Coconut shell-derived activated carbon-enhanced water phase change material for cold thermal energy storage.

In building cooling, the demand for cooling surges during specific times, stressing air-conditioner operation, and additional cooling is often wasted during low-demand periods. Water-phase change material (W-PCM)-based thermal energy storage (TES) allows for load shifting and effective management of peak demand by storing cooling energy when the demand is low. This stored energy can be deployed during peak hours, decreasing energy usage and associated CO2 emissions. However, the use of W-PCMs was hindered by phase separation, slow energy transfer, and high supercooling degree (SCD). We synthesized coconut shell (CNS)-produced activated carbon (ACC) to use as a thermal enhancer in W-PCMs for the first time. First, ACC was synthesized from CNS via steam activation. Then, transmission electron microscopy was used to confirm the pore morphology of the CNS-ACC. The synthesis of the W-PCM with various weight percentages (0.1, 0.6, and 1.2) of CNS-ACC was accomplished in two steps. Zeta potential distribution analysis revealed that the W-PCM with CNS-ACC exhibited colloidal stability. Thermal conductivity (TC) and thermogram analyses revealed that a dose of 1.2 wt% CNS-ACC enhanced liquid and solid TC by 9% and 22%, respectively, despite a 6% and 8% decrease in specific heat and latent heat. More specifically, solidification assessment in a spherical enclosure revealed 100% suppression of SCD with 1.2 wt% CNS-ACC. As a result of this and the enhanced TC, the overall solidification process was accelerated, reducing the overall duration by 18.5%. Thus, the combination of CNS-derived ACC and W-PCM for TES in building cooling could reduce energy consumption and associated CO2 emissions.

Enhancing the performance of a solar air heater by employing the broken V-shaped ribs.

This work aims to enhance the performance of a solar air heater (SAH) by introducing broken V-ribs as roughness elements on the absorber plate. The unit with a conventional flat absorber plate is referred to as the "FSAH," while the unit with a broken V-rib-shaped absorber plate is called the "VSAH." The experiment was performed for three air velocities: 25 m/s, 20 m/s, and 15 m/s and the corresponding air flow rates were 0.037 kg/s, 0.031 kg/s, and 0.023 kg/s, respectively. The results showed that the maximum temperature was experienced on the absorber plate, followed by the glass plate for both SAHs. Overall, the average absorber and glass plate temperatures of the VSAH were 0.6-1.4 °C and 0.4-1.9 °C lower than those of the FSAH. Compared to the FSAH, the experimental results showed that the VSAH experienced useful power and thermal efficiency that were 16.6-19.8% and 15.7-20.4% higher, respectively, while the top surface heat losses were found to decrease by 2.1-8.1%. Due to the disrupted air paths in the VSAH, the observed pressure drop was 113.3-133.3% higher than that of the FSAH. More impotently, the thermo-hydraulic performance factor was always higher 1 and the observed values were 1.48, 1.39, and 1.24 at the va (velocity) values of 15, 20, and 25 m/s, respectively. Therefore, the proposed VSAH had an admirable thermal performance as compared to FSAH. Further, optimization through varying the roughness parameters, namely, relative blockage width (W/w), relative pitch ratio (P/e), number of baffles (n), relative blockage height (e/H), and angle of attack (ß) could helped to achieve better performance.

Experimental investigation and optimization of dimple-roughened impinging jet solar air collector using a novel AHP-MABAC approach.

The effect of the flow and geometric parameters of a dimple-roughened absorber plate on the enactment of solar air collectors (SACs) with air-impinged jets was investigated in this study. The performance-defining criteria (PDCs) of a jet-impinged dimple-roughened SAC (JIDRSAC)-forced convection airflow system are significantly affected by variations in the system's control factors (CFs), such as the arc angle (αaa) ranging from 30° to 75°, dimple pitch ratio (pd/Dh) ranging from 0.269 to 1.08, and dimple height ratio (ed/Dh) ranging from 0.016 to 0.0324. The constant parameters of the jet slot are a stream-wise pitch ratio (Xi/Dhd) is 1.079, a span-wise pitch ratio (Yi/Dhd) is 1.619, and a jet diameter(Di/Dhd) is 0.081. Based on the combined approach of the analytic hierarchy process and multi-attributive border approximation area comparison (AHP-MABAC), the Reynolds number (Re) = 15,000, αaa = 60°, pd/Dh = 0.27, and ed/Dh = 0.027 depicted the best alternative (A-9) set among 16 alternatives to deliver the optimal performance of the JIDRSAC. The jet impingement pass compared to the smooth pass, the Nusselt number increased by 2.16-2.81, and friction factor increased by 3.35-5.95, and JIDRSAC was compared to the jet impingement pass, exhibiting an enhancement in Nusselt number and friction factor in the range of 0.55-0.80 and 0.05-0.15, respectively. In addition, sensitivity analysis is used to examine the ranking's stability and reliability in relation to the PDC weights.

Future refrigerants with low global warming potential for residential air conditioning system: a thermodynamic analysis and MCDM tool optimization.

Increasing CO2 emission due to the practicing of high global warming potential (GWP) refrigerant like R22 in split air conditioning (AC) units needs the best substitute to match with environment and safety protocols along with good energy efficiency. In this study, 14 alternative refrigerants have been chosen to replace R22 in a 1.5 TR capacity of split AC from the existing studies. The performance of each refrigerant has been analysed thermodynamically and compared their results with R22 by accounting for discharge temperature, power consumption, coefficient of performance (COP), total equivalent warming impact (TEWI) index, and life-time cost. Overall from this theoretical analysis, it was observed that the best refrigerant for each considered measure is not unique; for example, R290 was best in terms of refrigerant charge and discharge pressure, while R444B was chosen to be superior in terms of COP, TEWI, and life-time cost. Therefore, a multi-criteria decision-making methodology tool-based optimization has been carried out for selecting a single superior refrigerant for the future by considering thermal properties, COP, TEWI, and life-time cost. Results of the evaluation based on the distance from average solution envisage R290 and R1123 as superior and worst choices to replace R22.

A novel solar-powered milk cooling refrigeration unit with cold thermal energy storage for rural application.

This experimental study analyzed the use of solar photovoltaic energy for operating a novel twin-circuit DC milk chiller without batteries using water-based cold thermal energy storage for different seasons in Chennai, India. HFC-134a and HC-600a were used as refrigerants in the two individual circuits. For each season, the test was conducted continuously for 18 days to analyze the quantity of generated ice that could be utilized to chill 10 L of milk in the morning and in the evening. The average quantity of ice formed per day in the ice bank during monsoon, winter, and summer seasons was found to be 3.61, 19.75, and 27.97 kg, respectively. Thus, it is evident that the use of solar energy with thermal energy storage is effective for operating the milk chilling unit for two seasons, namely winter and summer. However, the system requires an additional power source for continuous operation during the monsoon season. It is noteworthy to mention that the use of a solar milk chiller instead of a conventional milk chiller resulted in 91.15% lesser CO2 emission with 27.6% less LCC. In this study, solar photovoltaic power was observed to be a good choice for chilling milk in the context of global warming and energy consumption. The use of thermal energy storage also allows the initial cost to be reduced.

Exploring the thermo-physical characteristic of novel multi-wall carbon nanotube-Therminol-55-based nanofluids for solar-thermal applications.

This work aims to develop a novel nanofluid using Therminol-55 (T-55) as heat transfer fluid and multi-wall carbon nanotubes (MWCNTs) as dispersants with various volume concentrations of 0.05, 0.1, 0.3, and 0.5% and assess its thermo-physical properties for solar-thermal applications. The pH values of nanofluid MWCNT/T-55 with various particle loading were too far-flung from the pH (I) value, which confirmed the good dispersion stability of nanofluid. The measured density shows tremendous deviation from predicted density with increasing MWCNT loading owing to the non-considering of microstructural parameters in Pak & Cho correlation predication. The highest augmentation in nanofluid thermal conductivity was 16.83% for 0.5 vol. % MWCNT at 60 °C. The maximum improvement in dynamic viscosity of nanofluid with 0.5 vol. % of MWCNT is found to be 44%, and this rise is reduced at higher temperatures. The thermal effectiveness of the nanofluids demonstrates that nanofluid with all volume fractions of MWCNTs was favorable at higher temperatures in the laminar region. Mouromtseff number ratio decreases with a rise in temperature and MWCNT volume concentration. It is concluded that the excellent thermo-physical properties and prolonged thermal stability of the MWCNT will be highly beneficial in improving the overall performance of various kinds of heat transfer fluids (HTFs) for process heating and solar-thermal applications.