Enhancement of Thermal Efficiency of Heat Exchanger using Titanium – Oxide nanofluid

Improvement of heat removal rate in heat exchanger using passive techniques is considered to be one of the most challenging task for engineers and scientist. In this study efficiency of the heat exchangers has been studied with TiO2 / water based nanofluid. The thermal properties, physical properties and heat removal efficiency of heat exchanger with nano-fluid as working fluid was investigated. Nanoparticle concentration of about 0.1 and 0.3 vol% was used. It was detected that the thermal conducting property and viscous property of the nanofluid increased proportionally with volume percentage. With the increased heat, the thermal conducting property increased while the viscous property of the nanofluid decreased. The heat removal rate on both shell outlet and tube outlet was estimated for different mass flow rate. The experiment results showed that with increased volume percentage and flow rate, the heat transfer performance improved. A maximum enhancement of 34% was observed at 0.3 vol% and 6l/min. Though there is increase in heat transfer rate the pressure dropped and pumping requirement increase with volume concentration and flow rate.

Effects of CeO2 on Viscosity, Structure, and Crystallization of Mold Fluxes for Casting Rare Earths Alloyed Steels

The CaO-Al2O3-based mold fluxes are proposed for the Ce-bearing heavy rail steel continuous casting because of the low reactivity. Effects of CeO2 on the melting temperature, the viscous property, and the crystallization behavior of the CaO-Al2O3-Li2O-B2O3 mold fluxes were studied using hemisphere melting point method, rotating cylinder method, and X-ray diffraction (XRD) in the present work. The microstructure of the mold fluxes was analyzed by Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of CeO2 would increase the melting temperature, but decrease the viscosity at each temperature due to its influence on increasing the depolymerization of the mold fluxes at high temperature. The precipitation of CaO was restrained and CaCeAlO4 generated with increasing CeO2 content since the crystal phases were affected by the microstructure of the melts. The change of the crystalline phases in mold fluxes influences the break temperature and the viscosity of the mold fluxes below the break temperature. These results obtained can provide guidelines for designing new mold fluxes for casting rare earth alloy heavy rail steels.

Influence of the Lubricant Thermo-Piezo-Viscous Property on Hydrostatic Bearings in Oil Hydraulics

In fluid power machinery hydrostatic bearings are frequently used, and a first approximation approach to design is determination of a balance ratio by analytical calculation of the hydrostatic pressure force. Usually this is performed assuming that the thermo-piezo-viscous property can be neglected. However, in applications as piston machines, where pressure in many cases exceeds 200 Bar, such assumption leads to considerable error in the balance ratio prediction, due to the piezo-viscous property of the lubricant. Furthermore, the thermo-viscosity relation also has a significant influence, which adds to the discrepancy of such simple design approach. In this paper the hydrostatic pressure force calculation is reviewed in terms of thermohydrodynamic (THD) lubrication theory, and simple analytical approximations of the hydrostatic pressure force, incorporating the piezo-viscous and thermo-viscous property of the lubricant, are presented. In order to investigate validity of the approximations a numerical THD model is developed. A comparison study of the numerical and analytical predictions is performed in order to validate the simple design approach. In addition, the assumptions that form the basis of these analytical approximations are explored in order to clarify the limits of application. In conclusion, it is found that the spatial gradient of the thermal field on the bearing surface is the significant factor in the thermo-viscous effect on the hydrostatic pressure profile, which leads to the conclusion that design engineers need to understand the thermodynamics of hydrostatic bearings, when using the conventional simple analytical approach, neglecting thermo-piezo-viscosity, in hydrostatic pressure force calculations.

Viscous Property of Clay

Viscous property of saturated, wet, air-dried and oven-dried clay was evaluated by performing a series of one dimensional compression tests including primary loading, creep, global unloading and reloading tests. In the tests, axial strain rate was changed stepwise many times during monotonic primary loading at a constant strain rate. Test results show that viscous property of clay with different water content under different test condition is similar. In order to evaluate the viscous property of clay, parameter β was introduced basing on the present test results of clay and author’s previous study. β value of clay with different water content under different test condition varied from 0.034 to 0.064. Test results show that β value of saturated clay is generally larger than that of dried clay.