Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

This is an open access article distributed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International license (CC BY-NC-ND 4.0) https://creativecommons.org/licenses/by-nc-nd/4.0/Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional (2D) numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.Peer reviewe

Surface Wetting and its Optimization to Cool Broiler Chickens

Surface wetting to cool broiler chickens (Ross . Ross male, 46 .3 d, 2.8 . 0.1 kg) was investigated under 18 acute thermal conditions formed by 3 . 2 . 3 factorial combinations of dry–bulb temperature (tdb) of 35.C, 38.C, and 41.C; dew–point temperature (tdp) of 19.4.C and 26.1.C; and air velocity (V) of 0.2, 0.7, and 1.2 m s–1. The synergistic effects of tdb and tdp were expressed in terms of vapor pressure deficit of the air (VPDair, kPa). Surface temperature of the cooled birds was 1.9.C to 2.5.C lower than that of their control counterparts. Core body temperature (tb) rise above the normal level for the cooled birds was 1.2.C, 1.6.C, and 1.7.C lower than that for the control birds at 35.C, 38.C, and 41.C, respectively. Increasing V tended to narrow the difference in tb between the cooled and the control broilers, 2.0.C, 1.4.C, and 1.2.C for V of 0.2, 0.7, and 1.2 m s–1, respectively. Increasing tdp from 19.4.C to 26.1.C produced only 0.2.C overall difference in tb. Results of this study demonstrate that surface wetting coupled with good air movement, as in the case of tunnel ventilation, is effective in relieving heat stress of the birds even under relatively humid conditions. The cooling water needs, expressed as spray interval at a nominal spray dosage of 22 mL bird–1 (SI22, min) and evaporation rate (ER, mL/min kg0.67), were optimized by relating the SI22 or ER to the thermal conditions: SI22 = 70.50 – 27.14 V – 4.84VPDair, and ER = –0.0471 + 0.1700 V + 0.0297VPDair

Dynamic stress response and fatigue life of cantilever beam under non-Gaussian base excitation

The stress response of cantilever beam to non-Gaussian random base excitation is investigated based on Monte-Carlo simulation. First, the statistical properties and spectral characteristics of non-Gaussian random vibrations are analyzed qualitatively; and the conclusion is that spectral method based on power spectrum density (PSD) is not applicable for non-Gaussian random vibrations. Second, the stress response formula of cantilever beam under non-Gaussian random base excitations is established in the time-domain, and the factors influencing the output kurtosis are subsequently determined. Two numerical examples representing different practical situations are analyzed in detail. The discrepancies of the stress responses to Gaussian, steady non-Gaussian and burst non-Gaussian base excitations are analyzed in terms of root mean square (RMS), kurtosis and fatigue damage. The transmissibility of RMS and high-kurtosis of steady non-Gaussian random base excitation is different from that of burst non-Gaussian case. Finally, the fatigue life corresponding to every base excitation is calculated using the rainflow method in conjunction with the Palmgren-Miner rule. Finite element analysis is also carried out for validation. The predicted fatigue lives corresponding to Gaussian, steady non-Gaussian and burst non-Gaussian base excitations are compared quantitatively. Finally, in the fatigue damage point of view, the discrepancies among the three kinds of random base excitations are summarized

Daily Variation of Thyroid Hormones in Broiler Under High-Temperature Conditions

Market-size (61-68 day-old) AA broiler chickens were exposed to simulated high-cyclic summer temperatures of North, Central and South China for 5 continuous days. Blood samples were collected at 0AM, 4AM, 8AM, 0PM, 4PM and 8PM each day, and concentrations of triiodothyronine (T3) and thyroxine (T4) were determined by double-antibody radioimmunoassay (RIA). T3, T4 concentration and T3/T4 ratio had two peaks, but the daily variation patterns of thyroid hormones were different between each other. T3 peaked at 12 AM and 12 PM, while T4 peaked at 8 AM and 12 PM, with the two peaks of T3/T4 ratio showing at 4 AM and 12 AM. The lowest concentrations of both T3 and T4 occurred at 4 PM. According to above results, the blood samples should be collected around the time corresponding to the peak of temperature sinusoid, when thyroid hormones (both T3 and T4 concentrations) are used to evaluate the heat stress status of broilers

Evaluation of Airborne Dust Concentration And Effectiveness of Cooling fan with Spraying Misting Systems in Swine Gestation Houses

Airborne dust in swine houses can cause serious health problems for humans as well as for animals. The aim of this experiment was to evaluate the airborne dust concentration range and effectiveness of cooling fan with spraying misting systems in the gestation houses in the management practices of China. The experiment was implemented in a gestation barn housed 239 gestation pigs in Hebei Province of China. The tests showed that the average airborne dust concentration was about 4.70 ±3.24 mg/m3 in cold weather and 2.18 ±1.61 mg/m3 in warm weather, respectively. The high dust concentration of 17.55 ± 1.18 mg/ m3 in winter and 15.25 ± 1.77 mg/m3 in summer happened in the feeding period. When the misting cooling system with droplet diameter of 20-50µ m turned on, the average airborne dust concentration could be reduced by 75%, from 7.94 ±4.67 mg/m3 to 1.98 ±1.80 mg/m3, during the feeding period