Head Of Distribution Research Articles

Parametric model and experimental investigation of a distribution header to relieve heat sink coolant maldistribution

Coolant maldistribution has obvious negative effects on the liquid cooled heat sink (LCHS) performance. This work proposed a distribution header parametric model to improve flow distribution and compared with conventional I-type LCHS. The distribution header was a symmetrical S-shaped structure with a drop-shaped baffle. The S-shaped outline was obtained through a streamlined design to reduce the flow resistance. The structure characteristics of the drop-shaped baffle, which first expands and then contracts, were conducive to change the flow direction and relieve flow maldistribution. The experimental and numerical results indicate that the S-shaped outline parameters exhibited small impact on fluid distribution improvement, but distinctly affected pressure drop. The parameters of the drop-shaped baffle had significant influence on the fluid distribution. Notably, compared with conventional I-type LCHS, the LCHS with distribution header can improve the heat transfer, fluid distribution and flow performance. The maximum temperature of the measuring points was significantly decreased by 12.12 %−14.62 %, pressure drop was reduced by 2.78 %–4.44 %, and the flow distribution was improved by 68.32 %. The conclusions proved that the distribution header is based on a simple design with lower energy consumption, and which can be used into LCHS to relieve the flow maldistribution.

Investigation of two-phase flow distribution in the vertical annular distribution header of a variable refrigerant flow heat pump system

The characteristics of two-phase flow distribution from a vertically installed annular refrigerant distribution header to multiple branch ports are investigated, with a specific focus on simulating a real variable refrigerant flow heat pump (VRF HP) system. A test section is fabricated to replicate an actual distribution header for empirical investigation, utilizing an air–water mixture as the working fluid. A series of experiments are conducted to examine distribution characteristics, involving variations in the location of the main inlet port, operational mode, total mass flow rate, and void fraction. The experimental results indicate that the two-phase mixture exhibits a relatively uniform liquid phase distribution to the branch ports when the main inlet port is positioned at the bottom side. However, maldistribution to branch ports is intensified as the inlet void fraction increases and the flow rate of the two-phase mixture decreases. Furthermore, a series of computational fluid dynamics analyses is performed to investigate the distribution characteristics of R410A, the actual working fluid utilized in VRF HP systems. These analyses are conducted under the operational conditions typical of VRF HP systems. Despite identical Reynolds numbers for the two-phase R410A flow and air–water mixture flow, the former exhibits a notably uneven distribution to branch ports owing to the distinct thermophysical properties, particularly density and viscosity. The findings from this investigation enhance the comprehension of two-phase flow distribution characteristics in a vertically installed refrigerant distribution header under real VRF HP system conditions, offering valuable insights into mitigating the maldistribution of refrigerant flow to branch ports.

Effects of header design on thermal characteristics of multi-nozzle steam spraying

The distribution header of small-scale steam systems, commonly employed in household items like steam cleaners, is pivotal for dictating the spray characteristics of the steam generated. For uniform spray performance across multiple outlets, it's imperative to discern the design factors influencing this outcome. We numerically assessed the flow characteristics of steam in a spraying system with three nozzle outlets and scrutinized the impact of header design parameters on uniformity. Through a multiphase numerical model, numerical simulations were conducted. Our analysis revealed that decreasing the diameter of the three outlets promoted a more even mass flow rate of the sprayed steam from each outlet, having a minimal effect on temperature consistency. In contrast, enlarging the tapering angle of the header improved temperature uniformity up to 62.5 % but negatively influenced the uniformity of the steam spray amount when outlet diameters were consistent. Notably, when the combined area of the outlets was increased, there was a decline of up to 85 % in the uniformity of the discharged steam mass among the outlets with an increased tapering. This research offers insights that are anticipated to inform future studies and advancements in steam spraying system optimization, enhancing performance and efficiency for applications such as steam cleaning and sterilization processes.

Numerical and experimental investigation of a multi-channel heat sink distribution header designed by topology optimization

The fluid distribution had a significant effect on the performance of the I-shaped multichannel heat sink. Previous researchers have improved fluid distribution by arranging baffles; however, this resulted in an increased pressure drop. In this study, a multichannel radiator distribution header was designed using a topological optimization method, and experimental and numerical studies were conducted. Both a numerical model and physical prototype were created and subsequently evaluated to assess the performance of the resultant distribution header. The effects of the distribution and conventional headers on the performance of a multichannel heat sink were compared. The results demonstrated that the distribution header designed using the topology optimization method can significantly improve multichannel performance. The optimized header design exhibited improved flow distribution rationality, enhanced heat dissipation, and reduced pressure drop compared to the two conventional designs. The volume flow rate was reduced by 58.66% and 59.29%, the heat transfer coefficient was increased by 29.39% and 21.42%, and the pressure drop was reduced by 9.38% and 16.98%. A peach-shaped baffle plays an important role in fluid distribution. These findings highlight the effectiveness and potential of topology optimization in the design of complex fluid distribution systems for heat exchanger.

Flow distribution in the air cooler of HTGR passive cavity cooling system

Passive Cavity Cooling System (PCCS) is an important safety related system for High Temperature Gas-cooled Reactor (HTGR). Air cooler is one of the key components of this system. The non-uniform flow distribution is a common issue encountered in similar Parallel Tube Heat Exchanger (PTHX). Improving flow uniformity is favorable for both thermal hydraulic performance and structure safety. In this work, the flow distribution characteristics of a compact parallel tube air cooler with U-type header arrangement are theoretically and numerically investigated. First, a theoretical discrete model is proposed for flow distribution in PTHX. It reveals that the static pressure distributions in the headers are influenced by static pressure recovery, friction resistance and local pressure drop, which is directly related with flow uniformity. Then, the flow uniformity of Z-type and U-type header arrangements is numerically investigated and compared in detail. Moreover, the effects of thermal hydraulic parameter and geometrical parameter on flow uniformity are successively evaluated. Numerical results show that the flow uniformity of PCCS air cooler with U-type header arrangement is more excellent than that of Z-type header arrangement. Thermal hydraulic parameters, such as tube-side water temperature and mass flow rate, have little impact on flow uniformity. Nevertheless, the flow distribution characteristics are very sensitive to the geometrical parameters, including the insertion angle configuration, the flow area ratio of header to parallel heat transfer tubes (AR) and the cross-sectional area ratio of distribution header to collection header (DCR). Reasonable insertion angle configuration and decreasing AR can effectively enhance the flow uniformity of PCCS air cooler. For header match, it should be avoided that the distribution header diameter below the collection header diameter. As a result, the optimal structure design determined in this work is an air cooler with U-type header arrangement, where the inlet insertion angle is 0°, the outlet insertion angle is 180°, and the diameters of distribution header and collection header are both 120 mm. Its flow uniformity is improved by more than 50% compared with present design. This work reports a promising design modification, as the potential structure optimization for HTGR PCCS air cooler.

Predicting Complex Erosion Profiles in Steam Distribution Headers with Convolutional and Recurrent Neural Networks

Predicting Complex Erosion Profiles in Steam Distribution Headers with Convolutional and Recurrent Neural Networks

ПРИМЕНЕНИЕ СХЕМ ТЕЧЕНИЯ И УЧЕТ ГИДРОДИНАМИЧЕСКИХ ЭФФЕКТОВ ПРИ СОВЕРШЕНСТВОВАНИИ РАЗДАЮЩИХ КОЛЛЕКТОРНЫХ СИСТЕМ ТЕПЛООБМЕННИКОВ И РЕАКТОРОВ ЯЭУ

The article deals with application of flow patterns and hydrodynamic effects in the course of upgrading distribution header systems (DHS) used in heat exchangers and reactors of nuclear power plants (NPP). Consideration is given to four typical axisymmetric DHSs of flat and cylindrical types, which differ in the ways of fluid supply to the collector and its removal from it. The schematic diagrams of flow patterns are shown for different DHS designs of the cylindrical types with central and lateral fluid inlets of the collector. Besides, the water flow pattern is given for the flow path of various DHS designs of a flat type, also with central and lateral fluid inlets of the collector. Hydrodynamic features of the fluid flow in the DHS have been analyzed. It is shown that in a restricted and free DHS the coolant flow is of a jet nature. The fluid flow in the header is characterized by transformation of some types of jets into others, by the presence of eddy and stagnant zones. The designs of heat exchangers and reactors for nuclear power plants with the considered typical DHS characteristics implemented are presented. The DHS designs upgraded with the use of the indicated patterns and effects are demonstrated. The revealed regularity of liquid distribution at the outlet of the DHS flow paths and the hydrodynamics identity property for axially symmetric DHS with flow reversal are analyzed.

LOCALIZATION OF EXPLOSION PULSES IN A CLOSED SPACE IN COAL MINES

The data on the prospect of using an artificial high pressure water barrier as a method of localizing the explosion impulse in the confined space of tunnels and mines are presented. The explosion impulse and the process of its decay in interaction with water fog have been studied. In the course of field research, an explosion was simulated in the shock installation, and a method for its localization was developed using four water screens (barriers). The water screen was created using a system of ring-shaped water distribution headers with high pressure nozzles installed in a circle. Hexogen was used as an explosive. Experiments on localization of explosions were carried out on the base of the "Grigol Tsulukidze Mining Institute of Georgia" in Tbilisi, Georgia, together with the research group of the Faculty of Chemistry and Chemical Technology of al Farabi Kazakh National University and the Institute of Combustion Problems. The influence of the water barrier on the process of shock wave attenuation at 3 points of overvoltage of the section is established. The test results showed that the average values of the overpressure in the three sections were reduced by 38.8%, 26.67% and 19.2%, respectively. The action of the shock wave occurs according to an exponential function, and all other wave changes along any other trajectory on the plane of h – t change are described by a single time dependence.

ТЕСТОВЫЕ РАСЧЕТЫ ГИДРОДИНАМИКИ РАЗДАЮЩИХ КОЛЛЕКТОРНЫХ СИСТЕМ ТЕПЛООБМЕННИКОВ И РЕАКТОРОВ ЯЭУ

The paper presents the results of test calculations of hydrodynamics for distribution header systems (DHS) in heat exchangers and reactors of nuclear power plants (NPP). The header system is a typical element of the flow path in the specified NPP equipment, their efficient and safe operation is a priority area for Rosatom State Corporation. The calculations have been performed with the use of computational fluid dynamics software systems known as CFD codes. The results of calculations are presented for the coolant turbulent flow in the flow paths of the flat and cylindrical DHS with different conditions for the coolant supply and removal. A comparative analysis of the calculation results and experimental data on hydrodynamics of DHS typical of the nuclear power plants has been carried out, their satisfactory agreement has been shown. An assumption is made of the legitimacy of using the CFD code for the calculation of hydrodynamics of various DHS types and their specific typical elements.

ГИДРОДИНАМИКА ТИПИЧНЫХ РАЗДАЮЩИХ КОЛЛЕКТОРНЫХ СИСТЕМ ЯЭУ: СОВРЕМЕННЫЕ ПРЕДСТАВЛЕНИЯ И ПЕРСПЕКТИВЫ ИССЛЕДОВАНИЯ

The paper considers the issues of hydrodynamics of typical distribution header systems (DHS) in heat exchangers and reactors of nuclear power plants (NPP). The analysis of hydrodynamic properties of coolant flow in DHS has been carried out. The paper presents typical flow patterns of a coolant in the flow paths of the specified DHS. The classification of different types of DHS is presented. The coolant flow is shown to have a jet nature in a relatively confined and unconfined DHS. Consideration is given to several types of jets and processes of transformation of some types of jets into other types. The paper presents a brief description and formula of the fluid distribution regularity (registered as a scientific discovery) at the outlet from the flat and cylindrical DHS with central and side fluid supply. Consideration is given to the similarity property of hydrodynamics in the flat and cylindrical RHS with different points of fluid supply to the header. Advanced areas of research into revealing hydrodynamic effects in DHS and obtaining additional information on the influence of various factors on the fluid flow in them are proposed.

Mathematical model of the distribution of the coolant flow rate in the group distribution header and its use to determine the flow rate in the RBMK reactor channel

The paper proposes an elementary mathematical model of the distribution of coolant flows through water communications in the group distributing header (GDH) of a power unit with an RBMK reactor. This model used to determine the flow rate in the channel with a “forbidden” flow meter. An equation is given based on the mass balance of the coolant in the allocated volume. The results of the solution are used to construct an algorithm for determining the flow rate of the coolant in the channel. The results of the application of the technique on the measurement data from the power unit are presented. It is shown that the relative discrepancy with the measured value of the flow rate at a constant position of the flow control valve is on the order of several percent.

Reliability and availability assessment and enhancement of water-cooled multi-chiller cooling systems for data centers

There are strict requirements and needs to avoid huge downtime cost for data center cooling systems to operate continuously for reliable data center services. Current design standards achieve this by installing redundant cooling equipment. Other equipment including distribution headers is also used. However, no study is found to quantify the reliability of these designs comprehensively using on-site performance data. It is unknown how much reliability can be improved by adopting these designs or if they are burdens to the cost of systems only. This study quantifies how different data center cooling system configurations enhance the reliability and availability of data centers. The results show that it is crucial to install a redundant chiller or redundant chiller plant with alternative cooling sources to meet the requirement of high-tier data centers, but other common practices such as distribution headers and the 2(N + 1) configuration do not improve the reliability and availability of data center cooling systems effectively.

Optimal design of data center cooling systems concerning multi-chiller system configuration and component selection for energy-efficient operation and maximized free-cooling

The large data center electricity consumption is a growing global concern. To be environment-friendly and to enhance energy efficiency in operation, data center cooling systems adopt a variety of advanced cooling and renewable energy technologies such as free cooling. However, these free cooling systems are not optimally designed in field practices, and their energy efficiencies are much lower than that of the ideal case. In this study, optimal designs in water piping, pumps and equipment sequencing control are introduced to maximize the cooling efficiency of free cooling systems. It finds that the use of distribution headers around cooling towers and pumps, the maximization of the number of operating cooling towers, the minimization of the number of operating pumps and the mixed use of large and small single-speed pumps can reduce the system's power consumption by 60% under certain operating conditions. The results also show that the designs can reduce the annual energy consumption by 3–15% depending on the climate conditions.

Pipe-work optimization of water flow window

Water flow window has been demonstrated an energy-efficient product that benefits both air conditioning and hot water systems. Its thermal performance was found affected much by the design geometry and system configuration. For those based on buoyant-driven flow, liquid water is at very slow movement; the magnitude depends on the overall flow-path friction loss and hence the connecting-pipe arrangement. In this study, the impacts of such recirculating pipe-work have been examined extensively. Firstly, experiment tests were executed to evaluate the system performances with and without distribution headers. Then their thermal and flow characteristics were compared using CFD analysis. Further on, the impacts of connecting-pipe dimensions were examined through the use of a validated FORTRAN program. The optimal pipe size was determined accordingly. It was found that without headers, more uniform temperature distribution close to the glazing surfaces could be achieved. The system thermal efficiency could be improved by around 5%. On the other hand, the variation in room heat gain was found around 1%, as a result of the self-regulating nature of the buoyant-driven flow. For the given window system, an optimal pipe size of 20–25 mm is recommended.

Verification of the Mathematical Model and Numerical Investigation into the Thermal–Hydraulic Parameters of Fuel Assemblies Containing Microspherical Fuel Elements

The article presents the results from numerical investigations into the hydrodynamics and temperature field in the KLT-40S reactor’s fuel assembly (FA) in the case of using microspherical fuel elements as nuclear fuel. The simulated FA has the same overall dimensions as the existing FA containing fuel rods, due to which it can be accommodated in the reactor core without the need of modifying the reactor design. The specific feature of an FA with micro fuel elements (MF FA) is the need to set up radial flow of coolant through the bed of micro fuel elements, which is achieved by using distribution and collection headers. The numerical simulation was carried out using the ANSYS Fluent computer code. The mathematical model implemented in the code has been refined and verified against the experimental data obtained by the authors on a model experimental setup whose design is similar to that of the considered FA containing micro fuel elements. Radial flow of coolant through the pebble bed is arranged in the model installation. The numerical and experimental data on pressure loss and temperature distribution in the bed estimated at different values of coolant mass velocity mass are compared with each other. The design of an FA containing micro fuel elements for the KLT-40S reactor is proposed. It has been found that almost purely radial flow of coolant can be set up with the perforation parameters (cross-section coefficients) higher than those mentioned in the literature. The serviceability of such a fuel assembly is demonstrated. The distributions of temperature, excess pressure, and coolant velocity and current lines are obtained. The perforation parameters of jackets confining the bed of micro fuel elements are presented.

Effect of design configurations on water flow window performance

Water flow window has very good application potential in zero carbon buildings of the warm climate. In this study, the effects of water-flow window configurations were investigated, such as the water layer thickness and glazing height-to-width ratio (GHTWR). The effects of distribution header design on the thermal and flow characteristics were also analyzed. Its long-term dynamic thermal performance was examined through a self-developed simulation program, of which the FORTRAN code was previously validated through comparison with experimental data. In the current study, the one-dimensional thermal simulation modelling approach was further justified through CFD analysis. Then the overall thermal performance of the window system was evaluated from the aspects of useful water heat gain and the impact on space air-conditioning power consumptions. A water layer of thickness around 15–20 mm and a GHTWR of 0.4 were found desirable for the tested cases. While the size and distribution of the header openings would affect the localized water flow and temperature distribution, their effect on the laminar upward flow and the final temperature rise is not significant.

Structural Optimizations of U‐ and Z‐Type Manifolds for Uniform Flow Distribution by Applying an Increaser and Baffle Plates

AbstractBased on previous experiments for U‐ and Z‐type manifolds, numerical models were established; then, investigations were conducted on the effect of the optimized designs on the flow distribution. An increaser and baffle plates were attached to the distribution header for the U‐ and Z‐type manifolds, respectively, considering various configurations and sizes. The results indicate that an increaser could markedly reduce the non‐uniformity with a simultaneous decrease of the pressure drop, and baffle plates could also drastically improve the flow distribution, but at the cost of a slight pressure drop increase. By comprehensively applying an increaser and baffle plates in the Z‐type manifold, this adverse effect could be eliminated.

Liquid-filled solar glazing design for buoyant water-flow

A water-flow window was constructed at the front wall of an environmentally controlled test cell to monitor its performance under full-scale real-building-like condition. The window was consisted of three layers, including one layer of clear glazing at the outside, one layer of insulated glazing unit at the inside, and one layer of water flowing in between. A heat exchanger was provided at the top of the window, and connected to the glazing cavity through connecting pipes and distribution headers. Through this, a cold feed water circuit removed the absorbed heat away from the buoyant water circulation in the window circuit. The heat removal allowed a reduction of energy consumption in air-conditioning and services hot water systems. Year round energy performance was then predicted by numerical models, which were successfully validated by the experimental data. A comparative study was also carried out with the use of different glazing types. The economical payback periods of the different glazing combinations are found less than 5 years under the Hong Kong subtropical climate. Amongst these, the energy performance of water-flow window with double absorptive glazing appears to be most promising.

Analysis of accidents leading to local flow stagnation in parallel fuel channels of RBMK-type reactors

The RBMK-type nuclear power reactors, still operating in Russia, are graphite-moderated with vertical fuel channels, using low-enriched nuclear fuel. The main challenge, which leads to the overheating of the fuel assemblies, fuel channels and other core components in channel type nuclear reactors, is a misbalance between heat generation in core structures and heat sink, which can appear due to the loss of coolant accident. In this accidental case, the emergency core cooling system ensures the core cooling. In RBMK-type reactors this system consists of hydro-accumulators and a number of pumps, taking water from large water reservoirs. This equipment injects water into the fuel channels through the group distribution headers at high pressure. However, the direct supply of cold water from emergency core cooling system into fuel channels is possible only if check valves on group distribution headers are closed properly. If these check valves failed, the part of water would be lost through the break, the flow stagnation in channels could occur, which might lead to overheating of fuel assemblies in the fuel channels. This paper presents the results of deterministic safety analysis, performed using system thermal hydraulic code RELAP5. Using this code the reactor cooling system of RBMK-1500 was modelled and analyses of loss of coolant accidents with failure of few check valves in group distribution headers were performed. The results of the calculations are used for the development of symptom-based emergency operating procedures for RBMK-1500. The basic principles that describe the complex distribution of water flows in vertical forced circulation circuit with parallel fuel channels can be adjusted for the RBMK-1000 reactors, still operating in Russia.

Turbulent flow in the distribution header of a PEM fuel cell stack

A numerical investigation of the flowfield in a model distribution header manifold of a polymer electrolyte membrane fuel cell stack is conducted. The computational model simulates two segments of an experimental setup of a pair of model headers which replicate the headers of a fuel cell stack. The model headers consist of an inlet and outlet sections connected with a plate containing an array of holes that replicate the unit cells. The flow structures in the outlet header are rather complex and are the result of the superposition of a series of impinging jets in a confined space in the presence of crossflow. The flow from each hole, which represents an individual cell outlet, enters the outlet header as a jet stream and is subjected to a crossflow. Large Eddy Simulations (LES) are performed for a portion of the outlet header to investigate the complex turbulent flow and related structures under different crossflow conditions, and are complemented by Particle Image Velocimetry (PIV) measurements. The LES results show that two large vortical structures are formed in the header cross-section, with a high-speed round jet from the cell outlet holes forcing a diversion of the crossflow, dividing it into two separate branches. Investigation of the flow restructuring after a blockage of one of the jets is performed. Simulation results using a slot opening for the jet show flow instabilities. The results of this study highlight the unsteady and highly turbulent nature of the flow in the header and provide a characterization of the complex three-dimensional structure of the flow. The flowfield and flow structures may impact the overall pressure drop along the header and the effective cross-sectional area for the flow leaving the header. The observations and insights obtained from the LES simulation and PIV measurements point to the need to further investigate the impact on flow sharing in a stack of the flowfield development in the outlet header.