Coaxial Pipe Research Articles

Performance enhancement of modified solar still using multi-groups of two coaxial pipes in basin

The new configuration of modified solar still with multi-groups of two coaxial pipes in basin have been experimentally investigated. The effects of the thickness of annular space between two coaxial pipes are investigated. Four types of the new configuration of modified stills (Types A, B, C and D) with different annular space between two coaxial pipes were studied. A comparison between the four types of modified still with multi-groups of two coaxial pipes in basin and the conventional still are investigated. The results of the experimental study show that, the modified solar still with multi-groups of two coaxial pipes in basin enhanced the distillate water productivity by 97.8%, 77.4%, 63.6% and 52.7% for Types A, B, C and D, respectively as compared to the conventional solar still. In the modified solar still for increase the thickness of annular space between two coaxial pipes from 5 to 14.5mm, the daily efficiency decreases from 67.6% to 53.46%. The percentage increases in the daily efficiency for the modified solar still with multi-groups of two coaxial pipes in basin (Types A, B, C and D) are approximately 90.8%, 75.7%, 62.6%, and 52%, respectively as compared to the conventional solar still. The calculated cost of one liter of distillate water productivity reaches 0.02$, 0.021$, 0.023$, 0.024$ and 0.021$ for modified stills (Types A, B, C and D) and conventional still, respectively.

Augmentation of thermal efficiency of the glass evacuated solar tube collector with coaxial heat pipe with different refrigerants and filling ratio

Modified coaxial heat pipes have been designed and manufactured to improve the thermal performance of the glass evacuated solar collectors. Heat pipes were made up of two concentric copper tubes so that the annulus volume space between the concentric tubes was charged with refrigerant. In addition, the air as the working fluid at four different mass flow rates 0.0051, 0.0062, 0.007 and 0.009kg/s flows through the inner tube of the heat pipe to the flow through the annulus between the heat pipe and glass evacuated solar tubes. The effect ofthe tilt angleofthe evacuated tube on thermal performance of the evacuated solar tube collector was examined to obtain the optimum tilt angle during the experiments period. The influence of filling ratio for the two types of refrigerant R22 and R 134a on the thermal efficiency of the coaxial heat pipe solar collector at filing ratio range from 30% to 60% was conducted experimentally. Results show that the maximum increased in the thermal efficiency reached 67% corresponding to without heat pipes at mass flow rate 0.009kg/s. The experiment results showed similarity between the two refrigerants.

Design and experimental investigations of a cylindrical microjet heat exchanger for waste heat recovery systems

Compact heat exchangers have more and more applications in many areas, including the HVAC, food and petrochemical industry. This paper describes the development of heat exchanger technology for waste heat recovery (WHR) from a range of processes. Case-study testing shows that the proposed heat exchanger can successfully enhance heat transfer and recover waste heat in a range of applications making them economically, environmentally and technically feasible. The heat exchanger is based on multiple jet impingement on the cylindrical heat transfer surface. It comprises four coaxial pipes (a supply channel and a return channel for two fluids). The design of the heat is based on available on the market standardized materials. The study of heat transfer in water-water flow allows determining the heat transfer efficiency and the heat transfer coefficient values. Data were collected for the pressure drops in heat exchanger not exceeding 15 kPa, i.e. such as in conventional heat exchangers. Hydraulic characteristics of a prototype heat exchanger were obtained. Experimental values of heat transfer for jet impingement were calculated. Obtained values of heat transfer coefficient were compared with literature correlations. A comparison of results of thermal-flow performance with double pipe heat exchanger indicated that the tested device in low flow rates obtains higher heat transfer coefficients, heat transfer increased 50%. The pressure losses of the novel heat exchanger are lower than standard double pipe heat exchanger.

A simulation-based analysis of variable flow pumping in ground source heat pump systems with different types of borehole heat exchangers: A case study

A simulation model of ground source heat pump systems has been used to investigate to what extent a variable flow of the heat-carrier fluid of the ground loop affects the energy efficiency of the entire system. The model contemporaneously considers the borehole heat exchangers, the heat pump, the building load, and the control strategies for the circulation pumps of the ground loop. A constant speed of the circulation pumps of the ground loop was compared with a variable flow controlled by means of a constant temperature difference across the heat pump on the ground side considering the load profile of an office building located in North Italy. The analysis was carried out for a single U-tube, double U-tube and coaxial pipe heat exchangers. The control strategies adopted to manage the flow rate of the heat-carrier fluid of the ground loop affect both the heat exchange rate of the borehole field and the heat pump’s long-term energy efficiency. The simulations show considerable differences in the system’s seasonal energy efficiency. The constant speed of the circulation pumps leads to the best results as far as the heat pump’s energy performance was concerned, but this advantage was lost because of the greater amount of electrical energy used by the circulation pumps; this, of course, affects the energy efficiency of the entire system. The optimal solution appears then to be a constant temperature difference in the heat-carrier fluid across the heat pump.

Influence of geometrical and material parameters on flow rate in simplified ADS dense granular-flow target: a preliminary study

ABSTRACTThe spallation target is one of the key components of an accelerator-driven subcritical system (ADS). Following previous designs such as plate targets, rod targets, rotating targets, and liquid metal targets, the gravity-driven dense granular-flow target (DGT), which combines the advantages of solid and liquid metal targets, becomes a new attractive choice. The geometry of DGT consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. In this paper, using discrete element method simulations on graphics processing units, we research into the relations of the flow rate with the geometrical as well as the material parameters. For geometrical parameters, it is found that the existence of an internal pipe does not influence the flow rate when the distance from the bottom of the pipe to orifice is large enough. The results also reveal how the material parameters influence the flow rate. The whole research is helpful for the design of DGT.

Transitional and Weir Flow in a Vented Drop Shaft with a Sharp-Edged Intake

AbstractAn experimental analysis of a vertical drop shaft with a sharp-edged horizontal intake section and a coaxial venting pipe is undertaken to obtain design criteria given the limited attention provided by literature. Three different flow regimes are observed, namely weir flow and pressurized flow for extreme discharges and transitional flow for intermediate discharges. Particular attention is paid to transitional flow, which is a periodical regime consisting of an alternate switch from weir to pressurized flow, with water heads ranging between a maximum and a minimum. For transitional flow a detailed characterization of water surface oscillations is provided, and nondimensional equations are given describing mean water head, oscillation amplitude and frequency as functions of pipe Froude number and dimensionless plunged length of the coaxial pipe. Also, a region of existence is provided in terms of pipe Froude number and different wave types are identified. For weir flow, a nondimensional head-discha...

Метод исследования устойчивости течений в трубах

Метод исследования устойчивости течений в трубах

ESTUDIO DE SIMULACIÓN SOBRE LA EFICIENCIA EN LA CLASIFICACIÓN POR HIDROCICLONES CON BOQUILLAS DE DOBLE VORTEX

Classification efficiency of hydrocyclone is one of the kernel problems requiring solutions to promote the development of a solid-liquid separation system. A new hydrocyclone model was proposed to improve traditional structure and precise classification efficiency. Consequently, a coaxial overflow pipe with a small diameter was inserted into the original pipe, thereby possibly obtaining three different products with different size grades in one cycle. Then, using computational fluid dynamics, the Reynolds stress model was introduced into the Reynolds-averaged Navier-Stokes; the mathematical model of solid-liquid mixture multiphase flow was established. Finally, a study on the numerical simulation of the effects of structural parameters (e.g., underflow orifice diameter, internal overflow pipe diameter, and inserted depth of internal overflow pipe) on the classification efficiency of underflow, internal overflow, and external overflow of double overflow pipe hydrocyclones was conducted. Results show that one classification can obtain three different narrow-grade-classification products, namely, underflow, inner overflow, and outer overflow. The structural parameters are proven to play an important role in the classification efficiency of the hydrocyclone with double vortex finders. This study provides a good reference for the optimization of structural parameters of double overflow pipe hydrocyclones. Keywords: Hydrocyclone with double vortex finders, Classification efficiency, Structural parameters, Numerical simulation

回転二重円筒と円管流れにおける流動場の等価性について

This paper suggests that there is equality in physics between coaxial cylinder and pipe flow on the friction force per unit area. Among rotational machinery, electric motors and turbines for example are common industry which may have concentric shell structure. As the speed of rotating cylinder ascend, particular flow will occur known as Taylor-vortex flow regime beyond certain rotating speed. The major circulation of which has distance at least between coaxial cylinders. This means mass-flow is stirred enough to transport between inner and outer cylinder to emerge universal turbulence representation. It is investigated that stress force within concentric structure is almost the same as of the pipe flow even if the boundaries have various roughness. Consequently, complex behavior of frictional force including bumped surface can be estimated algebraically using Moody diagram.

305 大気圧マイクロプラズマジェットの特性に及ぼす同軸二重管構造の効果(OS4-1 熱および物質輸送現象の基礎と応用(1),OS4 熱および物質輸送現象の基礎と応用)

305 大気圧マイクロプラズマジェットの特性に及ぼす同軸二重管構造の効果(OS4-1 熱および物質輸送現象の基礎と応用(1),OS4 熱および物質輸送現象の基礎と応用)

Simulation of Power Production from Dry Geothermal Well Using Down-hole Heat Exchanger in Sabalan Field, Northwest Iran

In this research, a simulation was performed for evaluating power production from an abandoned geothermal well as an enhanced geothermal system by injecting a secondary fluid. Abandoned wells, due to lack of fluid or very low transmissivity, are regarded among the low-to moderate-temperature resources that have the potential for heat production without any cost for deep drilling. Accordingly, they are taken as suitable sources of energy. In the present paper, an abandoned geothermal well at Meshkinshahr geothermal field in Sabalan district, northwestern Iran, with 3176 m depth was simulated. The bottom-hole temperature of 148 °C, as well as well casing size, and real thermal gradient for well were applied in the model. A 3D heat transfer simulation model was designed by considering a coaxial pipe as a down-hole heat exchanger between surrounding rocks of the well and injected fluid. Injected fluid to the well with specified pressure and temperature receives heat from rocks surrounding the well, until it reaches the bottom of the well and converts to vapor. The vapor returns to the surface from inner pipe with very low heat loss during its return. The inner pipe is isolated by a thin layer having a low heat conductivity to prevent heat loss from the returned fluid. It was observed that obtained heat in the well depends on temperature profile of the well, injection velocity, and fluid mass flow rate. The model results were optimized by selecting suitable parameters such as inlet injection speed and fluid flow rate to achieve the highest temperature of the fluid returned from the well. A binary power plant was also modeled to determine the extractable power using returned fluid as input using ammonia and isobutene, as working fluids in binary cycle. Finally, electric power of 270 kW was generated from well NWS3 using designed down-hole heat exchanger.

Measurement of enhanced heat transfer coefficient with perforated twisted tape inserts during condensation of R-245fa

The experimental conductive heat transfer results for flow through inserted perforated twisted tapes in a horizontal tube during condensation of pure R-245fa vapor. The test section consisting of two separate coaxial double pipes assembled in series, acted like a counter flow heat exchanger, where the refrigerant condensed inside the inner tube by rejecting heat to the cooling water flowing inside the outer tube in reversed direction. Data for three perforated twisted tapes having constant twist ratio of 7.1 mm and pitch of perforation as 12.5, 25.0 and 37.5 mm, inserted one by one in full length of test condenser by varying refrigerant mass flux from 100 to 200 kg/m2 s in steps of 50 kg/m2 s for the range of vapor quality from 0.1 to 0.9, were collected together with flow and without insert (plain tube). It has been found that the perforated twisted tape insert having pitch of perforation equal to in order of 12.5 mm gives the highest value of average heat transfer coefficient and is of the order of 37.5 % more than that of the plain one and the correlation predicts the experimental data within an error band of ±15 %.

Strong exchange of stabilities in rapidly rotating parabolic Poiseuille flow

Abstract Poiseuille flow between two coaxial cylindrical pipes, with inner pipe translating at just the rate so that the velocity is parabolic, is rotated around the common axis of symmetry, with a common angular velocity. If the rotation rate is very large and it is assumed that the wave length of the critical disturbances is small, the governing equations take an approximate form that is analogous, remarkably, to Couette flow between coaxial cylinders with a certain difference. It is proved that if the rotation rate meets this criterion, the strong principle of exchange of stabilities (PES) holds; that is, all eigenvalues are real, and there is a first unstable eigenvalue. From a physical viewpoint, the resulting unstable motion initially takes the form of steady spiral vortices.

Designing coaxial ground heat exchangers with a thermally enhanced outer pipe

Ground heat exchangers installed in boreholes are an expensive component of a ground-coupled heat pump system, where minimizing the borehole length with appropriate materials and configuration can reduce the overall cost of the system. Design calculations performed analytically indicate that the coaxial pipe configuration can be more advantageous than the single U-pipe configuration to reduce the total borehole length of a system. A decrease of the borehole thermal resistance and an increase of the thermal mass of water contained in the coaxial exchanger helped to reduce borehole length by up to 23% for a synthetic building load profile dominated by cooling. The decrease of the borehole thermal resistance was achieved with an outer pipe made of thermally enhanced high-density polyethylene, where the thermal conductivity is 0.7 W m-1 K-1. The coaxial configuration requires further investigations of the technical barriers related to the installation of ground heat exchangers in the field.

Flow regimes in a vertical drop shaft with a sharp-edged intake

The results of an experimental analysis are provided concerning the hydraulic behaviour of a vertical drop shaft with a sharp-edged circular intake, also taking into account a peculiar venting system consisting of a coaxial vertical pipe, projecting within the drop shaft with different plunging lengths. Three different flow regimes are experienced: a “weir flow” for low head values, where an air–water mixture at the atmospheric pressure can be observed; a “pressurized flow” for high head values, where water flows in a pressurized regime along the shaft; a “transitional flow” for intermediate water head values, consisting of a continuous, spontaneous switch between weir flow and pressurized flow with consequent water head variation for a fixed discharge. Pressurized flow regime is analytically explained, so that a head–discharge relation can be provided both for the non-vented and for the vented configurations, with specific assumptions about intake losses.

Течение вязкой жидкости в деформируемой коаксиальной трубе

Течение вязкой жидкости в деформируемой коаксиальной трубе

186 同軸二重管を用いた大気圧マイクロプラズマジェットの特性に及ぼすガス種の影響

186 同軸二重管を用いた大気圧マイクロプラズマジェットの特性に及ぼすガス種の影響

Fluid‐structure interaction of an elastic pipe immersed in a coaxial rigid pipe: a model for the Tullio Phenomenon

AbstractAn axisymmetric, elastic pipe is filled with an incompressible fluid and is immersed in a second, coaxial rigid pipe which contains the same fluid. A pressure pulse in the outer fluid annulus deforms the elastic pipe which invokes a fluid motion in the fluid core. It is the aim of this study to investigate streaming phenomena in the core which may originate from such a fluid‐structure interaction. This work presents a numerical solver for such a configuration. It was developed in the OpenFOAM software environment and is based on the Arbitrary Lagrangian Eulerian (ALE) approach for moving meshes. The solver features a monolithic integration of the one‐dimensional, coupled system between the elastic structure and the outer fluid annulus into a dynamic boundary condition for the moving surface of the fluid core. Results indicate that our configuration may serve as a mechanical model of the Tullio Phenomenon (sound‐induced vertigo). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The acoustic model of oscillations of gas combustion in coaxial pipes

Organization of pulse combustion mode is one of the possible solutions to the problem of energy efficiency installations using hydrocarbon fuel. For grate combustion of solid fuels, in particular, solid industrial wastes are considered to be promising coaxial system, allowing the admission of secondary air to the combustion zone. In this paper we proposed an acoustic model of oscillations of gas when burning solid fuel in the system is coaxially arranged pipes with natural air supply. The description of the motion of the gas in the system during one period of oscillation.

Modeling and analysis of water-hammer in coaxial pipes

The fluid-structure interaction is studied for a system composed of two coaxial pipes in an annular geometry, for both homogeneous isotropic metal pipes and fiber-reinforced (anisotropic) pipes. Multiple waves, traveling at different speeds and amplitudes, result when a projectile impacts on the water fillinhe annular space between the pipes. In the case of carbon fiber-reinforced plastic thin pipes we compute the wavespeeds, the fluid pressure and mechanical strains as functions of the fiber winding angle. This generalizes the single-pipe analysis of J. H. You, and K. Inaba, Fluid-structure interaction in water-filled pipes of anisotropic composite materials, J. Fl. Str. 36 (2013). Comparison with a set of experimental measurements seems to validate our models and predictions.