Horizontal Straight Tube Research Articles

Ammonia single-phase and two-phase frictional pressure losses in horizontal smooth and straight inner-grooved tubes

The experimental study of single-phase and two-phase frictional pressure losses has been performed with ammonia flow in stainless steel smooth tubes (internal diameter of 5.5 mm and 8.5 mm) and six straight inner-grooved aluminium tubes with different nominal diameters (7.15 to 13.3 mm), length (0.45 to 2.0 mm) and thickness (0.35 to 0.8) of fins. Single-phase test boundary conditions correspond to Reynolds numbers of 1000 to 20,000. Two-phase tests have been carried out at saturation temperature of 45 to 65 °C, mass velocity of 50 to 210 kg·m−2s−1 and vapour quality of 0.1 to 0.9. Comparison of obtained test data with the existing frictional losses approaches shows that the Blasius model is appropriate to single-phase flows in smooth tubes, and Müller-Steinhagen and Heck's (1986) model is most accurate in predictions of two-phase frictional losses in smooth tubes. Existing approaches of single-phase frictional pressure loss predictions in the pipes and channels with longitudinal fins (Carnavos, 1980; Edwards and Jensen, 1994) are not adequately suited to the ammonia test points obtained in the considered straight inner-grooved tubes. A new semi-empirical model has been proposed, based on generalisation around the revealed geometric dimensionless factor, which accurately describes friction pressure losses in the considered inner-finned profiles. The simplest homogeneous model for defining two-phase friction pressure losses, using McAdams et al.'s (1942) recommendation for mixture dynamic viscosity definition and a new model of single-phase friction factor, best fit both quantitatively and qualitatively to ammonia two-phase test points in most of the considered straight inner-grooved tubes.

Experimental study of buoyancy and centrifugal effects on supercritical heat transfer in U-bend and contiguous straight tubes

The buoyancy-induced thermal non-uniformity in heat transfer of supercritical fluids is a major issue that must be addressed in transcritical systems like organic Rankine cycle. In cases where U-bends are involved in heat exchangers, the introduction of centrifugal effect and its decaying nature makes the heat transfer process even more complex. In this work the buoyancy and centrifugal effects on local heat transfer to supercritical R410A were experimentally studied in a U-bend and its contiguous horizontal straight tubes (tube diameter d = 4.35 mm, bend diameter D = 43.5 mm). Measurements were performed at four circumferential positions along the heated length. Results show that bend-induced enhancement reached the maximum at the bend center, where heat transfer coefficients at the outside, top, bottom, and inside increase by 88%, 49%, 28% and 19% respectively. U-bend also caused a significant enhancement on contiguous horizontal straight tubes. In the upstream straight section, the affected distance can reach 11.5d, and the downstream affected range is more than 23d. The enhancement and the affected distance generally increased with heat flux, mass flux, and inlet temperature, but barely affected by pressure. Further analysis indicates that the centrifugal force dominated heat transfer in the bend section. Moving away from the bend, it gradually decayed, buoyancy force recovered and eventually played the major role. Existing dimensionless numbers failed to represent this transition, and a new parameter ψ* was proposed to evaluate the competition between the buoyancy effect and the decaying centrifugal effect. With a threshold value of 1, ψ* can quantitatively characterize the local heat transfer.

Application of the Temperature Oscillation Method to Laminar Flow in Straight Horizontal and Curved Minichannels

This work deals with the application of the temperature oscillation method to measure local values of the heat transfer coefficient in laminar flow in a straight horizontal pipe and in a pipe with a bend. This method, applied here for the first time in such experimental conditions, uses a time-varying heat flux as a boundary condition, which is a condition of the third kind. Since an analytical solution for such conditions could not be identified in the existing literature, a numerical study of this problem is applied here. Experimental data for a straight horizontal pipe confirm the numerical results within a reasonable level of error. Experimental measurements on a straight horizontal tube are consistent with predicted results in the literature for both total and local heat transfer coefficient values. The measurements on bent tubes show a very significant influence on the local values compared to the straight tube and in the overall values this change appears as an increase in the heat transfer coefficient.

Experimental Investigation of the Isothermal Pressure Drops in Mini-Elbows

An experimental setup was built in this study to measure the pressure drop for the horizontal mini-scale elbows under the isothermal boundary condition. Six stainless steel mini-elbows with various bending angles (45° and 90°) and inner diameters (0.6 mm to 4.5 mm) were used as the test section. The experimental setup was verified by comparing the current horizontal straight tube data with the well-known correlations. The Reynolds number range for this study was around 800 to 10,000. The experimental results clearly showed the effect of diameter and angle on the loss coefficient for the 45° and 90° elbows in the entire Reynolds number range. A critical region was shown to be obvious in the 45° elbows than that in the 90° elbows. Basically, the traditional fixed loss coefficient and the 2-K and 3-K methods did not predict the loss coefficients of the 45° and 90° mini-elbows with good accuracy. Therefore, an accurate correlation was developed for different diameters and angles of mini-elbows and the majority of loss coefficients data was predicted within an accuracy of ±20%.

Experimental study of the thermal-frictional behavior of a horizontal straight tube equipped with a vibrating string turbulators: A novel active method

The active methods are recently considered to increase the heat transfer rate. Compared to the passive methods, the active ones experience less pressure drop. Some inherent disadvantages, such as inefficiency in terms of energy consumption or the necessity of specific properties for the working fluid can limit using active methods. In this study, a novel idea is experimentally studied to explore the changes in the rate of heat carried by the fluid passing through a heated tube. To this end, a stretched string is implemented coaxially inside the tube and excited to vibrate at its natural frequency in the presence of an adjustable frequency AC magnetic field. This new approach to vibrating a starched oscillator remotely is called electro-magnetic vibration method (EMV). The vibration of a string inside the tube is predicted to cause severe turbulence and strong radial flow. The impacts of the changing diameter of the vibrating string turbulator (VST) and the position of the exciter on the heat transfer rate are studied at different mass flow rates. The thermal enhancement factor (TEF) is calculated to choose the best diameter and excitation location. The results showed that in the best scenario, TEF could reach up to 1.47, which indicates that the EMV method is an effective way to generate harsh radial flow to increase heat exchanger's thermal performance.

The impact of the pseudo-boiling on the thermal behaviors of supercritical CO2

Based on the comparative analysis of different turbulence models, the model is selected in the present study to simulate the flow of supercritical ) in horizontal straight tubes. First of all, the rationality and correctness of the numerical simulation is verified by experimental data. Secondly, to deeply investigate the effect of pseudo-boiling point on the convective heat transfer of the ideal gas model without peak specific heat and the actual model are established. The results show that the ideal gas model can increase the wall temperature at top generatrix for the outlet area of the heating section, reduce its heat transfer coefficient, and weaken the effect of absorbing heat from top generatrix. The pseudo-boiling point has a significant influence on density distribution but almost no effect on the velocity field. In addition, the pseudo-boiling point also affects buoyancy, which increases buoyancy near the outlet area of the heating section and reduces heat transfer effect. The research results can not only be used as a theoretical reference for heating device optimization and stability, but also provide new perspectives on the fundamental theories of research on various supercritical fluids.

Experimental Study of the Thermal-Frictional Behavior of a Horizontal Straight Tube with Equipped a Vibrating String Turbulators: A Novel Active Method

Experimental Study of the Thermal-Frictional Behavior of a Horizontal Straight Tube with Equipped a Vibrating String Turbulators: A Novel Active Method

Sensitivity Analysis of Influencing Factors of Supercritical Methane Flow and Heat Transfer in a U-Tube

Due to the existence of a Dean vortex in a U-tube, the flow and heat transfer process of supercritical methane is complex, and its thermophysical property are greatly influenced by different factors. Based on computational fluid dynamics theory, the numerical simulation of the turbulent flow and heat transfer characteristics of supercritical methane in a U-tube with an inner diameter of 10 mm and a radius of curvature of 27 mm carried out by using the finite volume method. On the basis of verifying the reliability of the model, the influences of inlet mass flux (G), heat flux on the tube wall boundary (q), pressure on the outlet (P), and gravity acceleration factors (g) on heat transfer characteristics were analyzed. The calculation results show that the sensitivity of the effects of G, q, P, and g on the heat transfer coefficient is, from large to small, in the order of P, G, g, and q. Compared with a horizontal straight tube, a U-tube can significantly improve heat transfer in the elbow part, but the presence of the elbow reduces heat transfer in the subsequent straight pipe section. The research in this paper has significance as a reference for the construction of the LNG gasification process.

Performance evaluation of horizontal straight tube equipped with twisted tape turbulator, with air–water two-phase flow as working fluid

In this study, the effect of combination of twisted tape turbulator and air injection on heat transfer augmentation is studied. The air injection as the active method and the twisted tape turbulator as the passive method were used simultaneously to increase the heat transfer rate. The rate of air flow as like to pitch of twisted tape tabulator was considered as the variants. Six different air flow rates were considered in this study which provides a superficial gas Re number range of 147.07–882.30. Also the superficial liquid Re number had the range of 2400–6000. For the twisted tape, three different twisted tapes with twist ratio (λ) of 11.66, 6.66 and 5 were considered to check the effect of twist ratio on the thermo-hydraulic properties of the considered tube. A horizontal copper-made tube was considered as the test section which was under constant heat flux. In order to better understanding the flow structure, the flow structure was captured via a Canon SX540 camera. Flow patterns, heat transfer coefficient, pressure loss and C.B.R (cost per benefit ratio) were the variants that were probed in the present paper. It was found that the presence of the twisted tape turbulator could significantly affect the flow structure of the two-phase flow. The flow maps presented that by the decrement of twisted tape pitch the transition of slug flow to bubbly flow occurs very soon. Also, by the decrement of twisted pitch a swirling bubbly flow was observed in the horizontal tube. The maximum increment in the Nusselt number and pressure loss was about 35% and 81%, respectively. Also, it was revealed that for the water superficial Re number of more than 2400 with the decrement of pitch of twisted tape turbulator, the amount of C.B.R factor decreases.

Heat Transfer and Pressure Drop of R1234yf Boiling in Helically Coiled Tubes

In the present study, the boiling flow of R1234yf refrigerant in a horizontal helically coiled tube is investigated to experimentally measure the heat transfer coefficient and pressure drop. A well-instrumented apparatus consisting of the test evaporator and other necessary equipment is used in this investigation. A preheater and a post-evaporator are used to achieve the required vapor qualities and test conditions. Experimental investigations are carried out for a straight tube of 8.7 mm inner diameter and 1,200 mm length as well as helically coiled tubes with three different coil diameters of 10.95, 13.45, and 15.95 cm. For each experiment, different characteristic parameters such as refrigerant flow rate, outside tube surface temperature at various locations, heat flux, and pressure drop within the test section are measured. The results reveal that under the flow conditions studied in this work, heat transfer coefficient is increased up to 299% for the helically coiled tube compared to the horizontal straight tube. In addition, it is observed that for a constant coil pitch, pressure drop increases up to 227% occurring at the minimum coil diameter of 10.95 cm. Moreover, it is found that among the available models, Gungor and Winterton correlation predicts the experimental data with the least error.

Influence of secondary flow on the thermal performance of exhaust gas recirculation (EGR) coolers

Soot particulate matter deposition on the tubes of exhaust gas recirculation (EGR) coolers would form an insulating deposit layer, which deteriorates the thermal efficiency of the cooler and increases the pressure drop substantially. The objective of this research is to examine the influence of using helical tubes instead of straight horizontal tubes on the development of deposit layer. An experimental setup has been designed and constructed to examine the thermal performance of different types of EGR coolers under both clean and fouling conditions. Two sets of experiments have been performed, i.e. with and without soot particles, and in each set three types of EGR coolers have been examined, namely straight tube cooler, and two helical tube coolers of 5 and 10 windings. The effectiveness of the helical tube cooler is highest in case of 10 windings and lowest in case of a straight tube cooler which is due to the increase in the heat transfer surface area. The thermal resistance of the fouling layer in case of a straight tube cooler and 10 windings cooler has stabilized, however the thermal resistance in case of 5 windings is not stable and it is increasing with time. It has been concluded that there is a cleaning action during the fouling experiment in case of the helical tube coolers, and that is due to the secondary flow, and the efficiency of cleaning is a function of the intensity of the secondary flow. The thermal performance of the 5 windings cooler is not stable due to the development of the fouling layers, while in case of the 10 windings is stable, and that means there is a critical number of windings for the helical tube EGR coolers above which fouling diminishes. This critical number of windings is a function of the gas speed, particles size, tube diameter, radius of curvature and the winding pitch. The secondary flow in helical tubes agitates the boundary layer and decreases the pressure drop, such that it is advised to use helical tube coolers with more windings from a thermal and a fluid mechanics point of view.

Pressure drop, local heat transfer coefficient, and critical heat flux of DNB type for flow boiling in a horizontal straight tube with R-123

As far as design safety and operation of heat exchangers with a horizontal flow are concerned, it is necessary to study local heat transfer coefficient, boiling pressure drop, and critical heat flux for flow in a horizontal tube. In the present experimental work, local axial distribution of heat transfer coefficient, two-phase pressure drop, and critical heat flux for the flow boiling in a horizontal straight tube with R-123 as working fluid has been studied. Experiments are performed in horizontal tubes of diameter 11.9 mm and wall thickness 0.4 mm of SS304, having a heated length of 400 mm, 600 mm, and 1000 mm for the mass flux of 180 to 1210 kg/m2s. The local wall temperature is measured using the Infra-Red thermal imaging technique. The local heat transfer coefficients are compared with six different well-known correlations. Also, the two-phase frictional pressure drop is measured and compared with eight different general correlations. In the present study, a sudden rise in wall temperature at any location of a test section is considered as the occurrence of a boiling crisis. The boiling crisis mechanism observed in the present study is of departure from nucleate boiling (DNB). It takes place in the subcooled, or low quality saturated boiling region and in-between the length of the test sections rather than at exit as in the dry-out type of CHF. The critical heat flux is compared with six different predictive correlations. The mechanism of occurrence of CHF in the present work is found to be a departure from nucleate boiling.

Experimental correlation for critical heat flux in helical coils

The present work experimentally investigated the Critical Heat Flux (CHF) phenomena in helical coils. Literature on the CHF in helical coils is scarce. The centrifugal force and hence secondary flows of fluid is generated inside the coil due to its curvature. The Secondary flows of fluids may affect the heat transfer mechanism and hence, CHF inside helical coils. In present work, the experimental CHF data is compared with correlation available in literature. Fifteen empirical CHF correlations, that include correlation developed for straight horizontal tubes and helical coils, are compared with the experimental CHF databank. The CHF databank contains 413 CHF data of different helical coils. The data includes two fluids namely refrigerant R123 and water. Data covers the parameter range of tube diameter 5.5–10 mm, coil to tube diameter ratio 14–58, mass flux 92–2062 kg/m2s, heat flux 37–2984 kW/m2, density ratio 31–1352 and exit quality −0.1 to 1.2. The data mainly covers CHF in redeposition zone. The helical coil correlations are working reasonably well for long length helical coils but not working for short length helical coils. The straight tubes correlations are working reasonably well for all helical coils data. A generalised correlation is suggested for CHF in helical coils. The experimental data of CHF is published to contribute to the databank for helical coils.

Numerical analysis on flow and heat transfer of supercritical CO<sub>2</sub> in horizontal tube

In the present study, the three-dimensional steady-state numerical simulation has been performed by using ANSYS Fluent15.0 with SST <i>k-ω</i> low Reynolds turbulence model to study flow and heat transfer characteristics for supercritical CO<sub>2</sub> in the horizontal straight tube with inner diameter <i>d</i><sub>i</sub> = 22.14 mm and heating length <i>L</i><sub>h</sub> = 2440 mm under heating condition. The reliability and accuracy of the numerical model was verified by the experimental data of flow and heat transfer of supercritical CO<sub>2</sub> in horizontal tube. Firstly, flow and heat transfer characteristics of supercritical CO<sub>2</sub> was studied in horizontal tube. Based on the assumption that the supercritical CO<sub>2</sub> will undergoes “phase transition” between liquid-like and vapor-like at pseudocritical temperature <i>T</i><sub>pc</sub>, the differences between top generatrix and bottom generatrix of horizontal tube at flow and heat transfer behaviors were revealed. The results show flow and heat transfer characteristics of supercritical CO<sub>2</sub> in horizontal tube are similar to those under subcritical pressure. Then, the influences of heat flux <i>q</i><sub>w</sub> and mass flux <i>G</i> on flow and heat transfer of supercritical CO<sub>2</sub> were analyzed. The higher heat flux <i>q</i><sub>w</sub> is or the smaller mass flux <i>G</i> is, the higher inner wall temperature <i>T</i><sub>w,i</sub> at top generatrix is. The reasons for difference in the distribution of inner wall temperature <i>T</i><sub>w,i</sub> at top generatrix under different heat flux <i>q</i><sub>w</sub> and mass flux <i>G</i> were explained by capturing detailed information about thermophysical properties distribution including specific heat at constant pressure <i>c</i><sub>p</sub> and thermal conductivity <i>λ</i>, axial velocity distribution and turbulent kinetic energy distribution in the fluid domain. It is observed that vapor-like film thickness <i>δ</i>, vapor-like film property characterized by specific heat at constant pressure <i>c</i><sub>p</sub> and thermal conductivity <i>λ</i>, axial velocity <i>u</i> and turbulent kinetic energy <i>k</i> are the main factors affecting the difference in inner wall temperature distribution at top generatrix. The present work can provide a theoretical guidance for design and safe operation of heat exchanger for supercritical CO<sub>2</sub> Brayton cycle.

Thermo-Fluidic Characteristics of Two-Phase Ice Slurry Flows Based on Comparative Numerical Methods

Ice slurry is a potential secondary refrigerant for commercial refrigeration systems because of its remarkable thermal properties. It is necessary to optimize the heat transfer process of ice slurry to reduce the energy consumption of the refrigeration system. Thus, this study investigates the heat transfer performance of single-phase (aqueous solution) and two-phase (ice slurry) refrigerants in a straight horizontal tube. The numerical simulations for ice slurry were performed with ice mass fraction ranging from 5% to 20%. The effects of flow velocity and ice concentration on the heat transfer coefficient were examined. The results showed that heat transfer coefficient of ice slurry is considerably higher than those of single-phase flow, particularly at high flow velocity and ice content, where increase in heat transfer with a factor of two was observed. The present results confirmed that ice slurry heat transfer ability is considerably affected by flow velocity and ice concentration in laminar range. Moreover, the second part of this paper reports on the credibility three distinct two-phase Eulerian–Eulerian models (volume of fluid (VOF), mixture, and Eulerian) for the experimental conditions reported in the literature. All two-phase models accurately predict the thermal field at low ice mass fraction but underestimate that at high ice mass fractions. Regardless of the thermal discrepancies, the Eulerian–Eulerian models provide quite reasonable estimation of pressure drop with reference to experimental data. The numerical predictions from the VOF model are more accordant with the experimental results and the maximum percentage error is limited to ~20% and ~13% for thermal and pressure drop predictions, respectively.

Experimental and numerical comparison of the heat transfer behaviors and buoyancy effects of supercritical CO2 in various heating tubes

For the different flow orientations and physical models, the influence of buoyancy effect on flow characteristics exist essential difference, the heat transfer behaviors change accordingly. To suppress heat transfer deterioration and improve heat transfer performance, it is quite necessary to discuss the heat transfer behaviors of supercritical CO2 in various heating tubes. The heat transfer and flow characteristics of supercritical CO2 heated in the vertically straight tube, horizontal tube, and vertical helical-coiled tube, with inner diameter of 4 mm, are comparatively studied by experiments and numerical simulations. The tests are conducted at operating pressures from 7.5 MPa to 9 MPa, the mass flow rate is in the range of 80–600 kg/(m2•s). The heat flux covers a range from 10 kW/m2 to 70 kW/m2. The coupling relationship of buoyancy effect and flow characteristics in different physical models are revealed, and the various buoyancy criteria are validated with experimental data. The experimental results confirm that the employment of buoyancy parameter needs to take full account of the interaction between buoyancy force and flow orientations. And experimental data indicate that the heat transfer deterioration in the vertical tube is more serious than it in the horizontal tube. Generally, the helical-coiled tube has a noteworthy advantage for the average heat transfer performance, especially in the case of strong buoyancy. The new empirical correlations for the horizontal tube and helical-coiled tube are proposed with experimental data.

Convective heat transfer of nanofluids TiO2/Thermo Oil XT 32 in concentric tube heat exchanger

This research was conducted to examine the heat transfer characteristic of nanofluids TiO2/Thermo XT 32 oil on a concentric tube heat exchanger. TiO2 nanoparticles with nominal diameter of 21 nm were dispersed in Thermo XT 32 oil as base fluid at three different particles concentration of 0.1%, 0.3%, and 0.5%, respectively. A straight horizontal stainless-steel tube of 1.2 m length, 0.012 m inner diameter, and 0.022 m outer diameter were used as a test section. Collecting data by varying the temperature of the heat transfer nanofluids and nanoparticle volume fraction. Nanofluids prepared using the method of two steps without the addition of a surfactant by using a magnetic stirrer for 1 hour then ultrasonic cleaner for 3 hours. The results of research conducted, the coefficient convection heat transfer of nanofluids TiO2/Thermo XT 32 oil increases along with the addition of fraction volumes; this is due to the increased thermal conductivity of the fluid as well with the rise of temperature against nanofluids TiO2/Thermo oil XT 32. So it is very worthy of nanofluids applied in industries related to heat transfer processes.

Optimization of ground heat exchanger using microencapsulated phase change material slurry based on tree-shaped structure

Taking into account the potential of the tree-shaped ground heat exchanger to reduce pressure losses and microencapsulated phase change material slurry to enhance heat transfer performance, a new attempt combining microencapsulated phase change material slurry with tree-shaped structure is proposed in this paper. Firstly, to obtain the optimal structure of tree-shaped ground heat exchanger, influences of structure parameters on thermo-fluidic performance of ground heat exchanger are explored. Based on this optimal structure, numerical simulations adopting Eulerian-Eulerian approach are conducted to study hydraulic and heat transfer performance of microencapsulated phase change material slurry flowing through horizontal tree-shaped structure under constant flux. Comparison studies between different working fluid: water and microencapsulated phase change material slurry and different types of tube: horizontal straight tube and Y tube (tree-shaped tube) are studied. The results indicate that the numerical results accordwellwith experimental results. For tree-shaped ground heat exchanger with bifurcation level of 1, the optimal pipe diameter ratio meets D0/D1=23/7, D1/D2=1 and the optimal length ratio is L0/L1=1. Furthermore, the combination of microencapsulated phase change material slurry and tree-shaped structure can efficiently enhance thermal performance and reduce pressure losses. Considering comprehensive performance of microencapsulated phase change material slurry, the optimal volume fraction is 12% for Y tube, whose overall performance is 38.9% higher than that of pure water flowing through straight tube.

Simulation of Turbulent Heat Transfer Augmentation with Hybrid Nanofluid

Study of heat transfer augmentation with hybrid nanofluid represents a new class of heat transfer augmentation. The CFD model by using commercial software depending on finite volume technique and adopting SIMPLE algorithm is performed. Mixture of Aluminum Nitride (AlN) and alumina (Al2O3) nanoparticles into water as a basefluid is classified as a new class of hybrid nanofluids that can augment heat transfer. The nanofluid volume fraction and Reynolds number are in the range of (1% to 4%) and (5000 to 17000) respectively. The size diameter of nanoparticles and heat flux around a horizontal straight tube are fixed at 30 nm and 5000 w/m2 respectively. The numerical solution has been successfully validated by using an experimental data available in the literature. Results show that combination of AlN - Al2O3 nanoparticles into water basefluid tends to augment significant heat transfer performance.

Optical determination of oxygen mass transfer in a helically-coiled pipe compared to a straight horizontal tube

The gas-liquid mass transfer of oxygen has been examined experimentally in a helically-coiled pipe using an optical colorimetric method. Two tracer redox-reactions have been used for this purpose: (i) methylene blue and (ii) resazurin. The gas hold-up has been varied from 0.1 to 0.6, and liquid flow rate from 0.37 to 0.68 l/min, both leading to plug-flow conditions in the helix for all parameter combinations. A progress variable has been defined to measure the advancement of the reaction and thus, oxygen transfer to the liquid. The resazurin reaction turned out to be more appropriate for mass transfer studies, due to the bigger time constant difference of oxidation and reduction. Therefore, it can be adapted more easily to the specific conditions of the set-up. It also possesses more intense colours and higher fluorescence intensity, which might be useful for other mass transfer studies. As expected, the oxygen mass transfer increases with gas hold up, but liquid flow rate has little influence. A comparison with a horizontal tube of the same diameter shows the drastically increased mass transfer in the helix, due to better radial mixing and different flow pattern. Depending on the experimental conditions, oxygen concentration in the helix was up to twice that of the horizontal tube. This can be explained by the much higher liquid side mass transfer velocity, which is determined in this study from the experimental kla-values and specific bubble surface per turn of the helix. For this purpose, bubble dimensions and gas-liquid cell volumes have been determined from the experimental images. The paper thus presents a locally resolved characterization of gas-liquid mass transfer in a helically coiled reactor. The high mass transfer especially during the first turns of the helix shows its advantages compared to a straight tube.