Heat Exchanger Model Research Articles

Long-term performance prediction of ground source heat pump system based on co-simulation and artificial neural network

Ground source heat pump (GSHP) systems are efficient and widely used form of shallow geothermal energy utilization. In practical application, GSHP systems face the problem in predicting the long-term performance and energy efficiency variations in GSHP systems in regions with thermal imbalances. In this study, a coupling heat transfer model of vertical ground heat exchanger (GHE), heat pump, and building load was established to achieve refined simulation calculations of the long-term operation of GSHP systems. Parametric modeling was conducted by employing the co-simulation of COMSOL and MATLAB, enabling dynamic simulations of 600 sets of GSHP system models throughout the entire year. A database was established by extracting the numerical results, and a prediction model was developed using artificial neural network (ANN) methodology to learn from the database. The model predicted the ground temperature, seasonal energy efficiency ratio (SEER), seasonal coefficient of performance (SCOP), annual electricity consumption, and annual energy savings of the GSHP system and the prediction model was valid. The results were used to estimate the ground temperature, coefficient of performance (COP), payback period for static investment, and carbon dioxide emission reduction. Finally, the prediction model was applied to a GSHP system engineering project in Yancheng, China, forecasting the operation performance of the system for 10 years. The accuracy of ANN in predicting 10 years of long-term performance is verified.

Multi-aspect exergo-economic/environmental study/optimization of an eco-friendly heat integration process for gas turbine modular helium reactors in integration with a Stirling engine

As a nuclear power source, gas turbine modular helium reactors (GT-MHR) can play a major role in the energy industry due to their high safety index and low operating costs. In light of the GT-MHR's high heat capacity, this study integrates a GT-MHR cycle with a Stirling engine to achieve a high-efficiency electricity production framework in an eco-friendly framework. Multi-aspect study from energy, exergy, economic and exergoenvironmental viewpoints are conducted. Detailed heat exchanger modeling is performed to accurately evaluate the system's performance conditions as part of the design process. The outcomes of this study reveal that in the optimum operating mode, the turbine's inlet temperature and expansion ratio are 1300 K and 2, respectively. The compressor compression ratio is 2.1, the Stirling engine inlet temperature is 850.6 K, and the regenerative effectiveness is 0.866. Consequently, the system's total electricity becomes 325.57 MW with 54.26 % energetic and 75.13 % exergetic efficiencies. The economic assessment of the system reveals that the unit electricity product cost is 8.9 $/GJ, and the total investment cost is 12737 $/h. Also, the optimal exergoenvironmental results show an exergoenvironmental index of 0.237, an environmental damage effectiveness index of 0.0031, and an exergetic stability factor of 0.24. Compared to GT-MHR, GT-MHR/KC, GT-MHR/APC, and GT-MHR/ORC, the newly designed system produces 44.57, 21.47, 29.74, and 25.17 MW more electricity and is more energetically efficient by 28.3 %, 24.45 %, 25.8 %, and 25.07 %, respectively.

Discretized and experimental investigation of thermo-hydraulic behavior in a compact heat exchanger manufactured via SLM process

The demand for a better understanding of the fluid thermal and hydrodynamic behavior along the heat exchanger makes it necessary to develop a discretized analysis. The temperature and pressure distributions from the local analysis allow the obtaining of mechanical and thermal stress fields, making the method advantageous in comparison to the conventional global analysis. This work developed a local thermo-hydraulic model for a compact heat exchanger manufactured via Selective Laser Melting (SLM) process. The cross-flow heat exchanger core, produced with American Iron and Steel Institute (AISI) 316L, has 100 mm height, 100 mm width, 100 mm length, and a 2 mm channel diameter. The local steady-state models were compared with experimental data. The experiments were performed with water on both sides, using different temperatures for the hot side, and Reynolds numbers ranging from 1748 to 12247. The local analytical models have a good agreement, with 14% average errors for the thermal and hydrodynamic models. Besides, the impacts of channel diameter and surface roughness in the pressure drop were studied.

Impact of vortex generator, magnetic field, and magnetic two-phase hybrid nanofluid on the performance of a dual-tube heat exchanger: Hydrodynamic and exergy analyses

In this study, a three-dimensional model of a counter-flow dual-tube heat exchanger is developed. The heat exchanger is equipped with a vortex generator, and the working fluid used is a hybrid nanofluid consisting of water and iron-copper oxide. The effects of using the hybrid nanofluid and pure water are investigated. Turbulent flow conditions are assumed within a Reynolds number (Re) range of 30,000 to 48,000, employing the realizable k-ε turbulence model. The coupled algorithm is employed to solve the velocity and pressure equations, and the equations are discretized using the least square method. The vortex generator is utilized with various pitch ratios (Ω). Furthermore, the magnetic field affects the middle section of the inner tube, with Hartmann numbers (Ha) of 35, 65, 95, and 125. The study reveals that an increase in the volume fraction (φ) positively impacts the exergy of the heat exchanger, while an enhancement in Ω negatively influences it. Furthermore, the energy efficiency improves with increasing Re. By applying the magnetic field, the maximum power of the system in producing work corresponds to Re = 36,000 because ηex is reduced when Re > 36,000. At all values of Re, the increase in Ha improves ηex.

Numerical Investigation on the Performance of Horizontal Helical-Coil-Type Backfill Heat Exchangers with Different Configurations in Mine Stopes

The application of ground heat exchanger technology in backfill mines can actualize subterranean heat storage, which is one of the most effective solutions for addressing solar energy faults such as intermittence and fluctuation. This paper provides a 3D unsteady heat transfer numerical model for full-size horizontal backfill heat exchangers (BFHEs) with five configurations in a mining layer of a metal mine by using a COMSOL environment. In order to ensure the fairness of the comparative analysis, the pipes of BFHEs studied have the same heat exchange surface area. By comparing and evaluating the heat storage/release characteristics of BFHEs in continuous operation for three years, it was discovered that the helical pipe with serpentine layout may effectively enhance the performance of BFHEs. Compared with the traditional SS BFHEs, the heat storage capacity of the S-FH type is significantly increased by 21.7%, followed by the SA-FH type, which is increased by 11.1%, while the performances of U-DH and SH type are considerably lowered. Also, the impact of the critical structural factors (pitch length and pitch diameter) was further studied using the normalized parameters C1 and C2 based on the inner diameter of the pipe. It is discovered that BFHEs should be distributed in a pipe with a lower C1, and increasing C2 encourages BFHEs to increase the storaged/released heat of BFHEs. By comparatively analysing the effect of thermal conductivity, it is found that the positive effects of thermal conductivity on the performance of SH, U-DH, SA-FH, and S-FH type BFHEs are found to decrease successively. This work proposes a strategy for improving the heat storage and release potential of BFHEs in terms of optimal pipe arrangement.

Methods, Thermodynamic Applications, and Habitat Implications of Physical and Spectral Properties of Hair and Haircoats in Cattle.

The physical properties (hair diameter, hair length, haircoat depth and haircoat density) and spectral properties (absorptivity, reflectivity, transmissivity) of the hair and haircoat of cattle are inputs to heat and moisture exchange between the skin surface and the surrounding environment, and thus play a critical role in body temperature regulation. Physical and spectral properties of haircoats also play an important role in protecting the skin against penetration of ultraviolet radiation. The focus of this review is to identify accurate and consistent measurement procedures of these properties. Additionally, the paper shows the utilization of the properties on heat exchange models and their implications on voluntary thermoregulation of cattle. To highlight the effects and benefits of haircoat color vis-à-vis solar radiation and its implication on ecological habitation, a brief explanation is provided using polar bears (white haircoat in a cold environment) and black goats in a hot desert environment.

Numerical Investigation and Machine Learning-Based Prediction of the Effect of Using Ring Turbulators on Heat Transfer Characteristics in a Counterflow Heat Exchanger

Background:: Pipe-type heat exchangers are commonly used in industrial applications to facilitate heat transfer between two fluids at different temperatures without mixing them. Method:: In this study, turbulators were employed in a counterflow concentric pipetype heat exchanger. Water at a flow rate of 50 l/h and a temperature of 298.14 K, and air at a temperature of 350 K were directed through the inner pipe. The different stages of circular turbulators placed inside the inner pipe were numerically investigated using the feasible κ-ε turbulence model. Heat transfer characteristics were examined for a turbulator-free heat exchanger and for turbulator-heat exchanger models with helical turbulators of 25, 50, 75, and 100 mm pitch at Reynolds numbers ranging from 4000 to 26000. The governing equations for three-dimensional and turbulent flow conditions in a steady state were solved using a computational fluid dynamics program based on the finite volume method. Temperature distributions and velocity contours in the heat exchanger were generated using the data obtained from numerical analysis. Additionally, predictions were made using artificial neural networks. Results:: The results revealed that the highest enhancement in heat transfer, amounting to 233.08% compared to the empty tube case, was achieved with the 25 mm pitch turbulator. Conclusion:: The predictions made using artificial neural networks were in good agreement with the numerical analysis results. The designed turbulators for the heat exchanger model promoted turbulent flow, increased the heat transfer area, and led to an improvement in heat transfer.

Advancements in heat exchanger design for waste heat recovery in industrial processes

This project shows the efficiency of the heat exchanger model and how effectively the model can transmit from one medium to another medium. The heat recovery in the industrial process gets improved after using this model in the industries. The heat exchanger model has good accuracy in transmitting heat from one medium to another medium.

Results of numerical modeling of three-pipe heat exchanger for livestock premises

Results of numerical modeling of three-pipe heat exchanger for livestock premises

Performance assessment of a real water source heat pump within a hardware-in-the-loop (HIL) testing environment

Over the last decade, the global fight against climate change through electrification has led to an increase in research on building heating, ventilation, and air conditioning (HVAC) systems that utilize intelligent control algorithms to provide demand-side grid service while also maintaining the thermal comfort of building occupants. As the pivotal point between building electricity consumption and indoor thermal comfort, high-efficiency electrical vapor-compression heat pumps are at the center of these emerging studies, and various grid-interactive and occupant-comfort control algorithms have been developed for them. The impact of these algorithms on heat pump operation and performance when subjected to different weather conditions, building loads, and grid requests calls for investigation and verification via experimental testing with actual heat pumps integrated with real-time building and grid responses. This study introduces a Water-Source Heat Pump (WSHP) Hardware-in-The-Loop (HIL) Test Facility that is the first of its kind. This testbed utilizes a 2-ton variable speed water-to-air heat pump that is capable of interacting with a virtual environment currently comprised of an EnergyPlus (E+) building simulation, an agent-based occupant behavioral model, and a single U-tube ground-loop heat exchanger (GLHE) model. Detailed descriptions of the testbed’s physical design and operation, virtual environement, as well as their mutual communication is provided. An uncertainty analysis is also performed under manufacturer specified heating and cooling design conditions. This analysis shows that the total load across the WSHP’s demand side heat exchanger, i.e., the sum of its latent and sensible components, can be measured with a relative uncertainty of ± 10.4% and ± 3.6% in cooling and heating mode respectively. The WSHP’s coefficient of performance (COP) can be measured with relative uncertainties of ± 10.4% in cooling mode, and ± 3.7% in heating mode. A preliminary 24-h experimental demonstration is then performed utilizing the DOE prototype small commercial office building model in E+. The simulation takes place in Atlanta, GA on the date of 08/26/15 from 12:00 AM to 11:59 PM using TMY3 weather data. . The results from this demonstration show that over the course of this experiment the simulated outputs of zone dry-bulb temperature, zone humidity ratio, and WSHP inlet water temperature can be tracked by testbed emulators up to a root mean squared error (RMSE) of ± 0.27 °C, ± 0.376 g/kg, and ± 0.85 °C respectively. The WSHP’s dynamic behavioral characteristics and performance are also captured, and correspond well with the authors’ previous understanding of heat pump efficiency as a function of evaporator and condenser fluid inlet conditions respectively.

Solar powered hybrid desalination system using a novel evaporative humidification tower: A numerical investigation

This research describes a hybrid solar desalination system that includes a humidification-dehumidification unit as well as a solar still unit. The current system is being studied numerically. A one-dimensional model of the important heat and mass exchanges, as well as the flow field, was built using the finite difference method. Freshwater productivity is calculated under various operating and weather conditions. The model has been modified to investigate the steady-state behavior of the system components. Four major parameters that have a significant impact on system water production are investigated: the feed flow rate of cooling water through the dehumidifier unit, the airflow rate, and the number and height of packing columns. According to the results, the proposed hybrid desalination system provides appropriate operational compatibility between HDH technology and solar energy. The system can provide a daily production of up to 35 liters per day. Increasing the number of packing columns results in a higher increase in fresh water productivity than increasing the height of the packing columns. The optimal air flow rate at a constant saline-water flow rate is obtained. For high airflow rates, the packing column height doesn't significantly affect the daily water production. System performance is investigated by four main parameters: gained output ratio (GOR), humidifier efficiency, exergy efficiency, and system efficiency. The system efficiency reached about 65% and the GOR reached 3.1. The humidifier’s efficiency varied between 50% and 75%. The maximum exergy efficiency reached about 5.2%.

An improved equilibrium optimizer for numerical optimization: A case study on engineering design of the shell and tube heat exchanger

The accurate design of the shell-and-tube heat exchanger (STHE) model is crucially important for industries such as process industries, oil refining, thermic devices, and power plants. However, determining its parameters is a challenging task due to the multimodality and nonlinearity of the cost function. Due to such nature, performing algorithms face the challenges of sluggish convergence speed and the proneness to local optima, making it difficult to reach satisfactory solutions. In line with the above challenges, this paper aims to contribute by developing an improved optimization algorithm that can effectively deal with such optimization issues. The proposed algorithm, named Levy-Opposition- Equilibrium Optimizer (LOEO), combines the Equilibrium Optimizer (EO) and the strategies of opposition learning (OL) and Levy flight learning (LFL) to overcome the dilemma of early convergence and getting trapped in local optima. It does this by employing the OL and LFL strategies after performing the EO phase to explore the search space in opposite directions and exploit the search space by means of the Levy distribution pattern, respectively. The proposed LOEO approach aims to enhance the algorithm's ability (provides enhanced exploration capability, effective search space exploitation, and enhanced convergence speed) and reach higher quality solutions to optimization problems. To assess the performance of the suggested LOEO, three stages of analysis are carried out. In the first stage, the performance of the proposed algorithm is investigated on some benchmark problems, including CEC 2005 and CEC 2020, using statistical verifications, convergence behavior, and the boxplot paradigm. The second stage involves the non-parametric Friedman test to assess the significance of results, where the results indicate that the LOEO outperforms the best existing one (equilibrium whale optimization algorithm (EWOA)) by an average rank of the Friedman test greater than 28% for CEC 2005 benchmark functions while outperforming enhanced EO (EEO) by 24% for CEC 2020. Finally, the LOEO's applicability is realized through determining the optimal design structure of the STHE model. The reported results indicate that the LOEO algorithm offers accurate performance compared to competing algorithms as it saves the cost of the device by 39.81% compared to the best existing results, and thus, it is commended to adopt for new applications.

Modelling of Floor Heating and Cooling in Residential Districts

In this study, a method is proposed to expand the utilization of an existing calculation model for a floor heat exchanger (HX) from room scale to small district scale. The model, namely Trnsys Type 653, is typically employed for the simulation of single or simultaneously controlled parallel heating circuits. It uses a simplified approach to calculate the heat exchange between fluid and screed, taking the HX effectiveness as an input. In order to calculate the effectiveness based on the HX design, fluid properties and mass flow rate, a Python model is developed to be coupled with Type 653. The results are compared to a reference finite element model set up in COMSOL® and depend on the HX design. The highest deviations range from over 1 K for 35 min to over 2 K for 175 min, while the lowest deviations range from below 0.5 K to below 1 K. Furthermore, the simplification of the floor HX model is analyzed by summarizing heating circuits from single rooms to a whole flat and from single flats to a whole floor. This approach results in deviations of approximately 2 and 4%, respectively, in the overall transferred heat over longer periods of time, while the switch-on frequency of the controller in an exemplary day is halved. While further analysis is required, the described simplifications seem promising for detailed district simulations with relatively low computational effort.

Dynamic modeling and performance analysis of metal hydride hydrogen storage system

Metal hydride hydrogen storage has the advantages of high hydrogen storage volume density, high safety, and high hydrogen purity, which can meet the hydrogen storage and supply needs of fuel cells in both mobile and fixed scenarios. It has become one of the most promising hydrogen storage methods. This work studies the dynamic performance of metal hydride hydrogen storage systems under absorption and desorption process by establishing dynamic models and heat exchange models. The dynamic properties of metal hydride hydrogen storage system are analyzed in different reaction process with the experimental test. Results show that when the ambient temperature is within a certain range, low temperatures are conducive to hydrogen absorption, while high temperatures can improve hydrogen release dynamics. Besides, raising the flow rate of hydrogen and reducing the volume fraction of hydrogen storage materials can help to improve the efficiency of hydrogen absorption and desorption reaction.

Hydrodynamic load on a multi-section heat exchanger

The article considers the issues of numerical modeling of a multi-section heat exchanger using the tools of the OpenFOAM open source package. The multi-section heat exchanger is operated at velocities ranging between 0.1 and 2 m/s. Numerical simulation is carried out for a complete assembly of 8 sections. Each section contains six transverse microchannels with internal fins to increase heat transfer. Hydraulic oil with a kinematic viscosity of 0.000032 m2/s is used as the working fluid. As a result of numerical simulation, the hydrodynamic characteristics at the entrance to the microchannels were evaluated depending on the number of sections, as well as hydraulic resistances were evaluated depending on the pressure drop and the flow velocity of the working fluid.

Computational Modeling of an Earth-Air Heat Exchanger Integrated with Phase Change Materials: A Case Study Performed for the Viamão City, Rio Grande do Sul State, Brazil

The earth-air heat exchanger (EAHE) is a sustainable option that allows the electrical energy consumption reduction in buildings. The objective of this study is to evaluate the influence of the incorporation of the thermal energy storage principle based on phase change materials (PCM) into the EAHE on its thermal potential. For this, a three-dimensional numerical model of the PCM coupled to the EAHE (EAHE-PCM) was developed based on the effective heat capacity method and adapted to the climatic conditions and soil characteristics of the Viamão city, Rio Grande do Sul State, Brazil. It was found that for a duct diameter and length of 0.11 m and 25.77 m, the incorporation of PCM to EAHE improved by 8.90% and 3.97% in the average annual thermal potential of heating and cooling, respectively. In addition, the average monthly thermal potential increased 19.70% (heating) and 8.48%(cooling), for the months of May and December, respectively, when the PCM was integrated into the system.

Life cycle assessment of microgreen production: effects of indoor vertical farm management on yield and environmental performance

The global production of plant-based foods is a significant contributor to greenhouse gas emissions. Indoor vertical farms (IVFs) have emerged as a promising approach to urban agriculture. However, their environmental performance is not well understood, particularly in relation to operational choices where global warming potentials (GWP) can vary between 0.01–54 kg CO2e/kg−1 of leafy greens produced. We conducted a life cycle assessment (LCA) of a building-integrated IVF for microgreen production to analyse a range of operational conditions for cultivation: air temperature, CO2 concentration, and photoperiod. We analyzed a dynamic LCA inventory that combined a process-based plant growth model and a mass balance model for air and heat exchange between the chamber and the outside. Results showed that the GWP of IVFs can vary greatly depending on the operation conditions set, ranging from 3.3 to 63.3 kg CO2e/kg−1. The optimal conditions for minimizing GWP were identified as 20 ℃, maximum CO2 concentration in the chamber, and maximum photoperiod, which led to a minimum GWP of 3.3 kg CO2e/kg−1 and maximum production of 290.5 kg fresh weight week-1. Intensification of production thus led to lower impacts because the marginal increase in yield due to increased resource use was larger than the marginal increase in impact. Therefore, adjusting growing conditions is essential for the sustainability of urban food production.

Optimization of heat transfer performance of a micro‐bare‐tube heat exchanger using a genetic algorithm

AbstractThis study presents the optimization of the heat transfer coefficient of a micro bare tube heat exchanger. A physical and mathematical model of a micro bare tube heat exchanger was built in Matlab using the simplified ε‐number of transfer unit method. Using a temperature of minus 30°C and a 0.5–1.0 mm tube outer diameter, a 1.7–8.0 mm longitudinal tube pitch, a 1.7–5 mm transverse tube pitch, and a 1.0–5.0 m/s velocity at minimum free flow area, with carbon dioxide as the refrigerant, a comparative variation analysis was performed to optimize the heat transfer coefficient of a micro‐bare‐tube heat exchanger. The results demonstrate that the heat transfer coefficient increases as the inlet air velocity is increased from 1.0 to 5.0 m/s, with a final gain of 93.17%. The growth rate of the heat transfer coefficient steadily decreases with increasing inlet air velocity and gradually approaches zero. The effect of the gradual decrease of the tube outer diameter from 1.0 to 0.5 mm on the heat transfer coefficient is 22.52% greater than that of the gradual decrease of the transverse tube pitch from 2.2 to 1.7 mm. The study also carried out an optimization analysis on the distribution of four different variables in the heat exchanger. With the use of a genetic algorithm, the study found an optimal distribution to maximize the heat transfer coefficient. The following parameter values resulted in the maximum heat transfer coefficient: a maximum inlet air velocity of 5.0 m/s, a minimum tube outer diameter of 0.5 mm, a 1.7 mm longitudinal tube pitch, and a 1.7 mm transverse tube pitch.

Technical-economic-environmental analysis of high temperature cascade heat pump with R718 (high stage) and six different low global warming potential refrigerants (low stage)

High temperature cascade heat pump with two separate refrigerants is a crucial system for decarbonizing industrial heating through electrification. The selection of optimal working refrigerants and temperature lifts relies on not only the thermodynamic analysis outputs such as coefficient of performance but also economic and environmental analyses. In this study, a technical–economic-environmental investigation was conducted for the proposed high-temperature cascade heat pump employing water as the high-stage refrigerant and six low global warming potential refrigerants in the low stage. To facilitate a detailed economic-environmental analysis, precise equipment sizing was undertaken. A comprehensive heat transfer model was developed to size the falling film shell-and-tube cascade heat exchanger, and empirical correlations were employed to size the internal heat exchanger at various cascade temperature lifts. The cascade heat exchanger model is validated against experimental data with less than 5 % error. The distribution of refrigerant charged mass was illustrated using instantaneous density and temperature data. To consolidate all thermal, economic, and environmental sub-indicators into a single parameter, the coefficient of performance, volumetric heating capacity, total annual cost, and total equivalent warming impact were combined as (COP × VHC)/(TAC × TEWI). This proposed comprehensive indicator can be applied to high-temperature cascade heat pumps to identify the optimum working pair and conditions. The results highlighted that R718 + R1234ze(Z) and R718 + R600 were the best working refrigerant pairs, considering all energy, economic, and environmental criteria.

Improvement methods for thermal backflow phenomenon in engine compartment blow-type air cooler module

Regarding the thermal backflow problem in the central area of the engine compartment's blow-type cooler module, a computational model for the entire machine's outflow field is first established and validated using experimental results. Next, the formation of thermal backflow phenomenon is analyzed, and a more accurate calculation method for the cooler that takes into account the thermal backflow phenomenon is proposed. Finally, a new structure that can eliminate the thermal backflow phenomenon is presented, and the heat dissipation effect is analyzed. The conclusion shows that the calculated values of the engine compartment cooler module are consistent with experimental results, verifying the correctness of the computational model. The negative pressure caused by the “pump” suction effect in the central area of the cooler module is the fundamental reason for the generation of the thermal backflow phenomenon. The dual heat exchanger model can significantly improve the calculation accuracy of the cooler when taking into account the thermal backflow phenomenon (by at least 10%), providing a more accurate method for evaluating the cooler's heat dissipation ability. The proposed new structure can eliminate the thermal backflow phenomenon in the cooler module and improve the heat dissipation uniformity. After the elimination of the thermal backflow phenomenon, the heat dissipation ability of the cooler is improved by at least 25%. In addition, the improvement of the heat dissipation uniformity of the cooler can effectively solve the problem that multiple coolers in the engine compartment have inconsistent heat dissipation capabilities. The proposed calculation method for the cooler taking into account the thermal backflow phenomenon and the new structure for eliminating the thermal backflow provide a reference for the development of similar products in the future.