• Energy Research

AbstractThe appropriate storage, transportation, and utilization of wood-based fuels, including woodchips, pellets, and sawdust, in the energy production process, depends on their efficient drying. Traditional drying methods include limitations such as high thermal losses, inefficient heat transfer, and sustainability issues. These barriers, coupled with the high costs and complexities of maintaining the desired moisture content, underscore the need for innovative solutions. This study introduces a novel approach to wood fuel drying through the integration of phase-change materials (PCMs) with hybrid solar drying systems, aimed at enhancing thermal efficiency and sustainability. Employing coconut oil as the PCM, experiments were performed under a consistent artificial radiation of 755 W m−2. The hybrid system demonstrated the capability to retain approximately 200 watts of useful heat for three hours post-radiation, marking a significant improvement in heat storage. Our findings reveal peak thermal and exergy efficiencies of 30–35% and 13–14%, respectively. An economic and environmental analysis predicts a system lifespan of five years, with the cost of generating one kilogram of hot air at 0.0058 EUR and an annual CO2 emission of 64.09 kg. This research offers a cost-effective and environmentally friendly method for wood fuel drying, presenting a significant advancement for large-scale producers and setting a benchmark for further exploration of wood fuel drying technologies.

Abstract This work evaluates the feasibility and determines a generalized drying characteristic curve in an indirect mode multi-tray solar cabinet dryer. The study considers a combination of tray reordering pattern and dryer performance index (DPI) method to map the influence of four primary factors, which influence the drying kinetics into a generalized curve. Three levels of each of the four factors, such as the mass flow rate (0.03–0.05 kg/s), heat input (500–1000 W/m2), loading density (1.0–2.5 kg/m2), and flake thickness (2–8 mm), represent twelve different drying kinetic curves. Therefore, the DPI value corresponding to the generalized curve would directly indicate the dryer performance and reduce the complexity in assessing the agro-product samples' drying behaviour in multiple trays. This study was initially validated, and it highlighted the merits of a tray reordering pattern in achieving drying uniformity per batch. Dimensionless drying process time ( τ ), a function of drying constant ( k ) and drying time ( t ), resulted in a maximum percentage deviation of 27.93% among the twelve drying kinetic curves. In contrast, expressing the moisture ratio as a function of DPI and drying process time ( τ ) reduced the maximum percentage deviation to 2.33%, with the value of correlation coefficient ( r ) above 0.972 for all the twelve drying kinetic curves. These consolidated findings pointed out that the adopted tray reordering pattern greatly influences the DPI method’s success in establishing a generalized curve in a multi-tray dryer.

Abstract The present work attempts to devise an efficient method utilizing an on-grid photovoltaic-thermal heat pump water heater (PV-THPWH) integrated with a real-time variable frequency controller to achieve the goal of energy-efficient buildings. The prime focus is to reduce the grid's dependence on the compressor's energy-intensive operation by employing a feedback-controlled variable frequency drive (VFD). Additionally, the possibilities involved with addressing the electrical and thermal energy requirements of an energy-efficient building was investigated utilizing the proposed system. R-32 refrigerant in the photovoltaic-thermal (PV-T) evaporator coils of the heat pump assembly help to cool the photovoltaic (PV) panel while delivering the absorbed heat in the condenser to heat water contained inside the storage tank. Outdoor experiments and theoretical investigations of the combined system were carried out to appraise the dynamic behavior under varying solar irradiation and ambient temperature conditions. The observations conveyed that the PV-THPWH system succeeded in reducing the PV panel operating temperature by 25%, which resulted in a 20% increment in PV power output. Also, the performance indicators, such as the instantaneous energy efficiency and instantaneous PV efficiency, were found to increase by 15% and 34%, respectively, resulting in an average coefficient of performance of 6.4. For a clear sky day, the recorded total PV energy output was 4.67 units, while the VFD compressor consumption was 3.42 units, and the surplus 1.25 units were sent to the grid. Furthermore, the economic analysis reported a payback period of 2.3 years for the developed PV-THPWH system.

The aim of this research was to develop a model for a solar refrigeration system (SRS) that utilizes an External Compound Parabolic Collector and a thermal energy storage system (TESS) for solar water heating in Chennai, India. The system parameters were optimized using TRNSYS software by varying factors such as collector area, mass flow rate of heat transfer fluid, and storage system volume and height. The resulting optimized system was found to meet 80% of hot water requirements for the application on an annual basis, with an annual collector energy efficiency of 58% and an annual TESS exergy efficiency of 64% for a discharge period of 6 h per day. In addition, the thermal performance of 3.5 kW SRS was studied by connecting it to an optimized solar water heating system (SWHS). The system was found to generate an average cooling energy of 12.26 MJ/h annually, with a coefficient of performance of 0.59. By demonstrating the ability to efficiently generate both hot water and cooling energy, the results of this study indicate the potential for utilizing a SWHS in combination with STST and SRS. The optimization of system parameters and the use of exergy analysis provide valuable insights into the thermal behavior and performance of the system, which can inform future designs and improve the overall efficiency of similar systems.

Abstract Drying uniformity and flexibility in product selection are the primary concern for the end-user in solar drying application. Hence, the present work attempts to determine the user flexibility to choose among different agro-products and simultaneously ensure the drying uniformity inside an active multi-tray indirect-mode solar cabinet dryer. The work considers unripe untreated banana and bitter gourd with an average initial moisture content of 180% (db) and 1328% (db), respectively. The present work tries to assess the influence of a tray-sequencing pattern on the drying behavior at different combinations of flake thickness (0.002 − 0.004 m), multi-tray spacing (0.1 − 0.15 m), tray mesh size (0.01 − 0.015 m), and mass flow rate (0.015 − 0.03 kg/s). For all the tested combinations, the proposed tray sequencing aided to achieve drying uniformity for banana flakes within 10 h and bitter gourd by 18 h. Energy utilization ratio (45.3% − 47.9%) and exergy loss decreased with an increase in mass flow rate. Among the tested combination, 0.03 kg/s, 0.002 m thickness, 0.15 m spacing, and 0.01 m mesh size resulted in higher average energy efficiency (15.34%), and exergy efficiency (60.3 − 94.1%). Further investigations on the proposed dryer are essential to bring out a suitable standardization to attain an upper limit among the agro-products.

The present work seeks to address the forced convection heat transfer behaviour of a double-pass solar air heater system (DPSAHS) provided with asymmetric channel flow configuration used for solar drying of agro-products. Outdoor experiments were performed on a DPSAHS having a constant channel depth ratio of 1.5. Thermal response of the DPSAHS under different influencing parameters such as flow rate, channel depth, and thermophysical properties of the working fluid was experimentally determined. The influence of ambient parameters such as solar intensity, ambient temperature, wind speed, and relative humidity on the thermodynamic behaviour of the DPSAHS was also investigated. Among which, solar intensity and ambient temperature were found to be the major parameters influencing the energy and exergy efficiency followed by wind speed. Relative humidity was found to have the least percentage contribution towards the thermal characteristics of the system. Overall thermal efficiency and exergy efficiency were found to vary in the range of 20–41% and 5.6–18% at two different mass flow rates of 0.02 kg s−1 and 0.03 kg s−1, respectively. The results also inferred that the influence of thermophysical property variation on the thermodynamic performance depends upon the operating temperature range and on the nature of working fluid. Air temperature in the lower channel was found to be an average 3 °C higher than that of upper channel passage corresponding to two different mass flow rates. Hence, the thermodynamic behaviour of DPSAHS was found to be strongly influenced by the variation in channel depth, ambient parameters, and mass flow rate. The obtained experimental results were also compared with the available literatures.

The direct emission of refrigerants from air conditioners and indirect carbon dioxide emissions from its associated energy usage in vehicles contributes significantly toward global warming. The primary objectives of this investigation are to present the performance comparisons and highlight the environmental benefits of R430A as a replacement to R134a in vehicle air conditioners. The influences of seven critical parameters such as compressor angular velocity, ambient temperature, condenser air velocity, evaporator air velocity, passenger load capacity, relative humidity and solar radiation were considered for thermodynamic analysis of vehicle air conditioners. The experimental results revealed that the R430A has 4–10% higher refrigeration effect, 4–11% lower compressor power consumption, 7–12% higher coefficient of performance and 5–12% lower exergy destructions than R134a. The discharge temperature in the compressor of vehicle air conditioners using R430A was found to be 2–6 °C higher than R134a. The lubricants used in R134a systems were found physically stable at 6 °C elevated temperatures. The R430A has lesser total equivalent global warming potential by 32–40%, 30–35% and 44–50% than R134a in petrol, diesel and liquefied petroleum gas-fuelled vehicles.

Abstract Uniform moisture removal inside a multi-tray mixed-mode solar cabinet dryer (MMSCD) within a limited time is a significant concern primarily due to the non-uniform temperature distribution. Primary factors such as heated air and flow rate along with preliminary considerations such as slicing, loading intensity, spacing, and choice of with or without pre-treatment influence the drying behaviour. Hence, the primary objective of the present work is to identify whether only tray sequencing can be sufficient to ensure drying uniformity inside the MMSCD. A double-pass flat plate collector containing discrete cylindrical macro-encapsulated energy storage units deliver the heated air. Untreated unripe bananas with an average initial moisture content of 180% (db) are tested. In this work, the effect of tray sequencing (peculiar pattern) under a single layer loading intensity per tray with different flake thickness, multi-tray spacing, and flow rate are studied. Drying characteristic curves revealed that with tray sequencing the final moisture content was reduced below 16% (db) in all the trays. The specific energy consumption, efficiencies (collector, pickup, drying), drying cost, and open sun drying are discussed. Thus, based on the requirement, the MMSCD along with energy storage offers greater flexibility in drying for the user and ensures drying uniformity.