Showing 8 results for Convective Heat Transfer
Volume 2, Issue 3 (2-2019)
Abstract
One of the miniaturization of heat transfer equipment is enhancing the convective heat transfer coefficient. The main aim of this study is design and producing a kind of nanofluid based on water and ethylene glycol. Graphene was synthesized via electrochemical method and its successful production was confirmed with XRD, FTIR spectrum and, SEM and TEM images. By using different amount of graphene i.e. 0.25, 0.5, 0.75, 1, 1.25, and 1.5%, water/ethylene glycol/graphene nanofluid was produced. Sodium dodecyl sulfate (SDS) was used as surfactant to improve graphene stability in the base fluid. The designed experimental setup was composed of spiral tube with constant wall temperature and equipped with flow meter and pressure and temperature indicators. Nusselt number and pressure drop were measured for pure water and compared with those obtained from theoretical relations and it was found that the setup works properly. Convective heat transfer coefficient, Nusselt number, and heat transfer rate were investigated for water/ethylene glycol (60/40 wt.%) and nanofluid with different amount of graphene using experimental setup. The results showed that by adding 1 wt.% graphene into the based fluid the convective heat transfer coefficient increased about 50% while pressure drop was also increased about 50%. Overall, the findings of this research work support the potential of water/ethylene glycol/graphene nanofluid for using in heating/cooling equipment.
Saeed Zeinali, Ebrahim Hosseini Pour, Mehdi Shanbedi,
Volume 14, Issue 13 (3-2015)
Abstract
In this study, forced convective heat transfer and pressure drop behavior of multi walled carbon nanotubes (CNT)-water nanofluid were evaluated under constant heat flux in a circular tube. For this purpose, first, homogeneous aqueous suspension of CNT using gum Arabic (GA) surfactant was prepared in concentrations 0.05%, 0.1% and 0.2% wt. Then, the above mentioned nanofluids were evaluated in Reynolds number range of 800-2000 under constant heat flux. The results indicate a significant increase in convective heat transfer coefficient of nanofluids with the addition of small amounts of CNT in deionized water. Also, heat transfer coefficient is enhanced with increasing concentration and Reynolds number. However, the effect of increasing concentrations of CNT is higher than the increase in Reynolds number. In addition, the pressure drop data on the different concentrations and Reynolds numbers are also investigated. At low weight concentrations of CNT, the deal of pressure drop of nanofluids containing CNT and base fluids is approximately similar and the gap between them is negligible. This means that no extra pump power is required for low concentration CNT/water nanofluid. The maximum increase in heat transfer coefficient is 42.8%, which occurred at Re=2027, and a concentration of 0.2% wt.
Mohammad Salimi, Seyed Mohsen Peyghambarzadeh, Seyed Hasan Hashemabadi, Alireza Chabi,
Volume 15, Issue 2 (4-2015)
Abstract
In this study, the forced convective heat transfer of pure water and alumina-water nanofluid with volume concentration of 0.5% and 1%, as a cooling fluid through a microchannel heat exchanger was experimentally investigated. This microchannel consists of 17 parallel channels with a rectangular cross section with 400 µm width, 560 µm height and 50 mm length. The experiments were performed in the range 600 to 1800 of Reynolds and constant heat flux conditions (19 W/cm2). Stability studies showed that alumina-water nanofluid at pH = 3 for 3 hours in a bath of the ultrasonic vibrating demonstrate the maximum stability. The variations of microchannel surface temperature, fluid temperature at the entrance region of the microchannel, average heat transfer coefficient of nanofluid and pure water, and their friction factor measured experimentally. Also comparison between average Nusselt number with existing heat transfer relationships was performed. The results show that heat transfer using nanofluid shows considerably increase in comparison to water. So that the maximum amount of average heat transfer coefficient for alumina-water nanofluid with 0.5% concentrations is about 32.8% and for alumina-water nanofluid with 1% concentrations about 49.7% in comparison to pure water. It was also found that the heat transfer coefficient increases with increasing Reynolds number and nanoparticle volume fraction.
Hadi Kargar Sharifabad, Mohammad Falsafi,
Volume 15, Issue 6 (8-2015)
Abstract
This numerical study forced convective heat transfer ferrofluid within a circular copper tube includes portions of the electromagnetic isolation under an alternating magnetic field is performed. Laminar flow through a tube under uniform and thermal flux passes. Intensifying transfer of particles and velocity increase in the boundary layer using nanoparticles to increase the effect of magnetic field onto more heat transfer, the main goal is. Convection regimens resulting from complex interactions between magnetic nanoparticles were studied under different conditions, with the concentration and volume of different the heat transfer process under different frequencies of the applied magnetic field were studied. Magnetic field effects on the convective heat transfer coefficient at different Reynolds numbers and volume percentages have been studied. Also when the electromagnetic is insulated pipe parts of have been studied and have been compared with the modes without insulation. Increase the frequency and volume fraction of magnetic field, resulting in increased heat transfer were better. Magnetic field at low Reynolds numbers have shown a greater impact. For prove the numerical results evaluated in this research work has been studied experimentally. The results showed that the modeling data were in very good agreement with experimental data.
Mohsen Nazari, Nasibe Babazadeh, Mohammad Mohsen Shahmardan, Mojtaba Ashouri,
Volume 15, Issue 6 (8-2015)
Abstract
Transient heat transfer from a storage fluid around a central tube is experimentally investigated in a wide range of Reynolds number, i.e. 700
Samira Khanjani, Akram Tavakoli, Davood Jalali Vahid, Meysam Nazari,
Volume 15, Issue 11 (1-2016)
Abstract
In this study, forced convective heat transfer characteristics of /water nanofluid flowing through a double pipe heat exchanger with plain twisted tape and cut twisted tape inserts is investigated experimentally to reveal the effect of cut twisted tape and nanofluid concentration on heat transfer. Experiments are conducted in a turbulent flow regime with Re number ranging from 4000-34000 and in the particle volume concentration range of 0<φ<0.1%.The results of thermal studies showed enhancement of convective heat transfer with nanofluids compared with flow of water. Also it was found that in higher Reynolds numbers the nanofluid has better heat transfer capability. The effects of twisted tape with and without cuts on edges on heat transfer coefficient and rate were investigated. It was found that the twisted tape with cut edges could enhance heat transfer rate better than twisted tape without cut edges. The pressure drop was investigated for flow of nanofluid and water. The results showed that there is a little difference between pressure drops in these cases. Friction factor and pressure drop in tube with plain twisted tape and cut twisted tape inserts are increased due to increasing flow resistance and contact surface between fluid and flow passage.
Volume 18, Issue 111 (4-2021)
Abstract
In the present study, a convective heat transfer coefficient
changes during deep fat frying was investigated. So, by keeping the oil temperature constant as a heat transfer medium, temperature changes in a potato strip (cube-shaped), in the center and left-right sides of the strip during frying by a three-channel thermocouple was measured. Processing temperature of oil was 150, 160 and 170
°C. The strip temperature was recorded by a data logger at ten-second intervals. Due to no significant changes in the temperature of different selected locations in potato strip, the center temperature was selected and recorded as an effective temperature. Also, heat transfer parameter included convective coefficient (
) was calculated in the range of 128_515 W/m
2.K .Result showed that
is high in high levels temperature because of increasing rate of moisture exiting and turbulence in the oil. Also, with increasing oil temperature, decreasing of oil content and decreasing in moisture content of slices were observed. The mass transfer parameters including the effective moisture diffusivity (
) and the oil diffusivity (
) were calculated in the range of 9.12×10
-9 _1.31×10
-8 m
2/s and 1.26×10
-5_1.52×10
-5 m
2/s , respectively
. By using the calculated coefficients, heat and mass transfer modeling, was done by mathematical equations and the relevant equations were solved by the method of separation variables. Simulation was also done with
COMSOL Multiphysics version 5.3a and the resulted profiles were also presented.
S. Omiddezyani , I. Khazaee, S. Gharehkhani , M. Ashjaee, F. Shemirani, V. Zandian,
Volume 19, Issue 8 (8-2019)
Abstract
Today, nanofluid is attracting intense research due to its potential to augment the heat transfer rate and the cooling rate in many systems. On the other hand, new research progresses indicate that graphene nanofluids even in very low concentrations could provide higher convective heat transfer coefficient in comparison to the conventional nanofluids. For this reason, we used nanofluid containing the CoFe2O4/GO nanoparticles as working fluid to perform experimental investigation of its effect on laminar forced convective heat transfer in the flow passing through a copper tube, which is under a uniform heat flux. It should be noted that utilizing magnetic field on nanoparticles is one of the active methods for improving the heat transfer rate. To achieve this objective, the effect of external magnetic field intensity and also the effect of applying different frequencies on the improvement of heat transfer in Reynolds number and different concentration is also investigated and the optimum frequency were obtained. The results showed that the heat transfer of the studied hybrid nanofluid has been improved in the presence of constant and alternating magnetic fields and the amount of heat transfer increment, due to an alternating magnetic field, is more significant compared with a constant magnetic field. The results also show that in the absence of magnetic field, using ferrofluid with concentration of φ=0.6%, improves the average enhancement in convective heat transfer up to 15.2% relative to the DI-water at Re=571, while this value is increased up to 19.7% and 31% by using constant and alternating magnetic field, respectively.
