Effect of perforated twisted-tapes with parallel wings on heat tansfer enhancement in a heat exchanger tube

AbstractThis article reports an experimental investigation on heat transfer and pressure drop characteristics of turbulent flow n a heating tube equipped with perforated twisted tapes with parallel wings (PTT) for Reynolds number between 500 and 20500. The design of PTT involves the following concepts: (1) wings induce an extra turbulence near tube all and thus efficiently disrupt a thermal boundary layer (2) holes existing along a core tube, diminish pressure losswithin the tube. The parameters investigated were the hole diameter ratio (d/W = 0.11, 0.33 and 0.55) and wing depthratio (w/W = 0.11, 0.22 and 0.33). A typical twisted tape was also tested for an assessment. Compared to the plain ube, the tubes with PTT and TT yielded heat transfer enhancement up to 208% and 190%, respectively. The valuation of overall performance under the same pumping power reveal that the PTT with d/W = 0.11 and w/W = .33, gave the maximum thermal performance factor of 1.32, at Reynolds number of 5500. Empirical correlations of he heat transfer, friction factor and thermal performance for tubes with PTTs were also developed. In addition, the wirling/axial flow patterns of tube with PTT were visualized using dye injection technique

Strategic review of the fishery situation in Thailand

Fisheries are an important source of animal protein for most of ThailandÆs population, particularly in provinces on or near the coast. Between 1978 and 1997 the per capita consumption of fish averaged 24 kg╖capita-1 annually. In 1995, about 535 210 people were involved in the fisheries sector and 44% of these were engaged in small scale marine capture fisheries. Since 1982, Thailand has faced problems with the development of marine capture fisheries and their over-exploitation which has increased fishery conflicts and disputes with neighboring countries. The Gulf of Thailand is the major fishing area of Thailand and in 1996, it contributed approximately 70% of the total marine catch in the country. The catch in the Gulf consisted of pelagic fish (33%), trash fish (32%), demersal fish (12%), squid and cuttlefish (6%), shrimps (5%), crabs (2%) and other fish (10%). However, demersal fish and some pelagic fish in the Gulf of Thailand have been over-exploited. This is due to a combination of factors including; increasing human population, increased pressure from Thai trawlers which have lost access to foreign fishing grounds after neighboring countries declared EEZs, development in fish processing techniques and increasing demand from animal feed producers that utilize trash fish. This paper provides a broad view of the fisheries situation in Thailand, focused mainly on the Gulf of Thailand. It covers aspects of the environment, the status of resources available, the socioeconomic situation, the existing framework for management and development, and also makes recommendations for government action to develop sustainable fisheries management. The main objectives proposed for improving fishery management are: (1) promote fishersÆ and fisher organizationsÆ participation in fishery development; (2) optimize fishery resources and their environment so as to be sustainable and equitable; (3) increase fishery products and stabilize fishersÆ and processorsÆ incomes; (4) progressively develop deep sea fisheries; (5) improve export competitiveness.Fishery resources, Catch/effort, Population characteristics, Coastal fisheries, Marine fisheries, Ecosystems, Economic benefits, Fishery industry, Capture fishery economics, Fish consumption, Fishery policy, Legislation, Fishery management, Demersal fisheries, Pelagic fisheries, Cephalopod fisheries, Socioeconomic aspects, Surveys, Marketing, Fishery organizations, Fishing gear, Cephalopod fisheries, Trade, ISEW, Thailand,

Preliminary analysis of demersal fish assemblages in coastal waters of the Gulf of Thailand

The 1995 trawl data of the research vessels Pramong 2 and 9 in the Gulf of Thailand were analyzed using TWINSPAN and DCA. Four main station clusters were identified related to geographic location and depth. Two clusters are associated with shallow water areas and the other two clusters are found in deeper areas with water depths > 30 m. Temporal analysis indicates clustering of monthly data into wet and dry seasons. Examination of species abundance data indicates that the seasonality may not be very pronounced. However, this may be due to the degree of disaggregation used in sorting the trawl survey samples.Fishery resources, Demersal fisheries, Fishery surveys, Biomass, Population density, Shrimp fisheries, Catch/effort, Trawling, Population characteristics, ISEW, Thailand Gulf,

Status of demersal fishery resources in the Gulf of Thailand

Data from trawl surveys (1961 - 95) and annual production statistics (1971 - 95) were used to examine the status of demersal fishery resources in the Gulf of Thailand. Analyses were focused on biomass trends, population parameters and exploitation rates of dominant species, and assessment of excess capacity from fishing effort and yield estimates. The results indicate by 1995, the trawlable biomass in the Gulf had declined to only about 8.2% of the biomass level in 1961. The substantial decline is true for major components (demersal fish and trash fish) and species groups (Nemipterus spp., Priacanthus spp., Saurida spp. and squids) comprising trawlable biomass. Estimates of exploitation rate (E) for 23 species indicate that most (particularly demersals) are over-fished. By 1995, 21 of the species had E values of 0.79 and higher. Analyses of standardized fishing effort and yield using the Fox model indicate that the 1995 fishing effort was about twice the level needed to harvest the maximum sustainable yield. Overall, the results illustrate that the resources are severely over-exploited. The excess demersal fishing effort is estimated to be about 50% of the number of registered boats in 1995.Fishery resources, Demersal fisherie, Fishery surveys, Biomass, Population density, Shrimp fisheries, Catch/effort, ISEW, Thailand Gulf,

Trophic model of the coastal fisheries ecosystem in the Gulf of Thailand

The biomass of 40 ecological groups, the diet composition of prey and predators, production/biomass (P/B) and consumption/biomass (Q/B) ratios, and catches were used as basic input to parameterize an Ecopath model of the Gulf of Thailand. Following construction of a mass-balance ecosystem model, a time-dynamic simulation model (Ecosim) was used to simulate the impact of change in fishing effort. This was done using time series data to validate the historic fisheries development in the Gulf of Thailand prior to using the model for forward-looking simulations. The time series data used in the analyses were catch and effort data from research vessel trawl surveys and landings data for six groups of fishing gear operating in the Gulf during the period 1973 to 1993. The fish market price and fixed and variable costs of each fleet (as well as profit) were also used as input for the time-series simulations using Ecosim. The results depict changes in biomass and trophic interactions in time (Ecosim) and space (Ecospace). The model was also used to investigate management options or measures for the fisheries of the Gulf of Thailand. Recommendations for future studies using Ecopath with Ecosim are also presented.Fishery resources, Fishery surveys, Biomass, Population density, Shrimp fisheries, Catch/effort, Trawling, Mathematical models, Coastal fisheries, Marine fisheries, Ecosystems, ISEW, Thailand Gulf,

Part Repair using a Hybrid Manufacturing System

Nowadays, part repair technology is gaining more interest from military and industries due to the benefit of cost reducing as well as time and energy saving. Traditionally, part repair is done in the repair department using welding process. The limitations of the traditional welding process are becoming more and more noticeable when the accuracy and reliability are required. Part repair process has been developed utilizing a hybrid manufacturing system, in which the laser aided deposition and CNC cutting processes are integrated. Part repair software is developed in order to facilitate the users. The system and the software elevate the repair process to the next level, in which the accuracy, reliability, and efficiency can be achieved. The concept of repair process is presented in this paper. Verification and experimental results are also discussed.Mechanical Engineerin

Influences of Spray Drying Conditions on the Physiochemical Properties of Karanda Fruit

Karanda fruits are widely cultivated in Thailand. The fruit has several vitamins and minerals. One of the most fascinating possibilities is to transform it into a powdered drink. This study aimed to determine the optimal conditions for preparing karanda juice powder considering its physicochemical properties. Three levels of inlet air temperature were evaluated, 160 oC, 180 oC and 200 oC. Subsequently, three levels of maltodextrin (dextrose equivalent 10, DE10) were evaluated, 30%, 40%, and 50% by weight. Finally, three levels of whey protein (WPI) were evaluated, 5%, 10%, and 15% by weight. The moisture content dropped by 48.51% when the input air drying temperature rose from 160-200 °C. Yield increased by 15.08% and solubility by 5.06%. The maltodextrin content was increased from 30% to 50%, resulting in a 23.17% increase in product yield, while the WPI content was increased from 5% to 15%, leading in an 82.88% increase in anthocyanin content. SEM investigation indicated that the particle morphology was spherical with smooth surfaces, but an increase in inlet air temperature led to greater deformation and particle surface roughness. Additionally, the optimal parameters for spray drying karanda fruit were an inlet air temperature of 174 °C, maltodextrin (MD) content of 32%, and WPI content of 15% of soluble solids, with a product yield of 55.93±0.25%, solubility of 85.51±0.54%, and anthocyanin concentration of 12.58±0.36 mg/l

Implicit Large Eddy Simulation of Flow in a Micro-Orifice with the Cumulant Lattice Boltzmann Method

A detailed numerical study of turbulent flow through a micro-orifice is presented in this work. The flow becomes turbulent due to the orifice at the considered Reynolds numbers (∼104). The obtained flow rates are in good agreement with the experimental measurements. The discharge coefficient and the pressure loss are presented for two input pressures. The laminar stress and the generated turbulent stresses are investigated in detail, and the location of the vena contracta is quantitatively reproduced