Numerical investigation of heat transfer enhancement in solar receiver tubes

Panchbhaya, Ziyauddin (2020-03)

Thesis (MEng)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Concentrated solar power (CSP) could serve as a viable means of meeting the demands of an increasing rise in electricity requirements, as well as, being a means to produce clean and renewable energy. In many CSP plants, steam, molten salts, and thermal oils have been used as the primary heat transfer uids. Although air has gained traction in recent years as a contender for the heat transfer uid in solar Brayton cycles, it has not been a viable option due to its poor heat transfer characteristics. This research focused primarily on nding a passive means of enhancing heat transfer inside solar receiver tubes, while minimizing pressure drop. The performance of the heat transfer enhancement was evaluated by performing numerical simulations to determine thermohydraulic behaviour. An appropriate turbulence model was selected and compared to existing literature. The use of multiple twisted tapes was initially investigated followed by the use of helically twisted tapes. A novel enhancer called the half-pitch helically twisted tape is proposed to be used in solar receiver tubes. Optimization was performed on the half-pitch helically twisted tape and a full simulation was then conducted at elevated temperatures and pressures with an applied non uniform one sided heat ux. The results showed that the half-pitch helically twisted tape performs satisfactorily with an acceptable pressure loss, obtaining a thermal enhancement factor of approximately ' 0:95.

AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag (CSP) kan gebruik word om aan die vereistes van toenemende elektrisiteitsbehoeftes te voldoen, en is ook 'n manier om skoon en hernubare energie te produseer. In baie CSP aanlegte word stoom, gesmelte soute, of termiese olies as die prim^ere hitte-oordragvloeistowwe gebruik. Howel lug in die afgelope paar jaar as 'n aanspraakmaker vir hitte-oordragvloeistof in sonkrag-Brayton-siklusse traksie opgedoen het, is dit as gevolg van die swak hitte-oordragseienskappe, nie 'n lewensvatbare opsie nie. Hierdie navorsing fokus hoofsaaklik daar op om 'n passiewe manier te vind om hitte oordrag binne sonkragontvangerbuise te verhoog, terwyl die drukval tot 'n minimum beperk word. Die werkverrigting van die hitte-oordragverbetering is ge evalueer deur numeriese simulasies uit te voer om termohidrouliese gedrag te bepaal. 'n Gepasteturbulensie-model was gekies en vergelyk met die bestaande literatuur. Die gebruik van veelvuldige gedraaide linte was aanvanklik ondersoek, en gevolg deur die gebruik van spiraalvormige gedraaide linte. Daar word voorgestel dat 'n nuwe versterker genaamd die half-draai heliese draailint in die sonbuise gebruik word. Optimering van die half-draaide heliese lint was uitgevoer en 'n volledige simulasie met 'n toepaslike nie-eenvormige hittevloed was daarna gedoen met verhoogde temperature en druk. Die resultate het aangetoon dat die half-draai heliese lint bevredigend presteer met 'n aanvaarbare drukverlies, verkry 'n termiese verbeteringsfaktor van ongeveer ' 0:95.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108308
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