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This paper provides an hitherto new approach of a heat transfer correlation based on heat flux to mass flux ratio for predicting wall temperature of supercritical water flowing in a bare vertical tube. Totally 10,174 numbers of experimental data were collected, Out of which 4236 data are heat flux/mass flux ≤0.4 and 5938 data are heat flux/mass flux>0.4. These data were obtained from various experimental resources and Lookup table and it covers q/G ranges from 0.085 to 1.295, mass flux ranges from 201 to 3500 kgm−2 s−1, heat flux ranges from 129 to 1600 kWm−2, pressure ranges from 225 to 320 bar, diameter of the tube 4.4 to 38 mm and bulk fluid enthalpy ranges of 250 to 3200 kJkg−1 of vertical tube working at various supercritical working conditions based on normal, enhancement and deteriorated heat transfer regions. By using these data, a new heat transfer correlation is derived for finding the wall temperature by Levenberg-Marquardt (LM) algorithm of multi dimensionless analysis method with Nonlinear curve fitting method. A general form of forced convection heat transfer correlation was obtained by Buckingham Π theorem. The Wall temperatures predicted by various 7 existing correlations along with this new correlation are found by Visual basic program and compared with experimental data for evaluating the deviations. The rank was provided based on error band from ±0.5% to ±50% etc., and error analysis were conducted for proving the best fitting correlation. [ABSTRACT FROM AUTHOR]

The main objective of the present paper is to investigate the effect of using connecting holes on the hydrothermal performance and irreversibility behavior of laminar forced convection flow of a nanofluid (NF) inside a microchannel heat sink (MCHS). The biologically synthesized silver/water NF is employed as coolant. The influences of the volume concentration of NF (φ), the Reynolds number (Re) and the number of connecting holes on the performance features of MCHS and NF are considered numerically. It was observed that the CPU temperature is reduced and became more uniform due to boosting of Re and φ , and the consequence augmentation of the convective heat transfer. However, the pumping power and frictional irreversibility get raised as Re and φ are increased. The figure of merit is above unity for all Re and φ which indicate that the utilization of connecting holes is a suitable option to improve the MCHS performance from the first-law point of view. The heat transfer irreversibility, however, increased by using the connecting holes. Also, the merit of NF over the pure water is observed for Re of 500 and 2000 and φ of 0.1% and 1%. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the hydrothermal and irreversibility behaviour of a biological water-Ag nano-fluid in a new heatsink with helical microchannels. Two-phase mixture model is applied to precisely simulate the behavior of nanofluid in the nanoadditive concentration (φ) range of 0–1% and Reynolds number (Re) range of 500–1500. The influences of φ and Re on the convective heat transfer coefficient, CPU surface temperature, pumping power, as well as the irreversibilities due to heat transfer and fluid friction are examined. The findings depict that boosting the Re and φ augments the performance of heatsink by intensifying the convective heat transfer coefficient of the working fluid which favourably declines the CPU surface temperature and the heat transfer irreversibility and importantly results in the temperature uniformity of the CPU surface. However, intensification in Re adversely affects the pumping power, the fluid friction and total irreversibilities in the system. Furthermore, it is revealed that the nano-fluid always has a superior cooling performance as compared with the pure water. Finally, it is found that the best hydrothermal performance of the nano-fluid in the proposed heatsink occurs at Re = 1500 and φ = 1%, while the minimum total irreversibility occurs at Re = 500 and φ = 1%. [ABSTRACT FROM AUTHOR]