ABSTRACT In many arid and water‐scarce regions, the need for new methods of desalination that are inexpensive and environmentally friendly remains high as access to drinking water continues to be insufficient. Solar stills offer a viable solution, but their widespread use is limited due to low freshwater production and poor thermal performance. The current research investigates a traditional single‐slope solar still (TSS), a double‐slope solar still, and four modified double‐slope solar stills (with iron scraps, black Kanchey, shaving blade fins, and pebbles as thermal energy storage, respectively) (MSS‐1, MSS‐2, MSS‐3, MSS‐4, MSS‐5). In the study, MSS‐1 was the unmodified double‐slope system. The daily water yield in mL/day for various stills was recorded as follows: TSS: 1330, MSS‐1: 1890, MSS‐2: 2370, MSS‐3: 2450, MSS‐4: 3150, and MSS‐5: 2250. The MSS‐4 system (shaving blades) outperforms TSS, presenting the highest yield, increasing productivity by 136%. The peak energy efficiency for different solar stills was as follows: TSS: 29%, MSS‐1: 36.6%, MSS‐2: 46.5%, MSS‐3: 49.5%, MSS‐4: 52.5%, and MSS‐5: 38.3%, with MSS‐4 achieving the highest value of 58.5%. The maximum exergy efficiency recorded was TSS: 10%, MSS‐1: 11.5%, MSS‐2: 15.5%, MSS‐3: 19.6%, MSS‐4: 23.7%, and MSS‐5: 17.4%. According to the economic evaluation, the lowest cost of freshwater production for the modified solar stills was for MSS‐4 (Rs. 0.98/L), and was less than Rs. 1.85/L for TSS, which is a reduction of about 46.2%. The findings demonstrate that integrating a double‐slope configuration with thermal energy storage materials and an enhanced heat‐transfer surface area leads to a substantial improvement in freshwater yield.
ABSTRACT Effective thermal management is critical to ensure the safety, reliability, and performance of lithium‐ion battery modules under high thermal loads. While hybrid phase change material (PCM)–liquid cooling systems have been widely explored, the present study introduces a novel material‐level enhancement through the use of an Ag 2 O–ethylene glycol Nano fluid, whose application in battery thermal management remains largely unexplored. A compact 4S5P battery module comprising 21 700‐type lithium iron phosphate (LFP) cells (14 V, 22.5 Ah) is experimentally investigated under 1C, 1.5C, and 2C discharge rates, along with 1C charging conditions. The proposed hybrid BTMS integrates PCM with active liquid cooling using Ag 2 O Nano fluid at varying concentrations (1–5 wt.%), enabling a systematic evaluation of its thermo‐physical impact. The results demonstrate that, in the absence of thermal management, the module temperature rapidly increases to approximately 60°C at 2C, indicating severe thermal stress. In contrast, the proposed system significantly enhances heat dissipation, maintaining the maximum cell temperature within 30°C–32°C, thereby achieving a reduction of 5%. Furthermore, increasing nanoparticle concentration improves convective heat transfer, with optimal performance observed at 5 wt.%, reaching temperature to 29°C resulting in improved temperature uniformity across the module. Results demonstrate the effectiveness of Ag 2 O nanofluid relative to base fluid under the investigated operating conditions. This study not only demonstrates the feasibility of Ag 2 O‐based Nano fluids in BTMS but also provides a scalable and high‐performance thermal management solution for high‐power cylindrical battery modules in electric vehicles and energy storage systems.
ABSTRACT Rock bed thermal energy storage (RTES) systems are increasingly used as affordable and scalable solutions for low‐temperature heat storage. However, experimental investigations of magnetite packed beds under repeated charge–discharge cycles remain limited. This study experimentally evaluates the thermal performance of a horizontal cylindrical RTES system filled with magnetite and operated as a low‐temperature thermal battery for greenhouse applications. Two airflow strategies are compared over two successive cycles of charging and discharging: (i) unidirectional airflow during both charging and discharging (Model 1) and (ii) reversed airflow during discharge (Model 2). Thermal performance is analyzed through temperature stratification, heat transfer dynamics, energy recovery, and dimensionless performance indicators, including the Thermal Efficiency Index ( TEI ), Temperature Uniformity Index ( TUI ), Normalized Temperature Standard Deviation ( NTSD ), and Temperature Gradient Ratio ( TGR ). Results show that airflow reversal significantly enhances thermal propagation and heat extraction. Model 2 achieves a more pronounced thermal‐front response, generally higher TUI and TGR values, and higher energy recovery, delivering up to 30% more recovered heat during the first discharge period and approximately 15.79% more during the second discharge period compared with Model 1. Moreover, Model 2 exhibits higher TEI values across the investigated operating periods, with particularly noticeable advantages during the first discharge and second charging periods. These findings demonstrate that discharge flow reversal is an effective operating strategy for improving the responsiveness and heat‐recovery performance of low‐temperature magnetite RTES systems.
ABSTRACT Heat exchange between circulating working fluid and thermal storage medium is an essential process in thermodynamic cycles of energy storage systems. Thermophysical properties of the working fluids therefore play an important role in such systems. Conventional heat‐transfer fluids, such as water and thermal oil, have relatively constant specific heat capacities, whereas high pressure CO 2 varies significantly with temperature near the critical region. Such a difference causes a specific heat capacity mismatch between these fluids, leading to temperature difference increase along the heat exchanger. The large temperature difference also increases entropy generation. Here we propose a new method to reduce the irreversibility through the adjustment of equivalent specific heat capacity based on phase‐change latent heat. To validate such an approach, a steady‐state model counterflow heat exchanger was used for high‐pressure CO 2 at 10–15 MPa. Eight paraffins with phase‐transition temperatures from 40°C to 58°C were combined to give a phase‐change material mixture. A genetic algorithm optimized the paraffin proportions, proportional coefficient, and temperature‐shift parameter. The optimized phase change mixture closely matched the temperature‐dependent specific heat capacity profile of CO 2 within the investigated range. The best agreement occurred at 11 MPa. Under the same pinch‐point temperature difference, the mixed phase‐change material mixture showed a lower entropy‐generation rate than water. This trend persisted throughout the investigated pressure range. The optimal temperature‐shift parameters were 2.8°C, 4.6°C, and 5.2°C, corresponding to pinch‐point temperature differences of 3°C, 4°C, and 5°C, respectively. These results show that tailoring the effective specific heat capacity of the phase‐change mixture can reduce thermophysical mismatch and heat‐transfer irreversibility.
ABSTRACT This paper proposes direct charging of lithium‐ion batteries in electric vehicles (EVs) using standalone solar photovoltaic (PV) systems at distributed charging stations. A PV plant can be operated in an adaptive optimal mode to dynamically regulate its output power to match the aggregate charging power drawn by multiple lithium‐ion batteries, as reflected in the DC‐link voltage. To stabilize the DC‐link voltage and balance power between PV generation and battery load, a master–slave control strategy is used. In this setup, the DC‐link voltage controller acts as the master, generating a corrective duty cycle to reduce voltage changes. The MPPT (Maximum Power Point Tracking) controller, acting as the slave, provides the base duty cycle to extract the maximum power possible from the PV array. The resulting composite duty ratio drives a multiple‐phase interleaved boost DC–DC converter, improving power conversion efficiency and reducing input current ripple. A distributed phase‐shifted full‐bridge converter (PSFBC) is used to charge the batteries following the constant current–constant voltage (CC–CV) method. The proposed architecture is implemented using a modular three‐leg inverter, which is scalable and allows integration of higher‐rated PV arrays and additional battery charging channels without requiring any major modification in the control strategy, owing to the flexibility of the master–slave coordination mechanism. A multiple‐modular boost‐PSFB converter using four three‐phase inverter modules has been used for implementing the four‐phase IBC‐PSFB converter for 10.44 kW solar PV to charge four 72 V, 100 Ah Li‐ion batteries through MATLAB Simulink software. The control algorithm is also validated in real‐time using Typhoon‐HIL in virtual HIL mode for implementing a two‐phase IBC‐PSFB converter, based on a practical setup comprising a 2.2 kW solar PV system and two 72 V, 26 Ah Li‐ion batteries.
