Heat Exchanger Model Research Articles

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.

Rapid performance prediction model for capillary heat exchangers in subway tunnel linings

Subways are typical underground spaces that help alleviate urban traffic problems; however, they also face challenges such as high energy consumption and deterioration of the thermal environment, which can seriously impact their safe and efficient operation. A subway source heat pump system (SSHPS) with tunnel-lining capillary heat exchangers (CHEs) is effective for addressing these issues. Current research has primarily focused on the heat transfer performance of tunnel lining CHEs, yet there remains a dearth of rapid prediction models for their heat flux that are suitable for efficient engineering design. In this study, numerical simulation systems for tunnel lining CHEs in rectangular and circular subway tunnels were established to analyse their heat transfer performance under different design conditions. The results show that the heat flux of flat and circular CHEs installed in tunnel lining ranges from 47.03 to 117.65 W/m2, and from 36.06 to 115.09 W/m2 in the cooling season, respectively. In contrast, in the heating season, the heat flux of flat and circular CHEs ranges from 27.03 to 89.90 W/m2, and from 19.35 to 87.77 W/m2, respectively. Based on the analysis of these results, rapid prediction models for the CHE heat flux were established using multivariate linear fitting. The established models passed a series of statistical tests, indicating high statistical significance. This study provides a theoretical basis for the engineering design and applications of tunnel lining CHEs.

Multi-Objective Optimization of a Bi-Metal High-Temperature Recuperator for Application in Concentrating Solar Power

Abstract Supercritical CO2 closed Brayton cycles are a major candidate for future power cycle designs in concentrating solar power applications, with high-temperature recuperators playing an essential role in realizing their high thermal efficiency. Printed circuit heat exchangers (PCHEs) are often chosen for this role due to their thermal-hydraulic and mechanical performance at high temperatures and pressures, all while remaining compact. However, PCHEs can be costly because of the high-performance materials demanded in these applications, and the heat exchanger internal geometry is restricted by their manufacturing process. Additively manufactured heat exchangers can address both of these shortcomings. This work proposes a modular bi-metal high-temperature recuperator with integrated headers to be produced with additive manufacturing. Beginning with existing PCHE channel geometries, a 1D heat exchanger model is developed. Then, multi-objective optimization is used to maximize the heat transfer effectiveness of a lab-scale device while limiting its size. Two distinct channel geometries emerge from the optimization. Optimal designs achieve up to 88% effectiveness with negligible pressure drop. Deterioration of effectiveness due to axial conduction of heat in the heat exchanger walls is found to be a notable problem for lab-scale PCHEs, and the optimal designs obtained here minimize its detrimental effects. A sensitivity analysis reveals that the effectiveness of the recuperator is much less sensitive to variation in mass flowrate in off-design operation when axial conduction is significant, while increasing the length of the device easily increases effectiveness.

Design and Analysis of Heat Pipe Heat Exchanger Efficiency

The heat pipe has a high thermal conductivity, and its basic working principle is to transfer heat through evaporation and condensation through the working medium inside the pipe. Heat pipe has good thermal conductivity, isotherm and other characteristics, and the heat transfer area at both ends can be changed at will, control the temperature and other advantages. Therefore, the heat pipe heat exchanger has the advantages of high heat transfer efficiency, compact structure, small fluid resistance loss, and beneficial to control dew point corrosion. At present, it has been widely used in metallurgy, chemical industry, oil refining, boiler, ceramics, transportation, light textile, machinery and other industries, as energy saving equipment for waste heat recovery and heat energy utilization in the process, and has achieved remarkable economic benefits. The design of the heat pipe heat exchanger on the development of the current situation, development trend, application, design principle and design process of a simple description, while focusing on the discussion of the heat pipe heat exchanger design process. The main content of the heat exchanger thermodynamic calculation, structural design and material selection. The model of heat pipe heat exchanger is established according to the actual situation and the calculated data.

Integrated application of gravity, aeromagnetic, and electromagnetic methods in exploring the Ganzi geothermal field, Sichuan Province, China

The Ganzi geothermal field is located in the Songpan-Ganzi orogenic belt in Sichuan Province. Many hot springs are exposed along the Yalahe valley in Ganzi geothermal field, which is a favorable area for high-temperature geothermal resource exploration. However, the geological model of heat exchange, the regional structure controlling hydrothermal convection and the development model of geothermal reservoirs are still unclear. Therefore, further studies are necessary to meet the geothermal exploration requirements in the middle and deep strata of this geothermal field. In this study, a geological model of the geothermal system of Ganzi geothermal field is proposed. We are convinced that there exists a hydrothermal convection system in the Ganzi geothermal field, the heat transfer of which is accomplished through deep-rooted major faults. Therefore, the identification of deep-rooted major faults and the description of geothermal reservoirs are the research objects of the integrated geophysical methods. The main factors controlling the geothermal reservoirs in the deep-rooted Xianshuihe major fault and Yalahe fault zones are analyzed by using gravity, aeromagnetic, and electromagnetic methods and techniques. The analysis results of regional gravity and aeromagnetic anomalies show that the Xianshuihe major fault has produced obvious gravity and aeromagnetic anomalies on the surface, and thus the position and strike of this fault can be accurately predicted by inversion of the aeromagnetic anomalies. Geothermal reservoirs show low-resistivity anomalies in the electromagnetic profile. The inversion results of the controlled source audio-frequency magnetotelluric (CSAMT) data show that geothermal reservoirs are mainly developed along the Yalahe valley, and the west side of the valley is more favorable for geothermal exploration. This study is of guiding significance to the efficient exploitation and utilization of the Ganzi geothermal field.

Performance enhancement of the simultaneous solvers for non-convex and ill-conditioned vapor compression systems utilizing gradient methods

Simultaneous solvers using gradient methods are desirable for solving complex vapor compression system (VCS) models due to their flexibility and computational efficiency; however, they often lack robustness. Recent research has contributed towards improving the robustness of the simultaneous solvers, but there is still a need to understand why these solvers lack robustness and how to improve their convergence as the solver variables are increased. Furthermore, for a thorough system analysis, it is important to decrease the computational cost while increasing prediction accuracy. In this study, the performance of simultaneous solvers in terms of robustness, accuracy, and computational cost is evaluated using the standard ejector cycle as a representative example of advanced VCS. To ensure the focus of the study is on the solver's performance, computationally efficient, and accurate component models are considered. Utilizing optimization theory and problem formulation with minimum variables, this study finds for the first time that the non-convex and ill-conditioned behavior of the residual equations causes the simultaneous solvers to be less robust. Non-convexity primarily comes from the enthalpy residual, while the ill-conditioned behavior comes from the pressure residuals and the difference in the order of magnitude of the residuals. A novel method of the failure grid is introduced for a fair comparison of different solvers’ robustness. A few methods to improve the solver’s performance using gradient methods are introduced. The robustness of unconstrained algorithms can be improved by almost four times using scaling factors in the residual equations. However, the improvement in convergence of constrained algorithms is found to be almost twice more than the unconstrained algorithms using the same scaling factors, proving that the constrained algorithms result in a more robust solver. The study also finds that the computational cost is reduced by almost half when using a problem formulation without nested loops. However, this results in a higher number of solver variables for which constrained algorithms are found to be more robust, indicating that robustness remains important in determining the most computationally efficient solver. The accuracy of all the solvers evaluated is found to be comparable. Overall, these findings can help in developing flexible, robust, and computationally efficient simultaneous solvers with a higher number of variables for advanced thermal systems that include both vapor compression systems and thermal power systems. The findings can also be extended to develop parallelized-finite-volume heat exchanger models to reduce their computational cost.

Evaluation of modified Hantush’s function: A tool for parametric study with the finite line-source model

A solution to the three-dimensional finite line-source (FLS) model for borehole heat exchangers (BHEs) is identical to Hantush’s M function, commonly used in groundwater pumping modeling. A modified Hantush function E appears in the steady-state solution to the moving finite line-source (MFLS) model for borehole heat exchangers (BHEs) with groundwater flow that takes into account heat conduction and advection by Péclet number. An exact series representation is obtained for this two-parametric function E, and from it two-types of approximate expressions for the E are derived. One is suitable for small values of a parameter Pe and the other for its large values. High accuracy of the approximate formulae is verified by comparison with the exact values provided by modified Hantush’s function E in those validity domains.These analytical expressions can be used for designing complex borehole configurations and may be useful in steady-state analysis of partially penetrated wells (PPWs) in a leaky aquifer.

Comparison and integration of simulation models for horizontal connection pipes in geothermal bore fields

The heat transfer along horizontal connection pipes in geothermal bore fields can have significant effects and should not be neglected. As practical and design-related applications require simple and efficient models, we investigate suitability of different models for the first time within this context. Three ground and three pipe models of different complexity are studied. All model combinations are coupled with a fixed ground load boundary condition on one side and a borehole heat exchanger (BHE) model on the other side. Models are tested under a variety of realistic conditions to evaluate performance. The investigations show that all investigated pipe models are equally suitable for the application. For the ground models, the horizontal finite line source model and the numerical 2D model produce identical results for homogeneous ground properties. The soil resistance model neglects the temperature accumulation in the ground and thus leads to considerable deviations and should be avoided. Based on the findings, we propose a computationally efficient approach using a novel combination of established simple steady-state models for the BHE and connection pipes. In the selected example scenario, the consideration of a 30 m connection pipe attached to the BHE leads to an increase in the BHE load by 40% for the heating case and a reduction in the BHE load by 5% for the cooling case.

An investigation of multistream plate-fin heat exchanger modelling and design: a review

Abstract In line with population expansion and industrial development, the world’s energy consumption has been rising gradually over the past three decades. As a result, methods for energy conservation have been sought. One of the most common strategies is heat recovery, which is efficient and cost-effective to the extent possible. Heat recovery is not just about saving energy for primary consumption; it is also about lowering emissions and protecting the environment. In this respect, one of the most important strategies for heat recovery is to develop heat exchangers and exploit the energy associated with many of the processes’ output products in order to use it in new processes. Many researchers working in the field of heat engineering are now looking into novel heat transfer techniques. Use of the heat exchanger as a compact is one of these ways that might be considered. The current review therefore concentrates on the design of plate-fin heat exchangers (PFHE) and multi-stream plate-fin heat exchangers (MSPFHE) based on various models. The current review offers some suggestions for upcoming studies on improving heat transfer and minimizing power use.

MT14 Defining Health States to Assess the Cost-Effectiveness of Interventions in Laryngectomized Patients

Current cost-effectiveness models of heat and moisture exchangers (HMEs) for laryngectomized patients, do not consider the potential changes in health-related quality of life (HRQoL) due to reduced cough and sputum symptoms and impact. The aim of this study is to investigate whether the Cough and Sputum Assessment Questionnaire (CASA-Q) can be used to identify health states that distinguish in HRQoL, or utility, for cost-effectiveness models.

Numerical simulation on triple helix ground source heat exchanger for improving its thermal performance using nanoparticles

Geothermal energy is a clean energy source which is being exploited in ground heat exchangers (GHE). GHE is of great interest to the community of researchers due to its advantages in offering a renewable and pollution free alternative. Although many research has been done on GHE but the use of nanoparticle in enhancing energy efficiency is novel. In the present work, the improvement towards the heat transfer and thermal performances of the triple helix ground heat exchanger (GHE) model is studied by mixing nanoparticles of different concentrations to the base fluid which is water. The numerical simulation of the present GHE model has been performed in Computational Fluid Dynamics software i.e. ANSYS FLUENT. The results show that the heat transfer and various other thermal performance characteristics such as outlet temperature of the water, rate of heat exchange, effectiveness, efficiency, and thermal resistance have been improved by the addition of nanoparticles in water. The heat transfer is increased by approximately 5 W, temperature difference is enhanced by 5 K and effectiveness is increased by 0.01 when compared to with 8 % nanoparticles and without addition of nanoparticles. It is also found that by increasing the concentration of nanoparticles from 2 to 8 % the thermal performance characteristics of triple-helical GHE are further improved.

Application of Combined Micro- and Macro-Scale Models to Investigate Heat and Mass Transfer through Textile Structures with Additional Ventilation

In this study, computational models of heat and mass exchange through textile structures with additional ventilation at the micro- and macro-scale were investigated. The finite element analysis of advanced textile materials provides a better understanding of their heat and mass transfer properties, which influence thermal comfort. The developed computational models can predict air permeability (AP), thermal resistance (Rct), and heat transfer (h) coefficients at the micro-scale. Moreover, the mesh size was taken into consideration and validated with experimental data presented in the literature. In addition, computational models were extended to micro- and macro-scale forced ventilation models. Macro-scale finite element models require input parameters such as an effective heat transfer coefficient that are usually obtained experimentally. In this research, the heat transfer coefficients (hmicrolayer = 25.603 W/(K·m2), htotal = 8.9646 W/(K·m2)) were obtained numerically from the micro-scale model and were applied to a macro-scale model. The proposed methodology and developed models facilitate the determination of average temperature and temperature distributions through different through-thickness positions along the axis Oz. The simulations were carried out using Comsol Multiphysics and Matlab software.

A black box based model for phase change heat exchanger in refrigeration system simulations using Kriging interpolation method

In the present study, a black box model for phase change heat exchangers is developed based on Kriging interpolation. The input and output of the heat exchanger black box model were established based on the mass-flow-guided method. Methods for the input domain determination of are established respectively for the application of system simulation and separate heat exchanger simulation. A training data set sampling method is established based on the Latin hypercube sampling method to achieve significant reduction in sample points while maintaining the integrity of the sample data characteristics. The heat exchanger calculation trend was determined by establishing a regression model; the accurate prediction of heat exchanger performance was achieved by making local corrections to the prediction results through a stochastic distribution process model. Validation results show that, for the condenser model, the average pressure drop prediction error is 0.25%, and the average heat transfer prediction error is 1.18%; for the evaporator model, the average pressure drop prediction error is 0.71%, and the average heat transfer prediction error is 0.80%. The model can achieve high prediction accuracy with a small amount of training data and has a good fitting performance in the range of general applications.

A critical assessment of nanoparticles enhanced phase change materials (NePCMs) for latent heat energy storage applications

Phase change material (PCM) laden with nanoparticles has been testified as a notable contender to increase the effectiveness of latent heat thermal energy storage (TES) units during charging and discharging modes. In this study, a numerical model is developed and implemented based on the coupling between an advanced two-phase model for the nanoparticles-enhanced PCM (NePCM) and the enthalpy-porosity formulation for the transient behavior of the phase change. Therefore, a porosity source term is added to the nanoparticles transport equation to account for the particles' frozen state in regions occupied by solid PCM. This two-phase model includes three main nanoparticles’ slip mechanisms: Brownian diffusion, thermophoresis diffusion, and sedimentation. A two-dimensional model of a triplex tube heat exchanger is considered and different charging and discharging configurations are analyzed. Compared to pure PCM, results show a substantial heat transfer enhancement during the charging and discharging cycle in which a homogeneous distribution of nanoparticles is considered as the initial condition. For this case, the two-phase model predictions are superior to the ones obtained with the classical single-phase model. In the case of multi-cycle charging and discharging, a significant deterioration of the heat transfer rate is observed using the two-phase model while such assessment is senseless using the single-phase mixture model due to the physical assumptions upon which this model is formulated. The two-phase model results reveal that, for a NePCM with high nanoparticles concentration (> 1%), the melting performance during the second charging cycle is reduced by 50% compared to the first one. This performance degradation is attributed to a noteworthy non-homogeneous distribution of the nanoparticles at the beginning of the second charging cycle. The dominant nanoparticles migration mechanism, in this scenario, is the one resulting from sedimentation effects.

Beyond heat exposure — new methods to quantify and link personal heat exposure, stress, and strain in diverse populations and climates: The journal Temperature toolbox

ABSTRACT Fine-scale personal heat exposure (PHE) information can help prevent or minimize weather-related deaths, illnesses, and reduced work productivity. Common methods to estimate heat risk do not simultaneously account for the intensity, frequency, and duration of thermal exposures, nor do they include inter-individual factors that modify physiological response. This study demonstrates new whole-body net thermal load estimations to link PHE to heat stress and strain over time. We apply a human-environment heat exchange model to examine how time-varying net thermal loads differ across climate contexts, personal attributes, and spatiotemporal scales. First, we investigate summertime climatic PHE impacts for three US cities: Phoenix, Miami, and New York. Second, we model body morphology and acclimatization for three profiles (middle-aged male/female; female >65 years). Finally, we quantify model sensitivity using representative data at synoptic and micro-scales. For all cases, we compare required and potential evaporative heat losses that can lead to dangerous thermal exposures based on (un)compensable heat stress. Results reveal misclassifications in heat stress or strain due to incomplete environmental data and assumed equivalent physiology and activities between people. Heat strain is most poorly represented by PHE alone for the elderly, non-acclimatized, those engaged in strenuous activities, and when negating solar radiation. Moreover, humid versus dry heat across climates elicits distinct thermal responses from the body. We outline criteria for inclusive PHE evaluations connecting heat exposure, stress, and strain while using physiological-based methods to avoid misclassifications. This work underlines the value of moving from “one-size-fits-all” thermal indices to “fit-for-purpose” approaches using personalized information.

Development of an integrated membrane condenser system with LNG cold energy for water recovery from humid flue gases in power plants

This paper investigates a detailed thermodynamic analysis of a modular-type membrane condenser system where a cooler or condenser is connected in series upstream of the membrane condenser module. A coolant circulates inside the cooler/condenser to cool down the industrial flue gas up to saturation conditions. The analysis covers water recovery rate and energy requirement for different combinations of flue gas humidity, flow rate, and temperature. Additionally, a case study is included which considers a practical industrial exhaust flue gas where the constituents of the flue gas with volumetric ratio and the feed parameters are referred from the literature. The case study investigated the utilization of cold energy obtained by LNG regasification facility as a cooling power source for the water vapor recovery process. A detailed heat transfer analysis based on the heat exchanger model is performed to determine the required mass flow rate of cooling water and natural gas. It is concluded that, the water self-sufficiency of a power plant can be achieved if the mass flow rate of the −50 °C natural gas which is entering the membrane condenser is kept around 0.3 kg s−1 for every 1 kg s−1 flow rate of the 168 °C flue gas.

Experiment and Simulation on a Refrigeration Ventilation System for Deep Metal Mines

Significant harm from heat has become a key restriction for deep metal mining with increasing mining depth. This paper proposes a refrigeration ventilation system for deep metal mines combined with an existing air cycling system and builds an experimental platform with six stope simulation boxes. Using the heat current method and the driving-resistance balance relationship, the heat transfer and flow constraints of the system were constructed. An artificial neural network was used to establish models of heat exchangers and refrigerators with historical experimental data. Combining the models of the system and stope simulation box, an algorithm that iterates the water outlet temperature of the evaporator and condenser of the refrigerator was proposed to design the coupled simulation model. The heat balance analysis and comparison of the air outlet temperatures of the stope, as well as the heat transfer rates of the heat exchangers with the experimental data, validated the coupled simulation model. Additionally, the effects of cooling fans and the air inlet temperature of the cooling tower were discussed, which provided a powerful modelling method for the coupled model of a refrigeration ventilation system, helps to reduce energy consumption, and improves the sustainability of mining production.

The energy saving potential of a new ventilation roof with stabilized phase change material in hot summer region

Roof is a weak part of the building envelope due to the high intensity of solar radiation in summer. Improving thermal performance of roof is crucial to reduce energy consumption. In this study, the thermal performance of a new ventilation roof with shape-stabilized phase change material (SPCM) is investigated. The dynamic heat transfer model for this roof is established by coupling the number of transfer units (NTU) heat exchange model with the resistance-capacity dynamic heat network model and used to analyse the heat transfer. The accuracy of the model is validated by experiment. The indoor air temperature, internal surface temperature of the roof, and cumulative cooling load in summer are simulated and analysed in Wuhan. The results show that PCM and night ventilation have great energy saving potential. When the 30 mm PCM is applied, the peak indoor air temperature and peak internal surface temperature decreased by 2.9 °C and 5.5 °C, respectively, and the cumulative cooling load of the building decreases by 19.2%. When night ventilation is applied (v = 3 m/s), the average latent heat utilization rate of the PCM layer increases, and the cumulative cooling load decreases by 22.9% and 37.5% compared with the PCM roof and the reference roof, respectively.