Smooth Tube Research Articles

Flow boiling heat transfer characteristics of zeotropic refrigerant/oil mixtures in horizontal smooth tube

In the Organic Rankine Cycle (ORC), the lubricant is inevitably mixed with the working fluid, which affects its flow boiling heat transfer characteristics in the evaporator. In this study, the flow boiling heat transfer characteristics of zeotropic fluid R141b/R245fa at different polyester oil (POE) concentrations were experimentally investigated. Meanwhile, the effects of heat flux, mass flux and vapor quality were also investigated. The results show that both the mass flux and vapor quality can increase heat transfer coefficient (HTC) and frictional pressure drop (FPD), while the heat flux decreases the HTC and increase the FPD. The maximum promotion of HTC is achieved at an oil concentration of 2.3% compared to other concentrations. Except for the oil concentration of 3%, the FPD of R141b/R245fa-POE mixture increases with the oil concentration. Additionally, the effects of lubricant oil on the HTC and FPD of refrigerant/POE mixture were discussed. The Schager-R22/150-SUS correlation can well predict the enhancement factor of HTC and penalty factor of FPD. The comprehensive factor is always greater than 1, so POE can enhance the overall heat transfer performance of refrigerant-POE mixture.

Numerical analysis of thermohydraulic and exergetic performance in corrugated spiral tubes with diverse arc corrugation configurations

This study numerically analyzes the thermohydraulic performance and exergy destruction in a corrugated spiral tube, considering inward, outward, and combined inward-outward configurations versus smooth spiral tubes. It explores how key corrugation geometries like width, height, and pitch as well as flow parameter such as Dean number influence friction factor, Nusselt number, exergy efficiency, and thermal performance factor. The turbulence and thermal aspects of the flow physics are modeled by incorporating the pertinent governing equations, utilizing the SST k-ω turbulence model and Reynolds-Averaged Navier-Stokes (RANS) equations. The results demonstrated that introducing corrugated walls in various configurations enhances the Nusselt number within the spiral tube compared to its smooth counterpart. Nevertheless, this enhancement is accompanied by an increase in both friction factor and exergy destruction. Employing inward corrugations leads to a remarkable 53% surge in the Nusselt number when compared to the smooth tube. Elevating the corrugation height amplifies heat transfer and Nusselt numbers for all configurations, with the inward corrugation (IC) exhibiting the most substantial escalation. Additionally, a corrugation width of (w/Dh=0.1) engenders maximum thermal performance factor values across scenarios. Augmenting the corrugation pitch increases the Nusselt number due to greater heat transfer area, with the inward topology (IC) conferring maximal values. Although the Nusselt number rises with escalating Dean number, the thermal performance factor declines for all tubes owing to a disproportionately larger pressure drop increase. The outward corrugation tube (OC) sustains the highest performance factor across Dean numbers, while the inward-outward configuration (IOC) possesses the lowest.

Effect of novel vortex generator on parabolic trough solar collectors using ionic liquid

In order to improve the overall thermal performance of parabolic trough solar collector systems, numerical simulation with different forms of vortex generators inserted in the absorber tube using [EMIM][BF4] ionic liquid is presented. The absorber tubes with eight vortex generators are compared with smooth absorber tubes and verified from the field synergy principle by combining the finite volume method and the Monte Carlo ray trace method. The thermal efficiency, Nusselt number, friction factor, performance evaluation criterion factor, and exergetic efficiency with varying parameters like Reynolds number, structure, and arrangement of vortex generators are discussed. The results show that the Nusselt number of common flow up double winglet pair structure increases by almost 77% when the Reynolds number is 5000, and its thermal efficiency and exergetic efficiency improvements are both the highest, which are 2.68% and 1.51%, respectively.

The Effect of Heat Exchanger Tube Structure on the Condensation Heat Transfer of R1234ze(E)/R152a Inside Smooth Tubes

Abstract In this paper, the flow condensation heat transfer characteristics of the environmentally friendly nearly-azeotropic refrigerant R1234ze(E)/R152a (mass ratio of 40:60) in smooth tubes with varying structures were numerically investigated. Under the operating conditions of mass flux of 400 kg/m2/s, heat flux of 12 kW/m2, and saturation temperature of 308.15 K, this study investigated the influence of circular tube inner diameter, elliptical tube aspect ratio, and installation orientation on condensation heat transfer, while the influence on pressure drop has not been taken into account in the present study. The results indicate that the condensation heat transfer coefficient in the tube increases as the inner diameter of the circular tube decreases. The condensation heat transfer coefficient increases by 1.086 times when the circular tube inner diameter is reduced from 10.7 mm to 5 mm. Under identical operating conditions, the condensation heat transfer coefficient of the mixed refrigerant in elliptical tubes increases with an increase in the aspect ratio. The average condensation heat transfer coefficient increases by 18.21% as the aspect ratio of the elliptical tube increases from 1 to 2. Compared to a vertical elliptical tube, a horizontal elliptical tube is more favorable for condensation heat transfer within the tube.

A robust and simple correlation for internal flow condensation

Accurate prediction of the heat transfer coefficient for internal flow condensation is essential for designing and optimizing condensers. Due to advances in manufacturing techniques and new environmental and safety regulations in recent years, applications arose with extensive use of microchannel condensers and low GWP refrigerants. Consequently, a new range of condensation flow conditions is emerging, which requires the evaluation of the accuracy of available correlations and the proposition of more accurate ones. In this work, the most extensive and updated experimental database for heat transfer coefficient (HTC) on internal flow condensation was gathered from the literature, which includes 69 working fluids, 12,017 data points, channel diameters ranging from 0.067 to 20.8 mm, and horizontal and vertical flow directions for smooth tubes. Correlations proposed from 1958 to 2023 were evaluated and compared to this database to verify their prediction error. A new simple HTC correlation was developed, showing that further improvement of available correlations is still possible. The new correlation predicted the database with a mean absolute error of 23.3 %, a 5.3 % relative improvement compared to the second-best-ranked and more complex correlation. This analysis showed that a few well-known dimensionless groups can accurately model the heat transfer process during condensation in a broad range of operational conditions.

Research on the application performance of the corrugated structures in gas wave tubes

This paper proposes a new corrugated gas wave tube to enhance the energy dissipation effect of a static gas wave refrigerator. The tube was based on enhanced heat transfer theory, and its heat transfer efficiency and flow field under different pressure ratios were analyzed. The results demonstrated that the corrugated structure improved heat transfer efficiency compared with smooth tubes. Furthermore, the study investigated the cooling efficiency of gas wave tubes with the application of the corrugated structure under different conditions. The findings indicated that increasing the corrugation percentage led to a fluctuating increase in cooling efficiency. At a pressure ratio of five, the highest cooling efficiency could be improved by 12.65%. By analyzing the motion state of the shock wave in the tube, the gas Nu number, and the law of motion of the wave system, it was determined that the corrugated structure effectively reduced the intensity of the reflected shock wave and enhanced energy dissipation at the end of the tube, increasing cooling efficiency. The experiment was conducted under consistent working conditions, and the efficiency showed varying increases. After thorough research, it could be concluded that using a 60% corrugated gas wave tube proportion yielded the greatest improvement in cooling efficiency.

Condensation heat transfer and pressure drop of low-global warming potential refrigerants in smooth aluminum tubes

In this work we report condensation heat transfer coefficient and pressure drop data for R-454B, R-32, and R-454C. These refrigerants are low Global Warming Potential (GWP) replacements for R-410A. We obtained these data in a smooth 7.2 mm outer diameter (5.94 mm inner diameter) aluminum tube. In these experiments, the key variables were condensation temperature (35 °C ≤Tcond≤50 °C) and refrigerant mass flux (151.1≤G≤347.3 kg m−2 s−1). In general, for similar nominal operating conditions, we measured the highest heat transfer coefficients for R-32 and the lowest for R-454C. Among the correlations we used to predict the heat transfer data for all three refrigerants, the one developed by Thome et al. (2003) predicted the data with the greatest accuracy. Deviations between experimental data and predictions of this correlation were 21.7% for R-454B (with SBG correction), 22.0% for R-32, and 18.8% for R-454C (with SBG correction). Experimental pressure gradient data were predicted by the Friedel correlation Friedel (1979) with deviations of 13.8% for R-454B, 9.8% for R-32, and 10.2% for R-454C. In this work, we also compare the predictions of the Cavallini et al. correlation Cavallini et al. (2006) for R-454B and R-32 in smooth copper versus smooth aluminum tubes. To improve this correlation’s predictive capability for aluminum tubes, we have proposed some modifications. After incorporating these modifications, the deviations between the correlation’s predictions and our data were 10% for R-454B (with SBG correction), 8.1% for R-32, and 5.2% for R-454C (with SBG correction). These data and findings will assist the HVAC and refrigeration industry to implement low-GWP refrigerants in condensers using smooth aluminum tubes.

Evaluating the heat transfer and pressure drop in the transitional flow regime for a horizontal circular tube fitted with wavy-tape inserts

Much research is available to support the thermo-hydraulic characteristics of heat exchanger tubes in laminar and turbulent flow regimes. However, very little work is available to support the thermohydraulic characteristics of heat exchangers in transition flow regimes, especially in turbulators. Therefore, this research experimentally evaluated the heat transfer and pressure drop characteristics of a circular tube fitted with wavy-tape inserts in the transition flow regime. Experiments were conducted in a circular tube having an internal diameter of 20 mm and a length of 2000 mm and the Reynolds number varied from 533 to 7002. The Nusselt number and friction factor for a smooth tube are validated by comparison with published research works in the laminar and turbulent flow regimes. A total of nine wavy tape inserts with different wave and width ratios were investigated. To determine the variation of Nusselt number and friction factor, three constant heat fluxes (q˙= 1, 2, and 3 kW/m2) were applied to the test section. The laminar, transition, and turbulent regimes were marked and identified by using the linear best-fit line method for all the cases considered during the investigation. The results obtained from the study showed a shift in the boundaries of laminar, transition, and turbulent flow regimes. For smooth tube with 1 kW/m2 heat flux, the transition starts and ends at Reynolds number 2202 and 3 804, respectively. It was also revealed that the onset of transition occurred further earlier when tapes were used. The boundaries of transition also shifted with a change in the constant heat flux condition. For wavy tape having w = 0.75, d = 0.8, the transition begins at Reynolds number 2 193, 2 021, 2029 and ends at 4 016, 3 997, 3989 for heat flux 1, 2 and 3 kW/m2, respectively. The transition began earlier for lower values of heat flux, while for higher values, the transition limit was delayed compared with that of lower heat flux. The boundary of transition also shifted with wave ratio and width ratio. An increase in wave and width ratios altogether delayed the start and end of the transition. Correlations were also developed to predict the Nusselt number and friction factor in laminar and turbulent flow regime.

The effect of swallow-shaped bionic ribs on the thermal-hydraulic performance of heat exchanger tubes

This paper combines the bionic structure and multi-vortex longitudinal swirl to enhance the heat transfer in the heat exchanger tube while reducing the increase in flow resistance. The design of the enhanced tube with swallow-shaped bionic ribs is inspired by the aerodynamic profile of the swallow flight process to improve the comprehensive performance. The SST k-ω model is selected for numerical simulation. The study of the effect of TCR (triangular concave rib) bionic rib and TVR (triangular convex rib) bionic rib on the flow field characteristics and thermal–hydraulic performance, and the analysis of the effect of pitch ratio (P*) on the thermal–hydraulic performance of TCR tube. The results show that both types of bionic ribs promote the formation and development of multi-vortex longitudinal swirl and transverse swirl in the tube, strengthening the mixing of hot and cold fluids in the tube, improving the synergy of velocity and temperature fields, and making the temperature distribution in the tube more uniform. When P* = 0.75, Nusselt number of the TCR and TVR enhanced tubes is increased by 52.3 %–65.8 % and 43.3 %–57.9 %, respectively, and friction factor is increased by 92.7 %–202.3 % and 78.7 %–263.9 %, respectively, over the smooth tubes. The effect of P* on the thermal–hydraulic performance of the TCR tube is studied, and the PEC value increases as P* decreases. Compared to smooth tubes, TCR enhanced tubes have improved Nusselt number by 26.4 %–95.6 %, friction factor by 50.4 %-345.8 %, and PEC can reach 1.335 when the pitch ratio P* = 0.5. Consequently, the enhanced tube obtains the good comprehensive performance.

Thermal-hydraulic characteristics analysis of steam–air condensation in vertical porous-wall corrugated tubes

In the passive containment cooling systems (PCCS) of Generation III nuclear power plants, the condensation performance of steam containing non-condensable gas (NCG) in condensate tubes is critical for removing heat from the nuclear power plant containment. By applying a novel porous-wall corrugated structure in the condenser tubes of this system, it was found that under certain conditions, a double vortex is formed inside and outside the porous layer, which is conductive to the transportation and condensation of steam to the condensing wall. The VOF multiphase relation and Brinkman–Forchheimerextended Darcy model in combination of local heat balance, condensation and species transport equations are employed to describe the heat and mass transfer in the porous-wall corrugated tube during condensation. The numerical analysis are conducted to investigate the effects of waveform channel, porous layer and its thicknesses, subcooling of cooling wall and inlet air mass fractions on flow and condensation under different inlet velocities, in which simulations agree with the experimental data. The results show that the condensation heat transfer is greatly influenced by the vortex distribution and air accumulation. At inflowing velocity of 1 m/s, the waveform with amplitude of 1 mm and wavelength of 18 mm can achieve the highest performance evaluation factor, φ (about 67.5 % enhancement than the smooth tubes). The ratio of waveform amplitude to wavelength needs to be chosen properly in consideration of convection between solid matrix and steam–air mixture in porous layer, and non-condensation gas distribution near cooling wall of condensation tube.

Comparative study on the thermal–hydraulic performance of tubes enhanced with three different types of teardrop protrusions

An attractive approach for improving heat transfer in tubes is creating protrusions on the inner surface of tubes. Protrusions can have various shapes. One of the attractive shapes in the literature is a teardrop. For a teardrop protrusion, different teardrop tails have been used in the literature, but no study has considered the effects of the type of these tails on the thermal–hydraulic performance of these protrusions. In this paper, three types of teardrop protrusions were defined to numerically study the effects of changing the tail curves of a teardrop protrusion on thermal–hydraulic performance. One of these teardrop protrusions with an elliptic tail is novel and not similar to any teardrop protrusion reported in the literature. The heat transfer performance of these teardrop protrusions is compared with each other and with ellipsoidal protrusions in a Reynolds number (Re) range of 10,000 to 40,000. The realisable k–ε model and the periodic boundary conditions were adopted for the numerical model. Six different tube configurations with different protrusion pitches were considered for each protrusion shape. The results showed that using a curved tail for teardrop protrusions results in better performance than a straight tail, which was the most used shape in the literature. Tear-circle protrusions with circular tail curves were superior to all protrusion shapes (other teardrop and ellipsoidal protrusions) considered in this study at the entire Re range. A tube enhanced with tear-circle protrusions with the optimum pitch improved thermal–hydraulic performance by up to 54% compared to a smooth tube.

Experimental study of the heat transfer coefficient during condensation of refrigerant R1234yf in a 4.8-mm internal diameter smooth horizontal tube

Experimental study of the heat transfer coefficient during condensation of refrigerant R1234yf in a 4.8-mm internal diameter smooth horizontal tube

Numerical study on a coaxial geothermal exchanger equipped with a new inner tube: Entropy generation, thermodynamic irreversibility analysis and exergy efficiency performance evaluation

This paper focuses on the effect of inner tube fitted with CSF of different widths (H = 5–11 mm), thicknesses (W = 1.5–9 mm) and pitches (P = 50–200 mm) on the entropy generation, thermodynamic irreversibility and exergy efficiency performance of CGHE and gives the direction of improvement of CSF geometric parameters. A performance evaluation chart of exergy efficiency was also established to evaluate the exergy efficiency of each working condition. The results show that the assembly of CSF on the inner tube of the CGHE can effectively reduce the heat transfer entropy generation rate S˙gen,h, lowest 67.9% lower than that of the smooth inner tube, but the friction entropy generation rate S˙gen,f is significantly higher, highest being 10.33 times higher than that of the smooth inner tube. Increasing the width H and thickness and decreasing the pitch P both increase the entropy generation rate, but changes in width and thickness have a small effect on entropy, while changes in pitch P have a large effect on entropy, and their W˙loss follow the same pattern of variation as S˙gen. From Be and Ns it is clear that 99% is frictionally irreversible when Re > 30000, and frictional entropy generation is minimized at Re < 15000. When evaluated in terms of heat transfer improvement number NH, the direction of improvement of the CSF geometry parameters should be to increase the width H, thickness W and pitch P. In terms of exergy efficiency, the exergy efficiency for all cases results in greater than smooth inner tube coaxial GHE for the same pumping power and pressure drop conditions, but deterioration occurs for the same mass flow rate.

Performance analysis of ice storage tank with smooth-tube and corrugated-tube heat exchangers based on numerical simulation

The ice storage system is of great value to improve the flexibility of building cooling load. In this paper, the two-dimensional physical models of smooth-tube and corrugated-tube heat exchangers ice-storage tank is established with consideration of natural convection. The ice storage process of tubes is numerically simulated using Computational Fluid Dynamics (CFD). The effects of structural parameters on the ice storage performance are comprehensively analyzed, including the pitch and height of corrugation. The results indicate that the ice storage duration of the corrugated-tube heat exchanger is shortened by 7.1% compared with that of the traditional smooth-tube heat exchanger, which is due to the fact that corrugations disrupt the development of the boundary layer and strengthen the fluid mixing. There is the thicker ice layer outside the corrugated tube in comparison with the smooth tube at the same time. In addition, the influence of the corrugated tube structure on its ice storage performance is studied by varying the corrugation pitch and height. If the corrugation pitch is decreased by 41.7% and the corrugation height is increased by 28%, the heat transfer performance of corrugated tubes is improved by 10.3% and 29.4%, respectively.

Optimizing Solar Parabolic Trough Receivers with External Fins: An Experimental Study on Enhancing Heat Transfer and Thermal Efficiency

Several researchers have shown that the heat transfer performance of solar parabolic trough (SPT) receivers may be improved by increasing their surface area or by adding internal fins to the tubes. Unfortunately, the manufacture of internally finned tubes involves complex processes, resulting in significant cost increases. On the other hand, the addition of external fins to tubes is more technically and economically feasible in a low-resource setting. This study investigates the potential benefits of integrating external fins on the receiver tubes of a low-cost SPT collector system. Experiments were conducted using an SPT system with a focal length of 300 mm and a collector length of 5.1 m, and they were positioned by an automated Sun tracking system. Tests were undertaken using both smooth and externally finned receiver tubes operating at five different water flow rates. The solar receiver with a finned tube was able to provide a maximum water temperature of 59.34 °C compared with that of 56.52 °C for a smooth tube at a flow rate of 0.5 L per minute. The externally finned absorber tube was also found to have a maximum efficiency of 18.20% at an average daily solar intensity of 834.61 W/m2, which is approximately 48% more efficient than the smooth tube. The calculations indicate that the experimental SPT system using finned tubes potentially avoids 0.2726 metric tons of CO2e per year, with finned tubes outperforming smooth tubes by up to 44%. The results show that using externally finned receiver tubes can significantly enhance the thermal performance of SPT collector systems.

Experimental and Numerical Dynamic Investigation of a Swirling Jet: Application to Improve the Efficiency of Air Diffusion in an Occupied Zone

When reducing the energy prerequisites of buildings, the correct distribution of fresh air flows injected into the living rooms poses a problem. If the problem of mixing the injected air in the ambient air is not effectively solved, there will be a strong deterioration in air quality and comfort. In this research, a new design of swirling diffuser is investigated experimentally and numerically using large eddy simulations. The influence of fins is studied for the improvement of air diffusion and jet mixing with ambient air. The study was carried out for a fins angle of 30° with the jet's axis and 60° with the blowing orifice's plane with the condition of uniform heat flux of the air. The working fluid used is air. It has been validated that using fins leads to a greater spreading of the jet and good air mixing compared to those obtained from smooth tubes (circular nozzle). To enhance the accuracy of the turbulence models' predictions, three turbulence models are tested: the wall-adapting local eddy-viscosity turbulence model (LES/WALEVM), Smagorinski-Lilly (LES/S-LM) model and the kinetic-energy transport model (LES/K-ETM). It is worth highlighting that the LES/K-ETM model is well established in the prediction of swirling flows, which have been successfully compared with experimental results.

Numerical simulation and structural optimization of spiral finned tube thermal energy storage

Thermal energy storage (TES) has emerged as a promising solution to enhance nuclear safety by passively removing decay heat during reactor shutdown and accidents, thus preventing overheating of the reactor core and protecting the integrity of containment barriers. The research of TES with different structures has broad application prospects and practical significance. In this study, the melting process of phase change material (PCM) in various TES structures was simulated by the numerical simulation method in two and three dimensions. The mechanism of gravity-driven natural convection enhancing heat transfer was revealed. The effects of different TES structures, fin pitch, fin height, and fin thickness on heat transfer performance were studied. The results showed that many vortices formed by liquid PCM are the main reason for enhancing the natural convection. Adding fins could greatly accelerate the heat storage process. The melting time of PCM in annular and spiral finned tube TES was 47.3% and 61.3% less than that in smooth tube TES, respectively. In the present study, the heat transfer effect was enhanced as the spiral fin pitch became small, the fin height increased and the fin thickness increased. Two opposite effects of fin structure on the natural convection were revealed: (1) positive effect provided by heat transfer enhancement and (2) negative effect produced by blockage.

Numerical simulation on flow boiling heat transfer of R1234ze(E)/R152a in a horizontal smooth tube

The understanding of two-phase flow and heat transfer characteristics of refrigerants in tubes is important for guiding the design and optimization of heat exchangers. Based on the volume of fluid (VOF) multiphase model, this paper established a numerical model of R1234ze(E)/R152a (mass ratio of 0.4/0.6) flow boiling heat transfer in a horizontal smooth copper tube with an inner diameter of 6 mm and a length of 900 mm. The distribution of vapor volume fraction is obtained, and the influence of mass flux, heat flux, saturation temperature, and vapor quality on heat transfer coefficient (HTC) are studied. Bubble flow, plug flow, stratified flow, and wavy flow can be observed during the whole process and the fluid temperature increases along the tube. Local and time-averaged heat transfer coefficients and temperature distribution along the axial direction were studied. And the results indicate that the HTC decreases first and then increases with the augmentation of mass flux while increasing with the rise of heat flux. In addition, the HTC rises along with saturation temperature and decreases along with vapor quality. The largest related standard deviation between the simulation value and the testing data is 6.31%. Thus, the numerical simulation has a high level of accuracy.

A comparative study of fluid flow and heat transfer in the tube with multi-V-winglets vortex generators

In this paper, a new multi-V-winglets vortex generator was proposed and its influence on fluid flow and thermal transfer was studied. It was found that the thermal transfer was enhanced with the increasing number of winglets, while the friction resistance was growing. Therefore, punching holes on the surface of vortex generators were used to enhance overall performance by reducing friction resistance. The simulation results showed that jet flow appeared when fluid passed through hole, which impacted the recirculation zone and removed the stagnant fluid. Thus, local heat transfer was enhanced and friction loss was decreased. Meanwhile, the pitch of multi-V-winglets vortex generator had an important role in heat transfer and friction loss, which could increased the Nusseltnumber of the smooth tube by 130.57–156.42%. Furthermore, the results were proved using the principle of entropy generation. The maximum performanceevaluationfactor was 2.83 when the number of winglets was 8, the holes were on the outer surface of winglets and the pitch was 25mm.

Experimental study of refrigerant condensation heat transfer and pressure drop in horizontal tubes with full and partial coiled wire inserts (CWIs)

The condensation heat transfer coefficient (HTC) and pressure loss in the horizontal smooth and wire-inserted tubes were investigated experimentally. Three different coiled wire inserts (CWIs) of the full length of 1000 mm and partial lengths of 100 mm and 200 mm with 0.8 mm wire thickness and 9.5 mm pitch were studied. The main condenser was a heat exchanger of double pipe type with an 8 mm inner diameter for the refrigerant and an active length of 1 m cooled by water circulating in the annulus. The experiments were conducted for different refrigerant mass velocities within 90–400 kg/m2s and low vapor mass fraction (x < 0.3). The findings revealed that using 1000 mm (full-length), 200 mm, and 100 mm length CWIs improved the HTC by 95%, 40%, and 18%, respectively, over the smooth tube. The HTC per unit pressure drop was also evaluated to assess the performance of full and partial CWIs. The results showed that the HTC per unit pressure loss decreases for all tubes as the mass velocity increases. In addition, the performance of the tubes with CWIs approached that of the smooth tube at higher mass velocities. The ratios of HTC per unit pressure drop at higher mass fluxes for full-length, 200 mm, and 100 mm length CWIs to that of the smooth tube were about 0.4, 0.78, and 0.9, respectively. Although the pressure drop increased almost linearly with the partial CWI length, the HTC increased sharply for the small inserts and gradually for the larger insert lengths. The results obtained for the condensation HTC in smooth and full wire-inserted tubes were also compared with the estimations of well-known correlations in the literature. Furthermore, three new correlations were developed to predict condensation HTC in smooth tubes and tubes with full and partial CWIs. It was shown that the new correlations are more accurate than the available ones.