Volume Goodness Factor Research Articles

Design correlations for a novel enhanced compact heat exchanger with offset circular fins

A novel core geometry for compact heat exchangers, termed “circular offset fins (cOF)”, is proposed and experimentally investigated in the present work. This core design resembles the well-known offset strip fins used in efficient compact heat exchangers, with a key difference that instead of having rectangular fluid flow passages between deflections, this design features circular paths, resulting in fins with semicircular profiles. An experimental study examined heat transfer and pressure drop characteristics for five different core geometries. These geometries varied in passage diameters, lengths, and degrees of obstruction. The experiments were carried out over Reynolds numbers ranging from 500 to 3000 at different core wall temperatures. Data was analyzed using Kays and London's steady-state steam-to-air heat transfer technique to determine the empirical Colburn factor. The empirical Fanning friction factors for these geometries were also obtained. The asymptotic behavior of the Colburn and Fanning friction factor data allowed for the development of correlations in the function of Reynolds number and geometry dimensionless parameters. The proposed correlations predict data within ±6 % and ±8 %, respectively. The impact of different geometric parameters on core performance was assessed using the Colburn and Fanning friction factors, as well as area and volume goodness factors, and compared to rectangular offset strip fins. Direct comparisons showed that circular offset fins consistently exhibited a lower friction factor than rectangular fins. Although its Colburn factor was lower than rectangular fins up to a Reynolds number of 2000, circular fins it surpassed that of rectangular fins beyond this point. For the area goodness factor, their performance was comparable at a Reynolds number of 500, with circular fins outperforming after this point, achieving a 1.8-fold advantage at a Reynolds number of 3000. In terms of the volume goodness factor, both types of fins performed similarly up to a Reynolds number of 1000. Beyond this threshold, circular offset fins demonstrated a 1.3-fold improvement at a Reynolds number of 3000, underscoring the potential of the novel core geometry for compact heat exchanger applications.

Mitigation of fouling with swirling flow induced in 3-D double-sided straight channel for printed circuit heat exchanger

Fouling should be considered in the design of a printed circuit heat exchanger (PCHE) for industrial applications. The swirling flow, which is known to mitigate fouling in heat exchangers, can incorporate this aspect; however, realizing these flow characteristics in compact heat exchangers such as PCHE is difficult. Thus, this study proposed a three-dimensional (3-D) designed PCHE channel. To induce swirling flow, it was designed to face two semicircular straight channels with angles such that the interaction between the mainstreams in different flow directions induced a swirling flow. Compared to conventional two-dimensional (2-D) PCHE channels (straight, zigzag, and airfoil channels), the swirling flow induced in the proposed 3-D PCHE channel uniformly increased the wall shear stress while minimizing flow separation or recirculation. This minimized the low wall shear stress that was more likely to be fouled. A comparative evaluation of the thermal-hydraulic performance of the investigated channels was conducted by comparing the volume goodness factors under the equal hydraulic diameter. The proposed 3-D channels exhibited the potential to mitigate fouling, as well as a thermal-hydraulic performance comparable to that of conventional 2-D PCHE channels. Therefore, the proposed 3-D channel can be suggested as an advanced PCHE design option for high thermal-hydraulic performance and mitigation of fouling. Furthermore, because the swirling flow is known to mitigate fouling in heat exchangers as well as the heat transfer deterioration of sCO2, a double-sided straight channel with swirling flow is expected to be competitive.

Enhanced Air-Flow Forced Convection Through Metal Foams: Contrasting Compressed and Uncompressed Foams

Abstract The influence of complex pore architecture, its characteristic length, and the contrast between compressed and uncompressed open-cell foam structures in forced convection are explored experimentally. Air-flow (Pr ∼ 0.71; 300 < Re < 10,000) data is presented and a critical issue of the appropriate definition of the hydraulic diameter, especially with foams of different pores/inch (ppi) and compressions, is addressed. Instead of the usual characterization, fin theory is applied and for this, the foam void volume structure is precision mapped by micro-CT scans. The veracity of defining the hydraulic diameter as 4× void volume divided by wetted area is supported by forced convection heat transfer results for different uncompressed and compressed metallic (aluminum) foam cores. All foams promote higher heat transfer coefficients, albeit accompanied with greater pressure drop. While the latter increases with foam ppi and compression (decreasing porosity), the former has a more complex interplay with these factors along with surface area changes and ligament fin effects. This scales with thermally effective surface area density βe (product of area density and overall fin effectiveness), and the overall convective-conductance of the foam (product of empty-duct-based heat transfer coefficient ho and βe) increases. The consequent enhancement, when evaluated by a modified volume goodness factor figure of merit, shows that the 40 ppi compressed foam (×3-in-x) performance is the highest (∼ 15–45 times an empty duct for the same fan power) with significant reduction in the volume of a heat exchanger.

Numerical investigation of louver edges effect on the performances of louvered fin compact heat exchanger

The rectangular channel louvered-fin compact heat exchanger (LFCHE) is the most efficient type that has been served in a radiator. However, with this type of heat exchanger, the pressure drop rises by three to four times as the heat transfer increases, which results in decreasing performance. This research is aimed to numerically investigate the louver edges (vertical, inclined, and horizontal) effect on LFCHE performance at different louver angle (θ) with air inlet velocities ranging from 1 to 30 m/s. A total of twelve models are made and simulated. The result revealed that the horizontal edge decreases the pressure drop up to 24.2% with a 1.01% increase in outlet air temperature over the base model (inclined edge). Thus, louver edge has design which results in higher and lower effect on pressure drop and temperature change, respectively. The research investigated the effects of louver edges using different performance evaluation criteria. At 10 m/s (Relp = 972.33) the horizontal edge increases the volume goodness (jf) factor up to 21.49% over the base model. Similarly, the horizontal edged fins resulted in maximum increment of jf-factor by 22% and 25% as compared with inclined edge for louver angles θ of 24 ° (at low Relp) and 20 ° (at high Relp), respectively. Generally, the horizontally edged LFCHE is proven to have higher performance in cooling the coolant with a minimum air side pressure drop.

Investigation of heat transfer and pressure drop characteristics in metal-foam filled channels in a plate heat exchanger: A comparative experimental study

An experiment was conducted on a single-phase system using water as the working fluid in a Gasket Plate Heat Exchanger (GPHE). The copper metal foam was employed on the corrugated profile in this experiment. The experiment was calibrated using iterative multiple linear regression analysis to find the coefficient of heat transfer on the hot water side for the given heat exchanger with a 60° corrugation angle. A comparative study was carried out between channels that were plain and modified with metal foam. The analysis focused on various factors, including the heat transfer coefficient, frictional pressure drop characteristics, pumping power, and volume goodness factor. The experiments were performed within a Reynolds number range of 200 to 1000, with the hot and cold water temperatures set at 60 °C and 30 °C, respectively. The experiments used copper metal foam with 50 pores per inch (PPI). The foam had a porosity ranging from 0.6 to 0.9, with a pore size of 1 mm. The Nusselt number for the modified GPHE was 1.97 times higher than that of the plain GPHE. Additionally, the frictional pressure drop for the modified heat exchanger was 1.89 times higher than that of the plain heat exchangers. The rate of frictional pressure drop increases at higher Reynolds numbers was higher than the heat transfer coefficient increase for both the plain and modified GPHE. The modified plate heat exchanger shows superior thermal performance compared to a plain GPHE at any given friction power conditions. Additionally, using metal foam-filled channels in contrast to plain corrugated plate channels suggests that the modified GPHE can achieve a more compact design for the same heat-duty application.

Numerical and experimental investigation of additively manufactured shell-lattice copper heat exchanger

Triply periodic minimal surface (TPMS) shell lattices have superior heat transfer properties due to their staggered channels. Based on these structures, a series of TPMS heat exchangers (HEs) are fabricated and investigated. However, the existing research is mainly limited to the performance investigation of HEs based on low-thermal-conductivity materials or the simulation study of the representative parts. In this study, we successfully fabricated a pure copper TPMS HE and performed a comprehensive numerical analysis. Three HEs, including Copper TPMS, SS316L TPMS, and SS316L plate were studied and compared to reveal the mechanism of their performance differences. Numerical analysis showed that TPMS HEs owned more uniform temperature and velocity fields than plate HE. The calculated heat-exchange effectiveness of the copper TPMS HE is about 58%–96% higher than that of SS316L plate HE, while the measured value of that of SS316L TPMS HE is about 38%–48% more than that of SS316L plate HE, respectively. The convective heat-transfer coefficient of copper TPMS HE is approximately 2.16–2.69 times that of SS316L plate HE and 1.17–1.33 times that of SS316L TPMS HE. The volume goodness factors of copper TPMS and SS316L TPMS HEs are about 1.49–1.87 and 1.2–1.41 times that of SS316L plate HE, respectively. The volumetric heat-transfer coefficient of copper TPMS HE is much better than that of metal plate HE and approximately 18–25 times that of the polymer TPMS HEs. This study indicates that the pure copper TPMS HE is a good candidate for next-generation HEs.

The thermo-aerodynamic performance of turbulent channel flow over dimples of different sizes

Dimples were introduced as a passive method for heat transfer enhancement and a potential drag reduction tool. However, besides the flow parameters, dimples have several design parameters that control their thermal and dynamic performance. To find the optimal design to improve dimples' performance, each parameter's effect has to be investigated. In this study, we show the effect of different dimples' sizes and flow Reynolds numbers on heat transfer and drag performance of a turbulent channel flow. Wall-resolved Large Eddy Simulation has been used to simulate the flow over the dimples fitted only on the bottom wall of the channel. The flow is simulated over three different sizes with dimensionless diameters D+=2.5, 4π/3, and 5 along with three different friction Reynolds numbers Reτ ≅180, 395, and 590. The dimples are arranged in a staggered form with smooth rounded edges of radius equal to half dimple's base radius along with constant maximum allowable coverage ratio and depth-to-diameter ratio of 5%. The thermo-aerodynamic performance of the cases under study shows an increase in drag for all the cases but accompanied by heat transfer enhancement. The thermo-aerodynamic efficiency, represented in area and volume goodness factors, shows an increase up to around 2%, and 6.8% compared to the flat channel, respectively, with the area goodness factor to be affected by the dimple size more than Reynolds number.

Designing a Turning Guide Vane Using CFD for an Economizer of a Non-Furnace Boiler

Non-furnace boilers can improve the efficiency of industrial once-through boilers. However, temperature non-uniformity occurs in the economizer connected vertically to the boiler. Heat transfer performance is degraded by temperature non-uniformity. To solve this problem, a corbel was installed on the side wall of the economizer, and a baffle was installed on the transition duct. Consequently, although the thermal efficiency of the boiler was improved, significant temperature non-uniformity was still observed in the area upstream of the economizer. To address this issue, this study designed a turning guide vane (TGV) at the economizer inlet using computational fluid dynamics (CFD). First, CFD was performed for a case without a guide vane and a case with an existing baffle installed. By analyzing the streamlines obtained using CFD, two TGV designs were proposed. In the first design, guide vanes were installed along the desired streamline, and the concept of the existing TGV was followed. In the second design, an attempt was made to minimize the pressure drop by arranging guide vanes at the inlet. Both designs reduced the standard deviation of temperature by more than 30% and improved the volume goodness factor by 25%.

Airside thermal–hydraulic performance evaluation of flue gas coolers for waste heat recovery

H-type finned tubes and integrally-molded spiral finned (IMSF) tubes are widely used in flue gas coolers for waste heat recovery, but it is difficult to design an efficient flue gas cooler in actual engineering by experience due to lack of a general factor to evaluate the thermal–hydraulic performance of different types of finned tube heat exchangers. Based on the correlations of the Nusselt Nu, the Colburn factor j, the friction factor f and the ratio Q/Wp, this paper proposed a comprehensive performance evaluation method to evaluate the thermal–hydraulic performance of different types of finned tubes, which includes the power consumption goodness factor (FQ/W) and volume goodness factor (FQ/V). The reliability of the evaluation method was verified through real engineer design. The thermal–hydraulic performance of the H-type finned tube bundle and IMSF tube bundle was obtained through computational fluid dynamics simulation using periodic physical models, and evaluated using the general evaluation method. The results show that the power consumption for H-4 and IMSF-3 is almost identical with the same heat transfer rate, but the compactness of IMSF-3 is better than that of H-4. The findings can guide the design and optimization of flue gas coolers.

Optimization of the thermal-hydraulic performance of zigzag-type microchannel heat exchangers using asymmetric geometry

• Experiments study were conducted in MCHEs with asymmetric zigzag flow channels. • Nusselt number and friction factor correlations were obtained experimentally. • Thermal-hydraulic performance of MCHE with asymmetric configuration is enhanced. Experimental studies of a microchannel heat exchanger (MCHE) assembly with asymmetric zigzag flow channels on the hot and cold sides were conducted to investigate the water-to-water heat transfer and flow resistance characteristics. Compared to the cold side, the hot side flow channels were designed with a larger hydraulic diameter, resulting in fewer flow channels but a larger heat transfer area. Nusselt number correlations were established by fitting the heat transfer experimental data conducted in different Reynold and Prantl numbers. Similarly, the friction factor correlations were established by fitting the flow resistance data conducted separately to eliminate the uncertainties associated with heat transfer and heat dissipation. The overall thermal-hydraulic performance of the MCHE with symmetric and asymmetric structures was compared using the volume goodness factor and the area goodness factor. The comparison results indicate that the MCHE with asymmetric structure is superior to the MCHE with symmetric structure in terms of volume, weight and area effectiveness, and the higher the working temperature, the better the superiority. Specifically, within the experimental range of this study, the maximum volume goodness factor and area goodness factor of the asymmetric configuration are 3.35 and 2.72 times that of the symmetric configuration. This paper demonstrated a new method for optimizing the overall thermal-hydraulic performance of MCHEs with zigzag flow channels, that is, to adopt asymmetric structure on the hot and cold sides.

Wet-dry thermohydraulic performance comparison on fin-and-tube geometries

Condensation on the surface of a heat exchanger takes place in several engineering applications, involving important energy consumption and a shift in the thermohydraulic characteristics from those observed under dry conditions. In this study, the condensation rate of six fin-and-tube geometries is numerically determined when saturated air is conducted through these surfaces. The condensation process is enabled by programming a function at the solid–vapor interface on commercial software. A thermohydraulic performance comparison using heat transfer, condensation rate, fin efficiency, Compactness factor, Volume Goodness Factor, and pressure drop is presented to give an insight into the geometry selection. Results show that the geometry increases the heat transfer in the latent heat transfer proportion under constant inner tube surface temperature conditions. Depending on the channel blockage percentage, the water retention on the surface might significantly contribute to the pressure drop. The geometries with better performance under dry conditions show a more significant condensation rate.

Experimental Study on Flow and Heat Transfer Characteristics in the Circular-Arc-Shaped Flow Channel

Different parameters of the circular-arc, trapezoidal and equal cross-section-shaped flow channels were analyzed, and the core volume goodness factor was used for the comparison of the three different types of flow channels. During the experiment, the Reynolds number (Re) on the air side ranged from 1200 to 5100. The results showed that the overall heat transfer performance of the three channels in this paper are circular-arc, trapezoidal and equal cross-section in order from good to bad. The overall heat transfer enhancement performance of the circular-arc flow channel is the best, which is 9–26.2% and 3.6–11.8% higher than that of the equal and trapezoidal cross-section flow channels, respectively. This showed that although the divergent flow channel structure reduces the fluid velocity in the flow process, it weakens the convective heat transfer performance in the flow channel. However, this gradually decreasing cross-sectional area improves the downstream heat transfer area and reduces the pressure drop in the flow process, thus promoting the overall heat transfer performance. With the increase in the circular radius (R), both the j and f factors increase, and the highest overall heat transfer performance is obtained at R = 300 mm. The convective heat transfer coefficient increases with the decrease in the inlet height.

Numerical investigation of the effect of chevron angle on thermofluids characteristics of non-mixed and mixed brazed plate heat exchangers with experimental validation

Effect of chevron angle on thermofluids characteristics of Brazed Plate Heat Exchangers (BPHEs) are studied experimentally and numerically. The simulations include the effects of brazing joints and inlet/outlet port distribution that were normally overlooked in the existing literature. Four types of non-mixed BPHEs are considered with various chevron angles: L (35°), M (50°), H (65°), and LH (35°/65°). These four types of non-mixed BPHEs are combined in order to produce four types of mixed BPHEs: L+M, M+H, L+H, and LH+H. Results show that rise of chevron angle leads to the augmentation of Nusselt number and friction factor. Hence, type H and type L have the maximum and the minimum Nusselt numbers and friction factors among all non-mixed and mixed BPHEs. However, type H has the worst performance based on volume goodness factor method, while type M has the best performance among all modeled BPHEs followed by type L+M. Detailed flow study illustrates that rise of chevron angle leads to change in flow pattern from chevron angle direction to zig-zag or straight direction, which causes increase in heat transfer rate and pressure drop. Correlations are developed for Nusselt number and friction factor of non-mixed and mixed BPHEs in a wide range of Reynolds number between 50 and 10,000 with mean deviations of 9%.

Numerical investigation of heat transfer and pressure drop characteristics in an offset strip fin heat exchanger

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f 1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing.

Pressure loss and heat transfer characteristics in a dimpled channel with crescent-shaped protrusion

Numerical simulations were conducted to study the flow and heat transfer characteristics of the dimpled channel with a protrusion. The protrusion was located upstream of the dimple to enhance the flow mixing inside the dimpled channel. The height of the protrusion, h, and the diameter of the protrusion, d, are the variables considered in the present study. The ratio of the height to the diameter of the protrusion, h/d, was varied in the range of 0.2 to 0.4. A direct numerical simulation (DNS) was performed with a Reynolds number of 2800 and a Prandtl number of 0.71 on a total 10 geometries, including a general dimpled surface. Flow and thermal characteristics were analyzed by the time-averaged flow and thermal fields and the local Nusselt number distribution according to the configurations of the dimpled channel. The normalized Fanning friction factor, f/f0, Colburn j factor, j/j0, and volume goodness factor, Gv/Gv0, were calculated to evaluate the performances according to the configurations of the dimpled channel in terms of the pressure drop, heat transfer rate, and compactness of the heat exchanger. The volume goodness factor, Gv, was 27% larger in the case of h = 0.2 and d = 1.0 (h/d = 0.20) than that of a general dimpled surface.

THERMAL PERFORMANCE IN A PIN FIN-DIMPLE/PROTRUSION DUCT WITH DIFFERENT OPTIMAL OBJECTIVES

In the present study, the optimal objective effect on the thermal performance of a rectangular duct with pin fins and dimples/protrusions is introduced. Four different optimal objectives are selected (entropy generation, entransy dissipation, enerty, and volume goodness factor). The baseline k-u turbulence model is applied to solve the governing equations. The multi-island genetic algorithm (MIGA) is used to find the optimal solution. The results indicate that the thermal performance is sensitive to the optimal objective. By using the dimple/protrusion configuration, the Nusselt number is increased remarkably in the pin-finned duct. Using the volume goodness factor as an optimal objective, the Nusselt number and friction factor reach their highest values due to the greatest strength of the horseshoe vortex. An optimal objective of enerty produces a minimal increase in the Nusselt number. A relatively low friction factor is found in the cases that use entransy dissipation and enerty as optimal objectives. (Less)

Effect of Fin Type on Performance of Compact Heat Exchangers with Mini-Channel

A comparative investigation is carried out to reveal the effect of plate-fin type variation on the performance of compact heat exchangers (CHX) with a mini-channel flat tube. The CHX prototypes with plain, louver, and offset strip fins with the same frontal area are tested in the same air tunnel under the same experimental conditions to provide a better comparison. Besides the typical performance measures namely Colburn j-factor, friction, and volume goodness factors, some rarely chosen measures are considered as well, such as the core volume goodness factor to evaluate the performance of the prototypes from all aspects. Due to the nature of the mini channel flat tubes, the flow depth is very narrow and one of the targets is to understand the importance of the fin-type on the performance in such a short flow depth. As regards to the outcomes, the CHX with plain fin shows better performance when it is evaluated by the typical approaches which is presented with respect to Reynolds number but when the compactness is considered in performance evaluation, CHX with louver fins achieves higher heat transfer indexes than other fin geometries.

Investigation on Thermal-Hydraulic Performance in a Printed Circuit Heat Exchanger with Airfoil and Vortex Generator Fins for Supercritical Liquefied Natural Gas

In this study, the thermal and hydraulic performances of six different printed circuit heat exchanger (PCHE) configurations with supercritical liquefied natural gas as the working fluid are studied by a numerical method. Firstly, the thermal and hydraulic performances of the PCHE with airfoil fins are investigated at different operating pressures, which indicate that the PCHE with airfoil fins has better thermal performance but worse hydraulic performance when it operates at higher pressure condition. Furthermore, the effects of different PCHE configurations on the thermal and hydraulic performances are analyzed in detail. The results show that delta vortex generators (VGs) arranged upstream the airfoils can provide better thermal performance than VGs arranged downstream the airfoils, and the thermal performance of the common-flow-up configuration is not always better than the common-flow-down configuration. Finally, the overall heat transfer performance of PCHEs is evaluated by the volume goodness criterion under the same mass flow rate. The results show that the straight channel PCHE with front common-flow-up delta VG and airfoil fins has the best volume goodness factor among the six PCHE configurations.

Analysis of heat transfer and flow characteristics in typical cambered ducts

The heat transfer and flow characteristics of the air-water cross flow over cambered ducts were experimental and numerical investigated. The sequence of their Core Volume Goodness Factor (CVGF) is cosinoidal, parabolic, circular, trapezoidal and rectangular ducts successively from superior to inferior. Cambered ducts have more uniform temperature difference distribution than the equal cross section duct, and it has the minimum temperature difference in inlet and outlet of the cosinoidal duct. With the optimal overall heat transfer performance, the cosinoidal duct is superior to that of the rectangular duct by 7.3%–28.1%. In the cosinoidal duct, the smaller the amplitude is, the better the heat transfer performance is. The thickness of the thermal and velocity boundary layers adjacent to the wall surface decreases constantly with increased Reynolds number. In the near wall region, n = 5um, the main heat transfer area is the peak and middle areas, but with weaker heat transfer performance in the trough region. Although gradually expanding cambered duct slows down the flow velocity, the structure form decreases the pressure drop loss during the flow process. While improving the convective heat exchange capability of the upstream, the heat transfer area of the downstream is also improved to boost the overall heat transfer performance.

COMPUTATIONAL INVESTIGATION OF CURVATURE EFFECTS ON JET IMPINGEMENT HEAT TRANSFER AT INTERNALLY COOLED TURBINE VANE LEADING EDGE REGIONS

This study is carried out by using numerical simulations to investigate the effect of target surface curvature and the nozzle-to-target surface distance on the flow structure and heat transfer characteristics in a pin-finned double-wall cooling structure. The flow is directly impinging on the target surface and is disturbed by the pin fins, and then released from the film holes after passing the double-wall chamber. The ratio between the radius of the concave outer surface and the chord length of the concave outer surface is varied from 0.500 to 1.300 and the ratio between nozzle-to-target surface distance and diameter of impingement hole is ranging from 0.5 to 2.0. The Reynolds number is between 10,000 and 50,000. Results of the flow structure in the chamber, heat transfer on the target surface, and friction factor of the pin-fi nned channel are included. It is found that an increase of the target surface curvature has signifi cant effects on the flow structure and thus the heat transfer on the target surface is augmented. The Taylor-Gortler vortices near the pin fins are also influenced by the target surface curvature. On the other hand, the nozzle-to-target surface distance influences the jet impingement and the vortices, which are generated by the curvature, remarkably. It is found that the area goodness factor and volume goodness factor are improved by the surface curvature. (Less)