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%)

Improvement of Seed Germination of Date-plum (Diospyros lotus L.) by Physical and Chemical Treatments

Persimmon (Diospyros kaki) is an important subtropical, monoecious, dioeocious and polygamous tree which belongs to Ebenaceae family. Because of low total seed and low viability seed in persimmon, grafting on seedling rootstock is generally used for its propagation. The common rootstock is Diospyros lotus, but its seeds have long dormancy. So, the study was carried out to investigate the effects of stratification (0, 25, 50 and 70 days) at 4-70C, scarification with (97%) sulphuric acid (0, 2.5, 5 and7.5 minute) and GA3 (0, 250, 500 and 750 mgL-1) on seed germination of D. lotus. Results showed that the most germination rate was observed in GA3 at 250 mgL-1. Stratification for 70 days had the most germination percent. The most germination uniformity was observed in GA3 at 500 mgL-1. In scarification plus stratification, the germination percent was lower than control and stratification

Melting and solidification characteristics of a double-pipe latent heat storage system with sinusoidal wavy channels embedded in a porous medium

The aim of this investigation is to explore the combined effects of porous medium and surface waviness on the melting and solidification of PCM inside a vertical double-pipe latent heat storage (LHTES) system. The results are compared with the cases of smooth channels and pure PCM. In the system, water is passed through the inner tube while composite PCM is placed in the annulus side. Different effective parameters including wavelength and wave amplitude of the sinusoidal wavy channels, porosity and pore size of the porous structure, Reynolds number and inlet temperature of water are examined to find the optimum geometric as well as operating conditions in both melting/solidification processes. The results show that utilizing both the high conductive porous structure and wavy channel reduces the melting/solidification times significantly. For the best case, the melting and solidification times of PCM reduce by 91.4% and 96.7%, respectively, compared with the smooth channels pure PCM system. The average rate of transferred heat for the wavy channel composite PCM are 10.4 and 18.9 times that for the smooth channel pure PCM case. Comparing with the pure PCM system, the presence of copper foam reduces the effect of channel waviness significantly for both melting/solidification processes

Free convection heat transfer and entropy generation analysis of water-Fe 3 O 4 /CNT hybrid nanofluid in a concentric annulus

© 2018, Emerald Publishing Limited. Purpose: This paper aims to numerically investigate the heat transfer and entropy generation characteristics of water-based hybrid nanofluid in natural convection flow inside a concentric horizontal annulus. Design/methodology/approach: The hybrid nanofluid is prepared by suspending tetramethylammonium hydroxide-coated Fe 3 O 4 (magnetite) nanoparticles and gum arabic (GA)-coated carbon nanotubes (CNTs) in water. The effects of nanoparticle volume concentration and Rayleigh number on the streamlines, isotherms, average Nusselt number and the thermal, frictional and total entropy generation rates are investigated comprehensively. Findings: Results show the advantageous effect of hybrid nanofluid on the average Nusselt number. Furthermore, the study of entropy generation shows the increment of both frictional and thermal entropy generation rates by increasing Fe 3 O 4 and CNT concentrations at various Rayleigh numbers. Increasing Rayleigh number from 103 to 105, at Fe 3 O 4 concentration of 0.9 per cent and CNT concentration of 1.35 per cent, increases the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 224.95, 224.65 and 155.25 per cent, respectively. Moreover, increasing the Fe 3 O 4 concentration from 0.5 to 0.9 per cent, at Rayleigh number of 105 and CNT concentration of 1.35 per cent, intensifies the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 18.36, 22.78 and 72.7 per cent, respectively. Originality/value: To the best knowledge of the authors, there are not any archival publications considering the detailed behaviour of the natural convective heat transfer and entropy generation of hybrid nanofluid in a concentric annulus

Using finite volume method for simulating the natural convective heat transfer of nano-fluid flow inside an inclined enclosure with conductive walls in the presence of a constant temperature heat source

In the present work, natural convective heat transfer of water/Al2O3 nano-fluid in an inclined square enclosure is investigated. The side walls of the cavity are cold and the upper and lower ones are insulated. A wall with a thermal-conductivity of 100 and a thickness of 0.5 is located on the cold walls. Moreover, there is a constant temperature heat source in the center of the enclosure. The enclosure is located under the influence of an inclined magnetic field (MF). The governing equations were solved using the finite volume method (FVM) and solved using the SIMPLE algorithm. The results show that the heat transfer rate intensifies up to 3.11 times with intensifying the Rayleigh number (Ra). The maximum heat transfer occurred at weak magnetic fields. By augmenting the angle of the enclosure, the heat transfer rate on the right and left walls intensifies by 33% and declines by 55%, respectively. The heat transfer rate on the right wall intensifies by 14% by augmenting the angle of the MF. The addition of nano-additives also results in intensification in the heat transfer rate

The effect of grape-seed oil on diabetes-related hyperglycemia, dyslipidemia, and inflammation in streptozotocin-induced diabetic rats

Background: Grape-seed oil has diverse biological functions and is beneficial in treating metabolic complications, such as metabolic syndrome, obesity, diabetes, and dyslipidemia. The purpose of this study was to investigate the anti-hyperglycemic, anti-dyslipidemic, and anti-inflammatory effects of Grape-seed oil in diabetic rats. Materials and methods: 16 streptozotocin-induced diabetic Wistar rats were used in this study. Diabetic rats were randomly allocated to either of two groups (n = 8): diabetic rats treated with grape-seed oil or diabetic control. Grape-seed oil (GSO) (25 mg/kg BW) was administered orally for 40 days, and at the end, blood samples were taken directly from the heart. Results: Diabetic rats treated with oil compared to control diabetic rats demonstrated a significant (p = 0.001) decline in serum glucose concentration. High plasma concentrations of TG, LDL, and VLDL were reduced (p = 0.001, p = 0.001, p = 0.001, respectively). Surprisingly, between inflammatory markers, TNF-α was significantly (p = 0.02) increased. Furthermore, GSO-treated diabetic rats experienced a significant (p = 0.014) weight gain during the study. However, total cholesterol, HDL, and CRP levels did not change significantly. Conclusion: Treatment with grape-seed oil ameliorated dyslipidemia and hyperglycemia in diabetic rats. However, further investigations in peculiar clinical studies are required.</p

Energy and exergy analysis of two novel hybrid solar photovoltaic geothermal energy systems incorporating a building integrated photovoltaic thermal system and an earth air heat exchanger system

In this paper, two novel configurations of the building integrated photovoltaic thermal (BIPVT)-compound earth-air heat exchanger (EAHE) system are proposed. Both the configurations operate in two modes, namely heating and cooling modes. In the heating mode of the configuration A, the cold outdoor air is twice preheated by passing through the EAHE and BIPVT systems. In the cooling mode of the configuration A, the hot outdoor air is precooled by flowing inside the EAHE system and the PV modules are cooled using the building exhaust air. The cooling mode of the configuration B is similar to the configuration A, while in the heating mode of the configuration B, the outdoor air first enters the BIPVT collector and then passes through the EAHE system. The energetic and exergetic performances of the configurations are investigated for climatic conditions of Kermanshah, Iran. In addition, the impacts of length, width, and depth of air duct located underneath the PV panels, air mass flow rate, length and inner diameter of the pipe of EAHE system on the annual average energetic and exergetic aspects of the best configuration of the BIPVT-EAHE system are evaluated. The outcomes revealed that the annual rate of thermal energy, electrical energy, and thermal exergy captured from the configuration A are respectively 3499.59, 5908.19, and 55.59 kWh, while these values for the configuration B are respectively 3468.16, 5969.87, and 51.76 kWh. In addition, it was found that the configuration A has superior energetic performance than the configuration B, while the overall exergetic performance of the configuration B is higher than the configuration A. Furthermore, it was depicted that both the energetic and exergetic performances of the suggested configurations intensify by augmenting the duct length, duct width, and tube diameter whereas they decline with an increase in the air mass flow rate and duct depth