Dimpled Plate Research Articles

Flow boiling in dimpled plate heat exchangers with different geometric parameters: Analysis of asymmetric channels

The evaporators of heat pumps extract heat from the environment. To improve the heat pump performance in cold environments, evaporators must operate with small temperature drops of the heat source, which requires large flow rates of the secondary fluid. This paper discusses dimpled plate heat exchangers (DPHEs) with flexible flow section areas. The flow boiling of R410A is measured in six channels. The flow section area ratios of neighboring channels are 0.86–2.83. To analyze outlet superheat, the two-phase and dryout zones are distinguished using infrared measurement. The dryout zone is a function of the superheat and mass flux, which is quantified. The heat transfer coefficients (HTCs) increase with increasing mass fluxes and heat fluxes. Compared with experimental results from a large scope, the present data fall into the combined regimes of convective boiling and nucleate boiling. Smaller hydraulic diameters slightly enhance the heat transfer. The experimental HTCs are accurately predicted by a correlation of chevron plate heat exchangers (CPHEs). The performances of the DPHEs and CPHE are compared for small temperature drops in cold environments. The DPHEs have superior performance by mitigating the unbalance of mass fluxes. The typical overall heat transfer coefficient is improved by 62%. The improvement depends on the flow section area ratios.

Numerical and experimental studies of a novel compact sandwich-type plate reactor for thermochemical energy storage

In this work, a novel compact sandwich-type plate reactor (CSPR) for thermochemical energy storage (TCES) with Ca(OH)2/CaO is proposed, where the essential unit is symmetrically comprised of steam channel in the center, orderly sandwiched by metal gauzes, reaction cavities, plates and heat transfer channels at both sides. Firstly, the flow-heat-reaction multi-field coupled modelling is conducted to comparatively investigate the flat, baffled and dimpled plates, where the dimpled plate (DP) stands out. Then, the entire CSPR comprised of three essential units with DPs is modelled to numerically predict its comprehensive performance and characteristics. Afterwards, the prototype of CSPR is manufactured based on the above numerical studies and experimentally evaluated on our exothermic and endothermic cycling performance test bench with loading of 1.667 kg of Ca(OH)2 pellets. The experimental data confirm that the charging stage takes 330 min with the final conversion up to 97.74 %, while the discharging stage takes 200 min with the maximal heat transfer fluid (HTF) output temperature reaching 385 ℃ and the duration for the HTF output temperature above 350 ℃ lasting for 130 min. Based on energy balance analysis, the energy storage efficiency for charging stage is 74.92 % and the round-trip energy efficiency for cycle is 60.24 % (including 2 h of buffering period) without heat recovery of product steam. Technically, these efficiencies can be respectively promoted to be 76.35 % and 71.59 % with heat recovery. The numerical simulation and experimental data are found to be mutually verified. We hope this work can provide a novel insight of reactor design for development of TCES technology.

An experimental investigation into the drag reduction performance of dimpled plates in a fully turbulent channel flow

Dimpled surfaces have gained increasing attention in recent years for their potential to reduce turbulent skin friction, a capability previously acknowledged for its beneficial implications on heat transfer. As a passive drag reduction method, dimpled surfaces offer significant advantages for marine applications due to their effectiveness and practical applicability. However, despite numerous studies, conflicting opinions and inconsistent drag reduction rates persist in the literature. This paper addresses these ambiguities and offers valuable insights into the effectiveness of dimpled surfaces for drag reduction in fully turbulent flows. We conducted an extensive experimental investigation involving various dimple configurations, including different depth-to-diameter ratios, diameters and orientations, utilising a specialised Fully Turbulent Flow Channel facility and a Particle Image Velocimetry system. Our findings demonstrated that circular dimple geometries, particularly those with low depth ratios, can achieve significant drag reduction of up to 27% as the Reynolds number increases. These results highlight the substantial potential of dimpled surfaces for improving energy efficiency in marine applications, where skin friction accounts for a significant portion of the total drag experienced by large vessels.

Effect of the plates geometry on the performance of a cross-flow recuperator for indirect evaporative cooling systems

In recent years, Indirect Evaporative Cooling (IEC) is becoming a very interesting technology, as it can guarantee a good cooling effectiveness with low energy demand, thus helping to face the issues of climate change. In this work, a Computational Fluid Dynamics (CFD) model has been used to evaluate the effects of the plates geometry on the performance of a recuperator for IEC systems with dry primary and secondary channels. The model was validated against experimental data for a cross-flow IEC system with dimpled plates, and the validation results were quite satisfactory. Therefore, five types of dimpled plates differing from the original one in shape and size of the dimples were investigated. The results showed that a good trade-off between the improvement of dry-bulb effectiveness and restrained pressure losses along the channels is obtained with dimples in the shape of right prisms with either triangular, or pentagonal, or circular base section, depending on the application.

Differential exergy investigation and environ-economic assessment of a dimpled plate and flat plate solar air heater under turbulent conditions

The current investigation explores the performance of a spherical dimple solar air heater (D-SAH) within the framework of the Second Law of Thermodynamics under turbulent conditions. This analysis considers component-wise exergy potential losses, their differentials, and the overall exergy efficiency (ηEx). Given the inherently entropic nature of turbulent flow, an evaluation is conducted to determine the limiting mass flow rate (MFR). To ensure long-term adaptability and a comprehensive understanding of the designed solar air heater (SAH), various matrices, including economic, environmental, environ-economic, exergo-economic, and energy, are assessed across four service life scenarios. The obtained results are benchmarked against those of a flat plate solar air heater (F-SAH). Exergetic analysis is conducted for six different MFRs on different days, revealing absorption losses as the most influential exergy losses. D-SAH incurs 3.99% higher absorption losses, leading to a lower ηEx. The design is deemed suitable for MFR 0.028 kg/s. The impact of higher Reynolds number (Re) and the temperature rise parameter (TRP) results in a decrease in ηEx for both SAHs. Specifically, D-SAH shows a 71% reduction in ηEx as Re increases from 5684 to 10352. However, D-SAH exhibits promising performance in terms of CO2 mitigation and carbon credits earned, surpassing F-SAH by 27.89% to 23.38%. Furthermore, these performance metrics increase by 50% when extending the service life from 20 years to 30 years. Statistical correlation and the coefficient of determination authenticate these findings.

Analisa Kekakuan Pelat terhadap Pembentukan Dimple Dies dengan Variasi Diameter Lubang dan Jumlah Lubang Dimple

The construction of the body of minibus passenger vehicles usually uses walls, roofs and floors called vehicle panels. The vehicle panel itself is the most important part that supports safety and comfort for the occupants of the vehicle. Generally, the vehicle panel will cause a sound that makes passengers uncomfortable because of the noise that occurs due to the vibration of the vehicle engine and damaged road conditions. Excessive vibration can be reduced by increasing the rigidity of the panel by changing the shape such as beads, embossing, stiffeners, spot welded stiffenes, and grooves. The purpose of this study was to determine the effect of borehole variation and the number of dimple holes on plate stiffness for its natural frequency response. This research method is shown as follows: making experimental designs, dimple manufacturing processes, measuring and analyzing the results of dimple-shaped plates with variations in boreholes and the number of dimple holes to stiffness for their natural frequency response response. Based on the results, the number of holes on the dimple plate affects the stiffness of the plate to its natural frequency response.

Experimental Investigation on Heat Transfer and Pressure Drop Characteristics of Food Additive in Dimple Plate Heat Exchanger

The present study attempts to examine the heat transfer and pressure drop aspects of a 11-channel dimple plate heat exchanger with hot water as the hot fluid and sodium benzoate (food preservative) as the cold fluid. The outcome of the mass flow rate of hot and cold fluids on the convective heat transfer coefficient and overall heat transfer coefficient were investigated. Furthermore, the effect of Reynolds number on the pressure drop and the Nusselt number were observed. The experimental results demonstrated that when the mass flow rate of the cold fluid increases, so does the overall heat transfer coefficient and the convective heat transfer coefficient. Convective heat transfer coefficient, overall heat transfer coefficient, pressure drop and Nusselt number were increased when sodium benzoate concentration is varied (0.2, 0.4, 0.6% w/w). A correlation is obtained on the basis of experimental results to estimate the Nusselt number as a function of Reynolds and Prandtl number.

Experimental and numerical study of heat transfer and friction factor characteristics of an inclined elliptical dimple channel having inline and staggered pattern

Experimental and numerical studies were carried out to examine the effect of staggered and inline inclined elliptical dimpled plate on Nusselt number (Nu) and friction factor (f) for higher Reynolds number (Re) values. Dimple dimensions of different elliptical dimple pattern were kept constant to compare their thermal performance effectively with the dimple depth (de ) and dimple diameter (dp ) kept as 3 mm and 10 mm respectively for the present study. The features, namely Nu, f and flow structure of the inclined elliptical dimpled plate were calculated for ‘Re’ values ranging from 11,300 to 62,000. The experiment showed that inclined elliptical dimple with staggered and inline arrangement has different effect on flow pattern and heat transfer characteristics. The staggered pattern has 24.8% greater heat transfer and 10.71% lower pressure drop corresponding to inline pattern. The three-dimensional numerical computations clearly show that different test plates have different vortex flow structures and these vortex flow patterns of dimpled plate result in improved heat transfer in comparison to flat plate.

Experimental investigations of thermal performance for flat and dimpled plate solar air heater under turbulent flow conditions

Conversion of solar energy into useful thermal energy through solar air heaters (SAH) enhances the practical application of the available solar energy. A comparative thermal analysis of two SAH’s having different absorber plates is elucidated here. Experiments were conducted on a flat plate solar air heater (FPSAH) as well as on dimpled plate solar air heater (DPSAH) during bright and sunny days from 0930 am to 1430 pm at IIT (ISM) Dhanbad on six different days for six different flow rates between 0.028 kg /sec to 0.051 kg /sec (i.e. Re value = 5500 to 10300). For these two SAH’s, different parameters and thermal properties were evaluated and compared. Quantitively, it is shown that the temperature difference, average extracted power, heat transfer coefficient, instantaneous efficiency and the effective efficiency of the DPSAH is higher than the FPSAH. Subsequently, it has been also observed that, the rise in effective efficiency of DPSAH at higher mass flow rates (MFR) is not significant; hence it is less suitable for high flow rate operations.

Computational Fluid Dynamics Modelling and Analysis of Heat Transfer in Multichannel Dimple Plate Heat Exchanger

In the present study, Computational Fluid Dynamics is used for the heat transfer studies in the dimple, and flat plate heat exchangers. By employing water as a working medium (fluid), the same and different flow analyses were numerically studied. SOLID WORKS 2018 software was used for the study. The study primarily investigated the effect of the flow rate of hot fluid on the overall heat transfer coefficient. The study also analyzed the influence of hot fluid’s Reynolds number on cold fluid’s Nusselt number. It was observed that an increase in the mass flow rate of the hot fluid from 0.016 to 0.067 kgs-1 resulted in an increase in the heat transfer coefficient from 65 to 298 Wm-2K-1 for dimple plate heat exchanger (DPHE). Meanwhile, an increase in the Reynolds number of the hot fluid (from 200 to 1000), induced an increase in the Nusselt number of the cold fluid from 1.9 to 8.7 for DPHE. A correlation was developed to calculate the Nusselt number for the same flow analysis of the flat plate heat exchanger (FPHE). The study also compared the performance of the DPHE with that of the FPHE. The results of the same flow analysis indicated that the DPHE exhibited a Nusselt number value 39% greater than the FPHE at the highest mass flow rate of 0.067 kgs-1, while in different flow analysis, the DPHE demonstrated a Nusselt number value 41% greater than the FPHE at the highest mass flow rate of 0.067 kgs-1.

Bioengineering of a scaffold-less three-dimensional tissue using net mould

Tissue engineering has attracted attention worldwide because of its application in regenerative medicine, drug screening, and cultured meat. Numerous biofabrication techniques for producing tissues have been developed, including various scaffold and printing methods. Here, we have proposed a novel tissue engineering method using a net metal mould without the use of a scaffold. Briefly, normal human dermal fibroblasts seeded on a dimple plate were subjected to static culture technique for several days to form spheroids. Spheroids of diameter ⩾200 μm were poured into a net-shaped mould of gap ⩽100 μm and subjected to shake-cultivation for several weeks, facilitating their fusion to form a three-dimensional (3D) tissue. Through this study, we successfully constructed a scaffold-free 3D tissue having strength that can be easily manipulated, which was difficult to construct using conventional tissue engineering methods. We also investigated the viability of the 3D tissue and found that the condition of the tissues was completely different depending on the culture media used. Collectively, this method allows scaffold-free culture of 3D tissues of unprecedented thickness, and may contribute largely to next-generation tissue engineering products.

Computational studies of pressure distribution of flow through inline dimpled plate

Dimple plates are widely used for construction and vehicles, especially in car bodies, trains, and aircraft wings. The dimples surface helps to overcome turbulent airflow around vehicles, thereby delaying the separation point and producing fewer vertices and drag. This study aims to predict the pressure distribution occurring over the plate surface with the formation of inline dimple rows on the upper back end. The test is carried out with Computational Fluid Dynamic (CFD) FLUENT program. The test model has a dimension of 300 mm in length, 100 mm in width, and dimples ratio (DR) of 0.5. Dimples are arranged inline as much as 1 to 6 rows. Upstream velocities through dimple plates range from 10 m/s to 20 m/s. The results of the study show that the minimum pressure coefficient occurs at the top front of the plate due to the flow separation that occurs at the front end of the plate. At x/L=0.25 x/L=0.5 and x/L=0.75 (before the dimples formation), a flow pattern returns to normal, this can be seen from the distribution of the relative pressure coefficient that does not change. At the measurement point x/L=0.95 (after dimples formation), there is a decrease in the pressure coefficient. This decrease occurs due to changes in flow characteristics. The pressure coefficient does not change significantly in dimple variations of 2 to 4 rows. Meanwhile, the pressure coefficient decreases with the variation of the 5 and 6-row dimples.

Experimental investigation of flow and heat transfer in a channel with dimpled plate

This study presents the experimental investigation on the effect of dimpled arrangements on flow and heat transfer characteristics. Three plate surfaces were prepared (smooth, evenly distributed spherical dimples and unevenly distributed spherical dimples) and were placed successively in a channel. The unevenly distributed dimpled plate had the same dimple density with the evenly distributed dimpled plate but had varying transverse pitches to concentrate the dimples at mid-plate in flow direction. Data obtained from the experiment were analysed to determine the performance of each dimpled plate channel. It was observed that the average Nusselt number due to the heat interaction with the air-flow increases with the Reynolds number. The evenly and unevenly dimple plate channels had respectively, 75.7% and 91.8% increase in Nusselt number over the smooth channel. The flow friction factors of the evenly and unevenly dimple plate channels were merely more than that of smooth plate channel by 0.59% and 0.67%, respectively. Thus, the unevenly dimple plate channel had the highest overall thermal-hydraulic performance, followed by the evenly dimple plate channel.

Effect of Dimpled Surface with Straight Spoiler Turbulators on Heat Transfer and Fluid Flow Characteristics for Channel

An experimental investigation has been carried out for heat transfer enhancement over dimpled surface using spoiler turbulators. The experimentation is carried out over the aluminum plate of 1000 mm x 10 mm x 5 mm and Reynolds number ranging from 10,000 to 33,000. The δ/d ratio for dimple is 0.3, which is kept constant. The pitch for dimples are varied as 16 mm, 18 mm and 20 mm. Turbulators were used over the dimples surface in inline and staggered arrangement which provides different flow structure and produces turbulence. Turbulators are mounted over dimples at an angle of 12o with respect to flat plate. Experimental results were validated using Dittus-Boelter and Blasius equations. Analysis is made using Nusselt number, friction factor and performance index. It has been found that compared to dimpled plate performance of dimpled surface with spoiler tabulator plate is higher. If we compare inline and staggered arrangement, performance of inline arrangement dimple plate with turbulator is higher compared to staggered arrangement. This is due to in staggered arrangement at some locations chocking of flow may takes place which reduces heat transfer rate.

Thermal performance investigation of the flat and spherical dimple absorber plate solar air heaters

An experimental investigation has been conducted to determine the thermal performance of a spherical dimple plate solar air heater (SDPSAH) and a flat plate solar air heater (FPSAH) at distinctive environmental conditions at IIT (ISM) Dhanbad (23.79°N), India. The study has been conducted for a mass flow rate of air varying from 0.009 kg/s to 0.028 kg/s. The results indicate that the SDPSAH shows the highest heat transfer rate, which is about 1.51 to 1.64 times higher than the corresponding FPSAH. The maximum rise of the outlet temperature of the SDPSAH is about 4.6 °C greater than the corresponding FPSAH for 0.009 kg/s mass flow rate of air. The instantaneous thermal efficiency of the SDPSAH is about 23.45% to 35.50% greater than the corresponding FPSAH.

Experimental study of turbulent forced convection heat transfer and friction factor in dimpled plate heat exchanger

In this work, heat transfer behaviour of γ-Al2O3/water nanofluid in turbulent flow condition in a dimple plate heat exchanger is investigated. The effects of flow rates of hot and cold fluids for different concentrations (0.1, 0.2 and 0.3%w/w) of suspended nanoparticles on the heat characteristics and effect of enhancement by the addition of nanoparticles to base fluid are also examined. The comparison of the heat transfer behavior of nanofluid with that of the base fluid (water) resulted in heat transfer augmentation with an increase in the concentration of the nanoparticle. The γ-Al2O3/water nanofluid possesses better heat transfer performance than the base fluid at higher nanoparticle concentrations. The studies on pressure drop are also investigated to determine the friction factor of the fluid in the Reynolds number range. Nusselt number correlations are developed for the working fluids for evaluation of heat transfer coefficient.

Testing strategies and failure modes of dimpled laminate plates

Ground reinforcing plates are designed to facilitate the access of rescue vehicles and equipment in soft and muddy ground, e.g. for fire engines and cranes. Such plates have to be light and easy to handle, hence the use of composite materials is favourable. The investigated ‘dimpled plates’ are designed with glass fibre reinforced polymer (GFRP) and built to withstand high loads and to allow maximum deformation.Design parameters for the dimensioning of the plates are derived from standard ASTM laminate testing, and the values are used for the optimization of the plates by means of FEM (shape; composites layup). The verification of the component resistance and strength, however, requires adapted test configurations and procedures. Global loading of the structure has to replicate the situation in the field, and the resulting failure modes have to be identified for further optimization of the system.The scale of the plate bending tests had to be minimized due to large deflections. Mainly shear failure (delamination) and compressive failure (fibre buckling or crushing) were observed. Negative boundary effects had to be minimize in the tensile test, too. Fibre tensile failure followed after delaminations in the fillet of the knop base. Transverse compression: Testing against hard parallel plates provided high strength values, but the setup did not reproduce the situation of a soft bedding in the field, with mud. Different scenarios of elastic bedding over rubber plates were compared.The results provided the basis to optimize the material choice for the laminate (resin type, fibre reinforcement). The durability of the final composite laminates was verified with extensive aging tests in a later study.

周期性正弦凸起凹凸板等效刚度的研究

The equivalent stiffness of sinusoidal periodic dimpled plates was derived according to the classical elastic thin plate theory, in view of the analysis of the mechanical properties of the unit cell structure and the homogeneous distribution of unit cells over the plate. The sinusoidal periodic dimpled plate with 4 sides simply supported under a concentrated load was taken as an example, the analytical results were compared with those of the finite element method (FEM), and the rationality and accuracy of the analytical equivalent stiffness were verified. Finally, the effects of some structural parameters on the equivalent stiffness of the dimpled plate were analyzed. The results show that, the presented method can effectively calculate the equivalent stiffness of the sinusoidal periodic dimpled plate. The bending stiffness and torsional stiffness of the dimpled plate are obviously higher than those of the basic plate, for the geometric change of the dimpled plate. The work has important meanings for the research on statics and dynamics of dimpled plates and the engineering application.

Fluid Flow Resistance Through Hemispherical Dimpled Plates in Parallel and Zigzag Configurations

Fluid Flow Resistance Through Hemispherical Dimpled Plates in Parallel and Zigzag Configurations

Experimental and Numerical Study Effect of Using Nanofluids in Perforated Plate Fin Heat Sink for Electronics Cooling

An experimental and numerical investigation of the effect of using two types of nanofluids with suspending of (Al2O3 and CuO) nanoparticles in deionized water with a volume fraction of (0.1% vol.), in addition to use three types of fin plate configurations of (smooth, perforated, and dimple plate) to study the heat transfer enhancement characteristics of commercial fin plate heat sink for cooling computer processing unit. All experimental tests under simulated conditions by using heat flux heater element with input power range of (5, 16, 35, 70, and 100 W). The experimental parameters calculated are such as water and nanofluid as coolant with Reynolds number of (7000, 8000, 9400 and 11300); the air is blown in the inlet duct across the heat sink with Reynolds number of (10500, 12300, 14200 and 16000). The distance fin-to-fin is kept constant at (2.00 mm), and the channel employed in this work has a square cross-section of (7 cm) inside. It was observed that the average effectiveness and Nusselt number of the nanofluids are higher compared with those of using conventional liquid cooling systems. However, the perforated fin plate showed higher air heat dissipation than the other configuration plate fin employed in this study. The experimental results were supported by numerical results which gave a good indication to heat transfer enhancement in studied ranges.