Pipe Spacing Research Articles

Influence of Subsurface Pipe Perforations on Transient Water Table Response and Steady Soil-Water Flux under Subirrigation

HighlightsWater table rise was slower under a sparsely perforated pipe as compared to a pipe that was densely perforated.Response time increased as buried pipe depth decreased for both combinations of perforation characteristics.Fluxes from buried pipes spaced at 15 m in loamy sand satisfied the water demand for cereal/grain crops (6 mm d-1).Increasing perforation density on the pipe wall is the most effective way to reduce exit head losses.Abstract. It is important to consider the water table rise into the unsaturated zone when designing subsurface irrigation systems that consist of buried perforated corrugated pipes. Corrections to pipe spacing equations for head losses due to perforations are based on the entrance resistance, which is derived for buried pipes operating in drainage mode. However, the boundary condition at the soil-pipe interface when operated in subsurface irrigation mode requires the use of the exit resistance to accurately account for perforations in the pipe wall. Simulations of a subsurface irrigation system with four soil textures, three lateral pipe spacings, and three buried depths were carried out, with the numerical model COMSOL, to demonstrate the effects of variable perforation characteristics on the transient water table rise into the unsaturated zone. Soil-water fluxes were also computed for the system when operated under steady-state conditions. The simulated water table rise exceeded or approached a predetermined target water level of 1.65 m above the buried pipes in coarse-textured soils (loamy sands and silt loams) with lateral pipe spacings as large as 10 m. Increasing the number and length of rectangular slots in the pipe wall (densely perforated) can reduce the water table response time to reach the target level by 15 h in a silt loam soil and 25 h in a clay soil. The optimum pipe spacing needed to sustain a soil-water flux of 6 mm d-1 (common to eastern Canada and the U.S. Midwest) can be increased from 15.1 to 16.2 m in loamy sands by using densely perforated pipes. In contrast, increasing perforations in pipes buried in clays and sandy clays will result in pipe spacing increases of less than 0.2 m because these fine-textured soils have lower hydraulic conductivity. This study has demonstrated that variable perforation characteristics can be included in the analysis and design of subsurface drainage systems for improving water management. Keywords: Corrugated perforated pipes, Exit resistance, Head loss, Subirrigation, Unsaturated zone, Water table response.

Optimization of energy tunnel heat extraction section design based on simulated annealing algorithm

Energy tunnel is an alternative energy-saving technology of ground source heat pump （GSHP）， which has been applied in China in recent years. However， the current engineering practice still lacks the mature design method， and the heat extraction section design of the energy tunnel usually depends on engineering analogy. It is necessary to develop a convenient and reliable method to assist energy tunnel design. To address this problem，an optimization framework is developed to guide the heat extraction section design of energy tunnel in the severe cold region based on numerical simulation and simulated annealing algorithm. With this framework， the location of the heat extraction section can be automatically selected based on the in-site geological and meteorological conditions. Then， sensitivity analysis in terms of different design parameters of the heat extraction section is conducted to investigate their influence on heat transfer efficiency and heat extraction section design. The results show that smaller pipe spacing， lower inlet water temperature， and higher flow rate of circulating medium in pipes will benefit the higher heat exchange efficiency， shorter design length of heat extraction section， and the resultant lower cost. In addition， the deviation of the starting position within several meters will not affect the total heat extraction capability for a certain length of the heat extraction section. The proposed methodology will provide important support for the energy tunnel design in engineering practice.

Study on the Deformation Mechanism of a Soft Rock Tunnel

The large deformation of soft rock tunnel is one of the key problems to be overcome in the tunnel construction stage. In the present study, the deformation mechanism of a representative tunnel and some related countermeasures are investigated using field tests and engineering geological analysis. Owing to the scarce performances of methods based on other criteria such as small pipe spacing, anchor bolt length and steel frame spacing, a new support scheme is implemented and optimized. Results show that shear failure and bedding sliding are produced under high horizontal stress conditions. The low strength of the surrounding rock results in the uneven convergence of both sides of the tunnel. With the aforementioned new support scheme, however, most of such problems can be mitigated leading to good stability properties and ensuing economic advantages.

Performance evaluation of a dynamic wall integrated with active insulation and thermal energy storage systems

Thermal energy storage systems in buildings can store cooling/heating energy during non-peak load hours or when renewable energy sources are available for later use when demanded. Using the building envelope as a thermal battery can help to shave the peak load, reduce the burden in electric grids, and enhance the occupant's thermal comfort. Sensible energy storage on wall systems such as thermally activated building systems can provide an active thermal storage strategy. However, most of the stored energy is used through passive means directed by the thermal lag, which can impede the on-demand release of the stored energy. Integrating active insulation systems with building thermal storage systems can increase the flexibility of charging and discharging time and duration. In this study, a wall system equipped with an active insulation system and thermally activated storage system was designed, and its performance on active cooling energy contribution was studied. The performances of energy storage (charging), release (discharging) of the thermal energy storage energy, and the active insulation system were studied separately and together as an integrated system. Results showed that the thermal properties of the thermal energy storage core material and the pipe spacing of both embedded pipes in the thermal energy storage and hydronic pipes used in the active insulation system affected the wall performance the most out of all the tested wall system parameters. During discharging, the heat flux into the wall was as high as 81.92 W/m2. The active insulation system's dynamic R-value varied between less than 1ft2•°F•h/BTU (0.18 m2•K/W) to 98% of the equally thick foam insulation's R-value.

Optimization of a Radiant System for Hydrothermal Performance Using Taguchi and Utility Concept

Abstract Radiant floor panel technology is gaining popularity as an alternative system over the conventional heating, ventilation, and air conditioning system to maintain the room temperature for the desired comfort. This research paper aims to optimize the hydrothermal performance of a radiant system by implementing the Taguchi technique and utility concept for cooling and heating mode of operation. Five geometrical and thermal parameters such as pipe diameter, pipe spacing, concrete layer thickness, wall temperature, and inlet and outlet water temperature difference with three levels are chosen as controlling factors to perform optimization. Considering five parameters and three levels, a total of 27 trial runs (L27) are constructed and computed by mathematical calculation. Two different sets of optimum parameters are obtained for maximizing heat flux and minimizing pressure drop. Furthermore, the utility concept is employed to get a single set of parameters to achieve maximum utilization of the radiant system. Taguchi analysis revealed that thermal parameters like temperature difference and wall temperature are the most influential parameters to reach maximum heat transfer and minimum pressure drop followed by geometrical parameters like pipe spacing and diameter for heat flux and pressure drop, respectively. Providing more weightage to heat flux than pressure drop, utility analysis showed 32% and 42% augmentation in heat flux for cooling and heating mode, respectively, at the cost of an increase in pressure drop.

Development and application of a new package for MODFLOW-LGR-MT3D for simulating regional groundwater and salt dynamics with subsurface drainage systems

Subsurface drainage systems have been widely used to help manage soil salinization worldwide. However, designing a subsurface drainage system requires predictions of regional groundwater and salt dynamics. While these dynamics can be obtained using MODFLOW’s drain package (DRN), this package requires that the drain conductance be specified, which is difficult to determine for subsurface drainage systems with different layout parameters, including the pipe spacing, depth and radius. In this study, a new subsurface drainage (SDR) package based on the Hooghoudt equation was developed within the MODFLOW-LGR-MT3D framework to simulate the effects of subsurface drainage pipes on groundwater flow and salt dynamics. The accuracy and applicability of SDR were tested by a synthetic case, a published indoor experiment and two field experiments. Comparison with indoor experimental data shows that the RRMSE of cumulative drainage volume was 5.08% and the RRMSE of groundwater table depth was 3.69%. The simulation results of outdoor experiment show that the RRMSE of drainage volumes of a single pipe ranged from 3.14% to 4.69%, and the relative errors of cumulative drainage volumes were below 6% and the relative errors of drainage discharge were 3.1–16.3%. The results demonstrate that SDR can accurately simulate leaching water and solute transport under transient flow conditions. The model was then applied to the Yonglian irrigation area of Inner Mongolia, China, for subsurface drainage system design, and 3 different layout schemes of subsurface drainage systems were presented. The total salt discharge increased by 38–54% after the application of the subsurface drainage system, 36–45% of which was discharged by subsurface drainage pipes. This study provides a pilot example for regional subsurface drainage system design.

Group Effect of Pipe Jacking in Silty Sand

Jacking force is one of the most important parameters in pipe jacking engineering, and also the key in pipe jacking design. A lot of research has been done on the prediction of jacking force of a single pipe. However, the research on jacking force of a row of steel pipes is relatively rare. A case of pipe jacking project is studied in this paper. In construction the test pipes were successfully jacked into the designed position, but the subsequent pipes were stuck because the jacking machine could not provide enough jacking force. Based on this phenomenon, the influence on the jacking force from the pipe spacing and the number of pipes have been jacked around the pipe being jacked is studied by field measurement and numerical simulation. The mechanism of the steel pipes stuck after the test pipes is analysed in detail. The results show that the jacking force decreases nonlinearly with the increase of the pipe spacing, and the influence range of pipe jacking is three times the pipe diameter; the jacking force increases with the increment of the number of pipes that have been jacked, but the increasing trend gradually slows down. Based on the above results, the pipe group effect of jacking force is proposed which is verified by the measured data. The results indicate that the amplification and superposition effect of the jacking force should be considered in the design stage to avoid pipes stuck in the jacking process.

A novel refrigerant-direct radiant cooling system: Numerical simulation-based evaluation

• A novel refrigerant-direct radiant cooling system is proposed. • The temperature distribution of the RDRC terminal surface is homogenous. • The mathematical and economic models of this terminal are established. • The sequencing of impact factors and the optimal structure are obtained. Split air-conditioners have deficiency in thermal comfort due to draught sensation and fan noise. The existing radiant cooling systems adopt chilled water as circulating medium, resulting in low energy efficiency because of the requirement of secondary heat exchange. To address these problems, a novel refrigerant-direct radiant cooling (RDRC) system is proposed. Experiments are conducted in a climate chamber to evaluate the thermal performance of this system. Results show that the RDRC terminal surface temperature is distributed homogenously and this system has excellent stability. The mathematical and economic models of this terminal are established and the mathematical model is validated with experimental data. The effects of different structural parameters on thermal and economic performances of the RDRC system are investigated, and then this terminal is optimized by orthogonal design method. The cooling capacity for per exterior area is considered as objective function and the initial cost less than 121.1 $ is taken as constraint condition. Results indicate that the fin height of 40.0 mm, the copper pipe diameter of 6.0 mm, the copper pipe spacing of 40.0 mm and the aspect ratio of 0.88 are recommended.

Multi-objective optimization of the refrigerant-direct convective-radiant cooling system considering the thermal and economic performances

The refrigerant-direct convective-radiant cooling (RCC) system is attracting widespread concern due to its advantages of good thermal comfort, high energy efficiency and simple structure. However, researches on thermal and economic optimization of this system are rare. In this study, a novel heuristic approach is proposed to optimize the aluminum column-wing type refrigerant-direct convective-radiant cooling (ACT-RCC) system, which adopts artificial neural network (ANN) integrated with multi-objective genetic algorithm (MOGA). The numerical and economic models of the ACT-RCC terminal are developed and the numerical model is validated by the experimental data. Besides, the ANN model is adopted to accelerate the prediction of the thermal and economic performances of this system. Results show that the training values of the ANN model are fitted well with simulated results and the ANN model can greatly improve the runtime in comparison with original numerical and economic models. Based on the heuristic optimization approach, the optimal structure of the ACT-RCC terminal is the copper pipe diameter with 8.7 mm, the copper pipe spacing with 25.5 mm and the rib height with 30.3 mm. Compared with the original structure, the cooling capacity of the improved ACT-RCC system is enhanced by 16.0% and the initial cost is reduced by 10.0%. The appearance area equals to the direct product of the length and width, and results show that the appearance area of the improved ACT-RCC terminal is decreased from 1.04 m2 to 0.78 m2. Therefore, the proposed heuristic approach provides guidance for improving the thermal and economic performances of the RCC systems.

Effect Of Design Parameters of Serpentine-Shaped Flat Plate Solar Collector Under Malaysia Climate Conditions

Solar thermal energy plays a vital role in the industrial sector, especially for water heating applications. Further research to improve the efficiency of flat plate solar collectors by focusing on collector design modification is imperative. This research aimed to carry out an experimental investigation on comparative designs and fabrication approaches that deal with the analysis of flat plate solar collector thermal performance, thermal efficiency, the effect of various mass flow rates, and pressure drop analyses. In this paper, a different design modification of pipe collector with serpentine-shaped was established with different tube diameters (3/4-inch and 3/8-inch), and different pipe spacing (18.5 cm and 27.0 cm). Under the same heat radiation intensity and constant mass flow rate, a pipe collector with a tube diameter of 3/4-inch achieved 3.5% and 9.4% higher thermal performance and collector efficiency respectively compared to the tube diameter of 3/8-inch. Furthermore, the pipe collector with pipe spacing of 18.5 cm exhibited 4.3% and 12.6% higher thermal performance and collector efficiency respectively compared to pipe spacing of 27 cm. The relationship between collector efficiency and temperature difference was also investigated. Moreover, the effect of different mass flow rates was studied upon and it was found that a flow rate of 0.03 kg/s exhibited optimum thermal performance for the pipe collector. Additionally, a pressure drop was observed with the increase in flow rate, while decreases when the fluid temperature increases.

Heat transfer efficiency of energy tunnel influenced by inlet temperature, flow rate and pipe spacing

Energy geostructures can be used in urban Heating Ventilating and Air Conditioning (HVAC) system to save energy and reduce emissions. Energy tunnel can extract shallow geothermal energy economically and efficiently without pollution. Based on the utility tunnel in Nanjing, China, heat transfer pipes are buried in the utility tunnel on the non-constant temperature zone to be an energy tunnel. Field test and numerical simulation on the heat exchange efficiency of energy tunnel are carried out. The inlet/outlet temperature and thermal induced stresses are measured and discussed. The results show that the unit heat area transfer efficiency of the energy tunnel is about 63W/m2, the heat transfer efficiency is positively correlated with the inlet temperature and flow rate, and negatively correlated with the pipe spacing.

Feasibility analysis of low thermal conductivity asphalt concrete bridge deck deicing by using geothermal energy

Deicing of bridge deck is studied based on ground source heat. In this paper, a COMSOL finite element numerical model is established, it considers the generalized heat flux, convective radiation heat flux and snow melting heat rate as the cold source. The designed pipe spacing of the model is 20cm, 25cm and 30cm respectively. The influence of low thermal conductivity of asphalt bridge deck on deicing effect is considered in the model, and the temperature and stress of bridge deck are simulated, and the relevant data results are obtained. The actual heat flux required for deicing is calculated, and it is concluded that the deicing effect increases gradually with the increase of pipe spacing, but the increase of 20cm spacing is smaller than that of 25cm spacing. 25cm spacing has good effect and is the most economical.

A simplified model to assess the thermal performance of pavement solar collectors

The assessment of thermal performance and efficiency of the Pavement Solar Collector (PSC) systems is essential in designing such systems. In this paper, a simplified simulation model is developed to predict PSC's performance at the design stage. Due to its simplicity, accuracy, and extremely quick simulation run-time, the model output can be linked with other thermal models and renewable heat sources to apply real-time changes in the PSC systems and used in the automation of a PID-controller. The output results show good compatibility between the predicted and simulated data, where the relative error values for model parametrization and validation are less than 0.21% and 0.5%. In terms of computational cost, a yearly long-term performance run time of the present model was simply 3 s (without parametrization), 300,000 times faster than a FEM model for only one month. A systematic sensitivity analysis on different design parameters shows that the efficiency index increases with an increase in pipe spacing, pipe embedment depth, and flow rate, while it decreases with an increase in the asphalt thermal conductivity in the wintertime. Also, the variation of the heat transfer coefficient UA* and correlation parameter k in different PSC configurations was established.

Deicing efficiency and snow melting on roof through heat exchange pipe

The energy pile can support the load of upper buildings and exploit the shallow geothermal energy by embedding the traditional ground-source heat pump in the pile foundation of buildings. The steel roof has a large span and poor load-bearing capacity, and it is easy to collapse in the ice and snow weather. Based on the model test and the numerical model, the differences of deicing efficiency on roof through heat exchange pipe under different heat exchange pipe materials, position of pipe layout and pipe spacing on the roof panel, etc. were analyzed in this paper, Results showed that, when the heat exchange pipes were arranged above the panel, the ice melting time was about 2 / 3 of that when heat exchange pipes were arranged under the panel; The shorter the pipe spacing and the denser the pipe arrangement, the faster the ice melting rate.

Impact on heat storage performance of concrete radiant floor with finned water supply pipes

To effectively improve the heat storage performance of concrete radiant floor, a kind of concrete radiant floor with finned water supple pipes (Finned Concrete Radiant Floor) was designed. In the present paper, the heat storage performance of the new type concrete radiant floor was discussed based on experiments and a new simplified model. Experimental results showed that the average heat storage rate of the Finned Concrete Radiant Floor for start-up stage was about 88.7 W/m2, 152.2 W/m2and 218.7 W/m2 under the condition of water supply temperature 25.0oC, 29.8oC and 34.6oC, which was about 2 times that of a non-Finned Concrete Radiant Floor. Calculation results showed that the average heat storage rate was relevant to both fin height and fin material, but irrelevant to fin thickness, and pipe spacing had a significant effect on the heat storage performance. This paper can provide a certain data basis for a better design of Finned Concrete Radiant Floor.

Comparison of long-term performance and initial cost of a horizontal ground source heat pump with an air source heat pump in hot regions

Ground source heat pumps (GSHPs) have received much attention due to their high coefficient of performance (COP). In these systems, the ground is used as a sink/source for heat pumps and the heat transfers between the ground and the heat pump is performed by the ground heat exchanger (GHE). In this study, the long-term performance and initial cost of these systems have been compared with conventional air-source systems in a hot region. To evaluate the performance of the GSHP, using fluent software, numerical modeling of a linear horizontal GHE was carried out in Bandar-Abbas. Also, the effect of various system operating parameters, i.e., length, distance, buried depth, and diameter of GHE pipes have been studied. According to results, the five-year COP and exergy efficiency of GSHP systems is 19.9% to 24.30% and 5.95% to 6.55%, respectively, more than that of the air-source system. However, 1.2 to 2.5 million Tomans is needed as the installation cost for each kW of maximum building load per year. Also, it is demonstrated that by reducing the length of the GHE, the initial cost is reduced, and the performance increases, the pipe spacing is the most important factor in the required ground surface, the depth has the most impact on the initial cost and the performance, and the pipe diameter does not affect the system performance.

Uncertainty and global sensitivity analysis on thermal performances of pipe-embedded building envelope in the heating season

Pipe-embedded building envelope, which is of particular interest to architects and engineers due to its excellent performances and invisibility characteristic, has been regarded as a potential technology for future buildings. Understanding the impacts of multiple uncertainties associated with design, construction, and operational control on its thermal performances is critical to the development of this burgeoning active insulation technology. Aiming at this goal, an in-depth uncertainty analysis (UA) and global sensitivity analysis (GSA) study was numerically conducted to investigate the influence mechanism of 12 different variables on 5 performance indicators in winter conditions. The UA results indicated that a dual-effect, i.e., better indoor thermal comfort and “zero” or even “negative” thermal load of the exterior walls, could be achieved only when relevant variables were properly selected. Due to the increase in the quantities and types of input variables, as well as the internal heat transfer process became more complicated, the importance rankings of variables obtained by two different GSA methods became different. Therefore, the treed Gaussian process method was proven to be more effective in identifying the uncertain variables. The GSA results stated that heat-source temperature, indoor set-point, charging duration, and thermal conductivity of pipe-embedded layer were the four most significant variables. For heat-source temperature and indoor set-point, there always existed an obvious mutual restriction relationship between them among all indicators except exterior surface heating loss. Meanwhile, the suggested value of the charging duration was no less than 6 h, and the optimal range of the thermal conductivity of pipe-embedded layer given by GSA was 0.5–2.75 W/m·℃. Under the blocking effect of the thermal barrier, the uncertainty of the climate zone on interior surface heating load was greatly reduced, and the climate zone was no longer a key variable affecting the cumulative subcooling duration. Besides, it was proved that the pipe spacing had a great influence on the heat accumulation inside the pipe-embedded layer, pipe location had a slight influence on interior surface heating load and exterior surface heating loss, and the pipe diameter did not influence thermal performances. From the perspective of energy density, the optimal range of the pipe spacing was 100–250 mm. Overall, this study highlighted the positive effect of the pipe-embedded system on the development of new-built and existing buildings towards zero-carbon targets, and also provided useful guidance for its further applications and investigations.

Effect of hydrophilic pipe structure of proton exchange membrane fuel cell on water removal from the gas diffusion layer surface

In a proton exchange membrane fuel cell (PEMFC), effective GDL surface water elimination is significant to water management. This paper used the volume-of-fluid method (VOF) method to carry out simulation research on transferring liquid water in the flow channel with a hydrophilic pipe. The findings indicated that compared with a straight channel, a hydrophilic pipe structure could effectively remove water from the gas diffusion surface (GDL) and reduce the surface water coverage of the GDL. With the increase in the diameter and height of the pipe structure, the GDL surface's water coverage first increased and then decreased, and it was less with the pipe structure than with the direct flow channel. The removal rate of water on the GDL surface was accelerated. The spacing of hydrophilic pipes has a significant impact on the transportation of water. As the spacing increases, the removal rate of water on the GDL surface slowed. A hydrophilic pipe structure with a diameter of 75 μm, a height of 400 μm, and spacing of 300 μm has good water removal performance on the GDL surface. This research work proposes a new internal structure design of the flow channel, which has specific implications for removing water on the GDL surface.

The influence of the thickness of an aluminium radiant sheet on the performance of the lightweight floor heating

The aim of this work is to determine the optimal thickness of aluminium radiant sheet in the lightweight floor heating, i.e. the smallest thickness of the aluminium, ensuring high efficiency and thermal comfort. The optimal operational and construction parameters are determined regards to the aluminium thickness. Finding the optimal aluminium thickness is important for economic and ecological reasons: less aluminium thickness, less aluminium consumption and less cost of construction. Numerical calculations were performed with ANSYS Steady-State Thermal Solver (Workbench 19.2) for floor heating with a dry screed, wood-like board and pipes embedded in the layer of tile adhesive. The influence of aluminium thickness changes in the range of 0.1–0.5 mm was analysed for variable water temperature, pipe spacing and constructions. The optimal aluminium radiant sheet thickness is 0.3 mm, 0.1 mm is not recommended. The optimal water temperature is 25–35 °C, 45 °C is not recommended. Constructions with a dry screed 25 mm thick should not be used. Constructions with pipes in tile adhesive should be used at a water temperature of 25–30 °C and an aluminium thickness of 0.3–0.5 mm. Constructions with wood-like board should be used at a water temperature of 25–35 °C and an aluminium of 0.3–0.4 mm. Results enable a conscious choice of such constructions and operational parameters of lightweight floor heating that ensure high efficiency, thermal comfort and low investment costs. The work includes the original specification of the lightweight floor heating efficiency depending on the radiant sheet thickness and specifies recommended radiant sheet thicknesses.

Reduction of Drag Resistance by Pressure Drop in Pipeline with 3-Dimensional Design Optimization

The searching for the most optimal pipeline route is a crucial problem in the maritime world because it consumes total designing time by 50%. Also, with different types of ships increases the design complexity. The usual design process has not considered the aspect of distance, cost, obstacles, drag, and pressure reduction in the pipeline very accurately. However, along with algorithms' development to optimize pipeline design, the time can be cut by 40%. This research uses computer-generated Dijkstra's algorithm to optimize pipeline design by considering several constraints in pipe spacing, the number of bends, crossings, pipeline stacks to improve drag reduction, and reducing pressure. This research was conducted to see the effect of pipe mapping on pressure drop, which is too influenced by human decisions that cannot consider bending, crossing, pipe piling, and bending of pipes that are too many to be considered by humans. Helping humans choose pipe mappings with various considerations that can affect pressure drop is advantageous because mapping helps to cut production times and produce a more efficient flow. In this study, this research aims to produce pressure drop by mapping pipes using the Djikstra algorithm by considering bending, crossing, and stacking, which are presented based on the 2-dimensional and 3-dimensional mapping. The data generated in the way of a comparison between drag reduction and pressure drop in pipe design optimization utilizing Dijkstra's and without using the Dijkstra's algorithm with 3-dimensional projections. The result shows the improvement of the drag reduction rate by 8% by decreasing pressure drop by 13%.