Pipe Parameters Research Articles

Effects of Structure Parameters of Gravity-Type Heat Pipe on Heat Transfer Characteristics for Waste Heat Recovery from Mine Return Air

In the condition of waste heat recovery from mine return air with a temperature of 20~30 °C and velocity about 4 to 8 m/s, the structure of gravity-type heat pipe with fin increases the heat exchange areas and meanwhile increases the resistance of air flow, which consumes a large amount of main fan power driven by a motor. Furthermore, the resistance of air flow increases greatly with the velocity of the air flow. In this paper, the gravity-type heat pipe with elliptical smooth surface is studied to decrease the resistance and loss of energy of the air flow. In order to obtain the influence of ellipticity on heat transfer efficiency and energy loss under the condition of a certain heat transfer area of the heat pipe, the heat transfer efficiency of a single pipe and a pipe bundle with different ellipticities is studied by using numerical simulation based on the equal section perimeter. The results show that the reasonable change of ellipticity can increase specific enthalpy and decrease entropy production. When the pipe is single, the ellipticity is 0.56 and the specific enthalpy is the largest, increasing by 12.08%. The ellipticity of the pipe bundle is 0.61, and the specific enthalpy is the largest, increasing by 19.28%. The entropy production slightly increased by 10.4%. Moreover, the empirical formula of single pipe heat transfer with an error less than 5% and the empirical formula of pipe bundle heat transfer with an error less than 2.2% are obtained. The empirical formula of pipe bundle heat transfer at different temperatures is modified, and the error is less than 5%, which provides the fundamental data for deep research, development, and engineering design of gravity-type heat pipe heat energy exchange system of underground return airflow in coal mines.

Monitoring and Analysis of Circumferential Pressure for Long‐Distance Pipe Jacking Construction in Composite Strata

ABSTRACTAt present, the monitoring methods of mechanical parameters of pipe in the process of pipe jacking construction generally have the disadvantages of low data reliability and poor timeliness. Especially in the jacking construction in complex strata, if the jacking parameters and lubrication grouting parameters cannot be adjusted in real time according to the circumferential pressure, it is easy to cause pipe sticking accident. Based on the Inner Mongolia Water Diversion Project from ChaorHe to Liaoning, this paper adopts the LPWA low‐power wide‐area network wireless sensing system based on 5G and IOT technology to realize the real‐time wireless monitoring of the contact pressure and lubrication grouting pressure of the underground pipe jacking pipe. Through the parameters obtained by the wireless sensing system, the stress characteristics of a specific pipe traversing different strata and under different working conditions were studied, and the change rule of circumferential contact pressure of the pipe and the influence of various factors on it were analyzed. The results show that: by analyzing the circumferential contact pressure obtained by the wireless sensing system, the pressure distribution of the pipe in the top soft and bottom hard strata is right>left>bottom>top; in the full‐section strata, the destruction of the lubricating mud sleeve will lead to the same contact pressure on one side and the bottom of the pipe; when the pipe traverse the interfaces of different rock strata, the stability of the lubricating mud sleeve will be affected, and thus the circumferential contact pressure will be altered. The above results are consistent with the theoretical prediction and can provide reference for the actual project. In conclusion, the wireless sensing system can accurately reflect the distribution of circumferential contact pressure of the pipe under different strata, and provide reliable data support for improving construction efficiency and safety.

Research on the pressure fluctuations and hydraulic resonance phenomena in the high-pressure pipelines of marine common rail systems

Increasing injection pressures in marine high-pressure common rail systems can lead to reliability issues due to pressure fluctuations. This study investigates the mechanism of hydraulic resonance caused by these fluctuations. A test bench assessed pressure fluctuations under various conditions and fuel pipe parameters, where hydraulic resonance was observed. Time-domain and frequency-domain analyses were conducted on the test results. The system pipeline was then optimized to eliminate hydraulic resonance. Resultsindicate that pressure fluctuations exhibit both high- and low-frequency coupling. Abnormal fluctuations are caused by hydraulic resonance, triggered by the proximity between the excitation frequency of the high-pressure fuel pump and the first-order natural frequency of the system. Resonance speed is influenced by the fuel pipe's structural parameters and the fuel's hydraulic properties. The frequency-domain model shows high predictive accuracy, identifying the interface between the pump and the pipeline as the most probable failure location. Optimization reduced pressure fluctuations at the pump end and the common rail by 73 % and 35.7 %, respectively, and eliminated hydraulic resonance at the original resonance speed. The maximum pressure fluctuation amplitude at the pump end decreased from 410 bar to 167 bar, a 59.3 % reduction. The research methodology presented in this paper provides a theoretical foundation for the structural design of the high-pressure pipeline in high-pressure common rail systems.

Ex Ante Construction of Flow Pattern Maps for Pulsating Heat Pipes

A novel methodology is proposed for the development of empirical flow pattern maps for pulsating heat pipes (PHPs), which relies on the concept of virtual superficial velocity of the liquid and vapour phases. The virtual superficial velocity of each phase is defined using solely the design and operational parameters of the pulsating heat pipe, allowing the resulting flow pattern map to serve as a predictive instrument. This contrasts with existing flow pattern maps that necessitate direct measurements of temperatures and/or velocities within one or more channels of the pulsating heat pipe. Specifically, the virtual superficial velocities are derived from the relative significance of the driving forces and the resistances encountered by each phase during flow. The proposed methodology is validated using flow visualisation datasets obtained from two separate experimental campaigns conducted on flat-plate polypropylene pulsating heat pipe prototypes featuring transparent walls and meandering channels with three turns, five turns, seven turns, and eleven turns, respectively. The PHP prototypes were tested for gravity levels ranging between 0 g and 1 g and heat inputs ranging from 5 W to 35 W. The proposed approach enables the identification of empirical boundaries for flow pattern transitions as well as the establishment of an empirical criterion for start-up.

Study on the influence of pipe effect on the vibration characteristics of electro-hydraulic exciter

In this paper, an electro-hydraulic exciter controlled by an alternating current distribution valve is proposed, and a systematic analysis of the influence of pipe effect on the vibration characteristics of the electro-hydraulic exciter is investigated by simulation and experiments. The vibration characteristics curves for different pipe parameters are obtained, and the relative errors between simulation and experiment are evaluated. Moreover, a significant regression model of pipe parameters and vibration characteristics of the electro-hydraulic exciter is established by using the quadratic regression analysis method and the Box-Behnken experiment design method. Significant differences in the influence of pipe parameters on vibration characteristics are obtained by ANOVA (Analysis of Variance), and the influence of pipe parameter interaction on vibration characteristics is discussed. The results show that the relative importance of pipe parameters on the vibration characteristics of electro-hydraulic exciter, from high to low, is as follows: pipe diameter, elastic modulus, and pipe length. Notably, there is also an interaction between the pipe parameters, and the significance of these interactions is ranked from high to low as the interaction between the layers of steel wire and diameter, the interaction between diameter and length, and the interaction between the layers of steel wire and length.

Research on Active Power Loss Distribution of Components in Magnetic Coupling Wired Drill Pipe

Abstract The magnetic coupling wired drill pipe achieves high-speed information transmission by installing cable at the rod and embedding magnetic couplers at the joints. However, significant energy attenuation in these connected wired drill pipes necessitates the addition of relay circuit compensation every few hundred meters, increasing system complexity and cost. The equivalent circuit of magnetic coupling wired drill pipe can be regarded as a series connection of a coaxial cable line, high-frequency transformer, and terminal load. Exploring better wired drill pipe parameters to distribute signal power across different frequencies will optimize power at the terminal load and improve relay distance. This research establishes a mathematical model for active power distribution in magnetic coupling wired drill pipes based on circuit analysis. The model’s accuracy is validated through circuit simulation and numerical analysis. Reducing signal energy attenuation in the cable and coupler is achieved by increasing the coil coupling coefficient, reducing the coil resistance, and altering the characteristic impedance of the coaxial cable. This research provides a theoretical tool for analysing active power loss distribution of components in wired drill pipe.

Ground test modeling of cylindrical aero-engine casing under high-temperature and high-pressure aerodynamic load

The aero-engine casing is subjected to high-temperature and high-pressure aerodynamic loads during operation. It is essential to perform the ground strength tests for the casing. To optimize the ground strength test and to improve the accuracy of temperature and pressure loading during the test, a mathematical model of high-temperature and high-pressure aerodynamic loading system for simulating the ground strength test of typical aero-engine casing is established to study the actual temperature and pressure loads on casing during ground test. The temperature and pressure results calculated by the mathematical model under typical loads matched well with the experimental measurements. The verification results show that under the test conditions, the thermal inertia of the heater, the radiation heating of the gas in the test chamber by the heater, and the heat transfer of gas mixing in the pressure process can be ignored. The sensitivity analysis of the parameters affecting the accuracy of pressure and temperature loading is carried out. We show that the pressure can be controlled quantitatively by adjusting the inlet and exhaust pipe parameters, and accurate temperature control can be achieved by designing reasonable heater power and selecting appropriate heating control parameters.

Comparative Analysis of Water Hammer Performance in Different Pipe Parameters with FSI

Water hammer (WH) is a critical phenomenon in fluid-filled piping systems that can lead to severe pressure surges and structural damage. The characteristics of the pipe material, geometry, and support conditions play a crucial role in the fluid–structure interaction (FSI) during WH events. This study investigates the impact of various pipe parameters, including material, length, thickness, and diameter, on the WH behavior using an FSI-based numerical approach. A comprehensive computational model was developed based on the algorithm presented in Delft Hydraulics Benchmark Problem (A) to simulate the WH phenomenon in pipes made of different materials, such as steel, copper, ductile iron, PPR (polypropylene random copolymer), and GRP (glass-reinforced plastic). This study examines the influence of pipe parameters on WH performance in pipelines, utilizing FSI to analyze the phenomenon. The results show that the pipe material has a significant influence on the pressure wave speed, stress wave propagation, and the overall system response during WH. Pipes with lower modulus of elasticity, such as PPR and GRP, exhibit lower pressure wave speeds but higher stress wave speeds compared with steel pipes. Increasing the elastic modulus, pipe wall thickness, length, and diameter enhances the pipe’s stiffness and impacts the timing, magnitude of pressure surges, and the likelihood of cavitation. The findings of this study provide valuable insights into the design and mitigation of WH in piping systems.

Study on the structure parameters and design method optimization of blade-type screw steel pipe pile

The rationality of structure parameters of the blade-type screw steel pipe pile is the major factor in determining the safety, applicability, and economy of a pile foundation, but the existing design methods have not defined the specific approaches to calculating structure parameters of blades and steel pipes. To address this issue, an analysis of the strength theory was performed on spatial helical blades, revealing the ratio of blade width to steel pipe radius as the core index to do the structure parameters design of blade-type screw steel pipe pile and established a mathematical calculation model between the vertical bearing capacity of single pile and a. The rational value of a is 2.0–3.0 using numerical calculation. The correlation between blade thickness and wall thickness of steel pipes was determined using the force analysis based on the synergy between blades and steel pipes. Then the structure parameters design method of blade-type screw steel pipe pile with coordinated parameters was proposed. The rationality and superiority of this design method were verified by comparing the existing test data and the finite element simulative analysis. Based on this design method and the current specifications, such as the Technical Code for Building Pile Foundations, a safe, applicable, and economical optimization design method and flow of blade-type screw steel pipe piles were further proposed for engineering design reference.

Study on Key Properties and Model Establishment of Innovative Recycled Aggregate Pervious Concrete.

In order to meet the needs of low-impact development and sustainable development, there is an urgent desire to develop an innovative recycled aggregate pervious concrete (I-RAPC) that is of high strength and permeability. In this study, I-RAPC was prepared based on response surface methodology (RSM) using recycled aggregate, river sand, and different types of pipes as the materials, and the effects of different pipe parameters (number, diameter, material, and distribution form) on the performance of I-RAPC were investigated. In addition, the calculation model of the compressive strength and the permeability coefficient of I-RAPC were proposed. The results showed that the frontal- and lateral-compressive strengths of I-RAPC were 39.8 MPa and 42.5 MPa, respectively, when the pipe material was acrylic, the position was 1EM, and the diameter was 10 mm-at which time the permeability coefficient was 3.02 mm/s, which was the highest in this study. The maximum relative errors of the compressive strength calculation model and the permeability coefficient calculation model were only 7.52% and 4.42%, respectively, as shown by the post hoc test. Therefore, I-RAPC has the advantages of high strength and permeability and is expected to be applied in low-impact development in cities with heavy surface sediment content and rainfall.

ОПТИМИЗАЦИЯ ПЕРЕПРОФИЛИРОВАНИЯ ВОСЬМИУГОЛЬНЫХ ТРУБ ИЗ КРУГЛЫХ ДЛЯ БАЛОЧНЫХ КОНСТРУКЦИЙ

A new method for converting round pipes into octagonal ones with a ratio of width and height 1/3.018 along the median line of the design section is presented, which maximizes their bearing capacity of bending strength. Its originality has been confirmed by patent examination. The calculation of the optimal parameters of thin-walled octagonal sections is given according to an approximate method tested using profiles from a standard assortment. The entire diagram of changes in the design parameters of octagonal pipes during the transformation of their cross sections from vertical to horizontal configurations is shown, including the transition through a modification with equal dimensions of width and height, the outlines of which have the shape of an equilateral (regular) octagon. The demand for octagonal profile pipes is revealed not only in metal, but also in pipe-concrete structures. A comparative analysis of the design parameters of optimized sections of profile pipes, repurposed from round to oval, flat-oval, semi-flat, rectangular, octagonal, has been performed. Optimized tubular profiles with increased bending strength can be attributed to beam modifications.

Experimental and numerical investigations of an auxetic support structure used for local repair of buried pipelines

Due to the ongoing disasters caused by local damage to underground pipelines in urban areas, a new method has been proposed for local trenchless rehabilitation of pipelines.This method utilizes the auxetic effect of an auxetic pipe structure to create support brackets inside the pipeline for repairing damaged sections, with the aim of reducing overall repair costs and improving efficiency. The main objectives of this study are to demonstrate the feasibility of using auxetic pipes for pipeline repairs and to enhance key parameters of auxetic support pipes. This paper presents a tube with auxetic support - the Surrounding Auxetic Tubular Structure (SATS). Using 3D printing technology, the preparation of SATS specimens was carried out, and the compressive properties of SATS were studied through finite element analysis and quasi-static compression test. The results show that the proposed SATS has a significant negative Poisson's ratio effect during the compression process and exhibits a high structural rebound rate after the load is removed. The size of the structure's boundary is the most influential factor on the auxetic effect. Additionally, the compression displacement of SATS increases with the increase of the elliptical short axis, and decreases with the increase of the elliptical long axis. The compressive load decreases with the increase of the short axis, and increases with the increase of the long axis. This demonstrates the excellent mechanical performance of the proposed auxetic support structure and lays the foundation for the feasibility of local repair work for trenchless rehabilitation.

Performance analysis of four-stage thermoelectric cooler for focal plane infrared detectors

A cooler provides a low-temperature working environment for refrigerated infrared detection chips and is an indispensable component in infrared detectors that ensures their smooth operation. In this paper, a thermodynamic model of a heat-pipe-type four-stage thermoelectric cooler with a large temperature difference applied to a focal plane infrared detector is constructed. The heat leakage of the detector is calculated using the model. The performance indexes of the coordination performance coefficient and module utilization coefficient are used to unify the cooling capacity and economic performance of the device. The impression of the working current, heat pipe parameters, and cross-sectional area of the thermoelectric leg on the performance of cooler are analyzed. A Pareto optimal solution is obtained using an NSGA-II algorithm and TOPSIS decision. A low cooling temperature is obtained using a multistage thermoelectric cooler to achieve a large cooling temperature difference. When the working current is 5.65 A and the cross-sectional area is 4.5 mm2, the maximum cooling temperature difference reaches 110.6 °C, and the lowest cooling temperature reaches -83.6 °C. When the working temperature of the detector is -60 °C, the current and cross-sectional area corresponding to the optimal solution of cooling capacity-COP-power consumption are 1.51 A and 2.74 mm2, respectively.

Application of Hydrus-2D Model in Subsurface Drainage of Saline Soil in Coastal Forest Land—A Case Example of Fengxian, Shanghai

The study aims to explore saline drainage modeling in coastal saline soils, particularly focusing on subsurface pipe drainage in the Shanghai coastal area. Utilizing Hydrus-2D/3D-2.05 software, dynamic changes in soil–water–salt under various subsurface pipe laying conditions in forested areas were simulated to identify optimal schemes. Indoor and outdoor experiments demonstrated the Hydrus model’s ability to effectively simulate soil–water–salt transport processes under complex conditions. Subsequent simulations under different parameters of underground pipe laying, including burial depths (D = 0.5/0.7/0.9/1.1/1.3/1.5 m) and pipe diameters (Ø = 8/10/12 cm), further corroborated model validation. Among the analyzed schemes, those with burial depths around 0.7 m and pipe diameters under 12 cm exhibited the most substantial salinity improvement. Regression analysis highlighted a significant impact of burial depth D on cumulative salt discharge, with a coefficient of 12.812, outweighing that of pipe diameter Ø. Furthermore, subsurface pipe laying schemes demonstrated long-term benefits and cost advantages, obviating the need for additional irrigation infrastructure. These findings underscore the significance of subsurface pipe drainage in enhancing soil quality, reducing construction expenses, and optimizing land utilization, providing a valuable foundation for the Shanghai Green Corridor development and related initiatives.

Review of Operation Performance and Application Status of Pulsating Heat Pipe

Due to the rapid development of science and technology in today’s era, electronic equipment is constantly upgrading. Today, the developmental trend of electronic equipment is miniaturization, portability and multi-functionality. However, multi-functionality often means multi-components, so it is undoubtedly a great test of heat dissipation ability to accommodate more components in a smaller volume. Without sufficient heat dissipation capacity, a large number of components will stop working or even be damaged because of the heat generated during operation. As a new passive cooling and heat exchange technology, pulsating heat pipes have many advantages, such as having no external energy input, a simple structure, changeable installation forms and low installation requirements. They have shown great potential in the field of thermal management, and have attracted a lot of scholars’ attention since they were put forward. Because of their operational stability and heat exchange ability in high heat flux environments, they are the best choice for cooling electronic equipment at present. If they can be fully studied and utilized, pulsating heat pipes can not only reduce the consumption of heat dissipation resources but also reuse heat energy to realize the sustainable utilization of resources. This paper briefly introduces the demand background and structural principle of pulsating heat pipes, and summarizes the research on the parameters of pulsating heat pipes and the application status of pulsating heat pipes. The parameters involve working fluid type, pipe diameter, elbow number, liquid filling rate, inclination angle, etc. After classifying the parameters that affect the operation results of pulsating heat pipes, this paper summarizes the research at this stage, and points out the lack of research fields, such as heat flux density, and new application fields of unconventional gravity environment by combining the literature content with the current scientific and technological development trends and experimental parameters, such as thermodynamics.

Optimal design of heat pipes for city gate station heaters by applying genetic and Bayesian optimization algorithms to an artificial neural network model

This study contains a novel idea to improve the performance of city gate station heaters, using pulsating heat pipes with optimized structure. In this research, a hybrid method including Bayesian and genetic algorithms is implemented to optimize the architecture of an artificial neural network (ANN) model and find the optimal operating point for heat pipes. In the previous study, the authors have proposed a neural network-based model to predict the thermal performance of heat pipes, based on a wide range of their design parameters, including dimensions of heat pipe, number of turns, working fluid, inclination angle, filling ratio, and heat input. In the present study, the prediction model architecture is optimized using Bayesian optimization algorithm. The best performance is achieved when iterations of the employed Bayesian optimization is set to 300 iterations or samples, which 150 samples are produced to train the Bayesian model and other 150 iterations are utilized in order to find the optimal ANN structure and hyper-parameter tuning of the model. The optimal ANN model with structure of 9-97-21-68-100-1 has evaluation parameters of 0.980 and 0.014 for R2 and MSE of total dataset, respectively. The performance metrics indicate an improvement in accuracy of the ANN model with a 53.33% reduction in MSE value and a 3.15% increase in R2 score. Then, the genetic algorithm is applied to the optimal model to find the optimum operating parameters of the heat pipe. In this regard, the design parameters of the best heat pipe in order to use in the city gate station heaters, are obtained by setting the genetic algorithm population equal to 300. Finally, as a practical case study, a real heater with capacity of 10,000 SCMH which is located in Iran is selected. Considering constraints and limitations of this heater, the proposed model indicates that a vertical pulsating heat pipe with four turns which is filled 55% with water as the working fluid, has the optimal thermal resistance of 0.104 K/W. Utilizing the optimal heat pipe in the mentioned heater is a promising solution for efficiency improvement and fuel consumption and CO2 emission reduction, which decreases the operating costs of the heater as well.

Myrmecia: Failure analysis and thermodynamic coupled simulation program for heat pipe in micro reactor based on MOOSE

The heat pipe cooled microreactor (HPMR) has become increasingly popular in the realm of research, largely due to its clean, efficient, and safe properties. This paper presents the development of Myrmecia, a simulation software built on the MOOSE framework. Myrmecia integrates the thermodynamic model and failure analysis model of a heat pipe, facilitating the assessment of the failure probability of a given heat pipe based on its thermodynamic parameters and design parameters. The verification of both models has been conducted. The findings demonstrate that increasing the wall thickness of the heat pipe leads to a reduction in its heat transfer capacity, while significantly decreasing the failure probability. Furthermore, appropriately elevating the initial temperature contributes to a decreased likelihood of a break event occurring in the heat pipe. Under the assumption of a fixed heat source/sink temperature, enlarging the inner diameter of the heat pipe exerts negligible influence on the failure probability, yet substantially enhances its heat transfer capability. In summary, various parameters of the heat pipe exert considerable influence on both its safety performance and heat transfer performance. Consequently, the trade-off between these two aspects represents a critical consideration for heat pipe designers.

Analysis on the Influence of Geometric Parameters of a Circular Steel Pipe with Flange Plates on Surface Settlement

Analysis on the Influence of Geometric Parameters of a Circular Steel Pipe with Flange Plates on Surface Settlement

Determination of Winter Irrigation Quotas for Corn and Oil Sunflower Considering Crop Salt Tolerance Threshold under Subsurface Pipe Drainage Technology

Subsurface pipe drainage (SPD) is an important technique for the improvement of saline–alkali lands in China. Winter irrigation after crop harvest is a key measure used in the Yellow River irrigation area in northwest China to reduce soil salinity in the root zone of crops. To optimize winter irrigation under SPD, the calibrated HYDRUS-2D model was utilized in this study to investigate the effects of soil texture (clay loam, silt loam, loam, and sandy loam), initial soil salinity (1, 3, 5 g/kg), and the winter irrigation quotas (80, 100, 120, 150, 180 mm) on the rate of soil desalination. In this study, soil salinity levels during the stable production of common crops such as sunflower and corn in the Yinbei Irrigation District in Ningxia, China, were taken as the thresholds, efficient utilization of irrigation water was considered, and suitable crops and appropriate winter irrigation quotas for different soil textures and levels of soil salinity were proposed. Soil with a salt content of 1~3 g/kg is suitable for the planting of corn with 80 mm of irrigation water. Sandy loam soil with a salt content of 3~5 g/kg is suitable for sunflower–corn intercropping with 120 mm of irrigation water. Sandy loam soil with a salt content exceeding 5 g/kg is suitable for the planting of sunflower with 80 mm of irrigation water. Other types of soils need to be improved by reducing the spacing between subsurface pipes, using desulfurized gypsum, biochar, and other additives. People engaged in agriculture can utilize this research to determine the appropriate volumes of irrigation water, crop types, planting systems, and subsurface pipe parameters based on local conditions.

Fluid Flow in Helically Coiled Pipes

Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes.