Large Pressure Loss Research Articles

Modeling and simulation of large-scale separated heat pipe with low heat flux for spent fuel pool cooling

The large-scale separated heat pipe consisting of large-diameter evaporators and condensers and tens of meters of connection tube is a promising approach to cool the spent fuel pool passively within a small temperature difference. In this study, a lumped model for this kind of large-scale separated heat pipe is developed. Ammonia, R134a and water are used as the working fluid. Due to the large diameter and low wall heat flux, flow patterns in the evaporator can be different from those in conventional pipes, which should be considered in the model. The simulation results agree with experimental data well. It is that the heat pipe changes its heat transfer capacity in a wide range with the variation of heat source temperature, and vapor quality at condenser exit is always 0, which indicates that the downcomer is always partially liquid filled. Heat transfer performance of heat pipe in long distance heat transport applications is also presented. In these applications, there exist large pressure losses, especially in the water heat pipe, which causes serious deterioration of heat transfer performance. However, for the ammonia and R134a heat pipe, the influence of heat transport distance is limited.

Numerical investigation on flow and heat transfer of pulsating flow in various ribbed channels

In this paper, numerical simulation is carried out to study the flow and heat transfer of pulsating flow in 30°, 45°, 60° and 90° ribbed channels (AR = 2). Turbulence model validation has been conducted for steady flow only, indicating that SST k-ω model predicts heat transfer in ribbed channels fairly well. The secondary flows and Nu distributions in ribbed channels are investigated for both steady flow and pulsating flow. Numerical results indicate that pulsating flow affects longitudinal secondary flow and transverse secondary flow in quite different ways. The time-averaged Nu on ribbed surface of pulsating flow is significantly higher than that of steady flow in most cases, especially for 90° rib case. There is an optimal frequency for each channel to achieve the best heat transfer. In addition, increasing pulsation amplitude and Re will noticeably promote heat transfer for all the cases. Though pulsating flow introduces large pressure loss, considerable improvement of thermal performance will be achieved at high Re. The 90° ribbed channel shows distinguished characteristics with pulsating flow, which gains an increment of 39% in overall thermal performance parameter at Re = 40,000, f = 150 Hz and A = 0.2.

Heat Transfer and Friction Characteristics of Turbulent Flow through a Circular Tube with Ball Turbulators

One of the most commonly used methods of heat transfer enhancement is flow turbulization. This effect can be achieved, e.g., by placing special turbulizing elements into the channel. In this paper, the effects of ball turbulators (BTs) on the heat transfer and fluid friction characteristics in a circular tube are investigated through numerical simulation. The Reynolds number (Re) is in the range of 5000–35,000 under a condition of uniform heat-flux. BTs with different diameter ratios (e.g., 0.5, 0.75, and 1) and spacer lengths (40, 51.77, and 62.5 mm) are inserted in the circular tubes. The results show that the heat transfer rates in the tube equipped with BTs are around 1.26–2.01 times that of those in the plain tube. The BTs with a ball diameter ratio of one provide higher friction factors than 0.75 and 0.5 by about 34.6–46.2% and 51.1–63.4%, respectively. A smaller ball diameter ratio is more able to decrease the friction factor. The performance evaluation criterion (PEC) data indicate that the use of a smaller ball diameter ratio (BDR) and a smaller spacer length are preferred. The results also reveal that BTs with a larger diameter ratio and a smaller spacer length yield the highest heat transfer rate as well as the largest pressure loss. Compared with the plain tube, the fluid flow velocity near the tube wall is significantly improved when BTs are used at the same Reynolds number.

Improved Core Design of a High Breeding Fast Reactor Cooled by Supercritical Pressure Light Water

The authors look for an attractive light water reactor (LWR) concept, which achieves high breeding performance with respect to the compound system doubling time (CSDT). In the preceding study, a high breeding fast reactor concept, cooled by supercritical pressure light water (Super FBR), was developed using tightly packed fuel assembly (TPFA) concept, in which fuel rods were arranged in a hexagonal lattice and packed by contacting each other. However, the designed concept had characteristics, which had to be improved, such as low power density (7.4 kW/m), large core pressure loss (1.02 MPa), low discharge burnup (core average: 8 GWd/t), and low coolant temperature rise in the core (38 °C). The aim of this study is to clarify the main issues associated with improvement of the Super FBR with respect to these design parameters and to show the improved design. The core design is carried out by fully coupled three-dimensional neutronics and single-channel thermal-hydraulic core calculations. The design criteria are negative void reactivity, maximum linear heat generation rate (MLHGR) of 39 kW/m, and maximum cladding surface temperature (MCST) of 650 °C for advanced stainless steel. The results show that significant improvement is possible with respect to the core thermal-hydraulic characteristics with minimal deterioration of CSDT by replacing TPFA with the commonly acknowledged hexagonal tight lattice fuel assembly (TLFA). Further design studies are necessary to improve the core enthalpy rise by reducing the radial power swing and power peaking.

Adequacy and security analysis of interdependent electric and gas networks

In this article, adequacy and security assessments on the coupled operations of the electric and gas networks are performed. Extreme operating conditions and fault of components are considered as events that can impact the interdependent systems. The electric and gas networks are represented by an event-based direct current power flow model and by a transient one-dimensional mass flow model, respectively. Furthermore, the automations and safety strategies enforced by transmission system operators are represented within an original modelling approach. A quantitative analysis is performed with reference to the simplified energy infrastructures of Great Britain. Results highlight the contingencies which can jeopardize security and identify the components that are prone to fail and induce large gas pressure instabilities and loss of supply, and the locations in the gas grid that are susceptible to pressure violation. Moreover, a simulated 30% increase of the peak gas demand in 2015 is a limit for safe operations of the gas network, but the coupled systems are robust enough to avoid the spread of a cascading failure across networks. These results allow preventing critical operating conditions induced by the interaction between networks and can guide safety-based decisions on system reinforcements and the development of mitigating actions.

Laminar convective heat transfer of shear-thinning liquids in rectangular channels with longitudinal vortex generators

Heat and fluid flow in a rectangular channel heat sink equipped with longitudinal vortex generators have been numerically investigated in the range of Reynolds numbers between 25 and 200. Aqueous solutions of carboxymethyl cellulose (CMC) with different concentrations (200–2000ppm), which are shear-thinning non-Newtonian liquids, have been utilised as working fluid. Three-dimensional simulations have been performed on a plain channel and a channel with five pairs of vortex generators. The channels have a hydraulic diameter of 8mm and are heated by constant wall temperature. The vortex generators have been mounted at different angles of attack and locations inside the channel. The shear-thinning liquid flow in rectangular channels with longitudinal vortex generators are described and the mechanisms of heat transfer enhancement are discussed. The results demonstrate a heat transfer enhancement of 39–188% using CMC aqueous solutions in rectangular channels with LVGs with respect to a Newtonian liquid flow (i.e. water). Additionally, it is shown that equipping rectangular channels with LVGs results in an enhancement of 24–135% in heat transfer performance vis-à-vis plain channel. However, this heat transfer enhancement is associated with larger pressure losses. For the range of parameters studied in this paper, increasing the CMC concentration, the angle of attack of vortex generators and their lateral distances leads to an increase in heat transfer performance. Additionally, heat transfer performance of rectangular channels with longitudinal vortex generators enhances with increasing the Reynolds number in the laminar flow regime.

Experimental Investigation on the Performance of a Twin-screw Expander Used in an ORC System

Abstract Organic Rankine Cycle (ORC) is an effective and promising technology to convert low-grade thermal energy to electricity. As a key component in an ORC system, the expander plays a significant role in energy conversion efficiency in the ORC system. In this paper, an ORC experimental system is developed to investigate the performance of a twin-screw expander under various working conditions. Pressure sensors with high sensitivity and accuracy are installed at appropriate locations in the expander casing to monitor the p-V (pressure-volume) indicator diagrams which indicates the performance of the expander. The effect of the key parameters such as expander rotating speed, the suction pressure on the expander performance is studied using the experimental data. The results show that high expander rotating speed leads to large suction pressure loss, low volumetric and indicated efficiencies. As the rotating speed increases from 900 rpm to 1900 rpm, the volumetric efficiency decreases by up to 17.2% from 1.004 to 0.831and the indicated efficiency reduces by up to 27.1% from 0.846 to 0.617. Furthermore, as the suction pressure increases from 550 kPa to 750 kPa the indicated efficiency rises up to a peak value of 0.815 and then falls. The volumetric efficiency does not show significant change as the suction pressure varies.

Optimization of wick shape in a loop heat pipe for high heat transfer

This paper presents a method to optimize wick shape in the capillary evaporator of loop heat pipes and capillary pumped loops. The evaporator heat-transfer coefficient is maximized using only the length of a three-phase contact line (TPCL) within the case, wick, and grooves as a variable wick dimension. The heat-transfer coefficient is formulated taking the following two particular aspects into account. The heat-transfer coefficient initially increases with TPCL length. However, when TPCL becomes too long, the heat-transfer coefficient decreases because of a large pressure loss in the grooves. The proposed model is validated experimentally. Both the model and experiment show the heat-transfer coefficient reached a local maximum in terms of the TPCL length. It is concluded that wick shape can be optimized by just using the TPCL length. The effects of the material of an evaporator’s case, wick, and working fluid are also discussed.

Development and experimental studies on a fully-rotary valve energy recovery device for SWRO desalination system

Isobaric energy recovery devices (ERDs) are developing rapidly and playing a significant role in reducing specific energy consumption (SEC) of seawater reverse osmosis (SWRO) desalination systems. However, leakage, abrasion and large pressure loss are still big challenges and remain big problems unsolved among the present ERDs. In this paper, a novel isobaric ERD based on so-called fully-rotary valves (FRVs) is developed to resolve these problems. The key fully-rotary valve energy recovery device (FRV-ERD) consists of only two FRVs and pipelines. The performance of the FRV-ERD is tested by means of an ERD performance test system. The hydraulic performance of the device is tested under laboratory conditions with the test pressure about 3.0MPa. Experiments show that the operation of the FRV-ERD is stable and the pressure fluctuations of high pressure streams are small. The leakage is not detected and therefore excellent seal performance is proved through tests as well. The measured pressure loss is low and the energy recovery efficiency is as high as 98.47% which is among the best of the reported values.

Research on Internal Flow and Performance of Swirlmeter with Different Swirler Cone Angle

The performance of a swirlmeter (or vortex precession flowmeter) was numerically and experimentally evaluated. With methods from computational fluid dynamics, the flow fields of the swirlmeter were analyzed, revealing their flow characteristics. To obtain detailed flow information with the Re-Normalization Group k – ε turbulence model and SIMPLE arithmetic, which couples pressure and velocity, the three-dimensional unsteady incompressible flow of a swirlmeter was numerically simulated. By varying the cone angle of the swirler, the performance of the swirlmeter was analyzed. The results show that the pressure fluctuation frequency inside has a linear response to flow rate, and the swirlmeter achieves high accuracy over a large measurement range. The pressure fluctuation near the region between throat and diffusor was stronger than other regions offering then an ideal location to mount the piezoelectric sensors. Different swirler cone angles were shown to influence both pressure drop and fluctuation; smaller cone angles produced higher frequency fluctuations but larger pressure loss.

A new design of foaming agent mixing device for a pneumatic foaming system used for mine dust suppression

To overcome the drawbacks of the conventional foam technology used for dust suppression, including large pressure loss, high water pressure and low driving pressure, a new pneumatic foaming system is introduced. Then an original design of foaming agent mixing device is proposed, and its performance is investigated and evaluated under different pressure compensations. Experimental results show that the maximum absorption amount increases by 2.9–6.7 times at a pressure compensation of 0.04–0.2MPa compared with no pressure compensation. The pressure loss and pressure fluctuation both reduce significantly with increasing pressure compensation. The critical outlet pressure increases by 30.4–240%. Field application indicates that the proposed mixing device ensures the reliable addition of foaming agent used for foam dust suppression. The effect of foam on dust suppression is remarkable, and the economic cost of foam is low. Therefore, there is reason to believe that the new mixing device will greatly promote foam technology to be widely used for suppressing dust in underground coal mines.

Internal Flow Characteristics and Aft-cone Angle on Performance of Swirlmeter

The swirler is the main component that leads the fluid spirally into a swirlmeter. The structure of the swirler thus directly affects the internal flow field and meter performance. The present study conducted a numerical simulation and experiment to investigate the effects of the aft-cone angle β of the swirler on the vortex precession characteristics and pressure loss inside a swirlmeter. The RNG k–e turbulent model was adopted in three-dimensional unsteady simulation and a sonic nozzle device was used for calibration in the experiment. The numerical and experimental results obtained for four values of β (0°, 20°, 30° and 40°) revealed the flow characteristics in detail. The results show that the pressure pulsation at the throat is stronger than that in the convergent region, the swirling flow through the swirler is affected by different outlet velocities with various values of aft-cone angle β, and the aft-cone angle directly affects both the pressure loss and vortex precession frequency of the swirlmeter; i.e., smaller β results in higher pulsation frequency and larger pressure loss.

Thermal–Hydraulic Analysis of ITER Component Cooling Water System Loop 2B

ITER cooling water system includes Tokamak cooling water system, component cooling water system (CCWS), chilled water system and the heat rejection system. The CCWS is further divided into CCWS-1, CCWS-2A, CCWS-2B, CCWS-2C, and CCWS-2D loops to provide independent chemical control and to prevent galvanic corrosion among the different clients’ materials (e.g. Cu, Al). The CCWS-2B is responsible to remove heat load generated by coil power supply components and the neutral beam injectors and diagnostics system during all the phases: commissioning, testing and conditioning and plasma operation. A CCWS-2B thermal–hydraulic analysis model was developed, by using the AFT Fathom code, to conduct the steady state thermal–hydraulic analysis of the system. In this thermal–hydraulic analysis model, the critical path with the largest pressure loss was used to size the pump head has been identified and the pressure loss on the control valve were used to establish the required flow balance at each piping connection points. This paper presents the results of this thermal hydraulic analysis which was composed by required pump head of the CCWS-2B loop and the main thermal–hydraulic parameters for each client (i.e. flow rate, velocities, pressure drops and outlet temperatures).

SIMULATION ANALYSIS OF PREHEATER CHARGE TO THE ROTARY FURNACE

Mathematical modeling of heat aggregates is one of the fundamental methods of the mathematical modelling research. A mathematical model based on the method of elementary balances was created for the thermal treatment of granular and lumpy materials. The adaptation of the selected aggregate model is based on prior knowledge and experiments. The paper presents an adaptation of the mathematical model for the magnesite processing rotary furnace using the mode of caustic and clinker production. A simulation of the charge preheater impact based on the thin layer principle is implemented into the model. The main advantages of using this type of preheater of rotary furnace are smaller dimensions for a large exchange surface and low pressure losses.

A Novel Gas Generator Concept for Jet Engines Using a Rotating Combustion Chamber

A gas generator—consisting of a single-stage shrouded mixed-flow compressor without a diffusor, a rotating combustion chamber, and a vaneless single-stage shrouded centripetal turbine—is presented and analyzed here. All components comprise a coherent rotating device, which avoids most of the problems usually associated with small gas generators. In other words, the concept avoids all radial clearances; it is vaneless, shortens the combustion chamber, minimizes the wetted area, and enables ceramic materials to be used, due to compressive blade stresses. However, the concept faces severe structural, thermal, and chemical reaction challenges and is associated with a large Rayleigh-type total pressure loss. All these features and their implications are discussed and their benefits and drawbacks for several jet engines are quantified, mainly by means of thermodynamic cycle calculations. As a result, it has been demonstrated that the concept offers a thrust-to-weight ratio which is higher than the standard when incorporated into small unmanned aerial vehicles (UAV)-type jet engines. It also enables an attractive multistage and dual-flow, but fully vaneless design option. However, the concept leads to a decrease in thermal efficiency if these were to be accomplished in the (small) core of turbofans with highest overall pressure ratios (OPRs) and high bypass ratios. In summary, the paper presents a gas generator approach, which may be considered by designers of small jet engines with high power density requirements, like those used in UAV applications. But this has been proven not to be an option for high-efficiency propulsion.

Study of the Dump Diffuser Optimization for Gas Turbine Combustors

Diffuser is one key component of the gas turbine combustor following the compressor. Its primary function is to slow down the air flow delivered by the compressor in order to promote efficient combustion and avoid large total pressure losses. The impacts of pre-diffuser wall angle and dump gap ratio on the performance of dump diffusers have been discussed in the previous work, but few work has been undertaken on designing diffusers with greater pre-diffuser wall angle. It was observed that apparent flow separation occurred on pre-diffuser wall when pre-diffuser wall angle amplified to certain degree. The pre-diffuser exit flow was distorted, indicating that the uniform exit conditions typically assumed in the diffuser design were violated. Skew distribution of the pre-diffuser outlet flow can result in strong transverse mixing for liquid, the total pressure loss of pre-diffuser increases significantly. In this paper, vortex generators were introduced to delay pre-diffuser separation. PIV system was used to obtain the velocity filed of dump diffuser in the non-reacting condition. Comparisons between experimental results and numerical simulations using different turbulence models show that Reynolds Stress Model (RSM) can better predict flow field of diffuser Calculations result indicated that vortex generators delayed pre-diffuser separation observably and the total pressure drop was reduced to five percent of previous value.

A New Design of Double-Stage Parallel Adding Equipment Used for Dust Suppression in Underground Coal Mines

In order to solve the problems of conventional single-stage adding equipment, such as high adding proportion, easy to generate cavitation, large pressure loss and low pressure ratio, an original design of double-stage parallel adding equipment is proposed. Its performance is investigated experimentally under different working flow and outlet pressure and compared with the single-stage jet equipment. Testing results show that the adding proportion of double-stage parallel adding equipment is less than that of the single-stage one, and the cavitation flow is higher. The new equipment can decrease pressure loss, inlet pressure and improve pressure ratio, which lowers the energy loss of adding equipment and raises its driving ability in application. An adding proportion of 4.6 ‰ and an outlet pressure of 0.16–0.18 MPa were realized when the double-stage parallel adding equipment was used to add foaming agent for dust suppression with foam (DSF). The marked reduction in the adding proportion of foaming agent significantly reduces foam production cost. Therefore, it is believed that the study would lay an important foundation for the widespread application of DSF in underground coal mines.

Boundary conditions for molecular dynamics simulations of water transport through nanotubes

This article compares both new and commonly used boundary conditions for generating pressure-driven water flows through carbon nanotubes in molecular dynamics simulations. Three systems are considered: (1) a finite carbon nanotube membrane with streamwise periodicity and ‘gravity’-type Gaussian forcing, (2) a non-periodic finite carbon nanotube membrane with reservoir pressure control, and (3) an infinite carbon nanotube with periodicity and ‘gravity’-type uniform forcing. Comparison between these focuses on the flow behaviour, in particular the mass flow rate and pressure gradient along the carbon nanotube, as well as the radial distribution of water density inside the carbon nanotube. Similar flow behaviour is observed in both membrane systems, with the level of user input required for such simulations found to be largely dependent on the state controllers selected for use in the reservoirs. While System 1 is simple to implement in common molecular dynamics codes, System 2 is more complicated, and the selection of control parameters is less straightforward. A large pressure difference is required between the water reservoirs in these systems to compensate for large pressure losses sustained at the entrance and exit of the nanotube. Despite a simple set-up and a dramatic increase in computational efficiency, the infinite length carbon nanotube in System 3 does not account for these significant inlet and outlet effects, meaning that a much smaller pressure gradient is required to achieve a specified mass flow rate. The infinite tube set-up also restricts natural flow development along the carbon nanotube due to the explicit control of the fluid. Observation of radial density profiles suggests that this results in over-constraint of the water molecules in the tube.

Displacement Control of Hydraulic Pump with Servo System for Energy Saving

The worst problem we are facing in the hydraulic system is the serious loss of energy, due to bad matching between the power components and the actuators and the large pressure loss when oil flowing though the various hydraulic elements, especially in speed governing system. However, Servo pump which is introduced in this paper can cover the problems mentioned above finely. The most difficult thing is its mathematical modeling, in the paper, it is established according to the actual situation. Here, the modeling between servo valve and cylinder, between cylinder and pump are established respectively, then these are connected by geometry relationship, finally ,the whole modeling is completed.

Large Convective Heat Transfer Enhancement in Microchannels With a Train of Coflowing Immiscible or Colloidal Droplets

We show that heat transfer in microchannels can be considerably augmented by introducing droplets or slugs of an immiscible liquid into the main fluid flow. We numerically investigate the influence of differently shaped colloidal or simply pure immiscible droplets to the main liquid flow on the thermal transport in microchannels. Results of parametric studies on the influence of all major factors connected to microchannel heat transfer are presented. The effect of induced Marangoni flow at the liquid interfaces is also taken into account and quantified. The calculation of the multiphase, multispecies flow problem is performed, applying a front tracking method, extended to account for nanoparticle transport in the suspended phase when relevant. This study reveals that the use of a second suspended liquid (with or without nanoparticles) is an efficient way to significantly increase the thermal performance without unacceptably large pressure losses. In the case of slug-train coflow, the Nusselt number can be increased by as much as 400% compared with single liquid flow.