Dirker, JacoJuggurnath, DikshaKaya, AlihanOsowade, Emmanuel A.Simpson, MichaelLecompte, StevenNoori Rahim Abadi, Seyyed Mohammad AliVoulgaropoulos, VictorAdelaja, Adekunle O.Dauhoo, M. ZaidKhoodaruth, AbdelObayopo, Surajudeen OlanrewajuOlakoyejo, Olabode T.Elahee, Mohammad K.De Paepe, MichelMeyer, Josua P.Markides, Christos N.2020-08-182020-08-182019-03-05Dirker J, Juggurnath D, Kaya A, Osowade EA, Simpson M, Lecompte S, Noori Rahim Abadi SMA, Voulgaropoulos V, Adelaja AO, Dauhoo MZ, Khoodaruth A, Obayopo SO, Olakoyejo OT, Elahee MK, De Paepe M, Meyer JP and Markides CN (2019) Thermal Energy Processes in Direct Steam Generation Solar Systems: Boiling, Condensation and Energy Storage – A Review. Frontiers in Energy Research 6:147. DOI: 10.3389/fenrg.2018.00147.2296-598X (online)10.3389/fenrg.2018.00147http://hdl.handle.net/2263/75786Data supporting this publication can be obtained on request from ceplab@ imperial.ac.uk.Direct steam generation coupled is a promising solar-energy technology, which can reduce the growing dependency on fossil fuels. It has the potential to impact the power-generation sector as well as industrial sectors where significant quantities of process steam are required. Compared to conventional concentrated solar power systems, which use synthetic oils or molten salts as the heat transfer fluid, direct steam generation offers an opportunity to achieve higher steam temperatures in the Rankine power cycle and to reduce parasitic losses, thereby enabling improved thermal efficiencies. However, its practical implementation is associated with non-trivial challenges, which need to be addressed before such systems can become more economically competitive. Specifically, important thermal-energy processes take place during flow boiling, flow condensation and thermal-energy storage, which are highly complex, multi-scale and multi-physics in nature, and which involve phase-change, unsteady and turbulent multiphase flows in the presence of conjugate heat transfer. This paper reviews our current understanding and ability to predict these processes, and the knowledge that has been gained from experimental and computational efforts in the literature. In addition to conventional steam-Rankine cycles, the possibility of implementing organic Rankine cycle power blocks, which are relevant to lower operating temperature conditions, are also considered. This expands the focus beyond water as the working fluid, to include refrigerants also. In general, significant progress has been achieved in this space, yet there remain challenges in our capability to design and to operate high-performance and low-cost systems effectively and with confidence. Of interest are the flow regimes, heat transfer coefficients and pressure drops that are experienced during the thermal processes present in direct steam generation systems, including those occurring in the solar collectors, evaporators, condensers and relevant energy storage schemes during thermal charging and discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.en© 2019 Dirker, Juggurnath, Kaya, Osowade, Simpson, Lecompte, Noori Rahim Abadi, Voulgaropoulos, Adelaja, Dauhoo, Khoodaruth, Obayopo, Olakoyejo, Elahee, De Paepe, Meyer and Markides. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Concentrated solar powerDirect steam generationFlow boilingFlow condensationEnergy storageEngineering, built environment and information technology articles SDG-04SDG-04: Quality educationEngineering, built environment and information technology articles SDG-07SDG-07: Affordable and clean energyEngineering, built environment and information technology articles SDG-08SDG-08: Decent work and economic growthEngineering, built environment and information technology articles SDG-09SDG-09: Industry, innovation and infrastructureEngineering, built environment and information technology articles SDG-12SDG-12: Responsible consumption and productionEngineering, built environment and information technology articles SDG-13SDG-13: Climate actionArticle