Amir Fartaj

Desirable airfoil features for smaller-capacity straight-bladed VAWT

In the small scale wind turbine market, the simple straight-bladed Darrieus type vertical axis wind turbine (SB-VAWT) is very attractive for its simple blade design. A detailed aerodynamic performance analysis was conducted on a smaller capacity fixed-pitch SB-VAWT. Brief analyses of the main aerodynamic challenges of this type of wind turbine were first discussed and subsequently the authors conducted further literature survey and computational analysis to shortlist aerodynamic characteristics of a desirable airfoil for a self-starting and better performing SB-VAWT. The required geometric features of the desirable airfoil to achieve the short listed characteristics were also discussed. It has been found out that conventionally used NACA symmetric airfoils are not suitable for smaller capacity SB-VAWT. Rather, it is advantageous to utilize a high-lift and low-drag asymmetric thick airfoil suitable for low speed operation typically encountered by SB-VAWT.

Analysis of the Design Parameters Related to a Fixed-Pitch Straight-Bladed Vertical Axis Wind Turbine

The fixed-pitch straight-bladed vertical axis wind turbine (SB-VAWT) is one of the simplest types of wind turbine. One of the main challenges of wide spread application of the smaller-capacity SB-VAWT is to design and develop it in a cost-effective manner. The overall cost of the SB-VAWT will mainly depend on judicious choice of multiple design parameters. An attempt has been made in this paper to identify and critically analyze the main design parameters related to smaller-capacity fixed-pitch SB-VAWT. It has been demonstrated in this paper that proper selections of these parameters are vital for a cost-effective smaller-capacity SB-VAWT which can be considered as a candidate for urban and off-grid rural applications.

Design of a Special-purpose Airfoil for Smaller-Capacity Straight-Bladed VAWT

Selection of airfoil is one of the most critical factors in achieving better aerodynamic performance and in determining the optimum dimensions of a fixed-pitch straight-bladed Darrieus type vertical axis wind turbine (SB-VAWT), along with solidity, radial arm parasitic drag, aspect ratio etc. Airfoil related design changes also have the potential for increasing the cost effectiveness of SB-VAWTs which is one of the simplest types of wind turbine and they are prospective candidate for diversified urban and rural applications. After identifying the main aerodynamic challenges of this type of wind turbine, the authors short listed the salient aerodynamic and geometric characteristics of a desirable airfoil for a self-starting and better performing SB-VAWT. Based on these findings, detailed performance analyses were done with several prospective airfoils. Finally a special-purpose airfoil has been designed for smaller capacity SB-VAWT.

Aerodynamic Factors Affecting Performance of Straight-Bladed Vertical Axis Wind Turbines

Unlike the conventional aerodynamic applications, the straight-bladed vertical axis wind turbines (VAWTs) operate in a circular motion and encounter a wide range of angle of attacks, especially at low tip speed ratios. When the blade angle of attack remains constant or varies slowly with time, it encounters the static stall. However, when the angle of attack changes rapidly with time, it experiences the dynamic stall which is far more difficult to analyze and predict than the static stall. Furthermore, the blade/blade wake interaction in straight-bladed VAWTs also presents modeling problem. In this paper, all of these aforesaid aerodynamic factors are discussed. It was found that these factors need special attention for designing a self-starting straight-bladed VAWT with optimum performance. A numerical method based on Cascade model, proposed by Hirsch and Mandal [1], that gives reasonable correlation with the experimental data available has been used. The effects of dynamic stall and flow curvature on the performance of a straight-bladed VAWT have been analyzed. It is observed from the analysis that aerodynamic forces due to dynamic stall are higher than those due to static stall. As a result, for the performance prediction of straight-bladed VAWTs, especially for the local forces, there can be substantial differences between the experimental data and the calculated values unless the dynamic stall effect is added.Copyright

Assessment of the small‐capacity straight‐bladed VAWT for sustainable development of Canada

Canada has a huge wind power potential of more than 28,000 MW, which represents a significant environmentally benign sustainable energy source. A small‐capacity (below 10kW) straight‐bladed vertical axis wind turbine can compete with conventional sources in niche markets. It converts wind energy to useful energy vectors or carriers, such as heat, electricity, and mechanical power. This paper discusses the applications of this turbine, so promising for the sustainable development of Canada. Furthermore, human health, natural environmental and national economic benefits of these applications in Canadian perspective are also described. It has been demonstrated that all these environmentally benign applications can contribute significantly toward Canada’s target of reducing greenhouse gas emissions by displacing the use of conventional fossil fuels, and take an essential step toward sustainable energy future.

Second law analysis of a multiport serpentine Micro-Channel Slab Heat Exchanger

Second law analysis is recognised as an effective tool to determine the thermodynamic performance of many systems. In the present work, it is used for a steady–state multiport serpentine slab cross–flow Micro–Channel Heat Exchanger (MCHX) to analyse its thermodynamic performance. Micro–scale devices have been widely used due to advancements in micro–scale fabricating technologies. This type of heat exchanger has been known for its higher heat transfer coefficient and higher area per volume ratio. Conservation of energy and the increase in entropy principles were used to create a mathematical model that uses different parameters such as heat capacity rate ratio, fluids inlet temperatures ratio, effectiveness and pressure drop for obtaining the entropy generation. Results were obtained on the basis of the behaviour of the dimensionless entropy generation number with the key parameters. A good agreement between the predicted and the measured results was found.

Heat Transfer Experiments of Ethylene Glycol-Water Mixture in Multi-Port Serpentine Meso-Channel Heat Exchanger Slab

In past few years, narrow diameter flow passages (≤3 mm) have attracted huge research attentions due to their several advantageous features over conventional tubes (≥6 mm) especially from the view points of higher heat transfer, lesser weight, and smaller device size. Several classifications of narrow channels, based on sizes, are proposed in the open literature from mini to meso and micro (3 mm to 100 μm). The meso- and micro-channels have not yet entered into the HVAC and automotive heat exchanger industries to the expected potentials to take the above-mentioned advantages. The reasons may be the limited availability of experimental data on pressure drop and heat transfer and the lack of consolidated design correlations as compared to what is established for compact heat exchangers. While a number of studies available on standalone single straight channels, works on multi-channel slab similar to those used as typical thermal heat exchanger core elements are inadequate, especially the research on multichannel serpentine slab are limited in the open literature. The 50% ethylene glycol and water mixture is widely used in heat exchanger industry as a heat transfer fluid. Studies of pressure drop and heat transfer on this commercially important fluid using narrow tube multi-channel slab is scarce and the availability of experimental data is rare in the open literature. Conducting research on various shapes of meso- and micro-channel heat exchanger cores using a variety working fluids are a definite needs as recommended and consistently urged in ongoing research publications in this promising area. Under present long-term project, an automated dynamic single-phase experimental infrastructure has been developed to carryout the fluid flow and heat transfer research in meso- and micro-channel test specimens and prototype microchannel heat exchanger using a variety of working fluids in air-to-liquid crossflow orientation. In the series, experiments have been conducted on 50% ethylene glycol and water solution in a serpentine meso-channel slab having 68 individual channels of 1 mm hydraulic diameter to obtain the heat transfer data and the general pressure drop nature of the test fluid. Current paper presents the heat transfer characteristics of ethylene glycol-water mixture and the Reynolds number effects on pressure drop, heat transfer rate, test specimen NTU and effectiveness, overall thermal resistance, and the Nusselt number.Copyright

Investigation of Low Reynolds Number Airfoils for Fixed-Pitch Straight-Bladed VAWT

Selection of appropriate airfoil is very important for improved aerodynamic performance of a smaller-capacity fixed-pitch straight-bladed vertical axis wind turbine (SB-VAWT). Recently, Islam et. al1 have identified the desirable features of an ideal airfoil for smaller capacity SB-VAWT to improve its starting characteristics and overall performance. They have shortlisted several aerodynamic characteristics of the desirable airfoil. Based on these desirable aerodynamic characteristics, an attempt has been made in this paper to investigate the experimental results of different types of airfoils which meet the ideal characteristics of the desired airfoil identified by Islam et. al1 . After performing a screening process, seven prospective candidate low RN airfoils are selected. In this study,only the low RN experimental datasets are sought which are proved to be difficult to find since most public domain datasets are for high RN. It has been found that most of the candidate asymmetric airfoils are performing better than conventional NACA 0015 airfoil which has been extensively used for SB-VAWTs, especially for 0°≤α≤90°.

Exergy analysis of advanced transcritical CO2 air conditioning cycles

The energy and exergy balance methods were performed on two advanced transcritical CO2 air conditioning cycles presented in the literature. In addition to the basic transcritical CO2 air conditioning cycle which has five main components, compressor, gas cooler, evaporator, expansion valve and internal heat exchanger, two advanced cycles are investigated; both have two-stage compressor (low stage and high stage) and intercooler, with one of them has an additional Flash Gas Removal (FGR) chamber. The results demonstrated that the compressor-low stage has the largest exergy loss, while the intercooler has the smallest exergy loss in advanced transcritical CO2 air conditioning cycles. Moreover, it demonstrated that the FGR had a minimal effect on improving COP of the system.

Performance analysis of a smaller-capacity straight-bladed VAWT with prospective airfoils

Modern wind turbines are categorized as horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs), which are currently being utilized for diversified applications. The basic theoretical advantages of VAWTs are: (i) they accept the wind from any direction, and (ii) the generator, gearbox etc. can be placed on the ground. Selection of airfoil is one of the most critical factor in achieving optimum aerodynamic performance and in determining the optimum dimensions of a fixed-pitch straight-bladed vertical axis wind turbine (SB-VAWT). Airfoil related design changes also have the potential for increasing the cost effectiveness of VAWTs. Most of the earlier research works carried out by different research organizations mainly used NACA symmetric airfoils which were unable to self-start properly. In this paper, detail systematic investigative analyses have been performed with high-lift asymmetric airfoils appropriate for self-starting and better performance of smaller capacity SB-VAWT. In order to do the performance analysis, a computational scheme has been developed using the Cascade Model and XFOIL, a sub-sonic airfoil design and analysis tool developed in MIT. It has been found out that the results obtained from the computational scheme conform reasonably well with the experimental results. Subsequently, three prospective airfoils have been identified using this computational scheme. It has been found that their performance is better than conventionally used NACA 0015 at low tip speed ratio range where the problem of self-starting happens.