Fin Pitch Research Articles

Thermal and flow characteristics of a channel formed by aligned round tube bank fins stamped with curve delta-winglet vortex generators

The primary purpose of present study is to reveal the roles played by CDVGs in vectoring the airflow and breeding longitudinal vortices for enhancing heat transfer. The thermal-hydraulic characteristics of a finned aligned round tube heat exchanger with stamped CDVGs were numerically studied by using the custom code with SIMPLE algorithm in a nonorthogonal curvilinear coordinate system. Four geometric parameters including vortex generator height, radial position, peripheral position and fin pitch, were programmed to ascertain parametric effects on fin side thermal performance, and the regression formulas of Nusselt number and resistance coefficient in the fin side passage with Reynolds numbers and four geometric parameters were secured. The findings suggest that the mean Nusselt number, resistance coefficient and secondary flow strength for the novel fin with CDVGs are all prevail over that in the reference plain fin under a certain Reynolds number. The body fitted CDVGs are ideally situated for finned round tube exchanger in aligned arrangement. The action of CDVGs can not only efficiently lessen the size of recirculation area behind tube but also produce strong longitudinal vortices, accordingly heighten evidently the fin side heat transfer ability in the recirculation zone. Using the studied optimum geometric parameters can make the thermal property factor up to 1.35 under the same pumping power constraint in comparison with the reference plain fin geometry when Reynolds number equals to 3000. This study can be a real application in compact heat exchanger with finned round tubes when heat transfer augmentation is under consideration.

Heat transfer factor j and friction factor f correlations for offset strip fin and wavy fin of compact plate-fin heat-exchangers

A unique model of heat transfer factor "j" and friction factor "f" are developed for different types of fins, which are rectangular offset strip fin, rectangular wavy fin compact heat exchangers by considering the geometric variables such as plate space (Hp), fin pitch (Pf), hydraulic diameter (Dh), wave amplitude (Aa), fin length (λ), and Reynolds number (Re). The proposed j and f models provided 98% of experimental data points within ±20% and 82.3% of experimental data points within ±10% accuracy for OSF fins. Also, they provided 100% of Kays and London's experiential data points within ±5% accuracy for wavy fins. These proposed j and f models for a wide range (120–10000) of Reynolds number flows, including laminar and turbulent flows. j model provides maximum RMSPE 15% and 2% accuracy values for PFHE offset strip fins and wavy fin geometries, respectively. f model provides maximum RMSPE 17% and 3% accuracy values for PFHE offset strip fins and wavy fin geometries, respectively. Based on RMSPE and experimental data analysis, proposed j and f models were validated and better than existing models for offset strip fins and wavy fins.

Thermal and hydraulic characteristics of multiple row spiral finned tube heat exchangers

An experimental investigation for the thermal and hydraulic characteristics of a spiral finned-tube heat exchanger was performed to understand its cooling performance for a developed novel defrosting technique. Two identical spiral finned-tube heat exchangers were manufactured; one having four rows and other having five rows. Both heat exchangers tubes were arranged inline. The heat exchangers had a tube diameter of 9.36 mm, spiral fins of 23.4 mm outer diameter, and 3.6 mm fin pitch (277 fins/m). The overall heat transfer coefficient was calculated using the measured temperatures and flow rates of each stream, and utilizing the logarithmic mean temperature difference method. The air-side heat transfer coefficient was determined using the calculated overall heat transfer coefficient and the tube-side heat transfer coefficient. The air-side pressure drop across the heat exchanger was also measured using a differential pressure digital manometer. The experimental data covered Reynolds number range of 1500 to 6000 and a Prandtl number of 0.7. Empirical correlations of Nusselt number, Colburn factor and friction factor versus Reynolds number were developed using least squares regression. The results showed that there is no significant variation in air-side heat transfer coefficient for the four and five rows spiral finned-tube heat exchanger and their Colburn factor is almost constant over the tested range of Reynolds number.

Phase change material aided thermal scheming of high power LED: Effect of PCM with varying pitch of hexagonal fins

ABSTRACT The current experimental investigation focused on the 16 W Light Emitting Diode (LED) with Phase Change Material (PCM)-filled heat sinks to augment consistency, high luminous flux and heat sink with low thermal resistance. Parameters such as input power, fin pitch value and quantity of fins were varied to study the heat transfer performance of the heat sink without and with PCM. Experimental results reveal that the hexagonal heat sink having a pitch of 10 mm performed well due to the increased melting rate of PCM as compared to other heat sinks. The thermal resistance of the H-10 heat sink with PCM was observed to be 3.3 °C/W, which is 73% lower than that of the H-10 heat sink without PCM at 16 W. The junction temperature enhancement ratio of 3.625 was observed for the H-10 heat sink with PCM at 16 W power input for SCT of 90 °C.

Effect of HTF flow direction, mass flow rate and fins on melting and solidification in a latent-heat-based thermal energy storage device

Latent-heat-based thermal energy systems (LHTES) have commonly been used as a potential energy storage mode over any other mode of thermal energy storage. Many heat transfer enhancement techniques have been proposed over the past years. These techniques reduce the melting and solidification times. Most of these techniques focus on the phase change material (PCM). However, the flow direction of the heat transfer fluid (HTF) can affect the heat transfer performance and pumping power requirement of the system. In this paper, the effect of HTF-flow direction, HTF mass flow rate and addition of the fins on the melting and solidification of the PCM in a shell-and-tube type of energy storage is numerically studied. Two-dimensional transient simulations are performed with ANSYS-Fluent where the phase-change process is modelled using the enthalpy-porosity formulation. The model is verified and validated by comparing with the available experimental data. A reasonable match is observed. The validated model, is used to study the effects of various parameters, such as, mass flow rate of the HTF, and triangular fin (at a fixed fin pitch) for both charging and discharging of the PCM. Finally, an influence of flow direction on the melting and solidification time has been studied. It is found that the contribution of HTF mass flow rate, the addition of the fin and HTF flow directions respectively is 1.3-3.01%, 16.97-17.62%, and 1.3-1.77% of overall heat transfer performance. A major contribution to the enhancement of overall heat transfer of the system is from the addition of fins.

Condensation heat transfer performance in multi-fluid compact heat exchangers with wavy and strip fins

The effect of different geometrical parameters of wavy and strip fins in a three-fluid plate-fin compact heat exchanger on the condensation heat transfer in the middle heat exchanger has been experimentally investigated. The three-fluid heat exchanger consisted of three heat exchangers with strip and wavy fins. In the examined system, the hot and cold fluids flowed through the adjacent heat exchangers (strip channels), while the middle heat exchanger (wavy channels) was occupied with a single-component two-phase flow (condensed vapor). The Nusselt number, the friction factor, the heat transfer surface contribution between the middle heat exchanger and each of the adjacent heat exchangers, and the thermal performance factor were calculated using the measured data at the inlets and outlets of the heat exchangers, and by using the thermal balance equations between the fluids passing through the heat exchangers. In the examined heat exchanger, the hot and cold flows had a cross-direction with the two-phase fluid flow. The two-phase Reynolds number, the vapor quality, and the heat transfer surface contribution of the middle heat exchanger with the adjacent heat exchangers were 50–4800, 0.1–0.67, and 0.19–0.7, respectively. The results show that the two-phase flow pattern in the wavy channels of the middle heat exchanger is stratified and wavy. According to the findings, a higher thermal performance factor is observed when the ratio of the wavy channel heat transfer surface to the heat transfer surface of the cold or hot flows is closer to 1. Also, with higher wave amplitude to wavelength ratios, lower pitch to height ratio of the fins, the lower wavelength to the fin length ratios, and lower fin pitch to wave amplitude ratios are obtained a higher thermal performance factor.

Experimental and numerical investigation on natural convection heat transfer characteristics of vertical 3-D externally finned tubes

Tubular heat exchangers for natural convection can be found in many industrial applications. In order to develop the high-efficiency natural convection radiator, the heat dissipation characteristics of vertically oriented 3-dimensional (3-D) finned tubes under the condition of non-forced convection were studied experimentally. The airflow and temperature distribution outside the tubes were analyzed by computational fluid dynamics. Results showed that the 3-D finned tube with fin height of 7 mm achieved the highest Nusselt number, which was up to 207% higher than that of a smooth tube. Nusselt numbers increased with the increasing of the fin height and the decreasing of the axial fin pitch, but were minimally affected by fin width and circular fin pitch. For comparison, the most important fin geometric parameter that affects the heat dissipation is the fin height. Finally, an empirical correlation for predicting Nusselt number was obtained based on the experimental data, which can be used in practical design.

Statistical analysis and shape optimization of a finned corrugated heat exchanger using RSM

The effect of geometry on the performance of a corrugated double-pipe heat exchanger with a hot inner tube was thoroughly investigated. The optimized exchanger geometry was determined by the Response Surface Methodology (RSM). Firstly, heat transfer parameters were numerically obtained using the finite volume method for various hot tube geometries, namely spiral, circular, cylindrical, spherical, and close-packed semi-cylindrical winglets. The maximum thermal performance was exhibited in Re = 400 for spiral fin, equal to 1.82. Secondly, the spiral inner tube was modeled to analyze the number of fins and the fin pitch. The RSM was subsequently employed to analyze for different velocities various geometries featuring 0–4 fins and fin pitches in the range of 300 mm to 600 mm. Also, to enable a more comprehensive application of the results, a statistically obtained accurate relation is presented for the convective heat transfer coefficient in terms of the number of fins, fin pitch, and flow velocity. By performing optimizations using various geometries with different boundary conditions for the first time, this article can serve as a solid base for heat exchanger selection.

Performance investigation on an air source heat pump system with latent heat thermal energy storage

This paper proposes an air source heat pump (ASHP) system integrated with a latent heat thermal energy storage (LTES) unit based on a specially-designed heat exchanger, condensing heat storage unit, to further improve system performance in cold region. The innovation of this device is that heat is transferred directly between refrigerant and phase change material (PCM), which significantly reduces heat loss. Experimental investigation on thermal performance of the system is carried out. Besides, a mathematical model of condensing heat storage unit is developed to investigate charging/discharging characteristics and validated by experimental data. Experimental results show that heat storage capacity reaches 31.83 kWh and average heat release power is 4.73 kW. Simulation results indicate that both smaller fin pitch and larger fin thickness accelerate the melting rate of PCM, but variations of tube diameter show little impact on it. In order to maintain heat release power, circulating water flow rate should be increased with discharging time. Three-stage PCM improves both energy and exergy performance compared to single-stage PCM. COP improvement could reach 4.01% and overall exergy efficiency is increased by 4.65%. Therefore, ASHP system combined with LTES unit is a potential approach to expand its application under extremely low temperature.

Fluid elastic instability and vortex induced vibration parameters in finned tube arrays with P/D ratio 1.79

PurposeThis paper aims to analyze the effect of fin geometry on mechanisms of flow induced vibration. Finned tube arrays are used in a heat exchanger to increase its efficiency. Therefore, it is necessary to investigate the effect of geometric parameters of the fin fluid elastic instability and vortex shedding. In this paper, the effect of fin height, fin density and tube pitch ratio for parallel triangular tube array on fluid elastic instability and vortex shedding is analyzed.Design/methodology/approachExperimental analysis was carried out on a parallel triangular finned tube array with a pitch ratio of 1.79 subjected to water crossflow. The experimentation aims to study fluid elastic instability and vortex-induced vibration mechanism responsible for flow induced vibration for finned tube array. A fully flexible finned tube array of the copper tube was used with its base diameter of 19.05 mm and thickness of 2 mm. Over the tube surface, crimped fins of height 6 mm and the same material are welded spirally with fin density 8.47 mm and 2.82 mm. Experimental analysis was carried out on a test setup developed for the same. The results obtained for the finned tube array were compared with those for the plain tube array with the same base tube diameter.FindingsFor parallel triangular tube array of copper material, test results show that critical velocity increases with an increase in fin pitch density for low pitch tube array. Before the occurrence of instability, the rate of growth in tube vibrations is high for plain tubes compared to that with fin tubes. The results based on Owen’s hypothesis show vortex shedding before the occurrence of fluid elastic instability. The effect of fin geometry on vortex-induced forces is analyzed. For the tube array pattern understudy, the values of Conner’s constant K for coarse fin-tube and fine fin tube array are obtained, respectively, 6.14 and 7.25.Originality/valueThis paper fulfills the need for research on the effect of fin geometry on fluid elastic instability and Vortex shedding on a tube array subjected to water cross flow when the pitch ratio is less than two, i.e. with a low pitch ratio.

A Comprehensive Study of Nanosheet and Forksheet SRAM for Beyond N5 Node

SRAM bitcell area reduction, lower SRAM parasitic resistance, and higher drive strength are necessary to continue with technology scaling. Nanosheet (NSH) technology improves SRAM cell write-ability by having 50 mV more write trip point (WTP) than FinFET (FF) SRAM due to reduced bit line (BL) resistance (due to wider metal CD) and more drive current strength (more than 15%) than FF for the same leakage. However, due to higher bitcell area (20% larger), BL, and word line (WL) parasitic capacitance than FF, NSH SRAM would not compete with FF SRAM in terms of the read delay (26% more delay) and energy at the 3-nm technology node. PFET to NFET (PN) spacing, composed of gate cut, gate extension, and Fin pitch in an SRAM bitcell, is critical for SRAM cell height because it can take ~46% of the 111 SRAM total cell height. The forksheet (FSH), achieving extremely scaled PN space in SRAM bitcell due to device structure with limited additional processing complexity, reduces the SRAM bitcell area. As a result, BL and WL parasitics reduce and improve the SRAM read delay and stability. FSH SRAM saves 6% area benefit and achieves 24% lesser read delay than FF high density (HD) SRAM.

Field synergy analysis for heat and mass transfer characteristics in adsorption-based desalination and cooling systems

Adsorption-based desalination and cooling system has gained particular interests for low-grade heat harvesting. In this study, field synergy analysis is conducted to illustrate the complicated heat and mass transfer characteristics in an adsorption-based desalination and cooling system with finned-flat beds via a dynamical three-dimensional computational fluid dynamics model. Two field synergy angles α and β reflecting the synergy effect of heat transfer and flow resistance with the adsorption driving force are examined. Results illustrate that smaller α and β result in better adsorption performance. Furthermore, guided by the field synergy analysis, adsorbent bed configurations (fin diameter, fin pitch, fin shape, and fin arrangement) are optimized. The fork-row arrangement results in a higher SCP and SDWP than that of the in-line arrangement. With the fin pitch of 20 mm and fin diameter of 12 mm, the system with fork-row arrangement demonstrates a SCP of 0.363 kW/kg and SDWP of 12.5 m3 per ton silica gel per day, which is 6.6% higher than that of the in-line arrangement as the field synergy parameter between heat transfer and the driving force factor (α) is more predominant at a relatively smaller fin pitch.

Influence of multi-structure optimization on the comprehensive performance of micro-cylindrical combustor inserting with spiral fin by using grey relational analysis and analysis of variance

Targeted at improving the energy output of thermophotovoltaic system, a novel micro combustor with spiral fin is proposed. The multi-structure factors of spiral fin concluding spiral fin length, spiral fin pitch, spiral fin number and spiral fin opening size impact the thermal and energy performance of micro combustor are investigated in this study. The method of Taguchi experimental design is introduced to determine the testing cases, Orthogonal design table L16(44). Then, grey relational grade is adopted to obtain the influence of four factors on performance parameters. The evaluation indexes of each testing case include mean outer wall temperature, outer wall temperature uniformity and pressure drop, which are closely connected with the thermal and energy performance of micro combustors. Moreover, the results calculated by grey relational grade are verified by analysis of variance. Results show that the optimal combination of the structure is micro combustor inserting with spiral fin, in which the spiral fin is 16 mm, the spiral fin pitch is 1.57 mm, the spiral fin number is 8 and spiral fin opening size is 0.2 mm. Meanwhile, the spiral fin length has the greatest impact on the comprehensive performance of the micro combustor, with a contribution of 48.522%.

An experimental investigation of the air-side performance of crimped spiral fin-and-tube heat exchangers with a small tube diameter

The performance of crimped spiral fin-and-tube heat exchangers (CSFTHXs) with a small tube diameter at a Reynolds number of 1500-6400 based on the tube's outer diameter is experimentally investigated. An important factor in this study is the small-diameter tubing, with an outer diameter of 9.53 mm. Copper tubes and aluminum fins are assembled as CSFTHXs. Test sections consist of a fin thickness of 0.5 mm, two tube rows, and various fin pitches and outer diameters of 3.18-6.35 mm and 23.0-28.5 mm, respectively. Hot water and fresh air are used as the working fluids. The effects of fin pitch and fin outer diameter on the heat transfer characteristics and friction factor (f) are also studied. The results show that the fin's pitch and outer diameter have little effect on the Nusselt number (Nu) and Colburn factor (j). On the other hand, they have a significant effect on the f. Furthermore, correlations between the Nu, j, and f for a CSFTHX with a small tube diameter are developed and proposed for designing heat exchangers in the thermal industry.

Heat Transfer Correlations for Star-Shaped Fins

Star-shaped fins are a newer type of fin for which correlations for heat transfer and pressure drop do not yet exist in the literature. Therefore, correlation equations for air-side heat transfer and pressure drop in a finned heat exchanger with star-shaped stainless-steel fins in staggered arrangement were developed in this work. To obtain these correlations, a numerical analysis of the basic heat exchanger geometry and another 21 variants of heat exchanger geometry was performed using computational fluid dynamics, and then the results of laboratory tests of a model of heat exchangers with star-shaped fins were used. In the numerical analysis, the fin pitch, the fin thickness, and the air velocity at the inlet to the heat exchanger were varied. The Nusselt (Nu) and Euler (Eu) numbers were determined for each variation analyzed. Initial correlations for Nu and Eu were derived using the least-squares deviation method. The correlation coefficients thus obtained were adjusted to agree with the results of the laboratory tests. The deviation of the final obtained correlation for Nu from the experimental test results was up to 10% in the range of Re < 3500, whereas for higher values of Re, the deviation was less than 2%. The Eu correlation deviated from experimental results up to 19% in the range of Re < 4000, whereas in the range of Re > 5600, the deviation was less than 1%. The correlations were valid in the range 2000 < Re < 16,000.

Experimental study of natural convection from vertical cylinders with branched pin fins

In this study, the natural convection heat transfer phenomena from vertical cylinders with branched pin fins are experimentally investigated. Experiments are conducted to measure the heat transfer rates from finned cylinders to the surrounding air at various cylinder wall temperatures, fin pitch angles, and fin heights. The experimental results indicate that the thermal resistance of vertical cylinders with branched pin fins is 20% smaller than that of conventional vertical cylinders with plate fins. The thermal resistance per unit fin volume of the former is 40% smaller than that of conventional finned cylinders. Moreover, a correlation for the Nusselt number is obtained from the calculated thermal resistance values. The error between the predictions from the correlation and experimental results is less than 20%. In addition, the effects of fin length and fin pitch angle on the thermal resistance are investigated using the proposed correlation.

A dynamic model for predicting condensation heat and mass transfer characteristics in falling film condenser

A mathematical model of falling film condenser is developed to predict the dynamic response of shell-and-tube condenser having R1233zd(E) as refrigerant for high temperature heat pump systems. The model incorporates a vapor-mass-flux ratio, which includes the relative velocity slip between vapor and liquid to examine the performance of tube bundles in falling film condensers. Discretization of governing equations and control-volumes method are applied to construct the dynamic model which is first validated with the well-known HTRI software in steady-state performance. The mean relative deviations are within 14.8% for temperature and 2.0% for heating capacity in steady state. The established model can be used to predict the dynamic heat transfer response to the change of operating conditions and geometric configurations of tubing. When compared to the change of inlet pressure of vapor refrigerant, the response of the condensation temperature is much slower, yielding some 1.7 times longer time to reach stable state than that of pressure. Further, various heat exchange tubes (smooth tubes and low-fin tubes with 3 different fin pitches) are examined. It is found that the heating capacity and water outlet temperature increase with the rise of fin density. Yet higher fin density also tends to reach stable state earlier. The heat transfer enhancement ratio ranges from 2.7 to 2.0 for low-fin tube with 1.3 mm fin pitch, and the enhanced tubes are more effective with the low subcooling temperature.

Experimental and numerical study on performance of hybrid refrigeration system that combines vapor compression and thermoelectric systems

As high-quality food preservation has become an important aspect of daily life, a need has developed for domestic household refrigerators with a wide refrigeration temperature range. The temperature range of domestic household refrigerators is generally above −20 °C. In this study, a hybrid refrigeration system that combined vapor compression refrigeration (VCR) and a thermoelectric refrigerator (TER) is investigated for the freezer compartment of a domestic refrigerator with a volume of 0.018 m3. Although an additional 99.5 W of electrical power is consumed, a lower temperature of −38.1 °C is experimentally achieved in the deep freezer compartment of a compact VCR–TER system, with no noise or mechanical parts. In contrast, a temperature of only −8.8 °C is obtained in a typical VCR system. A three-dimensional numerical model is applied to study the performance of the finned heat sink of the TER using FLUENT. The effects of the fin height and fin pitch on the thermal resistance and pressure drop are investigated. The results show that the thermal resistance decreases with an increase in the fin height and increases with an increase in the fin pitch. An optimized finned heat sink with a fin height of 50 mm is obtained, which has a thermal resistance of 0.05 °C/W. It has a higher cooling capacity of 53.6 W than the heat sink with the original fin height of 30 mm. The VCR–TER system has potential application to low-temperature domestic refrigeration systems with a small size and small cooling capacity.

Effect of heat transfer area distribution on frosting performance of refrigerator evaporator

The present study investigates the effect of the distribution of available heat transfer area on the thermohydraulic behavior of a typical fin-and-tube type evaporator used in a domestic frost-free refrigerator. Previous studies in the literature have not explored the effect of the number of fin rows and fin pitch distribution across the fin rows on the performance of fan-supplied evaporator geometries under frosting. The present study attempts to address this by developing a thermohydraulic model of the evaporator to predict the heat transfer rate, pressure drop and frost formation. A distributed evaporator model is developed by dividing the evaporator into individual control volumes and the balance equations are applied along with a suitable semi-empirical frost growth model to predict the rate of frost formation. Experiments were performed in a purpose-built test facility to validate the numerical model. The developed model is employed to compare different heat exchanger geometries with a constant area but varying in total fin rows and fin pitch distribution. Results show that distributing the available heat transfer area among a higher number of fin rows results in longer successive defrost intervals. However, the evaporator occupies more volume. For a given heat transfer area and fin rows, longer operating time can be achieved by selecting fin pitches that provide uniform blockage ratio across the fin rows. It is observed that for a specific fin pitch at the leading row, reducing the fin pitch linearly across the fin rows resulted in uniform blockage ratio across the fin rows.

Thermo-hydraulic and economic performance of a parabolic trough solar collector equipped with finned rod turbulator and filled with oil-based hybrid nanofluid

Parabolic trough solar collector (PTSC) is one of the best solar thermal systems for producing thermal energy. PTSC works in medium and high temperature levels, and due to their wide range of industrial applications, improving their performance is very important. In the present study, a combination of thermal oil-Al2O3−MWCNT (80%-20%) hybrid nanofluid and finned rod turbulator are employed to improve the performance of a PTSC. The Eulerian-Eulerian two-phase model is used to simulate the PTSC and assess its performance from thermo-hydraulic and economic viewpoints. Simulations are performed for different values of fin angle (γ), rod diameter (D), fin pitch (Q) and Reynolds number (Re). The performance metrics considered to evaluate the collector performance include Nusselt number (Nu), friction factor, Performance Evaluation Criterion (PEC), Thermal Efficiency Enhancement (TEE) and cost. The obtained results revealed that the use of finned rod turbulator is useful for Re less than 12,000 and should not be used in larger values of Re as it weakens the overall hydrothermal performance of the PTSC. In addition, the economic analysis revealed that the novel geometry can save 14% on material usage.