Coaxial Pipe Research Articles

Validation of heat transfer and friction loss data for fibre suspensions in a circular and a coaxial pipe heat exchanger

Heat transfer data obtained previously in a pipe heat exchanger were validated using an annular test unit with longer calming section and axial entry flow levels. Water and two suspensions of long-fibre softwood Kraft pulps with fibres having different coarseness (mass/unit fibre length) were used. Data in both systems were accumulated and compared over a range of flow rates with the fibre concentrations up to 0.4%. Heat transfer coefficient hc increased with increasing velocity for both water and fibre suspension flow. Various fibre dimensions and fibre characteristics are shown to vary systematically with hc at the same experimental conditions in both flow systems. The data from a pipe and an annular coaxial pipe heat exchanger for fibre suspensions of concentrations 0.2 and 0.4% show that the relationships among heat and momentum transfer and fibre characteristics and specific properties of paper can be obtained with confidence from either type of heat exchanger.

Коаксиальная тепловая труба для охлаждения отражателя лазера

The paper presents the development and research results for a coaxial heat pipe designed for cooling of a reflector of a solid-state laser. A coaxial cylindrical heat pipe, designed to cool the laser reflector, provides that the temperature of the heat-removing surface does not exceed 120°C at any orientation in the gravitational field, if the heat is removed by forced convection of air with the temperature of 60°C in a pulsed mode of heat flow supply of 300 W. Thermal resistance of the developed heat pipe is 0,03 K/W, the specific thermal resistance — 1,1*10–3 m2*K/W. The developed cooling system based on the evaporation-condensation principle, allows ensuring temperature uniformity of the cooling surface at low thermal resistance.

On part load recirculation of pumps and fans-a generic study

At part load in turbo machinery, there is a boundary layer separation resulting in a large vortex structure called part load recirculation. Up to now the influence of Reynolds number, relative roughness and degree of turbulence on this important stability limit of machines is not sufficiently understood. To shed some light onto these phenomena, in this work the simplest "machine" is considered by numerical and experimental studies. The apparatus we examine is a circular pipe at rest followed by a rotating co-axial pipe segment. By doing so, we have a generic test case which serves to study the critical flow number, defined by the onset of the separation and formation of a ring vortex.

Energy separation of gases with low and high Prandtl numbers

The process of energy separation of a gas with the Prandtl number which is not equal to unity is investigated. The gas flows through a heat exchanger consisting of two coaxial axisymmetric pipes with sub- and supersonic velocities. Heat exchange between the gas streams takes place as a result of the fact that the recovery factor is not equal to unity. The flow is described by one-dimensional gas dynamic equations for averaged quantities.

New TDR waveguides and data reduction method for monitoring of stream and drainage stage

Summary Less known in the field of hydrological measurements in civil engineering, time domain reflectometry (TDR) has been developed as a new solution to some of the more difficult level measurement problems. This study applied TDR methodology to provide two new designs for a water level sensing waveguide that can be applied in difficult field conditions such as in an underpass, tunnel, culvert, or sewer, etc. Two types of water level sensing waveguides are presented, including a rigid assembled coaxial pipe and a flexible adhered parallel wire. The corresponding data reduction procedure is also proposed to account for uncertainty of travel time analysis and calibrate the velocity of pulse propagation along the waveguides. The satisfactory performance of both the proposed TDR waveguides and data reduction method was experimentally validated. A field case study further demonstrated the feasibility of the TDR technique for water level measurements under typical urban drainage conditions.

3-D Simulation of Remote Field Eddy Current Detection for Stress Corrosion Cracks in Pipeline

Three-dimensional (3-D)finite element simulation models are conducted to simulate the in-serviceinspection of the axial stress corrosion cracking (SCC) in ferromagneticpipeline using remote field eddy current (RFEC) probes. In this paper, atypical remote field eddy current probe which is internal to and coaxial withthe pipe is firstly introduced. Then a 3-D finite element simulation model isestablished in ANSYS to analyze the detection of RFEC technology. Finally theRFEC signals are observed when changing the geometric parameters, and thedefinite influences of crack size on the amplitude and phase lag of REFCsignals are evaluated. The results of the investigations are beneficial to thedetection and sizing of SCC in pipelines

Experimental Analysis of a Vertical Drop Shaft

An experimental campaign is undertaken in order to investigate the hydraulic features of a vertical drop shaft, also considering the influence of a venting system consisting of a coaxial vertical pipe, projecting within the drop shaft with different plunging rates. Three different flow regimes are observed: a “weir flow” for very low head values, where the flow profile is subject to the atmospheric pressure; a “full flow” for high head values, where water flows in a pressurized regime along the whole shaft; and a “transitional flow” for intermediate water head values. Weir flow and full flow can be experimentally investigated under steady-state conditions, whereas transitional flow is a pulsating condition, alternately switching from full flow to weir flow. Considering some significant geometric parameters, a head-discharge relation is sought both for the non-vented and for the vented configurations, by means of an energy balance equation, with specific assumptions about intake losses.

Temperature conditioning in ornamental plant production with a prototype device: root zone cooling in protected environments

One of the greatest growing costs in greenhouse floriculture is for energy. To reduce energy costs for thermal conditioning was projected an innovative root zone cooling system characterized by two coaxial pipes with hydraulic countercurrent flows. This new system was compared with a traditional system with hydraulic flows cocurrent. The plants were equipped with coolers for obtaining flowering in the summer period by a culture of Alstroemeria spp and were measured energy consumption in each root zone cooling system. The tests also focused on a particular change, made during the tests of previous years, which allows the coaxial system in turning his operation from countercurrent flows to cocurrent flows. The results obtained show that the root zone coaxial cooling system allows to obtain, in comparison to the traditional type, a better temperature uniformity of the root zone ground, both when it is used with countercurrent flows both when it is used with cocurrent flow. The system also allows a slight overall reduction in energy consumption.

Temperature conditioning in ornamental plant production with a prototype device: root zone cooling in protected environments

One of the greatest growing costs in greenhouse floriculture is for energy. To reduce energy costs for thermal conditioning was projected an innovative root zone cooling system characterized by two coaxial pipes with hydraulic countercurrent flows. This new system was compared with a traditional system with hydraulic flows cocurrent. The plants were equipped with coolers for obtaining flowering in the summer period by a culture of Alstroemeria spp and were measured energy consumption in each root zone cooling system. The tests also focused on a particular change, made during the tests of previous years, which allows the coaxial system in turning his operation from countercurrent flows to cocurrent flows. The results obtained show that the root zone coaxial cooling system allows to obtain, in comparison to the traditional type, a better temperature uniformity of the root zone ground, both when it is used with countercurrent flows both when it is used with cocurrent flow. The system also allows a slight overall reduction in energy consumption.

Design and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS)

The present study considers the design, performance analysis and optimization of a downhole coaxial heat exchanger for an enhanced geothermal system (EGS). The optimum mass flow rate of the geothermal fluid for minimum pumping power and maximum extracted heat energy was determined. In addition, the coaxial pipes of the downhole heat exchanger were sized based on the optimum geothermal mass flow rate and steady-state operation. Transient effect or time-dependent cooling of the Earth underground, and the optimum amount and size of perforations at the inner pipe entrance region to regulate the flow of the geothermal fluid were disregarded to simplify the analysis. The paper consists of an analytical and numerical thermodynamic optimization of a downhole coaxial heat exchanger used to extract the maximum possible energy from the Earth's deep underground (2 km and deeper below the surface) for direct usage, and subject to a nearly linear increase in geothermal gradient with depth. The thermodynamic optimization process and entropy generation minimization (EGM) analysis were performed to minimize heat transfer and fluid friction irreversibilities. An optimum diameter ratio of the coaxial pipes for minimum pressure drop in both limits of the fully turbulent and laminar fully-developed flow regime was determined and observed to be nearly the same irrespective of the flow regime. Furthermore, an optimum geothermal mass flow rate and an optimum geometry of the downhole coaxial heat exchanger were determined for maximum net power output. Conducting an energetic and exergetic analysis to evaluate the performance of binary power cycle, higher Earth's temperature gradient and lower geofluid rejection temperatures were observed to yield maximum first- and second-law efficiencies.

Dependence of charge transfer phenomena during solid–air two-phase flow on particle disperser

An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact potential difference between the PMMA and the stainless steel. Furthermore, the current in air using the dual coaxial glass pipes was less than that using the ejector.

Microcontroller-Based Design within the Cone Flowmeter

The flow throttling device for the V-shaped cone-type cutting device, the throttling device to break the traditional flow through the throttling device will shrink to the concept of the pipeline near the central axis, the use of coaxial pipe installed in the V-shaped tip cone contraction of the fluid gradually cutting edge to the inner pipe wall, by measuring the V-shaped inner cone to measure the differential pressure before and after the flow of design ideas. This V-cone flowmeter in a shorter straight pipe conditions, to a wider range than on the clean or dirty fluids to achieve a more accurate and more effective flow measurement. This will be based on single-chip cone flowmeter air mixing systems used in ship gas flow measurements, experimental results show that the SCM-based cone flowmeter has a small size, light weight, high accuracy, easy to use security features .

Aeroacoustic power generated by a compact axisymmetric cavity: prediction of self-sustained oscillation and influence of the depth

AbstractAeroacoustic power generation due to a self-sustained oscillation by an axisymmetric compact cavity exposed to a low-Mach-number grazing flow is studied both experimentally and numerically. The feedback effect is produced by the velocity fluctuations resulting from a coupling with acoustic standing waves in a coaxial pipe. A numerical methodology that combines incompressible flow simulations with vortex sound theory is used to predict the time-averaged acoustic source power generated by the cavity. The effect of cavity depth on the whistling is addressed. It is observed that the whistling occurs around a peak-whistling Strouhal number which depends on the cavity depth to width ratio. The proposed numerical method provides excellent predictions of the peak-whistling Strouhal number as a function of cavity depth. Given the oscillation amplitude, the numerical method predicts the time-averaged acoustic source power within a factor of two for moderate fluctuation amplitudes. For deep cavities the time-averaged acoustic source power appears to be independent of the cavity depth.

Aeroacoustic power generated by multiple compact axisymmetric cavities: Effect of hydrodynamic interference on the sound production

Aeroacoustic sound generation due to self-sustained oscillations by a series of compact axisymmetric cavities exposed to a grazing flow is studied both experimentally and numerically. The driving feedback is produced by the velocity fluctuations resulting from a coupling of vortex sheddings at the upstream cavity edges with acoustic standing waves in the coaxial pipe. When the cavities are separated sufficiently from each other, the whistling behavior of the complete system can be determined from the individual contribution of each cavity. When the cavities are placed close to each other there is a strong hydrodynamic interference between the cavities which affects both the peak amplitude attained during whistling and the corresponding Strouhal number. This hydrodynamic interference is captured successfully by the proposed numerical method.

A Numerical Study of Air Flow in a Coaxial Pipe

A simulation study of a cold–flow in coaxial pipes was carried out with varying drivepipe diameter and entrance displacement (ΔL). The current work has studied the effect of the temperature of the entrance flow inlet with variation of ΔL to he entrained flow characteristics. To predict these flow characteristics, a numerical method was employed by the differencing scheme for integrating the continuity equation and energy equation. A k–ε turbulent model was used to simulate the turbulent transport quantities. The 2–D flow pattern was created as the result of using Fluent 4.4 CFD modeling package. Results showed that increasing the air entrained temperature until 600 K would decrease the airflow rate. It was found that the diameter ratio of 2.81 has the highest entrained flow rate.

Study on Vibration Deadening of Double Pipe-Filled Bead for Primary Piping System in Fast Breeder Reactor

There are a lot of earthquakes in Japan. For this reason, it is very important to evaluate the soundness of piping of a nuclear power plant for adequate safety of seismic design. Additionally, piping in nuclear power plant confronts the effect of aging. The object of this study is to clarify relations between damping characteristics of piping and several conditions of pipe. In this study, thickness of pipe test, support type test, damaged pipe test and double pipe-filled glass bead test were conducted with impact system. The results obtained through the study are as follows; (1)Pipe thickness and support type contribute to the damping characteristics of pipe.(2)Damaged pipe don't affect the damping, but the frequency of pipe decrease as damage grew. (3)Double co-axial pipe has high damping ratio. Especially, the damping ratio when glass bead are filled between the inner pipe and outer pipe is about 10%.

Validation of heat transfer data for fibre suspensions in coaxial pipe heat exchangers

Heat transfer data obtained previously in a small coaxial pipe heat exchanger were validated using a new, larger annular-area test unit with longer calming section and axial entry flow. Water and two suspensions of long-fibre softwood Kraft pulps with fibres having different coarseness (mass/unit fibre length) values were used. Data in both systems were obtained over a range of flow rates with the fibre concentration at 0.4% and compared. Heat transfer coefficient hc was found to decrease with increasing annular gap size for both water and fibre suspension flow at equal velocities. Various fibre dimensions and fibre characteristics are also shown to vary systematically with hc at the same experimental conditions. The effect of hydrodynamic annular entry length on heat transfer and pressure loss using water and fibre suspensions (concentrations 0.2% and 0.4%) are also described. It was found that that extending the central calming extension rod made no significant difference to hc values at the low fibre concentration of 0.2%, and only small differences at the higher concentration of 0.4%. The successful validation of data from the smaller-annulus coaxial pipe heat exchanger show that the relationships among heat and momentum transfer and fibre characteristics and specific properties of paper are also valid for both heat exchangers.

Experimental Research of Thermal Characteristics in Coaxial Radial Heat Pipe

In this paper, heat transfer model is assumed in coaxial radial heat pipe(CRHP) firstly. To verify the model , visualization and performance experiment are studied. Visualization experiments of CRHP are done under different filing radio of 20%, 30%, 35% and inclined angles of 0°(horizontal), 5°, 10°, 15°, 20°. Visualization experimental results show that CRHP of horizontal and 30% filling ratio is better on thermal characteristics. Its heat transfer model is preliminary analyzed from experimental phenomena. In performance experiment , the kind of CRHP is used to test heat transfer characteristics. The temperatures of the outside wall of outer pipe are determined and drawn diagrams. Lastly, heat transfer model is corrected anew by analyzing experimental datas.

Explosive welding of stainless steel–carbon steel coaxial pipes

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.

Developing the Coaxial Dual-Pipe Heat Pipe for Applications on Heat Pipe Cooler

This article presents significant experimental data about the coaxial dual-pipe heat pipe which is invented by our CCT laboratory. The coaxial dual-pipe heat pipe is built-in an inner pipe in the adiabatic section of a common heat pipe. A common heat pipe is composed of three sections: the evaporator section at the one end; the condenser section at the other end; and the adiabatic section in between. The vapor and the liquid phases of the working fluid flow in opposite directions through the core and the wick, respectively. This special heat transfer behavior causes a common heat pipe to yield the discrete heat transfer property. In process, the vapor directly brings large amounts of heat from heat source and rapidly flows through the adiabatic section to the condenser section. This intelligent heat transfer technique lets the heat pipe yield extremely large thermal conductivity. Unfortunately, a heat pipe integrated with cooling fin in the adiabatic section has changed its original heat transfer property. The integrated cooling fin in the adiabatic section has in advance taken heat of the vapor away and caused the vapor to be condensed in the adiabatic section. Therefore, the vapor cannot reach the condenser section and the condenser section hence loses its cooling capability. In other words, the effective cooling length of a common heat pipe which is integrated with cooling fin in the adiabatic section is shortened. The coaxial dual-pipe heat pipe is built-in an inner pipe in the adiabatic section of a common heat pipe to avoid heat of the vapor to be earlier taken away and even condensed in the adiabatic section. Experimental study in this work first built a home-made square coaxial dual-pipe heat pipe integrated with outside isothermal cycling cooling water as the coaxial dual-pipe heat pipe cooler. The home-made square coaxial dual-pipe heat pipe has an observation window. It is convenient to observe change of the two-phase flow inside the heat pipe influenced by the outside cooling water. The results show that the new developed coaxial dual-pipe heat pipe cooler has kept the original heat transfer property of the bare heat pipe. The vapor has reached the condenser section.