Thermal-hydraulic Performance Research Articles

Thermal–Hydraulic Performance of Flat‐Plate Solar Collector Plant Using Different Heat‐Transfer Fluids

The physical parameters such as density, specific heat capacity, and viscosity of the heat‐transfer fluid have an important influence on the performance of the solar collector system. If the physical parameters of heat‐transfer fluids are studied as constant physical properties, it will be difficult to reflect the influence of heat‐transfer fluids on the performance of the solar collector system. In this study, expressions are fitted for the physical parameters of heat‐transfer fluids and a coupled thermal–hydraulic performance model of the solar collector system is established. The coupled model is validated through performance‐testing experiments on the system and is used to investigate the impact of heat‐transfer fluid types and concentrations on the performance of the system under various solar radiation intensities, ambient temperatures, inlet temperatures, and flow rates. In the results, it is shown that in the case of anti‐freezing, a 50% volume concentration of ethylene glycol is more suitable for the heat‐collecting system. When selecting the heat‐transfer fluid, the heat‐transfer fluid with a lower concentration should be selected as far as possible while ensuring the freezing point. In the results of this study, a certain reference for the selection of the heat‐transfer fluid can be provided.

Investigation of thermo-hydraulics performance and vapour bubble behaviour over 5×3 smooth hybrid elliptical tube bundle under saturated cross flow boiling condition - An experimental study

In the current experimental study, the thermal-hydraulic behaviour of a novel smooth hybrid elliptical tube bundle (TB) is compared with the performance of the corresponding conventional smooth circular TB. The smooth hybrid elliptical tube, made up of AISI-304, is in the form of a conventional elliptical shape from the outside but a circular shape from the inside. The operating parameters encountered in the current investigation are Heat Flux (10–75 kW/m2), Mass Flux (19–100 kg/m2s), and pitch-to-diameter ratio (P/D) (1.25 - 1.95). The outcomes show that the thermal-hydraulics performance in the case of a smooth hybrid elliptical TB is higher than a conventional smooth circular TB. The augmentation in the heat transfer coefficient obtained with a smooth hybrid elliptical TB is limited to 12 % in the entire range. The pressure drop improvement is found to be 48 % to 120 % equated to the conventional smooth circular TB. However, the effective performance of the smooth hybrid elliptical TB measured in terms of H/P ratio (H/P = heat transfer coefficient/total pressure drop) is found to be in the range of 0.3–2.5 compared to the conventional smooth circular TB which is in the range of 0.2–1.1. This is evident from the present experimental study that the employment of the elliptical TB will lead to lower pumping power than a conventional smooth circular TB owing to its lower pressure because of the streamlined surface. The obtained two-phase heat transfer enhancement efficiency based on enhancement factor and pressure drop penalty factor showed a higher gap TB (P/D = 1.95) has higher performance. Moreover, for the first time, an effort has been made to analyze the physics associated with vapor bubble dynamics and interaction along the height of the smooth hybrid elliptical TB.

Numerical analysis of the effect of wave amplitude on thermohydraulic performance in a heat exchanger with sinusoidal wavy channels

With the increasing application of heat exchangers, the research has become increasingly comprehensive. Previous studies mainly focused on comparing the amplitudes to investigate the performance of heat exchangers, while the study of variable amplitude channel structures was limited. This study investigated the thermal-hydraulic performance of seven different sinusoidal channels with inclination angles of 20° and 30°, and their combinations. Using the CFD solver, simulations were conducted to assess the heat transfer capabilities of sinusoidal channels under various Reynolds numbers and different amplitude conditions, compared to straight channels and single amplitude sinusoidal channels. The results indicated that within one period, both the pressure drop and temperature difference exhibited a ripple trend of gradually decreasing amplitude. When evaluating the comprehensive performance of the channels, three trends emerged across the seven models, with the performance of the cold fluid and the hot fluid within the same group showing opposite trends. This suggested that more variations could enhance the overall performance of the hot fluid while reducing the performance of the cold fluid. For structures with the same amplitude, in terms of amplitude variation frequency, models with six periods per group exhibited higher overall heat transfer performance than those with three periods per group, with an average increase of 36.37%. For the arrangement of amplitudes (taking the hot fluid inlet as an example), configurations with a smaller amplitude at the inlet outperformed those with a larger amplitude, indicating that in combined amplitude models, a structure with a larger group and a smaller amplitude at the inlet (taking the hot fluid as an example) should be designed.

Numerical analysis of thermal-hydraulic comprehensive performance of composite corrugated tubes with different cross-section shapes

Composite corrugation is a structure transformed from traditional corrugation to improve the thermal-hydraulic comprehensive performance (THCP) of corrugated tubes. However, compared to simple corrugations, the mechanism by which composite corrugations enhance THCP is still unclear. Therefore, in this work, numerical simulations are performed within the Reynolds number (Re) range of 5000–20,000 to evaluate the mechanism of composite corrugation strengthening THCP. The distributions of flow velocity, streamline, turbulent kinetic energy (TKE), pressure, and normalized force are used to reveal the differences in the effects of simple and composite corrugations on THCP. In addition, the influence of composite corrugation cross-sections and distribution forms on THCP has been explored in detail. The results indicate that increasing the impingement of the fluid on the tube wall, disrupting the fluid boundary layer, and expanding the range of secondary flow are the main mechanisms by which composite corrugations further strengthen THCP compared to simple corrugations (CT-SC). The THCP of composite corrugation (CT-CC-A-F) can be increased by 31.5% at Re = 20,000 compared to CT-SC. Composite corrugations with different cross-sections cause differences in THCP due to their varying effects on the distribution of secondary flow and the impingement of the fluid on the tube wall. The difference in the influence of composite corrugation distribution forms on THCP is still caused by the difference in the impingement of the fluid on the tube wall. This work can provide a reference for the design of composite corrugations to achieve better THCP.

Numerical study on bionic airfoil fins used in printed circuit plate heat exchanger

Abstract Airfoil printed circuit heat exchangers (PCHEs) possess exceptional comprehensive performance. In recent years, extensive research has been conducted on the layout and structure optimization of airfoil fins. As biomimetic technologies gradually mature, bionics has achieved numerous outcomes in optimizing airfoil aerodynamic characteristic. Inspired by the sailfish geometry, four types of bionic airfoils are proposed based on the NACA 0015 airfoil, to enhance the thermal-hydraulic performance of the airfoil PCHEs. The results show that while the four types of sailfish airfoils are effective in terms of drag reduction, their overall performance at the same pumping power is suboptimal, with only one type providing an advantage at the low Re region. Moreover, airfoils with concave head curves further increase the weakening of heat transfer by the velocity boundary layer.

Effects of Channel Flow Blockage on Metal Foam Heat Transfer

Abstract High porosity aluminum foams have the potential to dissipate large heat flux in a channel flow configuration due to their large surface area-to-volume ratio and the ability to enhance mixing due to flow tortuosity. It is well documented that the interstitial heat transfer coefficient has a power law dependence on the flow velocity at the pore-scale. For asymmetrical heating (single wall), a flow blockage concept is proposed with an aim to locally enhance flow speed near the heated wall. To this end, experimental and numerical investigation is carried out on a high porosity (95%) aluminum foam (10 pores per inch) with flow blockages, both upstream and downstream of the metal foam placed in a square channel. The opening was provided closer to the heated wall, where flow blockage was varied from 0% to 87%. With air as working fluid, experiments were conducted for channel Reynolds number varying from 3000 to 13,000. It was found that all flow blockages resulted in enhanced heat transfer over no-blockage case, however, at a high pressure drop penalty. An upstream flow blockage of 70% was found to have the highest thermal-hydraulic performance among other flow blockages (including 0% blockage).

Effects of airflow direction on the thermal-hydraulic performance of louvered fin-common flow up vortex generator

To improve the thermal-hydraulic performance of the louvered fin and flat tube heat exchangers (LFHEs), this paper innovatively proposes the louvered fin-common flow up vortex generator (LF-CFUVG). Then, numerical simulations are conducted to study the effects of airflow direction γ on the thermal-hydraulic performance of the LF-CFUVG. The corresponding results indicate that the flow resistance of the LF-CFUVG is always greater than the Baseline (the LFHE without CFUVGs), as the CFUVGs reduce the minimum free flow area while forming low-speed wake zones behind them. The heat transfer capacity of the LF-CFUVG exceeds the Baseline as well, this is attributed to the longitudinal vortices induced by the CFUVGs, which is helpful to homogenize the temperature field and transport the high-speed and low-temperature airflow. And the thermal-hydraulic performance of LF-CFUVG also outperforms the Baseline. In comparison to the working condition of γ is 0°, the pressure drop Δp for the LF-CFUVG declines with increase of γ from 0° to 30°, thus a larger angle helps to reduce flow resistance. However, the heat transfer coefficients hLF and performance evaluation criteria (PEC) of the LF-CFUVG deteriorate with the increasing γ, so a smaller angle is recommended to obtain an intenser heat transfer and better PEC.

Thermal-hydraulic performance of modified Schwartz-Diamond solid-networks triply periodic minimal surface structures

The triply periodic minimal surface (TPMS) structures are widely used as disturbance core structure in high performance heat exchangers. In this paper, four modified Schwartz-Diamond solid-networks (SD-solid) TPMS structures, one structure compressed along the flow direction (β = 2), and three structures compressed along the spanwise direction (α = 2, α = 3, and α = 4) are designed. Flow and heat transfer processes in the structures are studied with computational fluid dynamics (CFD) and experimental method. The performance enhancement criterion (PEC) is employed to evaluate the overall heat transfer performance. As the results of simulation, the overall heat transfer coefficient (hoverall) of α = 2, α = 3, and α = 4 is 10.04 %, 34.34 %, and 62.03 % higher than that of SD-solid respectively. The PEC of α = 2, α = 3, and α = 4 structures is 27.35 %, 34.17 %, and 34.95 % higher than that of the original SD-solid structure, respectively. Two samples of them (β = 2 and α = 2) are fabricated using additive manufacturing and their thermal–hydraulic performance is experimented on a flow and heat transfer experimental platform. Comparing the experimental results of the hoverall, the β = 2 structure is 68.5 % higher and the α = 2 structure is 23.06 % higher than the original SD-solid structure. However, for the average pressure drop, the β = 2 structure is 448.5 % higher and the α = 2 structure is 66.77 % lower than the original SD-solid structure. It is proved that the modified SD-solid structure compressed along the spanwise direction has the performance of enhancing heat transfer and reducing the pressure drop.

Thermal-hydraulics performance evaluation of bubble swarms sweeping tube bundles in a direct contact gas-liquid-solid reactor

Direct contact gas-liquid-solid reactor pertains to an extremely high efficiency heat-exchange facility in industrial application. Nevertheless, the scarcity of quantitative analysis data hinders the optimal design of this type of reactor. In the present study, a novel variable bubbles size modeling approach which considers the bubble swarms breakup and coalescence rates, is proposed to evaluate the complex thermal-hydraulics performance of bubble swarms sweeping tube bundles. On the basis of verifying the responsibility of the numerical modelling with published experimental data, the intrinsic link of hydrodynamics and thermodynamics parameters on reactor features, including field characteristics, gas holdup, bubble swarms diameter distribution, gas–liquid interfacial area, temperature difference and heat flux inside different tube bundles regions, are deeply revealed. Results demonstrate that the temperature difference between bubble swarms and tube bundles walls is approximately equal to 2K. Interestingly, different positions of heat exchanging tubes affect the peak value of circumferential heat transfer coefficient. For typical Tube 1–2, the maximum value of 3146.28 W/m2·K appears around 162°. The presence of tube bundles gives rise to the well-distributed iso-surfaces of bubble swarms which contributes to enhance heat transfer. When superficial gas velocities are respectively 0.09 m/s, 0.12 m/s and 0.14 m/s, the average bubble warms diameters are 13.47 mm, 16.22 mm and 17.24 mm. When initial liquid phase height increases from 342 mm to 378 mm, the corresponding gas–liquid interfacial area decreases by 16.2 % in total. Finally, two new modified dimensionless correlations were developed for the prediction of gas holdup and Nusselt number. The prediction errors are respectively 10 % and 6 %. The findings can improve the awareness for promising applications in design and scale-up processes of direct contact gas-liquid-solid reactor.

Performance enhancement of high temperature fin-and-tube heat exchanger employing winglet combined vortex generators

The fin-and-tube heat exchanger (FTHE) has the advantages of high temperature resistance, compact structure and high efficiency, and has been regarded as the optimal choice for flue gas heat transfer. In this study, the novel winglet vortex generators (VGs) are proposed for the high temperature HTHE where the flue gas with the inlet temperature of 1233 K transfers heat to the water. The effects of the combined VGs and the winglet combined VGs on the flue gas thermal–hydraulic performances are numerically studied. Furthermore, three winglet shapes including the triangular, trapezoidal and rectangular are compared. Moreover, the variations of high temperature HTHE performances with the flue gas mass flow rate are investigated. Compared to the plain fins, the surface heat flux and pressure drop of the combined VGs fins are increase by 15.8 % and 78.9 %, respectively. The designed winglets in the wake region could further reduce the area of the “teardrops” after the tube. The rectangular winglet combined VGs are decided as the best structure, which could maximally increase the surface heat flux by 11.9 kW/m2 compared to the triangular winglet combined VGs, while the pressure drop is slightly increased. Compared to the plain fins, the Nu of the rectangular winglet combined VGs is maximally increased by 16.4 and the maximum hydrothermal performance factor (HTPF) is 1.14. The optimum flue gas mass flow rate is determined as 1 g/s for the designed structures. This work can provide valuable guidance for design and modification of the high temperature HTHEs.

Evaluation of plate heat exchangers comprising sections with different chevron angle arrangements

Gasketed Plate Heat Exchangers (GPHEs) are essential equipment for thermal control of oil facilities owing to their compactness and well-organized assembly concept. In order to satisfy heat loads of several megawatts, numerous and large plates are necessary. The application of GPHEs with plentiful plates yields flow maldistribution which affects GPHE thermal–hydraulic performance. With the purpose of matching different heat loads and processing conditions or as an alternative to reduce maldistribution effects, GPHEs with mixed arrangements, comprising sections where channels contain different geometrical features, may be selected. This works addresses the evaluation of flow and pressure distributions in GPHEs with mixed arrangements. The pressure drop in each GPHE section is initially approximated by the pressure drop in parallel pipes, neglecting the pressure drop in the ports. With this assumption, the inlet flow rate is divided into two different parts. The pressure distributions in each section are assumed to maintain flow features of m2-model for U-type arrangement. The friction factor for each GPHE segment was determined with independent experiments including only one section type and with a small number of channels as to avoid flow maldistribution. Friction factor correlations were determined for single section GPHEs where each channel can be formed with plates containing different chevron angles: 30°/30°, 60°/60°, 66°/66°, 30°/60° and 30°/66°, with channel Reynolds number ranging from 260 to 3,080. Subsequently, experiments with GPHEs containing mixed sections with high and low pressure drop channels were performed: 60°/60° and 30°/30°, 30°/30° and 66°/66°; with total number of channels up to 180. The channel pressure drop was measured in regularly spaced locations. The pressure drop in each GPHE segment has been predicted with the fractional RMS deviation equal to 2.2%. Although the mass flow rate per channel has not been measured, it is expected that the predicted flow rate distribution can reasonably stand for the real one and, therefore, assisting in proper thermal performance evaluation.

Numerical investigation of double-flame hot-water boilers under steady-state operation

This study investigates the optimal arrangement of combustion chambers in double-flame hot-water boilers using computational fluid dynamics (CFD) under steady-state and laminar conditions. The study considers two arrangements: horizontal and vertical. In the horizontal layout, the study tests three vertical distances of Y*=-0.25, 0, and 0.25 from the center of the boiler and three horizontal gap spaces of S*=0.05, 0.1, and 0.15 between two chambers. In the vertical layout, the study examines three vertical distances of S*=0.1, 0.2, and 0.3. The computations for both layouts are conducted for Richardson numbers ranging from 0.1 to 10 under a constant Reynolds number of 50. The Navier–Stokes equations along with the energy equation are implicitly computed based on the finite volume approach for single-phase water flow inside a simplified two-dimensional model. The results are validated for a single-flame hot-water boiler in terms of the Nusselt number and non-dimensional pressure drop, and a good agreement has been achieved. The study shows that the geometric parameters considered in the study, as well as the Richardson number, have significant impacts on the boiler performance. The study finds that the horizontal arrangement with S*=0.05 and Y*=-0.25 offers the highest thermal-hydraulic performance, regardless of the Richardson number.

Numerical investigation and comparison on thermal-hydraulic performance of H-type finned tube heat exchanger

H-type finned tube heat exchangers have been widely used in boilers and waste heat recovery devices due to their advantages of wear resistance and anti-fouling. In order to improve the energy-saving effect, the flow and heat transfer characteristics of H-type finned tube heat exchangers with different tube bundle arrangements were studied. It was found that, at the same Re number, the column staggered arrangement can compensate for the limited heat transfer performance of the in-line arrangement and reduce the high pressure drop associated with the row staggered arrangement. Honeycomb arrangement was proposed based on the column staggered arrangement. Then, the effects of Re and tube pitches thermal-hydraulic performance of tube bundles with in-line and honeycomb arrangements were examined. The critical tube pitch or velocity at which the honeycomb tube bundle achieves the same thermal performance as the in-line tube bundle are determined. The results provide valuable insights for the practical application of flue gas heat exchangers with honeycomb arrangement.

Analysis of thermal-hydraulic comprehensive performance of composite corrugated tubes composed of simple droplet-shaped corrugations

Corrugation parameter design seeks to maximize the thermal-hydraulic comprehensive performance (THCP) of corrugated tubes as much as possible. Among them, composite corrugations composed of simple corrugations are proposed to strengthen the THCP of corrugated pipes. However, the rule and mechanism regarding the impact of composite corrugations on the THCP of corrugated tubes, particularly when those composite corrugations are composed of simple asymmetric corrugations, are not well understood. Therefore, in this work, the effect of composite corrugations consisting of two simple droplet-shaped corrugations on THCP is assessed numerically, where the first composite corrugation is concave-convex (CTCC1) and the second composite corrugation is concave-concave (CTCC2). In addition, the effect of traditional corrugation (CTSC) on THCP is also examined to further highlight the advantages of composite corrugation in enhancing the THCP of corrugated tubes. The results of the study indicated a 49 %, 55 %, and 61 % increase in THCP at a Reynolds number (Re) of 5000 for CTSC, CTCC1, and CTCC2, respectively, compared to a smooth tube, indicating that the combination of composite corrugations in CTCC2 is superior to that in CTCC1. In addition, a smaller corrugation width on the upstream side of CTCC2 is more conducive to enhancing THCP. Furthermore, it should be ensured that the corrugation depth on the upstream side of CTCC2 is not greater than the depth on the downstream side to achieve better THCP. The work confirms the advantages of composite corrugations over traditional corrugations in enhancing THCP and guides the selection of composite corrugation combination forms and the design of composite corrugation width and depth distribution.

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

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

Numerical investigation of the thermal-hydraulic performance of a novel parabolic trough wavy tubular receiver by using FMWNCT/oil-nanofluid coupled with fins

This study employs a computational fluid dynamics (CFD) approach to assess the performance of a novel wavy profile tube receiver. It integrates rectangular fins and an Oil-based nanofluid, specifically utilizing Thermodyne GG-03 synthetic oil combined with Functionalized Multi-Wall Carbon Tubes (FMWNCT). The synthesis involves rigorous experimental procedures to characterize the thermophysical properties of the oil and nanofluid. Empirical correlations, validated against Bitam et al.'s model [1], guide the numerical analysis. The investigation, utilizing a steady-state κ - ω SST turbulence model with a non-uniform Gaussian thermal flux distribution, explores thermohydraulic performance in fully developed turbulent flow (Reynolds number range: 2 × 104 – 5 × 104). Comparative analysis with Bitam et al.'s work, employing Syltherm 800 oil as a reference, reveals a 25.76% average Nusselt number enhancement with Thermodyne GG-03. Additional improvements are observed: 124.69% with FMWNCT/oil-nanofluid, 137.04% with fins, and 236.54% with combined FMWNCT/oil-nanofluid and fins. These enhancements lead to increased heat transfer coefficients and rates. The friction coefficient rises by less than 60%, mainly attributed to the Nusselt number improvement. At RE = 20000, the Maximum Performance Evaluation Criteria (PEC) is 5.5, signifying significant improvement. Notably, a 300% PEC enhancement is observed compared to Roger and Mayhew's curved tube model [1]. In conclusion, these findings offer valuable insights for efficiently designing wavy tubular receivers in PTR collectors.

Numerical investigation of entropy generation for flow boiling of R600A in the corrugated U-bend tube heat exchangers

The development of compact and efficient corrugated heat exchangers for refrigeration and air conditioning systems is reliant upon thermal-hydraulic performance, which is quantifiable in terms of entropy generation. Hence, this study presents the generation of entropy analysis for flow boiling evaporation with an environment-friendly refrigerant (R600a) in the novel design of corrugated (outward circular ribs corrugated, inward circular ribs corrugated, outward triangular ribs corrugated, and inward triangular ribs corrugated) U-bend tube exchangers. The performance of the corrugated tube heat exchangers has been reported in comparison with the smooth U-bend tube heat exchanger. The numerical calculations were executed using CFD code for various masses ranging from 100 to 400 kg/m2s at the saturation temperature and vapor quality of 20 °C and 0.2 respectively while 15 kW/m2 heat flux was applied on the external surface of the straight tubes. The results revealed that the entropy generation increases as the mass flux increases with the inward circular and triangular ribs corrugated tube having the highest generated entropy followed by the outward circular and triangular ribs corrugated and then the smooth tube with the least entropy generation. In reference to smooth tube for the mass flux of 100 kg/m2s, the entropy generation for inward circular and triangular ribs corrugated increased by 46.88% and 130.93% respectively while the outward circular and triangular ribs corrugated increased by 18.35% and 39.26% respectively. Lower dimensionless Bejan numbers were obtained in the corrugated tubes with respect to mass fluxes compared to the smooth tube. The fluid flow irreversibility contribution to the overall entropy generated was higher in the corrugated tubes due to the corrugation surface which causes swirl mixing. The results of the numerical calculations were confirmed and corresponded with those established in the literature.

Numerical study on thermal-hydraulic characteristics of streamwise-interrupted flying-wing finned tubes

To improve the thermal-hydraulic performance, this study conducted numerical studies on streamwise-interrupted flying-wing finned tubes utilising both single- and double-channel interruption modes. The interruptions varied in width from 0.5 to 10 mm and were strategically positioned in nine distinct locations along the flow direction. The RNG k-ε turbulence model was applied for viscous flow simulation. The findings reveal that fin interruptions create a “breakpoint thermal expansion effect” at specific locations, enhancing heat transfer downstream while diminishing it upstream. For the single-channel interruption mode with a centrally positioned interruption channel, a 5–6 mm width is optimal at a low air velocity (150 Pa total pressure drop and a Reynolds number of 1282.31 for the continuous flying-wing finned tubes). However, at high air velocities (550 Pa total pressure drop and a Reynolds number of 2944.91), interruption is unnecessary. In both modes, standardising the interruption channel width to 2 mm is more effective when the interruptions are placed closer to the downstream end, as opposed to an even distribution. This study provides valuable insights for enhancing the thermal-hydraulic performance of flying-wing finned tubes and similar continuous-finned designs through strategic flow-channel interruptions.

Experimental investigation and performance prediction of SAH using different arc rib roughness geometries – A comparative study

This study aims to investigate and compare the thermal performance of a solar air heater using a passive technique to enhance heat transfer between the absorber plate and the flowing fluid. The technique involves generating turbulence near the heat transferring surface through the use of artificial rib roughness. The study focuses on two different novel roughness geome-tries: full symmetrical arc rib roughness and half symmetrical arc rib roughness. By introducing additional gaps and varying the number of gaps in the roughness geometries, the study examines their effects on the solar air heaters thermal performance. The artificially roughened surface creates different turbulent zones, which are essential to the development of different types of turbulence in the vicinity of the heat transferring surface. The study finds that an optimal escalation in Nusselt number and friction factor by 2.36 and 3.45 times, respectively, occurs at certain gap numbers as 6 and ng as 5 for full symmetrical arc rib roughness. The maximum thermal-hydraulic performance parameter of 1.66 is attained at a Reynolds number of 6 000. The study also conducts correlation, mathematical modeling, and performance prediction under different operating circumstances.

Numerical investigation of fluid flow and heat transfer characteristics of MWCNT-Al 2 O 3/H 2 O hybrid nanofluid flowing through a novel semi-arc ribbed square duct

This study carried CFD analysis to study the fluid flow and heat transfer characteristics of MWCNT- Al 2 O 3 / H 2 O hybrid nanofluid flowing through square duct equipped with novel semi-arc ribs. The turbulent flow simulations are performed at varying Reynolds numbers ( Re ) between 3,000 and 18,000 and nanoparticle volume concentration ( φ ) range of 1–4% for different rib parameters, namely relative stream pitch ratio ( X pr ) range from 2.67 to 3.67, Rib height ratio ( R hr ) range from 0.05 to 0.20, number of ribs ( n ) range from 1 to 4. Different performance indicators, such as Nusselt number ( Nu ), friction factor ( f r ) , and thermal hydraulic performance (THP) was examined to evaluate the system performance. The RNG k ‐ ε model was engaged to simulate turbulent nanofluid flow within the channel under constant temperature condition (T = 300 K). The findings indicated that the development of vortex flow and increased turbulence due to the effects of arcs can improve the heat transfer enhancement. The THP, Nu and f r were found to be highest for R hr = 0.15 , X pr = 3.34 , φ = 4 % , and n = 3 , yields to the best THP at 1.94.