توربين تسلا

(تم التحويل من Tesla turbine)
Tesla turbine at Nikola Tesla Museum

توربين تسلا هو توربين جريان نابذ بدون شفرات، اخترعه نيكولا تسلا عام 1913.[1] يعمل التوربين من خلال توجيه الفوهات لسائل متحرك نحو حواف مجموعة من الأقراص. يستخدم المحرك أقراصاً ملساء تدور داخل حجرة لتوليد حركة دورانية نتيجة تبادل الزخم بين السائل والأقراص. تُرتب الأقراص بشكل مشابه لتكديس أسطوانات مدمجة (CDs) على محور دوران.[2]

يستخدم توربين تسلا تأثير الطبقة الحدودية، بدلاً من الطريقة المستخدمة في التوربينات التقليدية التي يعمل فيها السائل على شفرات. يُعرف توربين تسلا أيضاً باسم "التوربين عديم الشفرات" و"توربين الطبقة الحدودية" و"توربين الالتحام" و"توربين طبقة براندتل". الاسم الأخير نسب إلى لودفيغ براندتل. كما أشار باحثو الهندسة الحيوية إلى توربين تسلا باعتباره مضخة طرد مركزية متعددة الأقراص.[3][4]

كان أحد التطبيقات التي تصورها تسلا لهذا التوربين هو توليد الطاقة الحرارية الأرضية، وهو ما وصفه في عمله طاقتنا المحركة المستقبلية.[5]


النظرية

تسلا، التوربين الذي كان ينبغي أن يحل محل كل شيء.

في المضخة، يُضاف الضغط الشعاعي أو الساكن (الناتج عن القوة الطاردة المركزية) إلى الضغط المماسي أو الديناميكي، مما يزيد من الضغط الفعال ويساعد في طرد السائل. في المحرك، على النقيض من ذلك، فإن الضغط الأول المذكور، كونه معاكساً لضغط التغذية، يقلل من الضغط الفعال وسرعة التدفق الشعاعي نحو المركز. مرة أخرى، في الآلة المُدارة (التي تستقبل الطاقة)، يكون عزم الدوران الكبير مرغوباً فيه دائماً، مما يستدعي زيادة عدد الأقراص وتقليل مسافة الفصل بينها، بينما في الآلة المُدارة (التي تنتج الطاقة)، ولأسباب اقتصادية عديدة، يجب أن يكون الجهد الدوراني أصغر ما يمكن، والسرعة أكبر ما يمكن تحقيقه.

— المؤلف: نيكولا تسلا[6]

في التوربينات البخارية التقليدية، يجب أن يضغط البخار على الشفرات لكي يستخرج العضو الدوار الطاقة من البخار؛ يجب توجيه الشفرات بعناية لتقليل زاوية الهجوم بالنسبة لمساحة سطح الشفرة. بعبارة أخرى، في النظام الأمثل، يعمل اتجاه الشفرات على تقليل الزاوية (انحدار الشفرة) التي يصطدم بها البخار بمساحة سطحها، وذلك لخلق تدفق بخار سلس ولتقليل الاضطراب. هذا الاضطراب يقلل من كمية الطاقة المفيدة التي يمكن استخلاصها من تدفق البخار الوارد.[7]

في توربين تسلا، ونظراً لعدم وجود شفرات ليصطدم بها البخار، فإن آلية قوى رد الفعل مختلفة. تتكون قوة رد الفعل لضغط عمود البخار بسرعة نسبية، على شكل "حزام" من ضغط البخار على طول محيط التوربين. يكون هذا الحزام في أعلى كثافة وضغط عند المحيط، لأن ضغطه، عندما لا يكون العضو الدوار تحت حمل، لن يكون أقل بكثير من ضغط البخار (الوارد). في وضع التشغيل العادي، يعمل هذا الضغط المحيطي على تحديد كمية تدفق التيار الوارد، وبهذه الطريقة، يمكن القول إن توربين تسلا ذاتي التنظيم. عندما لا يكون العضو الدوار تحت حمل، تكون السرعات النسبية بين "اللوالب المضغوطة بالبخار" (SCS، أي البخار الذي يدور حلزونياً بين الأقراص) والأقراص ضئيلة.[8]

عند تطبيق حمل على توربين تسلا، يتباطأ العمود؛ أي أن سرعة الأقراص بالنسبة للسائل (المتحرك) تزداد، بينما يحافظ السائل، على الأقل في البداية، على زخمه الزاوي. على سبيل المثال، في نصف قطر يبلغ 10 cm (3.9 in)، حيث تبلغ سرعات الأقراص المحيطية عند 9000 دورة في الدقيقة حوالي 90 m/s (300 ft/s) عندما لا يوجد حمل على العضو الدوار، تتحرك الأقراص بنفس سرعة السائل تقريباً. ولكن عندما يكون العضو الدوار محمّلاً، يزداد فرق السرعة النسبية (بين SCS والأقراص المعدنية)، وعند سرعة دوران للعضو الدوار تبلغ 45 m/s (150 ft/s)، تكون للعضو الدوار سرعة نسبية قدرها 45 م/ث بالنسبة لـ SCS. هذه بيئة ديناميكية، وهذه السرعات تصل إلى هذه القيم على مدى فترة زمنية وليس بشكل فوري. هنا، يجب أن نلاحظ أن السوائل تبدأ في التصرف مثل الأجسام الصلبة عند السرعات النسبية العالية، وفي حالة توربين تسلا، يجب أيضاً أن نأخذ في الاعتبار الضغط الإضافي. مع هذا الضغط والسرعة النسبية تجاه أسطح الأقراص، يجب أن يبدأ البخار في التصرف مثل جسم صلب (SCS) يسحب على أسطح الأقراص. الاحتكاك الناتج لا يمكن إلا أن يؤدي إلى توليد حرارة إضافية مباشرة على القرص وفي SCS، وسيكون أكثر وضوحاً في الطبقة المحيطية، حيث تكون السرعة النسبية بين الأقراص المعدنية وأقراص SCS في أعلى مستوياتها. هذه الزيادة في درجة الحرارة، الناتجة عن الاحتكاك بين أقراص SCS وأقراص التوربين، ستترجم إلى زيادة في درجة حرارة SCS، وهذا سيؤدي إلى تمدد بخار SCS وزيادة الضغط بشكل عمودي على الأقراص المعدنية وكذلك بشكل قطري على محور الدوران، وبالتالي يبدو أن النموذج الهيدروديناميكي هذا يمثل تغذية مرتدة إيجابية لنقل "سحب" أقوى على الأقراص المعدنية، وبالتالي زيادة عزم الدوران عند محور الدوران.[9]

التصميم

View of Tesla turbine system
View of Tesla turbine bladeless design

The guiding principle for developing the Tesla turbine is the idea that, to obtain the highest efficiency, the changes in the velocity and direction of movement of fluid should be as gradual as possible.[1] Therefore, the propelling fluid of the Tesla turbine moves in natural paths, or streamlines, of least resistance.

A Tesla turbine consists of a set of smooth disks, with nozzles applying a moving fluid to the edge of the disk. The fluid drags on the disk through viscosity and the adhesion of the surface layer of the fluid. As the fluid slows and adds energy to the disks, it spirals into the center exhaust. Since the rotor is a simple disk, it is more robust and easier to manufacture, compared to a traditional bladed turbine.

Tesla wrote:[10]

This turbine is an efficient self-starting prime mover which may be operated as a steam or mixed fluid turbine at will, without changes in construction and is on this account, very convenient. Minor departures from the turbine, as may be dictated by the circumstances in each case, will suggest themselves but if it is carried out on these general lines, it will be found highly profitable to the owners of the steam plant while permitting the use of their old installation. However, the best economic results in the development of power from steam by the Tesla turbine will be obtained in plants especially adapted for the purpose.

Smooth rotor disks were originally proposed, but these gave poor starting torque. Tesla subsequently discovered that smooth rotor disks with small washers bridging the disks in about 12 to 24 places around the perimeter of a 10″ disk and a second ring of 6–12 washers at a sub-diameter made for a significant improvement in starting torque without compromising efficiency.

الكفاءة والحسابات

Testing of a Tesla turbine

In Tesla's time, the efficiency of conventional turbines was low because turbines used a direct-drive system that severely limited the potential usable output speed of a turbine. At the time of introduction, ship turbines were massive, and included dozens, or even hundreds, of stages of turbines, yet produced extremely low efficiency due to their low speed. For example, the turbine on both the Olympic and Titanic weighed over 400 tons, ran at only 165 rpm, and used steam at a pressure of only 6 psi. This limited it to harvesting waste steam from the main power plants, a pair of reciprocating steam engines.[11] The Tesla turbine could run on higher-temperature gases than bladed turbines of the time, which contributed to its greater efficiency. Eventually, axial turbines were given gearing to allow them to operate at higher speeds, but the efficiency of axial turbines remained very low in comparison to the Tesla turbine.

Continued improvements resulted in dramatically more efficient and powerful axial turbines, and a second stage of reduction gears was introduced in most cutting-edge U.S. naval ships of the 1930s. The improvement in steam technology gave the U.S. Navy aircraft carriers a clear advantage in speed over both Allied and enemy aircraft carriers, and so the proven axial steam turbines became the preferred form of propulsion until the 1973 oil crisis, which drove the majority of new civilian vessels to turn to diesel engines. Axial steam turbines still had not exceeded 50% efficiency by that time, and so civilian ships chose to use diesel engines due to their superior efficiency.[12] By this time, the comparably-efficient Tesla turbine was over 60 years old.

Tesla's design attempted to sidestep the key drawbacks of the bladed axial turbines, and even the lowest estimates for efficiency still dramatically outperformed the efficiency of axial steam turbines of the day. However, in testing against more modern engines, the Tesla turbine had expansion efficiencies far below contemporary steam turbines and far below contemporary reciprocating steam engines. It also suffers from other problems, such as shear losses and flow restrictions, but this is partially offset by the relatively massive reduction in weight and volume. Some of the Tesla turbine's advantages lie in relatively-low-flow-rate applications or when small sizes are needed. The disks need to be as thin as possible at the edges in order to not introduce turbulence as the fluid leaves the disks. This translates to needing to increase the number of disks as the flow rate increases. Maximum efficiency comes in this system when the inter-disk spacing approximates the thickness of the boundary layer, and since boundary layer thickness is dependent on viscosity and pressure, the claim that a single design can be used efficiently for a variety of fuels and fluids is incorrect. A Tesla turbine differs from a conventional turbine only in the mechanism used for transferring energy to the shaft. Various analyses demonstrate that the flow rate between the disks must be kept relatively low to maintain efficiency. Reportedly, the efficiency of the Tesla turbine decreases with increased load. Under light load, the spiral taken by the fluid moving from the intake to the exhaust is tight, undergoing many rotations. Under load, the number of rotations drops, and the spiral becomes progressively shorter.[citation needed] This will increase the shear losses and also reduce the efficiency because the gas is in contact with the discs for less distance.

A man holding a Tesla turbine

The turbine efficiency (defined as the ratio of the ideal change in enthalpy to the real enthalpy for the same change in pressure[citation needed]) of the gas Tesla turbine is estimated to be above 60%.[citation needed] The turbine efficiency is different from the cycle efficiency of the engine using the turbine. Axial turbines that operate today in steam plants or jet engines have efficiencies of over 90%.[13] This is different from the cycle efficiencies of the plant or engine, which are between approximately 25% and 42%, and are limited by any irreversibility to be below the Carnot cycle efficiency. Tesla claimed that a steam version of his device would achieve around 95% efficiency.[14][15] The thermodynamic efficiency is a measure of how well it performs compared to an isentropic case. It is the ratio of the ideal to the actual work input/output.

In the 1950s, Warren Rice attempted to recreate Tesla's experiments, but he did not perform these early tests on a pump built strictly in line with Tesla's patented design (it, among other things, was not a Tesla multiple staged turbine nor did it possess Tesla's nozzle).[16] Rice's experimental single-stage system's working fluid was air. Rice's test turbines, as published in early reports, produced an overall measured efficiency of 36–41% for a single stage.[16] Higher efficiency would be expected if designed as originally proposed by Tesla.

In his final work with the Tesla turbine published just before his retirement, Rice conducted a bulk-parameter analysis of model laminar flow in multiple disk turbines. A very high claim for rotor efficiency (as opposed to overall device efficiency) for this design was published in 1991 titled "Tesla Turbomachinery".[17] This paper states:

With proper use of the analytical results, the rotor efficiency using laminar flow can be very high, even above 95%. However, to attain high rotor efficiency, the flowrate number must be made small, which means high rotor efficiency is achieved at the expense of using a large number of disks and hence a physically larger rotor. For each value of the flow rate number, there is an optimum value of the Reynolds number for maximum efficiency. With common fluids, the required disk spacing is dismally small causing [rotors using] laminar flow to tend to be large and heavy for a prescribed throughflow rate.

Extensive investigations have been made of Tesla-type liquid pumps using laminar-flow rotors. It was found that overall pump efficiency was low even when rotor efficiency was high because of the losses occurring at the rotor entrance and exit earlier mentioned.

— [18]:4

Modern multiple-stage bladed turbines typically reach 60–70% efficiency, while large steam turbines often show turbine efficiency of over 90% in practice. Volute rotor-matched Tesla-type machines of reasonable size with common fluids (steam, gas, and water) would also be expected to show efficiencies in the vicinity of 60–70% and possibly higher.[18]

التطبيقات

ملف:TeslaTurbine-00.png
A Tesla turbine with the top removed

Tesla's patents state that the device was intended for the use of fluids as motive agents, as distinguished from the propulsion or compression of fluids (though it can also be used for those purposes). As of 2016, the Tesla turbine has not seen widespread commercial use. The Tesla pump, however, has been commercially available since 1982[19] and is used to pump fluids that are abrasive, viscous, shear-sensitive, loaded with solids, or are otherwise difficult to handle with other pumps. Tesla himself did not procure a large contract for production. The main disadvantage was poor knowledge of material characteristics and behaviors at high temperatures. The best metallurgy of the day could not prevent the turbine disks from moving and warping unacceptably during operation.

Many amateur experiments have been conducted using Tesla turbines with compressed air or steam as the power source. Disc warping has been ameliorated by using new materials such as carbon fiber.

One proposed application for the device is a waste pump, in factories and mills where normal vane-type turbine pumps typically become fouled.

Applications of the Tesla turbine as a multiple-disk centrifugal blood pump have yielded promising results due to the low peak shear force.[20] Biomedical engineering research on such applications has continued into the 21st century.[21]

The device functions as a pump if a similar set of disks and a housing with an involute shape (versus circular for the turbine) are used. In this configuration, a motor is attached to the shaft. The fluid enters near the center, is energized by the disks, and exits at the periphery. The Tesla turbine does not use friction in the conventional sense, rather using adhesion (the Coandă effect) and viscosity instead. It uses the boundary-layer effect on the disc blades.

التاريخ

The turbine was patented by Nikola Tesla on October 21, 1913, which was his 100th patent.[1]

انظر أيضاً

المصادر

  1. ^ أ ب ت {{{1}}} patent {{{2}}}
  2. ^ "The Tesla turbine: a failed invention with amazing applications" (in الإنجليزية). Archived from the original on 2023-09-23. Retrieved 2023-08-01.
  3. ^ Miller, G. E.; Sidhu, A; Fink, R.; Etter, B. D. (1993). "July). Evaluation of a multiple disk centrifugal pump as an artificial ventricle". Artificial Organs. 17 (7): 590–592. doi:10.1111/j.1525-1594.1993.tb00599.x. PMID 8338431.
  4. ^ Miller, G. E.; Fink, R. (1999). "June). Analysis of optimal design configurations for a multiple disk centrifugal blood pump". Artificial Organs. 23 (6): 559–565. doi:10.1046/j.1525-1594.1999.06403.x. PMID 10392285.
  5. ^ Nikola Tesla, "Our Future Motive Power".
  6. ^ "TESLA patent 1,061,206 Turbine".
  7. ^ [citation needed]
  8. ^ [citation needed]
  9. ^ [citation needed]
  10. ^ Nicola Tesla in British Patent 179,043 on RexResearch.
  11. ^ Titanic: Building the World's Most Famous Ship By Anton Gill, P121
  12. ^ The Design of High-Efficiency Turbomachinery and Gas Turbines, David Gordon Wilson, P.15
  13. ^ Denton, J. D. (1993). "Loss mechanisms in turbomachines". Journal of Turbomachinery. 115 (4): 621–656. doi:10.1115/1.2929299.
  14. ^ Stearns, E. F., "The Tesla Turbine Archived 2004-04-09 at the Wayback Machine". Popular Mechanics, December 1911. (Lindsay Publications)
  15. ^ Andrew Lee Aquila, Prahallad Lakshmi Iyengar, and Patrick Hyun Paik, "The Multi-disciplinary Fields of Tesla; bladeless turbine Archived 2006-09-05 at the Wayback Machine". nuc.berkeley.edu.
  16. ^ أ ب "Debunking the Debunker, Don Lancaster Again Puts His Foot In", Tesla Engine Builders Association.
  17. ^ "Interesting facts about Tesla" Q&A: I've heard stories about the Tesla turbine that cite a figure of 95% efficiency. Do you have any information regarding this claim? And, why haven't these devices been utilized in the mainstream?. 21st Century Books.
  18. ^ أ ب Rice, Warren, "Tesla Turbomachinery". Conference Proceedings of the IV International Tesla Symposium, September 22–25, 1991. Serbian Academy of Sciences and Arts, Belgrade, Yugoslavia. (PDF)
  19. ^ Discflo Disc Pump Technology Archived فبراير 14, 2009 at the Wayback Machine
  20. ^ Miller, G. E.; Etter, B. D.; Dorsi, J. M. (1990). "February). A multiple disk centrifugal pump as a blood flow device". IEEE Trans Biomed Eng. 37 (2): 157–163. doi:10.1109/10.46255. PMID 2312140. S2CID 1016308.
  21. ^ Manning, K. B.; Miller, G. E. (2002). "Flow through an outlet cannula of a rotary ventricular assist device". Artificial Organs. 26 (8): 714–723. doi:10.1046/j.1525-1594.2002.06931_4.x. PMID 12139500.

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