Pentafluorophenyl (PFP) ester-functionalized poly(phenylacetylene)s (PPAs, P1, P2, and P3) were designed and synthesized in desirable yields and molecular weight by using organorhodium complexes as catalysts. Furthermore, these PFP-containing PPAs were used as precursors to prepare a series of mono- and dual-functionalized PPAs by the substitution of the activated ester moieties with functional amines. The structures of the PFP-containing PPAs and the derived functional PPAs were characterized by using multiple spectroscopic techniques including GPC, FTIR, 1H NMR, 13C NMR, and 19F NMR. The experimental details and the characterization data demonstrate that activated ester synthetic route to functional PPAs is facile (just stirring the precursor polymer with proper amine(s) at room temperature for hours), efficient (complete transition from ester to amide has been confirmed), and quantitative (the relative content of a specific functionality can be precisely preset by controlling the feed ratio of the functional amines). By reacting three PFP-containing PPAs with chiral amines or with chiral and nonchiral alkyl amines in a step-by-step way, a series of seven different PPAs with asymmetric carbon in the side chains were obtained. CD measurements indicated that the incorporation of chiral amine into polymer side chains induced helicity formation of P1 backbone. P1-C*Ph(L) and P1-C*Ph(D) backbones adopt predominantly right-handed and left-handed helical conformation, respectively. While the flexible spacer between the chiral center and the rigid PPA backbone blocked the induction of main-chain helicity by chiral pendants, thus no CD signals were recorded for P2-C*Ph(L) and P3-C*Ph(L). Substitution of PFP ester with amine-functionalized PEGs transited the hydrophobic PPAs to hydrophilic. All of the PEG-containing PPAs can be dissolved in water and form clear solutions. Meanwhile, all of the aqueous solutions exhibit LCST behavior and the hydrophilic PEG chains and hydrophobic alkyl spacers have positive and negative impact on the cloud point, respectively. Contact angles measurements showed that the length and content of the PEG chains contribute greatly to the hydrophilic property, and the length of the alkyl spacers and the content of the alkyl amine component played a contrary role. By controlling the ratio of the PEGylated and alkyl amines, the amphiphilic property of the PPAs can be well tailored.

No abstract

Steam is a common medium in thermal engineering. When it flows through a throttling element, the aerodynamic noise may occur due to the disturbance. In this investigation, superheated steam flowing through a Venturi tube, one of the main parts in a temperature and pressure regulation valve, at different thermal conditions is studied to analyze to effects of heat transfer on the acoustic power. With a high temperature and a low pressure, the superheated steam is treated as ideal gas. The flow velocity is high, so the k-epsilon turbulent model is used, with the compressible steam. The results show that under the adiabatic condition, the acoustic power mainly influenced by the turbulent characteristics, such as the dissipation rate and the turbulent kinetic energy. Comparing the acoustic power levels at different thermal conditions, it is found that a lower temperature results to a lower acoustic power.

Corrugated tubes are widely used in a range of applications for heat transfer enhancement. The spirally corrugated tube has a better heat transfer performance than the smooth tube. In this paper, the heat transfer performance of a hybrid smooth and six-start spirally corrugated tube is studied. With a validated numerical model, the effects of the corrugation part length on the vortex in the downstream smooth tube are studied for a range of high Reynolds numbers, where the existence of the corrugation part can turn out the secondary flow and enhance heat transfer. Meanwhile, it is found that in the smooth part, the fluid flow part with whirling can reach a maximum length, even if the length of the corrugation part continuously increases. Thus a series of critical corrugation lengths can be obtained. This work can reveal the enhanced heat transfer mechanism of the hybrid smooth and spirally corrugated tube and be of interest to researchers in heat transfer issues of corrugated tubes.

View related articles View Crossmark data Citing articles: 3 View citing articles A geometric study on shell side heat transfer and flow resistance of a six-start spirally corrugated tube

When liquids flow through a throttling element, the velocity increases and the pressure decreases. At this point, if the pressure is below the saturated vapor pressure of this liquid, the liquid will vaporize into small bubbles, causing hydraulic cavitation. In fact, a vaporization nucleus is another crucial condition for vaporizing, and particles contained in the liquid can also work as the vaporization nuclear. As a novel heat transfer medium, nanofluids have attracted the attention of many scholars. The nanoparticles contained in the nanofluids play a significant role in the vaporization of liquids. In this paper, the effects of the nanoparticles on hydraulic cavitation are investigated. Firstly, a geometric model of a perforated plate, the throttling element in this paper, is established. Then with different nanoparticle volume fractions and diameters, the nanofluids flowing through the perforated plate are numerically simulated based on a validated numerical method. The operation conditions, such as the ratio of inlet to outlet pressures and the temperature are the considered variables. Additionally, cavitation numbers under different operating conditions are achieved to investigate the effects of nanoparticles on hydraulic cavitation. Meanwhile, the contours are extracted to research the distribution of bubbles for further investigation. This study is of interest for researchers working on hydraulic cavitation or nanofluids.

When liquids flowing through a throttling element, such as a perforated plate, the velocity increases and the pressure decreases. If the pressure is below the saturated vapor pressure, the liquid will vaporize into small bubbles, which is called hydraulic cavitation. In fact, vaporization nucleus is another crucial condition for vaporizing. The nanoparticles contained in the nanofluids play a significant role in vaporization of liquids. In this paper, the effects of the nanoparticles on hydraulic cavitation are investigated. Firstly, a geometric model of a pipe channel equipped with a perforated plate is established. Then with different nanoparticle volume fractions and diameters, the nanofluids flowing through the channel is numerically simulated based on a validated numerical method. The operation conditions, such as the temperature and the pressure ratio of inlet to outlet, are the considered variables. As a significant parameter, cavitation numbers under different operation conditions are achieved to investigate the effects of nanoparticles on hydraulic cavitation. Meanwhile, the contours are extracted to research the distribution of bubbles for further investigation. This study is of interests for researchers working on hydraulic cavitation or nanofluids.

No abstract