Applications In Thermal Systems Research Articles

Experimental assessment of the thermal–hydraulic performance of packed-sphere oscillating-flow regenerators using water

Regenerators are storage-type heat exchangers with a wide-range application in thermal systems. In refrigeration, they can be used as passive thermal storage devices in Stirling and pulse-tube coolers, or as active magnetocaloric regenerators in magnetic refrigerators. In either case, the performance of the cooling system is significantly influenced by the regenerator thermal effectiveness and by viscous losses. A laboratory apparatus for testing passive regenerators that uses water as the thermal fluid was developed aiming at quantifying the fluid pumping power and the regenerator heat transfer effectiveness as a function of operating parameters such as frequency and thermal capacity ratio (utilization factor) for different regenerative materials and packing geometries. In the present paper, the experimental rig, data processing and test results obtained for packed beds of stainless steel, lead and gadolinium spheres with different particle diameters are described and discussed.

Fuzzy-GA inference technique to control three-input jet ejector system

Jet ejectors find many applications in thermal systems including refrigeration, heat treatment, and fuel injection. In this study, a three-input jet ejector model is developed and the resulting non-linear governing equations are used to design the corresponding controller. A fuzzy-based genetic algorithm (fuzzy-GA) technique is used to represent and control the system using linguistic fuzzy sets, which are tuned using a genetic algorithm code. The proposed controller is tested on different fluid types where simulation results showed the effectiveness and robustness of the technique.

Best Possible Tilt Angle for Optimal Solar Radiation on an Inclined Surface for Photovoltaic and Solar Thermal Application in Yenegoa city, Nigeria

Due to the increased use of solar energy resources globally, the study of the available solar resources is essential for systems that use solar energy. This paper uses the Duffie and Beckhman method for estimating the best possible tilt angle for solar radiation using some climatic data such as declination, latitude, and clear index for photovoltaic and solar thermal systems application in the city of Yenagoa. This research was conducted with different tilt angle ranging from 15° to 65° tilt and it was shown that the best tilt angle for solar energy system application for Yenagoa falls in the range of 15° to 45° tilt.

Effect of fin pitches on the optimum heat transfer performance of crimped spiral fin-and-tube heat exchangers

This study conducted experiments on the optimized fin pitch for crimped spiral fin-and-tube heat exchangers. The experiments covered a size range of 2.4–6.5mm, which is the manufacturing limitation for this kind of fin. The water-flow arrangement used in this experiment combined the parallel cross-flow and the counter cross-flow in a two-row configuration. Ambient air was used as the working fluid on the air-side, and hot water was used on the tube-side. The effects of fin pitches on the heat transfer coefficient and pressure drop characteristics were studied. The results clearly showed that the convective heat transfer coefficient (ho) for a fin pitch of 2.4mm is relatively low compared with that of other fin pitches with the same air frontal velocity. Using larger fin pitches (i.e., 4.2, 6.2, and 6.5mm) resulted in negligible differences in the pressure drop. Moreover, this work introduces the parameter of three performances indexes, which can be expressed as the ratio of the desired output to the required input, for optimization purposes. Due to the difference in optimum fin pitch obtained by these performance indexes, an intersection analysis was conducted. The results indicated that the optimum fin pitch is 4.2mm for this work, which could be valuable for the effective design for industrial thermal-system applications.

Electrochemical response of laser surface melted inconel 617 alloy

Inconel 617 alloy has superior high temperature properties and finds application in thermal systems. The alloying elements of chromium and molybdenum make the alloy resistant to corrosion. In the present study, the corrosion properties of Inconel 617 alloy, after 37,000 h of operation as a transition piece in the gas turbine engine, are examined. The workpiece surfaces are treated using an Nd : YAG pulsed laser. The electrochemical tests are carried out in 0.1 N H 2SO 4+0.05 N NaCl deairated aqueous solution at room temperature. It is found that the laser treated workpieces result in improved corrosion rates. The locally scattered shallow pits are observed at the workpiece surface after the electrochemical tests.