Cross-corrugated Plate Research Articles

Digital image analysis of gas-liquid flow in a cross-corrugated plate heat exchanger channel: A feature-based approach on various two-phase flow patterns

High-resolution photographs of the air-water flow in a transparent cross-corrugated channel are analyzed using digital image processing. Gas-liquid distribution is controlled via several inlet nozzles. Flow direction is varied between upward, downward, and horizontal flow.The image analysis algorithm is applied to a wide range of void fractions and flow patterns including bubbly, intermediate and film flow. Large bubble clusters are separated using edge detection. Local film and bubbly flow are identified with texture analysis. The method is suitable for locally inhomogeneous two-phase flow which is difficult to analyze visually.Objective and reproducible results are obtained by measuring features in the processed images: Mean and maximum bubble diameter, and the ratio of local film flow are determined. For non-uniform gas injection, expansion of two-phase flow across channel width is measured. Impact of flow direction and maldistribution on two-phase flow is demonstrated by calculating differences of the features. Uncertainties of image processing results are quantified. Bias is discussed based on visual analysis of the photographs in a previous study.Models for maximum bubble diameter and local film flow ratio, used to model flow pattern transitions in a previous study, are verified: For uniform two-phase distribution, models generally agree with measured values.

Thermal performance optimization of heat exchanger with mixed cross-corrugated sinusoidal plate channels

• The flow and heat transfer in cross - corrugated plate unit channels are investigated. • Effect of phase shift angles on heat transfer performance of wavy channels are analyzed. • The heat transfer performance of mixed wavy channel is optimal at a phase shift angle of 324°. • For each wavy channel, the heat transfer performance of the lower wall is always greater than that of the upper wall. The thermal performance of heat exchanger with mixed cross-corrugated plate plays a fundamental role in the efficiency of the heat exchanger. Based on RNG k-ε model, the heat transfer characteristics of unit channels of three different mixed cross-corrugated plate heat exchangers (30°-50°, 30°-60°, 30°-70°) under different Reynolds numbers ( Re ) are investigated. The distributions of the average Nusselt number ( Nu ¯ ), friction factor ( f ) and Performance Evaluation Criterion ( PEC) of the three mixed unit wavy channels under different phase shift angles (0°≤θ ≤ 360°) are researched. The results indicate that a vortex area is appeared at the bottom wall. As the Reynolds number increases, the vortex area increases, and the vortex shape of the 30°-70° mixed wavy channel is close to circular. In addition, the heat transfer performance of the lower wall is always greater than that of the upper wall for each channel. Moreover, the optimal heat transfer performance for three mixed wavy channels is obtained at phase shift angle of 324°.

Two-phase pressure drop and void fraction in a cross-corrugated plate heat exchanger channel: Impact of flow direction and gas-liquid distribution

Two-phase pressure drop is studied in a transparent cross-corrugated channel for uniform and non-uniform gas–liquid distribution. Both uniform and non-uniform distribution are created by injecting air and water through different numbers of nozzles directly into the channel. The frictional pressure drop clearly indicates the impact of maldistribution.The single channel is pivot-mounted to allow horizontal, vertical upward and downward flow. Two-phase frictional pressure drop can be directly measured only for horizontal flow, neglecting acceleration pressure drop. In vertical flow, a void fraction model is necessary to deduct gravitational pressure drop from the measured pressure difference.The two-phase friction factors of all flow directions are compared to the correlation of single-phase flow. In this manner, homogeneous flow is distinguished from slip. Homogenous flow is confirmed for homogeneous void fractions up to 0.7 at uniform and up to 0.25 at non-uniform gas injection. The single-phase correlation is valid for homogeneous flow when inserting two-phase variables. The experimental two-phase multiplier is compared to correlations from literature.The pressure measurement data are used to determine the actual void fraction. The results are compared to published void fraction models. The homogeneous model fits best for uniform two-phase distribution. For maldistribution, the correlations of Margat et al. (1997) and of Rouhani and Axelsson (1970) predict the experimental void fractions reasonably well, except for very small flow rates.Analysis of experimental results is facilitated by previously published research on flow pattern visualization and modelling in the same test channel. The cross-corrugated geometry generates a swirling motion inducing centrifugal forces often much larger than buoyancy, which thus loses impact on flow pattern, pressure drop and void fraction. The ratio of buoyancy to centrifugal force is expressed by the corrugation Froude number. Slip independent of buoyancy is identified by introducing the hydrostatic correction factor to evaluate friction factors deviating with flow direction.

Influence of the separation elements’ shape on the process of water-oil emulsion demulsification in the pipe

In order to intensify the demulsification of water-oil emulsions, various types of separation elements for the settling tanks are proposed, namely, the corrugated plates with different orientation of corrugations, located at an angle of 45°, 135° and the cross-corrugated plates. The experimental studies of water-oil emulsion demulsification by means of a laboratory unit, using the developed separation elements were conducted. The conducted studies showed that the use of various separation elements inside the settling tanks allows intensifying the process of water-oil emulsion demulsification. The separation elements, considered in this paper, allow the performance of demulsification process with minimum 62% efficiency at the average rate of emulsion movement of more than 0.04 m/s. In the course of studies, it was found that the most effective of the considered separation elements are the corrugated plates with an orientation of corrugations, located at an angle of 45°, allowing the process of water-oil emulsion demulsification with an average efficiency of 80.1% at the movement rate within the range of 0.04–0.053 m/s. It is also shown that for the various separation elements, there are the most effective ranges of emulsion rates, at which the maximum values of demulsification efficiency are achieved.

Numerical study on the effect of corrugation angle on thermal performance of cross corrugated plate heat exchangers

In the present work, the single-phase thermohydraulic performance of a cross-corrugated plate heat exchanger (PHE) with different corrugation angles 30°≤β≤80° is studied numerically. A three-dimensional numerical model using the finite volume method is developed and validated assuming laminar and turbulent flows in the Reynolds number range of 400–10000. The two-equation k-ω SST model is employed to analyse the turbulent flows in the PHE. It is found that for all the configurations of the PHEs, the pressure drop per unit length increases with the Reynolds number and the corrugation angle. The friction factor of the PHE with β = 80°–80° is higher by a maximum of 2.8 times than that of the flat PHE. The Nusselt number is found to be higher in the corrugated PHE as compared to that of the flat plate PHE. The Nusselt number is increased by a maximum of 3 times for the PHE with β = 80°–80° than that of the flat PHE. Further, single phase generalized correlations of Nusselt number with Reynolds number, geometrical parameters of the cross-corrugated plate heat exchanger and fluid properties are developed for high cross-corrugated angles and a wide range of Prandtl numbers within a maximum accuracy of 40%.

Visualization and modelling of flow pattern transitions in a cross-corrugated plate heat exchanger channel with uniform two-phase distribution

Plate heat exchangers are often used for two-phase applications such as evaporation or absorption. In order to predict heat and mass transfer and pressure drop more accurately, knowledge of flow patterns is essential.Most of the published flow pattern maps for plate heat exchangers are biased by non-uniform inlet conditions. The objective of this study is to eliminate inlet effects, to which end, a uniform and steady two-phase distribution is implemented.An adiabatic air-water mixture is visualized in a transparent cross-corrugated single channel. The flow direction is varied between horizontal, vertical upward and downward. Both phases are injected directly into the channel via multiple nozzles. All superficial velocities are determined for the actual operating conditions.Flow patterns are mostly not affected by flow direction. Instead, the centrifugal force often dominates over buoyancy due to the swirling flow induced by the corrugations. A corrugation Froude number is defined to explain the findings. So-called slug flow is not observed, although being reported by other authors. This is attributed to the inlet design.Simple model assumptions regarding flow pattern transitions in tubes are adapted to the cross-corrugated channel. An additional model is proposed to account for the gradual transition of flow patterns at higher void fractions. The minimum kinetic energy for bubble breakage is also modelled to explain the gas accumulation observed at slow down-flow.

Influence of geometric variables on the structural characteristics of brazed cross-corrugated sinusoidal plate with secondary corrugation

A cross-corrugated plate with secondary corrugation was proposed to improve the compactness and thermo-hydraulic performance of a compact heat exchanger. To achieve a reliable structural design and select the geometric shape of the corrugated plate according to the load condition requires research on the influence of the geometric variables on the structural characteristics under a variety of loading conditions. The aim of this study was to evaluate the influence of the geometric variables of a brazed cross-corrugated plate with secondary corrugation in terms of the structural characteristics. Three important geometric variables, namely, the pitch-to-height ratio, thickness of the plate and amplitude of the secondary corrugation, were considered. A thermo-mechanical FE simulation was conducted on a cross-corrugated plate with various geometric shapes according to various load types, such as pressure, temperature, and combined pressure and temperature loads. A DOE design matrix was generated using a full factorial design with every design combination considered. An analysis was conducted to observe the main effect of the various design variables in terms of the thermal, mechanical, and thermo-mechanical stress levels. The influences of geometric parameters on the structural characteristics under various loading conditions were presented. The proposed geometric variables were assessed as valid variables.

Parametric Study on the Thermal Performance and Optimal Design Elements of Solar Air Heater Enhanced with Jet Impingement on a Corrugated Absorber Plate

Previous works revealed that cross-corrugated absorber plate design and jet impingement on a flat absorber plate resulted in a significant increase in the performance of a solar air heater (SAH). Involving these two designs into one continuous design to improve the SAH performance remains absent in the literature. This study aimed to evaluate the achieved enhancement on performance parameters of a SAH with jet impingement on a corrugated absorber plate. An energy balance model was developed to compare the performance parameters of the proposed SAH with the other two SAHs. At a clear sky day and a mass flow rate of 0.04 kg/s, the hourly results revealed that the max fluid outlet temperatures for the proposed SAH, jet-to-flat plate SAH, and cross-corrugated plate SAH are 321, 317, and 313 K, respectively; the max absorber plate temperatures are 323.5, 326.5, and 328 K, respectively; the maximum temperature differences between the absorber plate and fluid outlet are ~3, 9, and 15 K, respectively; the max efficiencies are 65.7, 64.8, and 60%, respectively. Statistical t-test results confirmed significant differences between the mean efficiency of the proposed SAH and SAH with jet-to-flat plate. Hence, the proposed design is considered superior in improving the performance parameters of SAH compared to other designs.

Hydraulic and Thermal Simulations of a Cross-Corrugated Plate Heat Exchanger Unitary Cell

Simulations have been carried out by means of computational fluid dynamics for turbulent convective heat transfer in a cross-corrugated plate pattern heat exchanger unitary cell at a Reynolds number of 4930. Chen's high-Reynolds-number k-ϵ model, the Reynolds stress model (RSM), Suga's low-Reynolds-number k-ϵ model, and the V2F model were used. The predicted hydraulic and thermal behaviors using these models have been compared and explained. The simulations showed that the interaction between the upper flow and lower flow in the cell creates a shear zone at their interface with a rotating motion and as a consequence the heat transfer is enhanced. This phenomenon was captured best by the V2F model, which predicted the highest Nusselt number and friction factor. Chen's k-ϵ model provided results similar to the RSM. The fact that the RSM was instable and required more computational power makes it less interesting for further use in similar studies. It was also found rewarding to generate multiblock all-hexahedral grids to resolve the existing thermal and hydraulic phenomena in the domain.

Characterizations of aerothermal performance of novel cross-corrugated plate heat exchangers for advanced cycle aero-engines

The shape of the surface of cross-corrugated plate heat exchangers were parameterized, producing geometries with different surface profiles (sinusoidal and asymmetrical) and corrugation furrow shapes (straight and sinusoidal). A total of seven geometries were tested at laboratory scale using a Transient Liquid Crystal (TLC) heat transfer measurement technique, which produced data at high resolution (2.68×10-4m interval). Pressure drop as well as heat transfer measurements were carried out at Reynolds numbers ranging from 1300 to 13,000 with uncertainty of 5.5% and 8.5% respectively, where the range of Reynolds numbers tested were representative of the conditions seen in the aero-engine cycle. High resolution heat transfer distribution data for these novel heat exchange surfaces obtained in the current experimental campaign are presented for the first time in the literature. This allows local Nusselt number in the heat exchangers to be examined in great details, from which the flow patterns could be inferred; thus enabling further improvements to be made in the design iteration. Correlations for Nusselt number and Fanning friction factor as a function of Reynolds number were also developed; the data were further summarized as volume goodness and area goodness factors to allow sensible comparison between different heat exchanger surfaces. The results of the current study provide extremely useful reference data for future design optimization of plate heat exchanger.

Numerical and Experimental Study on the Heat Transfer and Pressure Drop of Compact Cross-Corrugated Recuperators

Recuperator is one of the key components in high temperature gas cooled reactors. Although cross-corrugated plates have been used to increase the thermal performance of the recuperators, the fundamental mechanisms of fluid flow and heat transfer are generally not clear. Fluid dynamics simulations and experiments are hence carried out to study the performance of the recuperators. A periodic cell is employed as the control volume. The flow field and heat transfer in sine-wave crossed-corrugated channels are investigated based on the Navier–Stokes and energy equations in the laminar flow regime between Re = 84 and 1168. The numerical results of the heat transfer factors and friction factors in different operating conditions show a fairly good agreement with the experimental measurements. The influence factors on the heat transfer and the hydraulic performance are also discussed in the paper. It is found that the heat transfer factor j and friction factor f decrease with the increase of the pitch-height ratio for a given Reynolds number.

Investigation into structural reliability of a brazed part in cross-corrugated plates

To ensure the reliability of a brazed cross-corrugated plate it is necessary to observe structural characteristics such as the stress level, deformation behaviours, and the location of maximal level stress caused by pressure and temperature. The aim of this study was to investigate the structural characteristics according to the design variables of a brazed corrugated plate shape under temperature and pressure load. The brazed corrugate plate shapes were proposed according to four design variables, such as pitch to internal height ratio, thickness of plate, corrugated shape, and radius of brazed filler metal. The finite element analysis and design of experiments were employed to investigate the structural characteristics as functions of the design variables of a brazed corrugate plate. A segmented model with the same internal unit flow channel volume is considered in order to perform an efficient analysis. Through this work, the main effects of the design variables were determined and discussed. The model obtained from the parametric analysis and optimization results according to the kind of loads was suggested.

Turbulence Models for Fluid Flow and Heat Transfer Between Cross-Corrugated Plates

Three-dimensional numerical predictions of fluid flow and heat transfer between cross-corrugated plates were obtained for the same geometry and grid using eight turbulence models, i.e., LBKE, SKE, RKE, RNGKE, RSM, KW, SST and LES, for the purpose of model performance evaluation. The average Colburn factor j, friction factor f, and local Nusselt number distribution were presented and compared with available experimental data. The velocity, temperature, and turbulent viscosity ratio distributions were recorded and discussed. It has been found that all models can predict practically satisfactory j and acceptable f within the current Reynolds number range. LBKE and SST provide the best overall agreement with experimental data and thus are highly recommended for application. Taking into account its robustness and economy, SKE with enhanced wall treatment is also recommended for CC channel flow and heat transfer simulation. In addition, near wall treatment approach seems to be significant for the current wall-bounded flow simulation. Since some models predict similar j and f values but very different velocity and temperature distributions, it seems not quite sufficient to only compare the overall heat transfer and pressure drop data between simulation and experiment for comprehensive model evaluations.

Influence of Corrugation Profile on the Thermalhydraulic Performance of Cross-Corrugated Plates

This article presents a numerical investigation on the thermalhydraulic performance of cross-corrugated plates, commonly employed in plate and compact heat exchangers. Three-dimensional numerical predictions were obtained using a finite volume method and a validated low Reynolds number k-ϵ turbulence model. The influences of Reynolds number, corrugation inclination angle, and especially corrugation profile on flow and heat transfer were studied and discussed. The velocity, temperature, local Nusselt number distribution, and the path line were presented for cross-corrugated plates with sinusoidal, isosceles triangular, trapezoidal, rectangular, and elliptic corrugations. The average Nusselt number Nu and the friction factor f were calculated and correlated with the Reynolds number. Thermalhydraulic performance was evaluated in terms of the heat transfer and pressure drop. Nu and f are about 1–4 times higher for the trapezoidal channel than for the elliptic channel, indicating significant influence of the corrugation profile. Optimal structures are among those with smooth corrugation shapes and small inclination angles.

Simulation and analysis of flow pattern in cross-corrugated plate heat exchangers *

Using numerical methodology, the flow fields between two corrugated plates with different values of the corrugation inclination angle β were simulated. The simulation results directly indicate that β affects the flow pattern between corrugated plates, and the results are in good agreement with the experimental results reported by interrelated literature. The results show that the flow pattern between the two plates changes from “double cross-flow” to “zigzag flow” with the increase in β. The reason for the effect on the flow pattern between the two corrugated plates was discussed from the view of the variation of momentum in the direction of corrugation with the variation in β.

Determination of a Mass-Transfer Coefficient Using the Limiting-Current Technique

In this work, mass-transfer coefficients of a cross-corrugated plate have been determined by the limiting-current technique. A simple Microsoft Excel spreadsheet has been created, which allows students to correlate data. Students will be able to calculate the mass-transfer coefficient of different processes, for example, cross-flow membrane filtration processes or membrane reactors. The possibility of using the spreadsheet with different correlations and to discriminate between them is also validated by comparing the model results with published experimental data available in the recent literature. It is possible as well to study the influence of different turbulence promoters on the flow.

Optimization of heat and mass transfers in counterflow corrugated-plate liquid-gas exchangers used in a greenhouse dehumidifier

Heat and mass transfers occuring in a counterflow direct contact liquid-gas exchanger determine the performance of a new greenhouse air dehumidifier designed at INRA. This prototype uses triethylene glycol (TEG) as the desiccant fluid which extracts water vapor from the air. The regeneration of the TEG desiccant fluid is then performed by direct contact with combustion gas from a high efficiency boiler equipped with a condensor. The heat and mass transfers between the thin film of diluted TEG and the hot gas were simulated by a model which uses correlation formula from the literature specifically relevant to the present cross-corrugated plates geometry. A simple set of analytical solutions is first derived, which explains why some possible processes can clearly be far from optimal. Then, more exact numerical calculations confirm that some undesirable water recondensations on the upper part of the exchanger were limiting the performance of this prototype. More suitable conditions were defined for the process, which lead to a new design of the apparatus. In this second prototype, a gas-gas exchanger provides dryer and cooler gas to the basis of the regenerators, while a warmer TEG is fed on the top. A whole range of operating conditions was experimented and measured parameters were compared with numerical simulations of this new configuration: recondensation did not occur any more. As a consequence, this second prototype was able to concentrate the desiccant fluid at the desired rate of 20 kg H2O/hour, under temperature and humidity conditions which correspond to the dehumidification of a 1000 m2 greenhouse heated at night during the winter season.