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•A hybrid nanofluid, Al2O3-MWCNT/water, in different concentrations was prepared.•The optical properties of prepared nanofluids and hybrid nanofluids were measured.•The hybrid ...nanofluids were applied in solar collector as volumetric absorber.•The thermal efficiency, embodied energy and water were analyzed.•Contaminants emission such as CO2 was calculated while nanofluid was used.
This study deals with the influence of hybrid nanofluids i.e., a mixture of Al2O3 and Multi-wall carbon nanotubes (MWCNTs) dispersed in water, on the environmental performance of a direct absorption parabolic trough collector. For this purpose, hybrid nanofluids in three volume concentrations i.e., 0.01%, 0.02%, and 0.04% were prepared and their optical properties were measured. Next, the nanofluids were used in the direct absorption parabolic trough collector (DAPTC) as a heat transfer fluid (HTF) to measure the effect of using hybrid nanofluids on its energy and environmental performances. Obtained data from the spectrometric experiment reveal that hybrid nanofluids have better optical properties than mono nanofluids and the base fluid, it would be suitable for use in the DAPTC in order to increasing the thermal performance. Using hybrid nanofluids with a volume fraction of 0.04% as the heat transfer fluid intensifies the maximum temperature difference parameter of the solar collector at 240.7%, 57.2%, and 8.2% compared to water, 0.04% alumina nanofluids, and 0.04% MWCNT nanofluids, respectively. Consequently, by using hybrid nanofluids, the thermal efficiency of the solar collector ameliorates by 197.1%, 69.2%, and 6.1% compared with cases in which water, alumina/water (0.04%), and MWCNT/water (0.04%) are used, respectively. The pressure drop in the absorber tube was gaged, and the results show that the increment of pressure drop for hybrid nanofluids can be negligible due to low volume fraction. Moreover, the saving of water along with other contaminants emissions such as CO2 was calculated for the nanofluid-based collector. The results reveal that using hybrid nanofluids instead of water leads to reductions in CO2 emission and water consumption as much as 450.33 kg and 2016.6 m3 per collector, respectively.
The utilization of porous‐fin microchannel (PFM) heat sinks has become prevalent for the cooling of microelectronic chips. This paper employs three‐dimensional simulation to examine the potential ...benefits of substituting a solid fin with a porous fin for enhancing the thermohydraulic performance. The influence of porous structure features on the thermal and hydraulic behavior of the PFMs at different geometrical configurations is investigated. Results show that in all configurations, employing a porous fin reduces the pressure drop. The heat transfer in PFMs is influenced by the convection in the main fluid path as well as convection in the porous fin structure. An increase in the permeability of the porous fins results in enhanced overall heat transfer due to the augmented convection within the fins. On the contrary, an increase in fin porosity leads to a heat transfer reduction as the effective thermal conductivity of the fin is diminished. The possibility of enhancing thermal performance via the substitution of the solid fin with a porous fin is diminished as the height of the microchannel increases. This is attributed to the weak vertical thermal diffusion of the porous material. Moreover, the findings indicate that the geometric configuration of microchannels has an essential role in heat transfer performance of the porous fin. For instance, the thermal resistance of the PFM with a height ratio of 1.5, porosity of 0.85, and permeability of K = 5 × 10 −8 m 2 is 10.4% less than that of the solid‐fin microchannel (SFM). However, by decreasing the permeability to K = 5 × 10 −10 m 2 , the thermal resistance of PFM was 26% higher than that of the SFM.
A numerical study was conducted to investigate the ability of wavy microchannels to damp the temperature fluctuations generates in electronic devices. Five wavy patterns are considered with the ...amplitude and wavelength in the ranges of 62.5 to 250 μm and 1250 to 5000 μm, respectively to study the effect of governing phenomena of flow within wavy patterns on thermal-hydraulic performance. The flow regime is laminar and the Reynolds number is in the range of 300 to 900, and a relatively high heat flux of 80 W/cm
is applied to the microchannels substrate. Also, variable flux condition is studied for heat fluxes of 80, 120, 160, 200, and 240 W/cm
and for the most efficient wavy and straight microchannels. Results showed that the geometries with larger amplitude to wavelength ratio have a lower radius of curvature and larger Dean number, and as a result of transverse flow (secondary flow) amplification, they have enhanced heat transfer. Also, by comparing the ratio of the transverse velocity components to the axial component, it was found that by decreasing the radius of curvature and increasing the Dean number, transverse velocity increases, which intensifies the heat transfer between the wall and the fluid. The appraisement of the performance evaluation criterion (PEC) illustrates that the wavy case with an amplitude of 250 μm and wavelength of 2500 μm is the best geometry from the thermal-hydraulic point of view in the studied range. Finally, with variable flux condition, the wavy microchannel has responded well to the temperature increase and has created a much more uniform surface temperature compared to straight pattern. The proposed wavy pattern ensures that there are no hotspots which could damage the electronic chip. Presented wavy patterns can be used in heat sinks heat transfer enhancement to allow the chip to run in higher heat fluxes.
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•The effect of using nano-silver on a commercial plate heat exchanger was studied.•An experimental rig was designed to investigate the thermo-hydrodynamic features of nanofluid.•The ...overall heat transfer coefficient becomes larger 16.79% for 100ppm nanofluid.•No significant growth in pressure drop values was observed.•The process temperatures have important role in nanofluid influence.
The purpose of this study is to verify the potential using of nano-silver dispersed water based nanofluid on efficiency improvement of a commercial corrugated plate heat exchanger. In this regards, an experimental rig was provided to recognize the heat transfer rate and pressure drop of Ag–water nanofluid as the working fluid. The two most key thermo-physical properties, i.e. dynamic viscosity and thermal conductivity of nanofluids were experimentally gauged. The findings, which were achieved, displayed that the overall heat transfer coefficient becomes larger, from 6.18% to 16.79%, for 100ppm silver nanofluid. While using nanofluid, no significant growth in pressure drop values was observed. Moreover, the process temperatures and flow rates have significant impacts on the helpfulness of applying nanofluid in a plate heat exchanger.
In this paper, experimental investigations on the thermal and electrical conductivities of three kinds of water based nanofluids are conducted. The experimental data are collected for Ag, SiC, and ...Graphene oxide (GO) nanofluids with respect to temperature and nanoparticle concentration. Results show that both the temperature and nanoparticle concentration have positive effect on the thermal and electrical conductivities of nanofluids. The effect of temperature and volume fraction of nanoparticles on the thermal conductivity of nanofluids is almost the same; however, the effect of nanoparticle concentration is much higher than the temperature for electrical conductivity. Furthermore, to better survey the benefit of nanofluids as coolant in electrically active heat transfer environments, the thermo-electrical conductivity (TEC) ratio was established based on the achieved experimental data and checked explicitly.
•The thermal and electrical conductivities of Ag, SiC and GO nanofluids were experimentally gauged.•Effects of temperature and nanoparticle concentration are examined.•The thermo-electrical conductivity (TEC) ratio is calculated.•Ag nanofluids resulted in the lowest TEC.
•The combination of wavy and oblique grooves finned was analyzed numerically.•Wetted area governs the appropriate pattern type.•Numax occurs in case of P = 375 and l = 250 µm.•Maximum pressure drop ...is created in case of P = 375 and l = 250 µm.•The secondary flow is one of the main contributors to heat transfer enhancement.•The performance index determined the effective pattern.
One of the crucial phenomena to enhance the heat transfer of microchannel heat sinks is the flow mixing and wall interaction through the secondary flow. In the present study, a combination of the wavy and the oblique grooved microchannel patterns was investigated to improve the performance of the microchannel heat sink. The oblique grooves with a pitch of 375 µm were combined with the wavy microchannel. The effect of fins with widths of 250 and 125 µm on thermal performance was investigated (Type-1 and Type-2). The amplitude of 250 µm and wavelength of 2500 µm were considered for wavy microchannels. Furthermore, the effect of pitches on the heat transfer was studied; subsequently, pitches of 750 and 1500 µm were analyzed (Type-3 and Type-4). Nusselt number, pressure drop, and performance evaluation criteria index were reported as the results. The results showed that secondary flow generation causes the thermal boundary layer to re-develop at each fin, continually developing fluid flow. Type-2 had the maximum average Nusselt number of approximately 80 and a pressure drop of approximately 50 kPa at Re = 850 compared to the other three cases. The performance evaluation criterion index (ƞ) was calculated for all cases to achieve a comprehensive conclusion about the performance of a heat sink. The results showed that in Type-2, the heat transfer increase exceeded the pressure drop penalty, and its eta was almost 2.5. Fluid flow patterns were investigated in detail as the most significant reason for efficiency improvement, and the wetted area was studied, which their maximum value equaled 1.2 at Type-2.
A direct absorption parabolic trough solar collector (DAPTC) integrated with porous foam as a volumetric absorber has the potential to be applied as an energy conversion integrant of future renewable ...energy systems. The present study comprehensively analyzes a DAPTC in terms of exergy, economic, and environmental analysis for different porous configuration inserts in the absorber tube. Ten different arrangements of porous foam are examined at several HTF flow rates (40–120 L/h) and inlet temperatures (20–40 °C). The exergy efficiency, entropy generation, Bejan number, and pumping power are investigated for all cases. Obtained results indicate that fully filling the absorber tube with porous foam leads to a maximum exergy efficiency of 20.4% at the lowest inlet temperature (20 °C) and highest flow rate (120 L/h). However, the Bejan number reaches its minimum value due to the highest pumping power in this case. Consequently, all mentioned performance parameters should be considered simultaneously. Finally, the environmental and economic analyses are conducted. The results show that fully filling the absorber tube with porous foam reflects the best heat production cost, which can reduced the embodied energy, embodied water, and CO2 emission by 559.5 MJ, 1520.8 kL, and 339.62 kg, respectively, compared to the base case at the flow rate of 120 L/h.
The cooling performance and water consumption of the wet cooling tower are two important parameters that must be balanced to achieve the optimum performance of this industrial component in its ...operating condition. The performance of the wet cooling towers can be analyzed by the thermodynamic models. On the other hand, fouling can drastically affect the cooling tower performance. In the present research, a thermodynamic model is developed and validated with numerical and experimental results in order to investigate the wet cooling tower's water consumption and cooling performance under various weather conditions. The model includes an accurate cooling tower model, considering the buoyancy force and droplets evaporation in the rain and spray zones. To achieve accurate results, an optimization algorithm is also utilized to solve the equations. This model was then applied to analyze the water consumption and cooling performance of a small cooling tower during the hottest months of Iran (July/August) in Ahvaz, Tabriz, and Yazd with different climate conditions. The non-dimensional parameter of the fill performance index (ηF) was used to describe the fouling in the packing. So, considering the simultaneous effects of the buoyancy force and droplet evaporation in the rain and spray zones and fouling in packing in the developed model, with utilizing a new and accurate method to solve the model's equation to analyze the performance of the wet cooling towers under different conditions, are the novelty of this study. Based on the results, a rise in fouling decreases the fill performance index. A decline in the fill performance index from 2.4 to 1.2 increases the monthly average of the cooling tower outlet water temperature from 24.24, 21.21, and 21.19 °C to 25.94, 24.14, and 24.11 °C in Ahvaz, Tabriz, and Yazd, respectively, while the monthly water consumption decreases from 1.74, 1.87, and 2.22 m3h to 0.99, 1.10, and 1.29 m3h in the mentioned cities, respectively. The maximum outlet water temperature was observed in case ηF=1.2, while the maximum water consumption occurred in ηF=2.4. So, ambient conditions and fouling simultaneously affect the performance of the cooling tower, which is well predicted by the suggested model.
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Abstract
In recent years, PCR-based methods as a rapid and high accurate technique in the industry and medical fields have been expanded rapidly. Where we are faced with the COVID-19 pandemic, the ...necessity of a rapid diagnosis has felt more than ever. In the current interdisciplinary study, we have proposed, developed, and characterized a state-of-the-art liquid cooling design to accelerate the PCR procedure. A numerical simulation approach is utilized to evaluate 15 different cross-sections of the microchannel heat sink and select the best shape to achieve this goal. Also, crucial heat sink parameters are characterized, e.g., heat transfer coefficient, pressure drop, performance evaluation criteria, and fluid flow. The achieved result showed that the circular cross-section is the most efficient shape for the microchannel heat sink, which has a maximum heat transfer enhancement of 25% compared to the square shape at the Reynolds number of 1150. In the next phase of the study, the circular cross-section microchannel is located below the PCR device to evaluate the cooling rate of the PCR. Also, the results demonstrate that it takes 16.5 s to cool saliva samples in the PCR well, which saves up to 157.5 s for the whole amplification procedure compared to the conventional air fans. Another advantage of using the microchannel heat sink is that it takes up a little space compared to other common cooling methods.
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