{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,8]],"date-time":"2026-02-08T01:02:48Z","timestamp":1770512568931,"version":"3.49.0"},"reference-count":52,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2020,7,9]],"date-time":"2020-07-09T00:00:00Z","timestamp":1594252800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Energies"],"abstract":"<jats:p>Due to the poor thermal characteristics of the air, the absorber roughness of solar air collectors is commonly artificially increased in order to enhance the heat transfer to the air stream. However, this is also accompanied by an undesirable increase in the pumping power due to increased friction losses. As a result, several authors have experimentally investigated several ways of maximizing the heat transfer while minimizing the friction losses of different absorbers, resulting in the development of semi-empirical functions relating the Nusselt number (a measure of heat transfer) and the friction factor (a measure of friction losses) to the Reynolds number and the roughness parameters considered for each absorber. The present paper reviews, considering the publications from the last ten years, these semi-empirical functions. Moreover, the optimum roughness parameters and operating conditions of the absorbers were estimated by finding the maximum values of two performance parameters (the thermo-hydraulic efficiency and effectiveness), calculated using the semi-empirical functions, in order to classify the absorbers in terms of their energy characteristics. This approach proves to be a rather effective way of optimizing the roughness characteristics of solar air collector absorbers. It is also concluded that, considering the range of absorbers analyzed here, generally, multiple V-shaped ribs with gaps provide the most effective roughness geometry.<\/jats:p>","DOI":"10.3390\/en13143536","type":"journal-article","created":{"date-parts":[[2020,7,9]],"date-time":"2020-07-09T10:45:19Z","timestamp":1594291519000},"page":"3536","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Thermo-Hydraulic Performance of Solar Air Collectors with Artificially Roughened Absorbers: A Comparative Review of Semi-Empirical Models"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-2879-1225","authenticated-orcid":false,"given":"Ant\u00f3nio","family":"Ara\u00fajo","sequence":"first","affiliation":[{"name":"Faculdade de Engenharias e Tecnologias, Universidade Lus\u00edada Norte, 4760-108 Vila Nova de Famalic\u00e3o, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2020,7,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Weiss, W., and Sp\u00f6rk-D\u00fcr, M. (2019). Solar Heat Worldwide: Global Market Development and Trends in 2018, AEE INTEC.","DOI":"10.18777\/ieashc-shw-2019-0001"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"100","DOI":"10.1016\/j.rser.2014.04.063","article-title":"A review of thermohydraulic performance of artificially roughened solar air heaters","volume":"37","author":"Kumar","year":"2014","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1189","DOI":"10.1016\/j.rser.2016.12.021","article-title":"Solar air heaters: Design configurations, improvement methods and applications\u2014A detailed review","volume":"70","author":"Kabeel","year":"2017","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"637","DOI":"10.1016\/j.solener.2019.12.057","article-title":"Overall performance analysis and GRA optimization of solar air heater with truncated half conical vortex generators","volume":"196","author":"Bezbaruah","year":"2020","journal-title":"Sol. Energy"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1327","DOI":"10.1016\/j.renene.2020.03.095","article-title":"Utilizing circular jet impingement to enhance thermal performance of solar air heater","volume":"154","author":"Singh","year":"2020","journal-title":"Renew. Energy"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Garg, H.P. (1987). Advances in Solar Energy Technology: Volume 1, Collection and Storage Systems, Reidel.","DOI":"10.1007\/978-94-017-0659-9_1"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Garg, H.P. (1987). Advances in Solar Energy Technology: Volume 2, Industrial Applications of Solar Energy, Reidel.","DOI":"10.1007\/978-94-009-3795-6"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Duffie, J.A., and Beckman, W.A. (2013). Solar Engineering of Thermal Processes, Wiley. [4th ed.].","DOI":"10.1002\/9781118671603"},{"key":"ref_9","unstructured":"Sayigh, A. (2012). Solar space heating and cooling systems. Comprehensive Renewable Energy, Volume 3, Elsevier. Chapter 3.13."},{"key":"ref_10","unstructured":"Sayigh, A. (2012). Low Temperature Stationary Collectors. Comprehensive Renewable Energy, Volume 3, Elsevier. Chapter 3.04."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"370","DOI":"10.1016\/j.rser.2014.04.077","article-title":"Artificially roughened solar air heater: Experimental investigations","volume":"36","author":"Yadav","year":"2014","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_12","unstructured":"Kalogirou, S.A. (2014). Solar Energy Engineering: Processes and Systems, Academic Press. [2nd ed.]."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"100685","DOI":"10.1016\/j.seta.2020.100685","article-title":"Review on the design modifications of a solar air heater for improvement in the thermal performance","volume":"39","author":"Arunkumar","year":"2020","journal-title":"Sustain. Energy Technol. Assessments"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"863","DOI":"10.1016\/j.rser.2014.11.059","article-title":"A thermodynamic review of solar air heaters","volume":"43","author":"Saxena","year":"2015","journal-title":"Renew. Sustain. Energy Rev."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1209","DOI":"10.1080\/15435075.2016.1183207","article-title":"Efficiency enhancement in solar air heaters by modification of absorber plate\u2014A review","volume":"13","author":"Aravindh","year":"2016","journal-title":"Int. J. Green Energy"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Sarbu, I., and Sebarchievici, C. (2017). Solar Heating and Cooling Systems: Fundamentals, Experiments and Applications, Academic Press.","DOI":"10.1016\/B978-0-12-811662-3.00008-6"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Garg, H.P., Mullick, S.C., and Bhargave, A.K. (1985). Solar Thermal Energy Storage, D. Reidel.","DOI":"10.1007\/978-94-009-5301-7"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"739","DOI":"10.1016\/j.energy.2006.05.009","article-title":"Effective efficiency of solar air heaters having different types of roughness elements on the absorber plate","volume":"32","author":"Mittal","year":"2007","journal-title":"Energy"},{"key":"ref_19","first-page":"57","article-title":"Determination of effective efficiency of artificially roughened solar air heater duct using ribs","volume":"30","author":"Kumar","year":"2015","journal-title":"Distrib. Gener. Altern. Energy J."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"143","DOI":"10.1080\/15435075.2014.917419","article-title":"Artificially roughened solar air heater: A comparative study","volume":"13","author":"Yadav","year":"2016","journal-title":"Int. J. Green Energy"},{"key":"ref_21","unstructured":"Munson, B.R., Okiishi, T.H., Huebsch, W.W., and Rothmayer, A.P. (2013). Fundamentals of Fluid Mechanics, Wiley. [7th ed.]."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Alam, T., Saini, R.P., and Saini, J.S. (2014). Experimental investigation of thermohydraulic performance of a rectangular solar air heater duct equipped with V-shaped perforated blocks. Adv. Mech. Eng., 6.","DOI":"10.1155\/2014\/948313"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"471","DOI":"10.1080\/01457632.2014.935218","article-title":"Thermal behavior in rectangular channel duct fitted with v-shaped perforated baffles","volume":"36","author":"Chamoli","year":"2015","journal-title":"Heat Transf. Eng."},{"key":"ref_24","unstructured":"\u00c7engel, Y.A., and Ghajar, A.J. (2019). Heat and Mass Transfer: Fundamentals and Applications, McGraw-Hill. [6th ed.]."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"253","DOI":"10.1016\/0306-2619(90)90001-T","article-title":"Improvement of the efficiency of a bare solar collector by means of turbulence promoters","volume":"36","author":"Piacentini","year":"1990","journal-title":"Appl. Energy"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1016\/j.renene.2012.04.001","article-title":"Heat and fluid flow characteristics of roughened solar air heater ducts\u2014A review","volume":"47","author":"Kumar","year":"2012","journal-title":"Renew. Energy"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"275","DOI":"10.1016\/j.solener.2016.02.040","article-title":"Experimental and CFD investigation of convection heat transfer in solar air heater with reverse L-shaped ribs","volume":"131","author":"Gawande","year":"2016","journal-title":"Sol. Energy"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"687","DOI":"10.1016\/j.renene.2018.06.076","article-title":"Nusselt number and friction factor correlation of solar air heater having twisted-rib roughness on absorber plate","volume":"130","author":"Kumar","year":"2019","journal-title":"Renew. Energy"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1647","DOI":"10.1016\/0017-9310(72)90095-6","article-title":"Application of rough surfaces to heat exchanger design","volume":"15","author":"Webb","year":"1972","journal-title":"Int. J. Heat Mass Transf."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/S1004-9541(14)60030-6","article-title":"Experimental investigation on turbulent convection in solar air heater channel fitted with delta winglet vortex generator","volume":"22","author":"Skullong","year":"2014","journal-title":"Chin. J. Chem. Eng."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1016\/j.icheatmasstransfer.2013.11.001","article-title":"Thermal performance of turbulent flow in a solar air heater channel with rib-groove turbulators","volume":"50","author":"Skullong","year":"2014","journal-title":"Int. Commun. Heat Mass Transf."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"720","DOI":"10.1016\/j.solener.2014.10.020","article-title":"Heat transfer behaviors in a solar air heater channel with multiple V-baffle vortex generators","volume":"110","author":"Tamna","year":"2014","journal-title":"Sol. Energy"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"45","DOI":"10.1016\/j.expthermflusci.2016.04.012","article-title":"Investigation of effect of the circular ring turbulators on heat transfer augmentation and fluid flow characteristic of solar air heater","volume":"77","author":"Ata","year":"2016","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"77","DOI":"10.1016\/j.expthermflusci.2016.07.022","article-title":"Heat transfer and friction factor correlations for a solar air heater duct roughened artificially with broken arc ribs","volume":"80","author":"Hans","year":"2017","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"788","DOI":"10.1016\/j.renene.2018.07.078","article-title":"Performance improvement and development of correlation for friction factor and heat transfer using computational fluid dynamics for ribbed triangular duct solar air heater","volume":"131","author":"Kumar","year":"2019","journal-title":"Renew. Energy"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"615","DOI":"10.21105\/joss.00615","article-title":"Optim: A mathematical optimization package for Julia","volume":"3","author":"Mogensen","year":"2018","journal-title":"J. Open Source Softw."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"65","DOI":"10.1137\/141000671","article-title":"Julia: A fresh approach to numerical computing","volume":"59","author":"Bezanson","year":"2017","journal-title":"SIAM Rev."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"898","DOI":"10.1016\/j.solener.2010.02.004","article-title":"Heat transfer and friction factor correlations for a solar air heater duct roughened artificially with multiple v-ribs","volume":"84","author":"Hans","year":"2010","journal-title":"Sol. Energy"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"5053","DOI":"10.1016\/j.energy.2011.05.052","article-title":"Heat transfer and friction factor correlations of solar air heater ducts artificially roughened with discrete V-down ribs","volume":"36","author":"Singh","year":"2011","journal-title":"Energy"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"4531","DOI":"10.1016\/j.energy.2011.03.054","article-title":"Heat transfer and friction in solar air heater duct with W-shaped rib roughness on absorber plate","volume":"36","author":"Lanjewar","year":"2011","journal-title":"Energy"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"151","DOI":"10.1016\/j.renene.2013.03.013","article-title":"Development of correlations for Nusselt number and friction factor for solar air heater with roughened duct having multi v-shaped with gap rib as artificial roughness","volume":"58","author":"Kumar","year":"2013","journal-title":"Renew. Energy"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"484","DOI":"10.1016\/j.renene.2016.01.067","article-title":"Performance analysis of solar air heater duct roughened with multigap V-down ribs combined with staggered ribs","volume":"91","author":"Deo","year":"2016","journal-title":"Renew. Energy"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"117","DOI":"10.1016\/j.expthermflusci.2014.02.004","article-title":"Heat transfer and friction factor correlations for multiple arc shape roughness elements on the absorber plate used in solar air heaters","volume":"54","author":"Singh","year":"2014","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"314","DOI":"10.1016\/j.solener.2016.05.007","article-title":"Experimental investigation of heat transfer augmentation using multiple arcs with gap on absorber plate of solar air heater","volume":"134","author":"Pandey","year":"2016","journal-title":"Sol. Energy"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"100978","DOI":"10.1016\/j.est.2019.100978","article-title":"Performance evaluation and optimization of solar assisted air heater with discrete multiple arc shaped ribs","volume":"26","author":"Kumar","year":"2019","journal-title":"J. Energy Storage"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"1109","DOI":"10.1016\/j.solener.2011.03.007","article-title":"Nusselt number and friction factor correlations for solar air heater duct having artificially roughened absorber plate","volume":"85","author":"Bhushan","year":"2011","journal-title":"Sol. Energy"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"2852","DOI":"10.1016\/j.solener.2012.06.024","article-title":"Correlations for solar air heater duct with dimpled shape roughness elements on absorber plate","volume":"86","author":"Sethi","year":"2012","journal-title":"Sol. Energy"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1016\/j.expthermflusci.2012.05.011","article-title":"Nusselt number and friction factor correlations for solar air heater duct having protrusions as roughness elements on absorber plate","volume":"44","author":"Yadav","year":"2013","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"458","DOI":"10.1016\/j.applthermaleng.2017.07.181","article-title":"Heat transfer enhancement in solar air heater duct with conical protrusion roughness ribs","volume":"126","author":"Alam","year":"2017","journal-title":"Appl. Therm. Eng."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"760","DOI":"10.1016\/j.expthermflusci.2012.09.019","article-title":"Heat transfer and friction factor correlations for impinging jet solar air heater","volume":"44","author":"Chauhan","year":"2013","journal-title":"Exp. Therm. Fluid Sci."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"966","DOI":"10.1016\/j.solener.2017.11.046","article-title":"Thermal performance improvement of a solar air heater fitted with winglet vortex generators","volume":"159","author":"Chamoli","year":"2018","journal-title":"Sol. Energy"},{"key":"ref_52","doi-asserted-by":"crossref","unstructured":"Kumar, B.V., Manikandan, G., Kanna, P.R., Taler, D., Taler, J., Nowak-Oc\u0142\u00f3n, M., Mzyk, K., and Toh, H.T. (2018). A performance evaluation of a solar air heater using different shaped ribs mounted on the absorber plate\u2014A review. Energies, 11.","DOI":"10.3390\/en11113104"}],"container-title":["Energies"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1073\/13\/14\/3536\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T09:49:15Z","timestamp":1760176155000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1073\/13\/14\/3536"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2020,7,9]]},"references-count":52,"journal-issue":{"issue":"14","published-online":{"date-parts":[[2020,7]]}},"alternative-id":["en13143536"],"URL":"https:\/\/doi.org\/10.3390\/en13143536","relation":{},"ISSN":["1996-1073"],"issn-type":[{"value":"1996-1073","type":"electronic"}],"subject":[],"published":{"date-parts":[[2020,7,9]]}}}