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

A numerical investigation is performed to study the effects of different geometrical parameters and nanofluids on the thermal and flow fields through circular tubes fitted with inserts with Reynolds number ranging from 500 to 1750 and heat flux of 1000 W/m(2). The two dimensional continuity, Navier Stokes and energy equations are solved by using the finite volume method. The optimization through twisted tape with eleven types of tube having 20 mm inner diameter was studied by changing the dimensions of twisted tape such as the width ratio (W/D) in the range of 0.2-0.8 and the twist ratio (H/D) in the range of 2.5-4 for water as a working fluid to reach the optimal geometry with maximum performance evaluation criterion (PEC). The effects of using different types of nanoparticles such as Al2O3, CuO, SiO2, and ZnO, different nanoparticles volume fractions in the range of 1% to 4% and different nanoparticles diameters in the range of 25 nm to 80 nm in water base fluid were examined. The effects of different Reynolds numbers and the dispersion of nanoparticle in different types of base fluid such as ethylene glycol, engine oil and water in circular tube were also analyzed. Simulation results show that the Nusselt number increased as the width ratio and Reynolds number increased and twist ratio decreased. The highest Nusselt number was obtained with W/D = 0.8, while the efficient flow (max. PEC) was achieved with W/D = 0.7 for H/D = 2.5. The Nusselt number through the circular tubes with insert was enhanced with the increase of the particle volume fraction and with the decrease of nanoparticles diameter.

Heat transfer enhancement using nanofluids in a circular tube fitted with inserts

In this study, the numerical conjugate heat transfer and hydraulic performance of nanofluids flow in a rectangular microchannel heat sink (RMCHS) with longitudinal vortex generators (LVGs) was investigated at different Reynolds numbers (200–1200). Three-dimensional simulations are performed on a microchannel heated by a constant temperature with five different configurations with different angles of attack for the LVGs under laminar flow conditions. The study uses five different nanofluid combinations of Al2O3 or CuO, containing low volume fractions in the range of 0.5% to 3.0% with various nanoparticle sizes that are dispersed in pure water, PAO (Polyalphaolefin) or ethylene glycol. The results show that for Reynolds number ranging from 100 to 1100, Al2O3–water has the best performance compared with CuO nanofluid with Nusselt number values between 7.67 and 14.7, with an associated increase in Fanning friction factor by values of 0.0219–0.095. For the case of different base fluids, the results show that CuO–PAO has the best performance with Nusselt number values between 9.57 and 15.88, with an associated increase in Fanning friction factor by 0.022–0.096. The overall performance of all configurations of microchannels equipped with LVGs and nanofluid showed higher values than the ones without LVG and water as a working fluid.

https://www.mdpi.com/2227-9717/8/2/231/pdf

Thermal-Hydraulic performance in a microchannel heat sink equipped with longitudinal vortex generators (LVGs) and nanofluid

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

The present study provides a comprehensive experimental work about fluidized bed gas-solid system characteristics by using different solid particles. Naphthalene, silica gel and sand (197 µm diameter) are utilized as a solid particles while air is used for fluidization. An experimental rig is build to test the various solid particles and to establish a good description of flow and heat transfer patterns for the fluidized bed gas-solid system. Based on the experimental tests, it is found that the solid particle type has a significant influence on the gas-solid flow dynamics. The experimental tests are performed for various fluidized bed velocities ( 0.8 , 1.2 and 1.6 m/sec ) and when the heat fluxes are varied as 80 , 120 and 160 W respectively. Experimental measurements are carried out under steady state situation. Depending on the experimental results , it can be concluded that sand solid particles are better than silica gel and naphthalene solid particles for heat transfer enhancement. Also, it can found for naphthalene , silica gel and sand solid particles that as the fluidized bed velocity and heat flux increase the temperature distribution along the fluidization column increases. Moreover, an empirical equation based on the experimental measurements which linking between Nusselt number (Nu) , Froude number (Fr) and Reynolds number (Re) is suggested. Comparisons with previously published works on gas-solid fluidized bed system are performed and good agreements between the results are observed.

http://textroad.com/pdf/JBASR/J.%20Basic.%20Appl.%20Sci.%20Res.,%203(7)293-304,%202013.pdf

Experimental Investigation of Various Solid Particle Materials on the Steady State Gas-Solid Fluidized Bed System

In this work numerical predictions of mixed convective nanofluids flow and heat transfer in an equilateral triangular duct are reported. Three dimensional, laminar Navier-Stokes and energy equations were solved using the finite volume method. Pure water and four different types of nanofluids such as Ag, Au, Cu, diamond and SiO 2 with volume fractions range of 1 â�¤; I¦ â�¤; 5 are used. This investigation covers Rayleigh number in the range of 1A� 10 4 â�¤ Ra â�¤ 1A� 10 6 and Reynolds number in the range of 100 â�¤ Re â�¤ 1000. The effects of different Rayleigh numbers, Reynolds numbers, nanofluid types, volume fractions of nanofluid, apex angles of the traingular duct, and radiation are investigated. The results presented in terms of streamlines, isotherms, Nusselt number, and pressure drop. The results revealed that the Nusselt number increases as Rayleigh number increases due to the buoyancy force effect. It is found that SiO 2 nanofluid has the highest Nusselt number while Au nanofluid has the lowest Nusselt number among other nanofluids. The apex angle of the triangular duct has remarkable influence on the Nusselt number. An increasing of the duct apex angle decreases the Nusselt number value. The pressure drop increases as Reynolds number increases and apex angle decreases.

Hussein A. Mohammed

Papers

Heat transfer enhancement using nanofluids in a circular tube fitted with inserts

Thermal-Hydraulic performance in a microchannel heat sink equipped with longitudinal vortex generators (LVGs) and nanofluid

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

Experimental Investigation of Various Solid Particle Materials on the Steady State Gas-Solid Fluidized Bed System

The application of nanofluids on three dimensional mixed convection heat transfer in equilateral triangular duct