Electrical Exergy Research Articles

Numerical analysis and deep learning algorithm for photovoltaic-thermal systems using various nanofluids and volume fractions at Riyadh, Saudi Arabia

Conventional photovoltaic (PV) systems have elevated temperatures in the hot climate of Riyadh, resulting in reduced electrical power generation. Therefore, nanofluids are employed in photovoltaic-thermal (PV-T) systems to absorb the self-generated heat that limits efficient operation. In addition, developing deep learning models would help improve the optimization and control of the proposed system. This study's primary goal is to numerically examine a PV-T system under the influence of using various nanofluids with varying volume fractions in the hot climate of Riyadh and to develop time-series deep learning algorithms based on the findings in this examination to predict the PV-T system's potential. A mathematical model to investigate the PV-T panel performance under various volume concentrations and nanofluids is proposed. The generated data from the different nanofluids is deployed to train a deep learning model, which is convolutional neural networks integrated with two layers of long short-term memory (CNN-LSTM), in order to predict the PV-T panel temperature. According to the investigation's findings, the best PV-T coolant is CuO nanofluid at 4 % volume concentration. Utilizing the aforementioned nanofluid can deliver an enhancement in the average daytime PV-T panel temperature, electrical, thermal, and total exergy efficiency by 34.5 °C, 16.7 %, 79.2 %, and 18.07 %, respectively. The developed deep learning algorithms were evaluated using the mean absolute error (MAE) and coefficient of determination (R2) and scored 0.18–0.35 and 97.5–98.75 %, respectively.

Active heating of greenhouse integrated semitransparent photovoltaic thermal system with series connected semitransparent photovoltaic thermal air collectors

In order to fulfill the demand for energy and food security, an active heating of a controlled environment greenhouse integrated semitransparent photovoltaic thermal (GiSPVT) system with N-semitransparent photovoltaic thermal (SPVT) air collector for cold climatic conditions has been analyzed in this paper. The proposed SPVT air collectors are connected in series and integrated with GiSPVT. It is used to generate thermal as well as electrical energy to meet the daily requirements of users. Based on the energy balance equation which is a function of design and climatic parameters, an analytical expression for various variable parameters namely plant, room air, and solar cell temperatures have been derived. Numerical computation has been made in Matlab for computing the thermal, electrical, and overall exergy of the proposed system. Based on numerical computation, the following observations have been made: (i) From a thermal point of view, the packing factor (0.5, 0.8) of the semitransparent PV module plays an important role and it must be optimized for maximum thermal heating. (ii) The selection of a number of collector N is an important parameter to generate electrical energy as well as thermal heating of GiSPVT room air in an optimum way.

Energy, exergy, economic and environmental (4E) analysis of a cryogenic carbon purification unit with membrane for oxyfuel cement plant flue gas

The carbon capture, utilisation and storage (CCUS) process chain is subject to increasing interest, and its overwhelming implementation on the industrial scale appears to be one of the main ways to reduce CO2 emissions. In this context, the optimisation of a CO2 purification process for oxy-combustion cement plant flue gases is proposed. This optimisation is based on a multidimensional study on the energy, exergy, economy, and environmental impacts of the process. The results of the optimisations carried out show that it is more favourable to increase the CO2 recovery above 90%, from an energy, exergy and economic point of view. The analysis of the evolution of the capture cost as a function of the CO2 recovery shows that for a given carbon tax, there is a minimum for the total cost which includes the sum of the carbon tax contributions for the uncaptured CO2 and the capture cost. As the unit uses only electrical energy, the cost and the electricity generation will directly impact the capture cost as well as the overall balance in terms of CO2 avoided. As the electricity price increases from 50 to 250 €/MWh, the CO2 capture cost increases by almost 250%. An analysis of the parameter uncertainties allows to observe their impacts on the results, and to define a standard deviation from the optimised points and show the robustness of these. Considering the technical parametric uncertainties, the standard deviation on the electrical consumption (3.65 kWh/tCO2), CO2 recovery (0.09%) and exergy efficiency (0.92%) is limited.

Numerical examination of exergy performance of a hybrid solar system equipped with a sheet-and-sinusoidal tube collector: Developing a predictive function using artificial neural network

Integrating cooling systems with photovoltaic-thermal (PVT) collectors has the potential to mitigate the exergy consumption in the building sector due to their capability for simultaneous power and thermal energy generation. The simultaneous utilization of nanofluid and geometry modification resulted in a synergetic enhancement in the performance of PVTs and thereby reducing their sizes and costs. In addition, there is still a lack of high accurate predictive model for the estimation of the performance of PVTs at a given Re number and nanofluid concentration ratio to be used in engineering design for the further product commercialization. To this end, the current numerical study investigates the exergy electricity, thermal, and overall exergies of a building-integrated photovoltaic thermal (BIPVT) solar collector with Al2O3/water coolant. The increase in nanoparticle concentration (ω) from 0 % to 1 % increased the useful thermal exergy and overall exergy efficiency (Exu,t/ Υov) by 0.3999 %/0.0497 %, 1.3959 %/0.2598 %, and 0.7489 %/0.1771 % at Re numbers of 500, 1000, and 1500, respectively, while Exu,t/ Υov exhibited a reducing trend at Re = 2000; 0.3928 %/0.1056 % decrease. In addition, the increase in ω from 0 % to 1 % caused the useful electricity and electrical exergy (Exu,e/ Υe) to be diminished by 0.0060 %/0.0025 % at Res 500 and 1000, and to be escalated by 0.0113 %/0.0055 % at Res of 1500 and 2000. Meanwhile, the Re augmentation, from 500 to 2000, improved the Exu,t, Exe, Υe, and Υov by 60 %, 1.26 %, 1.26 %, and 17.50 %, respectively, at different ω s. In addition, two functions were developed and proposed by applying a group method of data handling-type neural network (GMDH-ANN) to forecast the value of Υov based on two input values (Re and ω). The results showed high accuracy of the proposed model with MSE, EMSE, and R2 of 0.0138, 0.1143, and 0.99785, respectively.

Performance mapping of silicon-based solar cell for efficient power generation and thermal utilization: Effect of cell encapsulation, temperature coefficient, and reference efficiency

Characteristic Performance Maps (CPMAPs) are developed for silicon-based solar cells, based on a massive parametric study implemented by a validated thermal-fluid model. These CPMAPs reveal the variation of thermal-, energy-, and exergy-related performance indicators. The studied solar cell integrated with a generic heat sink satisfies the temperature demand within safe solar concentration range. The developed sets of CPMAPs investigate the effect of cell encapsulation, temperature coefficient, and reference efficiency. Findings indicate that reducing the thermal resistance of the intermediate layers between the silicon layer and the heat sink significantly elevates the maximum allowable concentration ratio. Besides, decreasing the thermal resistance of the intermediate layers enhanced the overall exergy efficiency. Furthermore, solar cells with lower temperature coefficients exhibit a minimal impact on expanding the safe range of solar concentration. However, the CPMAPs indicate that such cells are recommended for concentrator photovoltaic systems due to their ability to mitigate the inevitable decrease in electrical efficiency associated with high temperatures under high solar concentration. The use of high-reference efficiency cells slightly expands the safe range of solar concentration and leads to higher electrical exergy efficiency, albeit at the expense of reduced thermal exergy efficiency. Low-reference efficiency cells exhibit a higher potential for combined heat and power applications due to increasing the overall exergy efficiency. In contrary, high-reference efficiency cells are found to be more suitable for power generation applications. The proposed CPMAPs have significant implications, providing a novel roadmap for future research in the quantitative selection and design of photovoltaic systems.

Enhanced performance of photovoltaic thermal module and solar thermal flat plate collector connected in series through integration with phase change materials: A comparative study

The decline in photovoltaic cell efficiency due to temperature elevation, coupled with solar energy's inherent intermittency, presents challenges for solar systems, including photovoltaic panels and solar thermal (ST) collectors. The integration of phase change materials (PCMs) emerges as a promising solution to enhance thermal energy storage and regulation, thereby improving system performance and sustainability. This study investigates the performance of series-connected photovoltaic thermal (PVT) and ST systems with integrated PCMs from energy and exergy viewpoints, utilizing a 3D transient numerical simulation. The proposed system's performance is compared with that lacking a PCM across various heat transfer fluid mass flow rates. Suitable PCM selection based on melting temperature is explored, along with PCM layer thickness and nanoparticle augmentation. The research highlights that PCM integration effectively regulates PV cell temperature, enhancing electrical power and exergy rate. While increasing the mass flow rate improves thermal and electrical power, it reduces the thermal exergy rate. Comparing different PCMs (RT28 HC, RT35 HC, and RT44 HC), the RT28 HC PCM provides the lowest temperature of PV cells and the best electrical performance during the day. Moreover, increasing PCM layer thickness results in lowering PV cell and outlet temperatures and storing more heat. Nanoparticles added to PCMs lead to a marginal improvement in energy and exergy, especially for the system with RT28 HC. This analysis emphasizes PCM integration's role in enhancing solar thermal system performance, highlighting the importance of considering the PCM's melting temperature for effective thermal energy management.

Energy and exergy analysis of a novel solar-based system merged with power cycle

Parabolic Trough Solar Collector (PTC) is a power generation unit that works based on solar energy. This system provides a considerable amount of thermal power but no electrical energy. Hence, the current investigation attempts to boost the outputs of the PTC system by merging this unit with the Photovoltaic (PV) module and Organic Rankine Cycle (ORC). In this regard, the outputs of the conventional PTC system under multiple operating conditions are compared with those of PTC-PV, PTC-ORC, and PTC-PV-ORC systems. These systems are three-dimensionally simulated using the steady-state approach and the influences of variation in the solar flux and concentration ratio on the energy and exergy efficiencies are scrutinized. According to the obtained data, at the base case condition, the overall energy efficiencies of the conventional PTC, PTC-PV, PTC-ORC, and PTC-PV-ORC systems are 42.75%, 47.20%, 13.43%, and 21.46%, respectively. The performance of these systems from the exergy viewpoints is 5.51%, 14.31%, 4.19%, and 13.33%, respectively. Based on the simulations, from the electrical energy and exergy viewpoints, the PTC-PV-ORC system has the highest performance followed by PTC-PV and PTC-ORC systems. Nonetheless, the thermal exergy of the ORC-based systems is remarkably lower than that of single solar units. This study shows the integration of the PTC system with the PV module and ORC boosts the output of this conventional unit.

Comparative study on thermodynamic analysis of solid oxide fuel cells supplied with methanol or ammonia

The increasing demand for green hydrogen and power production necessitates the development of novel and upgraded power generation technologies. The solid oxide fuel cell combined heat and power (SOFC–CHP) system is a promising solution due to its high efficiency, clean operation, and fuel flexibility. In practical terms, SOFCs can operate using a variety of fuels such as alcoholic fuel, hydrogen, ammonia, etc. Recently, methanol and ammonia have become noteworthy alternative fuel options as it possesses advantages such as low transportation cost and high hydrogen storage capacity. In this paper, we have established two SOFC–CHP models fueled by methanol or ammonia integrated with the steam Rankine cycle. A comprehensive thermodynamic model is proposed for energy and exergy analyses. Sensitivity analysis is performed to study the system's characteristics. The results show that the SOFC–CHP system fueled by ammonia exhibits superior performance, the maximum electrical power, efficiency, and exergy efficiency is 430W, 7% and 10% greater than the methanol fueled system. The operating temperature is about 30K higher in methanol supplied system. The largest thermal power difference can reach 0.65 kW. Overall, the ammonia fueled SOFC–CHP system shows greater potential than that fueled by methanol.

Energy and exergy evaluation of a novel baffled water photovoltaic/thermal system using integrated collector storage as thermal system: An experimental study

This study analyzes a new baffled photovoltaic/thermal (PV/T) collector consisting of a baffled integrated collector storage (ICS) system integrated with a polycrystalline silicon PV panel. ICS systems have a significant advantage: combining absorbing and storage components causes a simple, affordable structure; furthermore, to improve the convection mechanism, several baffles are installed in the ICS. The energy and exergy analyses were carried out experimentally to discuss the efficiency of the PV/T collector comprehensively. The reserved water stratifies in the tank during daytime, and its temperature obtains the maximum values of 47.2 °C and 38.1 °C at the top and bottom of the tank. Interestingly, the mean water temperature is lower than the ambient temperature in the morning due to radiative sky cooling at night. The thermal, electrical, and overall energy efficiencies of the PV/T system are high in the early morning, nearly 21.67%, 15.22%, and 65.09%; then, these energy efficiencies reduce due to increasing ambient heat losses and PV temperature. Thermal exergy efficiency reaches nearly 0.15%, while electrical exergy efficiency varies between 21% and 22% during daily hours. Therefore, the simple structure with high overall efficiency, nearly 65%, causes the new baffled PV/T collector to be an affordable, robust PV/T system.

Energy, exergy, economical and environmental analysis of photovoltaic solar panel for fixed, single and dual axis tracking systems: An experimental and theoretical study

This investigation focuses on energetic, exegetic, economical and environmental analysis of PV solar system using fixed, single- and dual-axes tracking systems under climatic weather of Zakho city/north of Iraq. Experiments are carried out on 5th September 2022. The energy and exergy analyses are used to predict the performance of three solar panels. The theoretical work includes technical, economical and environmental analysis of proposed 1 MW PV solar power plant are presented using similar characteristics of the experimental data of hourly meteorological climatic conditions during 2022. The findings display that the tracking systems have significant influences on 4–E performances. The experimental results displayed that electrical output power gain and thermal exergy output are increased when using tracking systems, where the exergy losses for single- and dual-axes tracking systems are decreased as compared to fixed solar plane. The maximum improvements in the electrical output power gain of PV solar panels using dual– and single–axes tracking systems are nearly reached to 40 % at 8 a.m., 13 % (for single) and 20 %(for dual) at 12 p.m. and 30 % at 17PM as compared to fixed solar panel. The theoretical results display that the yielded produced energy for single- and dual-axes are increased by 16.5 % and 25.5 %, respectively, as compared to fixed panel. The economic findings display that the cost of energy for single-axes, dual-axes and fixed tracking systems are 4.89, 4.41 and 8.26, respectively. Finally, the use of tracking systems reduces the CO2 emission about 4000–4500 tCO2 annually.

Thermodynamic analysis of an integrated reversible solid oxide fuel cell system

To improve the efficiency of reversible solid oxide cell (rSOC) systems, an rSOC thermal management system architecture is proposed, achieving integrated and efficient operation of rSOC. A 20 kW level rSOC integrated thermal management system with fuel cell and electrolysis cell modes is established using ASPEN PLUS software. The system characteristics of different system operating parameters under fuel cell and electrolysis cell modes are studied. Exergy analysis and energy analysis are conducted on the system under different operating modes, The distribution of exergy flow, the exergy loss between the system and its components, and the influence of fuel utilization on the electrical efficiency and exergy efficiency of the rSOC integrated thermal management system are obtained. The results show that compared to traditional solid oxide electrolysis cell systems, the proposed rSOC integrated thermal management system can improve the electrolysis efficiency of the system to over 70%. In addition, the exergy loss of the system and components mainly exists in heat exchanger 1 in the fuel cell mode, and mainly in the stack in the electrolysis cell mode. The system efficiency of both fuel cell and electrolysis cell modes increases with the increase in fuel utilization rate. Compared to electrolysis cell mode, the system's exergy loss in fuel cell mode is more sensitive to fuel utilization efficiency.

Proposal and analysis of a novel CCHP system based on SOFC for coalbed methane recovery

To utilize the waste heat from coalbed methane, this study presents a novel solid oxide fuel cell (SOFC) system combined with a transcritical carbon dioxide cycle, lithium bromide absorption refrigeration cycle, ammonia vapor compression refrigeration cycle, and water heating cycle to provide power, cooling, and heating. An Aspen Plus model is developed to perform thermodynamic and exergy analyses, assessing system performance. The results indicate that critical parameters such as current density and operating temperature of the SOFC have a significant influence on the overall system. Increasing current density and air preheating temperature enhance thermal efficiency while raising the SOFC operating temperature reduces it. For the specified coalbed methane flow, the system achieves electrical efficiency, thermal efficiency, and exergy efficiency of 52.46%, 86.30%, and 75.58%, respectively. Additionally, the cooling capacity, power generation, and heat production are obtained as 1567.72 kW, 4879.1 kW, and 2476.43 kW, respectively. The SOFC system has the largest exergy destruction, accounting for 48.8% of the total exergy destruction, but the overall exergy efficiency remains at around 75%. The results illustrate that the proposed integrated system provides a high level of efficiency and reliability, thereby offering a new avenue for the efficient and rational utilization of CBM.

Second-law analysis of nanofluid-based photovoltaic/thermal system modeling and forecasting model based on artificial neural network

The PVT solar collectors can produce the thermal energy and power in a same frame. The improvement of the PVT's efficiency leads to reducing the system size and capital costs. To this end, this paper studied the irreversibilities of the Al2O3Cu/water hybrid nanofluid (NF) in a PVT solar collector considering two single and double serpentine channels (SS and DS). The influences of Re and nanoparticle concentration (φ) on the thermal and frictional entropy generation rates (S˙th and S˙fr) were investigated and the thermal, electrical and overall exergy efficiencies (ψth, ψe, ψov) of the PVT with SS and DS channels were compared and discussed. Based on the results, the DS channel exhibited S˙fr of almost 75 % lower than SS channel due to lower nanofluid inlet velocities and velocity gradients. In addition, S˙th for the DS channel is nearly 65 % lower and 26 % higher than that for the SS channel at Re numbers of 500 and 2000, respectively. Besides, the Re escalation from 500 to 2000 intensifies S˙fr by almost 94 % at different φs in the SS and DS channels. The increase in φ from 0 % to 1 % escalates S˙fr by almost 99.98 % times for two configuration regardless of the Re number. ψth of the DD channel is nearly 14.5 % and 12.77 % higher than that of the SS channel at Res of 500 and 2000, respectively. Besides, ψe of the PVT with the DS channel is 2.36 % higher than that with SS channel at Re=500 at four studied φs. Moreover, the maximum ψe for the PVT with the DS and SS were obtained as 22.29 % and 21.28 %, respectively, which are associated with Re=1500 and φ=0.25 %. Additionally, a predictive model was presented to determine the total entropy generation rate based in the Re and φ as the inputs.

Energy, exergy, economic, and environmental (4E) analyses of bifacial concentrated thermoelectric-photovoltaic systems

A concentrated photovoltaic-thermoelectric (CPV-TE) system could utilise the full solar spectrum for electrical energy generation. However, the output performance of the conventional CPV-TE system is low due to the high thermal resistance associated with the TE module that raises the surface temperature of the PV. This study presents comprehensive energy, exergy, economic, and environmental (4E) analyses of two conventional unifacial CPV-TE models and two bifacial CTE-PV models. The bifacial models receive solar energy from two directions. The results reveal that at a concentration ratio of 60, the highest electrical energy and exergy efficiencies of 32% and 35%, respectively, are obtained from the bifacial concentrated segmented thermoelectric-heat sink-photovoltaic (CSTE-HS-PV) model. The annual CO2 savings due to the energy generated by the CSTE-HS-PV, CTE-HS-PV, and CPV-HS-TE are 202 kg/year, 119 kg/year, and 13 kg/year, respectively. Moreover, the payback period (PBP) of the CSTE-HS-PV, CTE-HS-PV, and CPV-HS-TE models are 8.4 years, 10.5 years, and 45 years, respectively. Finally, the levelized cost of energy (LCOE) of the CSTE-HS-PV, CTE-HS-PV, and CPV-HS-TE models are 0.36 $/kWh, 0.55 $/kWh, and 5.06 $/kWh, respectively. Based on the 4E analysis, the CSTE-HS-PV model is found to be superior to the other state-of-the-art models.

Comparative analysis and optimization of waste-heat recovery systems with large-temperature-gradient heat transfer

Efficient utilization of waste heat is crucial for reducing waste heat emissions and minimizing environmental impact. Organic Rankine cycle (ORC) systems are commonly employed for waste heat recovery. However, conventional ORC systems have limitations in effectively harnessing waste heat resources because of differences in the pinch point temperature and the relatively small temperature difference between the heat source inlet and outlet. To address this issue, we designed two absorption organic Rankine cycle (AORC) systems in this study based on absorption heat exchangers. We analyzed the energy, exergy, and economy of three ORC system models with heat source temperatures within the range from 363.15 K to 413.15 K. The results indicated that the AORC system represented a optimal waste heat recovery system, capable of reducing the outlet temperature to 298.70 K and achieving a high temperature efficiency of 1.037. Thus, an AORC system can facilitate heat exchange with substantial temperature differences, enabling the efficient utilization of heat sources. The AORC system in this study exhibited a high net power of up to 151.8 kW, and an electrical exergy efficiency of 55.45%. Additionally, the AORC consistently outperformed other systems in terms of economy, as evidenced by its electricity production cost, which was the lowest among all three systems with heat source temperatures lower than 398.15 K.

Thermodynamic and dynamic analysis of a hybrid PEMFC-ORC combined heat and power (CHP) system

To improve the electrical efficiency of proton exchange membrane fuel cell (PEMFC) combined heat and power (CHP) systems, a novel hybrid CHP system combining PEMFC with organic Rankine cycle (ORC) has been proposed in this study. The proposed system recovers waste heat from the PEMFC stack, electrochemical reaction products, and air compressor, and then further generates electricity through the ORC subsystem. The ORC adopts seawater as the coolant to absorb the low-grade heat generated by the novel system. Based on a 60-kW typical PEMFC CHP system in a hydrogen-electric coupling demonstration project, a thermodynamic model of the novel system is established, and the steady-state, dynamic and economic analysis are performed. At rated stack current, the novel system shows an energy efficiency of 75% and an exergy efficiency of 51%. The electrical efficiency and the electricity exergy efficiency are improved by 4.3% and 5.1% respectively compared to the typical system. As the stack current increases, the electrical efficiency of the novel system declines more slowly. Moreover, the temperature sensitivity analysis shows that the lower the seawater temperature, the higher the system exergy efficiency. During 24 h dynamic operation, the novel system has higher electrical efficiency and exergy efficiency, the average response time of the cycle pump is reduced by 27.5%, and 4.56 kg hydrogen is saved compared to the typical system. In the economic analysis, the levelized cost of energy is 0.34 $/kWh for the novel system at rated operating condition, which is slightly better than the typical system. If the cost of PEMFC stack and hydrogen price decrease by 50%, the levelized cost of energy for the novel system will drop by 47.4% and reach 0.179 $/kWh.

Multi-criteria optimization of a renewable combined heat and power system using response surface methodology

Sun is one of the reliable sources of energy that is available in most locations in the world. Among various solar power units, the parabolic trough collector (PTC) is one of the most functional systems that can provide considerable thermal energy. However, this unit is not able to directly provide electrical energy. Thus, this study presents a non-dimension model of a renewable power system that incorporates a photovoltaic cell and a PTC unit. This hybrid system can simultaneously provide both heating load and electricity. The scheme is examined from the perspectives of exertion, energy, emission, entropy, and economics (5E). In this order, the influence of diverse operating factors on the outcomes of the unit, including saved cost, electrical and thermal exergies, CO2 emission, electrical and thermal energies, and entropy generation, are examined. On top of that, the performance of this innovative unit is optimized using both single-objective and multi-objective methods. The findings indicate that increasing fluid inlet temperature and solar radiation intensity lead to an increase in the temperature of every component of the unit. A stronger heat transfer from the receiver tube to the working fluid causes the temperature of the fluid and solid zones to decrease when the mass flow rate is increased. The analysis shows that the optimum value of solar radiation for the electrical exergy and saved cost is around 900 W/m2 and further reduction or increment in the value of this parameter has an unfavorable impact on both electrical exergy and saved cost. While, raising solar radiation improves all other output parameters of the unit, continuously. Also, it is found that the concentration ratio is the only parameter that elevation in its value leads to ascending the value of all output parameters of the presented system. Based on the findings, at the optimum operating condition, the value of saved cost, CO2 emission, and entropy generation are 70 USD/month, 803.956 kg/month, and 23.93 W/m.K, respectively.

Evaluation of the intermittent performance of heating terminals based on exergy analysis: Discriminate the impacts of heat and electricity input

Intermittent space heating is widely recommended for building energy conservation. Although various heating terminals have been developed, the performance improvement for intermittent heating is still worth evaluating to maximize the energy-saving potential. Currently, energy-based and entransy-based methods are commonly applied for performance analysis, but these methods cannot reflect the comprehensive utilization efficiency of various energy forms. Therefore, this work conducts a discrimination study on the intermittent energy utilization of different heating terminals based on an exergy-based evaluation method. Specifically, this study analyzes the intermittent exergy flow performance of the “heating source-terminal-indoor environment” process. Moreover, we compare how various energy forms impact performance improvement aiming to recognize the potential of different optimization strategies from the aspect of heat and electricity exergy. Furthermore, the holistic performance of heating terminals under different heating source plants is evaluated to support practical applications. The experimental results suggest that the convective terminals attained the best intermittent performance and that the exergy efficiency of the fan coil is the highest (32.9%), with a greater improvement achieved by raising the fan power and connecting the fan coil to the heat pump system. This study provides a novel aspect of analyzing heating performance and optimization path of heating systems.

Energy and exergy analysis of phase change material based thermoelectric generator with pulsed heat sources

Previous studies focus on the generation capacity of phase change material based thermoelectric generator (PCM-TEG) under a steady-state heat source or single pulsed heat source, which cannot fully reflect the dynamic characteristics of TEG under a diversified actual heat source. Meanwhile, the actual heat sources have unstable characteristics of intermittence and fluctuation, resulting in troubles for TEG to maintain effective thermal management and stable generation. In this work, a three-dimensional transient numerical model of PCM-TEG is proposed to characterize its energy harvesting process under multiple pulsed heat sources, including square, triangular, linear and sinusoidal patterns. The effect principle of heat fluxes and heat source periods on PCM-TEG is sensitively performed, aiming to detect the evolution laws of the temperature field and electric field. The energy and exergy analysis of PCM-TEG is determined to indicate its transmission and conversion process. A comparison analysis of PCM-TEG and TEG is carried out to appreciate the thermal management of PCM from temperature difference and failure-free cycle times. The power generation coupling mechanism of PCM-TEG is further developed concerning the phase transition process and power generation process. The results demonstrate that the temperature difference and output power of PCM-TEG change periodically with the pulsed heat sources. The electrical energy and exergy efficiencies of PCM-TEG under square pulsed heat source are 0.10% and 0.45%, higher than other heat sources. Simultaneously, the maximum output power and the electrical energy efficiency of PCM-TEG can be improved by 173.29% and 80% respectively with the enhanced heat flux. Furthermore, although the transient power generation capacity of TEG is weakened by integrating PCM on the hot side, it can alleviate the thermal fatigue of thermoelectric device and meet its thermal management requirements. This paper is informative to understand the dynamics characteristics and power generation coupling mechanism of PCM-TEG for energy harvesting.

Thermodynamic analysis of photovoltaic/thermal heat pump based on phase change slurry

To explore the feasibility and relative advantages of phase change slurry (PCS) as operating working medium, a solar hybrid vapor compression heat pump based on phase change slurry (PCS-PV/T-VCHP) is constructed by directly combining PCS as operating fluid with evaporator. Furthermore, performance of PCS-PV/T-VCHP under different initial conditions is studied and demonstrated by simulation method. PCS as operating medium has higher PV/PT and total efficiencies, which respectively reach 15.46%/83.17% and 98.63%. PCS has multiple advantages for VCHP applications due to high heat storage density and stable heat release. Under given initial conditions, PV/PT efficiencies are 15.15%–15.77%, 67.63%–84.03% respectively, and the maximum solar efficiency are 98.81%. The minimum and maximum values of VCHP coefficient of performance (COP) reach 2.23 and 5.82 respectively, and total COP is distributed in the range of 3.02 and 23.71. The maximum electrical exergy efficiency and thermal exergy efficiency are 15.77% and 7.57% respectively, and total exergy efficiency ranges from 16.61% to 23.25%. PCS-PV/T-VCHP shows good heating performance in typical cities, COP reaches 1.99–5.87 in selected cities. The feasibility of using PCS as operating fluid to supply heat has been confirmed, and PCS-PV/T-VCHP has significant performance advantages, low emissions and good economy.