An introduction to heat transfer

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A User’s Guide

Solar Engineering Of Thermal Processes

A review of the applications of nanofluids in solar energy

The limitation of hot spot cooling in microchips represents an important hurdle for the electronics industry to overcome with coolers yet to exceed the efficiencies required. Nanotechnology-enabled heat sinks that can be magnetophoretically formed onto the hot spots within a microfluidic environment are presented. CrO2 nanoparticles, which are dynamically chained and docked onto the hot spots, establish tuneable high-aspect-ratio nanofins for the heat exchange between these hot spots and the liquid coolant. These nanofins can also be grown and released on demand, absorbing and releasing the heat from the hot spots into the microfluidic system. It is shown that both high aspect ratio and flexibility of the fins have a dramatic effect on increasing the heat sinking efficiency. The system has the potential to offer a practical cooling solution for future electronics.

Dynamic nanofin heat sinks

Mechanical Engineering Department, College of Engineering, Universiti Tenaga Nasional, MalaysiaLaminar two-dimensional sudden expansion ﬂow of different nanoﬂuids is studied numerically. Thegoverning equations are solved using stream function-vorticity method. The effect of volume fractionof the nanoparticles and type of nanoparticles on ﬂow behaviour is examined and found signiﬁcantimpact. The ﬂow response to Reynolds number in the presence of nanoparticles is examined. Thepresence of nanoparticles decreases the ﬂow bifurcation Reynolds number. The size and the reat-tachment length of the bottom wall recirculation increase with increasing volume fraction and particledensity. The effect of volume fraction and density of nanoparticles on friction factor is reported. Thebottom wall recirculation strongly respond to the variation in volume faction and type of particles.However, weak response is observed for top wall recirculation.

Numerical Investigation on Laminar Forced Convection Flow Due to Sudden Expansion Using Nanofluids

This paper aims to investigate the effect of the flow pattern on the mixed convection heat transfer. A 28 thermocouples wire were installed along a 900mm copper tube to measure the temperature distribution. Three insulation layers of fiber glass, asbestos and gypsum were used to minimize to heat lost to the surrounding. A forced convection at the entrance region of a fully developed opposing laminar air flow was investigated to evaluate the flow direction effect on the Nusselt number. The
investigation covered a wide range of Reynolds number from 410 to 1600 and heat flux varied from 63W/m2 to 1260W/m2, with different angles of tube inclination of 30°, 45°, 60°, and 90°. It was found that the surface temperature variation along the tube for opposed flow higher than the assisted flow but lower than the horizontal orientation. The Reynolds number has a significant effect on Nusselt number in opposed flow while the effect of Reynolds number was found to be small in the case of assisted flow. The
Nusselt number values were lower for opposed flow than the assisted flow. The temperature profiles results have revealed that the secondary flows created by natural convection have a significant effect on the heat transfer process. The obtained average Nusselt number values were correlated by dimensionless groups as Log Nu against Log Ra/Re .

Heat Transfer by Mixed Convection Opposing Laminar Flow From the Inside Surface of Uniformly Heated Inclined Circular Tube

Mixed convection heat transfer inside a vertical circular cylinder has been experimentally studied for upward and downward flows for hydrodynamically fully developed and thermally developing laminar air flow under constant wall heat flux boundary conditions for Reynolds number range from 400–1600 and the Grashof number range from 1.1 × 105–7.4 × 106. The effects of the cylinder inclination angle and the flow direction on the mixed convection heat transfer process have been investigated. The experimental setup consists of an aluminum cylinder as test section with 30 mm inside diameter and 900 mm heated length (L/D = 30). The hydrodynamically fully developed condition was achieved by using aluminum entrance section pipes (calming sections) having the same inside diameter as test section pipe but with variable lengths. The entrance sections were included two long calming sections, one with length of 1,800 mm (L/D = 60), another one with length of 2,400 mm (L/D = 80), and two short calming sections with lengt...

Heat transfer measurements of mixed convection for upward and downward laminar flows inside a vertical circular cylinder

This study examined numericallythe Thermal-hydrodynamic properties of airflow in the fin-and-tube compact heat exchangers (FTCHEs) with considering different shapes of tubes in lowReynoldsnumbers The influence of applying flat, oval and circular tube adjustments on the thermal and hydraulic characteristics of air flow were analyzed on the in-line tube arrangements Establishing standard conditions, the study compared different geometries based on circular tubes of 10459 mm diameter tubes with 254 mm longitudinal pitches and 254 mm transverse pitches The other geometries of tubes were assumed in a stable and constant state preparing the same heat transfer surface area per unit volume as that of the nominal case The results showed that the FTCHE with flat tubes gives the best area goodness factor (j/f) with in a certainrange of Reynoldsnumbers In addition, FTCHE with flat tubes shown the best thermo-hydraulic performance and a significant augmentation of up to 1083% and 3563% in the average area goodness factor achieved accompanied by a decrease in the average friction factor of 1702% and 4341% in the flat tube case compared to the oval and circle tube shapes, respectively It is concluded that the average area goodness factorfor the oval tube is about 2504% higher than that of the circular tube, while the average friction factor for the oval tube is about 269% lower than that of the circular tube This means that the flat tube has a better-combined thermal–hydraulic performance than the oval and circle tube

Numerical evaluation of thermo-hydraulic performance in fin-and-tube compact heat exchangers with different tube cross-sections

Laminar mixed convection heat transfer in a lid driven square cavity filled with nanofluids is investigated numerically. In this current study, the vertical walls are purported at steady but dissimilar temperatures, whereas the bottom and top horizontal walls are insulated. The top wall is set with uniform velocity and insulated. Al2O3, CuO, SiO2 and TiO2 are the nanoparticles used with diameters 25nm, 40nm and 60nm. Results are presented in terms of streamlines, isotherms and Nusselt number for different parameters such as, the Reynolds number

Hussein A. Mohammed

Papers

Numerical Investigation on Laminar Forced Convection Flow Due to Sudden Expansion Using Nanofluids

Heat Transfer by Mixed Convection Opposing Laminar Flow From the Inside Surface of Uniformly Heated Inclined Circular Tube

Heat transfer measurements of mixed convection for upward and downward laminar flows inside a vertical circular cylinder

Numerical evaluation of thermo-hydraulic performance in fin-and-tube compact heat exchangers with different tube cross-sections

Mixed convection heat transfer of nanofluids in a lid driven square cavity: a parametric study