Heat Transfer Coefficient Of Flow Research Articles

Flow resistance and convective heat transfer by elastic turbulence in 1D/2D/3D geometries

Inducing elastic turbulence is a promising method to intensify flow and heat transfer at low Reynolds number Re. Different geometries shall have great impacts on the occurrence of elastic turbulence and its heat transfer effect, which are however seldom investigated especially for flow in 3D geometry. This work conducts a comparative experimental study of the dimension effect on elastic turbulence on 3D, 2D and 1D geometries with similar hydraulic diameters. Polyacrylamide is used to induce elastic turbulence and the corresponding flow resistance and heat transfer performance are obtained for different geometries under laminar flow conditions. The results provide strong evidence that curvatures are necessary for the onset of elastic turbulence in 1D geometry as shown by similar flow resistance and heat transfer coefficient between the Newtonian and viscoelastic fluids. Comparing to the 2D geometry, flow in 3D geometry achieves both reduced pressure drop gradient and increased heat transfer at the same time due to the unique interaction of elastic stress with the torsion and rotation effects. New correlations of Nusselt number Nu and Weissenberg number Wi are proposed in curved geometries as Nu∝Wi2.2 and Wi1.9 for the 3D and 2D flow structures, respectively, under the boundary condition of constant heat flux. The mechanisms of flow and heat transfer of elastic turbulence in different geometries are also discussed to help further optimization.

Experimental study of condensation heat transfer of R134a inside the micro-fin tubes at high mass flux

The flow condensation heat transfer coefficient of R134a inside two helical micro-fin tubes with outer diameter of 6.35 mm and helical angles of 18o and 28o respectively were experimentally studied at a high mass flux ranging from 500 to 1100 kg m−2 s−1. The condensation temperatures are 35°C, 40°C and 45°C, and the vapor qualities ranges from 0.95 to 1.00 at the inlet section and from 0.00 to 0.05 at the outlet section. Experimental results show that there are annular and intermittent flow regimes inside the tube under experimental conditions, the ratio of annular flow region to the total heat transfer region is about 70%. The liquid film flow changes from rotational flow to coexistence of rotational and horizontal flows when the vapor quality is 0.475±0.08, 0.486±0.06 and 0.521±0.05, respectively and the corresponding saturation temperature is 35°C, 40°C and 45°C. Based on the experimental data, the heat transfer coefficient increases with increasing mass flux and fin helical angle, and with decreasing saturation temperature and Reynolds number of cooling water. In addition, the heat transfer coefficient of annular flow is greater than that of intermittent flow, in other words, the heat transfer coefficient increases with increasing vapor quality. The heat transfer coefficient obtained at high mass flux was compared with the calculated data of some published correlations used at low mass flux. It was found that most correlations underestimate the experimental heat transfer coefficient inside the micro-fin tube, and these prediction deviation increases with increasing mass flux and fin helical angle. By introducing some dimensionless numbers as well as considering the flow mechanism of liquid film inside the tube, two heat transfer coefficient correlations were proposed based on the experimental data. The ratio of liquid film thickness to fin height was used to characterize whether the liquid film flow is rotational flow or coexistence of rotational and horizontal flows in the proposed correlation, which shows a better prediction accuracy with a mean deviation of less than 7.3%.

Effectiveness of actively adjusting vapour-liquid in the evaporator for heat transfer enhancement

• Active vapor–liquid adjustment is proposed to improve flow boiling heat transfer. • Principles and configuration of vapor–liquid adjustment evaporator are introduced. • Improved heat transfer and reduced pressure drop are simultaneously obtained. • Total temperature penalization ( TTP ) can be reduced by 14.4%. • Enhancement mechanisms of the novel evaporator are clarified. Vapor quality and mass flux are crucial parameters for heat transfer coefficient and pressure drop of flow boiling. In this paper, they are actively adjusted by means of draining and refilling liquid refrigerant in the paths for evaporator performance enhancement. Principles of the vapor–liquid adjustment evaporator are introduced and its corresponding configuration is proposed. The mathematical model of this novel evaporator is established and validated by experiment data. Under different separation efficiencies, inlet vapor qualities and inlet mass flowrates, the vapor–liquid adjustment evaporator (AE) is investigated and compared to the conventional evaporator without vapor–liquid adjustment (CE) from the perspectives of overall performance and local behaviors. At the studied conditions, the improved heat transfer coefficient and reduced pressure drop are simultaneously obtained at a separation efficiency of 40%. Its superiority over the conventional evaporator is generally confirmed in terms of total temperature penalization. However, the excessive separation efficiency leads to the deteriorated performance due to the appearance of superheating. The major differences of local heat transfer coefficient and pressure drop between the vapor–liquid adjustment evaporator and conventional evaporator take place in the first and second paths, which are the consequences of the competition of the enhanced vapor quality and decreased mass flux. The stratified wave flow is mostly encountered for both evaporators. The vapor–liquid adjustment evaporator can be further enhanced by optimization. This study offers an innovative approach for flow boiling heat transfer enhancements.

New method for the determination of convective heat transfer coefficient in fully-developed laminar pipe flow

New method for the determination of convective heat transfer coefficient in fully-developed laminar pipe flow

Heat transfer rates in hot shell, cold tube inclined baffled small shell, and tube heat exchanger using CFD and experimental approach

The work presented is an effort to realize the changes occurring for convective coefficients of heat transfer in STHX fitted with inclined baffles. Effort has been undertaken using Fluent, a commercially available CFD code ona CAD model of small STHX with inclined baffles with cold liquid flowing into the tubes and hot liquid flowing in the shell. Four sets of CFD analysis have been carried out. The hot liquid flow rate through shell compartments varied from 0.2 kg/sec to 0.8 kg/sec in steps of 0.2 kg/sec, while keeping the cold liquid flow condition in tube at 0.4 kg/sec constant. Heat transfer rates, compartment temperatures, and overall heat transfer coefficients, for cold liquid and hot liquid, were studied. The results given by the software using CFD approach were appreciable and comparatively in agreement with the results available by the experimental work, which was undertaken for the same set of inlet pressure conditions, liquid flow rates, and inlet temperatures of liquid for both hot and cold liquids. The experimental output results were also used to validate the results given by the CFD software. The results from the CFD analysis were further used to conclude the effect of baffle inclination on heat duty. The process thus followed also helped realize the effects of baffle inclination on convective heat transfer coefficient of the liquid flow through the shell in an inclined baffle shell and tube heat exchanger. The temperature plots for both cold and hot liquid were also generated for understanding the compartmental temperature distributions inclusive of the inlet and outlet compartments. The heat duty for a heat exchanger has been found to increase with the increase in baffle inclinations from zero degree to 20 degrees. Likewise, the convective heat transfer coefficients have also been found to increase with the increase in baffle inclinations.

Microchannel Liquid-Cooled Heat Exchanger Based on a Nonuniform Lattice: Study on Structure Calculation, Formation Process, and Boiling Heat Transfer Performance.

A microchannel radiator is advantageous due to its high efficiency and large boiling heat transfer coefficient of two-phase flow. Based on the research of uniform lattice structures, this study proposed a microchannel heat exchanger with a nonuniform lattice structure. The calculation, optimal formation, and boiling heat transfer performance of the nonuniform lattice structure based on selective laser melting (SLM) were investigated, and heat exchange samples were successfully prepared using SLM. The porosity and pore morphology of the samples were analysed, and the contrast experiments of boiling heat transfer were conducted with deionised water. The results revealed that the heat flow density of the lattice structure was a minimum of 244% higher than that of the traditional liquid-cooled plate. The critical heat flux density of the lattice structure is 110 W∙cm−2, and the critical heat flux density of the traditional flat plate is 45 W∙cm−2. In addition, the effects of cell structures indicated that for frame cells, the heat transfer effect of nonuniform frames was inferior to that of uniform frames; for face-centred cubic (FCC) cells, the nonuniform and uniform frames exhibited the same trend. However, the heat flow density of FCC cells was 25% higher than that of frame structures.

Evaluation of Heat Transfer Coefficient of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

Various experiments have been conducted on the heat transfer coefficient of two-phase flow boiling in mini channel tubes. In addition to obtaining data on the heat transfer coefficients through experiments, many researchers have also compared their experimental data using existing correlations. This research aims to determine the characteristics of the heat transfer coefficient of refrigerant R290 from the data used by processing and knowing the best heat transfer coefficient correlation in predicting the experimental data so that the results are expected to be a reference for designing a heat exchanger or for further research. The experimental data predicted is the two-phase flow boiling in a horizontal tube 3 mm diameter, with the mass flux of 50-180 kg/m2s, heat flux of 5-20 kW/m2, saturation temperature of 0-11 °C, and vapor quality of 0-1. The correlation used in this research is based on the asymptotic flow model, where the model is a combination of the nucleate and convective flow boiling mechanisms. The results show an effect of mass flux and heat flux on the experimental heat transfer coefficient and the predicted R290 heat transfer coefficient with asymptotic correlations had a good and similar result to the experimental data.

Investigations on porous media customized by triply periodic minimal surface: Heat transfer correlations and strength performance

Porous media are used widely in technological (e.g., transpiration cooling and heat sinks for electronic devices), and biological (e.g., bone tissue) applications. The requirement for performance optimization demands a transition from passive selection to actively designing the topology of porous media. Triply periodic minimal surface (TPMS) structures provided unique opportunities for customizing porous media. Further research is required regarding the quick topology customization, heat transfer correlation, and strength performance of TPMS porous structures. In this study, the correlations among the feature parameters in the TPMS equations in terms of the porosity (uniform and smooth graded), pore density, and equivalent pore diameter were also determined, thereby providing a rapid method for customizing the topology of TPMS porous structures. The correlations of flow resistance and heat transfer coefficient were determined in four TPMS porous structures (W type, P type, D type, and G type) by considering the Reynolds number (Reh = 10–129) and porosity (ɛ = 0.2–0.8). The strengths of TPMS-based porous structures were compared in experimental tests by combining with theoretical analysis. The results obtained in the present study provide valuable guidance for customizing the topology of TPMS porous media and predicting their performance in terms of flow resistance, and heat transfer, and strength.

Two-Phase Flow Regimes and Heat Transfer Coefficients With R245fa in Manifolded-Microgap Channels

Manifold microchannels have shown high performance in embedded two-phase cooling of high heat flux electronics, demonstrating several examples of heat dissipation of 1 kW from 1-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> chips, with low pumping power requirements. The heat transfer coefficients (HTCs) in previous studies of chip-scale manifold-microchannel coolers exhibited a peak at relatively low quality (about 0.2–0.4) and steeply declined thereafter with increasing quality. However, manifold microchannels—arrays of manifolded-microgap channels—are a more complex geometry than traditional, straight, and circular channels and therefore generate more complex two-phase flow phenomena, which influences the resulting heat transfer performance. To better characterize the flow and heat transfer in such channels, in this study, the fluid flow and wall heat transfer in a visualization test section was imaged with a high-speed optical camera and thermography. R245fa served as the working fluid due to its low-pressure operation (approximately 1.8 atm at 30 °C) and excellent thermal properties, including high latent heat, high specific heat, and high thermal conductivity. The results are reported in terms of the channel outlet flow regime and HTCs under varying heat fluxes and mass fluxes with two manifold designs. The flow regimes and HTCs are compared with well-regarded predictive relations developed for more traditional channel geometries. The emergence of intermittent, and then persistent, dryout was associated with intermittent rivulet flow at the channel outlet and was observed to cause declining average wall HTCs, even while high HTCs occurred at the consistently wetted inlet region.

Influence of Coiling Direction of Helical Tube Bundles on the Thermal-Hydraulics of the HTGR Steam Generator

Helical tube bundles were usually adopted in the steam generators (SGs) or intermediate heat exchangers (IHXs) of high temperature gas-cooled reactors (HTGRs). Heat transfer tubes in neighboring tube layers can be coiled in the same direction or in the opposite direction. The coiling direction has influences on the thermal-hydraulic performances of the SGs or IHXs. The cross flow convection over helical tube bundles with neighboring tube layers having the same coiled direction and opposite coiled direction were numerically investigated. Reynolds stress model with standard wall functions was used for the turbulence modeling. For a helical tube bundle with neighboring layers coiled in the same direction (parallel tube layers), the tangential velocity along the coiled circumferential direction could be observed obviously. For a helical tube bundle with neighboring layers coiled in the opposite direction (crossed tube layers), there is no average tangential velocity of the whole flow filed. And the streamlines of the fluid are very complex. The flow resistances and heat transfer coefficients over helical tube bundle with parallel tube layers and crossed tube layers were compared. Although the heat transfer over helical tube bundles with crossed tube layers was 9.39% smaller than that with parallel tube layers, the pressure drop over tube bundle with crossed tube layers was much smaller compared with those with parallel tube layers.

Flow boiling critical heat flux enhancement via different-mode-interacting boiling in narrow gaps

Flow boiling heat transfer has the potential to achieve the required phase-change performance cooling in narrow gaps. To further improve the critical heat flux (CHF) and heat transfer coefficient (HTC) in flow boiling, a method of different-mode-interacting boiling (DMIB) involving the interaction between neighboring boiling of different heat flux areas or different modes of nucleate and film boiling was utilized. We employed a nonuniform heating plate, in which copper and Polytetrafluoroethylene (PTFE) with different thermal conductances were alternately arranged near the upper surface to achieve a spontaneous nonuniform temperature distribution. Experiments were performed using a square heating surface (10 mm × 10 mm) with two material widths (W) of different materials. The results were compared with a uniform plate using deionized water as working fluid under the conditions of inlet subcooling ΔTsub = 2.0, 10, 20, and 30 K, flow velocity v = 0,1, 0.2, and 0.4 m/s, and gap size h = 1.0, 2.0, and 5.0 mm. The nonuniform surfaces of W = 0.5 and 1.0 mm are found to significantly enhance the CHF at all values of v, ΔTsub, and h. The enhancement of CHF and HTC was owing to the high efficiency of the DMIB and reasonable liquid supply on the nonuniform surfaces. In addition, v and ΔTsub had a significant effect on the CHF and HTC, whereas the trends were identical. The reduction in v and ΔTsub could increase the ratios of CHF, where the highest enhancement ratio achieved was 89% at h = 1.0 mm, ΔTsub = 2.0 K, and v = 0.1 m/s. Moreover, increments in v and ΔTsub led to higher HTC enhancements, whereas the highest ratio increased by a factor of 12 at h = 5.0 mm, ΔTsub = 30 K, and v = 0.4 m/s.

Universal condensation heat transfer and pressure drop model and the role of machine learning techniques to improve predictive capabilities

A novel, universal model is proposed to predict the condensation frictional pressure drop and heat transfer coefficient for horizontal microchannel and macrochannel flows. Over 4000 data points across the entire vapor quality range are collected with mass fluxes ranging from 50 – 800 kg m−2 s−1, reduced pressures from 0.03 – 0.96, and hydraulic diameters from 0.1 – 14.45 mm. The working fluids include synthetic refrigerants (R1234ze(E), R134a, R245fa, R404A, R410A), hydrocarbons (pentane and propane), and natural refrigerants (ammonia and carbon dioxide). Several models, including flow-regime based correlations and machine learning regression models (support vector regression, random forest, and artificial neural networks) are developed and compared with each other. Overall, machine learning algorithms, especially the random forest model, predict the data best for the pressure drop and heat transfer, with an absolute average deviation of about 4% for both models.

Experimental and modeling approach to heat and mass transfer in a porous bed of a rock-bed heat accumulator

The paper presents the results of the research concerning heat and mass transfer phenomena occurring in a porous bed of a rock-bed heat accumulator. The tests were carried out in a standardized semi-cylindrical foil tunnel, commonly used in horticulture farming, equipped with a rock-bed accumulator covering the area of 74.8 m2. Input data for the analysis were obtained from experimental studies carried out from April to October, including 435 charging and 409 discharging cycles. During the experiments, the process parameters, such as temperature, relative humidity and air flow velocity, in different measuring points of the system were recorded. Using modern mathematical modeling a multi-scale analysis was carried out to quantify the intensity of heat and mass transfer between the flowing air and bed particles, as well as the degree of humidification or drying of the air flowing out of the accumulator. The values of convective heat transfer coefficients and mass transfer coefficients for individual charging and discharging cycles were determined and correlation equations for them were found. The conducted analysis showed that the coefficients determined by measurements fit the proposed regression models with the following values of R2 (coefficient of determination): 0.83 and 0.86 for mass transfer coefficient (condensation and drying, respectively), and 0.85 for convective heat transfer coefficient. Using the similarity theory, the equations for calculating Nusselt and Sherwood numbers were found, from which the coefficients adopted for analysis can be derived. It was also analyzed to what extent the obtained results differ from the results presented by other authors describing similar issues. The originality of this research consists in determining the values of heat and mass transfer coefficients for the air flow through the porous bed and finding their functional dependencies on the input parameters. The research results fill the gaps in scientific knowledge; moreover, they can be applied in heat transfer engineering issues, such as modeling heat and mass processes occurring in a rock-bed accumulator in a greenhouse or in other facilities, thus enhancing the energy efficiency of the designed systems.

Performance investigation of a concentric double tube heat exchanger using twisted tape inserts and nanofluid

A horizontal double-tube counter-flow heat exchanger with and without twisted tape inserts (twist ratio of 3.2, 4, and 6) has been investigated experimentally using TiO2-H2O nanofluid. In this study, the heat transfer coefficient and friction factor of turbulent flow of TiO2-H2O nanofluid have been determined for Reynolds’ number varying from 5,000 to 25,000. Convective heat transfer coefficient for TiO2-H2O nanofluid (0.05% by vol.) is found to be higher than base fluid (4–6%). Also, an increase in the heat transfer coefficients up to 6%, 10.9%, 17.4%, and 23.4% are observed numerically for the 0.05%, 1%, 2%, and 3% volume concertation of nanoparticles of TiO2. On the other hand, when TiO2-H2O nanofluid (0.05% by vol.) is investigated using twisted tape inserts of twist ratio 3.2, the heat transfer coefficient is found to be increasing by 45%. The variation of the heat transfer coefficient for different types of nanofluids such as; TiO2-H2O, Al2O3-H2O, and CuO-H2O with 1% concentration of nanoparticles (by vol.) has also been studied at different Reynolds’ numbers. The simulated results show no significant effect of the size (30 nm and 50 nm) of nanoparticles (TiO2) on the heat transfer coefficient values of TiO2-H2O nanofluid at 0.05% volume concentration.

Steady state modeling of steam condensate cooler

Mathematical models for steam condensate cooler were developed. The models were deduced by applying the principle of conservation of energy and yielded an ordinary differential equation, which were solved by using MatLab ODE45 solver and validated using industrial data of a fertilizer company. The result gives minimum percentage absolute error or deviation between model predictions and industrial plant of 0.09% and 0.10% respectively for hot and cold fluid outlet temperature. These shows that the developed model predicted the fluid outlet temperature of the steam condensate cooler closely and the models were used to study the effects of process parameters such as fluid inlet flow rate and heat transfer coefficient on the performance of the steam condensate cooler.

Experimental study on single-phase convective heat transfer of interlocking double-layer counterflow mini-channel heat sink

This study proposes an interlocking double-layer mini-channel heat sink that can realize counterflow in which the flow direction is opposite in the adjacent channel. The heat sink consists of two-channel layers and a header/plenum structure serving as a pre-flow path for counterflow into the channels. The novelty and significance of the current study are that the counterflow multi-channel heat sink was first experimentally implemented through the design of a new internal flow distribution structure. The test data are obtained from the experimental evaluation of the single-phase flow cooling performance of the heat sink. The heat transfer characteristics of the heat sink are analyzed by separating the change in the single channel heat transfer coefficient increased by the counterflow channel effect. The thermal resistance representing the overall cooling performance of the proposed heat sink shows a significantly small value of 10-4 K-m2/W order, which indicates the heat transfer performance advantage of the new heat sink. The beneficial effect of counterflow is verified by comparing the heat transfer coefficient obtained from the proposed heat sink and the prediction using the previous correlation for unidirectional single-phase flow heat transfer coefficient. The measured heat transfer coefficients are much larger than the predicted values by all kinds of past correlations. The difference between the measured value and the predicted value is much greater at low flow conditions where the temperature gradient increases more significantly with the flow direction. It can be concluded that this indirectly implies the fact that temperature gradient mitigation by counterflow results in an additional heat transfer improvement that is unpredictable in the previous unidirectional flow correlations. A new correlation is proposed to predict the heat transfer coefficient affected by the counterflow. This study is the first to experimentally implement a counterflow heat sink, confirming the distinct advantage of improved cooling performance over conventional heatsinks. In addition, this study is meaningful in that it presents a performance prediction model that can be used in design for the practical application of counterflow heat sinks.

An empirical investigation on flow pattern, heat transfer, and pressure drop during flow boiling of R1234yf in an inclined plain tube

In the present study, the flow pattern, boiling heat transfer, and pressure drop of R1234yf are experimentally studied inside a plain tube with an inner diameter of 8.3 mm, the outer diameter of 9.52 mm, and the length of 670 mm, in seven different inclination angles from −90° (downward vertical flow) to +90° (upward vertical flow). The experiments are conducted at four mass velocities of 80, 160, 240, and 320 kg m−2 s−1, mean vapor quality range of 0.1–0.77, saturation temperature of 31 °C, and four heat fluxes of 4.5, 9.0, 13.5, and 18.0 kW m−2. The effects of different parameters on the heat transfer coefficient and frictional pressure drop have been investigated. Based on the results, the tube inclination angle has a significant effect on the flow patterns and heat transfer coefficient, which is more prominent at low vapor qualities and low mass velocities. For all mass velocities, the highest and lowest heat transfer coefficients are attained in the tubes with inclination angles of +90° (vertical upward flow) and −90° (vertical downward flow), respectively. The frictional pressure drop is considerably affected by the tube inclination angle, and the effect is more noticeable at high vapor qualities. At low vapor quality regions, the heat flux strongly affects the heat transfer coefficient while it has a negligible effect on the frictional pressure drop. Finally, the experimental results are compared to the existing correlations, and modified correlations are proposed to predict the heat transfer coefficient and the frictional pressure gradient of R1234yf during flow boiling inside an inclined plain tube.

Relationship Between Pressure Drop and Heat Transfer of Fully Developed Flow in Smooth Horizontal Circular Tubes and Spiral-Coiled Tubes in the Laminar Flow Regime

Abstract Studies on isothermal steady-state frictional pressure drop for flow of petroleum base oils SN70, SN150, diesel, and water are carried out in spiral coils with diameter to length ratio, 0.00042, 0.00047, 0.00073, 0.00164, 0.00189, 0.003, and 0.0037. An attempt is made to correlate friction factors with a better and more appropriate dimensionless group for flow of Newtonian fluids through spiral-coiled tubes. An innovative approach of correlating heat transfer data with the newly established dimensionless group is presented. Heat transfer experiments are performed for spiral coils with diameter to length ratio 0.000474, 0.00042, 0.001896, 0.00198, 0.000942, and 0.00164 in laminar flow regime. Suitable correlations for friction factors and Nusselt numbers are proposed. Relationship between pressure drop and heat transfer is studied. The incapability of the conventional analogy equations to estimate the heat and momentum transfer coefficients for laminar flow through straight or curved tubes is explained based on the viscous and form drag existing in straight and curved pipe flow. The limitations of the existing analogy equations are examined critically. A new general analogy equation is derived for laminar flow through spiral and straight tubes considering the influencing geometrical parameters of the tube.

The Effect of Mass Flow Rate and Heat Flux on Vertical Two-Phase Flow Regimes in a Small Diameter Tube

In recent years, there has been a rising concentration in investigating and researching the boiling of micro channel flow; since they afford high thermal effectiveness, small size, and low weight. In this paper, the boiling heat transfer was experimentally examined using water as the working fluid in small diameter tubes. Experiments for the flow model were performed using the same Pyrex glass tube test facility. The experiments of heat transfer were carried out using an internal diameter copper tube (10.922 mm). The range of other parameters was varied: mass flow rate (0.008–0.0214kg/s); heat flux (17351–80529W/m2); it has been found that the average coefficient of heat transfer depends on the form of flow pattern. The average heat transfer coefficient increases by about 37% when the flow pattern varied from slug flow to churn flow at a constant mass flow rate of 0.008kg/s. Besides, the heat transfer coefficient (h) in the two-phase flow, is 39%, which is more than that for single-phase flow, when the mass flow rate is 0.0214kg/s, and heat flux) increases from 17351W/m2 to 49105W/m2. Also, when mass flow rate rises from (0.008kg/s) to (0.0166kg/s), the pressure drop increases by about (15%) and increases by about (5%) when the mass flow rate rises from (0.0166kg/s) to (0.0214kg/s). The main regime of flow was a slug, churn, bubbly, dispersed bubbly, and confined bubbly flow.

Research on Flow and Condensation Heat Transfer Coefficient of multi-channel cylinder dryer in U-shaped Section

The cylinder dryer is the most energy-consuming part of the papermaking drying section. Whether the drying cylinder can effectively drain the drying cylinder affects the drying efficiency of the drying cylinder. The design of the multi-channel drying cylinder effectively improves the problem of the difficulty of the water accumulation discharge. In order to obtain a channel cross-sectional shape with better drainage and better heat transfer, two channels with different cross-sectional shapes are selected to study the flow and heat transfer of steam in this experiment. The changes of the channel heat transfer coefficient under different working conditions are studied and compared. The result show that the U-shaped channel heat transfer effect is better than that of other shape channels in the multi-channel dryer.