Numerical analysis of air flow specification in solar chimneys with vegetation layer
Arash
Miradollah Lavasni
Assistant professor, Department of Mechanical Engineering, Islamic Azad University, Central Tehran Branch
author
Mehrdad
Mohammadi
Msc. Student, Department of Mechanical Engineering, Islamic Azad University, Central Tehran Branch
author
Ramin
Mehdipour
Assistant professor, Department of Mechanical Engineering, Tafresh University
author
text
article
2016
per
Nowadays, the ever increasing demand to provide energy and the constant decrease of fossil fuels resources has made the usage of renewable energy resources vital. Solar chimneys are considered a significant approach to supply electricity. They are of particular interest due to the high absorption level of solar energy and also because of the advantages of using air as an absorber. However, these systems do not provide enough economic efficiency. Plant breeding in the collector’s section of a solar chimney was presented in this study as a mean to overcome the economical obstacles. Also possible geometrical and physical effects on air flow parameters were investigated by means of numerical simulation. Our simulation results were validated with comparison to the experimental model in Manzanares, Spain. Velocity as well as the temperature gradient at collector’s outlet was calculated. Our results showed excellent affinity to those of Spanish prototype as the error percentage was lesser than 5%. Vegetation layer was modeled as a porous media at the bottom of the collector and its possible effects was investigated on the air flow parameters at Ra = 1010. It was observed that due to the vegetation layer the velocity and temperature gradient at collector’s outlet were decreased 2.5% and 2%, respectively. These slight reductions show that plant breeding in large areas of collector’s bottom could be served as an outstanding idea to enhance the costefficiency challenges of solar chimneys while producing only negligible negative effects on air flow parameters.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
17
v.
4
no.
2016
6
22
https://jmep.isme.ir/article_22954_86c7587d40042662c97b74bea3abe418.pdf
Estimation of fouling profile in a heat exchanger pipe applying the conjugate gradient method based on the inverse algorithm
Kourosh
Goodarzi
Associate professor, Department of Mechanical Engineering, Yasouj University
author
Amin
Mousaei
Assistant professor, Department of Mechanical Engineering, Yasouj University
author
Allireza
Namdari
Msc. Student, Department of Mechanical Engineering, Yasouj University
author
text
article
2016
per
One of the factors reducing the efficiency of the heat exchanger during its operation is fouling. Fouling takes place as a layer on one side or both sides of surface heat transfer and the resistances of the heat transfer that it shows cause the decrease in heat transfer through the surface. The measuring scale of fouling is most important. Because accurate measurement of fouling and to ensure that the limit is higher, fouling removal and cleaning operations is essential. A conjugate gradient method (CGM) based on the inverse algorithm is used to estimate the unknown fouling-layer profile on the inner wall of a pipe system using simulated temperature measurements taken within the pipe wall. It is assumed that no prior information is available about the functional form of the unknown profile. Therefore, the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The accuracy of the inverse analysis is examined using the simulated exact and inexact temperature measurements. The results show that the excellent estimation of the fouling-layer profile can be obtained for the test case considered in this study. The technique presented in this study can be used in a warning system to call for pipe maintenance when the thickness of fouling exceeds a predefined criterion.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
17
v.
4
no.
2016
23
45
https://jmep.isme.ir/article_22955_e46863237461e5bbb8d56f26d65a4d82.pdf
Numerical study of non-uniform axial magnetic field effect on bubble growth in a boiling flow of nano ferro fluid in a microchannel
Mousa
Mohammadpour fard
Associate professor, Department of Mechanical Engineering, Shahid Mdani University of Azarbaijan
author
Mehdi
Ghorbani Firouzsalari
Msc., Department of Mechanical Engineering, Shahid Madani University of Azarbaijan
author
text
article
2016
per
In this research, growth of a vapor bubble in the nucleate boiling process in pure water and ferrofluids (water and 4 vol.% Fe3O4) was investigated numerically using VOF model and control volume technique. After verifying the results, effects of applying non-uniform axial magnetic fields on growth of the bubble in the boiling of magnetic nanofluids was investigated. Two positive and negative magnetic field gradients have been examined. Based on the obtained results, in the presence of magnetic field with a positive gradient pumping of heat from the side walls is increased and consequently it leads to reduce growth of the bubble unlike the magnetic field with negative gradient. It is concluded that using magnetic fields with positive gradients can increase the cooling efficiency of the micro-systems.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
17
v.
4
no.
2016
46
68
https://jmep.isme.ir/article_22956_de9421b79ea29e2303ce48426ed8ec3e.pdf
Experimental study of effects of windbreaker walls for increasing flow rate of Heller cooling tower
Mohammadali
Ardakani
Associate professor, Department of Mechanical Engineering, Iranian Research Organization for Science and Technology
author
Mohsen
Mazidi
Phd Student, Department of Mechanical Engineering, Iranian Research Organization for Science and Technolgy
author
Foad
Farhani
Assistant professor, Department of Mechanical Engineering, Iranian Research Organization for Science and Tehcnology
author
text
article
2016
per
Cross winds adversely affect the thermal performance of Heller dry cooling towers. In this experimental study, an isothermal model of Heller tower was used in wind tunnel to investigate the effect of windbreakers for increasing flow rate through the model under wind conditions. Windbreakers of various dimensions were installed at different angles around the model, and their effectiveness was studied under various wind directions. Results showed that use of windbreakers improved the flow rate by 30%. Moreover, with increase in wind velocity, effect of windbreaker length on the performance of the model was more pronounced. Results also indicated that for up to 30 degrees change in wind direction with respect to the diameter perpendicular to wind, there is no appreciable effect on the flow rate through the model.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
17
v.
4
no.
2016
69
84
https://jmep.isme.ir/article_22957_70d23df4a20aaf9562099d241e61c5bb.pdf
Theoretical an experimental study of nucleate pool boiling heat transfer on copper hydrophobicity surface
Seyed Sina
Arshadi
Msc., Department of Mechanical Engineering, Iran University of Science and Technology
author
Hamid
Saffari
Associate professor, Department of Mechanical Engineering, Iran University of Science and Technology
author
Amir
Mirzagheytani
PhD. Stu., Department of Mechanical Engineering, Iran University of Science and Technology
author
text
article
2016
per
In this paper, the effects of surface hydrophilicity on nucleate pool boiling of water under atmospheric pressure were theoretically modeled and experimentally examined. The proposed analytical model consider change of contact angle in bubble growing period Comparisons of the pool boiling curve based on the modified model with existing experimental data and previous model show the better agreement. Moreover, hydrophilic surfaces (with contact angles of 34, 22, ˂10) are made by immersing the copper in an aqueous solution of sodium hydroxide and potassium persulphate for different length of times (30, 60, 180 min, respectively) and the boiling experiment on these surfaces is compared with prediction of model. According to experimental results, the surface treating method applied in this research is an effective means to promote the surface wettability of a copper, and the more hydrophilicity of treated surfaces tend to yield a greater pool boiling heat transfer coefficient than the untreated surface.
Iranian Journal of Mechanical Engineering Transactions of ISME
ISME
2538-4775
17
v.
4
no.
2016
85
104
https://jmep.isme.ir/article_22958_5641ada64e0b2d2d9c000e6d80189477.pdf