Different nanofluids as coolant in heat exchanger network: Thermoeconomic modeling and multi-objective optimization

Modeling and optimization of a multi tube heat exchanger (MTHE) network considering the effects of different nanoparticles on the tube side are carried out using Fast and elitist non-dominated sorting genetic algorithm. After thermal modeling in [Formula: see text] method, optimization is performed by increasing the effectiveness and decreasing total annual cost as two objective functions using eight design parameters such as number of MTHE and particles volumetric concentration. In addition, optimization is performed at three various cold mass flow rates and different nanoparticles including Al2O3, CuO and ZrO2 and results are compared with the base fluid (water). For the reliability of the present code, the modeling results are validated with the results obtained from both the numerical and experimental model. The results show that the optimal Pareto front is improved in nanoparticles case, and the rate of improvement in CuO nanoparticles case, especially in higher effectiveness and lower cold mass flow rate is more significant compared with the other studied cases. In addition, because of improvement in the thermal performance of MTHE network with nanoparticles, the heat transfer surface area and consequently the total volume of MTHE network for the fixed values of effectiveness are noticeably reduced. Finally, the effects of design parameters versus effectiveness are demonstrated and discussed.

Elliptical Tabs as a Mixing Enrichment Tool for Jet Nozzles

Mixing efficiency helps to thrust gain and jet noise reduction. Aerospace and aviation research communities around the world are constantly demanding cleaner, quieter and more efficient commercial aircrafts. Though there are many sources of noise during flight, one such is deficient mixing of air at the rear of the nozzle, uneven expansion of nozzle and corresponding engine noise is quite dominant. The mixing proficiency is achieved by mixing of cold air at the surroundings with the hot air that exits through the nozzle. To reduce the engine noise, elliptical tabs are employed at the exit of convergent nozzle. These are passive noise controllers which create vortices to the existing flow and entrains cold mass from the surroundings in order to reduce noise level. This paper is concerned with the various shapes and sizes of tabs to test the mixing efficiency at different Mach numbers. Further, it is evaluated by both qualitative and quantitative analysis of shadowgraph system and the pressure identifying method using some of the propitious pressure scanner.

Analysis of Temperature Change in Uzbekistan and the Regional Atmospheric Circulation of Middle Asia during 1961–2016

Climate change and shrinking of the Aral Sea have significantly affected the region’s temperature variations. Observed interannual changes in Uzbekistan’s air temperature compared to the duration of synoptic weather types (SWT) in Middle Asia were analyzed. Nonparametric Mann–Kendall statistical test and climate trends coefficients were used to identify trend characteristics of observed temperature from 1961–2016 to the baseline period of 1961–1990. The results showed increasing temperature trends average to 1 °C in warm and cold half years over Uzbekistan. The 1991–2016 decadal temperature trend ranged from 0.25 °C/decade in the northwest to 0.52 °C/decade in the center, especially pronounced in the oasis and Aral Sea zones. There were also significant changes in the structure of regional SWT. The main difference in the structure of SWT in Middle Asia relative to the baseline period was expressed in a decrease of cold mass invasion duration from 113.4 to 76.1 days and an increase in low-gradient baric field duration from 65.8 to 134.6 days. The process of anthropogenic warming, which began in Uzbekistan in the 1960s of the twentieth century, has accelerated from the mid-1970s with a higher mean annual air temperature than the baseline period’s climate normals (1961–1990) and is associated with changes in the regional SWT over Middle Asia.

Study on Qualification for Cold Mass Support of ITER FEEDER CFT

Cold Mass Support (CMS) is a very important internal component of ITER Cryostat feedthrough (CFT), which acts as structure support who bears shear loads and sliding, as well as where heat load transfer from room temperature to 4.2K component. Base on the special functional requirements and importance, the design of CMS should be qualified before the real production used on ITER Feeder system. In this paper, the qualification process of CMS was studied, three kinds of qualification tests were done on CMS mockup and prototype, include structural mechanical strength test, sliding pad qualification tests, and thermal conductance test. Every testing process was introduced in detail, such as the load distribution of mechanical test, the setup of test platform, special test equipment and methods, etc. Some important performance parameters were obtained, such as the maximum deformation under mechanical load, the friction coefficient and some key performances of the Diamond-Like Carbon (DLC) coating, temperature gradient of CMS during cryogenic test, and so on. All these testing results could prove that the design of the CMS was satisfactory, and the qualification was successful.

Experimental Investigation of Performance Enhancement of a Vapor Compression Refrigeration System by Vortex Tube Cooling

This study aimed to analyze the difference in operation of the vapor compression refrigeration (VCR) system with vortex tube cooling. By using varied loads, experiments were conducted on the evaporator section of a vapor compression refrigeration system. In an attempt to improve the use of subcooling for the refrigeration, the effect of subcooling of refrigerant by vortex tube cooling was likewise examined. The test conditions included various loads (25%, 50%, 75% and 100%) and cold mass fractions (25%, 50% and 75%). This research described coefficient of performance (COP) as one of the significant parameters, in addition to heat rejection and refrigerating effect. The ideal efficiency appeared to be with the cold mass fraction of 25% and load of 100%, as identified by the results. Consequently, the COP could be enhanced by 5.16% along with an approximately 4.36% decline in average power use. Improved guidelines for vapor compression refrigeration systems to enhance the operation of the system are an expected benefit of this study.