Heat Transfer Units Research Articles

Heat transfer analysis and structure optimization of unit of flat plate based on a response surface test: An experimental teaching perspective in higher education

The Flat Plate is a common component of solar photothermal experiment and an important teaching tool in the new energy teaching experiment. Aiming at the problem of low heat transfer efficiency and poor teaching effect of traditional roll-bond flat plate, this paper conducts a numerical simulation study on the flow and heat transfer characteristics in the ”Y” -shaped channel unit. The four parameters of width, length, runner parting angle and runner width are used as control variables to optimize the heat transfer structure of the runner. Taking the ”Y” -shaped channel unit as the research object, the finite element model of conjugate heat transfer was established by using Fluent. Through numerical simulation analysis, it is concluded that in the defined length and width interval, the thermal efficiency increases first and then decreases with the increase of the length of the heat transfer unit, and the pressure drop coefficient has a negative correlation with the length and width of the unit. The runner width has a positive correlation with the thermal efficiency and a negative correlation with the pressure drop coefficient. Then, according to the Box-Behnken principle, a response surface test for heat transfer optimization was designed, an optimization model with thermal efficiency and pressure drop coefficient as the response indicators was established, and the optimal element design scheme was determined. The optimization results show that when the subunit length of the heat transfer runner is 40 mm, the width is 35 mm, the parting angle is 60°, and the runner width is 11 mm, the thermal efficiency of the ”Y”-shaped runner is 0.782, and the pressure drop coefficient is 0.121. Finally, a direct-expansion solar auxiliary heating system is built to test the scheme. The experimental results show that the collector using the ”Y”-shaped channel shows better solar energy utilization, which increases the COP of the system by 15.2%. This study provides a reference for the design and optimization of other types of flow channels to improve the heat transfer efficiency of the roll-bond flat plate. Through optimization, the system has innovated in the experimental mode, effectively made up for the shortcomings in the training of new energy professionals, and enriched and developed the experimental theory system and teaching methods of higher education of energy and power majors.

Designing an Environmental Wind Tunnel Cooling System for High-Speed Trains with Air Compression Cooling and a Sensitivity Analysis of Design Parameters.

Environmental wind tunnels for high-speed trains play a significant role in their development. The cooling system of the wind tunnel poses a challenge as it requires lower temperatures and a higher cooling capacity during operation. The conventional approach to wind tunnel refrigeration uses evaporative cooling, which is less efficient at low temperatures and comes with environmental and safety risks. In this study, we propose an innovative air compression refrigeration method based on the Brayton cycle. This method converts high-pressure air into low-temperature air at atmospheric pressure for wind tunnel refrigeration. The new cooling system has reduced energy usage by 3.72 MW, leading to a 13.15% improvement. The return cooler of the system is modeled using the effective number of heat transfer units and the mean temperature difference design method. Additionally, the turbine within the system is analyzed using one-dimensional flow characteristic analysis and the principle of similarity. This method has been validated by comparing it to other published papers. Subsequently, we perform a thorough sensitivity analysis on the key design parameters of the system. We observe that with a sufficient heat transfer area of the recooler, the cooling efficiency of the system exhibits a gradual decline from 64% to 60% as the mass flow rate of the system rises. For a fixed turbine, the cooling efficiency of the system rises from 20% to 62% and subsequently declines to 37%, with an increase in the mass flow rate. As a result, we conclude that the design parameters of the turbine have a more significant influence on the cooling efficiency of the system than the recooler. Our study will establish a foundation for selecting parameters to optimize the refrigeration system in the future.

Daily sorption thermal battery cycle for building applications

The study propose firstly an absorption thermal energy storage (ATES) system designed for repeated operations on a daily base without any additional manipulation. The performance of the sorption thermal battery was analyzed by varying four parameters (mass flow ratio, number of exchanger heat transfer units (NTU), heat source, and cooling water temperature). The lower the cooling water temperature, the better was the performance, particularly for improving the energy storage density (ESD). Additionally, if low-temperature cooling water is used, the coefficient of performance (COP) with a 65 °C heat source is comparable to that with 95 °C. ESD increased with the increasing the heat source temperature, and the maximum COP was obtained when using a 75–85 °C heat source. To solve the crystallization problem, [DMIM][DMP], a type of ionic liquid, was applied as an absorbent. However, the COP of H2O-[DMIM][DMP] with a heat source temperature of 120 °C was lower that of H2O–LiBr with 95–100 °C. Therefore, it is advantageous to use H2O–LiBr to improve the sorption thermal battery performance. ESD and COP of the sorption thermal battery are 451.13 kJ/kg and 0.728, respectively, when using a 95 °C heat source and 32 °C cooling water.

Study on Heat Transfer Performance and Parameter Improvement of Gravity-Assisted Heat Pipe Heat Transfer Unit for Waste Heat Recovery from Mine Return Air

One of the effective methods for energy conservation and emission reduction in coal mines is to utilize waste heat recovery technology to recover mine return air waste heat. The gravity heat pipe is widely used in mine return air waste heat recovery due to its sustainable and economic advantages, but its heat transfer is a complex process influenced by multiple parameters. A single-tube heat transfer resistance model and a heat transfer calculation model based on enthalpy difference were established for the heat exchange tubes. Four typical application cases of a low flow rate and a low number of tube rows were selected, and their heat transfer characteristics were tested onsite and analyzed. It was found that there were problems such as a low overall heat transfer efficiency, a low fresh air outlet temperature, and a risk of icing in the final tube section. The effects of the gravity heat pipe parameters on the heat transfer performance were studied, such as the tube outer diameter, tube spacing, and the finned tube outer diameter. It was found that the air-resistant force of the heat exchanger increased with the increase of the tube spacing and the finned tube outer diameter, the heat transfer resistance increased with the increase of the tube spacing and the decrease of the finned tube outer diameter, and the heat transfer coefficient first increased and then decreased with the increase of the tube outer diameter. A configuration improvement scheme with a high flow rate and a high number of tube rows is proposed here. Taking Case 2 as an example, the temperature distribution of the heat tube before and after improvement is compared and analyzed. The results show that the heat transfer performance of the heat exchange system significantly improved. Without increasing the air resistance of the heat tube, the temperature of the return air outlet after improvement was reduced to 1.1 °C, 4.1 °C lower than that before improvement, further recovering the waste heat of the mine return air. The temperature of the condensate water film was greater than 0.5 °C, avoiding the icing problem of the condensate tube section, the fresh air outlet temperature reached 5.2 °C, an increase of 7.8 °C compared to that before improvement, and the overall heat transfer efficiency increased from 56.7% to 66%.

The resistive heating, defrosting, and thermal performance of CFRPs as a heat transfer unit in a frozen environment

This study explored the feasibility of substituting the traditional aluminum heat exchanger units of the residual heat pump systems with carbon fiber reinforced polymers (CFRPs). The main objective was to investigate the potential advantages of employing a self-heating heatsink in frozen ambient regarding CFRPs resistive heating feature. The in-plane and through-plane thermal conductivity of PAN-based and Pitch-based carbon fiber laminates, as well as their resistive heating characteristics and surface temperature under various electrical conditions, were studied. Also, the impact of piping (fins to pipe connection) on CFRPs heat generation and defrosting performance of the heatsinks was examined. As a solution, the suggested three-point electrical connection demonstrated a positive effect on reaching uniform temperature throughout the samples, especially for the PAN-based case. In general, the PAN-based laminate exhibited lower power consumption to obtain the desired average surface temperature compared to Pitch-based CFRPs. However, the higher thermal conductivity of the Pitch-based samples led to better heat dissipation and a more uniform temperature contour. Finally, the thermal performance of the Pitch-based CFRPs and aluminum heatsinks were compared in a freezing chamber. The results revealed that under the given time interval, amount of transferred heat for the Pitch-based CFRPs heatsink equipped with defrosting feature was 2260 (kJ), 2.23 times higher than the aluminum (without defrosting element) with 967 (kJ).

Study on thermal-hydraulic performance of printed circuit heat exchangers with supercritical methane based on machine learning methods

In this study, a machine learning approach was used to predict thermal-hydraulic performance of supercritical methane flow in a printed circuit heat exchanger (PCHE). Local multiple physical parameters within the PCHE semicircular straight channel obtained from numerical simulations were employed and data of 6213 micro segments were obtained. Four machine learning models were used to predict local heat transfer coefficient and unit pressure drop at different operating conditions. By comparing the predicted results obtained after hyperparameter optimization, it shows that artificial neural network (ANN) can predict the parameters with higher accuracy. The ANN model can achieve a coefficient of determination (R2) of 0.9994 with mean absolute percentage error (MAPE) of 0.252% for the heat transfer coefficient, and R2 of 0.9996 with MAPE of 1.749% for the unit pressure drop. To verify the accuracy of machine learning model, a one-dimensional simulation model embedded with ANN model was built to calculate the temperature and pressure distribution in the entire PCHE channel. The results show the temperature and pressure distribution agree well with numerical results. This work provides an accurate machine learning approach to predict flow and heat transfer parameters, which is of great value for the simulation and design of the PCHE.

Experimental and numerical investigations on the thermal performance enhancement of a latent heat thermal energy storage unit with several novel snowflake fins

This article introduces a novel snowflake fin inspired by the crystal structure of snowflake to enhance the heat transfer performance of Latent Heat Thermal Energy Storage (LHTES) units. Initially, a numerical simulation model for transient heat transfer units with snowflake fin was established in a shell and tube LHTES unit. The accuracy and dependability of the model are verified through comparison with experimental results. Then, the effects of three placement methods of LHTES unit (vertical, horizontal-Ⅰ, and horizontal-Ⅱ) on melting and solidification performance are explored. Additionally, the effects of traditional longitudinal fins, snowflake fin, and four novel snowflake fins on melting and solidification behaviors are quantitatively compared. The single-factor method and response surface methodology (RSM) were employed to further optimize the selected optimal novel snowflake fin design. The research results show that the heat transfer performance of the vertically placed LHTES unit is the best. In comparison to traditional longitudinal fins and conventional snowflake fin designs, the novel snowflake fin design reduced the total melting and solidification time by 45.15% and 18.14%, respectively. The optimal size of the branch fins is a radial length of the root of 22.9 mm, self-length of 8 mm, and an angle of 60.3°.

Thermal effectiveness and NTU of horizontal plate drain water heat recovery unit - experimental study

The operating characteristics of plate heat exchanger in horizontal drain water heat recovery unit for domestic shower system were investigated in an experimental study. Based on test data the thermal effectiveness (ε) and number of heat transfer units (NTU) were calculated. The tests were carried out in simulated real-world conditions in three shower water flow rates (water consumption levels) for 4, 8 and 12 l/min, and two primary and secondary flows configurations (balanced and unbalanced), as a reflection of the three shower intensity standards and water temperature range of 30–50 °C covering the usual user-specific shower conditions. The least favorable test results (ε = 18.6% and NTU = 0.24) were obtained for the drain water temperature of 26.6 °C and cold water / drain flow rate at 12/12 l/min. The most beneficial results (ε = 50.0% and NTU = 0.99) were obtained for the sewage temperature of 50.8 °C and 4/12 l/min. It has been shown that the higher the flow on the drain water side and lower on the cold water side, the better the effectiveness. For a system with equal and low flows on both sides, the drain temperature change has a negligible effect on the effectiveness (4% growth with a drain temperature increase of 25.4 °C for 4/4 l/min). The paper presents developed easy-to-use charts of the variability of the effectiveness and NTU with the drain water temperature relates to a different set of primary and secondary flows in horizontal, plate, compact drain water heat recovery exchanger. The results of effectiveness obtained in the research were compared to the values presented in the literature for other drain water heat recovery units, both in vertical and horizontal applications.

Analysis of operation of heat exchangers of a heating system in the arrangement of reliable and safe heat supply of residential buildings

The arrangement of heat supply of residential buildings with independent connection to external heating networks is considered, which ensures the reliability of heat supply and the necessary comfort in the premises in cold weather conditions after the official termination of the heating season or before it begins due to the supply of water from the return main of the heating network after the DHW heat exchangers. A mathematical model describing the non-stationary modes of operation of heaters of the heating system under the conditions of the implementation of this arrangement is constructed and studied. Calculations were carried out using this model, including numerical simulation on a computer using the Monte Carlo method. It is established that in this case, due to fluctuations in the waste water consumption following the daily variation in water consumption at the DHW, there occurs a decrease in the average heat transfer coefficient of the heater of the heating system and its temperature efficiency due to the fact that these values depend on the flow rate in a non-linear way, and their growth during the period of increased water intake at the DHW does not compensate for the decrease during the reduction of water consumption. It is noted that in this case, the reduction of the heat transfer coefficient lies within the usual error of engineering calculation, and this effect can be neglected. It is proved that, with a small number of heat transfer units in the heater of the heating system attributed to the heated flow, the total amount of heat transferred can decrease quite significantly (by up to 30 percent); however, with a rational choice of the heater size, such a decrease is within the limits allowed by the margins applied when setting the flow rate of delivery water and determining the heat transfer area.

A modified efficiency-NTU method (m-ε-NTU) for calculating air coolers in dehumidifying or frost conditions. Part I

In this part of the article, a literary review of the methods of stationary calculations of air coolers operating in dehumidifying or frost conditions is carried out. The approaches used at the moment are reviewed, namely: dehumidification coefficient method; logarithmic enthalpy difference method (LMED); equivalent dry-bulb temperature method (EDT); as well as -NTU method (efficiency number of heat transfer units) for calculating counterflow chilled water coils. Their main differences are shown and the key expressions used in them are given. A comparison of the advantages and disadvantages of the considered methods showed the rationality of using -NTU approach due to the possibility of its application for both design and verification calculations of heat exchangers. Since the classical -NTU method is not directly applicable to dehumidifying or frost conditions, it becomes necessary to adapt it to the calculations of air coolers of all types (both counterflow and parallel-flow air coolers without phase transition of the cooling fluid, and for cases with its phase transition) to correctly describe the effect of the above processes on heat exchange.

Incipient fault diagnosis and trend prediction in nonlinear closed-loop systems with Gaussian and non-Gaussian noise

This paper proposes a methodology for incipient fault diagnosis and the corresponding trend prediction in nonlinear closed-loop systems considering stochastic Gaussian and non-Gaussian uncertainties. The proposed approach is based on the use of the particle filtering technique for estimating the system states and outputs. From these estimations, the residual signals would be generated through a mathematical filtering and augmentation technique, allowing the incipient fault estimation that is evaluated using the designed fixed and adaptive thresholds that consider system uncertainties. In this way, the fault detection performance is improved but also the false detection and false alarm problems are comprehensively addressed. Moreover, the augmented Gauss–Newton identification method is used for the incipient fault trend prediction. Finally, to evaluate the effectiveness of the proposed approach, the incipient fault diagnosis in the heat transfer unit built in the nonlinear closed-loop continuous stirred-tank reactor (CSTR) system is used. Besides, the confusion matrix is employed to assess the results from a quantitative point of view.

Experimental study of direct contact condensation of spent vapor in a cocurrent flow packed tower under negative pressure

AbstractCondensers are often required in power generation systems to condense the exhaust steam generated at the end of the turbine. This paper will investigate the enhanced condensation process of spent steam in a parallel flow type. The operating parameters of steam temperature (Tcond), steam flow rate (Gin), cooling water temperature (Tin), and cooling water flow rate (Lw) will affect the condensation effect by changing the gas–liquid arrangement in the tower. In this experiment, an orthogonal test was designed in the Raschig ring to investigate the significance of these four operating parameters on the experimental results. Different types of packings have different condensation effects due to different accumulation methods. The same type of packing has a different surface area, resulting in different contact areas between the gas and liquid phases during condensation. In this experiment, four different packings will be investigated to find their condensation performance. This paper uses the size of subcooling (ΔT) as an indicator to evaluate the effectiveness of condensation, and the values of condensation rate (R), number of liquid phase heat transfer units (NTUL), and total volume heat transfer coefficient (Kv) are used as a reference for the effectiveness of condensation. The results show that the overall condensation effect of regular packing is better than that of random packing, The average condensation rate of regular packing is 95%, the average condensation rate of random packing is 90%, the subcooling of regular packing is about three to five smaller than that of random packing, the heat transfer coefficient of regular packing is about 1.5 times of that of random packing. And by fitting the Kv data for different packings, an empirical formula was obtained that can be used to predict the Kv size of other packings.

Thermal performance characteristics of a tessellated-impinging central receiver

Current central receiver Concentrating Solar Power plants using molten salt as a heat transfer fluid add heat at around 565°C in a power plant. Adding heat at a higher temperature can improve the thermodynamic performance and may reduce the cost of power. One way to achieve this is by using pressurized air solar receivers. Current receivers have achieved thermal efficiencies of around 80% at an outlet temperature of 800°C. This paper investigates a novel central receiver technology that makes use of a tessellated array of heat transfer units. The units employ impingement heat transfer within a concave surface. The receiver can be scaled for a desired thermal rating by the number of heat transfer units. The convolution-projection flux modelling approach is used to model and project an incoming flux distribution on the receiver’s surface. This flux distribution is interpreted by a Computational Fluid Dynamics model as a volumetric heat source. Radiative and convective heat losses are considered. An initial performance outlook estimates that an outlet temperature of 801°C can be reached at a thermal efficiency of 59% and an exterior surface temperature of 1142°C for an aperture flux of 635kW/m2. A limitation is an insufficient exterior surface area to absorb the incoming flux which causes a high surface temperature and thermal losses. Similar thermal performance is estimated at high and low pressures, with increased pumping losses at low pressures. The efficiency may be improved by taking advantage of a larger surface area relative to the aperture area.

Pre-research on Enhanced Heat Transfer Method for Special Vehicles at High Altitude Based on Machine Learning

The performance of an integrated thermal management system significantly influences the stability of special-purpose vehicles; thus, enhancing the heat transfer of the radiator is of great significance. Common research methods for radiators include fluid mechanics numerical simulations and experimental measurements, both of which are time-consuming and expensive. Applying the surrogate model to the analysis of the flow and heat transfer in louvered fins can effectively reduce the computational cost and obtain more data. A simplified louvered-fin heat transfer unit was established, and computational fluid dynamics (CFD) simulations were conducted to obtain the flow and heat transfer characteristics of the geometric structure. A three-factor and six-level orthogonal design was established with three structural parameters: angle θ, length a, and pitch Lp of the louvered fins. The results of the orthogonal design were subjected to a range analysis, and the effects of the three parameters θ, a, and Lp on the j, f, and JF factors were obtained. Accordingly, a proxy model of the heat transfer performance for louvered fins was established based on the artificial neural network algorithm, and the model was trained with the data obtained by the orthogonal design. Finally, the fin structure with the largest JF factor was realized. Compared with the original model, the optimized model improved the heat transfer factor j by 2.87%, decreased the friction factor f by 30.4%, and increased the comprehensive factor JF by 15.7%.

Research on anti-frosting potential of air source heat pump evaporator in hot-summer and cold-winter zone

In this paper, the performance curve of a heat pump evaporator under critical frosting conditions was fitted. The functional relationship between the refrigerant evaporation temperature and the absolute air humidity ratio was obtained. In addition, the transfer unit model of the air source heat pump (ASHP) evaporator was established. The inlet air temperature, humidity ratio, velocity, fin pitch, and row number of evaporators were considered as input parameters. The anti-frosting potential of the heat transfer unit was simulated under critical frosting conditions. The results showed that, based on the heating potential of moist air unit mass under critical frosting conditions, the heating potential is at its minimum at an air humidity ratio of 3.39 g/kga. The maximum difference between the minimum temperature on the fin surface and the refrigerant evaporation temperature was found to be only 0.06 °C. The study findings highlighted that controlling the refrigerant evaporation temperature above the critical frosting temperature is an important method to prevent the evaporator from frosting. Under a low temperature environment, with the increase in the fin pitch and the inlet air velocity, the anti-frosting regulation performance of the two tube rows evaporator was found to improve compared to the single tube case. The aim behind increasing the inlet air velocity is to increase the heat transfer temperature difference between the inlet air and the critical frosting conditions. After optimizing the evaporator’s structural and operational parameters, the evaporator’s fin pitch is set according to the ambient air temperature. This was successful in meeting the requirement that the evaporator does not frost most of the time. Moreover, by adjusting the inlet air velocity, the evaporator will not frost at other times. In hot-summer and cold-winter zone, the operation of the ASHP evaporator with no frost can be achieved.

Design and multi-objective optimization of a new annular constructal bifurcation Stirling regenerator using response surface methodology

The irreversible losses such as the flow loss and axial heat conduction loss in traditional porous regenerators have limited the specific power and thermal efficiency of Stirling engines to a great degree. Thereby, the objective of this paper is to design and optimize a novel annular constructal bifurcation regenerator for diminishing the flow and axial heat conduction losses in the regenerator based on constructal concept and response surface methodology. First, the bifurcation type structure units with an inclined angle to the flow direction and the layered approach were applied to construct the regenerator matrix. Thereafter, the numerical simulations were employed to investigate the gas flow and heat transfer characteristics of the constructal bifurcation regenerator. Based on the numerical data, the quadratic polynomial regression models between the geometric parameters and the regenerator performance were established using response surface methodology, and the specific effects of the geometric dimensions were analyzed via 2-D and 3-D response surface plots. Subsequently, a multi-objective optimization was conducted to minimize the flow resistance and maximize the heat transfer rate by genetic algorithm. A most eclectic solution with the global friction factor f = 3.478 and the number of heat transfer units NTU = 1.135 was selected from the optimal Pareto front. Finally, the overall performance of the constructal bifurcation regenerator was compared with that of the porous regenerator and the parallel geometry regenerator. The results indicate that a low flow resistance, low axial heat conduction, and high thermal performance are obtained by the constructal bifurcation regenerator. Therefore, it is reasonable to conclude that the annular constructal bifurcation regenerator achieves a high comprehensive performance, with the potential to improve the performance of Stirling engines. The findings of this paper may provide some new ideas and guidelines for the design and optimization of the regenerator structures.

Comprehensive operational parameter analysis of cross-flow hollow fiber membrane humidifier for humidification dehumidification desalination

Experimental results show that the cross-flow hollow fiber membrane contactor is the controlling component of the humidification dehumidification desalination system performance. Three sets of main operating conditions sensitivity analyses are performed numerically, including solution conditions (temperature, salinity, flow rate), air conditions (temperature, relative humidity, flow rate) and dimensionless parameters (number of heat transfer units, flow rate ratio of solution to air). Increasing flow rate ratio can effectively promote freshwater production rate before flow rate ratio reaches a critical value of 6.0. It is useful to improve moisture effectiveness by increasing number of heat transfer units. Solution inlet temperature has an exponential promoting effect on membrane flux, which is consistent with the exponential upward trend of the solution phase equilibrium humidity. Membrane flux increases dramatically at first and then slowly after solution flow rate exceeds 228 kg/h and air flow rate exceeds 57 kg/h. Ambient air with high temperature and relative humidity as well as the high salinity of the solution will slightly degrade the membrane flux.

Heat transfer performance of a device integrating thermosyphon with form-stable phase change materials

Phase change materials (PCM) are applied worldwide as a thermal energy storage technology to reduce energy demands in buildings and solve environmental contamination issues. Form-stable phase change materials (FSPCM), as one branch of PCMs, can be improved by embedding them with thermosyphon, resulting in a better thermal performance. In this paper, a novel thermoplastic elastomer-based FSPCM was developed and tested. A device integrating FSPCM with thermosyphon was created, and the heat transfer mechanism of the unit was studied. The numerical model was established, and experiments were conducted accordingly. The average relative error between the experimental data and the model predictions was <3 %. Furthermore, a parameter study was conducted to investigate the effects of several essential factors. As a result, the evaporator length and PCM thermal conductivity were found to significantly influence the unit's heat transfer rate and overall thermal performance. However, the impact of the latent heat of the FSPCM on the heat transfer rate was negligible, for which it takes 1170 s, 1230 s, and 1394 s to finish changing phase with 136 kJ/kg, 160 kJ/kg, and 200 kJ/kg, respectively. This paper provides insights on the performance of thermosyphon integrated form-stable phase change materials and discusses its relevance for thermal energy storage applications.

Topology optimization of porous solid structures for heat transfer and flow channels in reactors with fluid-solid reaction coupling

In this paper, the optimization models for the heat transfer and flow channels with porous structures are developed. To enhance the heat transfer capacity of the thermal system, the topological optimization of the fin structure in the radial direction of the heat transfer unit is proposed and the influence of the initial conditions on the optimization of fins is studied. At the same time, the transient process of the heat transfer unit with topology optimization is investigated to verify the feasibility of the optimization model. The results show that the fins designed by topology optimization have coral-likestructure, and the width of the fin decreases as it moves outward from the center. For the optimization of flow channels, the optimum distribution of porous material with theoptimal reaction rate in laminar flow reactor is analyzed. The optimal structures for flow channels in porous media is obatined theoretically and simulatednumerically for obtaining the related transport characteristics. In addition, for the topologically optimized reactor, as the initial reaction parameters change, the fluid channels in the porous domain show different structures withtopology optimization.

Numerical simulation research on two-phase flow boiling heat transfer in helically coiled tube

In this paper, the partial geometric models of helically coiled tube type heat exchanger with different tube diameters (d = 12, 19, 25 mm), tube pitches (P = 50, 100, 150 mm) and helical radius (R = 100, 150, 200 mm), were established. Numerical simulation and performance comparison were carried out using water and water vapor as the working fluid. The gas–liquid phase distribution in the helically coiled tube, the gas volume fraction at different cross-sections, and the changes of heat transfer coefficient and pressure drop along the length of the helically coiled tube were analyzed. The results showed that the gas phase was concentrated in the inner side (near the side of the central axis) and the upper side of the helically coiled tube under boiling condition, and the liquid phase was concentrated in the bottom of the helically coiled tube and is stratified with the gas phase. As the helical radius and tube diameters increased, the heat transfer coefficient and unit pressure drop decreased gradually. Based on the simulated data, the boiling heat transfer correlation was fitted by the method of multiple nonlinear regression, and the mean absolute error was 4.5% compared with the modified Chen's correlation. Therefore, the numerical results were correct and trustable.