Experimental Evaluation of Water Dropwise Evaporation in a Solar Humidifier using Flat and Dimpled Absorbers
Main Article Content
Abstract
This work focuses on developing a Low-cost, low-grade electrical-thermal solar humidification system, as a promising solution for freshwater production. To increase the air humidity ratio at the humidifier exit, a designed and instrumented solar humidifier harnesses solar radiation and receives both a forced hot air stream from a solar air collector and water droplets falling onto its absorber plate, where the droplets evaporate. The solar humidifier dimensions were 330 × 50 × 1000 mm. PV panels supplied electrical power to circulate water and air for preheating by a flat-plate and an air solar collector. Key factors influencing air’s relative humidity (RH) are air flow rates (0.5 m3/min to 1.5 m3/min), water drip rate (4 to 10 drops/s), and the solar humidifier’s absorber surface geometry (flat or dimpled). Tests were extended from 8:00 to 17:00 to evaluate air RH and temperature on clear-sky days in Baghdad, Iraq. Results showed that the highest outlet air RH was 61.2%, 72.4%, and 69.9% for water dripping rates of 4, 7, and 10 drops/s, corresponding to 0.167, 0.297, and 0.423 g/s, respectively, with a constant airflow rate of 0.5 m3/min. The best dripping rate was 7 drops/s. The outlet air RH from the humidifier was 72.4% and 85.6% for flat and dimpled absorbers, respectively, at an airflow rate of 0.5 m3/min and 7 water drops/s (0.297 g/s). The humidifier’s effectiveness was 85% and 70%, respectively. It is concluded that the dimpled absorber achieves significantly better humidification performance than the flat-plate absorber across all airflow rates. The humidifier pressure drops increases from 0.13 Pa to 0.36 Pa for the flat plate and dimpled plate, respectively, at solar noon, for a flow rate of 0.5 m3/min.
Downloads
Article Details
Section
How to Cite
References
Abdullah, A.S., Elsayad, M.M., Almoatham, S. and Sharshir, S.W., 2024. 6E evaluation of an innovative humidification dehumidification solar distiller unit: An experimental investigation. Thermal Science and Engineering Progress, 56, P. 103052. https://doi.org/10.1016/j.tsep.2024.103052.
Abd-ur-Rehman, H.M., Al-Sulaiman, F.A. and Antar, M.A., 2016. Experimental analysis of solar driven multi-stage stepped bubbler humidifier for humidification-dehumidification (HDH) water desalination system. In Energy Sustainability, 50220, P. V001T13A002. American Society of Mechanical Engineers. https://doi.org/10.1115/ES2016-59209
Abdelaziz, G.B., Al-Nagdy, A., Kandel, M.G., Dahab, M. and El-Said, E., 2026. Experimental investigation of innovative hybrid solar desalination tower using heat storage and packing materials. Ren Energy, 15, P. 125185. https://doi.org/10.1016/j.renene.2026.125185
Ali, A., Sahu, N.K., Khan, M.I., Sharma, P. and Singh, V.R., 2024. Development of a solar device for jute filling based humidification dehumidification desalination. Australian Journal of Mechanical Engineering, 22(3), pp. 493-505. https://doi.org/10.1080/14484846.2022.2113618
Alnaimat, F., Ziauddin, M. and Mathew, B., 2025. Humidification and dehumidification desalination utilizing ultrasonic atomization and direct solar energy harvesting. Desalination 602, P. 118636. https://doi.org/10.1016/j.desal.2025.118636
Bahramei, R., Samimi-Akhijahani, H., Salami, P. and Behroozi-Khazei, N., 2025. Life cycle assessment and CFD evaluation of an innovative solar desalination system with PCM and geothermal system. Journal of Energy Storage, 120, P. 116116. https://doi.org/10.1016/j.est.2025.116116
Cengel, Y.A., 2007. Heat and mass transfer: a practical approach. 3rd ed. New York: McGraw-Hill. ISBN-13:978-0073250359
Chen, S., Zhao, P., Xie, G., Wei, Y., Lyu, Y., Zhang, Y., Yan, T. and Zhang, T., 2021. A floating solar still inspired by continuous root water intake. Desalination 512, P. 115133. https://doi.org/10.1016/j.desal.2021.115133
Chiranjeevi, C., Srinivas, T. and Shankar, R., 2019. Experimental investigation on a hybrid desalination and cooling unit using humidification-dehumidification technique. Desalination and Water Treatment, 156, pp. 148-160. https://doi.org/10.5004/dwt.2019.23680
da Silva Junior, L.G., de Oliveira, J., Ribeiro, G.B. and Ferreira Pinto, L., 2023. Experimental and numerical analysis of a low-cost solar still. Eng, 4, pp. 380-403. https://doi.org/10.3390/eng4010023
Duffie, J.A., Beckman, W.A. and Blair, N., 2020. Solar engineering of thermal processes, photovoltaics and wind. John Wiley & Sons.
Dizaji, H.S., Pourhedayat, S., Moria, H., Alqahtani, S., Alshehery, S. and Anqi, A.E., 2023. Performance boost of a commercial air-to-air plate heat recovery unit by mesh-net insert; thermal-frictional, economic, and effectiveness-NTU analysis. Energy, 290, P. 130037, https://doi.org/10.1016/j.energy.2023.130037.
Essa, F.A., Mohamed Othman, M., Mohamed Younes, M., Omara, Z.M. and Khalil, H., 2025. Enhancing freshwater production and cost-effectiveness in humidification-dehumidification (HDH) technology: Novel wheat straw packing and configuration optimization. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 47(1), pp.
11957–11975. https://doi.org/10.1080/15567036.2025.2504541
Guan, B., Liu, X. and Zhang, T., 2021. Exergy analysis on optimal desiccant solution flow rate in heat exchanger for air dehumidification using liquid desiccant. International Journal of Refrigeration, 128, pp. 129-138. https://doi.org/10.1016/j.ijrefrig.2021.03.024
Juarez, R.A., Xaman, J., Gabrierla, A.G. and Lopez, I.H., 2015. Numerical study of heat and mass transfer in a solar still device: Effect of the glass cover. Desalination, 359, pp. 200-211. https://doi.org/10.1016/j.desal.2014.12.034
Kabeel, A.E., Diab, M.R., Elazab, M.A. and El-Said, E.M.S., 2022. Solar powered hybrid desalination system using a novel evaporative humidification tower: Experimental investigation. Solar Energy Materials and Solar Cells, 248, P. 112012. https://doi.org/10.1016/j.solmat.2022.112012
Kaood, A., Abou-Deif, T., Eltahan, H., Yehia, M.A. and Khalil, E.E., 2019. Numerical investigation of heat transfer and friction characteristics for turbulent flow in various corrugated tubes. Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy, 233(4). 1 https://doi.org/10.1177/0957650918806407
Kays, W.M., Crawford, M.E. and Weigand, B., 2004. Convective heat and mass transfer. 4th ed. McGraw-Hill. ISBN-13: 978-0072468762.
Kline, S.J. and McClintock, F.A., 1953. Describing uncertainties in single sample experiments, Mech. Eng. 75, pp. 3–8.
Lafta, A.M. and Amori, K.E., 2022. Field study of absorbent media effect on the yield of solar desalination for Iraqi marsh water. International Review of Mechanical Engineering, 16(6), pp. 277-286. https://doi.org/10.15866/ireme.v16i6.22038
Li, Y.J., Yang, Y.Y., Luo, B.G., He, S.B., Liu, C., Chen, Y., Chen, P., Xu, Y.T. and Li, Y.W., 2025. Polyphenolic mechanochemistry-mediated liquid metal hydrogels for efficient solar-powered desalination and electricity generation. Advanced Functional Materials, 36(30), P. 28898. https://doi.org/10.1002/adfm.202528898
Mahmoudi, A., Valipour, M.S. and Rashidi, S., 2025. Potentials of porous materials and thermal control system for performance enhancement of humidification-dehumidification desalination unit powered by solar dish collector: Experimental study with 4E analysis. International Communications in Heat Mass Transfer, 164, P. 108958.
https://doi.org/10.1016/j.icheatmasstransfer.2025.108958
Manesh, M.H.K., Davadgaran, S., Rabeti, S.A.M. and Blanco-Marigorta, A.M., 2024. Optimal 4E evaluation of an innovative solar-wind cogeneration system for sustainable power and fresh water production based on integration of microbial desalination cell, humidification-dehumidification, and reverse osmosis desalination. Energy, 297, P. 131256.
https://doi.org/10.1016/j.energy.2024.131256
Messaouda, A., Hamdi, M. and Lazaar, M., 2026. Experimental thermal analysis of a clay-based solar desalination system enhanced with phase change material. Applied Thermal Engineering, 292, P. 130383. https://doi.org/10.1016/j.applthermaleng.2026.130383
Rahbar, N. and Esfahani, J., 2012a. Productivity estimation of a single-slope solar still: Theoretical and numerical analysis. Energy, 49, pp. 289–297. https://doi.org/10.1016/j.energy.2012.10.023
Rahbar, N. and Esfahani, J.A., 2012b. Estimation of convective heat transfer coefficient in a single-slope solar still: a numerical study. Desalination and Water Treatment, 50(1–3), pp. 387–396. https://doi.org/10.1080/19443994.2012.720442
Rahimi-Ahar, Z., Hatamipour, M.S. and Ghalavand, Y., 2018. Experimental investigation of a solar vacuum humidification dehumidification (VHDH) desalination system. Desalination, 437, pp. 73-80. https://doi.org/10.1016/j.desal.2018.03.002
Rajaseenivasan, T. and Srithar, K., 2016. Potential of a dual purpose solar collector on humidification dehumidification desalination system. Desalination, 404, pp. 35–40. https://doi.org/10.1016/j.desal.2016.10.015
Rajaseenivasan, T., Shanmugam, R.K., Hareesh, V.M. and Srithar, K. 2016. Combined probation of bubble column humidification dehumidification desalination system using solar collectors. Energy, 116, pp. 459-469. http://dx.doi.org/10.1016/j.energy.2016.09.127
Rastogi, G., 2021. Thermoelectric cooler-supported water condensation system development method. Ilkogretim Online - Elementary Education Online, 20, pp. 5205-5212. https://doi.org/10.17051/ilkonline.2021.04.551
Sánchez-Sutil, F., and Cano-Ortega, A., 2021. Performance evaluation and comparative analysis of a DHT22 sensor for applications in Internet of Things. Sensors 21(10), P. 3503. https://doi.org/10.3390/s21103503
Shah, R.K. and London, A.L., 1978. Laminar flow forced convection in ducts. A source book for compact heat exchanger analytical data. Academic Press, New York, ISSBN-13: 978-0-12-020051-1
Shaikh, J.S. and Ismail, S., 2023. Performance evaluation of a solar humidification dehumidification desalination system employing a multistage bubble column dehumidifier. Solar Energy 263, P. 111933. https://doi.org/10.1016/j.solener.2023.111933
Tiwari, A. and Kumar, A., 2025. Humidification-dehumidification desalination system based on solar air and water heaters. Solar Energy 297, P. 113637. https://doi.org/10.1016/j.solener.2025.113637
Tuğan, V., İnallı, M. and Işık, E., 2025. Experimental analysis of a double-slope solar still integrated with parabolic trough solar collector using nanofluid. Thermal Science and Engineering Progress 67, P. 104094. https://doi.org/10.1016/j.tsep.2025.104094
Tourab, A.E., Blanco-Marigorta, A.M., Elharidi, A.M. and Suarez-Lopez, M.J., 2023. A novel configuration of hybrid reverse osmosis, humidification–dehumidification, and solar photovoltaic systems: modeling and exergy analysis. Journal of Marine Science Engineering, 12 (1), P. 19. https://doi.org/10.3390/jmse12010019
Wang, B., Shen, J., Zhu, W. and Wang, W., 2024. Analysis of heat pump operated two-stage humidification- dehumidification desalination system with subcooler and heat regenerator. Desalination, 581, P. 117593. https://doi.org/10.1016/j.desal.2024.117593
Wang, D.Y., Bu, Y.M., Wu, X., Owens, G. and Xu, H.L., 2026. A 3D printed cu evaporator support for record-high interfacial solar evaporation. Material Horizons. https://doi.org/10.1039/d5mh02102b
Welepe, H.J., Gunerhan, H. and Bilir, L., 2022. Humidifying solar collector for improving the performance of direct solar desalination systems: A theoretical approach. Applied Thermal Eng., 216, P. 119043. https://doi.org/10.1016/j.applthermaleng.2022.119043
Wu, P., Wu, X., Wang, Y., Xu, H. and Owens, G., 2022. A biomimetic interfacial solar evaporator for heavy metal soil remediation. Chemical Engineering Journal, 435 P. 143793. https://doi.org/10.1016/j.cej.2022.134793
Zhang, C.H., Yan, Y., Wu, Y.H., Liu, C., Huang, J., Hu, Y., Li, Y. and Yang, Z.Q., 2026. Phase-change-integrated magnetic porous carbon for synergistic magnetothermal and photothermal interfacial evaporation. Energy Conversion and Management, 349, P. 120813. https://doi.org/10.1016/j.enconman.2025.120813
Ziauddin, M., Alnaimat, F. and Mathew, B., 2025. Solar humidification and dehumidification system: Integrating ultrasonic atomizer and solar still state-of-art. Sep. Purif. Technol. 378, P. 134550. https://doi.org/10.1016/j.seppur.2025.134550
Zubair, S.M. and Antar, M.A., Elmutasim, S.M., Lawal D.U., 2018. Performance evaluation of humidification-dehumidification (HDH) desalination systems with and without heat recovery options: an experimental and theoretical investigation. Desalination 436, pp. 161–175. https://doi.org/10.1016/j.desal.2018.02.018