Thermodynamic performance of boehmite alumina nanoparticle shapes in the counterflow double pipe heat exchanger

This work compares a theoretical model with a consolidated numerical model related to the thermodynamic performance of boehmite alumina nanoparticles in different formats in a counterflow double pipe heat exchanger. The shapes of the non-spherical nanoparticles under analysis are platelets, blades, cylindrical, and bricks. The second law of thermodynamics is applied to determine Nusselt number, pressure drop, thermal efficiency, thermal and viscous irreversibilities, Bejan number, and the out temperature of the hot fluid. The entropy generation rates associated with the temperature field and the viscous flow are graphical determined. The numerical model uses the k-ε turbulence model, which requires empirical factors to simulate turbulent viscosity and rate of generation of turbulent kinetic energy. Compatibility between the models was demonstrated. It was shown that the maximum absolute numerical error between the quantities Nusselt number, heat transfer rate, and pressure drop for established and specific conditions is less than 12.5 %

Impact of variable fluid properties on forced convection of Fe3O4/CNT/water hybrid nanofluid in a double-pipe mini-channel heat exchanger

The objective of this study is to assess the hydrothermal performance of a non-Newtonian hybrid nanofluid with temperature-dependent thermal conductivity and viscosity compared with a Newtonian hybrid nanofluid with constant thermophysical properties. A counter-current double-pipe mini-channel heat exchanger is studied to analyze the effects of the hybrid nanofluid. The nanofluid is employed as the coolant in the tube side, while the hot water flows in the annulus side. Two different nanoparticles including tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic-coated carbon nanotubes are used to prepare the water-based hybrid nanofluid. The results demonstrated that the non-Newtonian hybrid nanofluid always has a higher heat transfer rate, overall heat transfer coefficient, and effectiveness than those of the Newtonian hybrid nanofluid, while the opposite is true for the pressure drop, pumping power, and performance evaluation criterion. Supposing that the Fe3O4-carbon nanotube/water hybrid nanofluid is a Newtonian fluid with constant thermal conductivity and viscosity, there leads to large error in the computation of pressure drop (1.5–9.71%), pumping power (1.5–9.71%), and performance evaluation criterion (18.24–19.60%), whereas the errors in the computation of heat transfer rate, overall heat transfer coefficient, and effectiveness are not considerable (less than 2.91%)

Review of Thermal Energy Storage Technologies and Experimental Investigation of Adsorption Thermal Energy Storage for Residential Application

Thermal energy storage (TES) technologies can reduce or eliminate the peak electric power loads in buildings, and utilize benefits of waste heat recovery and renewable energy. This thesis work consists of TES literature review and experimental investigation of adsorption TES. Review work includes cold storage technologies for air conditioning and subzero applications, and heat storage technologies for residential application. Different technologies involving sensible, latent and sorption TES were compared and resolutions of their issues were summarized. In addition, adsorption TES was experimentally investigated and its energy and exergy flows were analyzed to evaluate the effects of different operating parameters, such as temperature and heat transfer fluid mass flow rate for different chambers on the system performance. Finally, a computer model was developed for the adsorption heat TES system integrated with a vapor compression heat pump to assess its performance. Simulation results showed that overall coefficient of performance (COP) and exergy-based COP are approximately 3.11 and 0.20, respectively

Comparison of the evaporation and condensation heat transfer coefficients on the outside of smooth, micro fin and vipertex 1EHT enhanced heat transfer tubes

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.An experimental investigation was performed to evaluate condensation and evaporation heat transfer on the outside of a smooth tube, herringbone micro fin tube and the Vipertex 1EHT enhanced heat transfer tube as a function of mass flux. Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in two phase heat transfer applications. Utilization of enhanced heat transfer tubes is an effective enhancement method that is utilized in the development of high performance thermal systems. Vipertex™ enhanced surfaces have been designed and produced through material surface modifications, creating flow optimized heat transfer tubes that increase heat transfer. Heat transfer processes that involve phase-change processes are typically efficient modes of heat transfer; however current energy demands and the desire to increase efficiencies of systems have prompted the development of enhanced heat transfer surfaces that can be used in processes involving evaporation and condensation. Surface enhancement of the 1EHT tube is accomplished through the use of a primary dimple enhancement coupled with a secondary background pattern made up of petal arrays. Enhancement of the herringbone is accomplished through the use of microfins. Convective condensation heat transfer and pressure loss characteristics were investigated using R410A on the outside of: (i) a smooth tube (outer diameter 12.7 mm); (ii) an external herringbone tube (fin root diameter 12.7 mm); and (iii) the 1EHT tube (outer diameter 12.7 mm) for mass flux ranging from 8 to 50 kg/ (m2 s); at a saturation temperature of 318 K; with an inlet quality of 0.8 and an outlet quality of 0.1. For these conditions, both the 1EHT tube, and the herringbone tube did not perform as well as the smooth tube. This was an unexpected result. Additionally the study also included a determination of the evaporation heat transfer coefficients using R410A on the outside of the same three tubes. The nominal evaporation temperature was 279 K; for a mass flux that ranged from 10 to 40 kg/m2 s; with an inlet quality of 0.1 and the outlet quality of 0.8. Excellent heat transfer performance is demonstrated by the 1EHT tube showing an enhancement ratio of approximately 1.4. Evaporation heat transfer coefficient enhancement values for the herringbone tube ranges from 1.5 to 2.2. For the considered conditions, both the herringbone and 1EHT tubes have higher pressure drops than smooth tubes. Microfins, surface roughness and three dimensional enhanced surfaces are often incorporated on the surface of tubes in order to enhance heat transfer performance. Under many conditions, enhanced surface tubes can recover more energy and provide the opportunity to advance the design of many heat transfer products. Enhanced heat transfer tubes are widely used in refrigeration and air-conditioning applications in order to reduce cost and create a smaller application footprint. A new type of enhanced heat transfer tube has been created using dimples/protrusions with secondary petal arrays; therefore it is important to investigate the heat transfer characteristics of the new Vipertex 1EHT enhanced surface tube and compare it to other tubes.am201

Magnetohydrodynamics flow of Ag-TiO2 hybrid nanofluid over a permeable wedge with thermal radiation and viscous dissipation

Hybrid nanofluids, which are made by suspending non-identical nanoparticles, have been a prominent research area because of their high efficiency in heat transfer. The analysis of the magnetohydrodynamics flow of Ag-TiO2 hybrid nanofluid over a permeable wedge with heat radiation and viscous dissipation is mathematically examined in this paper. Ordinary differential equations are deduced by applying the corresponding similarity transformations to the mathematical modelling of the governing partial differential equations. The dimensionless governing equations are solved using the built-in bvp4c function in the MATLAB package to compute the dual solutions and the stability analysis. A respectable degree of agreement has been obtained after comparing the current results with the earlier study. Prandtl number, magnetic parameter, radiation parameter, Eckert number, and other governing factors have all been studied, along with their physical impacts on fluid flow. The graphical results have been demonstrated and described in relation to the profiles of temperature and velocity distribution, skin friction as well as the Nusselt number. It has been established that the higher volume percentage of titania nanoparticles has the potential to improve thermal conductivity, and the first solution has been found to be stable in this flow

Investigation Of Laminar Convective Heat Transfer And Pressure Drop Of SiO2 Nanofluid In Ducts Of Different Geometries

Engineers are seeking alternatives to conventional heat transfer fluids and in an attempt to improve their thermal transport properties, they added thermally conductive solids into the conventional fluids resulting in a fluid called nanofluid. Nanofluid was suggested as an alternative solution to the problem and many publications reported its potential for heat transfer enhancement. This thesis describes the experimental study of 9.58% by vol. silica/water nanofluid flow through different flow geometries which are circular, hexagonal and rectangular ducts of close hydraulic diameter. The experiments are performed at uniform heat flux condition. The aim of this thesis is to determine experimentally the best duct geometry for optimal thermal performance in nanofluids. The effect of the cross-section of the flow geometry on the enhancement capability of nanofluid is the focus of this research and four different geometries of relatively equal hydraulic diameters were studied. This study compares the result from the different duct geometries in order to identify the best flow channel for optimal heat transfer using nanofluids. Based on the test data, the thermal performance comparisons are made under three constraints (similar mass flow rate and Reynolds number). It was observed from the comparisons that the rectangular duct showed the highest heat transfer capability through a higher Nusselt number and heat transfer coefficients at for the silica/water nanofluid flow. The circular duct was next to the rectangular duct in thermal performance. There was no significant change in friction factor between the ducts for both water and nanofluid flow

Hydrothermal performance of aluminium oxide/water and cupper oxide/water nanofluids in divergent-convergent minichannel heatsink with dimples

The recent trend in technological advancements in electronic devices offers high-performance compact systems. However, highly concentrated heat flux restricted their efficiency and reduced the Mean time before failure (MTBF). Many researchers exploit different passive heat transfer techniques like geometry modification to alleviate high heat flux. Despite the potential of divergent-convergent minichannel in mixing flow and a higher proportion of surface area to volume than conventional channels, research on it is inadequate. The study aims to develop and examine the influence of combined multi passive heat transfer techniques in an electronic device minichannel heatsink towards further augmenting heat transfer with minimal pressure loss and thermal resistance. This study combines corrugated geometry with innovative high thermal conductive nanofluid as hybrid passive techniques. The experimental validation concerning measured and predicted pressure drop and Heat Transfer Coefficient data indicated a maximum deviation of 19.1% and 13.8%, respectively. The numerical analysis employed a commercial CFD code based on the finite volume method. The investigation of forced convective heat transfer and nanofluids’ flow achieved with single-phase and two-phase mixture models in a divergent-convergent minichannel heatsink (DCMH) having a hydraulic diameter of 1.42mm. The numerical investigation employed Al2O3/water and CuO/water nanofluids with 0 - 2.5 volume%, fluid velocity from 3 – 6 m/s (corresponding to Reynolds number (5000 – 10000), and the inlet temperature 303 K. The two-phase model exhibits better agreement with established correlation than the single-phase model. A numerical analysis of an enhanced geometry with dimples on the minichannel floor was developed to augment the hydrothermal performance. The results found that the effects of principal parameters on the chip heat flux demonstrated the heat transfer coefficient’s growth with a rise in volume fractions and fluid velocity. Both nanofluids indicated better performance enhancement than water. Al2O3/water and CuO/water nanofluids augment over water by about 6.44% and 8.33% for 2.5 vol.%. Also, pressure loss rises when the velocity increases. The pressure loss relative to water at 2.5 vol.% and 5.5 m/s yields 15.14% and 18.56 % for Al2O3/water and CuO/water. The highest pumping power is 0.057 W for all the cases, which indicates the pumping demand is much lower than 1.0 W. The introduction of dimples on DCMH has considerably advanced hydrothermal performance with a PEC of 1.214 over the smooth model. The overall results established that the combined effects of DCMH and nanofluids have significantly improved the heat sink’s hydrothermal performance and can provide the desired heat dissipation from the enclosed chips in compact electronic devices

Recent advances of nanofluids in micro/nano scale energy transportation

As the continuing integration and size deflation of component dimensions in electronic circuits and increase in the number of transistors in modern microprocessor chips, especially for heat dissipation of micro/nano scale devise, traditionally used single phase fluid cannot meet the requirements for highly efficient heat transfer, which thus frequently results in the damage of electrical devices. Consequently, thermal conductivity enhancement of working fluids is of great significance for advanced thermal energy conservation and conversion. Nanofluids, which possess a superior thermal conductive performance, are studied towards an alternative to the traditionally used working fluids, have attracted ample attention within the past decades. In this paper, firstly, we summarized the recent progress in the preparation of nanofluids, in particular for a method involving a covalent concerning reorganization or generation; subsequently, the utilization of nanofluids in hitherto unsummerized micro/nano scale heat and mass transfer fields, especially for some chemistry relating applications were discussed. All works demonstrated in this review are aiming at clarifying the fact that advanced material technologies are required in preparation of recent nanofluids on the premise of continuing harsh energy transfer situation; on the other hand, nanofluids were also able to offer insights for novel micro/nano scale energy transportation which has not yet been reviewed before

Advanced surface and volumetric receivers to convert concentrated solar radiation

This thesis is the results of the work conducted during the three years of Ph.D. at the Department of Industrial Engineering of the University of Padova. The conversion of solar energy into heat in the medium-temperature range (between 80 °C and 250 °C) has recently encountered a renewed interest in heating and cooling applications of industrial, commercial, residential and service sectors. Concentrating solar thermal collectors at medium temperature are suitable for many commercial and industrial applications, such as industrial process heat, solar cooling and desalination of the seawater. It is expected that in the future, a significant technological development can be achieved for these collectors, provided that the conversion of solar energy becomes more efficient and cost-effective. The proper design of the receiver, which is considered the heart of any concentrating collector, is essential to the future improvement in the conversion efficiency of this technology. In this context, the present thesis investigates the application of two innovative concepts of receivers in a prototype of an asymmetrical parabolic trough concentrator installed in the Solar Energy Conversion Lab of the Industrial Engineering Department, at the University of Padova. In Chapter 1, a study on different estimation procedures for the assessment of the direct normal irradiance, which is the solar resource utilized by solar concentrators, is presented. The study includes an indirect evaluation from measurements of global and diffuse horizontal irradiances and the use of semi-physical/empirical models. A detailed analysis of the instrumentation and of the measuring technique as well as the expression of the experimental uncertainty is provided. In Chapter 2, the optical performance of the asymmetrical parabolic trough is experimentally characterized. As a result, a statistical ray-tracing model of the concentrator for optical performance analysis in different working conditions is validated and used to optimize the design of the proposed receivers. In Chapter 3, an innovative flat aluminium absorber manufactured with the bar-and-plate technology, including an internal turbulator, is tested in the asymmetrical parabolic trough collector under single-phase and two-phase flow regimes. A numerical model to predict its performance has been developed and validated against the experimental data. In Chapter 4, this model is used to evaluate the performance of a small solar-powered ORC system by coupling the aforementioned concentrating solar system with direct vaporization of a low-GWP halogenated fluid or by using an intermediate solar circuit to heat pressurized water and evaporate the same organic working fluid in a separate heat exchanger. Finally, in Chapter 5 a new direct absorption receiver is proposed to investigate the capability of a suspension of single-wall carbon nanohorns in distilled water to absorb concentrated sunlight. The volumetric receiver has been designed through the development of a three-dimensional computational fluid dynamics model for its installation in the focus region of the asymmetrical parabolic trough. The capability of the nanofluid in collecting solar radiation when exposed to concentrated and non-concentrated solar flux are experimentally investigated thanks to the cooperation with National Council of the Research (CNR), that provided the aqueous solution. The nanofluid was tested in several conditions, with and without circulation, to investigate its stability with time