Air-based System Research Articles

Utilizing novel industrialized heat exchanger plate in air-based photovoltaic/thermal collectors to enhance thermal and electrical efficiency

This study aims to design a highly efficient and applicable air-based photovoltaic-thermal (PVT) collector that maximizes both electrical and thermal energy efficiencies. An innovative industrialization-ready configuration of the air-based PVT system is proposed, utilizing an industrialized heat exchanger (GRIPMetal or GM) as the absorber plate for the PVT air channel. The heat exchanger consists of spikes and cavities to enhance the heat transfer coefficient in the air channel. The proposed heat exchanger plate minimally affects the dimensions and weight of the PVT collector. A numerical model, validated against experimental results, is used to ensure the accuracy of the simulation. The study is followed by a parametric study that investigates the geometric effects of the heat exchanger and air channel, as well as the airflow rate, on the overall performance of the PVT system. It is observed that the utilization of GM plates significantly reduces the average PV panel temperature (with a maximum of 28 ℃ reduction) and enhances the convective heat transfer coefficient in the air channel, the electrical and thermal efficiencies by approximately 164%, 16.1%, and 50%, respectively, when compared to a flat plate PVT collector. The results demonstrate that the proposed PVT collector effectively compensates for the pressure drops and excess fan power consumption at low Reynolds numbers due to the GM heat exchanger, resulting in higher overall system efficiency. The optimal configuration for the proposed PVT system is achieved by employing a low airflow rate, a narrow air channel, and GM spikes of the largest size available.

Random forest with feature selection and K-fold cross validation for predicting the electrical and thermal efficiencies of air based photovoltaic-thermal systems

The recent global energy transition policies emphasize the utilization of renewable sources as a primary energy solution. Solar energy systems, in particular, offer significant advantages in terms of cost-effectiveness and environmental friendliness. This work focuses on the modeling of a photovoltaic-thermal (PV/T) air-based system using machine learning (ML) techniques. The primary contribution lies in estimating the electrical and thermal efficiencies of the PV/T system through the application of the random forest (RF) technique and K-fold cross-validation. The results obtained are notably impressive when compared to the most commonly used techniques reported in the literature: Artificial Neural Networks (ANN), Support Vector Machine (SVM), and linear regression (LR). The assessment demonstrates that Random Forest outperforms these techniques in predicting both Electrical efficiency and Thermal efficiency with R² values of 99.9996 % and 81.2 % respectively, and MAE of 0.0034 and 2.64 respectively. Furthermore, selecting the most important features for electrical efficiency not only reduced the processing time but also improved the performance. The Random Forest model exhibited robust stability and demonstrated strong generalization capabilities, as evidenced by its consistent and promising electrical efficiency performance across a 10-fold cross-validation assessment. The proposed method could be a key solution to accurately model the electrical and thermal performances and serve as an alternative to traditional physical modeling approaches.

Sustainable biomass-driven heating, Bio-hydrogen, and power production scheme with desalination unit

In this study, a multi-generation energy system is modeled for the purpose of simultaneous producing distilled water as well as biofuels, electrical power, and thermal energy from wood chip biomass. The system is triggered by a gas turbine cycle with two different agents of steam and air. The system performance is evaluated by changing the gas turbine cycle working fluid and their performances are compared in details. The research findings indicate that the air-powered system demonstrated an efficiency of 67.38 %, surpassing the steam-powered system which exhibited a slightly lower efficiency rate of 67.17 %. The results indicated that the air-driven system displayed superior emission characteristics in comparison to the steam-driven system. The air-based system was found to release 510.3 g/kWh of carbon dioxide, whereas the steam-based system exhibited a marginally higher emission rate of 511.9 g/kWh. The study's results indicated that the air-powered system exhibited superior performance in comparison to the steam-powered system. The study illustrated that the integration of wood chip biomass into energy systems offers an environmentally sustainable and economically viable solution to address the increasing need for clean technologies.

Numerical and experimental analysis of instability in high temperature packed-bed rock thermal energy storage systems

Due to heat losses of preferential areas of packed-bed energy storage systems, transverse temperature variations may occur during the charging, discharging and standby processes. Furthermore, the heat losses of preferential areas of the storage tank cause a lower pressure drop in these areas resulting in an increased mass flow rate and further cooling, and thereby an enhanced transverse temperature variation, in a positive feedback loop – a phenomenon called instability. The transverse temperature variations may deteriorate the performance and thereby the economic feasibility of packed-bed energy storage systems. In this paper, numerical and experimental investigations of an air-based packed-bed rock thermal energy storage system for large-scale high temperature applications are presented. The objective of the study is to predict the instability and to analyze the effect of different standby durations and storage size on the instability of the air-based packed-bed system. Transient axisymmetric computational fluid dynamics models were developed for the standby and discharging processes of the packed-bed thermal energy storage systems. In addition, experimental investigations were carried out at a test facility located at Stiesdal Storage, Denmark, using magnetite rocks as heat storage material and air as heat transfer fluid. The results suggest that the numerical predictions are in good agreement with the test data. The instability phenomenon is found to increase with the standby duration, resulting in a maximum difference of 161 K between the maximum rock temperature and the outlet air temperature for a standby period of 10 h followed by a discharging process. Moreover, the results indicate that the maximum difference between the rock temperature and outlet temperature is 73 K and 56 K for a reduced-scale and a full-scale system (no standby period), respectively.

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials.

Modeling and comparative assessment of solar thermal systems for space and water heating: Liquid water versus air-based systems

This work pertains to the transient modeling and comparative study of active solar thermal space and water heating systems using liquid and air-type solar thermal collectors as the main energy source. The study utilizes TRNSYS to simulate the two systems in the context of Taxila's weather data (located at 33.74°N, 72.83°E), with the goal of meeting peak space and domestic water heating demands of 20 kW and 200 lit/day, respectively. The liquid water-based system (S-1) is primarily composed of a liquid solar collector, thermal storage, an auxiliary heater, connections to the hot water supply, and the space heating load through a water–air heat exchanger. In contrast, the air-based system (S-2), employs a pebble bed storage to store heat extracted from the solar thermal air collector. The heated air is subsequently used directly for space heating and passed through an air–water heat exchanger for water heating. Dynamic simulations of both systems span the entire winter season, and various performance metrics, including solar fraction, primary energy savings, and solar collector thermal efficiency, are computed. The results revealed that at the same collector area, the liquid water-based system (S-1) shows a higher solar fraction than the air-based systems (S-2) while the primary energy savings of the S-1 resulted in lower values than S-2 at smaller collector areas (< ∼30 m2) but surpasses the S-2 with increasing collector size. The optimal collector tilt for both systems is determined to be 50°, while specific storage volumes corresponding to maximum primary energy savings are estimated to be 100 and 40 L/m2 for S-1 and S-2, respectively.

Experimental study to understand the thermal environment of an office cooled by radiant ceiling panels and dedicated outdoor air system

This research aims to better understand the radiant environment of an interior space located in the tropical climate that is cooled by Radiant Ceiling Panels (RCPs). To do so, we have designed a highly instrumented 177m2 office testbed in Singapore installed with RCPs, Dedicated Outdoor Air System (DOAS) and Fan Coil Units (FCUs). An 11-day experiment is designed to monitor the radiant environment when being cooled by 1) RCPs + DOAS and 2) FCUs + DOAS with a fixed internal load of 2kW and humidity load of 8g/hr. We alternate between these two cooling modes, with variations in panels’ water supply temperature and window blinds. We expect to see a separation of Mean Radiant Temperature (MRT) and air temperature in mode 1 with the use of improved radiant sensors. However, results showed only minor differences in the radiant environment between the two modes of cooling. There was no significant MRT and air temperature separation (<1°C). These insights provide a better understanding of our radiant environment, which can potentially improve the way we control radiant systems. With better understanding, we can support high thermal comfort performance of a radiant systems as compared to a more common air-based system.

Review of recent research on photovoltaic thermal solar collectors

Photovoltaic (PV) technology can be categorized as a mature technology but its performance with its elevating temperature has a negative effect and opens a new area of research which led to the introduction of photovoltaic thermal collector (PVTC) systems. PVTC systems integrate PV modules and solar thermal collectors in a single unit to derive energies from uninterruptible solar sources. This review article is limited to the design and development of the heat exchangers used in typical air and water-based PVTC system. Heat exchangers are used to improve the heat transfer from the back surface of the PV module, thereby improving its overall efficiency. The review shows that for air-based PVTC, the electrical efficiency with various types of heat exchangers lies in the range of 4–24%, whereas for water-based PVTC is 5.1–15.8%. The maximum thermal efficiency achieved for the water-based system is observed to be 72% against the 87% for the air-based system indicating that a significant approach has been made in the air-based system with the novel concept of the heat exchangers as compared to the water-based system. At the end of the paper, some future recommendations are also commented on to make the PVTC system more viable.

Development of a novel computational fluid dynamics-based model for a solar photovoltaic/thermal collector-assisted domestic hot water system with sensible heat storage

This study proposes a novel numerical modelling approach to investigate the dynamic performance of a solar photovoltaic/thermal domestic hot water system. A three-dimensional numerical model of a flat-box solar collector developed in ANSYS-Fluent is coupled with a reduced one-dimensional model of all other system components. Coupling these models allows for a more accurate evaluation of the system’s overall performance as consideration is given to both the spatial variations inside the collectors, and the overall system’s temporal response. The city of Ottawa, Canada is used as the case study location and a monthly comparison is made between scenarios comprising two different working fluids (i.e. air and a water-ethylene glycol solution) and two photovoltaic/thermal collector design alternatives (i.e. with and without fins). To assess the performance of each scenario, the solar fraction, electricity fraction, and utilization factor are computed. Results show that the solar fraction is greater in the air-based system than in the water-based system for all months of the year, and values as high as 90.1% and 84.3% are obtained, respectively. Similarly, the addition of fins to these systems is shown to improve the solar fraction on an annual basis by 7.4%, and 1.4%, respectively. Similar trends are observed for the utilization factor, which indicates that the air-based system with fins is the most effective system with regards to utilizing incident solar radiation for meeting simultaneous heat and power loads. The annual average electricity fraction, on the other hand, shows little variation between scenarios on a month-by-month basis, which leads to the conclusion that adding fins and/or changing the working fluid has a negligible effect on the electrical performance of the system.

Optimization and evaluation of a municipal solid waste-to-energy system using taguchi technique in a tri-generation system based on gas turbine with air and steam agents

There is a recognized need for treating the municipal solid waste which causes serious environmental problems. There has been substantial research undertaken on the role of municipal solid waste in integrated energy systems. However, the contribution of Taguchi technique has received little attention within the field of municipal solid waste-to-energy systems. This study set out to examine the capability of utilizing the Taguchi technique in optimization and evaluation of a tri-generation system based on gas turbine. L25 orthogonal array of Taguchi technique has been utilized considering compression factor of compressor, maximum temperature of input stream to the gas turbine, and municipal solid waste fed to the combustion chamber as the input variables. Electrical power of the system, heating air and water capacities of the system, system efficiency, and normalized emission have been also considered as the tri-generation system performance indicators. The air-based system operates optimally at compression ratio of 10, maximum temperature of 900 °C, and fed MSW of 1 mol/s while compression factor of 15, maximum temperature of 1000 °C, and fed MSW of 1.2 mol/s are optimum conditions for steam-based system. Overall, air-based system operates better than steam-based system with electrical power of 317.6 kW, heating air capacity of 678.4 m3/min, heating water capacity of 288.7 L/min, efficiency of 79.3%, and normalized emission of 8.58 g/kW.min.

Recent developments in the production of inexpensive indoor air quality monitoring device

The level of pollution has increased with times by lot of factors like the increase in pollution, increased vehicle use, industrialization and urbanization which results in harmful effects on human wellbeing by directly affecting health of population exposed to it. In order to monitor quality of air-based system is purposed. Air quality plays very important role in safety, security, and health of the mankind. In this study, carbon monoxide (CO) and air quality (Qa) were measured using MQ135 and MQ7 sensors, respectively. Measuring air quality is a crucial step in raising awareness among the public about the need to ensure the health of future generations. Based on this, the Government of India has already taken some steps to outlaw motorcycles powered by single- and two-stroke engines, which are comparatively releasing significant levels of pollution. Using IoT platforms like Thingspeak or Cayenne, we are attempting to develop the same system so that we can educate everyone about the damage we are doing to the environment. New Delhi has already been noted as the most polluted city in the world with air quality readings over 300 ppm. The other papers have been fixed by us. We have updated the other publications where the sensor calibration and PPM projection were incorrect.

Experimental investigation of air-based active-passive system for cooling application in buildings

• The cooling effect of the interior PCM wall and ceiling was experimentally studied. • The PCM plates provided a cooling effect at constant and transient daily cycles. • Complete solidification of PCM is achieved at an air gap flow rate of 400 m 3 /h. • Complete solidification of PCM is achieved at an inlet temperature of 16°C. • The system is adequate for Mediterranean summer conditions and not for summer heatwaves. Due to the consequences of global warming, cooling of lightweight buildings is one of the main future challenges. The study presents an active-passive system (APS) with phase change material (PCM) plates integrated into the internal wall and ceiling substructure which during the day cools the indoor space passively. During the night, the air gap is ventilated actively to improve the PCM solidification process. The APS was experimentally tested in two identical test cells, PCM modified (cell-A) and reference cell (cell-B). Two different types of scenarios were investigated. First type tested the cooling effect of the PCM during the daytime cycle, determined by the temperature difference between the cell-B and cell-A. The same amount of heat was simultaneously added to both cells which was navigated by the setpoint air temperature in the cell-B (26°C, 30°C, 30°C with background ventilation, 35°C, TRY Ljubljana, TRY Rome and heatwave Ljubljana). Second type tested the PCM solidification time during the nighttime cycle (inlet air temperature ( T ai ) of 15°C, 16°C, and 17°C). The results showed that PCM plates provided the largest cooling effect at in 35°C-scenario. The complete solidification of PCM was achieved at T ai of 16°C. The system is adequate for Mediterranean summer conditions.

Seasonal Analysis of Solar Energy Utilization Effect of Air-based PVT System by Comparing with Photovoltaic System

Seasonal Analysis of Solar Energy Utilization Effect of Air-based PVT System by Comparing with Photovoltaic System

Comparative study on heat transfer characteristics of molten PCM in PV/PCM air-based system based on grey relation analyses

The operating temperature of photovoltaic (PV) panel have significant influence on its generating efficiency and life span. To improve the performance of PV panel, we performed comparative analyses on a novel PV panel cooling strategy by integrating PV panel with phase change material (PCM) and ventilation system (PV/PCM air-based system). The heat transfer characteristics of molten PCM in an inclined cavity with constant heat flux on one side and air flow boundary on another side are numerically investigated. The thermal performance including dimensionless temperature and temperature uniformity, the heat transfer capability including local Nusselt number and average Nusselt number, are compared and analyzed. The results indicate that flow boundary has a significant effect on the PV cooling. Cavity at top-down flow direction has better temperature uniformity and at bottom-up flow direction has greater heat transfer capability. Increasing Reynolds number can enhance the heat transfer efficiency and reduce the temperature at the same time. Further, the impact of each factor on heat transfer capability are quantified based on the grey relation analyses. Grey relation grade for average Nusselt number with Ra number, Re number, AR, ϕ, and flow direction is 0.51, 0.66, 0.69, 0.62, and 0.53, respectively. This indicates that heat transfer capacity is the most sensitive to AR, followed by Re number, inclination angle, flow direction, and Ra number.

Seasonal Performance Evaluation of Air-Based Solar Photovoltaic/Thermal Hybrid System

Recently, the use of novel renewable energy has attracted attention for suppressing the generation of carbon dioxide to prevent global warming. There is growing interest in energy reduction in buildings using solar energy because of its ease of use and repair and excellent maintenance. Therefore, in this study, air-based Photovoltaic thermal (PVT) systems, which can increase the utilization of solar energy, are compared with the existing PV system through measurement. PVT systems can increase the amount of power generation by lowering the temperature of the panel using air passing through the lower part of the panel. It is also possible to use the heated air obtained from the panel as indoor heating or for supplying hot water in a building. As a result of measuring the performance of existing PV panels and PVT panels under the same weather conditions, the power generation efficiency of PVT panels through which air passes increases compared to PV panels. Overall, an air-based PVT system can utilize solar energy about three times more than existing PV systems by utilizing solar heat and solar power. In summer, thermal collection and power generation by PVT were 51.9% and 19.0%, respectively, and power generation by PV was 18.0%. In contrast, the amount of thermal collection and power generation in winter was 43.5% and 20.3%, respectively, and the amount of power generated by PV was 18.7%. As such, it is necessary to review methods for utilizing the increase in power generation in winter and thermal collection in summer.

Process modeling and simulation of ethylene oxide production by implementing pinch and cost analysis

This study focused on the modeling and simulation of the Ethylene Oxide (EO) production process in Aspen plus software and energy optimization of the whole process using the Pinch analysis. This work focused on ethylene oxide production by the air-based system and modeled and simulated the whole process in Aspen plus® using the S.R.K. and PSRK thermodynamic models. By process design, modeling and simulation, the behavior of the actual process has been predicted. After process simulation, it has been concluded that control the oxygen concentration by controlling the airflow and controlling the reactor's temperatures causes an impact on our desired product. When the oxygen concentration increases, ethylene is oxidized completely and generated useless products such as carbon dioxide and water to enhance production. Energy optimization of ethylene oxide production is completed through Pinch analysis and saves 18.27million $ per year, which is consumed in heating or cooling streams.

The Diagnostic Performance of Machine Learning in Breast Microwave Sensing on an Experimental Dataset

<i>Objective:</i> This paper assesses the diagnostic performance of deep learning methods for tumour detection in breast microwave sensing (BMS). <i>Methods:</i> A convolutional neural network (CNN) was used to predict the presence of a cancerous lesion in data from experimental scans of MRI-derived phantoms. An experimental dataset containing data from 1257 scans was used. The CNN was compared to a similarly sized dense neural network (DNN) and logistic regression classifier. <i>Results:</i> The CNN was able to exploit the sinogram data structure to achieve diagnostic performance significantly better than random classification, while neither the DNN nor logistic regression classifiers could generalize to unseen test data. The area under the curve of the receiver operating characteristic curve of the CNN classifier was estimated to be between (78 <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 3)&#x0025; and (90 <inline-formula><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 3)&#x0025;, where the upper estimate was obtained when the testing set was constrained to consist of phantoms with breast volumes that are within the volume bounds of the training set and when the tumour was located at the same vertical position as the system antennas. <i>Conclusion:</i> The results obtained in this investigation demonstrate the potential of combining deep learning and BMS systems for breast cancer detection. <i>Impact:</i> This paper provides an estimate of the diagnostic performance of an air-based BMS system using deep learning methods for automatic tumour detection on a sizable experimental dataset. The performance was found to be comparable to that of AI-assisted mammography and marks a first step toward larger-scale investigations in BMS.

A new random vector functional link integrated with mayfly optimization algorithm for performance prediction of solar photovoltaic thermal collector combined with electrolytic hydrogen production system

Artificial intelligence techniques have become powerful alternatives to conventional modeling techniques in different engineering disciplines. They have been applied for modeling, control, prediction, optimization, forecasting, and identification of complex systems. In this paper, a novel optimized artificial intelligence method is developed to predict the performance of Photovoltaic/Thermal Collector (PVTC) incorporated with Electrolytic Hydrogen Production (EHP) system in terms of power output of PV, PV surface cell temperature, output temperature of cooling fluid, thermal and electrical efficiency, and hydrogen production yield. A new metaheuristic algorithm called mayfly based optimization (MO) algorithm has been implemented with Random Vector Functional Link (RVFL) network to maximize the prediction accuracy. The proposed hybrid artificial intelligence model was trained and tested using experimental data. The experiments were conducted outdoors for the proposed PVTC-EHP system operating with two different cooling fluids, namely, air and water under Indian weather conditions, and their results were compared with the predicted RVFL-MO and conventional RVFL results. Moreover, five statistical criteria were used to evaluate the performance of the investigated algorithms. The experimental results showed the hybrid PVTC-EHP system can produce a daily accumulated PV output power and hydrogen production yield of 1.66 kW/day and 3.60 kg/day for water-based PVTC-EHP system and 1.22 kW/day and 4.41 kg/day for air-based PVTC-EHP system, respectively, at a mass flow rate of 0.66 kg/min. Moreover, the statistical measures showed a perfect fit between the experimental and the proposed prediction model results. The results revealed that the root mean square error for the training phase of the RVFL and RVFL-MO was 0.25 and 0.65, respectively, while it was 1.63 and 2.04 for the testing phase, which reveals the important role of MO in determining the best parameters of RVFL network that maximize its prediction performance.

Development of flat-plate building integrated photovoltaic/thermal (BIPV/T) system: A review

The concept of building integrated photovoltaic/thermal system was introduced in the 1990 s and attraction towards this increased in 2000 because it provides net zero energy building by enhanced solar utilization. This work represents review of the flat-plate building integrated photovoltaic/thermal (BIPV/T) system, including current developments, experimental and numerical studies and parametric effect on the building performance. Flat-plate BIPV/T system reviewed here are: air-based system, water-based system and hybrid system in which, nano fluid, phase change material, cushion structure and heat pipe etc. are covered. From the study it is found that Performance of BIPV/T depends on design parameters and local weather condition. Also, more thermal energy is obtained by BIPV/water system as compared to BIPV/air system. This work provides overview of research, development, application and status of system. From most of the studies of BIPV/T systems and facades it has been observed that the variation of thermal efficiency is in the range of 22–55% for air-based systems and 30–60% for water-based systems. Further the electrical efficiency variation is in the range of 10–18% for air-based systems and 10–17% for water-based systems. It has been observed that the variation of thermal efficiency increases upto a mass flow rate of 0.1 kg/s after which the change is marginal to justify for thermal gain. Also, the electrical efficiency remains nearly unchanged at all mass flow rates. The highest thermal efficiency of 72% has been observed for Nano-PCM-PVT system which indicates that nano particles and PCM has a great potential for PVT systems.

Effect of Using Fins on Cell Temperature at Air-Based PVT

In this study, the effect of addition of fins in air-based PVT system on cell temperature investigated. Experimental tests were performed with frequent and sparse fins configurations and also empty(non-finned) state. Also, thermal camera images of cells were investigated and compared to images obtained by Fluent Ansys. Cell temperatures for all status of both polycrystal and monocrystal panel decreased between 8-20 °C. Panel surface was observed to have a uniform temperature distribution. Finally, temperature distribution images obtained with ANSYS Fluent were found to be quite compatible with thermal camera images.