Cross-flow Heat Exchanger Research Articles

Deep dehumidification characteristics of a silica gel coated cross-flow heat exchanger with a circulating blowing loop

Solid desiccant dehumidification systems offer an effective and energy-efficient alternative for deeply dehumidifying air. Desiccant coated heat exchangers (DCHEs), a type of solid desiccant dehumidification system, have garnered attention due to their ability to eliminate adsorption heat and thereby enhance dehumidification capacity, unlike desiccant wheels that perform adiabatic dehumidification. This study introduces a silica gel coated cross-flow DCHE equipped with a circulating blowing loop for deep dehumidification applications. A two-dimensional numerical model is developed to simulate deep dehumidification behavior of the DCHE. Parametric analysis is performed to explore the dehumidification characteristics under various conditions, setting different volume fractions ω of blowing loop air. Results indicate that the DCHE can effectively reduce the moisture content of humid air to a deep dehumidification threshold of 6.2 g/kg. Additionally, dehumidification capacity can be increased by incorporating a circulating blowing loop. The influence of process air velocity, cooling air velocity, process air humidity ratio, regeneration air temperature, and air channel length on the dehumidification performance are analyzed, focusing on metrics such as minimum outlet air humidity ratio Ya1,ad,out_min, effective deep dehumidification time teff, moisture removal capacity MRC and dehumidification coefficient of performance DCOP. It is determined that the regeneration air temperature should be raised to 80 °C to ensure deep dehumidification, and an air channel length of 0.2 m is optimal.

Role of physical structure on performance index of crossflow microchannel heat exchanger with regression analysis

Microchannel heat exchangers have become the preferred choice in contemporary technologies like electronics, refrigeration, and thermal management systems. Their popularity stems from their compact design and exceptional efficiency, which outperform traditional heat exchangers (HE). Despite ongoing efforts, the optimal microchannels for enhancing heat management, minimizing pressure drop, and boosting overall performance have yet to be identified. This study seeks to deepen our understanding of heat transmission and fluid dynamics within a cross-flow microchannel heat exchanger (CFMCHE). Utilizing numerical modeling, it examines how various physical aspects—such as channel geometry, spacing between channels, the number of channels, and the velocity at the inlet—affect key performance indicators like pressure drop, effectiveness, Nusselt number, and overall efficiency. To enhance the design, we analyze six unique shapes of crossflow microchannel heat exchangers: circular, hexagonal, trapezoidal, square, triangular, and rectangular. We employ the Galerkin-developed weighted residual finite element method to numerically address the governing three-dimensional conjugate partial differential coupled equations. The numerical results for each shape are presented, focusing on the surface temperature, pressure drop, and temperature contours. Additionally, calculations include the efficacy, the heat transfer rate in relation to pumping power, and the overall performance index. The findings reveal that while circular shapes achieve the highest heat transfer rates, they underperform compared to square-shaped CFMCHEs. This underperformance is largely due to the increased pressure drop in circular channels, which also exhibit a 1.03% greater reduction in effectiveness rate than their square-shaped counterparts. Consequently, square-shaped channels, boasting a performance index growth rate of 53.57%, emerge as the most effective design among the six shapes evaluated. Additionally, for the square-shaped CFMCHE, we include residual error plots and present a multiple-variable linear regression equation that boasts a correlation coefficient of 0.8026.

Application of nanofluids in industrial processes. The case of food processing

A crossflow heat exchanger for drying purposes integrated in a pasta manufacturing process is considered in the present work. Different nanofluids, i.e., Al2O3, TiO2, and CuO, are considered with particle dimensions ranging from 20 to 60 nm and volumetric concentration in the range of 0 %–5%. Base fluid is water. An analytical model of the heat exchanger is developed and the energy performance is evaluated from a Life Cycle Analysis perspective by considering the embodied energy of the different nanoparticles. The utilization of the nanofluids allows to reduce the dimensions of the device. In particular, a reduction in length of 26 %, 25 %, and 27 % is estimated for Al2O3, TiO2, and CuO respectively. Oppositely, there is not an enhancement of the energy performance. In particular, an increase of the operating energy is detected since the reduction of the dimension increases pressure losses and the saving in embodied energy due to the use of less material is not sufficient to offset the increase in embodied energy due to the utilization of the nanoparticles.

Anti-fouling rotating polymer-based heat exchanger for zero liquid discharge humidification-dehumidification desalination

The objective of this investigation is to assess the performance of various heat exchangers for application in a novel solar-powered zero liquid discharge humidification-dehumidification desalination system. In this study four heat exchangers (HX) having two different flow configurations namely counter flow (cf), cross flow (cr) made up of three different materials namely high-density polyethylene (HDPE), aluminum (Al), and Polypropelyne (PP) were compared in terms of their effectiveness and overall heat transfer coefficient under varying salinity levels (up to 10%) and mixing ratios (0.22–0.45). At a mixing ratio of 0.22 and 0% salinity, PP-HXcr and Al-HXcf exhibited similar effectiveness (∼85%), surpassing that of HDPE-HXcf (∼65%). Despite PP-HXcr's lower thermal conductivity in comparison to Al-HXcf, comparable effectiveness was achieved due to the superior flow distribution in PP-HXcr. Further investigations focused on the impact of salinity on heat exchanger performance. At 3.5% salinity, all heat exchangers experienced a decline in effectiveness and heat transfer coefficient (HTC), with Al-HXcf experiencing a more pronounced decrease compared to PP-HXcr. The higher thermal conductivity of Al-HXcf led to greater salt accumulation, while PP-HXcr demonstrated minimal fouling. As the experiment progressed, fouling increased for all heat exchangers, with the Al-HXcf being practically ineffective at 10% salinity with an effectiveness below 10%. To address the issue of fouling, a rotating cross-flow heat exchanger (RPP-HXcr) was introduced. While the effectiveness of the PP-HXcr drops from 85% to approximately 60% with increasing salinity from 0% to 10%, the RPP-HXcr demonstrates only a marginal decline in effectiveness with increasing salinity. For instance, at mixing ratio of 0.22 when the salinity is increased from 0% to 10%, the effectiveness of RPP-HXcr only drops from 83% to 77%. This exceptional performance was attributed to the continuous contact between the rotating tubes and the incoming feed, effectively preventing fouling and ensuring sustained efficiency. Rotating cross-flow heat exchanger (RPP-HXcr) is introduced and validated as a potentially reliable solution for mitigating fouling, as it demonstrates sustained efficiency and minimal performance degradation across different salinity conditions.

Dynamic simulation and thermoeconomic analysis of a novel indirect hybrid solar dryer

Indirect solar dryers represent a clean and sustainable solution for drying foods, fruits, and vegetables. In this research, the performance of a novel indirect hybrid solar dryer has been investigated numerically on apple slices using TRNSYS software. The solar dryer consists of a flat plate solar collector, a vacuum tube solar collector, a cross-flow heat exchanger, an auxiliary heater, and a drying chamber. With the assumption that there is no access to fresh fruits and vegetables in winter, the simulation was carried out in three days on April 15, July 15, and October 15 (from 8 a.m. to 5 p.m.) as representatives of spring, summer and autumn, respectively. The humidity content of apple slices reduced from 86 % to 11 % in about 270 min at 70 °C. The minimum power received from the auxiliary heater was on July 15 with 1497 W, which was about 1.5 h without needing a backup heater. (from 11:30 a.m. to 1 p.m.). The maximum thermal efficiency of the drying system was obtained on July 15 at about 60 % for the flat plate collector, 78 % for the vacuity tube collector, and 25 % for the drying chamber. Also, the return on capital in Iran, USA, UAE, and Turkey was equal to 1.49, 0.74, 0.95 and 1.35, respectively.

Numerical investigation of gyroid heat exchanger

A novel cylindrical gyroid surface-based tube is designed to investigate fluid flow and heat transfer characteristics numerically. The simulations are carried out using finite volume based CFD software Ansys Fluent. The numerical validation is performed to verify the robustness of the solver and grid independence study are also carried out to compute the simulations using optimum mesh. The heat exchanger (HX) tubes with gyroid surfaces are manufactured using additive manufacturing and a crossflow HX is fabricated with a bank of gyroid tubes where the experiments were conducted. The numerical results of the Realizable k-ε turbulence model with enhanced wall treatment is validated with in-house experimental data. The thermal performance of the gyroid tube HX is also compared with a conventional circular tube (CCT). Parametric analysis is also carried out by varying the gyroid design parameter and an optimum HX design is proposed. The results show that due to larger surface area and enhanced fluid mixing, the gyroid tube-based HXs show better thermal performance compared to CCT-based HX.

Numerical investigation on thermal-hydraulic performance of leeward cut annular finned tubes in crossflow heat exchangers: An insight on fin material saving

The objective of the current study is to analyse the hydro-thermal characteristics of leeward cut fins with various trimming values and finalise a specific fin that benefits by maximum material saving and negligible compromise in heat transfer. The leeward section of a fin is cut in two ways: angular and chordwise. For angular cutting, four different angles (15°, 30°, 60°, and 90°) are considered, while for chordwise cutting, a fin is trimmed along a chord present at D/3, 2D/3, and D mm from the vertical diameter. The spacing between fins is varied (2–4 mm). For turbulence modelling, the transition SST model is implemented. Streamlines reveal that the intensity of a vortex formed downstream of the tube depends on the fin-trimming value. For a higher fin cutoff, a lower pressure drop is obtained. The heat transfer rate analysis reveals that angular cutoffs of 15° (8.3 % material saving) and 30° (16.6 % material saving) have 2.5 %–3.1 % less heat transfer than the standard case. Chordwise cut at D gives 1.1 % less heat transfer but saves only 2.7 % fin material than the standard case of no cutoff. Z/E factor, a ratio of heat transfer for a unit temperature drop to power provided, is used to determine hydro-thermal performance. The value of the Z/E ratio is the highest for the benchmark case. However, for angular cutoffs of 15° and 30°, the Z/E factor is less by 4 and 6.7 %, respectively, than the standard case. Examining the outcomes of this study, we recommend using an angular cutoff of 30° or lower to get significant material savings for an equivalent heat transfer.

Revolutionizing energy flow: Unleashing the influence of MHD in the presence of free convective heat transfer with radiation

This study investigates the complex interplay between radiation and magneto-flow on a porous, perpendicular plate immersed in a viscoelastic Maxwell fluid. The significance lies in understanding how the Lorentz force shapes dynamics and energy transfer in such systems, which is crucial for various industrial applications. Utilizing a comprehensive model that accounts for heat generation and absorption, we transform partial differential equations into ordinary ones through flow similarity analysis, providing valuable insights into the system's behavior. Employing the bvp4c solver in MATLAB, we evaluate velocity and energy profiles in Maxwell fluid flow. Graphical representations allow for a thorough examination of the influence of thermophysical parameters. Our findings reveal an intensified velocity profile attributed to prolonged material relaxation times.Furthermore, temperature profiles progressively increase with higher radiation and porous parameters. These results hold significant implications for industrial applications, particularly in Maxwell fluids' heat transport studies. Insights from this research can inform the design and optimization of systems such as ovens, boilers, cross-flow heat exchangers, and solar panels, enhancing efficiency and performance. Overall, this study contributes novel insights that advance understanding beyond previous efforts in the literature, paving the way for further exploration in this field. The primary finding of this study indicates that as the Rayleigh number increases, the velocity profile experiences an increase, whereas the temperature profile shows a decrease.

Heat Transfer Performance Tests of a Circular-Fin Sodium-to-Air Heat Exchanger for Sodium-Cooled Fast Reactors

Shell and tube-type crossflow heat exchangers with circular fins are widely used in various industries, including nuclear power plants. This study focuses on the sodium-to-air heat exchanger, which is one of the key safety features in sodium-cooled fast reactors. Tube alignment inside the heat exchanger is important because it directly determines the performance. Although heat exchangers are generally designed to have staggered tube alignment, inevitable inline-aligned zones exist. Therefore, this paper proposes a hybrid tube alignment modeling approach that considers both staggered and inline tube heat transfer phenomena. The results of the hybrid model calculations are verified and validated with liquid sodium experiments. The hybrid approach to the tube arrangement reduced the temperature deviation between experimental and calculated values to a difference of 4.55% and 7.38% for both sodium and air sides, respectively, while for the heat transfer, the difference was 15.12% and 9.06% for sodium and air sides, respectively. The results of this study can also be used as a basis for the safety evaluation of nuclear reactors and licensing processes for sodium-cooled fast reactors. In addition, this study is limited not only to sodium heat exchangers but also to any serpentine tube arrangement or crossflow heat exchanger under high-temperature systems, such as concentrated solar power and thermal energy storage industries.

Theoretical study on the dehumidification behaviors of dual-desiccants coated cross-flow heat exchanger with staged adsorption-desorption process

The conventional desiccant coated heat exchangers (DCHEs) suffer from the inefficient utilization of regenerative energy and the inadequate dehumidification capacity of a single desiccant. In this study, a concept of dual-desiccants cross-flow DCHE with staged adsorption-desorption process was proposed to strengthen dehumidification capacity and energy efficiency simultaneously. In order to guide the construction of proposed DCHE, the steady-state dehumidification capacity of single-desiccant (specifically, silica gel, FAM Z01, FAM Z05 and EMM-8) cross-flow DCHE was investigated by thermodynamic analysis. The dual-desiccants cross-flow DCHE was thus constructed, and its numerical model was established to investigate the dehumidification characteristics. Theoretical analysis revealed that single-desiccant cross-flow DCHEs exhibit different optimal relative humidity ranges for dehumidification. The minimum regeneration temperature driving dehumidification cycle increases as the lower supply air humidity is required. Numerical results demonstrated that the staged adsorption process ensures a large dehumidification capacity across a wide humidity range, including low humidity conditions. Meanwhile, the staged desorption process facilitates the cascade utilization of energy and the direct recovery of regenerative waste heat. For dual-desiccants cross-flow DCHE utilizing silica gel and EMM-8, the moisture removal capacity and dehumidification coefficient of performance can reach 0.012 kg/kg and 0.41, respectively.

Experimental and numerical analysis of the impact of a liquid flow rate on the operational performance of a cross-flow tube-and-fin heat exchanger

The paper is dedicated to an issue of the influence of a nonuniform flow of mediums in a cross-flow water-air heat exchanger, the core of which is a bundle of elliptical finned tubes. The main purpose of the work is to determine the impact of non-uniform water inflow for various mass flow rates on the thermal efficiency of the heat exchanger. Multivariate analyses were carried out for various temperatures of water, and for measured nonuniform air distribution at the heat exchanger input. Two variants of water distribution were considered: non-uniform water distribution assumed considering a non-uniform air inflow and water distribution resulting from hydraulic resistances calculated for different locations of water inlet and outlet nozzles. Simulation results were compared with the experimental outcomes obtained in cases of the non-uniform natural inflow of both mediums and to the computation results for a case of the uniform media inflow. The results obtained in this work confirm the significant deterioration of the thermal efficiency of heat exchangers caused by a non-uniform media inflow (by as much as 18.5% compared to the case of a uniform media inflow) which is compliant with other numerous works. The control of the water flow through the individual heat exchanger tubes enables the improvement of thermal efficiency by 4.5% to 18.6% compared to the device with uncontrolled inflow of working fluids, which for some of the analyzed cases is even better than a completely uniform inflow of heat carriers.

Optimising thermal design for cross flow heat exchanger in fan coil units

ABSTRACT Analytical and numerical solutions for determining the dimensions of a cross-flow heat exchanger under different conditions have been developed in this study. The analytical solution using the ε-NTU method is used to find the initial dimensions of the cross-flow heat exchanger. The numerical solution is used to validate the analytical solution and optimise the cooling coil dimensions. The ε-NTU design results show the effect of water mass flow rate, air inlet velocity, and the outer tube diameter of the cooling coil. The distribution of air and water temperatures through the heat exchanger can be predicted by solving the basic Navier-Stokes equation and energy equation using numerical methods.

Study on the thermal performance of the cross-flow plate heat exchangers

The exhaust gas emitted by a stenter machine will lead to energy waste and environmental heat pollution. Therefore, designing an efficient waste heat recovery apparatus for exhaust gas not only protects the environment but also saves production costs. In the article, the heat transfer performance and pressure drop of three types of heat exchangers: flat-plate heat exchanger (PHE), wavy-PHE, and zigzag-PHE were numerically studied in the context of waste heat recovery from the exhaust gas of stenter machines. The heat transfer rate (Q), Nusselt number (Nu), Colburn factor (j), pressure drop, Fanning friction factor (f), and comprehensive performance factor (JF) were investigated while Reynolds numbers ranged from 1000 to 9000. An experimental measurement was devised to validate the accuracy of the numerical simulation. The results of the research indicate that the wavy-PHE exhibits improved heat transfer efficiency and reduced pressure drop, primarily attributed to the substantial generation of secondary flow. Three new correlations for Nusselt number in different PHEs were developed based on commonly existing empirical formulas. The prediction accuracy for the Nusselt number based on the new correlations has been significantly improved in the present study.

Studies on heat transfer performance of miniature cross-flow heat exchangers with perforated fins for direct methanol fuel cells

Despite the widespread industrial application of finned micro heat exchangers, there is still a need to enhance the heat transfer efficiency. This study focuses on fin perforation research to improve heat transfer efficiency. In this study, a miniature cross-flow heat exchanger (heat source is a heat stream at 351.35 K) was simulated. By employing a combination of experimental methods and numerical simulations, the investigation delves into the impact of mixed shapes and innovative spatial distributions of perforations on fin convective heat transfer characteristics. The findings demonstrate that square and square-and-diamond perforated fins exhibit a temperature drop increase of 10.1 % and 8.9 %, respectively, in comparison to unperforated fins during forced convection. Fin temperature drop is augmented by 12.3 % with differentially staggered perforations on adjacent fins (spatially staggered perforations) in contrast to parallel perforated fins, and by 23.6 % compared to non-perforated fins. Furthermore, the optimal performance of the fin heat transfer is observed at 5.74 % perforated area occupancy. The study reveals a positive correlation between the Nusselt and Reynolds numbers. Moreover, the spatial distribution of perforations significantly enhances the performance evaluation criteria compared to the perforation shape. Ultimately, the implementation of fin perforation technique is considered to offer more consistent power output and an extended range for direct methanol fuel cells.

Numerical investigation of thermal-hydraulic characteristics in cross-flow heat exchangers with different twisted oval tubes

This study presents a new strategy to strengthen the flow and thermal performance of gas-liquid tube bundle heat exchangers by combining oval tubes with variable-direction twist method. The effects of twist direction, twist angle and flow velocity on the overall performance were investigated. The variable-direction twisted oval tube enhances the mixing degree of the main stream and the tail vortex, thereby improving the thermal performance and reducing the pressure drop. Both heat transfer coefficient and pressure drop increase with the increase of twist angle, and the overall performance is negatively correlated. Twist period has little effect on overall performance. Convective heat transfer coefficient of the variable-direction twisted oval tube with a twist angle of 120° is increased by 5.8%–10.2%, pressure drop is reduced by 5.0%–7.8% and overall performance is increased by 7.4%–10.7%, as compared circular tube bundle. The proposed variable-direction twisted oval tube realizes the synergistic enhancement of thermal-hydraulic performance, and can directly replace the traditional circular tube. The work of this paper provides technical guidance for improving the processing technology of twisted oval tube and developing new heat exchangers.

A holistic approach for solar-driven HVAC evaporative cooling system: Comparative study of dry and wet channel

In HVAC, indirect evaporative cooling powered by renewable energy sources is the key factor for effectiveness with respect to thermal comfort, sustainability, exergy utilization, leading to a cooler and greener environment. In the cross-flow heat exchanger, the tubular wet channel is the main objective for analysis of 3E (exergy, economic, environmental) and sustainability, for dry and novel channels separately. In this research, both channels have been developed to evaluate exergy variations, sustainability, and specific total cost based on the influence of dead-state temperature, working air ratio, wet bulb depression, and the inlet flow parameters of working air. The results show that the wet channel's exergy efficiency is 18.8 % lower than that of the dry channel, and the exergy destruction of both channels is 0.08406 kW and 0.1311 kW, respectively. Moreover, the tubular wet channel demonstrates a significant economic advantage for cross-flow IEC device. The STC of the wet channel found to be 85.35 % higher, and value of sustainability was 25% lower than that of the dry channel. The values of annual emissions were found to be 4.09 kg/year for CO2, 0.304 kg/year for NOx, and 0.189 kg/year for SO2 for solar-drive device. A psychrometric chart has been drawn for thermal comfort assessment. The findings of the novel tubular channels have been presented in terms of sustainability, thermal comfort, and green energy solutions and the results of exergy variations have been compared with previous work in the literatures.

Comparative Analysis of Changing Channel Geometry of a Cross-flow Microchannel Heat Exchanger

Comparative Analysis of Changing Channel Geometry of a Cross-flow Microchannel Heat Exchanger

Numerical method for determining pressure distribution in tube cross-flow heat exchangers

This paper presents a numerical method for determining the pressure distribution along the fluid flow path in a cross-current hightemperature heat exchanger. The pressure drop across the superheater was determined using the momentum conservation equation, which was solved by the finite difference method. Local pressure losses at tube elbows were also taken into account. A new formula for calculating friction factor on rough tubes' inner surface is proposed. A straightforward model for the friction factor in tubes with a rough inner surface for Reynolds numbers in the interval 3000 - 108 has been proposed. The pressure distribution in the last stage of the live steam superheater in a 900 MWe supercritical boiler was calculated.

A Numerical Study on Cross Flow Heat Exchanger with Different Reynolds (Re) Numbers

Heat exchangers are highly popular in engineering and industrial applications. Numerical studies on heat exchangers to investigate the performance of heat transfer have been carried out widely by Computational Fluid Dynamics (CFD) in recent years. In this study, a circular pipe with hot water in cross flow is investigated in different Reynolds (Re) numbers. Flow is turbulent flow and the Re number varies from 3165 to 4643 in the circular pipe. The air is at a temperature of 303 K and the water is at 333 K. Variation of flow characteristics and thermal performance is observed according to an increase in Re numbers such as Wall Shear Stress (WSS), Skin Friction Coefficient (Cf), Nusselt Number (Nu), heat transfer coefficient (h) and surface temperature of the circular pipe. Results show that there are no significant changes for the WSS and Cf values in the specified range of the Re number. However, when the thermal performance is evaluated, the temperature of the surface of the circular pipe, heat transfer coefficient, and Nu number values are increased by an increase in the Re number. Here, the increase is approximately 2% for the specified range of Re number, and it is shown that it can be increased by the flow conditions. The maximum Nu number is 4482.37 at the Re number of 4643. As a result, the Re number is highly effective in controlling the heat transfer performance of a heat exchanger

Evaluation of Serrano Pepper Crops Growth under Controlled Conditions of Vapor Pressure Deficit in a Pilot-Scale Hydroponic Greenhouse

Controlled Environment Agriculture (CEA) has become an important field of study in recent years. The objective of this research is to evaluate the growth rate of the serrano pepper crop under controlled conditions of vapor pressure deficit in a pilot-scale hydroponic greenhouse. The controlled conditions were generated with the development of a control system composed of a non-mixed crossflow heat exchanger for internal temperature and a humidification system for internal humidity control. The comparison of variables and the growth rate of the crop was carried out in a controlled and a timed greenhouse. The best growth rate for serrano pepper cultivation was obtained under the following conditions: between 4.14 and 5.42 kPa with 0.251 and 0.225 cm/day in the controlled greenhouse. The results show that it is possible to obtain higher crop growth rates by controlling the vapor pressure deficit in a pilot-scale hydroponic greenhouse, using a heat exchanger for temperature control and a humidification control system. Controlling vapor pressure deficit can be a useful tool for agriculture in CEA.