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Experimental optimization of geometrical parameters on heat transfer and pressure drop inside sinusoidal wavy channels
, Article Thermal Science and Engineering Progress ; Volume 9 , 2019 , Pages 121-131 ; 24519049 (ISSN) ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The response surface methodology (RSM) is firstly employed to investigate the geometric and flow parameters on heat transfer, pressure drop and thermal performance of sinusoidal wavy channels with different phase shifts. The investigated flow and geometric parameters are axial Reynolds number 1106
Numerical investigation of different geometrical parameters of perforated conical rings on flow structure and heat transfer in heat exchangers
, Article Applied Thermal Engineering ; Volume 156 , 2019 , Pages 494-505 ; 13594311 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
A numerical study has been performed to investigate the flow and heat transfer characteristics of fluid flow through heat exchanger tubes fitted with perforated conical rings. The holes are circular, and the number of holes N is ranged from 0 to 10. The influences of perforated conical ring diameter ratios D2/D1=0.4,0.5and0.6 and the hole diameter ratios d/D=0.06,0.1and0.14 on average Nusselt number, friction factor and thermal performance factor are reported. This analysis is performed in the turbulent flow regime 4000⩽Re⩽14,000 and the governing equations are solved by using (RNG) k-∊ model. Due to strong turbulent intensity, perforated conical rings lead to more flow perturbation and...
Numerical and Experimental Investigation of Stator Grooves on Cooling of Generators
, Ph.D. Dissertation Sharif University of Technology ; Nouri Borujerdi, Ali (Supervisor)
Abstract
The aim of this thesis is experimentally and numerically investigation of annular flow between the inner rotating smooth surface and the outer stationary grooved surface with or without axial fluid flow. Mounting grooves on the surfaces is important in cooling of rotating machineries such as electric generators and rotating heat pipes. The effect of different parameters such as the air gap between the surfaces, the geometry of the grooves, axial flow and rotation speed are numerically and experimentally investigated. The experimental results with axial grooves show that the entrance length decreases up to 17% with increasing the grooves depth. The reason is enhancement of the mixing and the...
Cu-water nanofluid flow and heat transfer in a heat exchanger tube equipped with cross-cut twisted tape
, Article Powder Technology ; Volume 339 , 2018 , Pages 985-994 ; 00325910 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2018
Abstract
This paper presents a numerical analysis for Cu-water nanofluid flow through a circular duct inserted with cross-cut twisted tape with alternate axis (CCTA). Three dimensional (RNG) k − ϵ turbulence model is applied to simulate this problem. All simulations are performed for plain tube and nine different CCTA geometries in the range of width ratio (b/w) from 0.7 to 0.9, length ratio (s/w) from 2 to 2.5, Reynolds numbers in the range of 5000 to 15,000 and volume fraction of nanoparticles from 0 to 1.5%. The calculated results indicate that the swirl flow created by CCTA is transferred from the tube core to the near wall regions. This results in higher fluid mixing, which enhances heat...
Friction factor and nusselt number in annular flows with smooth and slotted surface
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; 2018 ; 09477411 (ISSN) ; Erfanian Nakhchi, M ; Sharif University of Technology
Springer Verlag
2018
Abstract
The purpose of this experimental work is to study the effect of slot depth to width ratio, rotational motion and inlet velocity on friction factor and Nusselt number in an annular flow between two concentric cylinders with smooth and slotted surface. The heated outer surface is stationary and the unheated inner one is rotating. This configuration is popular in industrial applications such as internal air system of gas turbine engines, cooling of rotating machinery, techniques of chemical vapor deposition and solidification of pure metals. The results show that the ratio of average slotted surface friction factor to that of the smooth one enhances by increasing the slot depth to width ratio...
Entropy generation of turbulent Cu–water nanofluid flow in a heat exchanger tube fitted with perforated conical rings
, Article Journal of Thermal Analysis and Calorimetry ; Volume 138, Issue 2 , 2019 , Pages 1423-1436 ; 13886150 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Springer Netherlands
2019
Abstract
Entropy generation analysis for the Cu–water nanofluid flow through a heat exchanger tube equipped with perforated conical rings is numerically investigated. Frictional and thermal entropy generation rates are defined as functions of velocity and temperature gradients. Governing equations are solved by using finite volume method, and Reynolds number is in the range of 5000–15,000. The effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated. The results indicate that the thermal irreversibility is dominant in most part of the tube. But it...
Numerical investigation of turbulent Cu-water nanofluid in heat exchanger tube equipped with perforated conical rings
, Article Advanced Powder Technology ; Volume 30, Issue 7 , 2019 , Pages 1338-1347 ; 09218831 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
Numerical analysis of the nanofluid flow characteristics of perforated conical rings in a heat exchanger tube has been investigated under constant wall temperature condition. The pitch ratio of the perforated conical rings is 4 and the number of holes is varied from 0 (typical conical ring) to 10. The flow regime is fully turbulent with the Reynolds number is varied from 5000 to 14,000 and Cu-water nanofluid 0<ϕ<1.5% is selected as the working fluid. The main novelty of this paper is to perform a 3D simulation of this problem because some previous studies using similar geometry were restricted to experimental analysis. The Reynolds averaged Navier Stokes (RANS) equations are solved with the...
Performance intensification of turbulent flow through heat exchanger tube using double V-cut twisted tape inserts
, Article Chemical Engineering and Processing - Process Intensification ; Volume 141 , 2019 ; 02552701 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
This paper aims to present a numerical model for heat transfer intensification in a heat exchanger tube equipped with novel double V-cut twisted tape. The effects of different cut ratios (0.6 < b/c<1.8)on the turbulent flow characteristics and thermal performance of the system are investigated over the Reynolds number range from 5000 to 15,000. The accuracy of (RNG)k-ε turbulence model used in the present study is validated by comparing with experimental results. The tube equipped with double V-cut twisted tape shows improved thermal performance in comparison with conventional twisted tape. This improvement is due to the additional vortex flow induced by the V-cuts which leads to more...
Sensitivity analysis of a heat exchanger tube fitted with cross-cut twisted tape with alternate axis
, Article Journal of Heat Transfer ; Volume 141, Issue 4 , 2019 ; 00221481 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2019
Abstract
Numerical simulations are used to analyze the thermal performance of turbulent flow inside heat exchanger tube fitted with cross-cut twisted tape with alternate axis (CCTA). The design parameters include the Reynolds number (5000 < Re < 15; 000), cross-cut width ratio (0:7 < b=D < 0:9), cross-cut length ratio (2 < s=D < 2:5), and twist ratio (2 < y=D < 4). The objective functions are the Nusselt number ratio (Nu=Nus), the friction factor ratio (f =fs), and the thermal performance (g). Response surface method (RSM) is used to construct second-order polynomial correlations as functions of design parameters. The regression analysis shows that heat transfer ratio decreased with increasing both...
Numerical investigation of rectangular-cut twisted tape insert on performance improvement of heat exchangers
, Article International Journal of Thermal Sciences ; Volume 138 , 2019 , Pages 75-83 ; 12900729 (ISSN) ; Esfahani, J. A ; Sharif University of Technology
Elsevier Masson SAS
2019
Abstract
A numerical analysis has been performed to investigate the flow structure and thermal hydraulic performance of turbulent flow through circular tube equipped with twisted tapes with different cut shapes. The geometries of cuts are rectangular with different cut ratios 0.25
Friction factor and nusselt number in annular flows with smooth and slotted surface
, Article Heat and Mass Transfer/Waerme- und Stoffuebertragung ; Volume 55, Issue 3 , 2019 , Pages 645-653 ; 09477411 (ISSN) ; Erfanian Nakhchi, M ; Sharif University of Technology
Springer Verlag
2019
Abstract
The purpose of this experimental work is to study the effect of slot depth to width ratio, rotational motion and inlet velocity on friction factor and Nusselt number in an annular flow between two concentric cylinders with smooth and slotted surface. The heated outer surface is stationary and the unheated inner one is rotating. This configuration is popular in industrial applications such as internal air system of gas turbine engines, cooling of rotating machinery, techniques of chemical vapor deposition and solidification of pure metals. The results show that the ratio of average slotted surface friction factor to that of the smooth one enhances by increasing the slot depth to width ratio...
Reaction Time Comparison of Unambiguous Statements with
Ambiguous and Garden Path Sentences
,
M.Sc. Thesis
Sharif University of Technology
;
Salehi, Mohammad
(Supervisor)
Abstract
The present study compares the reaction times in processing unambiguous sentences with three ambiguous statements of lexical, grouping and functional as well as garden path sentences. To this end, a special computer program was developed with the accuracy of micro seconds. Furthermore, a set of 25 items was prepared with acceptable levels of reliability and validity. Forty seven highly proficient subjects, all undergraduate students of Air Traffic Control, participated in this study. The results of the study showed no significant difference between the reaction times of grouping and functional ambiguities but garden path sentences showed the greatest difference with the other groups. All...
Probability of missed detection as a criterion for receiver placement in MIMO PCL
, Article IEEE National Radar Conference - Proceedings, 7 May 2012 through 11 May 2012, Atlanta, GA ; 2012 , Pages 0924-0927 ; 10975659 (ISSN) ; 9781467306584 (ISBN) ; Chitgarha, M. M ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
IEEE
2012
Abstract
Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar
An efficient method for the ring opening of epoxides with aromatic amines by Sb(III) chloride under microwave irradiation
, Article Journal of Chemical Research ; Issue 4 , 2008 , Pages 220-221 ; 03082342 (ISSN) ; Hashemi, M. M ; Mottaghi, M. M ; Foroughi, M. M ; Sharif University of Technology
2008
Abstract
SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity
Resource allocation for uav-enabled integrated sensing and communication (isac) via multi-objective optimization
, Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings ; Volume 2023-June , 2023 ; 15206149 (ISSN); 978-172816327-7 (ISBN) ; Naghsh, M. M ; Karbasi, M ; Nayebi, M. M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2023
Abstract
In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit...
MIMO radar signal design to improve the MIMO ambiguity function via maximizing its peak
, Article Signal Processing ; Volume 118 , 2016 , Pages 139-152 ; 01651684 (ISSN) ; Radmard, M ; Nazari Majd, M ; Karbasi, S. M ; Nayebi, M. M ; Sharif University of Technology
Elsevier
2016
Abstract
One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function...
Detection-localization tradeoff in MIMO radars
, Article Radioengineering ; Volume 26, Issue 2 , 2017 , Pages 581-587 ; 12102512 (ISSN) ; Radmard, M ; Chitgarha, M. M ; Bastani, M. H ; Nayebi, M. M ; Sharif University of Technology
2017
Abstract
Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance...
Antenna placement and power allocation optimization in MIMO detection
, Article IEEE Transactions on Aerospace and Electronic Systems ; Vol. 50, Issue 2 , April , 2014 , pp. 1468-1478 ; Chitgarha, M. M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive...
Ambiguity function of MIMO radar with widely separated antennas
, Article Proceedings International Radar Symposium ; 16 -18 June , 2014 ; ISSN: 21555753 ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas
Choosing the position of the receiver in a MISO passive radar system
, Article European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 9th European Radar Conference, EuRAD 2012 ; 2012 , Pages 318-321 ; 9782874870293 (ISBN) ; Majd, M. N ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
2012
Abstract
By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only...