Offset Strip Research Articles

Heat transfer and friction correlations for offset strip fins relative to the offset ratio

Heat transfer and friction correlations for offset strip fins relative to the offset ratio

Heat Transfer and Friction Correlations for R134a With Offset Strip Fin Surface

Single phase heat transfer analysis of R134a refrigerant (liquid phase) has been carried out using Computational Fluid Dynamics (CFD) approach for offset strip fin. Colburn j factor and Fanning friction factor are predicted for offset strip fin. The correlations are developed at Reynolds number range of 100-15000. The effect of fin geometry (fin spacing, fin height, fin thickness and lance length) on the enhanced heat transfer and pressure drops were investigated. Colburn j factor and fanning friction factor f, correlations have proposed in terms Re and geometry parameters (h/s, t/s, t/l) for liquid refrigerant R134a in the present study. Two separate correlations have proposed for the low and high Re regions i.e. Between Re of 100-1000 and Re of 1000-15000. The numerical results are validated with experimental results, results are found in good agreement with experimental results. Variation is found less than 5%.

Developed and quasi-developed macro-scale flow in micro- and mini-channels with arrays of offset strip fins

We investigate to what degree the steady laminar flow in typical micro- and mini-channels with offset strip fin arrays can be described as developed on a macro-scale level, in the presence of channel entrance and sidewall effects. Hereto, the extent of the developed and quasi-developed flow regions in such channels is determined through large-scale numerical flow simulations. It is observed that the onset point of developed flow increases linearly with the Reynolds number and channel width but remains small relative to the total channel length. Furthermore, we find that the local macro-scale pressure gradient and closure force for the (double) volume-averaged Navier–Stokes equations are adequately modeled by a developed friction factor correlation, as typical discrepancies are below 15% in both the developed and developing flow region. We show that these findings can be attributed to the eigenvalues and mode amplitudes, which characterize the quasi-developed flow in the entrance region of the channel. Finally, we discuss the influence of the channel side walls on the flow periodicity, the mass flow rate, as well as the macro-scale velocity profile, which we capture by a displacement factor and slip length coefficient. Our findings are supported by extensive numerical data for fin height-to-length ratios up to 1, fin pitch-to-length ratios up to 0.5, and channel aspect ratios between 1/5 and 1/17, covering Reynolds numbers from 28 to 1224.

Experimental study on low pressure heat transfer properties of water evaporator with screen separation element

Water evaporator is often used in spacecraft thermal management as heat sink. In a water evaporator, heat is transferred from the microchannels of cooled glycol liquid to the external water, which causes the phase transition of water near external fins. Due to the severe weight requirements of hypersonic vehicles, it is very important to study the heat transfer performance and water utilization of water evaporator. The present study experimentally investigated the boiling heat transfer of water evaporator on external rectangular fins (RF) at low pressure, and the heat transfer of cooled glycol liquid in microchannels with offset strip fins (OSF). At the same time, the experiment explored the effects of three types of screen devices on the heat transfer performance and water utilization efficiency of water evaporators. The heat transfer experiments of water evaporator were conducted at the pressure of 11 kPa. The inlet temperature of hot glycol liquid was controlled 85 °C, and the mass flow rate were at 1500 kg/h and 2500 kg/h, respectively. The experimental results show that when the mass flow rate of ethylene glycol is the same, the water consumption of the water evaporator significantly decreases and the water utilization efficiency increase with the increase of screen density, but it can weaken the boiling heat transfer performance. In addition, the empirical correlation of boiling in low-pressure is modified, and the maximum deviation is within ±10%. The screen separator element and the new modified correlation provide a reference for the design of water evaporator.

Improvement of Plate-Fin Heat Exchanger Performance with Assistance of Various Types of Vortex Generator

A 3-dimensional incompressible laminar flow and heat-transfer in a plate-fin heat exchanger (PFHE) where investigated numerically in this article. The influence of mounting a longitudinal vortex generator (LVG) on the offset rectangular-triangular fin (ORT) in the PFHE, on thermal and hydro-dynamic fields are presented. The novelty of this study is by attaching a LVG to an offset strip fin (OSF) surface. The cases of study for the PFHE are established, by using a built-in rectangular winglet pair type RWP longitudinal vortex generator carried out and fitted on this fin to improve the convective heat transfer of the (ORT) fin while minimizing pressure loss. The upper and lower plates are exposed to constant heat flux and the working fluid is air where chosen under a laminar range of RE (600 to 1400). The laminar flow and heat-transfer are governed by continuity, momentum and energy equations. ANSYS FLUENT (2021 R1) is used to get the numerical results, based on the finite volume method. The performance of the VG is assessed for an optimum winglet attack angle (45°), as well as by modifying the geometrical size parameters, namely the height and placement (L) of the RWP LVG. The result shows that the Nusselt number reaches its optimum enhancement values by using a common flow up CFU built-in rectangular winglet pair type RWP VG with a height and entrance length of (h=1.25mm, L=0.5mm), by 22.23% as compared with base case configuration (ORT). Finally, a two more LVG are tested with the optimum conditions of the RWP, which they are a delta winglet pair (DWP) and trapezoidal winglet pair (TWP). In addition, the temperature fields for the primary and secondary flows were shown in contour and streamline diagrams

Multi-objective optimization design of a plate–fin water evaporator in a low-pressure environment based on the MO-SHERPA algorithm

The aim of this study was to investigate the optimal heat transfer performance and structure of airborne water evaporators in low-pressure environments. To achieve this, a multi-objective optimization design was performed on a plate-fin water evaporator with offset strip fins, operating in a low-pressure environment at an absolute pressure of 7 kPa. The multi-objective Simultaneous Hybrid Exploration that is Robust, Progressive and Adaptive (SHERPA) (MO-SHERPA) algorithm was used to optimize the structure of the plate–fin water evaporator under a low pressure of 7 kPa. There are three conflicting optimization objectives, including comprehensive performance factor (JF), entropy generation (Sgen), and weight. The optimal Pareto frontier design points were compared and analyzed based on the three evaluation indicators. The optimization results showed that compared with the initial design point, the JF increased by 32.14% and the weight decreased by 48%, which indicated that the heat exchange performance has been significantly improved, and the weight of the heat exchanger was also reduced. The internal and external flow fields of the water evaporator, including temperature, pressure, and volume fraction of vapor, were qualitatively compared to prove the optimization effect. In addition, the influence of structural parameters on the heat transfer performance of the water evaporator were analyzed. The method proposed in this study can effectively optimize the fin structural design parameters, providing valuable guidance for the structural design of water evaporators operating in low-pressure environments.

Multi-objective optimization of an offset strip fin heat exchanger for waste heat recovery in electric vehicles

To increase short driving range of electric vehicle, it is important to reduce power consumption of heat pump system. In this study, an offset strip fin heat exchanger with perpendicular flow is investigated to improve the performance of an electric vehicle heat pump using waste heat. The correlations of the Colburn and friction factor are developed using the experimental data. The simulation results are compared to the experimental results and are validated within temperature and pressure errors of 1.51% and 1.55%, respectively. A multi-objective optimization is performed to maximize the thermal–hydraulic performance of the offset strip fin heat exchanger with six independent design variables via the approximation-assisted optimization technique. The five optimal designs exhibit a 3.7% increase in the heat transfer rate and a 42.1% decrease in the pressure drop for the main simulation condition. Sensitivity analysis and parametric studies are conducted to analyze the effects of each design variable. The results reveal that the fin wrinkle angle, fin height, fin length, and fin spacing had a significant impact on the thermal–hydraulic performance of the offset strip fin heat exchanger.

Comparative analysis of flow boiling characteristics of an R290/R1270 mixture and R290 in a plate heat exchanger with offset strip fins

In this study, saturated flow boiling characteristics of R290/R1270 (65 %/35 % w) mixture and pure R290 were investigated experimentally in a plate heat exchanger embedded with offset strip fins. The experiment was carried out at three mass fluxes (G = 20 – 60 kg m−2 s−1), four heat fluxes (q = 7.5 – 15 kW m−2), three saturation temperatures (Tsat = 5 – 15 °C), and eight mean vapor qualities (xm) at increasing inlet vapor quality (xin = 0.1 – 0.8). The results showed that convection dominated the boiling process at higher xm (0.49 – 0.9), irrespective of the fact that nucleate boiling dominated at lower xm (0.15–0.49) values regardless of the working conditions. The heat-transfer coefficient (HTC) and frictional pressure drop (FPD) of R290/R1270 were strongly influenced by the range of G. R290/R1270 exhibited a higher HTC value than R290 for xm (<0.5), whereas the HTC of R290 dominated at higher xm (>0.5) values. Consequently, R290/R1270 generally performed better in the nucleate-boiling region, whereas R290 performed better in the convective-boiling region. The average HTC of the R290/R1270 mixture was 3.34 % higher than that of R290, whereas the average FPD of the R290/R1270 was 18.11 % lower than that of R290. Finally, correlations for R290/R1270 in the form of Nusselt number and the two-phase friction factor have been established, and they demonstrated high reliability with mean absolute errors of 11 % and 12 %, respectively.

Condensation of R1234yf in a plate heat exchanger with an offset strip fin flow structure for electric vehicle heat pumps

The energy-efficient plate heat exchanger (PHE) and refrigerant R1234yf, which has a low global warming potential (GWP), can be used to realize an energy efficient heat pump (HP) system for electric vehicles (EV), extending their driving range. Therefore, the characteristics of R1234yf in an offset-fin strip (OSF) flow-structured PHE are critical for heat-exchanger design. This study investigates the condensation heat transfer coefficient (C-HTC) and two-phase frictional pressure drop (2P-FPD) of R1234yf during condensation in an OSF flow-structured PHE under various operating conditions. First, a modified Wilson plot method was used to determine the multiplier (C) and Reynolds number exponential (n) for the coolant side as −0.426 and 0.494, respectively. When the heat flux (q), average vapor quality (xa), and mass flux (G) increased, the C-HTC increased, whereas it decreased with saturation temperature (Tsat). Despite the force-convective condensation flow regime, the C-HTC increment was minimal with G at lower xa owing to the lesser significance of the shear effect. Additionally, the 2P-FPD was unaffected by q but increased considerably with an increase in xa and G and a decrease in Tsat. Based on the current experimental database, empirical correlations for forecasting friction factor and Nusselt number were developed with a 91% predictability.

Flow periodicity analysis in an additively manufactured metal microchannel heat transfer device using micro-PIV

The flow periodicity in an additively manufactured microchannel heat transfer device is analysed using the micro-particle image velocimetry technique. A metal offset strip fin (OSF) microchannel is additively manufactured using laser powder bed fusion to overcome the limitations of conventional production techniques in manufacturing small complex features. This study demonstrates the capability of measuring the velocity field in an OSF microchannel up to 1 mm deep with a resolution of 10μm and a velocity uncertainty smaller than 0.5% for laminar flows with a Reynolds number below 10. Higher measurement uncertainties are encountered in regions close to the channel walls due to particle deposition. A methodology aiming to evaluate and minimise the uncertainties is presented. The experimentally obtained velocity fields are compared to a numerical simulation of the flow in the offset strip fin microchannel. The results verify that flow periodicity can be observed and the extent of the flow development region can be studied. Nevertheless, in regions with a large velocity gradient, a considerable uncertainty on the velocity measurements exists due to manufacturing imperfections.

Experimental investigation on flow boiling characteristics in offset strip fin channels under different sloshing conditions

In order to reveal the effects of sloshing movement on the performance of the plate-fin heat exchangers applied in floating liquefied natural gas platforms and environment control system of aircrafts, the flow boiling characteristics in offset strip fin channels of plate-fin heat exchangers under different sloshing conditions were investigated experimentally, covering rolling, pitching and swaying movements. The results show that, the rotational type movements enhance the transient heat transfer coefficient by a maximum of 21.1% at low vapor quality condition and weaken the transient heat transfer coefficient by a maximum of 27.7% at high vapor quality condition, while the transitional type movements enhance the heat transfer at high vapor quality. Fast Fourier transform method was used in the spectrum analysis of flow instabilities, and there are two peak frequencies caused by the inlet fluctuations, the distribution of the liquid phase and the enhanced turbulence. The time-average factors were proposed to evaluate the average heat transfer performance during the sloshing period. The ranges of sloshing time-average factors for rolling, pitching, and swaying conditions are 0.861 ∼ 1.079, 0.923 ∼ 1.061, 0.834 ∼ 1.064 and 0.994 ∼ 1.090, respectively. As the mass flux and sloshing period increase, the time-average factors trend to 1.0, and increase at the transitional sloshing movement. With the increasing amplitude, the time-average factors increase from 1 to a maximal value of 1.093. The correlations to predict the time-average two-phase heat transfer coefficients under rolling, pitching, swaying, and heaving conditions for offset strip fins have been developed, and the deviations are within ± 10 %.

Interface Capturing Flow Boiling Simulations in a Compact Heat Exchanger

Abstract High-fidelity flow boiling simulations are conducted in a vertical mini channel with offset strip fins (OSF) using R113 as a working fluid. Finite-element code PHASTA coupled with level set method for interface capturing is employed to model multiple sequential bubble nucleation using transient three-dimensional approach. The code performance is validated against experiments for a single nucleation site in a vertical rectangular channel. To assess code performance, a study on the bubble departure from the wall in a mini channel with OSF is carried out first. Contributions from the microlayer are not considered due to low heat flux values applied to the channel (1 kW/m2). The influence of surface characteristics, such as contact angle and liquid superheat on bubble dynamics, is also analyzed as well as the local two-phase heat transfer coefficient. For higher void fractions, two conical nucleation cavities are introduced in the same channel with OSF. Observed bubble characteristics (departure diameter, bubble departure frequency) are evaluated and bubble trajectories are presented and analyzed. The local heat transfer coefficient is then evaluated for each simulation. The results show approximately a 2.5 time increase in the local heat transfer coefficient when the individual bubbles approach the wall. With smaller bubble nucleation diameters, the heat transfer coefficient can increase by up to a factor of two. Thus, the current work demonstrates the flow modeling capability of the boiling phenomena in complex geometry with OSF.

Numerical Calculation of the Irreversible Entropy Production of Additively Manufacturable Off-Set Strip Fin Heat-Transferring Structures

In this manuscript, off-set strip fin structures are presented which are adapted to the possibilities of additive manufacturing. For this purpose, the geometric parameters, including fin height, fin spacing, fin length, and fin longitudinal displacement, are varied, and the Colburn j-factor and the Fanning friction factor are numerically calculated in the Reynolds number range of 80-920. The structures are classified with respect to their entropy production number according to Bejan. This method is compared with the results from partial differential equations for the calculation of the irreversible entropy production rate due to shear stresses and heat conduction. This study reveals that the chosen temperature difference leads to deviation in terms of entropy production due to heat conduction, whereas the dissipation by shear stresses shows only small deviations of less than 2%. It is further shown that the variation in fin height and fin spacing has only a small influence on heat transfer and pressure drop, while a variation in fin length and fin longitudinal displacement shows a larger influence. With respect to the entropy production number, short and long fins, as well as large fin spacing and fin longitudinal displacement, are shown to be beneficial. A detailed examination of a single structure shows that the entropy production rate due to heat conduction is dominated by the entropy production rate in the wall, while the fluid has only a minor influence.

Saturation flow boiling characteristics of R290 (propane) inside a brazed plate heat exchanger with offset strip fins

An inclusive experimental study was conducted to explore the saturated flow boiling heat transfer coefficient (HTC) and frictional pressure drop (PDf) features of R290 in a brazed plate heat exchanger embedded with offset strip fins with an offset length of 2 mm, fin thickness of 0.3 mm, and fin height of 2 mm. The experiment was conducted at four different saturation temperatures (Ts = 5–20 °C), three mass fluxes (G =20–60 kg m−2 s−1), four heat fluxes (q = 7.5–15 kW m−2), and eight mean vapor qualities (Xm) at increasing inlet vapor quality (0.1–0.8). The findings revealed that nucleate boiling vanquished at lower Xm values, irrespective of the working conditions, despite the fact that at higher Xm, the boiling process was dominated by convection. There was a dry-out condition inside the heat exchanger at Xm = 0.42–0.63, except when G = 60 kg m−2 s−1. The result suggested that the HTC of R290 strongly depended on Xm and Ts compared with G and q. The PDf of R290 shows a strong dependence on Ts, G, and Xm, whereas it is less dependent on q. Moreover, PDf increases with an increase in G, Xm, and q values, and decreases with an increase in Ts. Furthermore, empirical correlations for Nusselt number and friction factor, which were developed for R290, accounted for the influence of equivalent and liquid Reynolds numbers and the liquid and vapor densities with a mean absolute error of 10% and 14%, respectively.

Experimental investigation on the heat transfer behavior of water in offset strip fin channels

This paper experimentally investigates the heat transfer behavior of water in offset strip fin (OSF) channels. 18 different OSF geometries, which are divided into three groups by the ratio of the front-fin-end area of a single cell to fin thickness squared (Affe/t2), are tested under a constant heat flux. The results show that when the Affe/t2 is large, the high and close-spaced OSFs with small fin length are unsuitable for water heat transfer, while high fin density, small fin height and small fin length can improve the water heat transfer performance for the OSFs with small Affe/t2. Further analysis indicates that there is a negative relationship between the j factor and Prandtl number, as well as between the j factor and fin efficiency. The comparison between the data for water and air reveals that the large difference between the heat transfer coefficient and the heat transmittance coefficient due to the low fin efficiency of water heat transfer makes it difficult to extend air data to water. Moreover, a j correlation of water for the different OSFs is developed based on the regression analysis. The correlation provides the water j factors that fall within the 2σ confidence interval with a standard deviation of 9.63%. The present study not only provides useful data for the design and development of OSF heat exchangers, but also offers strong support for a deeper understanding of liquid heat transfer behavior in OSF channels.

Energy and exergy analysis of microchannel central solar receivers for pressurised fluids

Within the new generation of advanced central solar receivers, microchannel pressurised gas receivers are emerging as reliable and efficient alternatives to operate at high temperatures and pressures. This paper presents an optimisation and comparative analysis of different compact plate-fin type structures, constituting the receiver’s absorber panels, classified according to the type of fin arrangement inside: plain rectangular, plain triangular, wavy, offset strip, perforated, and louvred fin. A versatile thermo-fluid receiver model is implemented, allowing simple variation of characteristic geometric parameters of each structure. Exergy efficiency is chosen as the optimisation function, as it considers both heat and pressure losses.The framework of the analysis is set by the receiver’s boundary conditions, operating at the design point conditions of a solar thermal power plant. For each compact structure, the optimal configuration is determined, providing interesting findings that have not been reported in the state-of-the-art to date. Although all geometries show good thermal performance, the perforated and plain rectangular configurations demonstrate the best exergy efficiencies of 59.21% and 58.80%, respectively, favouring taller and narrower channels. This analysis methodology could be seamlessly extrapolated to other gases and working conditions, owing to the thermo-fluid model’s versatility, to reveal the optimal configuration for each case.

Experimental and numerical investigation on conjugate performance of fan and heat exchanger of helicopter oil cooling system

• The overall performance of axial fan was studied with two flowrate adjusting modes. • HEs with different fin structures and flow lengths were designed and fabricated. • Coupling performances of fan and different HEs were studied experimentally. • The flow field of oil cooling system at different air flow rate was simulated. • The performance curves obtained by two modes form a hysteresis region. In this article, a combined experimental and numerical study has been performed to investigate the operating performance of axial fan and oil cooling system. A test rig was established, and six types of plate-fin heat exchangers (HEs) with offset strip and rectangular fins and three different flow lengths of 30 mm, 60 mm and 90 mm at side were designed and manufactured. The performance of an axial fan with front guide vane was experimentally studied by two different adjusting modes: gradually increasing and decreasing air flow rate. The conjugate performances of the axial fan and different HEs were discussed in detail. Moreover, a three-dimensional (3D) model was developed to investigate the flow distribution of the system including fan and 30 mm offset strip fins HE at different flow rates. The results show that: (1) the total pressure performance curve of the axial fan under two adjusting modes could form a hysteresis region near the stall boundary. In the hysteresis region, the fan performance curves showed significant difference under both adjusting modes; (2) when the offset strip fins HE with large flow resistance is considered, the system could have two theoretical working points in the hysteresis region. For the case of HE with 90 mm offset strip fins, the flow rates of the system at two theoretical working points were 25.1 m 3 /min and 34.2 m 3 /min, and the heat transfer capacity of the HE were 23.1 kW and 27.5 kW, respectively. In the current experiment, it was found that the system operated at the point with smaller flow rate; (3) when the HE flow resistance exceeded a certain value, the boundary layer separation of the airflow could occur at the rotor blade. The separation had a small effect on the inlet airflow due to its turbulence kinetic energy was low and basically the same at each blade passage. Therefore, the system did not surge or stall at small flow rate.

Nusselt number for steady periodically developed heat transfer in micro- and mini-channels with arrays of offset strip fins subject to a uniform heat flux

In this work, the Nusselt number is examined for periodically developed heat transfer in micro- and mini-channels with arrays of offset strip fins, subject to a constant heat flux. The Nusselt number is defined on the basis of a heat transfer coefficient which represents the spatially constant macro-scale temperature difference between the fluid and solid during conjugate heat transfer. Its values are determined numerically on a single unit cell of the array for Reynolds numbers between 1 and 600 and fin height-to-length ratios below 1. Two combinations of the Prandtl number and the thermal conductivity ratio are selected, corresponding to air and water. It is shown that the Nusselt number correlations from the literature mainly apply to air in the transitional flow regime in larger conventional channels if the wall temperature remains uniform. As a result, they do not correctly capture the observed trends for the Nusselt number in micro- and mini-channels subject to a constant heat flux. Therefore, new Nusselt number correlations, obtained through a least-squares fitting of 2282 numerical simulations, are presented for air and water. The suitability of these correlations is assessed via the Bayesian approach for parameter estimation and model validation. The correlations respect the observed asymptotic trends and limits of the Nusselt number for all the geometrical parameters of the offset strip fins. In addition, they predict a linear dependence of the Nusselt number on the Reynolds number, in good agreement with the data from this work. Nevertheless, a detailed analysis reveals a more complex scaling of the Nusselt number with the Reynolds number, closely related to the underlying flow regimes, particularly the weak and strong inertia regimes. Finally, through 62 additional simulations, the influence of the material properties on the Nusselt number is illustrated and compared to the available literature.

Overall Pressure Loss and Heat Transfer Performance of Additively Manufactured Offset Strip Fins Used in Compact Heat Exchangers

Abstract Preliminary heat exchanger design relies heavily on correlations for overall heat transfer and pressure drop performance, particularly for heat transfer augmentation features such as fins. Extensive work has been performed by the research community to develop these correlations for the numerous designs. However, with the new technology of metal additive manufacturing and the resultant surface roughness, the traditional correlations and design considerations related to performance need to be adjusted. As a result, two metal additively manufactured offset strip fin heat exchanger geometries with different fin spacing are studied for heat transfer and pressure drop performance and compared with traditional correlations. Deviations between the additively manufactured geometries and previous correlations for smooth fins are found and are further amplified as the surface roughness-to-hydraulic diameter ratio is increased. Furthermore, the surface roughness from the additive process results in a constant friction factor behavior at high Reynolds numbers, which is unlike behavior observed for conventionally manufactured fins. Considerations for both the laminar and turbulent flow regimes are needed for correct performance prediction. A final offset strip fin geometry with a change in the fin spacing every third of the way through the flow path is tested. This study found that the orientation of fin spacing, wider spaced to tightly spaced or tightly spaced to wider spaced, did not have a significant effect on pressure drop or heat transfer. However, the study found a method for predicting the performance which will become important as additive manufacturing increases the complexity of heat exchanger designs.

Boiling of R290+CF3i mixture inside an offset strip fin plate heat exchanger

In this study, evaporation characteristics of mildly flammable R290 + CF3i mixture (35 % + 65 % by weight) were conducted experimentally in an offset strip fins (OSSF) embedded plate heat exchanger (PHEX). Various operating conditions, namely, saturation temperature (Tsat), heat flux (q), inlet vapor quality (xin), and mass flux (G), were considered in the range of 5–15 °C, 4–10 kW m−2, 0.1–0.8, and 40–80 kg m−2 s−1, respectively. From this study, it was found that nucleate boiling was quenched at lower xin regardless of the operating conditions, although the boiling process was led by convection at high xin. Except at higher G, there was a presence of dry-out at a mean x ranging between 0.36 and 0.50, while the two-phase frictional pressure drop increased steadily with mean x. The heat transfer coefficient was largely augmented with increments in G of 50.15 %, followed by increments in q and T of 15.1 % and 12.3 %, respectively. Similarly, the two-phase frictional pressure drop was increased by 12.3 % and 175.4 % with increases in q and G, respectively, although it diminished by 21.9 % with Tsat. Compared to R1234yf, the mean HTC of R290 + CF3i was 6 % lower with 7 % increased TP-FPD. Additionally, Nusselt number and friction factor correlations have been developed with excellent predictability of 7 % and 12 % of mean absolute error, respectively.