Fluid Inlet Temperature Research Articles

Prediction of Heat Transfer in a Hybrid Solar–Thermal–Photovoltaic Heat Exchanger Using Computational Fluid Dynamics

Solar energy is one of the main renewable energy resources due to its abundance. It can be used for two purposes, thermal or photovoltaic applications. However, when the resource obtained is mixed, it is called photovoltaic thermal hybrid, where the solar panels generate electricity and are provided with a heat exchanger to absorb energy through a water flow. This is one of the techniques used by the scientific community to reduce the excess temperature generated by solar radiation in the cells, improving the electrical efficiency of photovoltaic systems and obtaining fluid with higher temperature. In this work, the thermal behavior of a heat exchanger equipped with fins in its interior to increase the thermal efficiency of the system was analyzed using CFD (Computational Fluid Dynamics). The results showed that the average fluid outlet temperature was 75.31 °C, considering an incident irradiance of 1067 W/m2 and a fluid inlet temperature of 27 °C. The operating conditions were obtained from published experimental studies, achieving 97.7% similarity between the two. This was due to the boundary conditions of the heat flux (1067 W/m2) impinging directly on the coupled cells and the heat exchanger in a working area of 0.22 m2.

Geothermal bridge deck de-icing using a novel external hydronic heating system with insulated pipe loops

A geothermal-based external hydronic heating system (EHHS) has been developed as an effective solution to address the de-icing needs of in-service bridges with minimum negative impacts on the structure, traffic, and environment. This paper discusses the implementation and operational response of a new design of the EHHS in which rather than the whole bottom surface of the bridge deck, only the hydronic heating loops are covered with insulation material and provides the accessibility for visual inspection of the bridge deck. The first full-scale external hydronic heating system with an insulated loop (EHHS-IL) was installed on a mock-up bridge deck in north Texas and tested in a record snowstorm with a low ambient temperature of −19.5 ˚C. The system operated in three different stages, and the inlet fluid temperature was adjusted according to the weather forecast. Overall, during a 10-day operation, three ice and snow events and 209 hours of freezing ambient temperature were observed. The heating system was able to maintain the heated bridge deck surface temperature above freezing except for 1.3 hours when the −19.5 ˚C low ambient temperature coincided with snowfall. The average surface heat flux during the test varied from 34.8 – 84 W/m2, and the average heating efficiency was estimated at 17.7 %. The seasonal performance factor (SPF) of the system remains consistently greater than 1 during the heating period. Also, 422 kWh of electrical energy was consumed during 10 days of operation by the entire geothermal de-icing system. This new geothermal bridge deicing system offers a practical solution to icy bridges by retrofitting.

Experimental study on the influence factors of falling film heat transfer characteristics outside different types of horizontal tubes

An experimental setup was established to analyze the performance of a spiral wound heat exchanger applied to natural gas liquefaction. The boiling behavior of subcooled flow over a small diameter, non-round, horizontal tube was investigated using n-pentane as the working fluid. The effects of flow rate, heat flux, fluid inlet temperature and tube spacing on heat transfer performance were investigated. Based on the experimental conditions of this study, the results indicate that: (1) raising the Reynolds number can effectively enhance the heat transfer coefficient; (2) the increasing in heat flux also has a positive impact on heat transfer performance, but the extent of which is related to the Reynolds number; (3) increasing the tube spacing resulted in higher heat transfer coefficients; (4) under the same working conditions, the heat transfer performance of non-round tubes is higher than that of round tubes; (5) correlation equations were developed to calculate the Nu for smooth, round, elliptical, and egg-shaped tubes. The predictions made by these correlation equations deviated by less than 10 % from the experimental results for the entirety of the experimental conditions.

Numerical study on hydrogen desorption performance of a new MgH2 solid-state hydrogen storage device

To explore the factors affecting the hydrogen evolution performance of a new MgH2 solid-state hydrogen storage heat exchanger, this paper designs the MgH2 solid-state hydrogen storage device. The study numerically investigates the influence of operating parameters and structural parameters on the hydrogen release reaction. The results demonstrate that the hydrogen desorption rate increases as the pressure decreases from 0.3 MPa to 0.1 MPa. Moreover, the hydrogen evolution reaction rate significantly rises with an increase in the inlet temperature of the heat transfer fluid (HTF) from 600 K to 700 K. Similarly, the rate of hydrogen evolution reaction increases with an increase in the flow rate of the HTF from 0.5 m/s to 1.25 m/s. The hydrogen evolution reaction time can be notably reduced by increasing the thickness of the annular HTF layer. Compared to no annular fluid layer, the completion time of the hydrogen desorption reaction is shortened by 558 s with a 5 mm thickness. The arrangement of heat exchanger pipes plays a crucial role in the hydrogen evolution reaction, and thus a comprehensive index M is defined to evaluate its influence. A higher M value indicates slower hydrogen release efficiency of the device. By optimizing the operating conditions, the hydrogen desorption time can be shortened by 93.4 %.

Numerical Study of an Energy Storage Container with a Flat Plate Phase Change Unit Characterized by an S-Shaped Flow Channel

China’s rapid economic development and rising energy consumption have led to significant challenges in energy supply and demand. While wind and solar energy are clean alternatives, they do not always align with the varying energy needs across different times and regions. Concurrently, China produces substantial amounts of industrial waste heat annually. Effective recycling of this waste heat could substantially mitigate energy supply and demand issues. The Mobile Thermal Energy Storage (M-TES) system is a key solution to address these challenges, as it helps manage the uneven distribution of energy over time and space. This article establishes a packaged M-TES based on a plate-type phase change unit. Based on different placement methods of the plate-type phase change unit, different inlet temperatures and phase change temperature differences, and different inlet and outlet directions, the complete charging and discharging process of the packaged phase change thermal storage system was simulated using ANSYS FLUENT 2022 R1 software. The results showed that during the heating process of the entire system, the horizontal placement of the plate-type phase change unit and the inlet and outlet methods of the heat transfer fluid (HTF) significantly improved the heating effect of the system, increasing it by 15.9%. Increasing the temperature difference between the inlet temperature of the heat transfer fluid and the melting temperature of the phase change material (PCM) from 4 K to 19 K can increase the melting rate of PCM by approximately 54.9%

Assessing the Impact of Transport Phenomena on Modeling and Optimization of Solid-State Fermentation for the Revalorization of Agro-Industrial Residues in a Wall‐Cooled Packed‐Bed Bioreactor

This work assesses the influence of transport phenomena on the growth of Yarrowia lipolytica 2.2ab (Yl2.2ab) and protease production during Solid-State Fermentation (SSF) in a bench-scale wall-cooled tubular bioreactor packed with substrate-based pellets derived from agro-industrial residues. Our engineering methodology, in a novel manner, includes: (i) developing a new pseudo-heterogeneous model, (ii) identifying and quantifying the impact of all transport phenomena on microbial kinetics, (iii) elucidating how fluid dynamics enhances heat and mass transfer processes, and hence microbial kinetics, and (iv) determining the operational and geometric parameters for optimal bioreactor performance. As main results: (i) all transport phenomena occurring within the bench-scale bioreactor are fundamental for its reliable simulation and will be essential for its scale-up, and (ii) the maximum production of proteases, 420 U kgDS‐1−1, is achieved under the following operational conditions: a tube to particle diameter ratio of 5.6, a bath temperature of 45°C, an inlet airflow rate of 1 L min−1, and inlet fluid temperature of 43 °C. Finally, the pseudo-heterogeneous model is assessed by describing SSF-based observations from the literature, appropriately predicting the performance of Yl2.2ab in a bench-scale bioreactor. These results pave the way for future exploration of Yl2.2ab in SSF within larger-scale packed-bed bioreactors.

Numerical study on heat restoration cycle performance of energy pile with backfilling PCM

The numerical analysis of energy pile backfilled with phase change material (PCM) was performed for the renewable geothermal energy utilization in building energy savings. Different operation modes and the melting temperature, latent heat, thermal conductivity of the PCMs within the energy piles were discussed to obtain the optimal parameters. Further, the restoration and heat transfer performance of energy piles were also analyzed for the prolonged operation. It was concluded that relatively higher latent heat and thermal conductivity were preferable to enhance the heat transfer rate per meter (Qm) of the PCM-backfilled energy pile. However, a relatively lower PCM latent heat may help to full utilization and restoration of PCMs during every cycle of cooling and heating when energy pile works. An ideal melting temperature of PCM is probably close to the initial soil temperature to achieve preferred restoration and heat transfer performance, rather than the inlet fluid temperature. In heating 12 h and cooling 12 h alternate mode, taking continuous operation as a reference, the Qm and the restoration rate of pile wall temperature of the PCM-backfilled energy pile were increased by 32.7 % and 52.5 % after operating 720 h.

Hybrid nanocomposites impact on heat transfer efficiency and pressure drop in turbulent flow systems: application of numerical and machine learning insights

This research explores the feasibility of using a nanocomposite from multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) for thermal engineering applications. The hybrid nanocomposites were suspended in water at various volumetric concentrations. Their heat transfer and pressure drop characteristics were analyzed using computational fluid dynamics and artificial neural network models. The study examined flow regimes with Reynolds numbers between 5000 and 17,000, inlet fluid temperatures ranging from 293.15 to 333.15 K, and concentrations from 0.01 to 0.2% by volume. The numerical results were validated against empirical correlations for heat transfer coefficient and pressure drop, showing an acceptable average error. The findings revealed that the heat transfer coefficient and pressure drop increased significantly with higher inlet temperatures and concentrations, achieving approximately 45.22% and 452.90%, respectively. These results suggested that MWCNTs-GNPs nanocomposites hold promise for enhancing the performance of thermal systems, offering a potential pathway for developing and optimizing advanced thermal engineering solutions.

A comparative analysis of ammonia and supercritical carbon dioxide in horizontal microchannels

Supercritical carbon dioxide (sCO2) and ammonia (NH3) can be used as coolants in high power-density microelectronics. sCO2 at the micro scale provides enhanced heat transfer solutions for a range of microelectronics cooling applications·NH3 can also potentially provide appropriate cooling solutions as it has favorable thermophysical properties at high pressure, and it can be used as an energy carrier as it contains Hydrogen atoms. Near its critical and pseudocritical condition sCO2 exhibits abrupt changes in its thermophysical properties and at similar pressures liquid NH3 too has adequate properties that make it a good coolant. While sCO2 is non-toxic, NH3 is a toxic substance and should only be used in closed loop micro heat exchangers.The current study compares the convective heat transfer performance of supercritical carbon dioxide (sCO2) and ammonia for microchannel cooling. A total of 144 numerical cases inside a square microchannel of hydraulic diameter of 200 µm with a total length of 52 mm and a heated length of 50 mm at constant surface temperatures in laminar flow conditions were examined. Two scenarios were investigated, in one the inlet mass flux was kept constant at 100, 150, and 200 kg/m2s, and in the second the pressure drop across the microchannel was maintained at 200, 400, and 600 Pa. Both scenarios were investigated at pressures of 8 and 10 MPa and at surface temperatures of 32, 40, 50, 60, 70, and 80 °C. In all cases the inlet temperature of both fluids was kept at 21 °C. At the same mass flux, NH3 yielded a higher average heat transfer coefficient (havg) but at the same pressure drop, sCO2 resulted in higher havg at certain surface temperatures. The havg for NH3 didn’t show significant variation but for sCO2 it showed significant change with surface temperature, and this was due to the significant change in the thermophysical properties of sCO2. The havg showed a mixed behavior with respect to the pumping power. The coefficient of performance (COP) was as high as 600,000 for sCO2 and it was significantly higher than that for NH3. Near the pseudocritical region, the COP for sCO2 witnessed a significant improvement, more than double, for 8 MPa compared to 10 MPa.

Performance of an additive-manufactured precooler under high-temperature and negative pressure environment

This paper introduces an original plate-fin precooler designed for potential applications in extreme low-pressure environments. Utilizing additive manufacturing technology, the heat transfer plate thickness is constrained to 2.0 mm, with channel widths inside the plate achieving 0.8 mm. Through experimental methods, this study aims to assess the precooler’s performance and identify critical influencing factors. Experimental results indicate that the hot fluid inlet temperature to the precooler exceeds 1100 K, with static pressures dropping below 30 kPa. Despite these conditions, the precooler demonstrates an impressive pressure recovery coefficient exceeding 97 % and achieves a maximum temperature drop of 731.4 K for the hot fluid. Furthermore, it is observed that the overall performance of the precooler diminishes with increasing mass flow rates of the hot fluid, showing fluctuations of up to 25 % when assessed by the j/f1/3 factor. Additionally, while the hot fluid inlet velocity exceeds 90 m/s, laminar flow predominates during the heat transfer process. Moreover, regardless of whether the cooling fluid experiences a phase change within the precooler, its heat transfer performance show priority than that of the hot fluid. Thus, changes in the mass flow rate of the cooling fluid have minimal impact on the overall precooler performance. Finally, the first-stage heat exchanger plays a critical role in the heat transfer process, accounting for over 2/3 of the total temperature and pressure drop for the hot fluid. This research is expected to contribute to the design of high-efficiency, low-resistance precoolers, particularly those applied for operation under negative pressure conditions.

INVESTIGATION OF FLOW AND HEAT TRANSFER PERFORMANCE OF GYROID STRUCTURE AS POROUS MEDIA

There are active and passive methods used to improve heat transfer. One of the passive methods is utilising porous media with high heat transfer surface area. Porous media are divided into two groups: regular and irregular structures. One of the regular structures is triply periodic minimal surfaces (TPMS), which have been studied quite frequently recently. In this study, heat transfer and flow analysis of a Gyroid geometry, one of the most used TPMS in the literature, is investigated numerically considering the conjugate heat transfer conditions. A single porosity is considered (ε = 0.6), and aluminium, ceramic and PLA are selected for the heat exchanger material to examine the temperature change in the heat exchanger. To understand the different flow characteristics, Reynolds numbers (Reh) are assumed to be 19.12, 95.61 and 172.09. The fluid inlet temperature is assumed to be constant at 298.15 K, and the initial temperature of the heat exchanger is assumed to be constant at 278.15 K to be consistent with the regenerative heat recovery temperature difference in ventilation standards. Nu numbers under different operating conditions are compared, and it is the ceramic material with low thermal diffusivity is at the highest level despite its low thermal conductivity. At the highest Re number, it provided approximately 6% better heat transfer than the aluminium heat exchanger.

Experimental investigation of thermohydraulic performance, entropy minimization, and exergy efficiency in red mud nanofluid

Red mud consists of valuable metal oxides as part of its chemical composition. This research investigates the use of water-based red mud nanofluids in circular copper tube under turbulent flow conditions for heat transfer applications. The focus is on entropy and exergy analysis, with an inlet fluid temperature of 60 °C. The study explores the thermophysical properties and stability of the nanofluid at concentrations ranging from 0 to 0.75 vol%. The findings reveal that both the heat transfer coefficient and pressure drop of the red mud nanofluids improve with concentration and Reynolds number. The maximum observed enhancement in Nusselt number is 28 % for the 0.75 vol% compared to water. Interestingly, the minimum total entropy generation of 0.13 and the maximum exergy of 1.8 are also observed for the 0.75 vol% nanofluid. While the friction factor of the red mud nanofluids increases with concentration, it decreases at a higher Reynolds number. The maximum Performance Index (PI) of 1.61 is achieved for the 0.75 vol% concentration.

Experimental Study on Convection Heat Transfer of CO2 in C/SiC Composite Porous Material at Subcritical, Transcritical, and Supercritical States

Using C/SiC as the structure for transpiration cooling is prospective for new hypersonic vehicles, based on clarification of heat transfer process in porous media. But there are still gaps due to the complexity of pore structure of C/SiC, together with the effects of capillary force and strong variation of thermophysical properties for subcritical and supercritical flow. In this study, heat transfer analysis for C/SiC with CO2 as the coolant is presented by experiments. Heat transfer characteristics in typical C/SiC sample under various mass flow rates (0.003–0.018 kg/s), inlet fluid temperatures (20–40 °C) and pressures (5.9–10 MPa) are analyzed. Heat transfer and pressure drop correlations have been developed. The results show heat transfer coefficient at supercritical state behaves non-monotonic under varying flow rates caused by the combined effect of sharp increase of specific heat and the change of flow rate. The effect of pressure on heat transfer can be neglected compared to that of flow rate, while for Reynolds number (Re) >100, the pressure drop of supercritical cases are smaller than that of phase-change cases under similar Re, due to the effect of capillary force in C/SiC. This study can provide basic support for further study of transpiration cooling using C/SiC and CO2.

Convective Heat Transfer Analysis of Supercritical CO2 in Artificial Rock Fractures

Geothermal energy has emerged as a promising renewable and sustainable resource. This research article explores the utilization of supercritical CO2 and convective heat transfer in porous rock to enhance geothermal extraction. Artificial cement rock with a smooth and manmade slotted surface fracture was used as a working sample for heat transfer source in the test. Heat transfer characteristics under various flow rates, fluid inlet temperature and pressure, rock initial temperature are analyzed. The results indicate that the geometry characteristics of fracture surface impact the overall heat transfer intensity to a certain extent, whereas lithology has little influence on the heat transfer intensity. In addition, it is found that increasing injection pressure affects the operating temperature and density of the injected fluid, which helps to improve the production effect, to obtain more heat. However, limited by the heat transfer area, low injection flow is required. The maximum error of the heat transfer coefficient model is 7.05% compared with the empirical value and less than 10% compared with the experimental results. By examining the interaction between fluid and porous fractures, we aim to provide insights into the potential of these techniques for maximizing energy efficiency and tapping into deep geothermal resources.

Experimental evaluation of localized air temperature profile and performance of serpentine copper tube heat exchanger for energy-saving crop cultivation

The objective of this study is to examine the localized air temperature profile and heat transfer performance of a serpentine copper tube heat exchanger. Particularly, the air temperature nearby the plants is controlled by the heat exchanger. The novelty of this study is to provide localized climate control only near the plants targeting periodic air temperature control with the proposed heat exchanger. This study focuses on heating and cooling for cultivation in temperate and tropical regions. In contrast to fin-and-tube heat exchangers, the serpentine heat exchanger has a simple design, provides minimal shade for plants, and is easy to maintain. This study was conducted in a laboratory. The experimental system was constructed under with the assumption that a part of actual plant cultivation was being left out. The experiments were implemented by varying the experimental operating conditions such as the inlet fluid temperature and fluid flow rate in the heat exchanger. The pressure drop in the heat exchanger was also measured. The results revealed that this heat exchanger could provide localized air temperature control. The maximum air temperature difference can be obtained at approximately 12 °C during cooling and heating from their initial air temperature even though the heat exchange is simple. The effects of decreasing the inlet fluid temperature for cooling and increasing the inlet fluid temperature for heating were more dominant than the effect of the flow rate. This simple, low-maintenance, and low-cost serpentine copper tube heat exchanger can effectively provide alternate heating and cooling for plant cultivation.

Experimental study on liquid immersion preheating of lithium-ion batteries under low temperature environment

An experimental platform to examine the effects of single-phase immersion preheating on lithium-ion battery performance at low temperatures was set up in this study. The performance of lithium-ion batteries at low temperatures can be improved through immersion preheating. After preheating from −15 °C to 15 °C, the battery capacity can recover to over 80 % of its rated capacity. The three influencing factors are inlet flow rate, fluid temperature, and cell spacings. The inlet temperature exerts the most influence on the preheating performance. The warming rate can reach 1.63 °C/min at a temperature of 50 °C. While the increase in flow rate has less influence on the heating rate, it has a greater impact on the temperature difference between cells. The maximum temperature difference between cells can still be kept below 4 °C. The impact of spacing on the heating rate and temperature difference is minimal. The temperature difference can be controlled within 6 °C. Finally, it's important to note that immersion preheating consumes significant amount of energy. The energy consumption of preheating at an ambient temperature of −25 °C exceeds 80 % of the rated capacity of the experimental battery pack.

Experimental thermal performance intensification of gravitational water vortex heat exchanger using hexagonal boron nitride-water nanofluid

One of the main concerns presently is the rapid improvement of thermal technology for widespread heat exchanger applications involving energy conservation and intensification of heat transfer process. For the enhancement of heat exchange processes, nanofluids have been considered as a potential substitute for conventional fluids, which in general have subpar thermal characteristics. Therefore, the present study focusses on the heat transfer enhancement and the intensification of overall thermal performance of the developed gravitational water vortex heat exchanger (GWVHE). The experimental investigation first involves the preparation and characterization of water-based hexagonal-boron nitrides (h-BN) nanofluids as well as the computation of thermophysical properties of different volume fractions of h-BN nanofluids. Subsequently, a comparative analysis evaluating the thermal energy exchange capabilities of water-to-water and water-to-h-BN nanofluids combination of two fluids has been conducted to investigate the intensification in thermal performance of the developed GWVHE. The experimental investigation is primarily based on calculating the thermal energy balance, overall heat transfer coefficient, log-mean temperature difference (LMTD) and the effectiveness of the developed GWVHE using effectiveness-NTU method. The experimental results reported that 0.02 % volume fraction of water-based h-BN nanofluids is more suitable for further testing of the developed GWVHE to mitigate the stability concerns at higher concentrations. The minimal thermal losses, that lie within the 10 % confirms the thermal energy balance and by using the h-BN nanofluids −to-water strategy for two fluids. The maximum value of heat exchange rate significantly increased from 8490 W to 9998 W with the utilization of h-BN nanofluids-to-water as compared to water-to-water combination. Furthermore, the maximum values of LMTD employing h-BN nanofluids are found to be reduced from 21.15 K to 17.53 K compared to the water-to-water combination confirming the intensification in thermal performance of GWVHE. The overall heat transfer coefficient values are also found higher when h-BN nanofluids are substituted instead of water. The maximum value of overall heat transfer coefficient for h-BN nanofluids-to-water combination is improved from 874 W/m2K to 1142 W/m2K compared to water-to-water combination. Moreover, by utilizing the h-BN nanofluids-to-water combination, the values of effectiveness are intensified by an average of 13.5 % and 9 % in both sets of testing parameters, respectively. All these maximum improvement in findings for heat exchange, overall heat transfer coefficient, effectiveness, and reduction in LMTD values are obtained by maintaining the inlet mass flow rate of cold fluid at 0.142 kg/s, while the inlet mass flow rate of hot fluid was varied in the range from 0.092 kg/s to 0.133 kg/s. Additionally, the inlet temperatures of hot and cold fluids are kept at 330 K and 296 K, respectively. Hence, the utilization of h-BN nanofluids is proven to be highly effective for boosting thermal energy exchange and enhancing the overall thermal performance of the developed GWVHE.

Comparative energy, exergy and entropy generation study of a minichannel and a conventional solar flat plat collectors

Considering the importance of using renewable energies for human societies, it is necessary to optimize the devices used. Flat plate solar collectors play a prominent role in the domestic and industrial sectors, so it is very important to enhance their performance. Changing the structure of the collector and using minichannel flat plate collectors (MFPCs) instead of sheet and tubes conventional flat plate collectors (CFPCs) is one choice. This study examines and compares the performances of a MFPC and a CFPC based on the energy, exergy and entropy generation perspectives. The working fluid is water and the fluid flow is laminar. Both collectors have the same contact surface between the working fluid and the inner surface of the riser tubes or the minichannels. In order to solve the equations, a thermal model is developed and the engineering equation solver is used. The results show that for all of the investigated conditions, the thermal and exergy efficiencies of the MFPC are higher than those of the CFPC and the maximum energy and exergy superiorities of the MFPC are 13.8 and 14.08 %, respectively. The study of the energy performance criteria shows that the MFPC is more suitable at lower volumetric flow rates and higher inlet fluid temperatures. Investigating the entropy generation and exergy destruction indicates that for every similar case the entropy generation and exergy destruction of the MFPC are lower than those of the CFPC. These interpretations, which are based on the energy, exergy, entropy generation and exergy destruction evaluations, recommend utilization of MFPCs instead of CFPCs.

Utilizing a CNN-RNN machine learning approach for forecasting time-series outlet fluid temperature monitoring by long-term operation of BHEs system

The Borehole Heat Exchanger (BHE) plays a pivotal role in enhancing heat exchange efficiency within Ground Source Heat Pump (GSHP) systems. The accurate prediction of the BHE's outlet fluid temperature is crucial for optimizing GSHP performance, energy storage, and resource conservation. However, conventional machine learning methods encounter challenges in manual feature extraction, learning complex nonlinear relationships, and adapting to real-world scenarios. To address these limitations, this research proposes a crossbreed model integrating Convolutional Neural Network (CNN) and Recurrent Neural Network (RNN) architectures to forecast long-term outlet fluid temperature in BHE systems. The model framework encompasses data preprocessing, utilizing refined data in the CNN module for temporal feature extraction, subsequently passed to the RNN module to capture sequential and temporal patterns from each dataset. Specifically, the advanced CNN-RNN architecture is designed to establish a comprehensive input-output mapping, leveraging essential input features such as inlet fluid, ambient air, and subsurface temperatures at varying depths (0, 10, and 20 m). Performance evaluation metrics, including R2, RMSE, MAE, and AARE, are employed to compare and assess prediction accuracy across various models, including LSTM, CNN, and SimpleRNN. The obtained results demonstrate the superior performance of the proposed model, achieving an RSME of 0.818, MAE of 0.642, AARE of 0.0305, and an R2 value of 98.75 %. This surpasses the performance of traditional prediction models (LSTM, CNN, and SimpleRNN) by 3.01 %, 5.80 %, and 19.52 %, respectively. Notably, the remarkably low MAE of 0.642 exhibited by a CNN-RNN model underscores its capability to outperform traditional approaches, especially when handling large datasets. These findings emphasize the significance of the developed model in facilitating efficient operation, positioning it as a valuable tool for advancing the long-term sustainability of BHE systems.

Split flow principle implementation for advanced subcritical double stage organic rankine cycle configuration for geothermal power production

The main goal of research is to find the most suitable combination of working fluids, for double stage Organic Rankine Cycle configurations which ensure maximum net power output for low to medium enthalpy geothermal sources with temperatures from 120 °C to 180 °C. All obtained results are compared with the values obtained in simple Organic Rankine Cycle configuration. In general, it can be concluded that the highest net power output is produced by the double stage Organic Rankine Cycle configuration in the geothermal temperature interval from 120 °C to 132 °C. In the geothermal fluid inlet temperature interval from 143 °C to 180 °C double stage Organic Rankine Cycle configuration achieves the highest net power output values at 150 °C, 160 °C, 170 °C and 180 °C and that 40,93 (kW) with a combination of working fluids R236fa/R1234yf (high temperature stage/low temperature stage), 49,85 (kW) with R236ea/R227ea, 59,03 (kW) with R236ea/R227ea and 69,40 (kW) with n-Butane/R1234ze(E). In the temperature interval from 132 °C to 142 °C all considered configurations achieve similar values of net power output.