Computational Fluid Dynamics Analysis of a Heat Exchanger Provided with Helical Baffles

Abstract

In the article, a three-dimensional numerical solution of two real shell-and-tube heat exchangers, with different types of baffles, segmental, and pseudohelical, is presented, through the use of commercial codes, in order to evaluate the influence of the baffles type on heat exchanger performance. The parameters to be evaluated, which influence the efficiency of the thermal exchange and the maintenance and pumping costs, are the pressure drops, the heat transfer coefficient, and the fouling resistance. The fluid dynamic study of the shell-and-tube heat exchanger is conducted under stationary flow conditions. In the article, furthermore, the results of the thermohydraulic analysis, performed under stationary flow conditions, more "helical baffles" exchangers, with different baffles helix angle, are presented. Exchangers with pseudohelical baffles inclined by 7°, 20°, 30°, 40°, 45°, and 50° are analyzed. The simulations are carried out considering a real fluid, approximately incompressible, under laminar flow conditions. Finally, to verify the correctness of the results, they are compared with correlations in the literature.     

Data-based method for creating electricity use load profiles using large amount of customer-specific hourly measured electricity use data

The recent technological developments monitoring the electricity use of small customers provides with a whole new view to develop electricity distribution systems, customer-specific services and to increase energy efficiency. The analysis of customer load profile and load estimation is an important and popular area of electricity distribution technology and management. In this paper, we present an efficient methodology, based on self-organizing maps (SOM) and clustering methods (K-means and hierarchical clustering), capable of handling large amounts of time-series data in the context of electricity load management research. The proposed methodology was applied on a dataset consisting of hourly measured electricity use data, for 3989 small customers located in Northern-Savo, Finland. Information for the hourly electricity use, for a large numbers of small customers, has been made available only recently. Therefore, this paper presents the first results of making use of these data. The individual customers were classified into user groups based on their electricity use profile. On this basis, new, data-based load curves were calculated for each of these user groups. The new user groups as well as the new-estimated load curves were compared with the existing ones, which were calculated by the electricity company, on the basis of a customer classification scheme and their annual demand for electricity. The index of agreement statistics were used to quantify the agreement between the estimated and observed electricity use. The results indicate that there is a clear improvement when using data-based estimations, while the new-estimated load curves can be utilized directly by existing electricity power systems for more accurate load estimates.     

An assessment of the natural gas supply potential of the south energy corridor from the Caspian Region to the EU

Security and diversification of EU energy supply underlines the importance of an energy corridor bridging the natural gas reserves of the broader Caspian Region with the EU consumption centers. This paper examines the supply potential of this corridor, the major natural gas fields and the already existing networks. An assessment of the supply cost up to the Turkish borders is carried out, while the case of Egypt as a future supplier is also investigated. Conclusions review the prospects for the construction of the considered energy corridor.     

Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterisation

Understanding gas evolution and two-phase flow behaviour are critical for performance optimization of polymer electrolyte membrane water electrolysers (PEMWEs), particularly at high current densities. This study investigates the gas-bubble dynamics and two-phase flow behaviour in the anode flow-field of a PEMWE under different operating conditions using high-speed optical imaging and relates the results to the electrochemical performance. Two types of anode flow-field designs were investigated, the single serpentine flow-field (SSFF) and parallel flow-field (PFF). The results show that the PFF design yielded a higher cell performance than the SSFF design at identical operating conditions. Optical visualization shows a strong relationship between the flow path length and the length of gas slugs produced, which in turn influences the flow regime of operation. Longer flow path length in the SSFF results in annular flow regime at a high current density which degrades cell performance. The annular flow regime was absent in the PFF design. It was found the effect of flow rate on performance depends strongly on operating temperature in both flow patterns. Results of this study indicate that long channel length promotes gas accumulation and channel-blocking which degrades performance in PEMWEs.     

Lipid and protein oxidation of α-linolenic acid-enriched pork during refrigerated storage as influenced by diet supplementation with olive leaves (Olea europea L.) or α-tocopheryl acetate

The objective of this study was to evaluate the effect of diet supplementation with olive leaves or α-tocopheryl acetate on lipid and protein oxidation of raw and cooked n-3 enriched-pork during refrigerated storage. Enrichment of pork with α-linolenic acid through diet supplementation with linseed oil enhanced (p≤0.05) lipid oxidation in both raw and cooked chops but had no effect (p>0.05) on protein oxidation during refrigerated storage while decreasing (p≤0.05) the sensory attributes of cooked pork. Diet supplementation with olive leaves or α-tocopheryl acetate had no effect (p>0.05) on the fatty acid composition of pork but decreased (p≤0.05) lipid oxidation while exerting no effect (p>0.05) on protein oxidation in both raw and cooked α-linolenic acid-enriched chops stored and chilled for 9days. Moreover, olive leaves and α-tocopheryl acetate supplemented at 10g/kg and 200mg/kg diet, respectively, exerted (p≤0.05) a beneficial effect on the sensory attributes of cooked α-linolenic acid-enriched pork chops.     

Effect of Different Raisin Juice Preparations on Selected Properties of Gluten-Free Bread

Incorporation of sucrose and raisin juice (in concentrated or in dried form) at 3 and 5% of flour weight to commercial wheat starch (Codex Alimentarius) gluten-free flour was carried out to examine the effects on baking, textural, and sensory properties of bread. Breads made with gluten-free flour are usually characterized by poor color and baking characteristics, as well as short shelf life. The current study was conducted to help solve these problems by using raisin juice, a natural sweetener that contains no preservatives, has lower caloric content than sucrose, and includes a number of important vitamins and minerals that are very important for the coeliac disease patients. The study showed that 3% raisin juice in concentrated form contributes to a great improvement in loaf volume, color, and hardness characteristics of gluten-free bread during the first day after baking but a higher staling rate because of its high moisture content. Dried raisin juice gave bread higher loaf volume and better color compared to the control gluten-free bread and also increased its shelf life because of its moisture absorption properties. Sensory analysis revealed a preference for breads containing concentrated raisin juice because of its fruity flavor, whereas all the samples that contained 5% raisin juice had very dark color.     

Non‐freezing points below zero induce low‐temperature breakdown of kiwifruit at harvest

To induce low‐temperature breakdown (LTB) at harvest, a post‐storage disorder of kiwifruit, kiwifruit were exposed to ?2 °C (a temperature determined to be above the freezing point), for 0 (control), 6, 12, 18, 24, 30, 36 and 42 h, followed by 5 days at 20 °C. Kiwifruit were also stored at ?0.5 °C for 16 and 24 weeks plus 5 days at 20 °C. LTB incidence and severity were measured on the cut surfaces following slicing at the upper, middle and lower parts of each fruit subjected to ?2 °C, whereas in stored fruit LTB incidence was measured following slicing at the middle part. Electrolyte leakage (ELL) was also determined. Exposure of fruit to ?2 °C resulted in induction of LTB incidence and severity, which increased with the duration of exposure, particularly, on the upper fruit part. Maximum ELL during exposure at ?2 °C for 36 h or during storage at ?0.5 °C for 16 weeks was as high as 50% of that of the frozen fruit. Fruit exposed to ?2 °C or stored at ?0.5 °C had similar LTB symptoms but both differed from those observed in frozen fruit. LTB of fruit stored at ?0.5 °C for 24 weeks was 27% and corresponded to LTB induced at harvest by exposure at ?2 °C for 24 h. The results of this study confirm that LTB is inducible by low but not freezing temperatures at harvest and therefore it might be considered as the physiological basis towards the development of an LTB incidence index for harvested kiwifruit. Copyright © 2006 Society of Chemical Industry     

Growth of Aeromonas hydrophila in the whey cheeses Myzithra, Anthotyros, and Manouri during storage at 4 and 12 degrees C

The fresh whey cheeses Myzithra, Anthotyros, and Manouri were inoculated with Aeromonas hydrophila strain NTCC 8049 (type strain) or with an A. hydrophila strain isolated from food (food isolate) at levels of 3.0 to 5.0 x 10(2) CFU/g of cheese and stored at 4 or 12 degrees C. Duplicate samples of cheeses were tested for levels of A. hydrophila and pH after up to 29 days of storage. At 4 degrees C, A. hydrophila grew in Myzithra and Anthotyros with a generation time of ca. 19 h, but no growth was observed in Manouri. In Myzithra, average maximum populations of 8.87 log CFU/g (type strain) and 8.79 log CFU/g (food isolate) were recorded after 20 and 22 days of storage at 4 degrees C, respectively. The average maximum populations observed in Anthotyros stored at 4 degrees C were 6.72 log CFU/g (food isolate) and 6.13 log CFU/g (type strain) and were observed after 15 and 16 days of storage, respectively. A. hydrophila grew rapidly and reached high numbers in cheeses stored at 12 degrees C. The average generation times were 3.7 and 3.9 h (Myzithra), 4.1 and 6.1 h (Anthotyros), and 8.0 and 9.2 h (Manouri) for the type strain and the food isolate, respectively. Among the different whey cheese trials, the highest A. hydrophila population recorded (10.13 log CFU/g) was in Myzithra that had been inoculated with the food isolate after 8 days of storage at 12 degrees C. To prevent A. hydrophila growth in whey cheeses, efforts must be focused on preventing postprocessing contamination and temperature abuse during transportation and storage.     

Kinetics of endoglucanase and endoxylanase uptake by soybean seeds

The uptakes of endoglucanase and endoxylanase by soybean were studied by measuring the fluorescent intensity of a carboxyfluorescein. The disappearance rates of these enzymes from solution were compared with predictions from different models. The Freundlich model provided the best fit for our data. Enzyme concentration in the solution did not change significantly after 11 d, and therefore it was assumed that equilibrium was reached. Average mass transfer coefficient was calculated for both endoglucanase and endoxylanase from the plot of the rate of uptake against (C(l av) -Cl*) and a value of 4 x 10(-5) ms(-1) was obtained. K value was used to calculate the effective diffusivities of the two enzymes assuming a slice. It is found that K was asymptotic with long residence times, and a value of 4.8 x 10(-10) m2 s(-1) was obtained.     

Valorisation of low quality edible oil with tomato peel waste

The aim of this study is to enrich edible oils with carotenoids and lycopene from tomato purée or tomato peel, an industrial tomato waste. These tomato derivatives were incorporated in refined olive oil, extra virgin olive oil and refined sunflower oil. The incorporation of peel enhanced the concentration of β-carotene and lycopene more than tomato purée. Furthermore, the incorporation of both tomato purée and peel induced better thermal stability of the refined olive oil compared to extra virgin oil and sunflower oil. A decrease on total phenols as well as some prooxidant activity account for this, when tomato purée was incorporated. In our oil preparations, rutin and naringenin, as flavonoids coming exclusively from tomato purée or peel, were detected. The enrichment of oils with tomato carotenoids and lycopene, in particular low quality oils like refined olive oils, might be an alternative approach to elaborate new functional foods.