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[en] Highlights: • Heat transfer characteristics of three types of EGR coolers (Semi, Full spiral and Full-smooth) were investigated. • Pressure drop in the F-Spiral EGR cooler is more than other EGR coolers. • The F-spiral and S-spiral EGR cooler is suggested to be utilized in diesel engine. • Heat transfer efficiency of the S-spiral is 0.17 higher than that of the F-smooth EGR cooler. • The heat transfer efficiency of the S-spiral and F-spiral EGR cooler are same. - Abstract: In this study, the flow and heat transfer characteristics of three types of EGR coolers including Semi-spiral EGR cooler (S-Spiral EGR cooler), Full-Spiral EGR cooler (F-Spiral EGR cooler) and Full-Smooth EGR cooler (F-Smooth EGR cooler) were investigated. The fluid and heat transfer properties of the new S-spiral EGR cooler system were studied experimentally and numerically using CFD, but the other two types, F-Spiral EGR cooler and F-Smooth EGR cooler were studied only numerically using CFD. Numerical simulation results showed that an acceptable compatibility exists between the experimental and the numerical results; such that for heat transfer efficiency, the difference between experimental and numerical results was reported to be about 8%, for Nusselt number, the difference between the experimental and numerical results was reported to be 6–8%, and for overall heat transfer coefficient, the difference between the experimental and numerical results was reported to be 9%. The experimental results of the study showed that for the newly built cooling system, S-spiral EGR cooler, the average heat transfer efficiency is 63.2%. The results showed that at a same flow rate, the heat transfer efficiency of S-spiral EGR cooler is more than F-Smooth EGR cooler, but the heat transfer efficiency of F-Spiral EGR cooler is more than the other two, also the pressure drop in F-Spiral EGR cooler is more than semi-Spiral EGR cooler and F-Smooth EGR cooler, therefore the use of the new cooling system (S-spiral EGR cooler) has many benefits, in term of pressure drop and heat transfer efficiency, over the other two types.
[en] Highlights: • Concentrator improved electrical, thermal and overall efficiency 36, 42.2 and 40.5%. • Diffuser with concave side walls can diffuse air more uniform. • Uniformity of air flow achieved by employing right number of deflectors. • Concave side walls diffuser deflectors solved hot spot problem on the PV. • Elec., ther. Effic. improved 13.5, 22.75 by increasing air flow from 0.008 to 0.016 kg/s. In this study, to prevent local excessive temperature on a photovoltaic module, uniformity of air flow as cooling fluid in a low concentrated photovoltaic/thermal (LCPV/T) collector has considered. To obtain a uniform distribution of airflow taking into account the overall operating conditions, eight different geometries of diffuser were investigated theoretically by using computational fluid dynamics (CFD). Simulations were conducted on the most appropriate sketch with acceptable uniform air flow distribution on the PV module. The experimental results showed that the new designed diffuser significantly developed an even distribution of air velocity throughout the collector. Comparing the results with the previously published results showed that the new diffuser concave side walls and three inner deflectors improved the electrical efficiency of the PV/T collector by 20%. Also the effects of air flow rates (three levels) and concentrated solar illumination on the performance of a PV/System was experimentally measured. Using a concentrator improves electrical, thermal and overall efficiency by 36%, 42.2% and 40.5% respectively. By increasing air flow rate from 0.008 to 0.016 (kg/s); the electrical, thermal and overall efficiency were improved by 13.5, 22.75 and 22.41% respectively.
[en] Highlights: • Stack-type EGR cooler had highest heat transfer coefficient and Nusselt number. • Heat transfer characteristics of three types of EGR coolers were investigated. • With increasing the mass flow rate, stack-type EGR cooler efficiency is reduced. • In all three types of EGR coolers, the coolant temperature changes very little. • To improve the heat transfer in EGR cooler, an optimized structure was used. In this study, the heat transfer characteristics of three types of EGR coolers, such as Shell and tube-type EGR cooler (6 mm), Shell and tube-type EGR cooler (8 mm), and stack type-EGR cooler, were numerically investigated. The accuracy of predictions was verified by experimental results. A maximum difference between the numerical result and the experimental result for heat transfer efficiency of 9.22% was obtained. The results showed that the heat transfer efficiency of stack type-EGR cooler is higher of 36.6% and 27.7% than Shell and tube-type EGR cooler (6 mm) and Shell and tube-type EGR cooler (8 mm) was higher respectively. The results showed by increasing the mass flow rate, the heat transfer efficiency in the stack type-EGR cooler almost remain constant. When the stack type-EGR cooler is used, the heat transfer coefficient and Nusselt number improve significantly compared to the Shell and tube-type EGR cooler (6 mm) and Shell and tube-type EGR cooler (8 mm).
[en] Nanofluid that made up of fluid and solid nanoparticles has gained attention from diverse fields due to its superior thermophysical properties to enhance the performance of different systems which require flowing medium with excellent heat transfer behavior. Many past researchers have proven that conventional heat transfer fluid can be replaced by the rising nanotechnology–nanofluid which showed astonishing performance under different circumstances. In this paper, we attempt to present a recent review on the consequences of implantation of nanofluid, especially in vehicle engine cooling system and other heat transfer applications such as solar collector, electronics cooling system, flow boiling and thermal energy storage system. Thermophysical properties and heat transfer performance of nanofluids obtained in simulation, test rigs and even real vehicle engine experiments are discussed thoroughly. Models and correlations used by past researchers to compute thermophysical properties are also included. In the last part, various advantages from using nanofluid are summarized, and suggestions for research gap between past studies are discussed to further improve the investigation work in the future.
[en] The use of automotive air conditioning (AAC) nowadays is essential because of the hot climate and global warming. The AAC increases the overall fuel consumption in order to cool down the car cabin, hence releases more CO2 into the atmosphere. Nanotechnology can be implemented into the lubricant of the AAC compressor which can aid in reducing the power consumption. Therefore, this paper investigates the effect of SiO2/PAG nanolubricants on the AAC performance and energy saving. The SiO2/PAG nanolubricants were prepared using the two-step method. The sedimentation observation and UV–Vis spectrophotometer evaluation confirmed the stability of the nanolubricants. The tribology analysis revealed the coefficient of friction of SiO2/PAG nanolubricants better than the original PAG lubricants. The performance parameters and power consumption (energy saving) of AAC system using SiO2/PAG nanolubricants were compared with PAG lubricants. The condenser pressure and the pressure ratio of the AAC system decreased by an average of 10.8% and 5.6%, respectively. The volumetric heat absorb increased up to 3% and the coefficient of performance increased by an average of 21%. The compressor work and power consumption of the AAC system reduced by 16.5% and 4%, respectively. As a conclusion, it was recommended to use 0.05% volume concentration of SiO2/PAG nanolubricants in AAC compressor for optimum system performance and energy saving.
[en] The current investigation has presented a new synthesis technique to prepare pentaethylene glycol-treated graphene nanoplatelets (PEG-GnP) and pentaethylene glycol thermally treated graphene (PEG-TGr). The covalently functionalized (PEG-GnP and PEG-TGr) at various mass concentrations were dispersed in distilled water by ultrasonication for preparing nanofluids. The functionalization process effectiveness was established by using the surface characterization and morphology analysis with FTIR, Raman spectroscopy, FE-SEM, and TEM. The thermo-physical properties and stability of functionalized nanofluids were investigated utilizing numerous measuring devices. Dispersion stabilities of the functionalized nanofluids were observed for a long period of time (30 days). Water-based functionalized nanofluids revealed very Newtonian behavior with the increment in the experimental values of dynamic viscosity as temperature decreases and mass concentration of sample increases. Thermal conductivity of GnP and TGr dispersed in distilled water nanofluids show the enhancement of 32 and 31%, respectively, at 50 °C and 0.1% mass concentration.
[en] The thermo-physical properties enhancement of nanolubricants can improve the heat transfer performance in refrigeration system. In this study, thermo-physical properties of Al2O3–SiO2/PAG nanolubricants were investigated at 30–80 °C temperatures for different nanoparticle ratios. Al2O3 and SiO2 nanoparticles were dispersed in the polyalkylene glycol (PAG 46) lubricant using the two-step method of preparation. Thermal conductivity and dynamic viscosity of the nanolubricants were measured by using KD2 Pro thermal properties analyser and LVDV-III Rheometer, respectively. All the hybrid nanolubricants are witnessed to behave as Newtonian fluids. A maximum thermal conductivity enhancement of 2.41% occurred at the temperature of 80 °C. Meanwhile for dynamic viscosity, the highest percentage increment was found up to 9.34% at 70 °C temperature. Increments in both properties were recorded for 50:50 nanoparticle ratio. The property enhancement ratio (PER) evaluation was suggested 60:40 as the optimum nanoparticle ratio with the lowest PER in comparison with other nanoparticle ratios at all temperatures by considering of both properties. Finally, new correlations have been proposed based on the experimental data to predict the thermo-physical properties of Al2O3–SiO2/PAG nanolubricants. As a conclusion, Al2O3–SiO2/PAG nanolubricants with nanoparticle ratio of 60:40 and volume concentrations of less than 0.1% are highly recommended for application in refrigeration system.
[en] The emphasis of this paper is to evaluate the thermophysical properties of crystalline nanocellulose (CNC)-based nanofluid and the optimized machining parameters (cutting speed, feed rate and depth of cut) for machining using CNC-based nanofluid. Cutting tool temperature and formed chip temperature during machining are determined with CNC-based coolant and metal working fluid. Minimum quantity lubrication technique is used to minimize the usage of the coolant. Nanocellulose coolant with a concentration of 0.5% shows better thermal conductivity and viscosity. Total heat produced at the cutting tool and the temperature generated at the chip during machining shows significant improvement using CNC-based nanofluid. Statistical analysis reveals that feed rate and depth of cut contribute around 27.48% and 22.66% toward cutting temperature. Meanwhile, none of the parameters significantly affects the heat transfer. The multi-objective optimization reveals that the optimum parameter for machining using CNC-based nanocoolant is: cutting speed = 120, feed rate = 0.05 and depth of cut = 1.78 which produces heat transfer of 379.44 J and cutting temperature of 104.41 °C.
[en] Nanotechnology has emerged to be an essential aspect of science and technology. The growth of this field has been enormous specifically in the development of nanomaterials. Till date, numerous nanomaterials have been developed and designed to suit various applications from mechanical to biomedical. Among the developed nanomaterial, alumina (Al) has been subject of interest due to its notable chemical and physical properties. Specifically, in thermal properties, Al has been shown to have superior thermal conductivity, convective heat transfer coefficient and heat transfer coefficient properties. As such, Al has been utilized in different forms in various fields of applications and verified for its importance, significance and efficiency. Though it had shown outstanding results in the field engineering and sciences, their effect towards the environment and human health is yet to be explored extensively. The present paper aims to review the significance of Al nanoparticle addition in mono- and hybrid nanofluids. Also, this paper intends to provide the reader with an overview of the works that have been carried out using Al nanoparticles and their findings.
[en] The effect of compressor speed, initial refrigerant charge and volume concentrations of SiO2/PAG nanolubricant on the performance of automotive air-conditioning (AAC) system are investigated in this study. Response surface method (RSM) was used in designing the experimental work and is based on face composite design. The developed quadratic models from RSM were helpful to envisage the response parameters namely heat absorbs, compressor works, and coefficient of performance (COP) to identify the significant relations between the input factors and the responses. The results depicted that adding SiO2 nanoparticle into PAG lubricant will enhance the COP of AAC. Optimization of independent variables was performed using the desirability approach of the RSM with the goal of maximizing the heat absorb and COP, consequently, minimizing the compressor work. The results revealed that the optimal condition with a high desirability of 73.4% for the compressor speed of 900 rpm, refrigerant charge of 95 g and volume concentration of 0.07%. At this condition, the AAC system operated with 193.99, 23.28 kJ kg−1 and 8.27, respectively, for heat absorb, compressor work and COP. DoE based on RSM was capable of optimizing the significant parameters which affect AAC performance.