Pipe Spacing Research Articles

Study of critical free-area ratio during the snow-melting process on pavement using low-temperature heating fluids

Critical free-area ratio (CFR) is an interesting phenomenon during the snow-melting process on pavement using low-temperature heating fluids such as geothermal tail water and industrial waste water. This paper is performed to further investigate the mechanism of CFR and its influencing factors. A simplified theoretical model is presented to describe the heat and mass transfer process on pavement. Especially the variation of thermal properties and the capillary effect of snow layer are considered. Numerical computation shows that the above theoretical model is effective for the prediction of CFR during the snow-melting process. Furthermore, the mechanism of CFR is clarified in detail. CFR is independent of the layout of hydronic pipes, the fluid temperature, the idling time, and weather conditions. It is both the non-uniform temperature distribution and complicated porous structure of snow layer that lead to the occurrence of CFR. Besides, the influences of operation parameters including the fluid temperature, the idling time, the pipe spacing and buried depths on snow melting are analyzed, which are helpful for the next optimal design of snow-melting system.

Mooring forces in horizontal interlaced moored floating pipe breakwater with three layers

The paper presents the results from model scale experiments on the study of forces in the moorings of horizontally interlaced, multi-layered, moored floating pipe breakwaters. The studies are conducted with breakwater models having three layers subjected to waves of steepness H i/ L ( H i is the incident wave height and L the wavelength) varying from 0.0066 to 0.0464, relative width W/ L ( W is the width of breakwater) varying from 0.4 to 2.65, and relative spacing S/ D ( S is the spacing of pipes and D the diameter of pipe) of 2 and 4. The variation of measured normalized mooring forces on the seaward side and leeward side are analyzed by plotting non-dimensional graphs depicting f/ γW 2 ( f is the force in the mooring per unit length of the breakwater, γ the weight density of sea water) as a function W/ L for various values of H i/ d ( d is the depth of water). It is found that the force in the seaward side mooring increases with an increase in H i/ L for d/ W values ranging between 0.081 and 0.276. The experimental results also reveal that the forces in the seaward side mooring decrease as W/ L increases, up to a value of W/ L=1.3, and then increases with an increase in W/ L. It is also observed that the wave attenuation characteristics of breakwater model with relative spacing of 4 is better than that of the model with relative spacing of 2. The maximum force in the seaward side mooring for model with S/ D=4 is lower compared to that for the breakwater model with S/ D=2. A multivariate non-linear regression analysis has been carried out for the data on mooring forces for the seaside and leeside.

Effect of drainage systems on the water release rate in the process of drying wheat and corn grain

AbstractThe basic aim of this research is to determine the influence of various types of pipe drainage upon the water release rate in the process of drying wheat and corn kernels grown on a hydromorphic type of soil. The research was conducted during a period of three years (1998–2001). Seven different types of drainage systems were built on pseudogleyic‐gleyic soil (various spacings of drainage pipes with gravel used or not used in the drainage trench above the pipes). Based on soil moisture measurement data (to a soil depth of 60 cm), acquired by means of the gravitational method in the period of vegetation, it is clear that the most favourable humidity occurred on soil with spacing of drainage pipes being 25 m, gravel used, with both cultures. The yield gained also shows that this drainage type is the most favourable. The process of drying the kernels to the storage humidity value took the shortest time with this type of drainage.Results of this research contribute to energy savings in the process of drying wheat and corn crops. Additionally, the results can be used for selecting systems of drainage in dealing with excess water on hydromorphic soil types. Copyright © 2007 John Wiley & Sons, Ltd.

Numerical Modeling of Greenhouse Floor Heating

A numerical simulation model of a greenhouse floor heating system was developed and validated using data collected in a research greenhouse located at Cook College, Rutgers University, New Brunswick, New Jersey. The model was then modified and used to evaluate two different heat pipe diameters and spacings that are typical in the greenhouse industry today: 13 mm (0.5 in.) diameter pipe placed on 22.9 cm (9 in.) centers, and 19 mm (0.75 in.) diameter pipe placed on 30.5 cm (12 in.) centers. Two heat pipe elevations within the solid concrete floor system were also simulated, and the effects of the pipe's vertical position, diameter, and spacing on surface heat flux, surface temperature, and surface temperature uniformity were evaluated. The simulation results showed that the smaller diameter pipe placed closer together and at a lower elevation provided the best temperature uniformity without compromising other performance criteria. The model was then further modified to simulate flats with growing media placed on the floor surface. Model simulations were conducted for six different supply water temperatures ranging from 32.2°C (90°F) to 60°C (140°F), while maintaining a target ambient greenhouse air temperature of 15.6°C (60°F). The simulation outputs showed that using the smaller diameter pipe placed closer together resulted in a higher surface heat flux, a higher growing media temperature, and greater temperature uniformity within the growing media, for each supply water temperature simulated.

COMPUTATIONAL MODELING ANALYSIS OF RADAR SCATTERING BY CLOTHING COVERED ARRAYS OF METALLIC BODY-WORN EXPLOSIVE DEVICES

In this study, we address the problem of detecting body- worn improvised explosive devices (IEDs) from a safe distance using radar. We have used a finite difference frequency domain (FDFD) model to simulate the radar signature of a typical scenario for body- worn IEDs, and have analyzed wrinkled clothing as a possible source of clutter, as well as the possibility for uniform versus nonuniform array spacing of explosive-filled metal pipes. Our analysis shows distinct characteristics of the pipe backscattered farfield signal for uniformly spaced pipes, with no significant clutter added when the metallic pipe is covered with wrinkled clothing.

Minimum ground pre-freezing time before excavation of Guangzhou subway tunnel

Abstract Artificial Ground Freezing (AGF) has been in use for more than a century. However, there are few published papers concerning about thermal and mechanical calculation and analysis of AGF. Especially, in the practical project, when other factors such as freeze temperature, quantity and spacing of freeze pipes, are same, the ground pre-freezing time affects the project cost as well as the strength of frozen wall. So, in this paper, a subway double-line tunnel in Guangzhou constructed by AGF is taken as an example. At first, a numerical model for thermal and mechanical analysis is proposed. Then, based on this model, the surface settlements are calculated and compared by using finite element method (FEM) when the ground pre-freezing time are 60, 50, 40 and 30 days, respectively. According to the criteria of code that the maximum surface settlement is less than 30 mm, a minimum pre-freezing time could be selected. At last, under the condition of this minimum pre-freezing time, the temperature fields, stress fields and displacement fields at every excavation step are calculated and analyzed. The safety of frozen earth wall is also evaluated by applying long-term strength equation of frozen soil.

Leachate injection using vertical wells in bioreactor landfills

Leachate recirculation or liquid injection in municipal solid waste landfills offers economic and environmental benefits. The key objective of this study was to carry out numerical evaluation of key design variables for leachate recirculation system consisting of vertical wells. In order to achieve the objective, numerical modeling was carried out using the finite-element model HYDRUS-2D. The following design parameters were evaluated by simulating liquid pressure head on the liner and the wetted width of the waste under steady-state flow conditions: (1) hydraulic conductivities of the waste and vertical well backfill; (2) liquid injection rate and dosing frequency; (3) well diameter, screen height and screen depth; and (4) hydraulic conductivity of the leachate collection system, slope of the leachate collection system and spacing of the leachate collection pipes. The key findings of this study are as follows. The well diameter, hydraulic conductivity of the well drainage pack, and screen height and screen depth of the well have very little effect on the wetted width for a given liquid flux. The wetted width and the injection pressure for a given liquid flux decrease with the increase in the hydraulic conductivity of the waste. The pressure head on the liner increases with the decrease in the vertical distance between the bottom of the well screen and the top of leachate collection system. The liquid injection flux increases with the decrease in hydraulic conductivity of the leachate collection system. Unlike sand ( k ∼ 10 −4 m/s), pea gravel ( k ∼ 0.01 m/s) resulted in less than 0.3 m pressure head on the liner for all simulations carried out in this study.

Numerical Modeling of Gas Tubular Distributors in Bubbling Fluidized-Bed Incinerators

The use of a suitable gas distributor is essential for satisfactory performance of gas−solid fluidized-bed incinerators that are burning solid wastes. In the present study, the flow behavior of bubble and particles in bubbling fluidized beds with tubular distributor are performed using a two-fluid model. The computed instantaneous and time-averaged particle distributions, and the velocities of gas and particles, were analyzed. The effects of the jetting gas velocity and pipe spacing of tubular distributor on the quality of fluidization were investigated. The optimum pipe spacing is proposed to be in the range of 1.5−1.75, based on numerical results.

CFD ANALYSIS FOR SEA-CHEST DESIGN

ABSTRACT This paper presents a series of numerical simulations intended to determine whether the use of CFX, a commercially available computational fluid dynamics software may provide a viable alternative to the use of physical models for predicting the occurrence of vortices and swirl in pump intakes. Single pump sump experimental data are used for validating the CFX analysis. Experimental setup for the Sea-Chest model of scale 1:4 was fabricated and experiments are conducted for different parameters like baffle positions, suction pipe spacing and suction depths. Velocity measurements and dye injections were used to characterize the flow in the physical model. In experimental runs presence of the vortices were observed. Results from experimental investigation and from CFX simulations are compared to obtain optimal parameters. With these optimal parameters CFX analysis is made for the SEA-Chest prototype size.

Thermal Management of Outdoor Electronic Cabinets Using Soil Heat Exchangers

Telephone companies utilize densely packed electronics in outdoor metal cabinets for routing calls between customers. As a result of the increasing power densities of electronics, companies are looking for innovative methods of providing system level cooling such as using soil heat exchangers. Numerical simulation using a system of lumped thermal capacitances coupled to a soil finite element model is used to predict the transient thermal behavior of a cabinet. The cabinet model has been verified in previous studies by comparison with experimental measurements on a commercial telecommunications cabinet and is shown to predict temperature trends well. The effects of transient heat load, soil properties, and heat exchanger geometry are examined. Results reveal soil heat exchangers have the capability to provide the necessary cooling for relatively low power outdoor cabinets. However, the temperature of the soil surrounding the heat exchanger may increase daily if the number and spacing of pipes is not adequate to handle the desired heat dissipation load.

613 The Methodological Study of Under-soil Heating System (USHS) for Warm-season Grass

Recently, full-green turf on sports fields in the winter is highly desirable. The negative factor for warm-season grass pitch is its winter dormancy. Winter overseeding (WOS) is one successful method to make turf seem green. However, maintenance cost for WOS turf is relatively expensive and brings some difficulties. Undersoil heating (USH) has been used for cool-season grass pitch or warm-season grass pitch to make turf green in winter. Our objectives were 1) to confirm USH effectiveness for warm-season grass, 2) to make the specified system itself, and 3) to estimate the approximate heat demand. The results indicate that USH can make warm-season grass green and maintain much higher turf quality even in severe winter conditions. Weed invasion, pests, and diseases levels are quite low during the test period. The characteristics needed to create the system include heating pipe spacing and depth, initial media temperature, and required soil temperature. In addition, USH needs a plastic cover for insulation that is light and that air and water can penetrate. Compared with WOS, USH can reduce maintenance fees and procedures, such as preparation for WOS in a fall and transition into spring. Thus, UHS can prolong total playing period. Moreover, it is easy to maintain the higher turf quality and lower maintenance cost than WOS. In the future, we should concentrate on creating more concrete maintenance program for this method.

Energy from a two-pipe, earth-to-air heat exchanger

Solar energy accumulated in the soil may be utilized with an air-to-earth heat exchanger (ATEHE) which has two pipes buried in the soil, one made of PVC and one of steel. During the winter, air is heated; during the summer, it is cooled and then used in an air-conditioning device. To obtain the mathematical model of the ATEHE, we divided the soil and pipes into elementary volumes, used steady-state energy equations, and applied a time-marching method. We determined how the season, soil thermal conductivity and pipe spacing influence energy transfer from the soil to the ATEHE and also the steel-pipe contribution to this energy transfer.

Performance Prediction of a Sub-Slab Heat Exchanger for Geothermal Heat Pumps

A large portion of the installation cost of a ground-coupled heat pump system is for the excavation necessary for ground coil placement. One possible method of reducing this cost is to place the ground coils beneath the slab floor of the building. This configuration of ground coil placement has not been specifically addressed in previous research. Freezing of the soil must be avoided in such a system. To simulate the temperature response of the surrounding soil to heat pump operation, a computer model was developed which incorporates line source theory in the form of a system of rings. The fluid temperature change along the length of the coil was used to determine the distribution of the ground load throughout the ring system. The model includes an adiabatic upper boundary, seasonal soil temperature variation, and thermal interference throughout the system. Using these results, the minimum soil temperature over a season was predicted. Based on these results, design recommendations for ground coil installation are provided based on available area, soil type, heat extraction rate, depth of coil beneath the slab floor, and depth of slab floor below grade. These include recommendations for pipe spacing, flow direction, and a method to determine whether this type of system is feasible for installation in a particular location.

The Methodological Study of Under-soil Heating System (USHS) for Warm-season Grass

Recently, full-green turf on the sports fields in a winter period is highly required. The negative factor for warm-season grass pitch is its winter dormancy. Winter overseeding (WOS) is one of the successful methods to make them seem green. However, maintenance cost for winter overseeded turf is relatively expensive, and WOS itself involves some difficulties. On the other hand, under-soil heating (USHS) has been used only for cool-season grass pitch, but for warm-season grass pitch for the purpose to make them full green in a winter term. The objectives of this study are: 1) to confirm USHS's effectiveness for warm-season grass, 2) to make the specified system itself, and 3) to estimate the approximate heat demand. The results indicate that USHS can make warm-season grass green and maintain much higher turf quality, even in a severe winter period. The parameters needed to create the system are obtained. Those includes: heating pipe's spacing and depth, initial media temperature, and required soil temperature. In addition, USHS needs plastic cover for insulation, which light, air and water can pass through. Compared with WOS, this method can reduce maintenance fee and procedures such as preparation for WOS in a fall and transition in a spring. Thus, it can prolong total playing period. Moreover, it is easy to maintain the turf quality higher and maintenance cost can be less than WOS. The future subjects are to assess weed invasion, pests and diseases levels induced by USHS or by excess humidity, and to create a special maintenance program for this method.

Experimental and theoretical studies of space cooling using ceiling-embedded piping

Abstract Space cooling is considered, in which the heat produced within or inserted into occupied spaces is transferred to a cold fluid flowing through piping embedded in the ceiling slab. Theoretical and experimental studies are conducted for the above transient thermal problem. The theoretical investigation is based on numerical and analytical solutions, while for the measurements an experimental set-up of physical size has been built up. A comparison of measurements and predictions shows that the theoretical procedures are reliable. A systematic parametric study is conducted and the ceiling slab cooling capacity (W/m 2 ), which is found to be the most important quantity for practical applications, is expressed as a function of the embedded pipe spacing and depth, and the temperatures of the inflow water and the indoor environment.

5542968 Enthalphy wheel

Space cooling is considered, in which the heat produced within or inserted into occupied spaces is transferred to a cold fluid flowing through piping embedded in the ceiling slab. Theoretical and experimental studies are conducted for the above transient thermal problem. The theoretical investigation is based on numerical and analytical solutions, while for the measurements an experimental set-up of physical size has been built up. A comparison of measurements and predictions shows that the theoretical procedures are reliable. A systematic parametric study is conducted and the ceiling slab cooling capacity (W/m2), which is found to be the most important quantity for practical applications, is expressed as a function of the embedded pipe spacing and depth, and the temperatures of the inflow water and the indoor environment.

Subsidence-sinkhole development in light of mud infiltrate structures within interstratal karst of the Coastal Plain, southeast United States

Mud infiltrate structures (MIS) are a class of clastic sedimentary structures that have formed by high-angle gravitational sedimentation in vadose cavernous limestones beneath the Miocene Hawthorn Group. Observations of MIS in caves beneath the Pelham Escarpment, southwest Georgia, suggest three main types occurring either beneath, within, or contiguous to subvertical feeder pipes in the ceiling: (1) rubbly, conical masses; (2) polished, striated, cylindrical masses; and, (3) mud-flow, -drape, and-splash forms. MIS abundance suggests gravitative deposits are a major component to the total volume of cave mud. The muds apparently do not include soil-mantle materials; rather, their sources are poorly cemented clay-rich layers within the overlying Hawthorn Group. In cases where an individual MIS volume is large in proportion to the clastic-cover thickness, but no surface depression is found, the MIS location hypothetically predicts a directly overlying site of potential cover-collapse sinkhole development. Smaller-volume and/or shallower MIS predict the location of potential cover-subsidence sinkholes. The MIS forms suggest plastic and fluid behavior of the sediments occurs during displacements. The capacity for subsurface voids to accept mobile sediments depends on several factors that influence sinkhole development: (1) void size and interconnectedness; (2) spacing and size of subvertical solution pipes which can act as MIS feeders; (3) depth beneath the sediment source of any main horizontal cave development; (4) thickness of the cover sediments; and (5) the presence and depth of any breakout domes. The Hawthorn is present over more than 50 percent of the area underlain by the Floridan Aquifer system and is the system's major upper confining unit. MIS-forming processes are likely to be widely distributed within this stratigraphic setting, promoting ground subsidence and subsurface porosity obliteration. Given the existence of feeder pipes, MIS also are expected to form within the phreatic zone.

Computer analysis, design and simulation of horizontal ground heat exchangers

This paper presents a new computerized procedure for dealing with the design of horizontal ground heat exchangers (HGHE). The computer program is based on the transient model of coupled nonlinear partial differential equations governing heat and mass flow in soils. The model is two-dimensional and delineates the operation of ground heat storage with the HGHE and such phenomena as freezing/thawing and drying/rewetting of soil moisture. Comprehensive climatological data, such as ambient temperature, solar radiation, wind velocity, rainfall, snowfall, snow characterstics, and water vapour pressure is used to simulate conditions at the ground surface over any required length of time. The package can be applied to any geographical location by changing climatic and soil data input. The designer has the possibility of selecting any of 12 types of soils from sand to clay, 12 commercial heat pumps, nine different configurations of the HGHE, 16 plastic pipes for ground coils, and 13 ground coil fluids. The program, however, does not calculate the length of the HGHE but it evaluates the thermodynamic performance of a ground heat pump system and provides comprehensive data on thermal and hydraulic conditions in ground heat storage. The length of the ground heat exchanger is obtained from a line source theory model or from site dimensions and pipe spacing. Computed results for ground heat exchanger operation correlate fairly well with experimental data. Simulation of temperature and moisture content in the ground for natural conditions (no heat extraction/deposition) showed a fair agreement with field data. The entire computer program is user-friendly, interactive, menu-driven, and written in FORTRAN 77.

Periodic steady-state heat transfer in cooling panels

A slab is considered to be exchanging heat internally with a fluid flowing through pipes embedded in the slab and externally by convection and radiation with the ambient surroundings in a periodic fashion. In practice, such cases are encountered in panel cooling of buildings, in which the heat produced within or inserted into a room is absorbed by a cold fluid flowing through pipes imbedded in the roof slab of the room. A method is developed for predicting the performance of such systems, which is based on a finite-difference solution of the transient two-dimensional heat conduction differential equation within the roof slab containing the cooling pipes. The boundary conditions on the upper surface are periodic, i.e., it is assumed that the daily cycle of the ambient temperature and the incident solar radiation are repeated on consecutive days, thus leading to a periodic steady-state solution. In the case of floor slabs, the problem becomes steady-state unless intermittent operation is to be examined. A parametric study is presented, in which the effect is examined of the most important parameters, including the pipe spacing and the cooling fluid temperature.

Simulation studies on pipe spacings for a collector and tank sizes for a solar water heater

The work reported in this paper was embarked upon with the objective of obtaining information to guide solar thermal systems designers, particularly in water heating, where the number of collector pipes as well as the tank sizes are important parameters. The approach adopted is the employment of a mathematical model of the system whose solution was validated by way of comparison with experimental data. The simulations provided very encouraging results which enabled the deduction of optimum pipe spacing and tank size conditions to be made.