Smooth Tube Bundle Research Articles

Heat Transfer Enhancement in a 3D-Printed Compact Heat Exchanger

The study describes experimental data on thermal tests during the condensation of HFE7100 refrigerant in a compact heat exchanger. The heat exchanger was manufactured using the additive 3D printing in metal. The material is AISI 316L steel. MPCM slurry was used as the heat exchanger coolant, and water was used as the reference medium. The refrigerant was condensed on a bundle of circular tubes made of steel with an internal/external diameter of di/de = 2/3 mm, while a mixture of water and phase change materials as the coolant flowed through the channels. Few studies consider the heat exchange in condensation using phase change materials; furthermore, there is also a lack of description of heat exchange in small-sized exchangers printed from metal. Most papers deal with computer research, including flow simulations of heat exchange. The study describes the process of heat exchange enhancement using the phase transition of coolant. Experimental data for the mPCM slurry coolant flow was compared to the data of pure water flow as a reference liquid. The tests were carried out under the following thermal and flow conditions: G = 10–450 [kg m−² s−1], q = 2000–25,000 [W m−²], and ts = 30–40 [°C]. The conducted research provided many quantities describing the heat exchange in compact heat exchangers, including heat exchanger heat power, heat exchange coefficient, and heat exchange coefficients for working media. Based on these factors, the thermal performance of the heat exchanger was described. External characteristics include the value of the thermal power and the heat exchange coefficient as a function of the mass flow density of the working medium and the average logarithmic temperature difference. The performance of the heat exchanger was presented as the dependencies of the heat exchange coefficients on the mass flux density and the heat flux density on the heat exchange surface. The thickness of the refrigerant’s condensate film was also determined. Furthermore, a model was proposed to determine the heat exchange coefficient value for the condensing HFE7100 refrigerant on the outer surface of a bundle of smooth tubes inside a compact heat exchanger. According to experimental data, the calculation results were in good agreement with each other, with a range of 25%. These data can be used to design mini condensers that are widely used in practice.

Heat transfer enhancement of different ribbing pitched semi-closed microstructure tube bundles fabricated by deformational cutting method

The study investigates the limitations posed by low-value heat transfer coefficients and higher wall superheat in conventional tube bundles, which adversely impact the performance of heat exchangers. To address this challenge, semi-closed microstructure tubes, created via deformational cutting at ribbing pitches of 300 µm and 400 µm, are proposed as a potential solution. The research centers on analyzing the two-phase boiling heat transfer performance of these microstructure tubes arranged in 2 × 3 staggered tube bundles. A comparative analysis is conducted, evaluating the thermal effectiveness of the microstructure tube bundles against a 2 × 3 smooth tube bundle and a copper-coated tube bundle under varying mass flux, heat flux, and pitch-to-diameter ratios. The experimental findings indicate the superior heat transfer performance of both microstructure tube bundles, with reduced wall superheat compared to other tube bundles. The findings further indicate that the 2 × 3 semi-closed microstructure tube bundle with a higher ribbing pitch outperforms the microstructure with a lower ribbing pitch. The 2 × 3 high-pitched microstructure tube bundle exhibits a maximum enhancement of 420 % over the 5 × 3 smooth tube bundle and 340 % over the 2 × 3 smooth tube bundle. Moreover, it surpasses the performance of copper-coated tube bundles by 230 % and outperforms its lower-pitch counterpart by 70 %. Particularly, the use of microstructure tube bundles allows for a reduction in the number of tubes required in the heat exchanger configuration without compromising its performance, promoting compactness and cost-effectiveness. Overall, the study highlights the feasibility of implementing these tubes in the two-phase heat exchanger owing to their superior performance compared to conventional tubes.

Prediction and comparison of aerodynamic performance and flow control for smooth and wavy tube banks in crossflow at subcritical Reynolds numbers using a 3D RANS approach

This paper investigates the effects of introducing wavy cylinders of appropriate wavelength into tube bundles for the passive control of flow-induced vibration. The Reynolds-averaged Navier–Stokes approach RANS was used to study the turbulent flow characteristics within staggered tube bundles having transverse and longitudinal pitch-to-diameter ratios of 3.8 and 2.1, respectively. Two wavy models are tested with different wavelength-to-mean diameter ratios, namely: Model-A with [Formula: see text] and Model-B with [Formula: see text], and their performances are compared with those of a smooth circular tube bundle Model-C ([Formula: see text]), in a range of subcritical Reynolds numbers [Formula: see text]. Mean velocity and pressure fields as well as aerodynamic coefficients are presented and compared. According to the obtained results, the wavy tube bundle with [Formula: see text] exhibits the best performance, with slightly smaller [Formula: see text] values than the smooth tube bundle. However, results show that the wavy model with [Formula: see text] is clearly the worst with an increase of [Formula: see text] up to 40%. Numerical outcomes also reveal that the interaction of neighboring rows and columns affects the fluctuation of [Formula: see text] values relative to each tube position. Moreover, [Formula: see text] evolutions depend significantly on the variation of Re as well, where drag reduction is more substantial by increasing Re. Thus, wavy-shaped tubes with optimum parameters could be more suitable for flow control by enhancing the secondary flow, turbulence and fluid mixing.

Experimental study and performance evaluation of an air source heat pump (ASHP) system with a frost-free evaporator

The air source heat pump (ASHP) is operated in a low temperature and high humidity working environment. There is always a lot of frost forming on the outdoor heat exchanger, which hinders the heat transfer rate of the heat exchange surface, leading to the decrease of performance of the ASHP system. This paper presents a new type of frost-free evaporator for ASHP system. The heat transfer zone of the evaporator is composed of three parts: non-packing zone, plain finned-tube falling film zone and horizontal smooth tube bundle falling film zone. The experimental system of the frost-free evaporator is established, and the reliability of the experimental data is verified. The effects of refrigerant flow rate, inlet air temperature, fan frequency and solution spray mode on energy efficiency ratio, heat transfer expansion coefficient, air side pressure drop and exergy loss of the evaporator are studied. The performance of the evaporator is evaluated. The results show that with the increase of inlet air flow and temperature, the energy efficiency ratio of frost-free evaporator increases by about 8%–12%, and the air side pressure drop also increases. As the inlet air temperature increases from −10 to 15 °C, the heat transfer expansion coefficient of evaporator decreases by about 3%–6%, indicating that the increase of inlet air temperature will lead to an increase of sensible heat transfer ratio and a decrease of latent heat transfer ratio. The results also show that compared with no spray mode and continuous spray mode, the intermittent spray mode is more recommended as a feasible operation scheme to realize the continuous, efficient and stable operation of the new evaporator.

Heat transfer and gas dynamics numerical modelling of compact pipe bundles of new design

Weight and size characteristics, heat transfer efficiency across the surface, pressure losses in the flow paths for each heat transfer medium, and other parameters that characterise the heat exchanger play an important role in the development of new types of heat exchanger designs. This predefines the research relevance and the need for a solution. The research aims to develop and implement fundamentally new approaches to the design parameters of shell-and-tube heat exchangers, in which smooth-tube bundles are placed as compactly as possible in their crossflow. For this purpose, numerical modelling in the heat exchanger channels and studies of heat transfer and gas dynamics were carried out. The ANSYS Fluent software package was used to calculate the hydrodynamics and heat transfer in the tube bundle channels. Numerical modelling of hydrodynamics and heat transfer processes in the flow of a compact bundle of small-diameter pipes was carried out. The mathematical model includes the Navier-Stokes equation, the energy equation, and equations describing the turbulence of the external flow. The turbulence model was chosen as a model that describes turbulence in channels well. The results of numerical modelling showed a compact bundle of pipes at the outlet of the channels, with an average value of +20.1ºС. Notably, the local temperature values near the channel walls are close to +30 °C. The air velocity at certain points of the duct reaches 85.1 m/s. At the same time, the average air velocity in the cross-section of the channel is about 41.2 m/s at Re=21420. It is demonstrated that the maximum values of local heat transfer coefficients for pipes in a compact bundle are observed in the areas where the flow joins the pipe surface and at the beginning of the boundary layer formation. The maximum values of the heat transfer coefficient reach up to 1335.5 W/m2·ºС for the second and third rows, and at the front point of the first order, it is 1042.3 W/m2ºС. These results will improve the weight and dimensions of shell-and-tube heat exchangers and reduce their cost

APPLICATION OF DIMPLES AND HELICAL GROOVES ON THE OUTTER SURFACE OF TUBES TO INCREASE THERMAL-HYDRAULIC EFFICIENCY OF TUBE BUNDLES AT CROSS FLOW

The flow structure and thermo-hydraulic efficiency of cross flow of tube bundles with dimples and helical grooves have been analyzed. The Reynolds number range (103-104) was typical for industrial heat exсhangers. It was found that dimples and grooves decrease scientifically the cylinder wake area and reduces the hydraulic losses. The heat transfer augmentation in five-row tube bundle by dimples is 35-40% while pressure drop increase by 10-15%. The hydraulic resistance of two-row bundle of tube with helical grooves is 20% lower than that of a smooth tube bundle, while heat transfer augmentation is absent. The value of Reynolds analogy factor for tube bundles with dimples and helical grooves exceeds unity. The high thermo-hydraulic efficiency of tube bundles with dimples and helical grooves, allows us to recommend it for practical use in the development of modern heat exchange equipment of the tubular type.

Simulation of convective heat transfer of a bank of pipes when using turbulators with cutouts

The article discusses the mathematical modeling of the intensification of convective heat transfer of a smooth tube bundle. Turbulators with cutouts were used as heat transfer intensifiers. The mathematical model of the heat exchanger consisted of a section of a rectangular channel with a turbulator device. To solve the differential equation, the finite difference method was used, approximated by difference equations. On the basis of the calculations, for the purpose of choosing the size of the experimental object, the profiles of the velocity distribution before and after the turbulizer were obtained. Keywords: m

Study on enhanced heat transfer characteristics of metal foam solar receiver in Solar Power Tower plants

In order to explore the mechanism of heat and mass transfer of metal foam absorber based on electrodeposition, the numerical simulation study of metal foam absorbers with different structures was carried out, and the heat transfer model of the coated metal foam tube bundle with a tube spacing of 3D × 1.5D was analyzed and established. Compared with the smooth tube bundle, with the Re number varying from 100 to 1500, the Rext of the tube bundle coated with stainless steel foam decreased from 0.061 K/W to 0.009 K/W, and the thermal resistance ratio outside the tube increased from 2.75 to 4.76. The pressure loss of the tube rose from 1.89 Pa to 80.10 Pa, and the pressure loss outside the tube dropped from 5.15 to 3.12. The overall performance index PEC of the tube increased from 1.59 to 3.26. Compared with rows of staggered tube bundles from 2.5D to 2.2D, the heat transfer coefficient can reach 4621 W/m2/K and the pressure loss is 1.67%.

Investigation of Heat Transfer in a Large-Scale External Heat Exchanger with Horizontal Smooth Tube Bundle

In the research work, energy transport between a dense fluidized bed and submerged horizontal tube bundle is analyzed in the commercial external heat exchanger (EHE). In order to investigate the heat transfer behavior, the authors carried out eight performance tests in a fluidized bed heat exchange chamber with a cross-section of 2.7 × 2.3 m in depth and width and a height of 1.3 m. The authors have been developing a mechanistic model for the prediction of the average heat transfer coefficient, which includes the effect of the geometric structure of the tube bundle and the location of the heat transfer surface on the heat transfer rate. The computational results depict that the average heat transfer coefficient is essentially affected by superficial gas velocity and suspension density rather than bed particle size. The empirical correlations have been proposed for predicting heat transfer data since the existing literature data is not sufficient for industrial fluidized bed heat exchangers. On the basis of the evaluated operating conditions of an external heat exchanger, the optimal conditions where heat transfer occurs could be deduced. The developed mechanistic heat transfer model is validated by experimental data under the examined conditions.

ВОДОГРІЙНІ КОНДЕНСАЦІЙНІ ТЕПЛОУТИЛІЗАТОРИ ІЗ ЗАСТОСУВАННЯМ НАНОКОМПОЗИЦІЙНИХ МАТЕРІАЛІВ ДЛЯ ГАЗОСПОЖИВАЛЬНИХ ОПАЛЮВАЛЬНИХ КОТЛІВ

Викладено результати досліджень ефективності використання в теплоутилізаційних технологіях газоспоживальних опалювальних котельних установок із глибоким охолодження їхніх відхідних газів водогрійного теплоутилізаційного устаткування різного типу. Розглянуто устаткування, теплообмінні поверхні якого компонувались з пучків поперечно-оребрених труб двох видів та гладкотрубних пучків. Визначено для різних режимів роботи котельних установок протягом опалювального періоду такі відносні характеристики даних поверхонь, як теплопродуктивність на одиницю маси цієї поверхні та її об'єм на одиницю теплопродуктивності. Виконано порівняльний аналіз зазначених характеристик при використанні для поверхонь теплообміну традиційних матеріалів і полімерних мікро- і нанокомпозитів з різними коефіцієнтами теплопровідності. За значеннями робочих температур теплообмінної поверхні із мікро- і нанокомпозитів визначено її полімерну матрицю, а за величиною теплопровідності - необхідний склад наповнювачів полімеру, якими можуть слугувати мікрочастки алюмінію або вуглецеві нанотрубки. Показано, що для опалювальних котельних установок водогрійне теплоутилізаційне устаткування із вказаних нанокомпозиційних матеріалів за питомою теплопродуктивністю має істотні переваги над традиційно застосовуваними аналогами цього призначення.

Heat Transfer in Air Flow Across a Single-Row Bundle of Tubes With Spiral Grooves

An experimental study has been made of the heat transfer and hydraulic resistance in air flow across a single-row bundle of tubes with spiral grooves on the exterior surface and of a bundle of smooth tubes of the same diameter. Cutting a spiral groove of width 3 mm and depth 2 mm with a pitch of 20 mm on a tube with an outside diameter of 22 mm increased the heat-transfer coefficient in the range of Reynolds numbers 6200–16,000 by 40–53% compared to the smooth-tube bundle. The hydraulic resistance of the tube bundle decreased by 22%. The Reynolds analogy factor increased, on the average, by 41%. Tubes with spiral grooves, in the investigated range of the velocities of flow, have shown a certain increase in the Strouhal number to values of 0.24–0.36. Computer simulation has been carried out of the hydrodynamics of the single-row bundle of smooth-wall tubes and the tubes with spiral grooves. It has been shown that the enhancement of heat transfer and the decrease in the hydraulic resistance alike are attributable to the appearance of nonsymmetric vortex structures induced by the flow across the spiral grooves.

USING OF TUBULAR HEAT EXCHANGE SURFACE WITH DIMPLES IN THE GAS TURBINE REGENERATORS

Comparison of heat transfer and hydraulic resistance of bundles of smooth tubes and pipes with the surface formed by dimples. Calculations performed for the gas turbine capacity of 16 MW allows minimizing the mass of the regenerator.

Heat transfer evaluation of an enhanced heat transfer tube bundle

Demands to increase performance of modern heat exchange systems are constantly being made. Typical requirements include the removal of larger amounts of energy or the development of process units that occupy a smaller unit footprint. Vipertex™ 1EHT enhanced surfaces have been designed and produced through material surface modifications in order to create flow optimized heat transfer tubes which increase heat transfer with only a modest increase in the friction factor. Considerations in the development of the enhanced, three dimensional 1EHT enhanced heat transfer surfaces include: maximization of heat transfer; minimization of operating costs; and/or a minimization of the rate of surface fouling. This study details the performance of a horizontal oriented 1EHT enhanced surface tube bundle and compares heat transfer results to a horizontal bundle of smooth tubes for single phase and two phase conditions. Results for the 1EHT bundle show an increase in the overall heat transfer coefficient up to 200% when compared to the heat transfer performance of a smooth tube bundle using typical fluids (n-Pentane, p-Xylene and water); for midpoint shellside Reynolds number values in the range of 2010–20,400; with effective mean temperature difference (EMTD) values between 8.6 °C and 65.7 °C. More nucleation sites are produced on the 1EHT tube surface than on an equivalent length of unenhanced commercial tube. Results from this bundle study indicate that the 1EHT enhanced tube surface is well suited for applications where nucleate boiling is significant. Enhanced heat transfer tube bundles using the 1EHT tubes are capable of producing efficiency increases making 1EHT tubes an important alternative to be considered in the design of high efficiency processes. Vipertex 1EHT tube bundles recover more energy and provide an opportunity to advance the design of many heat transfer products.

ТеплообміН пучкіВ труБ З рівнорозвиненоЮ поверхнеЮ

Наведено результати експериментальних досліджень конвективного теплообміну шахових пучків труб з рівнорозвиненою поверхнею в діапазоні зміни чисел Рейнольдса від 5000 до 70000. Запропоновано узагальнену залежність для розрахунку конвективних коефіцієнтів тепловіддачі таких пучків. Показано, що коефіцієнт Сq при числі Рейнольдса в рівнянні подібності залежить від геометричних характеристик пучків та труб.

Boiling on a Tube Bundle: Part I—Flow Visualization and Onset of Dryout

A novel visualization method was developed and implemented in a refrigerant-flooded evaporator tube bundle. Specifically, a method to visualize the two-phase flow inside plain tube bundles was developed using a dummy tube with a tubular glass section for visual access with a digital high-speed video camera and a laser light/photodiode. These were used to observe and characterize the two-phase flow structure and improve understanding of the physical phenomena taking place. In particular, a dryout line was objectively identified in a flow pattern map separating high- and low-performance heat transfer data measured locally on the bundle. The database was recorded for vertical flow of R134a and R236fa over smooth tubes at saturation temperatures of 5–15°C. The tests span low mass velocities applicable in flooded evaporators, and heat fluxes include adiabatic and diabatic tests of 7–25 kW/m2. A new prediction method for onset of dryout on smooth tube bundles is proposed.

Convective boiling of R-123/oil mixtures on enhanced tube bundles having pores and connecting gaps

The effect of enhanced geometry (pore diameter, gap width) on convective boiling of R-123/oil mixture was investigated. Three enhanced tube bundles as well as a smooth tube bundle were tested. Test range covered oil concentration, heat flux, mass flux and vapor quality. Significant heat transfer degradation is observed for the present enhanced tubes. Compared with the pool boiling counterpart, however, the heat transfer degradation is much smaller. The two-phase convection in a bundle may remove the oil-rich layer near the heating surface, and reduce the thermal degradation by oil. Of the three enhanced geometries, tube with the largest pore diameter (correspondingly larger gap width) shows the smallest degradation. However, d p = 0.23 mm tube, which yielded the highest heat transfer coefficient with pure refrigerant, maintains the highest heat transfer coefficient even with oil. Correlations, which account for the heat transfer degradation with heat flux, oil concentration and enhanced geometry as parameters, were developed.

A universal relation for calculating convective heat transfer in transversely streamlined bundles of smooth tubes

Experimental data on convective heat transfer in smooth-tube bundles streamlined by a transverse flow in the range of Reynolds numbers from 3 × 103 to 1 × 105 are generalized. A universal relation is obtained that allows heat transfer in bundles with staggered and in-line arrangements to be calculated in the range of pitch characteristics covering all practical applications with better accuracy as compared with the well-known calculation procedures.

The Effect of Novel Plasma-Coated Compact Tube Bundles on Pool Boiling

Boiling heat transfer of R-134a on a porous, plasma-coated tube bundle was investigated experimentally to determine the effects of the number of tube rows and the total tube number. The bundle consists of up to four tubes with a pitch-to-diameter-ratio of 1.33. Heat transfer coefficients for a single tube with a porous copper coating were up to four times higher than for a smooth tube. Observations showed that the plasma coating enhanced the heat transfer coefficient in tube bundles as well. The bundle factor of the coated tube bundle showed a similar, slightly increased trend as the smooth tube bundles. The enhancement effect of the coated tubes decreases to a certain extent with an increasing heat flux and decreasing saturation temperature. However, it is significantly less pronounced than trends that have been reported from other investigations. The aim of a stable enhanced coating was confirmed by long-term experiments with steady results.

Local thermal and aerodynamic characteristics in intertube channels with attached vortices

The results of an experimental study of thermal and aerodynamic characteristics (static pressure, surface friction, and heat transfer) in diverging smooth-tube bundles are presented. The results obtained make it possible to develop vortex models of flow and heat transfer in intertube channels with attached vortices.

Heat transfer characteristics of air cross-flow for in-line arrangement of spirally corrugated tube and smooth tube bundles

An experimental study on heat transfer and resistance coefficients of linearly arranged smooth and spirally corrugated tube bundles in cross-flow was performed. The heat transfer and resistance coefficients are presented in this paper with transverse and longitudinal tube-pitch and tube geometries taken into account. The experiment’s results can provide technical guidelines for application to horizontal air preheater with arranged in-line spirally corrugated tube bundles, especially to the air preheater for CFBCBs (Circulating Fluidized Bed Combustion Boilers).