Condensation heat transfer and flow characteristics of R-134a flowing through corrugated tubes

This article presents the condensation heat transfer and flow characteristics of R-134a flowing through corrugated tubes experimentally. The test section is a horizontal counter-flow concentric tube-in-tube heat exchanger 2000 mm in length. A smooth copper tube and corrugated copper tubes having inner diameters of 8.7 mm are used as an inner tube. The outer tube is made from smooth copper tube having an inner diameter of 21.2 mm. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm, respectively. The test conditions are performed at saturation temperatures of 40–50 °C, heat fluxes of 5–10 kW/m², mass fluxes of 200–700 kg/m² s, and equivalent Reynolds numbers of 30000–120000. The Nusselt number and two-phase friction factor obtained from the corrugated tubes are significantly higher than those obtained from the smooth tube. Finally, new correlations are developed based on the present experimental data for predicting the Nusselt number and two-phase friction factor for corrugated tubes.     

Efficiency of Ultrasonic Incorporated Glutathione Treatment in Preserving the Physicochemical Quality and Preventing the Browning of Lotus Rhizome Slices

This study investigated the efficacy of 40-kHz (200 W) ultrasonication (US) for 2 min combined with glutathione (GSH) at 0.5% w/v (US + GSH) in preventing browning and preserving the physicochemical quality of lotus rhizome slices stored in a 4 ± 1 °C refrigerator. According to the visual appearance of the slices, US + GSH treatment more effectively inhibited the browning of the cut surface than did GSH or US treatment alone. US + GSH and GSH treatments were more effective than US and control treatments in preserving the slices’ colour attributes, such as their lightness and whiteness index values, and potentially retarded enzymatic browning reactions and increases in browning index and total colour difference values. Moreover, the application of US and US + GSH treatments noticeably preserved the texture of the slices. None of the treatments affected the total sugar content during storage. The US + GSH treatment markedly enhanced the ferric reducing antioxidant potential of the slices during storage. The slices treated with US, GSH, and US + GSH exhibited slower reductions in 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity than did the controls. In conclusion, US + GSH treatment is a feasible approach for inhibiting browning, maintaining texture, and inducing antioxidant activity in lotus rhizome slices during storage.     

Influence of Heat-Treated Bovine Bone-Derived Hydroxyapatite on Physical Properties and in vitro Degradation Behavior of Poly (Lactic Acid) Composites

In this work, nano-size HA was produced from bovine bone. At various heat treatment temperatures, poorly crystalline, partially crystalline and crystalline forms of HA were obtained. PLA composites were prepared by incorporating various forms and contents of HA into PLA matrix. The characteristics of the obtained HA powders affected properties of PLA composites including mechanical properties, morphologies, PLA molecular weight, in vitro bioactivity and in vitro degradation behaviors of the composites. In the case of in vitro bioactivity study, all composites illustrated the induction of bone-like calcium phosphate compounds on their surfaces, especially the PLA/a-HA composites.     

An experimental study into the evaporation heat transfer and flow characteristics of R-134a refrigerant flowing through corrugated tubes

The effects of corrugation pitch on the evaporation of R-134a flowing inside horizontal corrugated tubes are investigated. The test section is a tube-in-tube heat exchanger with refrigerant flowing in the inner tube and hot water flowing in the annulus. Smooth and corrugated tubes having similar inside diameters are used as the inner tube. Three corrugated tubes having a corrugation depth fixed at 1.5 mm and corrugation pitches of 5.08, 6.35 and 8.46 mm are examined. The data obtained from smooth tube are plotted and compared with the flow pattern map established by Censi et al. (2003) and Zurcher et al. (2002). The effects of average vapour quality, equivalent Reynolds number and corrugation pitch are discussed. The maximum ratios of heat transfer enhancement factor to pressure drop penalty factor (Nu_c/Nu_s)/((ΔP/L)_c/(ΔP/L)_s) is approximately 1.2.     

A comparison of the effect of the electrohydrodynamic technique on the condensation heat transfer of HFC-134a inside smooth and micro-fin tubes

The results of the condensation heat transfer enhancement and pressure drop of HFC-134a by using the electrohydrodynamic (EHD) technique are presented. The test section is a horizontal tube-in-tube heat exchanger where the refrigerant flows in the inner tube and water flows in the annulus. The outer tube is a smooth copper tube havign outer diameter of 21.2 mm. Two types of inner tubes, smooth and micro-fin copper tubes, are tested. The outer diameter and length of both inner tubes is 9.52 mm and 2.5 m, respectively. A stainless steel cylindrical electrode of 1.47 mm in diameter is placed in the center of the tube. Experiments are conducted under conditions providing mass flux of 400 kg/m²s, saturated temperature of 40°C, heat flux of 20 kW/m² and applied voltage of 2.5 kV. The experimental results indicate that the EHD enhancements of the smooth tube are higher than those of the micro-fin tube over the range of average quality. The maximum heat transfer enhancements for smooth and micro-fin tubes are 1.1. times and 1.08 times, respectively. For a smooth tube, the pressure drop induced by EHD is considerably small. However, the application of EHD in a micro-fin tube can lead to 10% increase in the pressure drop.     

Physicochemical changes in fresh-cut wax apple (Syzygium samarangenese [Blume] Merrill & L.M. Perry) during storage

Physicochemical changes, such as peel and flesh colours, total anthocyanin content, browning index, firmness, total soluble solid (TSS), titratable acidity (TA), sugar acid ratio (TSS/TA), antioxidant capacity, total phenolic content and ascorbic acid content, in fresh-cut Taaptimjan wax apple fruit stored at 4 ± 2 °C and 12 ± 2 °C for 7 days were investigated. The skin of fresh-cut fruit stored at 4 ± 2 °C showed higher a^∗ value, chroma and total anthocyanin content and lower hue angle than those stored at 12 ± 2 °C. Lightness (L^∗ value) and whiteness index of the fresh-cut fruit flesh stored at 12 ± 2 °C showed significantly lower than those stored at 4 ± 2 °C which related to an significant increase in browning index. Firmness, total soluble solid, titratable acidity and sugar acid ratio did not significant changes during storage. Antioxidant capacity and total phenolic content increased throughout storage. Ascorbic acid content of the fresh-cut fruit stored at 4 ± 2 °C remained constant throughout storage whilst ascorbic content at 12 ± 2 °C decreased and was lower than that at 4 ± 2 °C. At 4 ± 2 °C antioxidant capacity and ascorbic acid content were higher than that stored at 12 ± 2 °C whilst there was no significant difference in total phenolic content. In conclusion, the reduction of whiteness index and the increase in browning index of fresh-cut wax apple flesh were the key factors affecting its quality and storage at 4 ± 2 °C could reduce the change in the flesh colour and maintained the peel colour and nutritional values of fresh-cut wax apple fruit during storage.     

Efficiency of pre-process anoxia treatment on quality of fresh-cut pineapples cv. ‘Phulae’ during storage

The aim of this study was to investigate the competency of pre-process anoxia treatment on physicochemical quality of fresh-cut pineapples cv. ‘Phulae’ during storage. The fruits were kept in anoxia atmosphere (N₂) for 16 h before processing. The fruits were processed immediately after treatment (G1) and after storage at 13 °C for 6 days (G2). Anoxia treatment delayed the weight loss and had no effect on the L* value of both G1 and G2 fresh-cut pineapples. The yellowness (b*) value of G1 fresh-cut pineapple was maintained by anoxia. The PPO activity of anoxia-treated G1 and G2 fresh-cut pineapples was lower than that of untreated fresh-cut fruits (control). Total sugars contents of both G1 and G2 anoxia-treated fresh-cut pineapples trended to be higher than that of control samples. Anoxia had no influence on the total ascorbic acid content during storage. The increases in total bacteria and yeast of both G1 and G2 fresh-cut pineapples were retarded by anoxia. In conclusion, anoxia is a feasible alternative to maintaining quality and delaying microbial increases in fresh-cut pineapples during storage.     

The Effect of 1-Methylcyclopropene (1-MCP) on Quality and Cell Wall Hydrolases Activities of Fresh-Cut Muskmelon (Cucumis melo var reticulatus L.) During Storage

The effects of 1-methylcyclopropene (1-MCP) on quality and cell wall hydrolases activities changes in fresh-cut muskmelon fruit stored at 4?±?1 °C for 7 days were investigated. The results showed that ethylene production of the fresh-cut fruit remained constant during refrigerated storage. 1-MCP treatments delayed the loss of fresh weight and the increase in electrolyte leakage and maintained the firmness of the fresh-cut fruit. The best results are showed in the fresh-cut fruit treated with 1.0 μL L^?1 1-MCP. The use of 1-MCP had no influence on the total soluble solids (TSS) content and pH of the fresh-cut fruit which they remained constant over storage. The titratable acidity (TA) of the fresh-cut fruit decreased during storage and the sample treated with 1.0 μL L^?1 1-MCP showed the lowest data. TSS/TA ratio increased during storage and the TSS/TA ratio was lower in 1-MCP-treated samples than that for the control one. The use of 1-MCP inhibited polygalacturonase (PG), β-galactosidase (β-Gal) and β-galactanase activities, whereas the increases in these enzymes activities were found in the control. Antioxidant capacity and total phenolics content of both 1-MCP-treated and untreated samples remained constant over storage. The reduction of total ascorbic acid content was detected after 7 days of storage. The ascorbic acid content in 1-MCP-treated sample was slightly higher, although not significantly different, than that of the control after 7 days. These results suggest that the loss of firmness was the key factor affecting quality of fresh-cut muskmelon fruit and the use of 1-MCP maintained the quality and inhibited the loss of firmness by retarding the increase in electrolyte leakage and inhibiting cell wall hydrolases activities.