Pressure Penalty Research Articles

Thermohydraulic Performance and Flow Structures of Diamond Pyramid Arrays

Abstract Surface features are a common heat transfer enhancement method used in a myriad of applications including gas turbines and heat exchangers. One such style of surface feature is diamond pyramids, which offer significant heat transfer augmentation for moderate increases in overall pressure losses. This study investigated a suite of additively manufactured pyramids in a variety of sizes and arrangements at relevant scale contained in test coupons. Designs were printed with low surface roughness relative to typical additive components (Ra < 5 μm), and pyramids were printed within 100 μm of the design intent. Experimental and computational results indicate that the pressure penalty and heat transfer increased as the pyramids increased in size with aligned pyramids on both channel walls having higher values than staggered pyramids. It was found that implementing the pyramids onto a rough surface had a lesser impact on the friction factor than implementing it on a smooth surface, but that the relative increase in heat transfer was the same regardless of the roughness of the endwall. The greatest enhancement to local heat transfer and pressure loss was offset from the location of the minimum flow area due to local acceleration around the wake regions. The vortices formed in the wake of the pyramid structures enhanced the endwall heat transfer and shear stress. The performance of the pyramids investigated in this study follows a similar trend to prior studies investigating smooth rib geometries, though certain rib designs had higher heat transfer at lower pressure losses.

Experimental analysis of double layer microchannel heat sink with distinct fin configurations in upper and lower layers

In the present experimental study, two distinct configurations of double layer microchannel heat sinks (DL MCHS) are proposed. It consists of rectangular parallel channels in the bottom layer and an array of square pin fins in the upper layer. Pin fin height (Hf) in the first configuration is equals to the channel height (Hc) (i.e. Hf/Hc=1). However, in the second configuration, pin fin height is equivalent to 75 % of Hc such that Hf/Hc=0.75. The proposed modified DL MCHS configurations are then compared with the conventional double layer microchannel heat sink (CDL MCHS). Hence, the idea of the current work is to develop a novel DL MCHS with improved heat transfer capabilities and reduced pressure penalties. Heat dissipation rate, pressure data and coolant flow behaviour are carefully measured and analyzed. Findings reveal that thermal performance of the modified heat sink with Hf/Hc=1 is not appreciable because it delivers almost similar to conventional configuration. Whereas, modified heat sink of Hf/Hc=0.75 has consistently exhibited better heat transfer rate and thermal performance factor. As compared to CDL MCHS, thermal performance factor was found ≈38 % higher in this case. Overall thermal and hydraulic performance of the DL MCHS is significantly influenced by the flow pattern of the coolant, which is a result of the novel channel design.

Numerical Study on Flow Field and Heat Transfer Enhancement in a Cooling Channel With Novel Ribs Based on Battery Thermal Management System

Turbulent flow and heat transfer characteristics in a cooling channel with novel ribs have been numerically studied to improve thermal efficiency inside future electric vehicle batteries. In this study, the essential ratios of channel length, rib height, and rib pitch were all set to 6.67, 0.13, and 8.66, respectively. The realizable turbulent kinetic energy - epsilon model was used for the numerical simulation work under the Reynolds number varied from 10,000 to 50,000. The results showed that the heat transfer enhancement on a surface depended on the secondary flows due to the ribs. The enhancement of the wavy-winglet rib was approximately 9.8%−32% compared to other rib cases. Nevertheless, the improved heat transfer came at the expense of a higher pressure penalty. Above 29.7% of the friction factor for the wavy-winglet rib was obtained, compared to orthogonal ribs. In addition, the wavy-winglet rib gave the best thermal-hydraulic performance of the designs explored.

Error Analysis of a Pressure Penalty Scheme for the Reformulated Ericksen-Leslie System with Variable Density

Error Analysis of a Pressure Penalty Scheme for the Reformulated Ericksen-Leslie System with Variable Density

Heat transfer and flow analyses of microchannel heat sink with twisted blade-like fins

To enhance heat transfer coefficient, decrease pressure penalty, and improve wall temperature uniformity, a twisted blade-like fin with low-drag airfoil section is proposed in this study. The flow and heat transfer performances of microchannels with the fins are numerically investigated at Re = 50–700. Results show that the novel fins improve the heat transfer (Nu/Nu 0) significantly with a small pressure penalty (f/f 0), and thus show an excellent comprehensive thermal performance (TP). The ranges of Nu/Nu 0, f/f 0 and TP are 1.16–4.76, 1.51–2.36, and 1.01–3.58, respectively. The TP of TAMCHS reaches 3.58, exhibiting an increase of 46.7, 37.7, 22.6, and 16.6% compared to four models in previous study. The reduced pressure penalty is attributed to the streamlined configuration, and the improved heat transfer coefficient is attributed to the normalwise secondary flow stimulated by the twisted fins, which enhances heat transfer in the upper portion of the channel. Compared to a smooth microchannel heat sink (SMCHS), the major advantages lie in the significant reduction of sidewall temperatures and notable improvement in temperature uniformity on the top and bottom walls. The average and maximum wall temperature are reduced by 48.1 and 49.0 °C at most, respectively, and the greatest decline of wall temperature gradient is 55.0 °C.

Employment of roughened absorber palate and jet nozzles with different hole shapes for performance boost of solar-air-heaters

In this study, roughened absorber plate and jet nozzle are simultaneously employed to enhance the efficiency of a solar based air heater. The impact of jet nozzle hole shape is comprehensively investigated for the mentioned system which have not been investigated before. Three-dimensional steady-state simulations of incompressible turbulent fluid flow and heat transfer are performed using the Reynolds-Averaged Navier-Stokes (RANS) equations to model the jet solar air heater (JSAH). Five different jet hole shapes (circular, triangular, square, hexagonal, and rectangular) are examined and results are compared with conventional structure. The thermal and hydraulic performance of the JSAH is assessed using a variety of geometric and operating parameters, including jet diameter ratio (dj/Dh), jet hole streamwise pitch (Lj/Dh), and Re number (Re). The results show that the ratio of (Nu/Nus) initially increases and then decreases as the hydraulic diameter of the jet holes increases. Circular jet holes consistently outperform other shapes, while rectangular and triangular jet holes perform poorly. The pressure penalty (f/fs) decreases with increasing (dj/Dh), with circular jet holes exhibiting the lowest value. Increasing the Reynolds number enhances heat transfer and pumping power but leads to a decrease in (Nu/Nus) and negatively affects the THPP of the JSAH compared to a conventional smooth solar air heater. The study also reveals that the THPP initially increases with streamwise pitch (Lj/Dh) but then declines, following the trend of (Nu/Nus). The results demonstrate up to 4.5 times higher Nusselt numbers with a jet solar air heater versus a smooth solar heater. A maximum thermal-hydraulic performance parameter of 1.64 indicates the proposed design's efficacy. This research furnishes critical insights into optimizing solar air heater performance by examining jet nozzle hole shape, streamwise pitch, and Reynolds number. It enables enhancing thermal efficiency and thermo-hydraulic performance.

Magnetohydraulic flow in a rectangular channel filled with stream-wise obstacles

The Water-Cooled Lead Lithium (WCLL) Breeding Blanket (BB) is one of the two leading candidates for implementation as driver blanket in the European DEMO reactor, which is expected to start operation in the late 2050s and serve as a BB test facility. One of the main risks associated with the current WCLL concept is the large number of welds necessary to realize its horizontal (toroidal-radial) breeding zone cooling system and stiffening structure, which negatively affects its reliability. Hence, an alternative variant concept has been proposed which relies on vertical (radial-poloidal) “double-bundle” cooling tubes and stiffening plates: the WCLL double-bundle (WCLL-db). In this paper, we report the results of numerical analyses performed to characterize the Magnetohydrodynamics (MHD) regime in the WCLL-db where the liquid metal breeder flows vertically and it is obstructed by a large number of electrically conductive obstacles aligned with the stream-wise direction.Direct numerical simulations are performed with the aid of computational MHD tools to characterize the flow features and pressure losses in the WCLL-db breeding zone. The presence of many stream-wise obstacles affects the velocity distribution since the cooling tubes provide additional paths for the electric current closure. The most striking feature is the breaking down of the classic MHD slug core flow into many separate smaller regions, separated by internal layers. These occur tangential to the pipe walls, featuring velocity overshoots, and tend to propagate along the imposed magnetic field. A moderate (3.83–9.73%) pressure penalty is found compared with the analytical prediction for a channel devoid of obstacles.

Heat transfer enhancement and temperature uniformity improvement of microchannel heat sinks with twisted blade-like fins

To enhance heat and fluid exchange between main flow and near-wall flow in microchannels, a twisted blade-like fin with an advantage in stimulating both spanwise and normalwise secondary flow is proposed. The cross sections of the fin are low-drag airfoils in different orientations. The flow and heat transfer performances of microchannels with fins are numerically investigated at Re = 50–700. The results show that the twisted blade-like fin improves heat transfer process significantly, especially wall temperature uniformity, and reduces the flow separation region behind the fin, resulting in an obvious small pressure penalty. At small inflow (Re = 50), the best heat transfer and lowest pressure penalty are obtained in the microchannel with a single fin. When Re > 150, better heat transfer is obtained in the microchannel with three fins, and the highest comprehensive thermal performance (TP) reaches 3.58. The twisted direction of fins has a significant effect on heat transfer but less on flow drag. Due to the twisted fins, left and right walls experience an overall decline in temperature, and the temperature uniformity of top and bottom walls is improved. Compared with a smooth microchannel, the average and maximum temperature of the investigated microchannels are reduced by 48.1 K and 49.0 K at most respectively.

Improved flow boiling characteristics in minichannel with open-cell porous ribs

Porous metal has been proven to exhibit significant heat transfer enhancement in minichannel. Focusing on fully utilizing the advantages of porous metal in heat transfer and reducing pressure penalty, a porous ribs minichannel (PRM) heat sink employing open-cell porous copper as rib was designed and fabricated. PRM heat sink has 19 minichannels that are 1 mm in width and 2 mm in depth. Commercial open-cell porous copper with a porosity of 0.85 and 120 PPI (Pore per Inch, PPI) was selected. Flow boiling experiments were carried out with ethanol as the working fluid. The flow patterns of two heat sinks were recorded with a high speed photograph system and comparative analyzed. High-frequency periodic motion of vapor core boundary in width direction of porous ribs minichannel was recorded. This is considered a fluctuation of density wave along the channel width direction. Cooperating with capillary force, movement of vapor core boundary induces mass transfer between adjacent channels, compensating for uneven flow distribution between channels. The results show that PRM heat sink has better heat transfer performances and flow stability with a slight increment in pressure drop compared with solid ribs minichannel (SRM) heat sink. The porous ribs minichannel heat sink provides a new way to relieve flow insatiability for heat exchangers and thermal management systems.

Effect of relative rib roughness pitch on the thermohydraulic performance of roughened duct of solar air heater

Solar energy is widely available, inexhaustible, endless, cost-free source of energy which is suitable for both domestic and commercial applications. Utilizing solar energy would help several difficult problems, like climate change, energy security, unemployment, etc. The process involves examining how heat transfer and flow friction are affected by rib roughness pitch (p/e) in a rectangular artificially roughened duct for Re ranges between 2000 and 16000. The different values of p/e are taken as 6, 8, 10 and 12 during experimentation. The p/e = 10 shows higher value of heat transfer augmentation and also shows higher value of pressure penalty as comparison to other values of p/e.

Relative assessment of various annular fin shapes for heat transfer and pressure penalty

Three dimensional numerical investigations are carried out to analyse the effect of different shapes of annular fin on heat transfer characteristics and pressure drop across a tube surface. Shear stress transport based k-ω turbulence model is used to analyse flow physics and heat transfer characteristics in flow domain. Weak zones of heat transfer across a circular tube surface are identified for 2500 < Re < 13000. Three different shapes of annular fin are considered to test the possibility of optimum heat transfer characteristics in weak zones. Results are compared with circular shape annular fin. Circular shape annular fin outperforms in terms of overall rate of heat transfer at the cost of highest pressure drop. The heat transfer rate decreases by 18%, 21% and 31% in sectorial fin, elliptical fin and sectional fin as compared to that of circular fin at 12965 Reynolds number, but at other end pressure drop across a tube surface in case of these fins also decrease as compared to that of circular annular fin. Potential rate, ratio of heat transfer rate to required pumping power, is calculated to evaluate optimum fin performance. Potential rate of an elliptical fin is highest among all the reported cases.

Effects of Jet-to-Target Surface Spacing and Pin-Fin Height on Jet Impingement Heat Transfer in a Rectangular Channel

Abstract An experimental study was completed to quantify heat transfer enhancement, pressure loss, and crossflow effect within a channel of inline impinging jets. The jet diameter is 5.08 mm; the jet-to-jet spacings in the streamwise and spanwise directions are fixed at x/d = 11.1 and y/d = 5.9, respectively. The effect of jet-to-target surface spacing was considered with z/d = 3 and 6. For both jet-to-target surface spacings, smooth, short pin-finned, and long pin-finned target surfaces were investigated. Both roughened surfaces have a staggered array of 120 copper pin-fins. The pin-to-jet diameter ratio is fixed at D/d = 0.94. The pin height-to-jet diameter ratio for the short and long pins are H1/d = 1.5 and H2/d = 2.75, respectively. Regionally averaged heat transfer coefficient distributions were measured on the target surface, and these distributions were coupled with pressure measurements through the array. The heat transfer augmentation and pressure penalty were investigated over a range of jet Reynolds numbers (10k–70k). The results show high discharge coefficients for all the cases. The channels with the small jet-to-target surface spacing experience double the crossflow effect of the large spacing channels. The addition of surface roughness showed a negligible effect on the crossflow. The best heat transfer performance was observed in the narrow impingement channel with the long pins.

Design Optimization, Thermohydraulic, and Enviro-Economic Analysis of Twisted Perforated Tape Insert-Based Heat Exchanger With Nanofluid Using Computational Fluid Dynamics and Taguchi Grey Method

Abstract In this paper, the effect of perforated twisted tape insert (PTTI)-based heat exchanger (HX) utilizing nanofluid as working fluid undercooling, turbulent flow model has been investigated numerically. Parameters, i.e., nanofluid mass flow rates (0.018–0.038 kg/s), perforated pitches (20 mm–40 mm), and perforated diameters (2 mm–4 mm) variation effects on fluid outlet temperature, Nusselt ratio, Friction ratio, pressure drop, overall thermal performance, CO2 discharge, and heat exchanger operating cost (HXOC) have been investigated. This work also focuses on design optimization with three different factors and three levels for higher heat transfer coefficient (HTC) and minimum pressure drop based on the Taguchi–Grey method. Computational fluid dynamics (CFD) output is used as an input value for statistical analysis. Results revealed that the PTTI in HX successfully achieved overall heat transfer enhancement in the range of 19.2% to 28.5%, but at the cost of pressure penalty of 126% to 163% higher than the plain tube. Critical Reynolds number 7927, above which PTTI in HX is least suitable for heat transfer enhancement as fluid velocity dominates over heat transfer and 1.7–2.5 times higher carbon discharge to the environment and HXOC. Preference sets of geometrical and fluid parameters are obtained using Grey analysis. Based on statistical analysis, in the considered levels, a group of parameters to attain higher HTC and minimum pressure drop are mass flow rate of 0.018 kg/s, a perforated pitch of 20 mm, and a perforated diameter of 4 mm.

Study Investigates Foam Use for Control of Pipeline Slugging

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22235, “Foams To Control Slugging Issues in Pipelines—From Laboratory to Simulation,” by Ivy C.C. Hsia, Bishop Falope, and Nor Hadhirah Halim, Petronas, et al. The paper has not been peer reviewed. Copyright 2022 International Petroleum Technology Conference. Reproduced by permission. _ In one of the operator’s Malaysian fields, hydrodynamic slugging, or two-phase liquid/gas flow instability in the pipeline, has caused losses in flow capacity and intense vibration at the separator, leading to integrity issues. To understand how the behavior of foams in a pipeline affect or alleviate slugging performances, foam behavior was simulated using the OLGA (short for “oil and gas”) simulator, a commercial dynamic multiphase-flow-simulation software. This study showed that foams were able to slow gas velocity and diminish liquid fluctuations, thus reducing slugging in a problematic pipeline. Challenges Posed by Slugging Hydrodynamic slugging or instability of waves at certain liquid/gas flow rates in the pipeline were concerns in several fields in Malaysia. In one such field, almost 50% of the loss in flow capacity (i.e., liquid holdup) from a producing pipeline was the result of slugging, causing gas-production deferments of as much as 30 million scf/D. Severe vibrations from the pipeline to the separator often were felt at the platform, leading to questions about the mechanical integrity of the separator and anticipated high maintenance costs. The issues of slugging can be solved with the use of foams introduced into the pipeline to slow down gas velocity and enhance mixture with liquid. Foam injection into the wellbore has proved to act as a flow stabilizer, thus removing the slugging in the well and improving gas lift. Foams from surfactant injection increase the viscosity of gas, thus reducing gas movement and velocity but with a pressure penalty. Surfactant concentration also decreases the liquid’s surface tension to a minimum value reached when micelles start to form, called the critical micelle concentration (CMC). A thorough understanding of reduction of liquid surface tension is critical. The inclusion of crude oil into the authors’ laboratory tests is intended to establish the actual performance of the surfactant and the effect of crude oil on viscosity and interfacial tension (IFT) to replicate actual fluid properties (i.e., water cut and emulsion tendencies of the field). The software used simulates flow under actual pipeline conditions. A base model was built to establish slugging conditions using parameters obtained from the field. The model was modified to include input parameters of foams such as viscosity and IFT between two phases to determine if they can suppress foams; this was achieved by reading changes in the total liquid volume flow coming from the pipeline throughout the extent of the pipeline. In the complete paper, the authors sought to understand how to determine foam viscosity and interfacial tension in the presence of crude oil using precision laboratory instrumentation and then used these measurements as inputs into the simulation software to calculate the percent reduction in liquid flow volume and fluctuations of an actual pipeline facing slugging issues.

Performance assessment of a rock aggregate heat exchanger exposed to daily temperature variation

Opportunities exist to utilize rock aggregate to condition ventilation air at mine sites in humid continental climates. Vale’s Creighton mine in Canada proved that a natural heat exchanger offered significant energy savings; however, the system was not suitable to establish design guidelines. A novel prototype-scale outdoor 30 m3 rock pile heat exchanger experiment was constructed to characterize the thermal response to measurable aggregate parameters with insight shared regarding their sensitivity. This paper validates an unsteady 3D CFD numerical methodology involving the thermal non-equilibrium porous zone model with lab-scale-derived correlations against weather-influenced temperature data and proposes guidelines for improving performance: Increasing pile flatness was beneficial for damping whereas increasing hemispericality was beneficial for phase shifting. A CFD case study requiring 47 m3/s (100,000 cfm) ventilation flow found that a rock pile constructed using traditional methods could achieve 100% damping with 6,000 m3 of granitic rock aggregate at a pressure penalty of 2,500 Pa.

Numerical investigation to analyse the effect of fin shape on performance of finned tube heat exchanger

Numerical investigations are carried out to determine the effect of change in geometrical parameter of annular fin on thermal and hydraulic characteristics. Fin shape is changed by varying horizontal diameter of fin. Three different cases of annular fin are investigated corresponding to fin diameter ratio (X) of 0.65, 0.85 and 1. Turbulence is modelled using k-ω shear stress transport model. Relative assessment of tube with annular fin of different horizontal diameter (D01) is done for 2500 < Re < 13000. The comparison of Nusselt number reveals that circular tube with annular fin enhances heat transfer rate. Nusselt number augments by 35% and 10% in case of annular fin with diameter ratio of 0.65 and 0.85 as compared to that of annular fin with diameter ratio of 1.00 for 2500 < Re< 13000. Pressure drop augments with increase in horizontal diameter of fin and Reynolds number. Annular fin with diameter ratio of 0.65 performs better in terms of heat transfer and pressure penalty as compared to other cases for range of reported Reynolds number.

Effect of Utilizing Staggered Semi-Porous Fins on Channel Flow Heat Transfer Enhancement

A comprehensive numerical investigation of fluid stream and laminar forced convection were conducted to simulate the effects of the semi-porous fins, which are a new combination of porous and solid parts, inside a partially heated channel with a staggered arrangement. The present numerical approach is based on the Navier-Stocks and Darcy-Brinkman-Forchheimer equations in the fluid and semi-porous regions, respectively. The effects of various parameters such as Reynolds number, Darcy number, fin height, and aspect ratio of the porous region’s height to total fin height were studied. Also, the effects of these parameters are illustrated further as a variation of dimensionless pressure penalty and heat transfer enhancement ratio in the flow domain. The results demonstrate that using a new type of fin with both solid and porous parts in a single fin, enhances the heat transfer up to 6% compared to the porous fin and decreases the pressure penalty up to 23% compared to the solid fin at Darcy number of 10−4 when the percentage of aspect ratio is equal to 20%. Furthermore, it was found that the Darcy number of 10−5 is a critical value for the optimum utilization of semi-porous fins.

Numerical Study of Fin-and-Tube Heat Exchanger in Low-Pressure Environment: Air-Side Heat Transfer and Frictional Performance, Entropy Generation Analysis, and Model Development.

Heat transfer and frictional performance at the air-side is predominant for the application and optimization of finned tube heat exchangers. For aerospace engineering, the heat exchanger operates under negative pressure, whereas the general prediction models of convective heat transfer coefficient and pressure penalty for this scenario are rarely reported. In the current study, a numerical model is developed to determine the air-side heat transfer and frictional performance. The influence of air pressure (absolute pressure) is discussed in detail, and the entropy generation considering the effect of heat transfer and pressure drop are analyzed. Furthermore, prediction models of air-side thermal and frictional factors are also developed. The results indicate that both the convective heat transfer coefficient and pressure penalty decrease significantly with decreasing air pressure, and the air-side heat transfer coefficient is decreased by 64.6~73.3% at an air pressure of 25 kPa compared with normal environment pressure. The entropy generation by temperature difference accounts for the highest proportion of the total entropy generation. The prediction correlations of Colburn j-factor and friction factor f show satisfactory accuracy with the absolute mean deviations of 7.48% and 9.42%, respectively. This study can provide a reference for the practical application of fined tube heat exchangers under a negative pressure environment.

Numerical Optimization of a Premixer for an Internal Combustion Engine using Producer Gas as a Fuel

Gasification seems to be one of the sustainable green energy solutions to fulfill the current and future energy needs. For efficient utilization of producer gas on existing IC Engines, carburetor/premixer needs to be carefully designed and developed to achieve uniform mixing quality. A long radius nozzle type premixer has been designed for natural gas engine to be operated on producer gas as an alternate fuel. Different configurations of T – Type premixers with single air entry and twin air entry with different throat diameters and hole sizes are numerically analysed using ANSYS® CFX. Turbulence is modelled using RNG k - ε closure model. Mixer performance is compared in terms of constituents’ mass fraction, flow Uniformity Index (UI) and pressure penalty. Numerical analysis reveals that throat diameter, air entry type and air hole diameter governs mixing and pressure drop. Out of all configurations, twin air entry type premixer provides better mixing of producer gas and air. The optimized design of premixer shows that the absolute deviation in mass fraction of individual constituent lies in the range of ± 1.73% with respect to the actual mass fractions obtained. The average absolute deviation calculated is 1.37% with Uniformity Index 0.958 at the exit plane while the pressure drop across the premixer is 951 Pa.

Study of hydrothermal transport phenomena and performance characteristics for a flow through a diamond (diverging-converging) microchannel

A three-dimensional computational module is undertaken to assimilate the hydrothermal transport phenomena and performance characteristics of a single-phase laminar flow through a diamond (diverging-converging) microchannel. The fluid flow and heat transfer characteristics are investigated as a function of divergence-convergence angle, width ratio (ratio of bigger width to smaller width), and Reynolds number. The results are explained with the help of velocity and temperature profiles. The present study also utilizes thermal enhancement factor, pressure penalty factor, performance evaluation index, frictional and thermal entropy generation, Bejan number, and augmented entropy generation number to analyze the hydrothermal and thermodynamic performance characteristics of a diamond microchannel. The Nusselt number is found to be a direct function of the divergence-convergence angle, while it varies inversely with the width ratio. The varying divergence-convergence angle effectively constrains the rise in the overall temperature gradient, while the width ratio has a weak but opposite effect on the temperature gradients. The results also indicate that the diamond microchannel exhibits better hydrothermal and thermodynamic performance than the uniform microchannel. For a given range of parameters, the maximum value of the performance evaluation index is 1.42, and the maximum reduction in entropy generation is 28% relative to a uniform microchannel. These results would serve as a valuable guide for designing and optimizing microchannels with diverging-converging profiles required in several heat transfer applications.