A correlation has been proposed for mean drop diameter in a Rotating Sieved Disc Contactor (RSDC) considering drops break up, as well as drops coalescence with static holdup in the case of no mass transfer. The proposed correlation is a function of a number of stages, rotating speed in the form of Reynolds number, static hold-up and mother drop size. The effects of the last two terms have not been considered by other researchers. Therefore, the results are compared with two reported correlations to show how these two important terms influence the size of drops. Distilled water was used as a continuous phase and toluene was applied as a dispersed phase in the experiments. The absolute average relative error and standard deviation for the correlation were 14.74% and 10.08%, respectively.
Considering the importance of liquid static holdup in liquid-liquid extraction columns, a novel experimental approach for predicting the mentioned parameter in a rotary sieved disc contactor has is presented in this research. One chemical system without mass transfer was used, in which distilled water and butyl acetate were employed as the continuous and the dispersed phase, respectively. The static holdup has been measured using the draining method. Based on the experimental results, one correlation was proposed to predict the static holdup as a function of stage position in the column and rotating speed in the form of Reynolds numbers and also the dimensionless mother drop size. Changes in static holdup caused by each factor have been discussed and graphically illustrated. It was revealed that an increase in mother drop size will cause the growth of static holdup, while the rise of rotating speed will decrease the amount of static holdup. Furthermore, it was proven that static holdups in upper positions in the column are less than those in the lower positions.
Background and objective:The development of technology in many developed communities has resulted in sedentary living and the appearance of many noninfectious diseases. In order to solve this problem and change the activity patterns, the factors affecting the physical activity should be clarified. This study tried to determine the benefits and perceived barriers of regular physical activities of the employees.
Materials and methods:In this cross-sectional study, 117 employees of health center in Kalat, in Razavi Khorasan Province in Iran, affiliated with Mashhad University of Medical Sciences (MUMS), were studied in 2012-2013. In order to gather the data, a standard questionnaire of perceived benefits and barriers of physical activity was used. The data were analyzed using SPSS 16. Results: The average age of the employees were 34.09 ± 8.08 years and 66 of them (56.4%) were female. Overall, 34.2% of the employees had regular physical activity-53% of male and 20% of female ones. The mean of perceived benefit scores was 100.3. ±1.4 and the mean of perceived barrier scores was 25.9±6.14. There was a significant relationship between physical activity and the age (p < 0.01) as well as the level of education (p = 0.01) but the presence or absence of physical activity had no significant relationship with the perceived benefits (p <0.58). Conclusion: Lack of adequate facilities for physical activities such as being far away, time-consuming and tiring due to exercise were the barriers for doing physical activities and some other factors like being interested in the exercises motivate the employees to do the physical activities.
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