Flow Pressure Drop Research Articles

Numerical simulation on gas-solid separation characteristics of in-situ pyrolysis products of tar-rich coal

ABSTRACT Tar-rich coal holds the potential to substitute the supply of oil-gas resources. The in-situ pyrolysis contributes to efficient resource utilization and can potentially achieve net-zero CO2 emissions. However, it is challenging to efficiently separate oil-gas resources, which are predominated by tar, from multiphase products of in-situ pyrolysis of tar-rich coal. Additionally, the difference in fluid properties yields significant influences on separation performance, while the understanding of the separation characteristics of high-viscosity fluid remains insufficient. In this study, the separation process of pyrolysis products from tar-rich coal was investigated using the computational fluid dynamics simulation approach. The flow field, pressure drop, separation efficiency and distribution characteristics were analyzed. The simulation results indicate that the volute cyclone separator exhibits commendable separation efficiency, exceeding 98%. Meanwhile, in handling tars containing a high concentration of light oil, the separator demonstrates remarkable adaptability. The separation efficiency of solid particles decreases from 89% to 83% when the system contains a high content of pitch. The particle diameter exerts great influence on the flow field. The separation efficiencies are 99% and 0.37%, respectively, when the particle sizes are selected as 0.1 mm and 0.001 mm. In the scope of this study, the optimal working conditions of the cyclone separator were determined, which provides data support for improving the separation efficiency and recovery rate of the oil-gas resources.

Study on the effect of immersion thermal management for high-current rate fast charging of 21700 Li-ion batteries

During high-rate fast charging, power batteries will generate significant heat. Therefore, it is more necessary to have an efficient thermal management system. This paper presents a thermal behavior simulation model for a 21700 NCM Li-ion ternary battery module, obtaining the onset temperature of each stage of the overheating decomposition reaction. On this basis, we developed an immersion cooling model for the battery module. And its cooling effect at different spacing (5-20 mm) and two different flow rate ranges (5-20 mm/s and 40-200 mm/s) in the fast charging process is simulated and analyzed. The results show that a 5 mm spacing exhibits a good heat transfer effect at low flow rates, while a flow rate of at least 20 mm/s is required for stable boiling heat transfer. In the high flow rate range, decreasing spacing or increasing flow rate will both reduce the temperature and temperature difference of batteries. Compared to 20 mm spacing and 40 mm/s flow rate, 5 mm spacing and 200 mm/s flow rate reduce temperature and temperature difference of batteries by 9.3 °C and 14.9 °C, respectively. Finally, the addition of the disturbing structure enhances coolant flow uniformity while minimally increasing flow pressure drop, and increases the heat flux by 157 W/m2, thereby further optimizing the cooling effectiveness.

Thermal hydraulic assessment on the full banana model of COOL blanket for CFETR

The Supercritical Carbon Dioxide (S-CO2) cOoled Lithium-Lead (COOL) blanket is under development for Chinese Fusion Engineering and Test Reactor. The thermal hydraulic assessment plays an important role for the comprehensive performance evaluation on the fusion blanket among the multi-physics fields. As the fusion reactor will enter into the engineering construction stage, it is important to study the thermal hydraulics performance on basis of the full model. Because it can accurately check the heat removal capability and thermoelectricity conversion efficiency, as well as provide essential input for the other physical fields. In this demand-driven, the analyses and optimization on the cooling system are put into priority on basis of the full banana model, including the manifold design and inlet/outlet pipes locations. Finally, the coolant pressure drop is highly reduced and the mass flow distribution becomes much more uniformly. For the S-CO2, 82.3% of the total mass flow rate is distributed into the key component first wall, and this is beneficial to face the high radiation heat flux. Besides, under different level of heat flux, the required total mass flow rate and pressure drop are obtained on premise that the coolant has enough ability to safely remove the heat away. For the Lead–Lithium (PbLi), the distribution of mass flow rate is designed as ‘ladder’ shape to adapt the unevenly spatial distributed nuclear heat along the radial direction, and the ratio is 8:2:1. Furthermore, the first law of thermodynamics is adopted for the trade-off analysis, which converts the total pressure drop of the two coolants into the pumping power, and it occupies only 1.3% of the total thermal power. This provides accurate and valuable data for the primary and secondary loop design, as well as the economic assessment on the fusion reactor. Finally, the Two Dimensional thermal hydraulic model containing the detailed layouts of different materials is used to study the coupling heat transfer effects between PbLi and S-CO2, as well as the MagnetoHydroDynamics (MHD) effects. The boundary conditions are derived from the results of full banana model, and the results show that the temperature of all materials is not exceeding the upper limits.

Numerical study on flow characteristics in the primary side of a once-through steam generator under ocean conditions

The flow characteristics of the primary side of the helical coil once-through steam generator (OTSG) have a significant impact on the safe operation of the reactor. Different from the land-based stationary working conditions, the flow of the primary side of the OTSG is influenced by sea waves and winds under ocean conditions. The rigid body motion model is used to calculate the flow of the primary side under different ocean conditions, including heeling, trimming, rolling, pitching, heaving, and combined conditions. The results show that under heeling and trimming conditions, the static pressure of the primary side is different from that under vertical conditions due to the influence of gravity, but its impact on the flow field is relatively small. Under rolling and pitching conditions, the mean flow velocity and pressure drop change periodically with the movement of the OTSG, and the smaller the sway angle, the smaller the variation amplitude of the mean flow velocity and pressure drop. Under the heaving condition, the variation amplitude of the mean flow velocity is greater than that under rolling and pitching conditions, and reverse flow occurs. Under the combined heaving and rolling condition, the mean flow velocity and pressure drop are influenced by the period and amplitude of both the two motions.

Frictional pressure drop of two-phase flow in a horizontal tube under low void fraction

The frictional pressure drop of air-water two-phase flow is a crucial parameter in hydrodynamic calculations. Solving for precisely calculating frictional pressure drop in it remains a significant challenge due to the various factors affecting two-phase flow characteristic. Currently, various scholars have proposed multiple frictional pressure drop prediction models of two-phase flow. Typically, these models exhibit great errors under low void fraction. To more accurately predict the frictional pressure drop of two-phase flow under low void fraction, this paper experimentally investigated the flow characteristics of air-water two-phase flow in a horizontal tube. The flow rates for water and air are 3-6 kg/s and 0.0004-0.003 kg/s, respectively. The void fraction ranged from 0 to 0.07%. The experimental data and flow patterns of two-phase flow were analyzed, and these data was compared with commonly used frictional pressure drop prediction model of two-phase flow. The results indicated that: (1) Within the scope of this paper, two-phase flow pattern observed include bubbly flow and slug flow. With changes in the void fraction, the number of bubbles and the length of slugs have undergo alterations; (2) All three commonly used prediction models underestimated the frictional pressure drop under low void fraction. Therefore, Considering more influencing factors to improve the accuracy of prediction model is the next research direction. This research has showed the limitations of existing prediction models and emphasized the importance of research on frictional pressure drop of two-phase flow.

Pore-scale Simulation of Two-phase Flow in Foamed Porous Materials

This paper establishes a pore cell model of foamed silicon carbide material based on a tetradecahedron structure, and uses FLUENT software to numerically study the flow rate and pressure drop changes in the porous structure at different flow rates and the gas-liquid two-phase flow state of the channel. The research results show that the porous skeleton structure has a great influence on the velocity and pressure distribution in the calculation domain; the inlet flow velocity has a certain impact on the gas-liquid mixing zone and gas-liquid interface area in two-phase flow. The application of tetradecahedral porous media increases the thickness of the gas-liquid mixing zone and the phase interface area are increased, with a maximum increase of 11.5%, thus promoting gas-liquid heat and mass transfer.

Numerical investigation on cavitation performance for centrifugal pumps with different impeller inlet geometry

In the centrifugal pump, cavitation often leads to the noise and pressure pulsation, further affects the performance and operation of the pump. Therefore, it is essential to improve cavitation performance at the stage of pump design. In this paper, three centrifugal pump impellers are designed by using different inlet geometry, where one is the conventional type and has cross section diffusion of flow passage along flow direction, and other two impellers are proposed and have cross section contraction of flow passage from impeller inlet to exit. For comparison of cavitation performance, the three-dimensional cavitating turbulent flows are simulated using the RANS method for the pumps. The results show that the pumps with the proposed meridional section have much better cavitation performance at design point while their hydraulic efficiency is also improved at larger flow rate, compared with that with the conventional meridional section design. Extending the blade leading edge of the proposed impeller is very helpful to obtain better cavitation performance further due to the uniform flow and smaller pressure drop around impeller inlet.

Anisotropic flow physics in diamond microchannels: Design implications for microfluidic rectifiers handling Newtonian fluids

The study explores anisotropic flow behavior in microchannels, which is crucial for advancing microfluidic rectifiers. Specifically, the investigation focuses on the directional flow behavior of Newtonian fluids within diamond-shaped microchannels, a topology holding significant promise across various disciplines. Unlike non-Newtonian fluids, Newtonian fluids lack inherent directional traits, needing high Reynolds numbers for inertial effects necessary for effective rectification in asymmetric flow structures. High Reynolds numbers in microchannels are challenging, but diamond microchannels uniquely exhibit inertial effects even at low Reynolds numbers, yet their potential for designing rectifiers is largely unexplored. The study presents two unique asymmetric diamond microchannel designs and conducts thorough three-dimensional numerical analyses to assess fluid flow across different design parameters. Rectification is quantified through fluid diodicity, demonstrating that configurations with higher width and aspect ratios and shorter lengths produce significant rectification effects. Examining velocity profiles and flow resistances in both directions illustrates irreversible flow physics. Notably, the observed maximum diodicity for the proposed design reaches 1.61 for Newtonian fluids, surpassing most previous designs by 11%–40%. Quantitative relationships between flow resistances in both directions and design variables through regression analysis allow determining flow resistances within ±8% and fluid diodicity within ±7% and ±10%, respectively, based on constant flow rate and pressure drop. These correlations provide valuable insights for the initial design of microfluidic rectifiers using these configurations. The results offer essential guidance for effectively designing microfluidic rectifiers using diamond microchannels in various scientific applications.

Investigation on conduction heat dissipation for thermal management in distributed multi-point electronic chips

A conduction thermal dissipation system is designed for the thermal management of distributed multi-point electronic chips. The heat from the chips is conducted to the flow channel on the two sides with the help of heat pipes. For the purpose of improving the heat dissipation performance, the influence of different flow channel structures was analyzed with the help of numerical simulations. When the fin thickness and spacing are 0.4/0.5 mm, the heat transfer performance is optimal with acceptable flow pressure drop. The results indicated that temperature and uniformity meet the requirements of the electronic chips. The temperature of the chips is lower than 80°C at 1500 W under the condition of the 35°C ethylene glycol solution with 200 L/h. The impact of thermal interface materials on thermal performance was also experimentally studied. The results showed that the graphite interface material has an excellent comprehensive performance with good thermal conductivity and convenient application. This method of distributed multi-point chips and two-sided heat dissipation is more effective in fully utilizing the advantage of heat pipes compared to the traditional usage of evaporation and condensation located on the two sides.

Impact of catalyst carrier with TPMS structures on hydrogen production by methanol reforming

As the core part of a microreactor, the reaction carrier provides reaction site and energy supply for hydrogen production. Among various types of reaction carriers, porous reaction carriers with complex flow path structures can effectively improve hydrogen production performance, and thus are widely applied in fuel cells. To optimize the structure of catalyst carriers and improve the efficiency of hydrogen production of methanol reforming, we designed four TPMS porous carrier structures, namely structures D, G, P and IWP, and analyzed the effect of carrier structure and parameters on hydrogen production reaction in theory. After that, we manufactured TPMS carriers with varied structures and parameters using 3D printing, and designed and carried out loading tests, flow velocity simulation experiments and pressure drop calculation to study the influence of the structure morphology on load intensity, heat and mass transfer and other performance indexes with catalyst load. Finally, we carried out hydrogen production experiments in microreactors with different TPMS structures, from which we obtained an pattern influence of hydrogen production conversion rate and hydrogen velocity etc. At different velocities and temperatures. The experimental results indicate that structure type and parameters of TPMS node and porosity have a great effect on the performance of hydrogen production. Specifically, structure D performs the best and structure P performs the worst in hydrogen production. When the velocity is 1.7 ml/h and the temperature is 250 °C, the maximum difference of the hydrogen conversion rate between D and P structure can reach to 22 %, and that of the hydrogen velocity can reach to 0.02 mol/h.

Gas-liquid two-phase flow pressure drop in flattened tubes: an experimental and numerical study

Experimental, numerical and empirical research is carried out on pressure drop features of air-water two-phase flow in horizontal flattened tubes. Circular tubes of 10.5 mm I.D. made of copper were successively flattened into inner heights of 9, 8, and 6 mm (AR=1.27, 1.5, and 2.2, respectively). The experiment operation conditions were 200, 500, and 1000 kg/m2s for mass velocity, 6, 8, 10 LPM for flow rate, and 0 to 0.005 for gas quality. Also, the pressure drop for R134a and R410A was estimated numerically using ANSYS Fluent. The simulation test condi-tions were for vapor quality of 0.1 to 0.9 and saturation temperature of 40°C, while the condi-tions for mass velocity and flowrate are taken as that of the experiment test. The experimental data were examined to see how different factors affect on the pressure gradient. According to the outcomes and as compared to the circular tube, the pressure gradient was raised up to 27%, 95%, and 218% for tubes flattened with aspect ratio of 1.27, 1.5, and 2.2, respectively. More-over, the pressure drop for either air-water or refrigerant fluids is increased dramatically with increasing flow rate, but it decreases with increasing vapor quality. When compared to known circular tube correlations, a good agreement was achieved. Finally, the minimum difference between the experimental, numerical, and correlated results was less than 3% for gas quality of 0.0048 and aspect ratio of 2.2.

An artificial neural network-based numerical estimation of the boiling pressure drop of different refrigerants flowing in smooth and micro-fin tubes

Abstract In thermal engineering implementations, heat exchangers need to have improved thermal capabilities and be smaller to save energy. Surface adjustments on tube heat exchanger walls may improve heat transfer using new manufacturing technologies. Since quantifying enhanced tube features is quite difficult due to the intricacy of fluid flow and heat transfer processes, numerical methods are preferred to create efficient heat exchangers. Recently, machine learning algorithms have been able to analyze flow and heat transfer in improved tubes. Machine learning methods may increase heat exchanger efficiency estimates using data. In this study, the boiling pressure drop of different refrigerants in smooth and micro-fin tubes is predicted using an artificial neural network-based machine learning approach. Two different numerical models are built based on the operating conditions, geometric specifications, and dimensionless numbers employed in the two-phase flows. A dataset including 812 data points representing the flow of R12, R125, R134a, R22, R32, R32/R134a, R407c, and R410a through smooth and micro-fin pipes is used to evaluate feed-forward and backward propagation multi-layer perceptron networks. The findings demonstrate that the neural networks have an average error margin of 10 percent when predicting the pressure drop of the refrigerant flow in both smooth and micro-fin tubes. The calculated R-values for the artificial neural network’s supplementary performance factors are found above 0.99 for all models. According to the results, margins of deviations of 0.3 percent and 0.05 percent are obtained for the tested tubes in Model 1, while deviations of 0.79 percent and 0.32 percent are found for them in Model 2.

Experimental investigation of two-phase flow in Chevron-type compact plate heat exchangers: A Study on pressure drops and flow regimes visualization

Compact plate heat exchangers are a very promising technology and lately they are being considered for potential use as steam generators in Small Modular Reactors. However, there is a lack of scientific literature on their operation with two-phase flows, especially with non-refrigerant fluids. In this study, we conducted experiments to visualize and measure the pressure drop of a two-phase flow in a Chevron-type Plate Heat Exchanger. An air–water mixture was used in adiabatic conditions as the operating fluid in upward-flow configuration. Visualization was achieved through high-framerate videos. This study covers a wide range of operating conditions, surpassing those documented in existing literature by specifically analyzing also the region of very low mass flux for both phases. The tested conditions ranged from 6 to 365 kg/m2s of water and from 0.02 to 5 kg/m2s of air. Single-phase pressure drops were measured to establish a correlation for the Darcy friction factor. Instead, measurements of the pressure drop in two-phase conditions were processed and presented using a non-dimensional form referred to as the two-phase multiplier. The adoption of a void-fraction model played a crucial role in accurately extrapolating the frictional component of the pressure drop from the measurements, resulting in less scattered data on the Lockhart–Martinelli plot. In addition, the observed flow structures were categorized into distinct regimes (fine-coarse bubbly, Taylor-like bubbly, heterogeneous, partial film, and film flow) based on visual observation and were represented on a flow map. Finally, these data were used to develop new criteria for predicting flow pattern transitions.

Theoretical and Experimental Investigation of Liquid and Gas Flow Pressure Drop through Different Sections of A Partially Closed Piping system

Multiphase flow is found in various places in nature and practice. However, multiphase flow is prevalent in the petroleum production industry. This phenomenon gives rise to a significant issue of pressure loss within piping systems, resulting in a loss in production. Multiphase flow has been studied for decades; however, with the increase in unconventional engineering methods, there is now a greater need for its study. This study investigates phenomena related to multiphase flow, such as flow regimes and pressure loss produced by friction, pipe orientation, and various fluid phase properties. An experimental system was designed, and different fluid phases were used to represent varying situations in piping systems. The system included sections of horizontal, inclined, and vertical pipe orientations experienced during hydrocarbon migration from the reservoir to the surface. To replicate industry multiphase flow in the experimental system, we used water to represent the oil and compressed air to represent gas. The pressure differences throughout the system were calculated using the Beggs and Brill Correlation, the Lockhart-Martinelli Parameter, and the Chisholm Equation. Experimental pressure differences and the effect of the choke valve positions were also recorded for the different sections of the system while observing the flow regimes produced by multiphase fluid interaction. Through the research methods, we found that most pressure losses occurred in the elbows, and most frictional pressure loss occurred in the vertical 3ft pipe, while the 45° and 90° downhill pipes experienced increased pressure.

A Numerical Simulation Approach for Superheated Steam Flow during Multipoint Steam Injection in Horizontal Well

Superheated steam flow during multipoint steam injection technology has a good effect on improving the steam absorption profile of heavy oil thermal recovery wells, enhancing the production degree of horizontal section of thermal recovery wells, and enhancing oil recovery. Based on the structure of multipoint steam injection horizontal string, considering the characteristics of variable mass flow, pressure drop of steam-liquid two-phase flow, and throttling pressure difference of steam injection valve in the process of steam injection, this paper establishes the calculation model of various parameters of multipoint steam injection horizontal wellbore and calculates the distribution of steam injection rate, temperature, pressure gradient, and dryness along the section of multipoint steam injection in horizontal wellbore. The results show that the temperature and pressure decrease gradually from heel to toe, and the steam dryness decreases gradually. Considering the influence of throttle pressure difference of steam injection valve and pressure drop of gas-liquid two-phase flow in the wellbore, the traditional calculation model of steam injection thermodynamic parameters is optimized, and the optimization of wellbore structure and steam injection parameters is an effective method to achieve uniform steam injection in horizontal wells. The steam injection uniformity of horizontal wells can be effectively improved by adjusting the steam injection valve spacing and steam injection parameters. When the steam injection volume is 200 m3/d and the steam injection valve spacing is 20 m, a more stable steam injection effect can be obtained. The findings of this study can help for better understanding of improving the uniformity of steam injection and enhancing the recovery factor.

Effect of lubricating oil on non-azeotropic refrigerant in flow boiling: an entropy generation analysis

ABSTRACT Entropy generation analysis is a useful method for studying the relationship between heat transfer and pressure drop in flow boiling. The flow boiling process in an actual refrigeration system is inevitably affected by oil. Therefore, the effect of oil on entropy generation needs to be investigated. A new non-azeotropic ternary refrigerant mixture, R447A, was selected as working fluid. Subsequently, flow boiling entropy generation models of R447A with and without oil were established. The effects of individual parameters on entropy generation were investigated. The entropy generation per unit tube length under different conditions was proposed as the benchmark for comparison. The results show that there is an optimal mass flux corresponding to minimum entropy generation per unit tube length at a specific oil concentration, and optimal mass flux decreases with increasing oil concentration. The tube diameter also affects the optimal mass flux of the fluid with oil, which increases with decreasing tube diameter and is smaller than that without oil for the same diameter tube. When the oil concentration is 0–4.95%, the total entropy generation exhibits a decreasing trend. Therefore, within the scope of this research, the addition of oil is beneficial for reducing the entropy generation of heat exchangers.

Saturated water flow boiling heat transfer and pressure drop in scalably microstructured plain and finned copper tubes

Well established understanding of flow boiling heat transfer and its hydrodynamic driving mechanisms have led to the inception of surface geometry augmentation techniques that can enhance thermal-hydraulic performance. Enhancing the flow boiling heat transfer at a reasonable pressure drop enables the deployment of more compact and efficient heat exchangers and thermal systems. To enable ease of manufacturing, simplicity, and reliability, passive augmentation techniques that do not require external stimuli are preferred. In this study, a scalable copper microstructuring technique was developed on both smooth and internally finned 0.25” tubes to investigate how it affects the thermofluidic behavior of relatively higher surface tension water during saturated flow boiling. The internally finned tubes used in this study comprised of 50 fins with a helical angle of 13°. To apply the conformal microstructures on the internal tube surfaces, chemical oxidation via an alkaline mixture was used, resulting in structures having characteristic length scales approaching 200 nm −1 µm. Our results show that microstructuring of plain copper tubes provides a water flow boiling heat transfer coefficient enhancement ranging from 10 % to 90 % compared to untreated specimens for vapor qualities ranging from 0 to 0.1 and mass flow rates ranging from 255 to 485 kg/(m2·s). Augmentation is attributed to the increased roughness of the plain copper tubes that creates additional nucleation sites for enhanced liquid entrapment and increases wettability. Associated with this heat transfer augmentation is an increased pressure drop ranging from 0.5 % to 38 % relative to untreated tubes due to the increased skin friction as well as add fluid flow disruption. Overall, the performance factor ranged between 0.86 to 1.81 demonstrating that the augmentation in heat transfer overshadowed the increase in pressure drop. Interestingly, applying the conformal microstructures on internally finned copper tubes decreased the heat transfer coefficient and pressure drop by as much as 75 % and 45 %, respectively, when compared to the un-structured finned copper tubes counterparts. The decrease in heat transfer performance and pressure drop was attributed to partial wetting of the fin roots due to the presence of a vapor layer near the inner tube walls. Our work develops a mechanistic understanding of the role that microstructures play during flow boiling of water on industrially applicable smooth and finned tube geometries and designs.

Demystifying Dry Powder Inhaler Resistance with Relevance to Optimal Patient Care.

The selection of an inhaler device is a key component of respiratory disease management. However, there is a lack of clarity surrounding inhaler resistance and how it impacts inhaler selection. The most common inhaler types are dry powder inhalers (DPIs) that have internal resistance and pressurised metered dose inhalers (pMDIs) that use propellants to deliver the drug dose to the airways. Inhaler resistance varies across the DPIs available on the market, depending largely on the design geometry of the device but also partially on formulation parameters. Factors influencing inhaler choice include measures such as flow rate or pressure drop as well as inhaler technique and patient preference, both of which can lead to improved adherence and outcomes. For optimal disease outcomes, device selection should be individualised, inhaler technique optimised and patient preference considered. By addressing the common clinically relevant questions, this paper aims to demystify how DPI resistance should guide the selection of the right device for the right patient.

Improved flow boiling performance and temperature uniformity in counter-flow interconnected microchannel heat sink

Microchannel flow boiling is one of the most effective solutions to the problem of heat dissipation caused by high power electronic devices. However, inherent drawbacks such as low critical heat flux due to dry-out of the liquid film near the channel exit, relatively high two-phase flow pressure drop, severe temperature nonuniformity and boiling instability at high heat flux still prevent widespread commercial application. In this study, based on the idea of uniform vapor quality along the flow direction, a copper Counter-Flow Interconnected Microchannel (CFIM) was proposed to address the main issues currently faced by two-phase microchannel heat sink. A comprehensive comparative study of CFIM, Co-Current Microchannel (CCM) and Counter-Flow Microchannel (CFM) was carried out from the aspects of boiling stability, boiling heat transfer characteristics and temperature uniformity. Three slots of 0.2 mm, 0.5 mm and 0.8 mm in width, denoted as IM0.2, IM0.5 and IM0.8, respectively, are considered. Experiments are conducted at mass fluxes of 291–618 kg/m2·s, saturation temperature of 40 °C and effective heat fluxes of 3–293 W/cm2, using the dielectric fluid R1233zd(E) as the working fluid. The results show that the CHF and average two-phase heat transfer coefficient (HTC) of CFIM are increased by 40.6 ∼ 100.5 % and 70.4–83.6 %, respectively, while the two-phase pressure drop is decreased by 17–32.6 % compared to CCM. The design of the counter-flow interconnected structure can manipulate the void fraction and two-phase flow pattern, resulting in a near uniform void fraction and flow pattern. The structure of these connecting slots promotes nucleate boiling and fluid mixing of neighboring channels. More importantly, the flow boiling instability and temperature non-uniformity in CFIM are well suppressed. In addition, IM0.2 has higher heat dissipation than IM0.5 and IM0.8 due to enhanced bubble nucleation, reducing superheat requirements and periodic rewetting to the center of the channel. The results of this research reveal that utilizing a microchannel heat sink with a counter-flow interconnected configuration can effectively improve heat transfer performance during flow boiling. Furthermore, it helps to mitigate issues such as flow boiling instability and temperature non-uniformity.

An experimental study on pressure drop of air-oil flow in horizontal pipes using two synthetic oils

This study focuses on the frictional pressure drop in gas-liquid two-phase flow, characterized by nonlinear behavior under various flow conditions due to complex two-phase phenomena. The experimental investigation involves an air-oil mixture flowing through horizontal pipes with diameters of 20 mm and 40 mm, aiming to observe the flow patterns and quantify the pressure drop. Two oils with different thermophysical properties are used as the liquid phase. The operating temperature and pressure of the test pipes are controlled within the range of 24–44°C and 1–3 bar, respectively. Seven air-oil flow patterns are identified based on visualization results: stratified smooth, stratified wavy, annular, plug, slug, bubbly, and dispersed bubble flows. On analyzing 1043 data points from the experiment, this study explores the effects of total mass velocity, flow quality, pipe diameter, operating temperature, operating pressure, and oil type on the frictional pressure gradient. Particular attention is given to the variation of the frictional pressure gradient concerning operating pressure, and its relationship with total mass velocity, flow quality, and flow pattern is discussed. Additionally, the study examines predictions from 55 previous correlations against the current pressure drop data. The predictive capability of these correlations is evaluated for the entire dataset and its subsets, categorized by oil type, pipe diameter, operating pressure, flow condition, total mass velocity, flow quality, and flow pattern. Evaluation metrics include mean absolute errors and the proportions of data points within 30% and 50% of absolute error. In addition, average and standard deviation values are calculated for each dataset to provide a comprehensive assessment.