In this study, heat transfer though a porous fin with rectangular cross section is investigated. The Darcy model is utilized to simulate heat transfer in this porous media. It is assumed that the fin ...is one-dimensional, homogenous, the flow is laminar, and the generated heat is a linear function of temperature. In this research, three different analytical methods are used to obtain the temperature distribution after deriving the heat transfer equation. In order to validate the obtained solution the collocation method (CM) is compared with the results by a numerical method, in order to validate the solutions, homotopy perturbation method (HPM) and homotopy analysis method (HAM) are employed. This problem is solved for the general case, and the output is obtained as a relationship for one iteration. The effects of various parameters including convection (Nc), porosity (Sh), Rayleigh number (Ra) are examined in this research.
Nowadays, the freshwater is one of the most critical issues for humans. In this regard, desalination systems can be beneficial. In this research, at first different types of desalination systems and ...their governing equations is studied. Then the energy consumption of evaporative vacuum easy desalination system with brine tank is modeled. This modeling and the equations governing the energy consumption of new subsets such as the evaporator, condenser, vacuum pump, and other pumps are presented. In the end, the economic modeling of the system is investigated. The feasibility of using the system is reported in three cities (Abu Dhabi, Las Palmas, and Perth). The results shown that the annual operating cost of the pumps is estimated to be 0.19 M€ yr
−1
, 0.51 M€ yr
−1
and 0.14 M€ yr
−1
for Abu Dhabi and Las Palmas and Perth respectively. Also, the annual cost of fresh water production is compared with other reaches in these cities. The results are shown that Perth has the lowest cost of the fresh water output at 0.67 M€ yr
−1
and Las Palmas has the highest cost of fresh water production with 0.104 M€ yr
−1
. The reason is the difference in the electricity prices in these cities.
In this paper, a typical combined cycle power generation unit in Iran is simulated by a mathematical method in order to perform sensitivity analysis on environmental emission and electricity price. ...The results of this study demonstrate that the efficiency of the power plant depends on both gas turbine design parameters such as gas turbine inlet temperature, compressor pressure ratio and steam cycle design parameters such as HRSG pinch point temperature, condenser pressure. The results demonstrate that an increase in TIT and compressor pressure ratio have a significant effect on exergy efficiency and destruction.
Purpose
The purpose of this paper is to investigate the heat transfer of laminar and turbulent pulsating Al203/water nanofluid flow in a two-dimensional channel. In the laminar flow range, with ...increasing Reynolds number (Re), the velocity gradient is increased. Also, the Nusselt number (Nu) is increased, which causes increase in the overall heat transfer rate. Additionally, in the change of flow regime from laminar to turbulent, average thermal flux and pulsation range are increased. Also, the effect of different percentage of Al2O3/water nanofluid is investigated. The results show that the addition of nanofluids improve thermal performance in channel, but the using of nanofluid causes a pressure drop in the channel.
Design/methodology/approach
The pulsatile flow and heat transfer in a two-dimensional channel were investigated.
Findings
The numerical results show that the Al2O3/Water nanofluid has a significant effect on the thermal properties of the different flows (laminar and turbulent) and the average thermal flux and pulsation ranges are increased in the change of flow regime from laminar to turbulent. Also, the addition of nanofluid improves thermal performance in channels.
Originality/value
The originality of this work lies in proposing a numerical analysis of heat transfer of pulsating Al2O3/Water nanofluid flow -with different percentages- in the two-dimensional channel while the flow regime change from laminar to turbulent.
•A tacholess order tracking methodology for large speed gradients is proposed.•Probabilistic information is used for robust maxima tracking.•The methodology is validated on numerical and experimental ...data.
Rotational speed or phase measurements are important in the rotating machine condition monitoring field. Rotating machines often operate in the presence of fluctuating rotational speeds and its components generate signals which are periodical in the angle domain. Hence, it is essential to perform order tracking when condition monitoring is performed under varying speed conditions. Computed order tracking is performed with a measured tachometer signal and it requires additional hardware to be installed on the machine, which may not be feasible nor practical. This article presents a tacholess order tracking method which is capable of accurately estimating the phase of a shaft of interest in the presence of large angular accelerations and noise. An improved maxima tracking procedure is used with an angular-displacement Vold-Kalman filter and the Hilbert transform to estimate the instantaneous phase of the shaft under consideration. The estimated instantaneous phase is used to resample the vibration signal from the time to the angle domain. The proposed tacholess order tracking technique is critically investigated on three numerical and three experimental rotational speed profiles. The minimum and maximum phase error obtained for the experimental data was 0.037697 and 0.05022 radians respectively, which highlights the potential of the technique.
•A stochastic hybrid blade tip timing approach is proposed and demonstrated.•Turbomachine blade damage is identified and classified using this approach.•Probabilistic damage identification is ...achieved through natural frequency tracking.•Damage classification utilises a K-means clustering approach.•The proactive scheduling of a turbomachine outage is thus demonstrated.
Blade Tip Timing (BTT) has been in existence for many decades as an attractive vibration based condition monitoring technique for turbomachine blades. The technique is non-intrusive and online monitoring is possible. For these reasons, BTT may be regarded as a feasible technique to track the condition of turbomachine blades, thus preventing unexpected and catastrophic failures. The processing of BTT data to find the associated vibration characteristics is however non-trivial. In addition, these vibration characteristics are difficult to validate, therefore resulting in great uncertainty of the reliability of BTT techniques. This article therefore proposes a hybrid approach comprising a stochastic Finite Element Model (FEM) based modal analysis and Bayesian Linear Regression (BLR) based BTT technique. The use of this stochastic hybrid approach is demonstrated for the identification and classification of turbomachine blade damage. For the purposes of this demonstration, discrete damage is incrementally introduced to a simplified test blade of an experimental rotor setup. The damage identification and classification processes are further used to determine whether a damage threshold has been reached, therefore providing sufficient evidence to schedule a turbomachine outage. It is shown that the proposed stochastic hybrid approach may offer many short- and long-term benefits for practical implementation.
•The shaft Instantaneous Angular Position (IAP) is calculated using a State Space Model.•More accurate answers are obtained using the IAP for transient conditions.•Tip deflection accuracy is ...dependant on blade circumferential location.•A new validation approach for BTT tip deflections is presented.
Rotor blade condition monitoring is considered an important aspect of turbomachine management, especially with the current trend of systems operating at higher speeds, loads and temperatures. Blade Tip Timing is a non-intrusive method of performing rotor blade condition monitoring during turbomachine operation. The technique uses sensors embedded into the turbomachine casing in conjunction with a shaft encoder. A BTT system calculates the difference between the true and expected Angle of Arrival (AoA) of each blade at each sensor. This difference can be used in many ways to perform diagnostics. When calculating the AoA, the shaft speed within each revolution is often assumed as constant. This assumption is incorrect for transient conditions such as a run-up. The incorrect assumption leads to errors in the calculated AoAs. This article proposes a more accurate method for calculating the AoA. A state space equation for the shaft Instantaneous Angular Speed and Instantaneous Angular Position is derived and solved using a Kalman filter. The proposed method is validated using laboratory and field tests.
•Optical flow accurately measured vibrations 450 times smaller than a pixel.•Optimal processing parameters must be chosen to obtain accurate results.•A systematic method of determining the parameter ...values should be researched.
As digital cameras become cheaper and faster, new opportunities for measuring structural vibration are unlocked. Measuring vibration through video sequences can provide full field measurements of a structure’s motion. Digital image correlation is an established method for measuring structural vibration but requires visual surface preparation of the object being measured. Recently, a new method based on optical flow analysis of video sequences has surfaced that can measure structural vibration without any surface preparation whatsoever. This article presents an experiment to test the accuracy of the new method. The accuracy of the technique is evaluated for several sub-pixel vibration displacement amplitudes. The response is measured by an accelerometer, a laser vibrometer and marker tracking and compared to the optical flow method’s results. The results obtained indicate that it is possible to measure vibration amplitudes 450 times smaller than a single image pixel accurately.
•A new technique is used to combine machine and operating condition information.•The relevance of machine condition models is automatically inferred from the data.•The technique is developed for ...environments with large varying operating states.•The technique is used to successfully detect, isolate and trend gear damage.
In this paper, a fault diagnostic methodology is developed which is able to detect, locate and trend gear faults under fluctuating operating conditions when only vibration data from a single transducer, measured on a healthy gearbox are available. A two-phase feature extraction and modelling process is proposed to infer the operating condition and based on the operating condition, to detect changes in the machine condition. Information from optimised machine and operating condition hidden Markov models are statistically combined to generate a discrepancy signal which is post-processed to infer the condition of the gearbox. The discrepancy signal is processed and combined with statistical methods for automatic fault detection and localisation and to perform fault trending over time. The proposed methodology is validated on experimental data and a tacholess order tracking methodology is used to enhance the cost-effectiveness of the diagnostic methodology.
•Blade Tip Timing proximity probe signals are converted into the angular domain.•Instantaneous phase information, using a quadrature filter, is used to calculate tip deflections.•Experimental tests ...against other triggering criteria are performed.•The proposed method demonstrates increased robustness against noise.
Blade Tip Timing (BTT) is a non-intrusive measurement technique that can be used to estimate the vibration characteristics of rotor blades during turbomachine operation. BTT uses proximity probes mounted into the turbomachine casing to measure the Time-of-Arrival (ToA) of rotor blades at these proximity probes. The ToAs are determined using a triggering criterion on the proximity probe signal. Rotor blade tip displacements are then calculated from these ToAs. It is therefore imperative that the triggering criterion be as accurate as possible. This article proposes a new method to determine the tip displacement of rotor blades from a proximity probe signal. The method first converts the signal into the angular domain and then obtains the tip deflection through manipulation of the instantaneous phase in the signal. Three experimental tests are conducted where existing triggering criteria are compared to the proposed method. It is found that the proposed method is highly accurate in determining the tip deflections for a constant rotor speed.
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