Improvements in heat transfer in thermal desalination operation based on removal of salts using ultrasound pretreatment
ULTRASONICS SONOCHEMISTRY
Authors: Banakar, Vikram V.; Sabnis, Sarvesh S.; Gogate, Parag R.; Raha, Abhijit; Saurabh
Abstract
Scaling is a major problem in the thermal desalination operation which is mainly attributed to the deposition of salts on the tube, thereby increasing the resistance to heat transfer. To reduce or prevent the formation of scale on heat transfer surfaces, treating desalination concentrates and precipitating sparingly soluble salts can be a promising method. In the present work, the effect of ultrasound pretreatment to the synthetically prepared sea water as desalination feed has been investigated with an objective of intensifying salt removal process and avoiding scale formation leading to better heat transfer rates. A lab scale double pipe heat exchanger setup was designed and operated under simulated conditions of the thermal desalination operation. Total operational volume of 2000 ml was used for all experiments with a fixed flow rate of 5 ml/s. To understand the process of scaling, synthetic seawater was prepared as per the ASTM D 1141-98 and was used for scale deposition experiments. The experiments conducted using untreated synthetic seawater confirmed substantial scaling and drop in the heat transfer coefficient from an initial value of 776 W/m(2) K to 603 W/m2 K (about 22%) after 24 h operation as compared to deionized water. SEM-EDX analysis was performed to investigate the morphology and main components of the scale. Subsequently, synthetic seawater was treated with ultrasound under continuous flow condition for removal of salts responsible for scaling. It was demonstrated that pretreatment resulted into salt crystallization, after which, the crystals were separated and the filtered solution was passed through the heat exchanger to check the effects on heat transfer rate. It was confirmed that the heat transfer rate was found to be higher with a value of 797 W/m2 K. Overall an effective approach based on ultrasound to remove the scale forming components has been demonstrated with established best conditions as 70% amplitude for 30 min of irradiation at fixed frequency of 20 kHz and 50% duty cycle.
Effects of dietary phosphorus level and stocking density on tiger puffer Takifugu rubripes: Growth performance, body composition, lipid metabolism, deposition of phosphorus and calcium, serum biochemical parameters, and phosphorus excretion
AQUACULTURE
Authors: Xu, Houguo; Zhang, Xiao; Wei, Yuliang; Sun, Bo; Jia, Linlin; Liang, Mengqing
Abstract
An 8-week feeding trial was conducted to comprehensively investigate the effects of dietary phosphorus level and stocking density on tiger puffer. A 3 x 3 factorial design was used. The three dietary phosphorus levels were 0.68% (LP), 0.98% (MP), and 1.31% (HP) of dry matter, of which the available phosphorus level was 0.44%, 0.76%, and 1.06%, respectively. The three stocking density grades were 1.53 (LD), 2.30 (MD), and 3.06 (HD) kg m(-3). The feeding trial was conducted in an indoor flow-through seawater system. Three replicate tanks were used for each group. The results showed that HP resulted in the highest growth rate. Higher dietary phosphorus levels reduced the whole-body lipid content, serum cholesterol contents, and hepatic mRNA expression of lipid metabolism-related genes such as ACAC beta, DGAT1, and PPAR alpha 2. High stocking density levels reduced the growth rate and feed intake, but rarely affected other physiological parameters. Significant interactions were observed between effects of dietary phosphorus level and stocking density on phosphorus and calcium metabolism, but not between effects of both variables on the growth performance. Synergetic enhancement of phosphorus excretion by high phosphorus level and high stocking density was observed. These results shed new lights into the phosphorus physiology of marine fish and the interactions between phosphorus nutrition and rearing condition.