 45 °C. A higher concentration enhanced the HTC and CHF during the pool boiling experiment. The highest increases in HTC and CHF were reported to be 212.23 % and 85.80 %, respectively, for 0.1 % hybrid nanofluid in comparison with the basic fluid (DI water). Additionally, the boiling heat transfer was negatively impacted by every additional volume concentration rise above 0.1 %.

The transportation of quick latent heat during phase change heat transfer (boiling) guides its prospective application in various heat transfer devices. The stability of the fabricated cavity/porous surfaces with the base substrate is a significant concern for the degradation of boiling performance. Therefore, a new three-step surface fabrication method (wet etching, electrochemical deposition, and sintering) is proposed in this work. Initially, the three micro/nanostructured surfaces (ES#3, ES#2, and ES#1) are fabricated by using wet/chemical etching. The best-performing wet/chemical etching surface (ES#3) is further used as a cathode for next-of-surface fabrication, i.e., electrochemical deposition. The electrochemically deposited surface (ES#4) is sintered in a predefined atmosphere to increase the bonding between the coated surface (copper-alumina) and the etching surface (ES#3). The higher boiling performance found on the final surface (ES#4) is due to the proper bonding between the ES#3 and electrodeposited copper-alumina nanoparticles. A decrease in the intermediate resistance due to proper binding boosts the percentage of heat transmission by keeping the temperature constant between the top surface of the heater and the tip of the fin. For ES#4, the critical heat flux (CHF) improvement over bare copper is 98%. Comparing the ES#4 coated surface to the bare copper surface results in a 260% increase in heat transfer coefficient (HTC). The effect of various macro and micro-scale constraints on pool boiling heat transfer phenomena is also investigated. Following multiple testing cycles, the decrease in superheat temperatures, surface morphology, and wettability for ES#4 is significantly lower, which indicates healthier stability of ES#4 surface.

There are several industrial applications where boiling is used, for example boilers, refrigeration systems, nuclear reactor cooling, and microelectronic chip cooling. Experimental research has been carried out to determine the flow boiling heat transfer capabilities of copper-alumina-coated surfaces for application in heat transfer equipment. De-ionized (DI) water is used as the coolant for experimentations in a minichannel with dimensions 10 × 1.5 × 10 mm. Copper surfaces coated with thin copper-alumina nanocomposite films are created using the electrodeposition process. The coated layer created using an electrochemical technique offers strong adhesiveness with the base copper and is therefore anticipated to be suitable for real-world heat transfer appliances as part of the ongoing scientific development in subcooled flow boiling. The electrochemical technique offers easier control over its various parameters, such as current density, duration and electrolyte composition, making it possible to easily achieve a variety of surface characteristics, such as crystallinity, wettability and porosity. as required in the coated surfaces. Additionally, the copper-alumina is a hydrothermally stable oxide material that is well suited for use in boiling heat transfer devices. The boiling (subcooled flow) heat transfer tests are carried out at various mass flows. The improvement in the two-phase heat transfer coefficient (HTC) and critical heat flux (CHF) can reach up to 90 % and 93 %, respectively. The coated surfaces have improved CHF and HTC because of improved wettability, increased surface roughness, and the existence of active nucleate sites in high-density.

This paper focuses on computational and experimental analysis of a simple serpentine microchannel without obstacles and serpentine microchannel with semicircular obstacles of different sizes. The work has been performed in three phases- computational analysis, experimentation and flow physics study. The 3D models of a simple serpentine microchannel (without obstacles) and serpentine microchannels with semicircular obstacles (with radius as 50, 100, 150 and 200 µm) have been developed using COMSOL Multiphysics software. The effect of obstacle size on pressure drop and mixing length for achieving index 1 has been analyzed. A simple serpentine qmicrochannel and a serpentine microchannel with 150 µm radius semicircular obstacles have been fabricated with polydimethylsiloxane using soft lithography process. The experimental analysis for pressure drop as well as mixing index has been performed. A good agreement has been observed between experimental and computational results. The validated computational model is then used to study the mixing index for the same microchannels for different flow conditions, i.e. for different Reynolds numbers. The mixing lengths are observed to be lesser for Re 0.28 and 30. Further, the effect of diffusion and generation of secondary flow due to advection on mixing length for the considered Reynolds numbers are analyzed through the flow physics study.