Return Pipe Research Articles

The Study on Advancing Velocity of Hydraulic Support

Based on modeling and simulation technology, this paper puts forward a new method of studying quantitatively advancing velocity of hydraulic support, which is helpful to the optimization design of hydraulic support. Taking a certain type of hydraulic support as an example, the influence of hydraulic parameters such as flow rate, pressure, and pipe diameter on the advancing velocity of hydraulic support is analyzed. In order to increase advancing velocity, the flow rate of pump station and the diameter of main return pipe should be increased.

Transverse Plane-Wave Analysis of Short Elliptical End-Chamber and Expansion-Chamber Mufflers

The flow-reversal end chambers are used quite often in commercial automotive mufflers. The conventional axial plane-wave theory is not able to predict their acoustic performance because of the fact that the length of the end chambers is not enough for the evanescent three-dimensional modes generated at the junctions to decay sufficiently for frequencies below the cut-off frequency. Also, due to the large expansion ratio at the inlet, the first few higher- order modes get cut on even in the low-frequency regime. This necessitates a finite element or boundary element analysis, which is cumbersome and time-consuming. Therefore, an ingenious one-dimensional method has been developed. It models plane-wave propagation in the transverse direction between the incoming pipe and the return pipe, with the lateral-end cavities being modeled as variable-area quarter-wave resonators. Making use of this novel approach, the transfer matrices have been derived for elliptical and circular cross-section mufflers, which enable these elements to be analyzed along with the rest of the muffler elements by means of the transfer matrix-based muffler program. Through a comparison with a full, three-dimensional analysis on commercial software, it is shown that the one-dimensional approach presented in this paper is able to predict the transmission loss quite accurately up to about 1000 Hz for typical automotive mufflers.

Drop-in Test of Microchannel Evaporators Using R-22 for Residential Air Conditioners

The drop-in test of microchannel evaporators using R-22 for residential air conditioners was conducted. Five prototype microchannel evaporators were manufactured and tested in psychrometric calorimeter test facilities. Each evaporator was made with two parallel flow heat exchangers connected with several return pipes. The parallel flow heat exchanger had 41 microchannel tubes with eight rectangular ports. Performance comparisons were made between microchannel evaporators with and without hydrophilic coating to assess the effect on condensate on evaporator surface. Also, various performances of prototype microchannel evaporators were presented. Note that the cooling capacities of prototype 2, with a flow area ratio of 73/58%, and prototype 3, with six return pipes, were larger than prototype 1 by 15% and 9%, respectively. The cooling capacity of prototype 4 with three rows was larger than prototype 1 by 14%. Both refrigerant-side and air-side pressure drops for prototype 2 with the best cooling capacity were 29 kPa and 2.5 mmAq, which are acceptable for residential air conditioners.

Chilled water circuit designs for in situ chiller performance measurement

Determining the full- and part-load performance of chillers through short-term in situ measurements requires complicated arrangements. It will take a long time if consistently logged performance data under normal plant operation are used instead. Chilled water circuit designs that allow the full- and part-load performance of chillers to be measured conveniently and expeditiously are presented in the paper. The circuit designs require just minor extra provisions, including the installation of supplementary pipes and fittings, and a few additional control devices. Besides making it possible to conduct full-load tests on chillers at most of the time in the year, simulation results based on a building model in Hong Kong show that part-load performance data that cover the entire capacity range of chillers can be captured in less than 2 weeks, both in hot and cold months. Practical application: With the proposed chilled water circuit designs, the time and effort required for measuring the full- and part-load performance of new or existing chillers can be largely reduced. The method will work provided that each chiller is connected in series with a dedicated chilled water pump and the return chilled water will flow from one end of the main return pipe to another with connections to all chiller branches in between. The circuit design can be incorporated easily into new plant designs. For existing buildings, the required pipe modification work will interrupt plant operation.

Comparison of macroscopic flow properties obtained by three methods of operation in a liquid–solid circulating fluidized bed

Experiments were conducted in a liquid–solid circulating fluidized bed (LSCFB) to study the flow regimes, operational instability, critical transitional velocity to circulating fluidized bed (CFB) regime, solids holdup and solids circulation rate by three experimental methods. The results indicate that the operational instabilities such as arch formation, liquid–solid separator blockage and solids return pipe blockage were observed in two of these methods at large primary and auxiliary liquid velocities. The critical transitional velocity that demarcates the expanded bed from CFB regime was observed to be different by these three methods. Each of these methods has its own merits and demerits in terms of operating range of CFB regime, solids holdup, solids circulation rate and application.

Performance comparison of microchannel evaporators with refrigerant R-22

An experimental study on the performance comparison of microchannel evaporators with refrigerant R-22 was conducted. Six microchannel evaporators were designed and manufactured for a residential air-conditioner. They were tested with psychrometric calorimeter test facilities. The experiment was performed with both vapor compression system and refrigerant circulation system. Each evaporator was made up of two parallel flow heat exchangers connected with several return pipes. The parallel flow heat exchanger had 41 microchannel tubes inserted between inlet and outlet headers. The microchannel tube had 8 rectangular ports with the hydraulic diameter of 1.3 mm. For the vapor compression system, the flow area ratio and the number of return pipes had a great effect on the cooling capacity. Type 3 with a flow area ratio of 73% and 58% showed the best cooling capacity. It had 12 return pipes and 3 circuits. There is a merging manifold in it. The effect of the number of circuits and merging manifold on the cooling capacity was relatively small. For the refrigerant circulation system, the effect of the mass flow rate on the cooling capacity was slightly superior to that of inlet quality. The effect of the number of circuits on the cooling capacity was different from the result of the vapor compression system. The effect of merging manifold was negligible, which was consistent with the result of the vapor compression system. The cooling capacity proportionally increased as the vertical inclination angle of the evaporator increased due to gravity force.

Fatigue data acquisition, evaluation and optimization of district heating pipes

District heating (DH) transmission piping, composed of supply and return pipes, has been used to transmit heat efficiently without heat loss. This research aims to systematize the data processing of transition temperature, evaluate the temperature effects on pipe fatigue life, and optimize the size of DH pipes. For this purpose, a total of about 5 million temperature data were measured for 1 year at 10 locations. Then, available fatigue life estimation schemes were examined and applied to quantify the specific thermal fatigue life of each pipe. With regard to Korean DH pipes, a relational database management system as well as reliable fatigue life evaluation procedures was established. As prototypal optimization analysis results, the mean value of the original cross-sectional areas of the selected pipes was reduced by 18.6% while sufficient margins against fatigue failure was maintained. Therefore, the optimization analysis results can be used as useful information for setting a suitable operating condition and stabilizing the water temperature for design, operation and energy saving of DH heating piping in the future.

Fuel line failure from stress corrosion cracking

Following a head-on car accident in which one driver was seriously injured, the cause was established by police as a leaking diesel return pipe on a recovery vehicle. Examination showed that the pipe had separated radially, and the Forensic Science Service attributed the failure to vandalism. Closer inspection revealed a brittle fracture which showed several growth phases, the first. being initiated by stress corrosion cracking of the nylon connector in the pipe. The junction was immediately below the battery and it is likely that a drop of acid spilled onto it, starting the crack. it then grew at each successive start-up until final breakage. ESEM inspection showed fatigue-like striations and EDAX revealed the presence of sulphur. The injured driver was awarded substantial damages. There are continuing dangers from fuel line failures, both in car fires and creating hazards for other road users.

운전이력을 고려한 지역난방 열배관의 피로수명 평가 및 관리 체계 구축

A district heating(DH) system supplies environmentally-friend heat and is appropriate for reduction of energy consumption and/or air pollutions. The DH transmission pipe, composed of supply and return pipes, has been used to transmit the heat and prevent heat loss during transportation. The two types of pipes are operated at a temperature of 75~115℃ and 40~65℃, respectively, with an operating pressure of less than 1.568MPa. The objectives of this paper are to systematize data processing of transition temperature and investigate its effects on fatigue life of DH pipes. For the sake of this, about 5 millions temperature data were measured during one year at ten locations, and then available fatigue life estimation schemes were examined and applied to quantify the specific thermal fatigue life of each pipe. As a result, a relational database management system as well as reliable fatigue life evaluation procedures is established for Korean DH pipes. Also, since the prototypal evaluation results satisfied both cycle-based and stress-based fatigue criteria, those can be used as useful information in the future for optimal design, operation and energy saving via setting of efficient condition and stabilization of water temperature.

Abundance and Consumption of Fish by California Gulls and Ring-billed Gulls at Water and Fish Management Structures within the Yakima River, Washington

During 1999-2002, we studied the abundance of fish-eating birds, primarily Ring-billed Gulls (Larus delawarensis) and California Gulls (L. californicus), and estimated their consumption of fish at Horn Rapids Dam and the Chandler Irrigation Canal return pipe on the Yakima River in eastern Washington. Earlier observations of gulls at these structures suggested a high level of predation of juvenile salmonids. The relationship between river flow, gull use at the sites and fish taken was also examined. Numbers of gulls (instantaneous counts of foraging and non-foraging individuals) at the structures varied daily between their arrival in late March-early April and departure in late June. Daily averages across the four years were 9.8 (SE ± 1.5) and 19.1 (SE ± 2.5) gulls at Horn Rapids and Chandler, respectively. Gull numbers at Horn Rapids peaked dramatically during the last two weeks in May, reaching maxima of 37 (SE ± 2.2) to 133 (SE ± 4.2) gulls/day. This increase appeared to be associated with the hatchery release of one to two million juvenile autumn Chinook (Oncorhynchus tshawytscha) above the dam. A comparable peak in gull abundance was not observed at Chandler. Diurnal patterns of gull abundance differed between sites and among years. Relationships between fish take and water flow also varied within and among years at the two sites. Low seasonal flows were associated with increased predation at Chandler, whereas high seasonal flows were associated with increased predation at Horn Rapids. Assuming all fish taken were salmonids, consumption at both sites combined was estimated to be ≤10.3% of the juvenile salmonids passing the two sites.

Single, twin and triple buried heating pipes: on potential savings in heat losses and costs

In order to make district heating systems competitive in areas with single family houses or in other areas with low heat demands it is necessary to reduce the heat losses from the pipes. In recent years the twin pipe has become popular in the Nordic countries. In the article we describe how the heat loss and the heat loss coefficients can be calculated. We introduce the triple pipe with three media pipes (two supply pipes and one return pipe). The temperature dependency and the ageing of polyurethane insulation are briefly discussed. A comparison is made for different 80 mm distribution pipes and for different service pipes with respect to heat losses and to resources, i.e. materials needed for the casing and polyurethane insulation and the gravel in the excavations. For the distribution pipe we found that an egg-shaped twin pipe can reduce the heat loss by 37% and the investments by 12% compared with a pair of single pipes. For the service pipes we found that the triple pipe reduces the heat loss by 45% compared with a common pair of single pipes and by 24% compared with circular twin pipes. The reduction in investment index is 21%. The article also addresses the question of the heat exchange between the two media pipes in a twin pipe. Copyright © 2005 John Wiley & Sons, Ltd.

Muffler for an engine

A muffler including a long outlet pipe 20 having an exhaust gas inlet pipe portion 21 , a return pipe portion 22 , an exhaust gas outlet pipe portion 23 , and two turnaround pipes 24, 25 for connecting the three pipe portions 21, 22, 23 together in series. These pipe portions 21, 22, 23 are arranged in parallel with one another along a longitudinal direction of a shell 2 , and in such a manner that longitudinal axes 21 L, 22 L, 23 L of the pipe portions are positioned at respective vertices of a triangle.

Numerical simulation of two-phase Helium II stratified flow in cryogenic units of TESLA

Numerical simulation has been carried out for two-phase Helium II stratified flow in 12 horizontal or declining cryogenic units each with a length of about 2.5 Km for the proposed 500 GeV TESLA (TeV Superconducting Linear Accelerator). The simulation predicts the He II level, the vapor mass flow rate in the two-phase tube, and the pressure profile through the gas return pipe of all units as well. Based on the numerical results the flow pattern and the stability of He II/vapor two-phase flow are discussed.

Solid circulation in a liquid spout-fluid bed with multi draft tubes

Considering the application of the technique of liquid spouting with multi draft tubes to heat exchangers, the solids circulation rate was studied both experimentally and theoretically. It was found that the solids circulation rate increased with the liquid velocity and with the amount of solids used. Experimental results were found to be lower than the calculated values. It was concluded that the friction forces between closely packed particles and between particles and the wall of the return pipe at the zone of entrainment retard the solids circulation rate. The rate of the calculated to the experimental circulation rates was observed to be lower as the concentration of solids increased. The effect of the slip velocity on the particle velocity and the calculated values of solids circulation rate was also investigated. © 1998 SCI

Solid circulation in a liquid spout‐fluid bed with multi draft tubes

Considering the application of the technique of liquid spouting with multi draft tubes to heat exchangers, the solids circulation rate was studied both experimentally and theoretically. It was found that the solids circulation rate increased with the liquid velocity and with the amount of solids used. Experimental results were found to be lower than the calculated values. It was concluded that the friction forces between closely packed particles and between particles and the wall of the return pipe at the zone of entrainment retard the solids circulation rate. The rate of the calculated to the experimental circulation rates was observed to be lower as the concentration of solids increased. The effect of the slip velocity on the particle velocity and the calculated values of solids circulation rate was also investigated. © 1998 SCI

A Finite Element Study of Heat and Fluid Flow through a Skirting Heater

This article describes a numerical study of buoyancy-driven laminar flow through an enclosure modelling a skirting heater used in building environ ment. The flow is induced by two heat sources of circular shape representing the flow and return pipes. A finite element method is used to solve the govern ing equations of momentum and energy in two dimensions. A combined con vection and radiation heat transfer coefficient coupled with an iterative proce dure have been used to set the wall boundary conditions. The flow field and temperature distribution within the enclosure are presented. The results also include the predicted distributions of the temperature along the enclosure walls which are in contact with the surrounding environment. The effects of changes in the basic geometry and its boundaries on the flow are also dis cussed. It is shown that the method can provide a means of optimizing the design of such heaters.

Study on the heat-flow controllable heat exchanger (1st report): Thermal characteristics of heat-flow controllable heat exchanger

To regulate temperature in passive solar houses and green houses, the authors have developed a heat exchanger capable of controlling the heat flow. It has a thermal switch mechanism without mechanically moving parts. It consists of an evaporator, a condenser, a vapor passage pipe, a liquid return pipe having an inverted-U-pipe, and a heater mounted on the inverted-U-pipe. The heat exchanger can transfer, or reduce to zero, heat from the evaporator to the condenser by regulating a slight heater input. The authors have fabricated a model of the heat-flow controllable heat exchanger to examine its thermal switching and heat exchange characteristics, and then compared the obtained results with calculation results. It was clarified that the experimental results agree with the calculation results.

A Finite Element Study of Heat and Fluid Flow through a Skirting Heater

This article describes a numerical study of buoyancy-driven laminar flow through an enclosure modelling a skirting heater used in building environment. The flow is induced by two heat sources of circular shape representing the flow and return pipes. A finite element method is used to solve the governing equations of momentum and energy in two dimensions. A combined convection and radiation heat transfer coefficient coupled with an iterative procedure have been used to set the wall boundary conditions. The flow field and temperature distribution within the enclosure are presented. The results also include the predicted distributions of the temperature along the enclosure walls which are in contact with the surrounding environment. The effects of changes in the basic geometry and its boundaries on the flow are also discussed. It is shown that the method can provide a means of optimizing the design of such heaters.

Development and use of microtunnellers in the UK : Washbourne, J Tunn TunnlgV25, N3, March 1993, P69–71

There is a growing demand for the use of tunnelling rather than trenching for ducts which are less than man entry such as those used to install cables and pipes. The article describes the design and development of microtunnellers in general giving details of the Hawker Siddeley Dosco slurry microtunnelling system. This system is capable of being used in a wide range of ground conditions. The system has a specially designed high output crusher that uses a stator and rotor configuration that crushes progressively around the circumference. Auger extraction of spoil is preferable for drives of length less than 80m. A slurry system is used for longer drives, and where there is a head of groundwater at the face. Maximum spoil particle size is limited to one-third of the exit pipe diameter for slurry spoil removal, or one-quarter of the auger pipe diameter. A high flow velocity is needed in the excavation of coarse grained soils to ensure saltation of the largest particles during spoil removal. This causes considerable loss of pressure on long return pipes and the spoil can be mined with a low rate of slurry flow using low charging pump pressure. The consistency of the spoil removal slurry is monitored and flow rates are adjusted accordingly. An efficient lubrication system is vital with small diameter pipes if acceptable jacking distances are to be maintained.

Thermal design of district-heating distribution networks

The behaviour of a double-pipe arrangement, consisting of a hot supply pipe and a warm return pipe enclosed within a relatively cold, rectangular, air-filled trench was considered. The minimum rates of steady-state heat losses occurred with the supply and the return pipes at displacement ratios E s = 0·45 and E r = −0·38 respectively; the hot pipe being in the upper region and the warm pipe vertically below it. The pipes were symmetrically placed with respect to the side walls. There is an optimal separation of 11·4 mm ± 1·1 mm for the gap between the supply and the return pipes for the temperature ranges and component sizes employed. This interesting result agrees quantitatively with those from previous experimental studies, but its significance had not been realised previously. By employing this optimal arrangement, a reduction in the total rate of heat loss from the supply pipe was obtained compared with that from this pipe placed anywhere else in the enclosure, but with similar temperatures for the pipes and trench walls as in the optimal arrangement.