Pillow-plate Heat Exchangers Research Articles

A thorough investigation of geometric and thermohydraulic features in pillow-plate heat exchangers

Determining the thermohydraulic characteristics in pillow-plate channels (PPCs) is challenging due to their intricate structure. This work introduces novel geometric parameters specific to a flow cross-sectional area in PPCs and employs a two-stage optimized algorithm for artificial neural networks (ANNs) to enhance its thermohydraulic feature predictions significantly. These parameters enable practical consideration of various PPC structures and help develop a new mean hydraulic diameter (MHD) correlation. Besides the general parameters in PPCs, the novel parameters are incorporated into two two-stage optimized ANNs to predict thermohydraulic characteristics. The traditional method for approximating MHD neglects the actual channel structure and only considers the maximum channel height, leading to deviations of −16.93% to +52.00% from finite element simulated PPCs. Our new MHD correlation and the first ANN, which consider the channel structure, yield more accurate results with deviations of −6.97% to +13.07% and −7.85% to +13.21%, respectively. The second ANN predicts Nusselt numbers and Darcy friction factors with errors of less than 13.04% and 15.83%, respectively, across a wide range of geometric and thermohydraulic conditions. These promising results and presenting the maximum and minimum possible MHD in PPCs by the novel correlation pave the way for more accurate future studies and industrial development of PPCs.

Numerical investigation on pillow plate heat exchangers: Effects of nanofluid and geometry

The current research involves a comprehensive numerical simulation of nanofluid flow within a pillow-plate heat exchanger. Al2O3-water nanofluid and water are used as the working fluids, simulated using a two-phase mixture model. The study explores the influence of geometric properties on the heat exchanger’s hydrodynamic and thermal performance. It also delves into the utilization of nanofluids as the working medium and its impact on dimensionless pressure drop, Nusselt numbers, and dimensionless temperature. An innovative aspect of this research lies in the integration of artificial intelligence (AI) techniques for heat exchanger design optimization. Specifically, a Random Forest Regressor (RFR) AI model is employed to predict crucial parameters, including heat transfer coefficient (HTC) and pressure drop, based on input design variables. Key findings reveal that non-linear hole layouts in heat exchangers significantly improve Nusselt numbers by up to 25 percent. Conversely, larger holes result in higher pressure drops. The use of nanofluids enhances thermal efficiency by up to 10% while increasing pressure drop by around 7%.

Thermo-Hydraulic Performance of Pillow-Plate Heat Exchangers with Secondary Structuring: A Numerical Analysis

Pillow-plate heat exchangers (PPHEs) represent a suitable alternative to conventional shell-and-tube and plate heat exchangers. The inherent waviness of their channels promotes fluid mixing in the boundary layers and facilitates heat transfer. The overall thermo-hydraulic performance of PPHEs can further be enhanced by applying secondary surface structuring, thus increasing their competitiveness against conventional heat exchangers. In this work, various secondary structures applied on the PPHE surface were studied numerically to explore their potential to enhance near-wall mixing. Computational fluid dynamics (CFD) simulations of single-phase turbulent flow in the outer PPHE channel were performed and pressure drop, heat transfer coefficients, and overall thermo-hydraulic efficiency were determined. The simulation results clearly demonstrate a positive impact of secondary structuring on heat transfer in PPHEs.

Recent advances in design and performance optimization of pillow-plate heat exchangers: a critical review

Recent advances in design and performance optimization of pillow-plate heat exchangers: a critical review

Evaluating two-phase fluid flow and heat transfer in pillow-plate heat exchangers with nanofluids for organic Rankine cycle in municipal solid waste power plant: A numerical simulation study

One of the key considerations in the design and operation of process industries nowadays is reducing energy waste. The purpose of this research is to assess fluid flow and heat transfer in pillow-plate heat exchangers (PPHEs) using nanofluids for the Organic Rankine Cycle (ORC) in Municipal Solid Waste (MSW) power plants. The thermal performance and hydraulic features of the PPHE were investigated using a two-phase numerical modeling approach. three nanoparticles of Cu, TiO2, and Al2O3 were examined. To precisely determine the temperature distribution within the heat exchanger, various boundary conditions were used. The results demonstrate a strong correlation between the velocity field and temperature, underlining the importance of boundary conditions in determining the temperature profile. Furthermore, the two-phase model illustrates that nanofluids are extremely reliant on inlet velocity and volume fraction. such that at a 2 m/s inlet velocity, increasing the volume percentage to 12.8% contributes to heat transfer coefficient improvements of 7.57%, 12.15%, and 2.71% for water_TiO2, water_Al2O3, and water_Cu, respectively. These findings give significant insight into the fluid flow and heat transfer properties of PPHEs, as well as prospective pathways for increasing thermal performance and decreasing pump power in ORC systems using nanofluids in MSW-generating plants.

Thermal and hydraulic optimization of supercritical CO2 pillow plate heat exchanger with ellipse weld spots in CSP system

Pillow plate heat exchangers (PPHE) with compactness and high thermal performance are applying widely. In present article, PPHE with ellipse weld spots is first proposed, and turbulent flow and heat transfer of supercritical carbon dioxide (S-CO2) in PPHE channel is analyzed and optimized. The channel is made of many periodically overlapped metal plates, and the plate is a flat plate with many staggered convex-concave spots. Compared with channel section with concave spot, channel section with convex spot has higher flow velocity, lower flow fraction and higher heat transfer coefficient, so it dominates heat transfer process. Along flow direction, heat transfer coefficient in channel section with convex spot gradually increases to maximum in flat region, and then it drops to minimum in downstream region of convex spot, while friction factor has opposite tendency. A meaningful phenomenon is found that higher heat transfer coefficient (h) and lower friction factor (f) appear simultaneously in the same region. The flow and heat transfer behavior are significantly affected by weld spot geometries, and elliptic weld spot with larger ratio of spot length and width Ψ results in weaker vortices and fluid impingement, which remarkably reduces friction factor. The elliptic weld spot with Ψ = 1.4 is optimum geometry for maximum index of Nu/f1/3. In addition, correlations of f and Nusselt number (Nu) for Ψ = 0.6–1.4 and Re = 4132–6650 are developed.

Numerical analysis of burst pressure and maximum inflation height of aluminium made pillow plates

Pillow plates represent an efficient type of heat transfer equipment with a high degree of flexibility in terms of manufacturing and applications. Their thermo-hydraulic behaviour has been the focus of numerous scientific investigations over the last decade. However, along with the realisation of the thermal task, it is also important to ensure an adequate level of operational safety when designing equipment based on pillow plates. At present, for the approval of a pillow plate based apparatus, an experimental proof of the permitted operating pressure must be provided in accordance with the regulatory standards. In this process, this pressure is calculated from the burst pressure, which must be determined in time-consuming and cost-intensive experiments. For this reason, we propose a new approach in which the burst pressure of pillow plates is determined numerically based on the finite element methods, eliminating the need for experiments. Furthermore, the simulation results were used to derive equations for calculating the burst pressure and the maximum achievable inflation height of pillow plates made of the aluminium alloy EN AW- 5083. This part of the work has been motivated by the findings of a preliminary study showing a more than 25% thermal resistance reduction of counterflow operated pillow plate heat exchangers when the pillow plates are made of aluminium instead of the standard material stainless steel.

Parametric study of low-temperature thermal energy storage using carbon dioxide as the phase change material in pillow plate heat exchangers

Industrial low-temperature freezing applications are often batch processes, requiring a lot of energy, exerting stress on the electrical grid. To relieve this stress, thermal energy storage can be used. However, there is a lack of suitable storage material for low temperature applications (around −50 °C). Under high pressures, carbon dioxide can be used as the phase change material for storage temperatures around −55 °C. In this study, a parametric study was conducted on the design and operational parameters of an industrial-scale pillow plate heat exchanger with carbon dioxide. Two responses were selected for the analysis where R1 considered the storage size over the phase change time (kWh/h), while R2 indicated the cost over the storage size (USD/kWh). Using design of experiments, a total of 52 simulations were carried out to investigate the parameters under constant heat transfer surface area. Analysis of variance was then carried out followed by correlation development and optimization. It was found that regardless of the process (charging or discharging), for R1 and R2, the difference between refrigerant and carbon dioxide phase change temperatures followed by plate material had the highest significance. In contrast, the refrigerant flow rate had the lowest significance in almost all cases. Moreover, considering an equal weight for the responses, overall optimal conditions were determined for the processes. The recommended values for plate pitch, plate material, difference between refrigerant and carbon dioxide phase change temperatures and refrigerant flow rate were 25 mm, aluminum, 15 °C and 4 kg/s, respectively.

Potentials and challenges for pillow-plate heat exchangers: State-of-the-art review

For a long time, shell-and-tube heat exchangers have been the most common choice in the industry. Despite some limitations, their main advantage is that they have been extensively investigated and reliable design tools are readily available. In other words, any alternative design should not only outperform shell-and-tube heat exchangers, but also be equipped with a comparably reliable and robust design platform for engineers. In recent years, a growing market share can be observed for plate heat exchangers, particularly for a special class known as pillow-plate heat exchangers. Recently, the research on pillow-plate heat exchangers has gained momentum primarily due to their relative low cost, compact design and structural integrity. However, a comprehensive literature review on the advancements so far and challenges ahead of their widespread application is missing. This study aims to fill this gap in the literature by systematically, critically and comprehensively surveying earlier studies on pillow-plate heat exchangers and providing an in-depth discussion regarding the achievements so far. The findings of this study are expected to help direct the forthcoming research on pillow-plate heat exchangers, especially towards more robust design tools. Overall, further investigation is needed on cost, plate material, flow configuration, heat transfer enhancement, correlation development, two-phase flow, etc.

Flow in Pillow-Plate Channels for High-Speed Turbomachinery Heat Exchangers

In numerous turbomachinery applications, e.g., in aero-engines with regenerators for improving specific fuel consumption (SFC), heat exchangers with low-pressure loss are required. Pil low-plate heat exchangers (PPHE) are a novel exchanger type and promising candidates for high-speed flow applications due to their smooth profiles avoiding blunt obstacles in the flow path. This work deals with the overall system behavior and gas dynamics of pillow-plate channels. A pillow-plate channel was placed in the test section of a blow-down wind tunnel working with dry air, and compressible flow phenomena were investigated utilizing conventional and focusing schlieren optics; furthermore, static and total pressure measurements were performed. The experiments supported the assumption that the system behavior can be described through a Fanno–Rayleigh flow model. Since only wavy walls with smooth profiles were involved, linearized gas dynamics was able to cover important flow features within the channel. The effects of the wavy wall structures on pressure drop and Mach number distribution within the flow path were investigated, and a good qualitative agreement with theoretical and numerical predictions was found. The present analysis demonstrates that pressure losses in pillow-plate heat exchangers are rather low, although their strong turbulent mixing enables high convective heat transfer coefficients.

Investigating thermo-hydraulic behavior of pillow plate heat exchangers using entropy generation approach

Pillow plate heat exchanger (PPHE) is a modern type of plate heat exchanger composed of wavy shape parallel plates. Adjustment of the geometrical parameters has been broadly made to enhance the heat transfer performance of PPHEs. However, there has been limited attention to the thermo-hydraulic features and entropy generation of fluid flow through such heat exchangers. Addressing this gap could help further understanding of such heat exchangers. In the present study, Ansys CFX is used to simulate turbulent flow and heat transfer in inner pillow plate channels. The local entropy generation due to thermal effects and friction is calculated as a post processed task. The influence of the channel height, Prandtl number, diameter and arrangement of spot welds on the overall entropy generation of pillow plates are analyzed. The results indicate that by increasing the channel height, thermal entropy generation increases. Besides, increasing the spot weld diameter leads to a higher frictional loss in pillow plate channels, while the effect of spot weld size on thermal entropy generation is negligible. Also, the spot weld arrangement significantly affects the thermal and hydraulic characteristics of PPHEs. The results show that exergy analysis can be considered as a potential tool for investigating thermo-hydraulic behavior of PPHEs.

Pillow-Plate Heat Exchangers: an Overview on Advances, Limitations and Prospects

Pillow-plate heat exchangers (PPHEs) represent an innovative and promising alternative to conventional equipment. The waviness of the pillow-plates promotes lateral mixing and turbulence, which results in a good thermo-hydraulic performance, offering a significant energy-saving potential. Since PPHE also offer several important structural and cost related advantages over conventional heat exchangers, e.g. compact, light and pressure-resistant construction, low pressure drop on the product media side, as well as low capital and operating costs, their use in process industries is growing. However, the implementation of PPHE is still limited due to the lack of comprehensive data and publicly available proven design methods, while their range of applicability has not yet been fully determined.The purpose of this contribution is to present the current state of the art of PPHE, with particular attention to recent advances in terms of modelling and prediction of the performance of such equipment, while highlighting the advantages in terms of sustainability and efficiency of the various applications compared to conventional solutions. In addition, the future prospects in modelling and application of these devices will also be delineated.

Numerical investigation of conjugate heat transfer in a pillow-plate heat exchanger

Pillow Plate Heat Exchangers (PPHX) are composed of several pillow plates arranged parallel to each other, with one flow path inside the plates (inner channel flow) and another in the spaces between adjacent plates (outer channel flow). In research studies published by now, the transport phenomena in these two flow paths have mostly been treated in a separate manner. Such a treatment does not permit to identify important effects, e.g., unfavourable thermal interaction between the inner and outer channel flow caused by predominant recirculation zones, or the influence of the material used for the pillow plate manufacturing. In this work, for the first time, conjugate heat transfer modelling and CFD-based simulations were carried out for a PPHX operated in countercurrent mode. This allowed a detailed analysis of the individual thermal resistances in a PPHX. Based on the results of this analysis, approaches for the correct calculation of these thermal resistances were created.

Study on thermo–hydraulics in a Pillow Plate Channel

In this work, the details of a numerical investigation carried out on the flow and heat transfer characteristics in the wavy pillow plate channels used for pillow plate heat exchangers have been presented. Water is used as the cooling medium. It is observed that in the thermally developing region, the recirculation zone contributes a higher proportion in the total heat transfer as compared to the thermally developed part. High heat transfer is observed in the developing region is due to the lower average temperature of the hot recirculating zones. Further, a parametric study is conducted by varying the geometric parameters of the channel. The study is based on the transversal and equal pitch pillow plate configurations. The numerical results are validated against the experimental results available in the literature. Based on the numerical results, a heat transfer correlation is developed. Also, a sensitivity analysis is carried out to quantify the effect of various geometric parameters and Reynolds number on the thermo – hydraulic performance of the pillow plate channel.

Investigation of heat transfer and hydraulic resistance in small-scale pillow-plate heat exchangers

Pillow-Plate Heat Exchangers (PPHEs) represent an innovative equipment type, with space-effective, light and pressure-resistant construction. In this work, an experimental study of air cooling by water in small-scale PPHEs was carried out and an analysis of the hydraulic resistance and heat transfer was performed based on the experimental data. A semi-empirical correlation for friction factor inside pillow-plate panels which is based on main geometric parameters is proposed. This correlation is reliable in a wide range of Reynolds numbers, both for laminar and turbulent flow regime. For the external channel between pillow-plate panels, the correlations for pressure drop and heat transfer were obtained based on experimental data. The CFD simulations were carried out to investigate heat transfer in the external channel of the PPHE. The deviation between the experimental and simulated values of heat transfer coefficient is maximum 17%. The received correlations enable to calculate the overall heat transfer and pressure drop in small-scale PPHEs and can be applied for preliminary design of PPHEs. The case study of the PPHE application for water heating is considered. The designed heat exchanger with minimal heat transfer area has 30% less surface area then chevron-type plate heat exchangers traditionally used for such application.

Heat transfer enhancement in pillow-plate heat exchangers with dimpled surfaces: A numerical study

Pillow-plate heat exchangers (PPHE) represent an innovative, fully welded plate-type heat exchanger. They consist of a stack of panels, which are characterized by “pillow-like” surface. The waviness of the channels enhances mixing in the fluid boundary layers, which consequently augments heat transfer. However, PPHE need further optimization in order to compete with corrugated plate heat exchangers with respect to compactness. In this study, a method to enhance heat transfer in PPHE is proposed, based on a surface modification of pillow plates by secondary dimple structures on their primary wavy surface. The new structured surface of the pillow plates promotes stronger near-wall mixing.

An approach for pillow plate heat exchangers design for single-phase applications

Pillow-plate heat exchangers (PPHEs) represent a novel equipment type. For their application in industry, reliable preliminary design techniques are required. In this article, the existing methods for heat exchangers design are analysed and the approach for selecting the PPHE design with minimal heat transfer area is proposed. It is based on the mathematical model of thermal and hydraulic PPHE behaviour, in which the overall heat transfer coefficient and pressure drop in PPHEs are expressed through the fluid velocity. The estimation of fluid velocities in PPHE channels is based on the condition that the predefined allowable pressure drop is fully exploited. Two case studies for water heating and crude oil preheat train operating conditions are discussed, in which the flowrates of the fluids on the hot and cold sides differ significantly. The PPHE design with minimal heat transfer area for the considered case studies is presented, with specified pillow-plate geometry parameters and distance between pillow-plate panels. The resulting pressure drops and velocities in PPHEs channels as well as the obtained heat transfer surface areas are compared with existing data for chevron-type plate heat exchangers (PHEs) designed for the same operating conditions. This comparison shows that PPHEs have higher velocities in channels, longer plates and lower heat transfer area. It can be concluded that PPHEs can be successfully used for operating conditions, under which the flow rates for hot and cold fluid are significantly different and the application of chevron-type PHEs with single-pass arrangement is complicated.

Heat transfer and pressure loss in small-scale pillow-plate heat exchangers

In this work, an experimental study of heat transfer between air and water in a small-scale pillow-plate heat exchanger (PPHE) consisting of two pillow plates assembled together in one unit was carried out. In the experiments, cooling water flows in two inner channels (i.e., channels inside welded pillow plates), whereas air is directed to the outer channel between the plates. Heat transfer and hydraulic resistance in inner and outer PPHE channels are analysed based on the experimental data. The measurements were used to develop correlations for the pressure loss and heat transfer coefficients in both inner and outer channels. For the detailed investigation of pressure loss and wall shear stress in the outer channel between pillow plates, CFD simulations were carried out for the considered geometry. The Reynolds number was equal to 5,173, which ensured fully developed turbulent flow. The proposed correlations derived from experimental data were compared with the CFD simulation results. They can be used to predict thermal and hydraulic performance of small-scale PPHEs.

New design equations for turbulent forced convection heat transfer and pressure loss in pillow-plate channels

Pillow-plate heat exchangers (PPHE) represent a stack of pillow plates characterized by a wavy surface and fully welded construction. The benefits of PPHE over conventional heat exchangers have made them increasingly attractive for numerous applications in the process industry. However, the lack of verified design methods and reference applications for PPHE hinders their widespread application. This work aims at overcoming this “bottleneck” by providing new equations for the thermo-hydraulic design of pillow plates.In particular, design methods for pressure loss and heat transfer are proposed for turbulent forced convection in pillow-plate channels over a wide range of Reynolds numbers (1000≤Re≤8000), Prandtl numbers (1≤Pr≤150) and characteristic geometry parameters (e.g., welding spot arrangement, inflation height). For the determination of heat transfer coefficients, two different approaches are presented. The first approach is based on the method typically suggested in literature, whereby the well-known Dittus-Boelter type power law function (cf. [1]) for the Nusselt number is applied and fitted to numerical data largely obtained in Ref. [2]. The second approach is based on the characteristic flow pattern in pillow plates suggested in Ref. [2]. In this pattern, the initial complex flow is broken down into two simpler flows, which can then be modeled separately. For both methods, the relative deviations between the numerical data obtained in Ref. [2] and in this study are less than 15%.

On the coupled condensation-evaporation in pillow-plate condensers: Investigation of cooling medium evaporation

Pillow-plate heat exchangers (PPHE) represent a promising alternative to conventional equipment, e.g., in the process industries; however, the lack of published design methods still hinders their widespread application. The present work represents a first step towards investigation of a particular PPHE operation mode, which comprises process medium condensation between adjacent pillow plates and simultaneous cooling medium evaporation in the plates. An experimental set-up was built and used for heattransfer experiments, in which 1,1,1,2-tetrafluoroethane evaporated in both thermosyphon and forced-convection operation mode. The focus was on the investigation of heat transfer during the evaporation process in the wavy pillow-plate channel, and the (virtual) enthalpy of condensation was imitated using dissipation of electrical current in the walls of a single pillow plate. Along these lines, two-phase heat transfer coefficients for the evaporating fluid flow in the inner channels of the plates were determined. The results reveal a promising heat transfer performance, which can be utilised to increase energy efficiency in the process industries. A correlation proposed by Kandlikar for saturated two-phase flow boiling heat transfer inside tubes was found suitable for the prediction of heat transfer in pillow plates, with slight underestimation. The results of this study can further be applied for the description of a number of heating and cooling processes.