بررسي تحليلي اثر پارامترهاي نانو سيال بر كلكتورهاي خورشيدي جذب مستقيم

چكيده انگليسي :

Theoretical Investigation of Nanofluid Parameters on Direct Absorption Solar Collectors Nader Zarin n zarrin@me iut ac ir Date of Submission 2013 01 15 Department of Mechanical Engineering Isfahan University of Technology Isfahan Iran Degree M Sc Language Farsi Supervisor Ali akbar Alemrajabi rajabi@cc iut ac ir Abstract Solar energy is almost an interminable source that can supply the required energy of the world The cheapness and renewability of this unlimited energy source have led to research activities in order to develop new techniques for using it Meanwhile by the emergence of nanofluids which are suspension of nanoparticles in base liquids new class of solar collectors known as direct absorption solar collectors has emerged In these collectors nanofluid which is directly exposed to sun rays serve as both the absorbent and the carrier medium The sun rays are absorbed by the nanofluid and are converted to heat which is then conveyed away by the fluid flow So far only few aspects of direct absorption solar collectors have been studied The goal of the present research is to investigate the parameters affecting the efficiency of these collectors The key step in modeling the direct absorption is estimation of the nonofluids extinction coefficient First the extinction coefficients of nanofluids are calculated by using three different theories i e Rayleigh Mie and Maxwell Garnett theories However comparison of the results with experimental one s shows that the Mie theory is the best one among the three theories for estimation of extinction coefficient In order to calculate the efficiency of a direct absorption collector one needs to solve the two dimensional energy equation and one dimensional radiative transfer equation Effect of various parameters on the efficiency of a direct absorption solar collector is then evaluated The parameters whose effects are investigated are diameter of nonoparticles volume fraction of nanoparticles collector geometry transmissivity of the glass cover and effect of installing an ideal reflector at the bottom of the collector Also effect of base fluid on the collector performance is investigated The results show that increase in the nanoparticle diameter increases the efficiency moderately By increasing the volume fraction of nanoparticles the collector efficiency grows rapidly at first and then remains constant Increasing the length of the collector has less impact on the collector efficiency than its height The higher the glass transmissivity the higher is the efficiency Using an ideal reflector at the bottom of the collector is a suitable way to reduce the cost of the collector The results show that the collector height is a key parameter to the collector efficiency because as the collector height and depth of nanofluid increases sun rays are absorbed more efficiently Also effects of four different base fluids i e water ethylene glycol propylene glycol and Trminol VP 1 on the collector efficiency is investigated In practice use of these liquids depends on the operating temperature of the collector Results show that among these 4 liquids water is the best absorber that can be used in direct absorption solar collectors at low temperatures such as solar water heaters A new method for evaluating the extinction coefficient of a mixture of water and ethylene glycol is developed This method is based on the Maxwell Garnett theory and the results are presented This mixture is a suitable working fluid for direct absorption solar collectors at relatively low temperatures Finally almost 10 increase in efficiency is observed when the performance of a direct absorption solar collector is compared with a conventional flat plate collector under similar atmospheric conditions Keywords direct absorption solar collector extinction coefficient nanofluid Mie Theory Rayleigh theory Maxwell Garnett theory

زرين، نادر

بررسي تحليلي اثر پارامترهاي نانو سيال بر كلكتورهاي خورشيدي جذب مستقيم

ضريب اطفاء نانو سيال , تئوري ماي , تئوري رايلي , تئوري ماكسول گارنت , ضزيب اطفاء آب اتيلن گليكول