Fluid Outlet Research Articles

Thermodynamic Characteristics Study with Pyrolysis Steam Coupled Multi-Stage Condensers

A four-stage condensers in series system was adopted to solve the problems of insufficient condensation of high-temperature pyrolysis steam and difficulty in the classification and recovery of pyrolysis oil, where the internal fluids conducted countercurrent convection heat exchange. A steady-state physical and mathematical model of a single condenser was established to clarify the discipline of heat transfer between the internal fluids. Meanwhile, the model of pyrolysis steam coupled multi-stage condensers was proposed with the help of the model compound firstly. A numerical simulation was carried out and the results showed that when the number of condensers in series was four, the heat transfer process of the system reached saturation, and the heat exchange of the cold and hot fluids was completely realized, and it was of little significance to continue to connect more condensers in series for the condensation of pyrolysis steam. To quickly condense the hot fluid, the key was to increase the mass flow rate of the cold fluid in the first-stage condenser. Compared with the experimental values, the calculated values of hot fluid outlet temperature were not higher than 10%, indicating that the model was highly reliable.

Thermo-Hydraulic Optimization of Shell and Externally Finned Tubes Heat Exchanger by the Thermal Efficiency Method and Second Law of Thermodynamics

The application aims to determine the thermal and hydraulic performance of externally finned, counter-flow, Shell, and Tube Heat Exchangers (STHE). The application refers to the cooling of machine oil flowing in the annular region, including non-spherical cylindrical nanoparticles of Boehmite Alumina. The oil inlet temperature is equal to 80 °C. Sea water is a coolant with an inlet temperature of 20°C. The main parameter in the optimization process is the number of finned tubes used for oil cooling. Another optimization factor is the number of heat exchanger units connected by hairpin. The number of fins per tube is fixed, equal to 34. The oil flow is set and equal to 4.0 kg/s. The inlet water flow varies, with a maximum flow of 5.0 kg/s. The quantities determined for analysis are: the thermal effectiveness, the actual and maximum heat transfer rates, the pressure drops caused in the tubes and by the flow in the annular region and fin system, the thermal and viscous irreversibilities, and the fluid outlet temperatures, and the thermodynamic Bejan number. It was determined that increasing the number of finned tubes from two to six tubes leads to better thermal and hydrodynamic performance. That is, it produces a favorable cost-benefit, to the detriment of the high viscous dissipation caused by the oil in the annular region. As an object of analysis, the inclusion of nanoparticles showed a significant improvement in thermal performance and an increase in viscous dissipation, with a slight decline in the Bejan number.

The effects of a novel baffle-based collector on the performance of a photovoltaic/thermal system using SWCNT/Water nanofluid

• The baffle-based PVT systems are more efficient than simple-based modules. • Baffled-water-based PVT unit reduces cell temperature and rises outflow temperature significantly compared to the simple one. • A baffled collector system allows less temperature increase in the panels as more solar radiation is received. • The improvement of the baffle-based PVT can be amplified by increasing the flow rate. The paper presents a novel baffle-based collector for a photovoltaic/thermal system (PVT) to increase output from the system using solar power. A three-dimensional numerical model of the baffled-based PVT system was developed using the Finite volume scheme and pure water and SWCNT/Water nanofluid as the working fluids. Validation of the model was carried out using experimental and numerical results. The results of both tests showed that the relative errors of the results were less than 2.25\% and 3.54\% , respectively, which confirmed the model's accuracy. We evaluated the effects of concentration of SWCNT nanofluid, solar radiation, and flow rate on both panel cells and outlet fluid flow temperatures and also on PVT systems' electrical and thermal efficiency, using both baffle and simple channel heat collectors. The proposed baffle-based collector outperforms the straightforward collectors in all examined cases. As a result of the baffles installed in the collector, the heat transfer area and convectional heat transfer coefficient are increased, which leads to better heat transfer between the solar cells and the collector fluid. As the baffles in the collector disrupt the flow, vortices are generated, which increases the rate of heat absorbed from the PV panel by the working fluid. The solar panel temperature increases less with a baffled collector system than with a simple one as more solar radiation is captured. Additionally, in the baffle-SWCNT-based PVT framework, solar cell temperature decrease by 3.83\% , and outlet temperature, electrical and thermal efficiencies increase by 1.63\% , 0.83\% , and 4.39\% , respectively, in comparison with the simple collector. The baffle-water-based system's overall efficiency is 66.45\% , while the simple-water-based system is 63.85\% . Among the obtained results, the SWCNT/water nanofluid does not offer a significant advantage over the water-based PVT module. Furthermore, the baffle-water-based PVT system was chosen as the optimal case in this study.

Device Modeling for GHE Experimental Test

Ground Thermal Response (TRT) tests are employed to calculate ground thermal characteristics for Ground Heat Exchanger (GHE) design and optimization purposes. There are plenty of 3D models to increase the accuracy of the calculated characteristics, with which the fluid outlet temperature is obtained based on the experimental inlet temperature. To simulate other behaviours not tested in the GHE, it is necessary to correctly simulate the conduct of the fluid inside the test equipment. For this reason, a simple model has been obtained which considers the absorption of heat by the elements of the equipment during an initial time through a variable equivalent heat capacity term and a load factor.

Theoretical-Experimental Analysis of the Performance of Geothermal Heat Pumps for Air Conditioning Greenhouses in Arid Zones

This study shows the results of a simulation tool using the TRNSyS 2017 simulator, validated with experimental data from a greenhouse in an arid zone in northwestern Mexico. Additionally, experimental data on the performance of geothermal heat pumps are shown during the year 2020 in heating and cooling mode. With this information, an average deviation of the simulator for the outlet fluid temperature of the geothermal heat exchanger (GHE) of 2.77% and an average deviation of the coefficient of performance in cooling mode (EER) of the geothermal heat pump (GHP) of 3.7% was obtained. In the experimental study, it was observed that in the last 2 weeks of July and the first 2 weeks of August, the subsoil is saturated, which causes a decrease in the thermal inertia of the GHE. During the experimental study, it was possible to determine that the flow indicated in the GHE to obtain the highest performance of the GHP system in greenhouses in arid zones corresponds to 1 GPM, obtaining an EER of 3.24.

Reuse of Abandoned oil and gas wells for Power generation in Western Dessert and Gulf of Suez fields of Egypt

This study investigates the capable outcome of using existing abandoned oil and gas wells as a geothermal energy source in Egypt. Geothermal resources of Egypt are mainly located along the Gulf of Suez and Red Sea in addition to some additional spots with lower potential in the Western Desert of Egypt. In Gulf of Suez the geothermal potential identified data and parameters dignified from oil and gas wells under the regulation of the Egyptian General Petroleum Corporation. Using abandoned oil and gas well which already lost their economic value would save drilling time and cost which would decrease the ROR of the investment. In this paper a simulation model cycle has been made by ASPEN HYSYS software to show the reliability of using the abandoned oil and gas wells outlet fluid as a source geothermal energy in Egypt by mapping the geothermal favorability locations with the oil and gas field area. Mapping shows that in Egypt there is potential of extracting low, medium and high temperature extractions from wells according to the location. Results demonstrates that the output power for the simulation geothermal power plant in different locations of Egypt and at various temperatures. Showing that in western desert the maximum output power that can be generated from the modified binary cycle is 3.063 MW at output temperature of 125 °C. Whereas in the Gulf of Suez proposed maximum output is 44.6 MW that can be produced from modified Flash steam cycle at an output temperature of 300 °C.

Model-based sizing of a CO2 heat pump for residential use

CO2 heat pumps have advantages of reducing ozone layer damage and offering high-temperature hot water in comparison with traditional heat pumps. However, sizing of CO2 heat pump components that guarantees reliable performance is still challenging. Therefore, this study proposed a model-based sizing method to remedy this research gap. The quasi-dynamic model of the CO2 heat pump was developed by integrating dynamic and steady-state models. Model validation results demonstrated that average relative error for the outlet fluid temperature of evaporator and gas cooler were 7.8 % and 1.4 %, respectively. This indicated that the developed quasi-dynamic model was reliable. Modelling results indicated that coefficient of performance (COP) for the heat pump was 3.99 when the inlet water temperature in gas cooler and expansion valve opening were 24 °C and 28 %, respectively. The proposed model-based sizing method could effectively determine the optimal gas cooler area enlargement ratio in different compressor and expansion valve features. The results showed that higher priority to the operation and higer COP value, would favour larger gas cooler area, while higher priority on the investment cost would prefer lower gas cooler area. This study is useful to properly design and operate the CO2 heat pump.

Thermal-fluid topology optimization with unconditional energy stability and second-order accuracy via phase-field model

This paper aims to establish a novel and efficient topology optimization method for the thermal-fluid. To adaptively design the fluid–solid coupling structure and make the objective energy to dissipate, the proposed method considers several constraints, such as the volume conservation, inlet and outlet flow velocity field and fluid–solid boundary constraints. The governing system includes the phase-field model, the steady state Darcy equation and the heat transfer equation. Under the constraints of multiple physical fields, we prove the existence of minimal solutions to the optimization problem. We use a Crank–Nicolson (CN) type scheme to discretize the governing system. The multigrid method is used to solve the resulting system of discrete equations. We prove the boundedness and unconditional stability of the original energy, which implies that a large time step can be used. The proposed discrete system is both spatially and temporally second-order accurate. Various computational tests have been performed to demonstrate that the numerical approach is efficient in designing the complicated structures of thermal fluid flows.

Design and Performance Analyses of Evacuated U-Tube Solar Collector Using Data-Driven Machine Learning Models

Abstract In this study, the implementation of data-driven machine learning (ML) models for design analysis and performance prediction of evacuated U-tube solar collectors (ETSCs) is investigated for the first time. Although evacuated U-tube solar collectors are widely investigated both numerically and experimentally, the implementation of data-driven machine learning models as an efficient predictive tool was not explored for the ETSC. So, to fill this literature gap, seven ML models such as linear regression with repeated K-fold cross-validation (LR), K-nearest neighbors (KNNs), principal component analysis (PCA), partial least-square regression-I (PLSR-I), partial least-square regression-II (PLSR-II), support vector regression (SVR), and stochastic gradient descent regression (SGDR) are employed using three hundred experimental data points and are reported in the literature. The heat transfer fluid outlet temperature (Thtf,o), thermal energy gained by heat transfer fluid (Q˙htf), and ETSC efficiency (ɳETSC) are considered as output/performance parameters. The outcome of the predicted results suggests that the SGDR ML model is superior in predicting all the performance parameters showing R2 values of 0.98, 0.981, and 0.99 for “Thtf,o,” “Q˙htf,” and “ɳETSC,” respectively. Moreover, the KNN ML model showed weaker performance for predicting the output parameters. In addition, it is observed that the SGDR ML model has a low training time of 0.45 s when compared to other ML models. For the given operating range, the predicted optimal performance parameters such as “Thtf,o,” “Q˙htf,” and “ɳETSC” obtained from the SGDR ML model are 45 °C, 0.44 kW, and 71%, respectively. Furthermore, the recommendations and shortcomings associated with the ML models for the design and performance optimization of ETSC are also presented in detail.

Effect of PCM melting temperature on solar ponds performance: Design and experimental investigation

Salt gradient solar pond (SGSP) is a technology which uses a renewable source such as solar energy to store thermal energy in a saline solution. Traditional SGSPs work in the sensible zone, increasing its temperature as the solar radiation is absorbed. SGSPs suffer from a low stability and energy efficiency, mainly caused by the high temperatures reached. At high temperatures, higher heat losses correspond. PCMs are characterized by high latent heat and a solid-liquid phase change at a nearly constant temperature. A pond integrated with PCMs can store the same amount of energy at a lower temperature, improving thermal efficiency and stability. In this paper, a pond integrated with PCM (RT35 HC) and a traditional one were designed, built and tested to evaluate the different performance. According to results, over ten days, the average temperature in the pond with the RT35 HC is about 4 °C lower (corresponding to the 5.7 %). Then a second experimental analysis was conducted comparing two different melting temperatures (RT35 HC and RT44 HC). Results show that a higher melting temperature enables to smooth the high peaks of temperature. While a lower melting temperature guarantees a higher and more stable temperature at night, due to the release of latent heat, making the application useful in case of constant temperature demand at the outlet fluid. Results are widely discussed in the paper.

Study on Microscopic Water Flooding in Porous Carbonate Reservoirs by Numerical Simulation

The study on the flow behaviors of oil and water two phases in porous media and their influencing factor is very important to adjust the porous carbonate reservoir development strategy and enhance the oil recovery. Based on the CT (computed tomography) scanning of real carbonate reservoir core sample, the micropore structure was reconstructed, and the effects of different factors (injection rate, oil-to-water viscosity ratio, and contact angle) and secondary development methods (higher injection rate and water displacement direction optimization) on the flow behavior of oil and water two phases were explored by numerical simulation in this paper. It is found from the study that the pores in the porous carbonate reservoirs have good structural connectivity. During the displacement process, the oil-water interface mainly resides at the pore throat junction with a large change of pore size, and the Haines jumps exist in the oil-water movement; the areal sweep efficiency of the water phase is jointly affected by the viscosity effect, interfacial tension, pore structure, and injection rate. Under the minimum injection rate and oil-to-water viscosity ratio, the maximum oil recovery can be obtained, and the oil recovery is 52.62% and 57.01%, respectively. The recovery efficiency and swept area are better in a water-wet system than oil-wet system. During the secondary development, the remaining oil is hardly displaced even with the injection rate increased by a factor of 50, and it shows improvement after 250 times of initial injection rate. Changing the position of water inlet and the produced fluid outlet results in better recovery since the remaining oil near the new inlet and outlet can be effectively produced.

No-vacuum Mono-Tube Compound Parabolic Collector Receiver for Linear Fresnel Concentrator: Numerical and Experimental Approach for Dynamic Behavior Assessment

The present paper aims to develop a novel simplified transient model to investigate the dynamic behavior of a no-vacuum mono-tube receiver equipped with a compound parabolic collector. Considering the intermittency of solar radiation, predicting receiver thermal behavior is critical for linear Fresnel concentrator design and operation. From this standpoint, this research focuses on determining whether or not the steady-state assumption influences the receiver’s performance. Unlike the current models accounting for all the receiver components, the proposed model considers the absorber tube as the primary node and focuses on the heat transfer fluid temperature distribution. The remaining components form an equivalent thermal resistance through which heat loss occurs. The global heat losses are then characterized using an experimental receiver prototype with tube diameter of 70 mm, an aperture of 500 mm, and a secondary reflector. The overall receiver heat loss coefficient was determined at different absorber temperatures ranging between 60 and around 265 °C. The heat loss coefficients measured varied from 4.7 to 8.5 W/m2 K. The model computes receiver performance using the measured overall heat loss coefficient based on real solar data. The receiver response at steady and transient states has been conducted and discussed according to several design parameters, including the heat transfer fluid nature and mass flow rate, the receiver length, and the absorber tube thickness. For the same working conditions, synthetic oils fluid allows achieving higher efficiencies whereas molten salts enable reaching higher outlet temperatures. For the metal wall thicknesses ranging between 2 and 3 mm and the fluid outlet temperature varying between 250 and 300 °C, the receiver thermal efficiency during the day remains relatively close to 75 %. The impact of the absorber tube thermal inertia has been investigated by analyzing the dynamic behavior under various close-to-real-world scenarios. Results have shown that the steady-state assumption does not influence if the metal wall tube thickness is lower than 3 mm.

Numerical Investigation of Seepage and Heat Transfer in Rocks with Various Fracture Patterns for Geothermal Energy Extraction

Unraveling the seepage and heat transfer coupled process between the working fluid and the fractured rocks in geothermal reservoir is of great significance to the exploitation and utilization of geothermal resources. In this study, based on the numerical modeling of fracture flow in geothermal reservoirs, the seepage and convective heat transfer behavior of fractured granite during geothermal extraction were investigated, and the effects of different fracture patterns, fluid injection temperature, and injection velocity on the temperature evolution of rock mass were comparatively analyzed. The results clearly revealed the influence of five different fracture patterns, i.e., single fracture, echelon fracture, parallel fracture, Y-shaped fracture, and crossfracture, on heat transfer capacity. Generally, the echelon fracture has the highest fluid outlet temperature, while the crossfracture has the largest total heat and shows the strongest heat transfer capacity. Besides the fracture shape, the fluid injection temperature and injection velocity also play significant roles in the heat transfer performance. The increase of fluid injection temperature would improve the total outlet heat of the crossfracture system and also benefit the system life. When the fluid injection temperature raises from 20°C to 35°C, the system life and the total outlet heat would be increased by 58.76% and 22.42%, respectively. However, higher fluid injection velocity would damage the system life of the geothermal reservoir, which obviously results in a decrease in total outlet heat. With the fluid injection velocity increasing from 0.004 m/s to 0.006 m/s, the system life could drop by 72.47%, and the total outlet heat was reduced by 55.72%. This work contributes to the preliminary understanding of the coupled seepage and heat transfer behavior in rock mass with various fracture patterns, and it could provide some practical implications for the rational exploitation of geothermal resources.

Exergy and thermoeconomic analyses of serpentine tube flat-plate solar water heaters coated with CuO nanostructures

This study aims to evaluate the effect of cuprous absorber plate coated with copper oxide nanoparticles (CuO NSs) on exergy and economic changes and performance of flat plate collector solar water heater and compare the absorber performance with simple and black painted absorber. For this purpose, three solar water heaters were fabricated with the simple flat copper absorber plate, black painted copper absorber plate, and copper absorber plate coated with CuO NSs. All the three water heaters were tested together under the same conditions. The results revealed the performance of water heaters coated with CuO NSs improved compared to that of water heaters with black and simple copper absorber plates. The efficiency of water heaters coated with nanoparticles improved by 18.8% and 35.8% compared to that of water heaters with black and flat absorber plates, respectively. Analyzing exergy efficiency indicated nanostructures coating on the absorber surface increased absorption of incoming solar radiation and outlet fluid temperature and, consequently, improved exergy efficiency of solar collector by 11.2% compared to matte black absorber. Using solar water heaters coated with nanostructures saved more cost and electricity and shortened the payback period by 0.6 years compared to solar water heaters with simple cuprous absorber.

The deeper the better? A thermogeological analysis of medium-deep borehole heat exchangers in low-enthalpy crystalline rocks

The energy sector is undergoing a fundamental transformation, with a significant investment in low-carbon technologies to replace fossil-based systems. In densely populated urban areas, deep boreholes offer an alternative over shallow geothermal systems, which demand extensive surface areas to attain large-scale heat production. This paper presents numerical calculations of the thermal energy that can be extracted from the medium-deep borehole heat exchangers in the low-enthalpy geothermal setting at depths ranging from 600 to 3000 m. We applied the thermogeological parameters of three locations across Finland and tested two types of coaxial borehole heat exchangers to understand better the variables that affect heat production in low-permeability crystalline rocks. For each depth, location, and heat collector type, we used a range of fluid flow rates to examine the correlation between thermal energy production and resulting outlet temperature. Our results indicate a trade-off between thermal energy production and outlet fluid temperature depending on the fluid flow rate, and that the vacuum-insulated tubing outperforms a high-density polyethylene pipe in energy and temperature production. In addition, the results suggest that the local thermogeological factors impact heat production. Maximum energy production from a 600-m-deep well achieved 170 MWh/a, increasing to 330 MWh/a from a 1000-m-deep well, 980 MWh/a from a 2-km-deep well, and up to 1880 MWh/a from a 3-km-deep well. We demonstrate that understanding the interplay of the local geology, heat exchanger materials, and fluid circulation rates is necessary to maximize the potential of medium-deep geothermal boreholes as a reliable long-term baseload energy source.

On the thermal performance of evacuated tube solar collector integrated with phase change material

The aim of present work is to analyze a U-type of evacuated tube solar collector in which phase change material (PCM) is employed to store surplus solar energy in daytime and reuse it at nighttime when the solar irradiation vanishes. Both charging and discharging processes are considered and modeled. Two critical points should be considered in designing the proposed collector; the stable requirement outlet temperature of the domestic solar collector during daytime (about 40°C) and assurance of a complete melting/solidification process to reach the maximum energy storage and release. Since the absorbed energy from solar radiation by heat transfer fluid and PCM in both day and nighttime strongly depends on the U-type tube's diameter, three values of which (namely, 6, 8, and 10 mm) are selected to attain the best case. The results show that the case with 6 mm diameter yields a 25% and 13.5% improvement in the liquid fraction and fluid outlet temperature, respectively, at 3:00 PM in the charging process, compared to other cases. Also, this case has achieved a 20% delay in the thermal energy release process and has increased the fluid outlet temperature by 24%, compared to other cases, at 9:00 PM in the discharging process.

COMPLICATIONS DEVELOPED IN PATIENTS WITH CONTINUOUS RENAL REPLACEMENT THERAPY IN THE INTENSIVE CARE UNIT AND NURSING INTERVENTIONS

This study is to determine the complications developing in patients undergoing continuous renal replacement therapy in an intensive care unit and nursing interventions to prevent these complications. Along with the socio-demographic and clinical characteristic of the patients, complication development status and nursing interventions for developing complications were determined. Data were evaluated with mean, standard deviation and frequency. In this descriptive study, a total of 48 CRRTs were applied to 27 patients hospitalized in the general intensive care units of a university hospital between 02 January 2019 and 02 January 2020. The average age of the patients is 62.92+20.13, APACHE II 25.92+5.33, the duration of stay in intensive care is 23.73+23.67 days. Common first three complications in patients undergoing CRRT; 75.0% hypotension, 47.9% vascular access problem, 43.8% system clotting. Nursing interventions related to common complications have been defined as giving the patient an appropriate position, checking the pressure indicators of the hemofiltration device, checking the arterial and venous pressures and ultrafiltration rate on the indicators of the device, hourly fluid inlet and outlet was followed, vital signs were monitored hourly. It was found that many complications developed in patients undergoing CRRT and nurses in the intensive care unit applied basic nursing interventions. There were not sufficient.

Heat transfer effectiveness characteristics maps for additively manufactured TPMS compact heat exchangers

Increased power density in modern miniaturized electronics caused difficulty in keeping electronic performance effective. This challenge leads to the search for high-performance compact heat exchanger as one of the thermal management solutions. Conventionally manufactured heat exchangers had limitations that thwart the development of geometrically complex heat exchangers which are capable of exploiting topological aspects to enhance thermal performance. Subsequently, additive manufacturing (AM) is proposed as a powerful fabrication technique for compact heat exchanger based on the mathematically known triply periodic minimal surfaces (TPMS). In this work, we present 3D compact crossflow heat exchanger computational fluid dynamics (CFD) modelling of geometrically complex structures based on TPMS using STARCCM+ CFD platform. Moreover, CFD modelling is used to obtain new characteristics maps that relate heat transfer effectiveness (Ɛ) and number of transfer units for the proposed heat exchanger. The convection heat transfer coefficient, pressure drop, and inlet and outlet fluid temperature are all examined.

Estimation of Ground Thermal Properties of Shallow Coaxial Borehole Heat Exchanger Using an Improved Parameter Estimation Method

Ground thermal properties are prerequisites for designing the size of borehole heat exchanger. In this study, a 3D heat transfer model is developed to simulate the thermal response test (TRT) of shallow coaxial borehole heat exchanger (SCBHE), and effects of ground thermal properties on the slope of the mean value of inlet and outlet fluid temperatures are studied. The results show that the slope is strongly affected by ground thermal conductivity and is slightly affected by ground thermal capacity, and that ground thermal capacity only has a small effect on the slope. Then, by using the difference between the experimental slope and calculated slope as the objective function to estimate ground thermal conductivity, an improved parameter estimation method (PEM) is proposed to estimate ground thermal properties of SCBHE using the simulated TRT data, and it is compared with the direct method. The results show that ground thermal conductivity and thermal capacity estimated by the improved PEM are accurate for different ground thermal properties, and that ground thermal conductivity estimated by the direct method probably has some errors especially for small ground thermal conductivity or thermal capacity, indicating that the improved PEM has much higher precision than the direct method and can be applied for estimating the ground thermal properties of SCBHE.

Modeling and analysis of steam-water two-phase flow distribution and wall temperature distribution in parallel heated pipes with different manifold types

In solar tower receiver, boiler water-wall and various heat exchangers, the uneven distribution of two-phase flow often occurs among parallel heated pipes, which seriously reduces the operating efficiency and may further induce heat transfer deterioration and soaring wall temperature. In this paper, a coupling model for the flow distribution and heat transfer process of steam-water two-phase flow in parallel heated pipes was established based on the discrete methods. In the present model, two main improvements were proposed as below. On one hand, the calculated equations for the pressure drop and the phase distribution of two phase fluid in both the combining T-junction and dividing T-junction were established to consider the coupling effects of the inlet manifold and outlet manifold on the flow distribution characteristics. On the other hand, the calculation module for the heat transfer and wall temperature along the branch pipes was also coupled in the present model with considering of different heat transfer regions (saturated nucleate boiling region, liquid deficient region, and superheated steam region) along the pipe. The present model was then verified and used to investigate the effects of system pressure, inlet fluid flow, inlet steam quality and manifold type on the flow distribution characteristics of high temperature and high pressure steam-water in parallel vertical upward pipes, and the effect of the uneven distribution of the gas-liquid two phases on the system safety was analyzed and evaluated. It was found that gas phase preferentially enters the first branch pipe near the inlet of the dividing manifold affected by buoyancy, and this results that the inlet steam quality of the corresponding branch pipe is always obviously higher than that of the subsequent pipes. As the system pressure decreases, the outlet fluid enthalpy distribution and outlet wall temperature distribution among branch pipes become more uneven. Moreover, the outlet fluid enthalpy and outlet wall temperature of the branch pipes closer to the inlet of the dividing manifold increase sharply with the decrease of system pressure. In the U-type parallel pipe system, the branch pipes away from the inlet of the dividing manifold are more prone to wall overheating at the outlet, while the opposite is true for the Z-type parallel pipe system.