•Comparative study was conducted on thermal performance of gallium for CPU cooling.•Gallium showed a superior thermal performance compared to nanofluid.•Nanofluid showed reasonable thermal ...performance at low heat flux condition.•Gallium remained at single-phase region during cooling process.•Small penalty was reported for pressure drop for CUO/water.
This work aims to experimentally investigate the thermal performance of a cooling liquid block working with gallium, CuO/water nanofluid and water. The CPU used in this research is evaluated at three states of standby, normal and overload working modes. Results demonstrated that gallium is the most efficient coolant amongst the nanofluid and water in terms of convective thermal performance, however, the considerable penalty for pressure drop and pumping power is associated with the application of gallium liquid metal. CuO/water nanofluid instead, presented a higher thermal performance in comparison with water, while has lower pressure drop and pumping power, offering a trade-off situation against the gallium. Results also revealed that CPU is cooled more efficiently with gallium at overload and normal working modes. Experimental data were examined for the available correlations and two new correlations for estimating the Nusselt number were obtained via the regression analysis with an accuracy of 20% when compared to the experimental data.
In this paper, silver nanoparticles are produced via green synthesis method using green tea leaves. The introduced method is cost-effective and available, which provides condition to manipulate and ...control the average nanoparticle size. The produced particles were characterized using x-ray diffraction, scanning electron microscopic images, UV visualization, digital light scattering, zeta potential measurement and thermal conductivity measurement. Results demonstrated that the produced samples of silver nanoparticles are pure in structure (based on the x-ray diffraction test), almost identical in terms of morphology (spherical and to some extent cubic) and show longer stability when dispersed in deionized water. The UV-visualization showed a peak in 450 nm, which is in accordance with the previous studies reported in the literature. Results also showed that small particles have higher thermal and antimicrobial performance. As green tea leaves are used for extracting the silver nanoparticles, the method is eco-friendly. The thermal behaviour of silver nanoparticle was also analysed by dispersing the nanoparticles inside the deionized water. Results showed that thermal conductivity of the silver nano-fluid is higher than that of obtained for the deionized water. Activity of Ag nanoparticles against some bacteria was also examined to find the suitable antibacterial application for the produced particles.
•Thermal performance of CuO/water nanofluid in heat exchanger is investigated.•Pressure drop is measured inside the nanofluid loop.•Low frequency vibration was used to mitigate the fouling ...rate.•Vibration intensified the thermal performance of the system as well.
In the present work, experimental investigation is performed on the thermal performance of a chevron type flat plate heat exchanger working with CuO/water nanofluid with the especial emphasis on the fouling formation of nanoparticles inside the heat exchanger. Over a transient study, low frequency vibration was implemented to mitigate the fouling of nanoparticles inside the heat exchanger. To investigate the influence of fouling formation on the thermal performance of the system, fouling thermal resistance parameter was defined. Results showed that fouling of nanoparticles can be mitigated via low frequency vibration and fouling thermal resistance is decreases by applying the vibration into the system. Likewise, overall thermal performance of the system is intensified, when vibration is continuously applied into the heat exchanger. In the absence of vibration, fouling of particles is continually formed on the inner walls of the heat exchanger, which causes a thermal resistance. More importantly, fouling layer apparently can enhance the roughness, friction factor and the pressure drop inside the heat exchanger. In addition, it was found that there is an optimum point for the concentration of particles, which in this study was wt.%=0.3 for CuO/water nanofluid. Frequency and amplitude of the vibration waves were found to increase the thermal performance of the heat exchanger.
•Thermal performance of a copper made microchannel heat sink is investigated.•Silver nanoparticles are synthesized and used in the cooling loop.•37% enhancement in overall thermal performance of the ...system is reported.•Small penalty for friction factor and pressure drop is reported.•Fouling was found to reduce the thermal performance of the system.
Thermal performance of a copper-made heat sink with rectangular microchannel was assessed within laminar flow regime. Silver nanoparticles were synthesized and dispersed into the deionized water as a potential coolant. Pressure drop, friction factor, heat transfer coefficient and fouling thermal resistance parameter of the system were experimentally investigated for mass concentrations of 0.01%, 0.05%, and 0.1%. Results showed that the heat transfer coefficient of the microchannel is enhanced when deionized water (as a traditional coolant) is replaced with the nanofluid. Importantly, a small increase in pressure drop, friction factor and fouling thermal resistance parameter were reported when nanofluid is used in the system. With an increase in the flow rate and mass concentration of nanofluid, the heat transfer coefficient and pressure drop of the Microchannel Heat Sink (MCHS) increased. Likewise, the local heat transfer coefficient and overall thermal resistance of the microchannel decreased along with the length of the microchannel. The highest heat transfer coefficient (as a thermal performance index) was also seen in the entrance region of the microchannel. The highest value for the fouling thermal resistance parameter was observed for the highest mass concentration of nanofluid which was 1.07 for wt.% = 0.1. The flow rate of fluid was found to enhance the fouling thermal resistance parameter over the 1000 min of the operation. Despite the enhancement in the fouling thermal resistance parameter and friction factor, there was an optimum concentration for silver-water nanofluid in which the overall thermal performance of the system was maximized such that the overall thermal performance of the system can be enhanced up to 37% at Reynolds number 1400 and at wt.% = 0.05.
•Experimental investigation on thermal performance of microchannel heat sink.•Aqueous CNT nanofluids at wt.%=0.05–0.1 were used as the coolant.•Lower temperature profile and higher HTC were recorded ...for nanofluids.•Fouling thermal resistance showed an asymptotic behavior over the time.
Experimental investigation is performed on the thermal performance of a copper-made heat sink with rectangular microchannel. Carbon nano tube aqueous nanofluid is used as a coolant inside the microchannel at mass concentrations of 0.05–0.1%. Influence of different operating parameters including applied heat flux, fluid flow rate and mass concentration of nanofluid on the local and average heat transfer coefficients, fouling thermal resistance, overall thermal resistance and local (axial) temperature profile is investigated. Results showed the higher heat transfer coefficient and lower temperature profile inside the heat sink in comparison with the base fluid (water). Fluid flow rate and mass concentrations were found to increase the heat transfer coefficient significantly, while slight improvement was seen when higher heat fluxes were applied into the microchannel heat sink. Fouling thermal resistance was found to asymptotically increase with an increase in operating time and strongly depends on the concentration of nanofluid such that the required operating time to reach a constant value was different. The higher the mass concentration, the lower operating time is required to reach the constant fouling thermal resistance. However, overall thermal resistance of the microchannel (without considering the fouling effect) was found to linearly decrease with the mass concentration of nanofluid.
Convective boiling heat transfer coefficient of spherical CuO (II) nanoparticles dispersed in water is experimentally quantified inside the vertical heat exchanger. Influence of different operating ...parameters including applied heat and mass fluxes, sub-cooling temperature and concentration of nano-fluid on forced convection and nucleate boiling heat transfer mechanisms is experimentally investigated and briefly discussed. Results show that by increasing heat and mass fluxes, the heat transfer coefficient considerably increases for both heat transfer regions, while by increasing the nanoparticle weight concentration, the heat transfer coefficient increases in convective heat transfer (about 35% at the maximum concentration) and deteriorates the heat transfer coefficient (about 9% at maximum concentration) in nucleate boiling region due to the formation of nanoparticle deposition on heating surface. Experimental results are then compared to well-known correlations. Results of comparisons reveal good agreement between experimental data and those obtained by some correlations. In addition, thermo-physical properties of CuO nano-fluid are experimentally measured and represented, which are a good reference for other nano-fluid-related studies. Key words: convection, nucleate boiling, nano-fluids, heat transfer enhancement, heat transfer deterioration
Experimental investigation on the thermal performance of a flat heat pipe working with carbon nanotube nanofluid is conducted. It is used for cooling a heater working at high heat flux conditions up ...to 190 kW/m
2
. The heat pipe is fabricated from aluminium and is equipped with rectangular fin for efficient cooling of condenser section. Inside the heat pipe, a screen mesh was inserted as a wick structure to facilitate the capillary action of working fluid. Influence of different operating parameters such as heat flux, mass concentration of carbon nanotubes and filling ratio of working fluid on thermal performance of heat pipe and its thermal resistance are investigated. Results showed that with an increase in heat flux, the heat transfer coefficient in evaporator section of the heat pipe increases. For filling ratio, however, there is an optimum value, which was 0.8 for the test heat pipe. In addition, CNT/water enhanced the heat transfer coefficient up to 40% over the deionized water. Carbon nanotubes intensified the thermal performance of wick structure by creating a fouling layer on screen mesh structure, which changes the contact angle of liquid with the surface, intensifying the capillary forces.
This paper experimentally focuses on the pool boiling heat transfer characteristics of gamma Fe
3
O
4
aqueous nano-fluids on a flat disc heater. The nano-fluid used in this research was prepared ...using two-step method and was stabilized using nonylphenol ethoxylate nonionic surfactant, pH setting, and sonication process as well. Influence of different operating parameters such as heat flux (0–1546 kW/m
2
), mass concentration of nano-fluids (weight concentration 0.1–0.3 %), bubble formation, critical heat flux (1170 kW/m
2
for water, 1230 kW/m
2
(wt% = 0.1), 1320 kW/m
2
(wt% = 0.2), 1450 kW/m
2
(wt% = 0.3) and fouling on pool boiling heat transfer coefficient of nano-fluid as a thermal performance index were experimentally investigated and briefly discussed. Results demonstrated that the pool boiling heat transfer coefficient increases with increasing the mass concentration and the applied heat flux. In addition, the rate of bubble formation is significantly intensified at higher heat fluxes and subsequently, larger bubbles detach the surface due to the intensification of bubble coalescence. In terms of fouling formation, it can be stated that fouling of nano-fluids is a strong function of time and rate of deposition is increased over the extended time while the pool boiling heat transfer coefficient was not decreased over the time, as porous deposited layer on the surface are detached from the surface by bubble interactions. In terms of critical heat flux, capillary action of the deposited layer was found to be the main reason responsible for increasing the critical heat flux as liquid is stored inside the porous deposited layer, which enhances the surface toleration against the critical heat flux crisis.
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•CuO–water nanofluid is utilized as possible energy saving coolant inside the HEX.•Fouling behavior of nanoparticles on the surface is experimentally investigated.•Asymptotic behavior ...of particulate fouling is registered in nucleate boiling domain.•A correlation based on the isothermal-diffusive particulate flow is proposed.
Because of potential of energy saving and wide utilizations of nanofluids in industrial and commercial aspects, sedimentation and scale formation of nanoparticles inside the heat transfer media has been an indispensible challenge. In the present work, experimental investigation is conducted on the convective boiling of dilute CuO–water nanofluids in an upward flow inside the conventional heat exchanger. Nanofluids are stabilized using the stirring, pH control and sonication processes. For different operating conditions, influences of heat and mass flux, concentration of nanofluids on scale formation in term of fouling resistance are investigated in convective and nucleate boiling heat transfer heat transfer domains. Since, particulate fouling has not been correlated for nanofluids, a new correlation based on the experimental data at isothermal/diffusion flow conditions is introduced which can predict the fouling resistance of CuO/water nanofluids with Absolute Average Deviation of (less than) 30% which implies on a fair agreement to experimental data. Since, experiments are carried out in a heat exchanger with conventional dimensions; interpreted results can be generalized and applicable for any present/future industrial heating tools engaged with nanofluids as coolant.
In this work, thermal conductivity, viscosity, and boiling heat transfer coefficient of a biologically produced nano-coolant were experimentally quantified. The nanoparticles were produced from ...silver nitrate via the plant extraction method and by means of green tea leaf extract. The mean size of the particles was 50 nm, with spherical morphology and single-phase structure of Ag (silver). The synthesized particles were dispersed in coconut oil as base fluid. Thermal conductivity and viscosity of the nanofluid were experimentally measured and correlated based on temperature and concentration of nanoparticles via the regression analysis. Thermal performance of the nanofluid inside an annular heat exchanger with convective boiling conditions (in forced convection and nucleate boiling heat transfer regimes) was assessed. The results demonstrated a superior thermal performance in both heat transfer regions over the base oil, and revealed that this nanofluid can be used as a coolant as well as a lubricant in engines with high heat flux conditions, as its thermal conductivity and viscosity were enhanced due to the presence of Ag particles inside the oil.Key words:silver nanoparticle, thermal conductivity, viscosity, boiling heat transfer, plant extraction
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