Optimisation of a high-efficiency solar-driven organic rankine cycle for applications in the built environment

Energy security, pollution and sustainability are major challenges presently facing the international community, in response to which increasing quantities of renewable energy are to be generated in the urban environment. Consequently, recent years have seen a strong increase in the uptake of solar technologies in the building sector. In this work, the potential of a solar combined heat and power (CHP) system based on an organic Rankine cycle (ORC) engine is investigated in a domestic setting. Unlike previous studies that focus on the optimisation of the ORC subsystem, this study performs a complete system optimisation considering both the design parameters of the solar collector array and the ORC engine simultaneously. Firstly, we present thermodynamic models of different collectors, including flat-plate and evacuated-tube designs, coupled to a non-recuperative sub-critical ORC architecture that delivers power and hot water by using thermal energy rejected from the engine. Optimisation of the complete system is first conducted, aimed at identifying operating conditions for which the power output is maximised. Then, hourly dynamic simulations of the optimised system configurations are performed to complete the system sizing. Results are presented of: (i) dynamic 3-D simulations of the solar collectors together with a thermal energy storage tank, and (ii) of an optimisation analysis to identify the most suitable working fluids for the ORC engine, in which the configuration and operational constraints of the collector array are considered. The best performing working fluids (R245fa and R1233zd) are then chosen for a whole-system annual simulation in a southern European climate. The system configuration combining an evacuated-tube collector array and an ORC engine is found to be best-suited for electricity prioritisation, delivering an electrical output of 3,605¿kWh/year from a 60¿m2 collector array. In addition, the system supplies 13,175¿kWh/year in the form of domestic hot water, which is equivalent to more than 6 times the average annual household demand. A brief cost analysis and comparison with photovoltaic (PV) systems is also performed, where despite the lower PV investment cost per kWel, the levelised energy costs of the different systems are found to be similar if the economic value of the thermal output is taken into account. Finally, a discussion of the modelled solar-CHP systems results shows how these could be used for real applications and extended to other locationsPeer ReviewedPostprint (updated version

Off-design operation of ORC engines with different heat exchanger architectures in waste heat recovery applications

Organic Rankine cycle (ORC) engines in waste-heat recovery applications experience variable heat-source conditions (i.e. temperature and mass flow rate variations). Therefore maximising the ORC system performance under off-design conditions is of key importance, for the financial viability and wider adoption of these systems. In this paper, the off-design performance of an ORC engine with screw expander and two heat exchanger (HEXs) architectures is investigated, while recovering heat from an internal combustion engine (ICE). Firstly, nominal system sizing results indicate that the screw expander isentropic efficiency exceeds 80%, while the plate HEXs (PHEXs) heat transfer area requirements are 50% lower, than the respective ones for double pipe (DPHEX) design. Next, the ORC engine operation is optimised at part-load (PL) ICE conditions. Although, the HEXs heat transfer coefficients decrease with part-load, the total HEX effectiveness increases, due to higher temperature difference across the working fluids. Findings also reveal that the PHEX performance is less sensitive to the off-design operation. Off-design power output maps indicate that the optimised ORC engine PL reduces to 72%, for ICE PL of 60%, while ORC engines with PHEXs generate slightly more power, for the same heat source conditions. Overall, the modelling tool developed can predict ORC performance over an operating envelope and allows the selection of optimal designs and sizes of ORC HEXs and expanders

Off-design comparison of subcritical and partial evaporating ORCs in quasi-steady state annual simulations

The subcritical ORC (SCORC) is considered the industry standard due to its simple configuration, acceptable efficiency and low costs. However, it is known that alternative ORC configurations have the potential to increase efficiency. A cycle modification which closely resembles the SCORC is the partial evaporating ORC (PEORC), where a two-phase mixture of liquid-vapour enters the expander instead of superheated vapour. In theoretical studies at design conditions, higher power outputs are achieved for the PEORC compared to the SCORC. This work aims to go a step further by investigating the performance of the SCORC and PEORC under time-dependent operating conditions. A direct comparison between the SCORC and PEORC is made for identically sized systems using as input the waste heat stream of a waste incinerator plant and the changing ambient conditions. Performance maps of both cycle configurations are compiled and the benefit of an expander operating at variable speed is briefly discussed. The results indicate that for the specific case under investigation, the PEORC has an increased annually averaged net power output of 9.6% compared to the SCORC. Use of annually averaged input conditions results in an overestimation of the net power output for both the SCORC and PEORC, and furthermore, the relative improvement in power output for the PEORC is reduced to 6.8%. As such, the use of time-averaged conditions when comparing cycle architectures should preferably be avoided

Chemical and Biological Characterization of the Anticancer Potency of \u3ci\u3eSalvia fruticosa\u3c/i\u3e in a Model of Human Malignant Melanoma

Malignant melanoma is one of the most aggressive types of skin cancer with an increasing incidence worldwide. Thus, the development of innovative therapeutic approaches is of great importance. Salvia fruticosa (SF) is known for its anticancer properties and in this context, we aimed to investigate its potential anti-melanoma activity in an in vitro model of human malignant melanoma. Cytotoxicity was assessed through a colorimetric-based sulforhodamine-B (SRB) assay in primary malignant melanoma (A375), non-malignant melanoma epidermoid carcinoma (A431) and non-tumorigenic melanocyte neighbouring keratinocyte (HaCaT) cells. Among eight (8) different fractions of S. fruticosa extracts (SF1-SF8) tested, SF3 was found to possess significant cytotoxic activity against A375 cells, while A431 and HaCaT cells remained relatively resistant or exerted no cytotoxicity, respectively. In addition, the total phenolic (Folin–Ciocalteu assay) and total flavonoid content of SF extracts was estimated, whereas the antioxidant capacity was measured via the inhibition of tert-butyl hydroperoxide-induced lipid peroxidation and protein oxidation levels. Finally, apoptotic cell death was assessed by utilizing a commercially available kit for the activation of caspases - 3, - 8 and - 9. In conclusion, the anti-melanoma properties of SF3 involve the induction of both extrinsic and intrinsic apoptotic pathway(s), as evidenced by the increased activity levels of caspases - 8, and - 9, respectively

Ofeleein i mi Vlaptin-Volume II: Immunity Following Infection or mRNA Vaccination, Drug Therapies and Non-Pharmacological Management at Post-Two Years SARS-CoV-2 Pandemic.

The persistence of the coronavirus disease 2019 (COVID-19) pandemic has triggered research into limiting transmission, morbidity and mortality, thus warranting a comprehensive approach to guide balanced healthcare policies with respect to people's physical and mental health. The mainstay priority during COVID-19 is to achieve widespread immunity, which could be established through natural contact or vaccination. Deep knowledge of the immune response combined with recent specific data indicates the potential inferiority of induced immunity against infection. Moreover, the prevention of transmission has been founded on general non-pharmacological measures of protection, albeit debate exists considering their efficacy and, among other issues, their socio-psychological burden. The second line of defense is engaged after infection and is supported by a plethora of studied agents, such as antibiotics, steroids and non-steroid anti-inflammatory drugs, antiviral medications and other biological agents that have been proposed, though variability in terms of benefits and adverse events has not allowed distinct solutions, albeit certain treatments might have a role in prevention and/or treatment of the disease. This narrative review summarizes the existing literature on the advantages and weaknesses of current COVID-19 management measures, thus underlining the necessity of acting based on the classical principle of "ofeleein i mi vlaptin", that is, to help or not to harm

Genetic prediction of ICU hospitalization and mortality in COVID-19 patients using artificial neural networks

There is an unmet need of models for early prediction of morbidity and mortality of Coronavirus disease-19 (COVID-19). We aimed to a) identify complement-related genetic variants associated with the clinical outcomes of ICU hospitalization and death, b) develop an artificial neural network (ANN) predicting these outcomes and c) validate whether complement-related variants are associated with an impaired complement phenotype. We prospectively recruited consecutive adult patients of Caucasian origin, hospitalized due to COVID-19. Through targeted next-generation sequencing, we identified variants in complement factor H/CFH, CFB, CFH-related, CFD, CD55, C3, C5, CFI, CD46, thrombomodulin/THBD, and A Disintegrin and Metalloproteinase with Thrombospondin motifs (ADAMTS13). Among 381 variants in 133 patients, we identified 5 critical variants associated with severe COVID-19: rs2547438 (C3), rs2250656 (C3), rs1042580 (THBD), rs800292 (CFH) and rs414628 (CFHR1). Using age, gender and presence or absence of each variant, we developed an ANN predicting morbidity and mortality in 89.47% of the examined population. Furthermore, THBD and C3a levels were significantly increased in severe COVID-19 patients and those harbouring relevant variants. Thus, we reveal for the first time an ANN accurately predicting ICU hospitalization and death in COVID-19 patients, based on genetic variants in complement genes, age and gender. Importantly, we confirm that genetic dysregulation is associated with impaired complement phenotype.- Pfizer Pharmaceuticals(undefined

Optimisation of high-efficiency combined heat and power systems for distributed generation

Distributed combined heat and power (CHP) systems have the potential to cover a significant amount of the global energy requirements for power, and heating. Small-to-medium scale CHP systems, in the built environment and in the industry (up to a few MWs), are typically driven by internal combustion engines (ICE). In CHP-ICE systems, more than 55% of the energy input is transferred as heat in the exhaust-gas stream and the jacket water cooling circuit. Unless these thermal outputs are utilised, the energy will be released to the atmosphere as waste heat, deteriorating the system’s efficiency. Organic Rankine cycle (ORC) engines are a promising heat-to-power technology, for converting waste heat into power. Therefore, coupling ORC engines as bottoming cycles to CHP-ICEs can maximise overall system efficiency, and reduce energy costs. In this thesis, the design of ICE-ORC CHP systems is investigated from thermodynamic, operating and economic perspectives, aiming to fully unlock the potential of such advanced high-efficiency cogeneration systems. An integrated ICE-ORC CHP optimisation tool is developed, which, unlike previous studies, captures the performance trade-offs between the two interacting engines, to optimise the combined system performance. A dynamic ICE model is developed and validated, along with a steady-state model of subcritical recuperative ORC engines. Multiple working fluids are investigated, along with naturally aspirated and turbocharged ICEs. By optimising the combined ICE-ORC CHP system simultaneously: i) the total power output increases by up to 30%, in comparison to the conventional approach where the two engines are optimised separately; ii) the electrical efficiency increases by up to 21%, in comparison to the stand-alone ICE; and iii) in the integrated system the ICE operation is adjusted to promote the ORC power output, which generates up to 15% of the total power, improving fuel efficiency. When focusing on maximising power output only, this comes at the cost of higher fuel consumption. In contrast, when optimising the integrated ICE-ORC CHP system for specific fuel consumption (SFC), the fuel consumption decreases by up to 17%. These findings prove that by taking a holistic approach in the design of ICE-ORC CHP systems, considering the combined system interactions, these can generate more power, with lower fuel consumption and costs. ORC engines in ICE-ORC CHP systems will experience variable heat-source conditions (temperature and mass flow are), while the ICE load fluctuates. To maximise the running hours of ORC engines, and improve their economic proposition, the system should maintain high efficiency, not only at the design point, but also at off-design operation. An off-design optimisation tool is therefore developed to generate optimised off-design operation maps. This work differs from previous studies in that the tool considers explicitly the time-varying operational characteristics and interactions of the ORC engine components in the integrated system. Double-pipe (DPHEX) and plate-frame heat exchanger (PHEX) models are used for sizing the ORC evaporator and condenser, and piston and screw expander models for sizing the expander. The ORC system is first sized for full-load ICE operation (design point). Then, ICE part-load (PL) conditions are obtained and new ORC operating points are optimised. Results reveal that the ORC engine power output is underestimated by up to 17%, when the off-design operational characteristics of the components are not considered. The piston expander efficiency increases by up to 16% at PL operation, while the ORC thermal efficiency increases by up to 7% at off-design operation. Optimised ORC engines with screw expanders operate always with two expansion stages. Although the latter generate slightly more power at their design point than when using piston machines, pistons perform better at off-design conditions. ORC engines with PHEXs generate 5-12% more power than DPHEX designs, while having U-values almost double that of DPHEXs. Although, heat transfer coefficients decrease by 25-30% at off-design, the HEX effectiveness increases, by up to 15%. By considering the time-varying characteristics of the ORC components, as the ICE PL reduces, the optimised ORC engine power output decreases at a lower rate: at ICE PL of 60%, the optimised ORC engine with fluids, such as R1233zd, operates at 77% of its nominal capacity (with piston expanders). An ORC thermoeconomic optimisation tool is then developed. Unlike other studies where the component types are predefined, the tool scans alternative components’ typologies, sizes, and configurations, to obtain the best-performing design. New cost correlations are presented to assist with predicting ORC costs. ORC engines optimised for maximum power output have the highest SICs, falling in the range of 1,000-7,500 GBP/kW for piston expanders, and 1,500-5,500 GBP/kW for screw expanders, due to high HEX areas, and high volumetric flow rates. In contrast, when minimising SIC, power output reduces by 15-50%, but the cost also reduces by up to 35%. In the optimised designs, the evaporator is selected to be a PHEX, the condenser is a DPHEX, whilst ORC engines with screw machines operate with two-stage expansion. Multi-objective optimisation reveals optimal ORC systems with a range of power outputs between 70-100 kW, for which increasing power by 33%, results in an increase of SIC of less than 10%. This indicates a promising range of capacities for next-generation ORC engines. ORC engines optimised for high power output result in high net present value (NPV), but also high discounted payback period (DPP). In contrast, engines optimised for low SIC achieve DPPs of 2.8-6 years, making them an attractive investment. Overall, these findings can be used by ICE and ORC engine manufacturers, and integrators, to inform component design decisions, and by ORC plant operators to maximise their system performance, under variable operating conditions.Open Acces

N-phenylpyrrole as a scaffold of aldose reductase inhibitors: Design, synthesis, in vitro biological evaluation and calculation of physicochemical properties

Aldose reductase (ALR2) has been characterized as both a “dream” and a “dread” therapeutic target. Its initial implication in diabetes mellitus long-term complications, followed by findings for a central role in inflammation and cancer signaling pathways have established ALR2 as a dreamy target, though the apparent difficulty in discovering effective inhibitors in clinical trials, while having a favourable profile in preclinical studies, even after forty years of research on the field, leaves researchers in awe. Subsequently, with ALR2 as a key-enzyme in a number of common pathological conditions, the search for novel aldose reductase inhibitors (ARIs) has become the epicenter of many studies. Most of the known ARIs are carboxylic acid derivatives or cyclic spiroimides and have been presented with unwanted characterists such as toxicity or low in vivo efficacy. Recent studies are therefore orientated towards novel chemotypes in order to combine a satisfying pharmacodynamic and pharmacokinetic profile. In our previous studies a bioisosteric replacement of a carboxylic acid group was accomplished with the use of the non-classical bioisosteric groups 2,6-difluorophenol and tetrazole in the scaffold of a N-phenylpyrrole. Since those derivatives are expected to present extended ionization in physiological pH, a replacement of the acidic group was attempted, so that the novel derivatives would have improved physicochemical properties and the ability to readily penetrate biological membranes. By using the ratio logD/logP as an index, we selected substitutions where logD logP. Under this framework, 3-benzoyl-N-phenylpyrrole derivatives were synthesized, incorporating groups that have the ability of hydrogen bonding as a donor or acceptor and are mostly non-ionized in physiological pH. From the synthesized compounds, the 2-fluorophenol derivative (17) was selected for further optimization based on its optimal activity and physicochemical properties. Substitutions over the 3-benzoyl ring were explored, as well as a second pyrrole substitution. The routes of synthesis have been reported in the literature or are modifications of them. The most significant modifications that were attempted concern an aromatic nitro-group reduction in the synthesis of compound 9, a Clauson-Kaas pyrrole formation in the synthesis of compounds 10-13 and the regio-specific, or not, Friedel-Crafts reaction of the intermediates 10-13. From the synthesized compounds, the bis-substituted analogue 41 exhibited the optimal ALR2 inhibitory activity, on partially purified rat lens ALR2, with an IC50 value in the low micromolar range (IC50 = 1.04 μΜ). As a measure of selectivity, the inhibitory activity of the closely-related enzyme aldehyde reductase (ALR1) was evaluated on partially purified rat kidney ALR1. The most active compounds were studied and compound 41 appeared as the most selective with selectivity index value IC50[ALR1]/IC50[ALR2] = 19.60. We also proceeded to a computational evaluation of key physicochemical properties in order to estimate the drug-likeness of the most active compounds, with satisfying results. Summarizing the above, the development of the novel potent and selective ARI (41) was accomplished, that besides micromolar inhibitory activity also possesses improved physicochemical properties and can be used as a lead compound in the design of novel, more efficacious ARIs.Η αναγωγάση της αλδόζης (ALR2) έχει χαρακτηριστεί ως ένας «ονειρεμένος» αλλά και ταυτόχρονα «τρομακτικός» στόχος για τη θεραπευτική. Η αρχική ανάμιξή της στην παθογένεση των χρόνιων επιπλοκών του σακχαρώδους διαβήτη και η στη συνέχεια συσχέτισή της με σηματοδοτικά μονοπάτια που εμπλέκονται στη φλεγμονή και σε καρκίνους την έχουν καταστήσει ως έναν ονειρεμένο στόχο, αλλά ταυτόχρονα η δυσκολία στην εύρεση αποτελεσματικών αναστολέων της σε κλινικές δοκιμές, παρά την προκλινική αποτελεσματικότητά τους, ακόμη και μετά από σαράντα χρόνια διερεύνησης, προκαλεί ένα σχετικό δέος. Επομένως, με την ALR2 ως ένζυμο κλειδί στην παθογένεση ενός αριθμού διαδεδομένων παθήσεων, η διερεύνηση για την εύρεση νέων αναστολέων της ALR2 (ARIs) είναι στο επίκεντρο ερευνητικών προσπαθειών. Οι αναστολείς που έχουν αναφερθεί μέχρι σήμερα στην βιβλιογραφία αποτελούν κατά κύριο λόγο παράγωγα καρβοξυλικών οξέων ή κυκλικών σπειροϊμιδίων και τους αποδίδονται χαρακτηριστικά που αποτρέπουν την ευρεία χρήση τους λόγω εμφάνισης τοξικότητας ή μικρής in vivo αποτελεσματικότητας. Νεότερες μελέτες προσανατολίζονται λοιπόν προς νέους χημειότυπους που δε θα εμφανίζουν τα παραπάνω χαρακτηριστικά, ώστε να επιτευχθεί ένα ικανοποιητικό φαρμακοκινητικό και φαρμακοδυναμικό προφίλ. Έχοντας μελετήσει στο παρελθόν την αντικατάσταση της ομάδας του καρβοξυλικού οξέος με τη μη κλασική βιοϊσοστερή ομάδα του τετραζολίου και της 2,6-διφθοροφαινόλης σε Ν-φαινυλο-υποκατεστημένα πυρρολικά παράγωγα με ενθαρρυντικά αποτελέσματα, στην παρούσα εργασία έγινε μια προσπάθεια για την παραπέρα βελτίωση των φυσικοχημικών ιδιοτήτων αυτών. Καθώς τα παράγωγα αυτά, όντας ιονισμένα σε σημαντικό ποσοστό σε φυσιολογικό pH, αναμένεται να παρουσιάζουν προβληματική διαπερατότητα στους ιστούς και χρησιμοποιώντας ως δείκτη για τη διαπερατότητα διαμέσου μεμβρανών το λόγο logD/logP προχωρήσαμε στο σχεδιασμό ενώσεων όπου ο λόγος αυτός τείνει στη μονάδα. Στα πλαίσια αυτά συντέθηκαν παράγωγα του 3-βενζοϋλο-Ν-φαινυλοπυρρολίου με υποκαταστάσεις, επί του Ν-φαινυλίου, ομάδες που φέρουν την ιδιότητα σχηματισμού δεσμών υδρογόνου ως δέκτες ή ως δότες και είναι ελάχιστα ή καθόλου ιονισμένες σε φυσιολογικό pH. Από αυτές, επιλέχθηκε για περαιτέρω διερεύνηση το παράγωγο της 2-φθοροφαινόλης (17) καθώς εμφάνισε την καλύτερη δράση σε συνδυασμό με ευνοϊκές φυσικοχημικές ιδιότητες. Στη συνέχεια επιχειρήθηκαν υποκαταστάσεις επί του 3-βενζοϋλο-υποκαταστάτη, καθώς και δεύτερη υποκατάσταση επί του πυρρολικού δακτυλίου. Οι ενώσεις συντέθηκαν με την εφαρμογή γνωστών μεθόδων της βιβλιογραφίας καθώς και τροποποιήσεων αυτών. Οι σημαντικότερες τροποποιήσεις που επιχειρήθηκαν αφορούν την αντίδραση αναγωγής αρωματικής νιτρο-ομάδας κατά τη σύνθεση του παραγώγου 9, την αντίδραση σχηματισμού πυρρολικού δακτυλίου τύπου Clauson-Kaas κατά τη σύνθεση των παραγώγων 10-13 και regio-εκλεκτική ή μη αντίδραση Friedel-Crafts στα ενδιάμεσα 10-13. Από τις ενώσεις που συντέθηκαν, τη βέλτιστη αναστολή επί ενζυμικού παρασκευάσματος ALR2 από φακούς επιμύων εμφάνισε το δισ-υποκατεστημένο παράγωγο 41 με IC50 = 1,04 μΜ. Επίσης, υπολογίσθηκε η εκλεκτικότητα των ενώσεων σε σχέση με το συγγενές ένζυμο αναγωγάση των αλδεϋδών (ALR1), επί ενζυμικού παρασκευάσματος της ALR1 από νεφρούς επιμύων. Μελετήθηκαν οι δραστικότερες ενώσεις και ως περισσότερο εκλεκτική αναδείχθηκε η ένωση 41, με δείκτη εκλεκτικότητας IC50[ALR1]/IC50[ALR2] = 19,60. Υπολογίζοντας τέλος τις τιμές σημαντικών φυσικοχημικών ιδιοτήτων των ενώσεων έγινε μια πρώτη εκτίμηση για την εν δυνάμει φαρμακοομοιότητά τους, αποδίδοντας θετικά αποτελέσματα για το σύνολο αυτών. Συμπερασματικά, επιτεύχθηκε η σύνθεση πρωτότυπου και εκλεκτικού ARI (41), ο οποίος κατέχει βελτιωμένες φυσικοχημικές ιδιότητες και μπορεί να αποτελέσει αρχική οδηγό ένωση για την εύρεση νέων και αποτελεσματικότερων ARIs

Optimisation of a high-efficiency solar-driven organic rankine cycle for applications in the built environment

Energy security, pollution and sustainability are major challenges presently facing the international community, in response to which increasing quantities of renewable energy are to be generated in the urban environment. Consequently, recent years have seen a strong increase in the uptake of solar technologies in the building sector. In this work, the potential of a solar combined heat and power (CHP) system based on an organic Rankine cycle (ORC) engine is investigated in a domestic setting. Unlike previous studies that focus on the optimisation of the ORC subsystem, this study performs a complete system optimisation considering both the design parameters of the solar collector array and the ORC engine simultaneously. Firstly, we present thermodynamic models of different collectors, including flat-plate and evacuated-tube designs, coupled to a non-recuperative sub-critical ORC architecture that delivers power and hot water by using thermal energy rejected from the engine. Optimisation of the complete system is first conducted, aimed at identifying operating conditions for which the power output is maximised. Then, hourly dynamic simulations of the optimised system configurations are performed to complete the system sizing. Results are presented of: (i) dynamic 3-D simulations of the solar collectors together with a thermal energy storage tank, and (ii) of an optimisation analysis to identify the most suitable working fluids for the ORC engine, in which the configuration and operational constraints of the collector array are considered. The best performing working fluids (R245fa and R1233zd) are then chosen for a whole-system annual simulation in a southern European climate. The system configuration combining an evacuated-tube collector array and an ORC engine is found to be best-suited for electricity prioritisation, delivering an electrical output of 3,605¿kWh/year from a 60¿m2 collector array. In addition, the system supplies 13,175¿kWh/year in the form of domestic hot water, which is equivalent to more than 6 times the average annual household demand. A brief cost analysis and comparison with photovoltaic (PV) systems is also performed, where despite the lower PV investment cost per kWel, the levelised energy costs of the different systems are found to be similar if the economic value of the thermal output is taken into account. Finally, a discussion of the modelled solar-CHP systems results shows how these could be used for real applications and extended to other locationsPeer Reviewe

Bioactive Profile of Distilled Solid By-Products of Rosemary, Greek Sage and Spearmint as Affected by Distillation Methods

By-products of essential oils (EOs) in the industry represent an exploitable material for natural and safe antioxidant production. One representative group of such by-products is distilled solid residues, whose composition is properly modulated by the distillation method applied for the recovery of EOs. Recently, in terms of Green Chemistry principles, conventional extraction and distillation processes are considered outdated and tend to be replaced by more environmentally friendly ones. In the present study, microwave-assisted hydro-distillation (MAHD) was employed as a novel and green method for the recovery of EOs from three aromatic plants (rosemary, Greek sage and spearmint). The method was compared to conventional ones, hydro-distillation (HD) and steam-distillation (SD), in terms of phytochemical composition of distilled solid residues, which was estimated by spectrophotometric and chromatographic methods. Total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity (ABTS, DPPH and FRAP) results highlighted the distilled solid residues as good sources of antioxidants. Moreover, higher antioxidant activity was achieved for MAHD extracts of solid residues in comparison to HD and SD extracts. A metabolomics approach was carried out on the methanolic extracts of solid residues obtained by different distillation methods using LC-MS analysis followed by multivariate data analysis. A total of 29 specialized metabolites were detected, and 26 of them were identified and quantified, presenting a similar phenolic profile among different treatments, whereas differences were observed among different species. Rosmarinic acid was the most abundant phenolic compound in all extracts, being higher in MAHD extracts. In rosemary and Greek sage extracts, carnosol and carnosic acid were quantified in significant amounts, while trimers and tetramers of caffeic acid (salvianolic acids isomers) were identified and quantified in spearmint extracts, being higher in MAHD extracts. The obtained results pointed out that MAHD extracts of distilled solid by-products could be a good source of bioactives with potential application in the food, pharmaceutical and cosmetic industries, contributing to the circular economy