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    A comprehensive review of miscellaneous heat transfer enhancement designs of phase change material integrated heat exchanger
    (Elsevier Ltd, 2025) Erdinç, M. Tahir; Dalgıç, İrem; Kutlu, Cagri; Dik, Abdullah; Tokgoz, Nehir; Su, Yuehong; Riffat, Saffa
    This comprehensive review focuses on the specific investigation of heat transfer enhancement with a primary objective of achieving more uniform melting/solidification within heat exchangers employing phase change materials (PCM). The paper begins highlighting the crucial role of heat exchangers and introduces the unique studies associated with achieving uniform phase changes. The main body of the paper seeks to explore heat transfer enhancement strategies, particularly within shell-and-tube structures and plate heat exchanger (PHE). Moreover, the study discusses the role of these strategies in achieving more uniform melting/solidification in phase change materials. Special attention is applied to examining advancements and methodologies aimed at optimizing heat transfer for improved performance in applications requiring control of phase changes. As a new contribution, the paper examines the application of PCM in PHEs, providing insights into their effectiveness in facilitating more uniform phase change and PCM usage in these heat exchangers. Notable improvements were also observed from literature studies with specific fin geometries, where longitudinal and spider-web-like structures reduced solidification times by as much as 63 % and enhanced melting uniformity by 47.9 %. Operational parameter optimization, particularly through increasing heat transfer fluid (HTF) inlet temperature by 10 °C, resulted in a 35 % decrease in charging time, underscoring the importance of temperature control in Thermal energy storage (TES) applications. The literature studies mentioned that enhanced PHE configurations, including corrugated and zigzag plate designs, have demonstrated up to nine times faster charging and discharging rates compared to traditional concentric systems due to increased surface area. This study provides essential insights for researchers and practitioners aiming to enhance heat exchanger designs for critical applications in thermal energy storages. © 2025 Elsevier Ltd
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    A study on the combination of crystallization-controllable phase change materials and solar-assisted heat pump for electricity demand shifting in space heating
    (Pergamon-Elsevier Science Ltd, 2025) Kutlu, Cagri; Erdinc, Mehmet Tahir; Dik, Abdullah; Chen, Ziwei; Lyu, Qinghua; Su, Yuehong; Riffat, Saffa
    Supercooled phase change materials offer a promising solution for space heating due to their ability to release latent heat upon crystallization initiation, even when stored at ambient temperatures. This unique property makes them ideal for solar-assisted space heating, where external activation enables on-demand heat release, addressing the critical need for energy-efficient heating solutions. In this study, a system promoting demand shifting is proposed, aiming to transfer energy consumption from morning and evening peak periods to daytime and high solar irradiance days, thereby enhancing the efficiency of solar heat pumps and reducing grid stress through the use of supercooled crystallization-controllable phase change materials. A model was developed, consisting of evacuated tube collectors, a buffer tank, heat storage tanks with crystallization-controllable phase change material, and a building heating demand model. The study introduces a novel system control methodology, focusing on an effective operation of tank shifting based on the heating requirement and solar energy availability. Real weather data were used to calculate system performance. With 50 m2 of collectors, a 1000-liter buffer tank, and a heat pump with a maximum output of 7 kW, the heat storage tanks are charged and discharged following the developed operational methodology. The system achieved a weekly coefficient of performance of 3.56 and successfully shifted electricity demand to solar hours, with only 28.5% of the total consumption occurring during domestic morning and evening peak times.
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    Comparative Analysis of Solar Photovoltaic/Thermal Assisted Heat Pump Systems Coupled with PCM Storage and EV Charging with Reference to the UK's National Carbon Intensity
    (Mdpi, 2025) Kutlu, Cagri; Dik, Abdullah; Erdinc, Mehmet Tahir; Su, Yuehong; Riffat, Saffa
    Emerging trends in heat pump (HP) and electric vehicle (EV) adoption within communities aim to reduce carbon emissions in the heating and transportation sectors. However, these technologies rely on grid electricity, whose carbon intensity varies over time. This study explores how the carbon-saving potential of these technologies can be further enhanced through demand-shifting operations and renewable energy integration. The research compares photovoltaic-thermal (PV/T) and hybrid solar heat pump systems that integrate EV charging and PCM-enhanced heat storage to improve space heating efficiency under low solar irradiance in the UK while reducing CO2 emissions. The study simulates solar collector configurations and sizes, combining PV modules and heat pumps to enhance system performance. Control systems synchronize operations with periods of low grid CO2 intensity, minimizing the environmental impact. The analysis evaluates PV/T systems, separate PV and thermal collectors, highlighting their energy efficiency and CO2 reduction potential. Control systems further optimize HP operation and EV charging during periods of high renewable energy availability, preventing uncontrolled use that could result in elevated emissions. Using real weather data and a detailed building model, the findings show that a solar-assisted HP with 100% thermal collectors achieves a daily COP of 3.49. Reducing thermal collectors to 60% lowers the COP to 2.57, but PV output compensates, maintaining similar emission levels. The system achieves the lowest emission with high-efficiency evacuated flat plate PV/T collectors.
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    Evaluate the validity of the empirical correlations of clearance and friction coefficients to improve a scroll expander semi-empirical model
    (Pergamon-Elsevier Science Ltd, 2020) Kutlu, Cagri; Erdinc, Mehmet Tahir; Li, Jing; Su, Yuehong; Pei, Gang; Gao, Guangtao; Riffat, Saffa
    This study presents a scroll expander modelling methodology for small scale power generation systems by combining scroll geometry and semi-empirical model. Although the semi-empirical model is quite popular, its dependence on several experimentally-determined scroll geometrical and operational parameters makes this approach inflexible for different capacities and operating conditions. Some studies have sought to improve its flexibility in terms of using different working fluids and more accurate empirical parameters, however, those improved models still depend on a considerable number of experimentally-obtained scroll parameters. Therefore, in this study, a practical methodology for a simpler semi-empirical model combined with the operational flexibility of the scroll geometry is presented. Firstly, the flow rates of mainstream and leakage flows are analysed, where a correlation between scroll clearance and pressure ratio is determined. Secondly, a simpler approach to the semi-empirical model of scroll expander is proposed, whereby dependent parameters have been reduced to two parameters by using scroll geometrical calculations. The model is further improved to predict the rotational speed and electricity output by considering the overall friction coefficient of the coupled expander-generator unit. The findings are then compared with the results of an experimental study. The results show that the effective clearance values between scrolls vary according to pressure ratios, increasing from 20 mm to 34 mm. Mass flow rate can be predicted within 10% deviation from the experimental results for the same inlet conditions and rotational speed at a transient state. Additionally, considering steady state conditions, modelling results show that the rotational speed and electricity output can also be predicted within 8% and 7.5% of deviation, respectively. (C) 2020 Elsevier Ltd. All rights reserved.
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    Performance improvement potential of a PV/T integrated dual-source heat pump unit with a pressure booster ejector
    (Elsevier, 2023) Erdinc, M. Tahir; Kutlu, Cagri; Unal, Saban; Aydin, Orhan; Su, Yuehong; Riffat, Saffa
    Dual-source heat pump unit can utilize the evaporation of the refrigerant at two different pressures. By adopting an ejector, high-pressure refrigerant stream can be used to lift compressor inlet pressure which results in a higher coefficient of performance (COP). This study proposes a renewable energy sourced and high-efficiency heat pump system which can be easily building integrated to offer a renewable heating solution. The system is devised on the complementation of dual thermal sources; one is air and the other one is solar, to maximize the utilization of ambient energy for highly efficient operation of heat pump. Using the advantage of the relatively lower operating temperature in the solar collector line, the thermal efficiency of the collector would be sufficient in winter. Adaptation of photovoltaics in the collector as a PV/T unit, will benefit the system from the produced electricity for further reduction of the demand from the grid. Along with the use of PV/T collector, the system can be potentially carbon neutral for larger collector areas. In this study, the performance improvement potential of a dual-sourced heat pump unit with an ejector as a booster is investigated for different locations in Turkey which presents different solar and weather profiles. The optimum collector evaporation temperatures are determined, and COP improvement potentials are discussed for different conditions. For a heating supply of 5 kW, the COP of the system can be improved by 22.6 % under 400 W/m2 and 10 degrees C ambient using 15 m2 PV/T collector. Including the electricity generated from the PV, reduction of the electricity demand from the grid can reach to 75 % for the same conditions.