Twin Pipe Research Articles

A Similarity Model of Specific Heat Loss Determined by Dimensional Analysis

This article describes an innovative method for the determination of heat flow (specific heat loss; linear heat flow density) from a one-metre length of a twin pipe directly-buried heat network. Such heat losses are currently described by applying analytical procedures based on the heat transfer theory. It is rather complicated to accurately express the heat loss using such procedures, due to the necessity to determine the individual values of thermal resistance. A simpler method to express heat loss is the balance method, as it requires measuring a temperature gradient Δt between the starting point of the heat network and the end point of the heat collection. A suitable measuring device must provide high-accuracy measurements of the temperature. In the case of very well-insulated distribution pipelines and short pipes, the temperature measurements must be accurate to the hundredths of a degree Celsius. It is impossible to install such devices as fixed equipment on every heat distribution network, due to such networks measuring many kilometres and the cost of the appropriate measuring technology. For the aforesaid reasons, the authors created a mathematical model for specific heat losses based on dimensional analysis. This method facilitates the identification of dimensionless criteria based on the relevant dimensional quantities. Functional correlations between the identified criteria may be identified on the basis of the results of physical or numerical experiments. In this study, a database of the results obtained from physical experiments conducted on two heat networks was used. The output of the similarity model was a function describing the heat flow from a one-meter pipe length that was applicable to various alternatives in relation to the geometrical, physical and boundary conditions. The standard deviation of a difference in the heat losses identified by applying the balance method and using the proposed criterial equation for a twin pipe directly-buried pre-insulated heat network was 0.515 W·m−1.

Mathematical modelling and model validation of the heat losses in district heating networks

Today the most popular system of district heating systems is based on pre-insulated pipes arranged in parallel or twin-pipe configuration. One of the greatest difficulties with heat distribution through pipelines is thermal loss from the distribution. The most efficient solution to that problem is optimising the insulation wall thickness layer according to the pipe diameter. Heat losses should be minimised at a relatively low investment cost to find the most suitable insulation thickness economically. Numerous studies focus on analytical (1D model) calculations and numerical simulations. However, there is a research gap related to laboratory devices that allow measuring the operation parameters (fluid flow, the temperature of the fluid in the supply pipe and the return pipe). This paper presents an analysis of the heat losses from pre-insulated pipes and twin pipes in the heating system network. This study compares the heat losses in the ground calculated by analytical solution (1D model) with the measurements on the dedicated experimental setup. The calculations have been made for several heating network pipe variants: twin pipes: DN40, DN50, DN65, and their counterparts in a single parallel pre-insulated system. The insulation thickness used in all cases is 30.85 mm for DN40 and 32.00 mm for DN50 and DN65. The insulation is made of rigid polyurethane foam that meets the requirements of the PN-EN 253 standard. During the investigation, the thermal conductivity of insulation material is examined. The obtained thermal conductivity results are used in the calculations. The results from laboratory devices and analytical models have been compared, demonstrating good agreement – with a low error level in the range of approximately 8%, depending on the type of district heating pipe. The validated mathematical model of the heating network is then used to calculate the heat losses in a heating network connecting an underground storage tank with a ground source heat pump. The economic analysis shows that after 5 y, a return on investment is expected when comparing twin-pipe systems and single-pipe pre-insulated heating networks.

Thermal performance analysis of a double pipe heat exchanger using biosynthesised silicon carbide and carbon nanotubes

ABSTRACT A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers.

FLUID FLOW ANALYSIS OF CONCENTRIC HEAT EXCHANGER WITH DIFFERENT NANO FLUIDS AND MASS FLOW RATES

In this article, the overall performance of water and other nano fluids mixed with base fluid water in a twin pipe warmth exchanger is investigated. At quantity fractions of 0.35 percentage, the nano fluids are Silicon Oxide and silver nano fluid. The traits of nano fluids are decided the usage of theoretical calculations, which can be then utilised as inputs for analysis. CATIA parametric software program is used to create a 3D model of the dual pipe heat exchanger (plain and coil insert tube). CFD research of a dual pipe warmth exchanger with water, silicon oxide, and silver nano particle at diverse mass float fees of zero.32, zero. Fifty two, 0.72,zero.Ninety two, and 1.12 kg/sec is performed. Theoretical calculations on the twin pipe warmness exchanger had been additionally finished.

Effects of spoiler and piggyback on local scour under single and twin submerged pipes

A series of laboratory experiments was carried out to investigate the effects of spoiler and piggyback on the flow field and local scour formation under single and twin submerged pipes. The shape and orientation of spoiler and piggyback were tested in single and twin pipes with different distances from each other. Three piggyback shapes of rectangular, triangular, and circular were designed and the local scour profiles were measured for five orientation angles of θ = 90, 135, 180, 225, and 270°. Flow visualization was employed to study the effects of spoiler and piggyback on the rear vortex field. The velocity field was measured with an Acoustic Doppler Velocimeter (ADV) probe and the magnitudes of Turbulent Kinetic Energy (TKE) around pipelines were extracted from the time series of velocity data. Quadrant analysis was performed based on velocity data to study the effect of spoilers on turbulent momentum transfer between twin pipes. The energy and momentum coefficients were extracted from velocity profiles indicating significant disruption of velocity field and causing additional drag in the rear pipe. A comparison of the equilibrium bed profiles indicated that the minimum and maximum peak scour depths occurred when a rectangular spoiler with θ = 180° and a circular piggyback with θ = 270° were installed, respectively. The self-burial mechanism was examined by alternating the positions of piggybacks and spoilers in twin pipes. The downstream pipe was buried when either spoiler or piggyback is in the upstream pipe. It was found that the rate of self-burial reduced as the distance between two pipes increased.

New Dimensionless Correlations for the Evaluation of the Thermal Resistances of a District Heating Twin Pipe System

The heat losses from pre-insulated double-pipe district heating (DH) systems buried in a homogeneous soil are studied numerically. The study is conducted using the diameter of the pipes and their distance, the size of the insulation, the thermal conductivity ratio between the insulation and the soil, as well as the burial depth of the double-pipe system, as controlling parameters. A computational code based on a control-volume formulation of the finite-difference method has been developed using the open-source framework OpenFOAM with the purpose to compute the heat transfer rate across adjacent solid regions with different thermophysical properties. The main scopes of the study are: (a) to investigate in what measure the geometry and the relative position of the warm and cold pipes, as well as the temperature imbalance, the burial depth and the physical properties of both the insulation and the soil, affect the heat losses; (b) to analyze the existence of an optimal configuration of the DH system by the thermal resistance enhancement viewpoint; and (c) to develop accurate correlating equations for the evaluation of the thermal resistance existing between each pipe and its surroundings, useful for practical thermal engineering applications.

Augmentation of Heat Transfer in Shell and Coil Type Heat Exchanger Using Nano Fluid

The heat transfer efficiency of most thermal devices can be enhanced by increasing it. Some process sectors, such as power plants and automobiles, require heat transfer enhancement in either heating, cooling, or evaporation on equipment such as air conditioning, radiators, freezers, and condensers. The approaches that are accessible can be divided into two categories: passive and active techniques. The goal of the study was to use passive strategies to improve heat transmission in a twin pipe heat exchanger. Water and titanium dioxide nano-fluid are examples of nanofluid.

Ground Response to Pipe-Roof Tunneling of a Large Underpass in Shanghai Soft Soil

Pipe roof method is an effective way for urban underpassing scheme. Due to the successive jacking of multiple pipes, the characteristics of ground response are distinctly different from single pipe or twin pipes. In this paper, the gradual ground loss by successive pipe-jacking and the causes of settlement are analyzed. The conclusions drawn from this paper show that: (1) The maximum incremental was right above the pipe axis which could be controlled within 1mm. (2) The shield effect of the former pipe on the latter one resulted in a 50% reduction of maximum incremental settlement. (3) The distribution of cumulative settlement curve was reflected by superimposed effect of staged ground settlements. (4) The results of settlement monitoring illustrated that the field measured settlements were basically tally with those of the simulated values, the goodness of fit was more than 85%.

Reduction of Heat Losses Using Quadruple Heating Pre-Insulated Networks: A Case Study

The paper presents an analysis of heat loss and reductions of annual emissions of air pollutants of a quadruple pre-insulated heating network by comparing this solution with the existing pre-insulated network consisting of four pre-insulated single pipes and the variant consisting of two twin pipe pre-insulated. For calculations, an existing heating network located in central Poland was adopted, where heat is transported for heating purposes of buildings and domestic hot water with circulation of domestic hot water through four separate pre-insulated underground pipes. The idea of the construction of four pre-insulated pipes presented in the paper consists in the location of four steel pipes in a common round thermal insulation, which perform the role of heat transport for heating purposes in multi-family buildings (supply and return) and two pipes transporting hot water (a pipe with domestic hot water with circulation). In Poland, heating pipes used in multi-family housing have a larger diameter compared to domestic hot water pipes, which is why standard twin pipe heating pipes have been used in the construction of four pre-insulated networks, in which the domestic hot water pipe has been added to the thermal insulation and circulation of domestic hot water. In order to determine heat losses, a simplified two-dimensional model of conductive heat transfer was developed using Fortran to create a computer program. The results of numerical simulations show that the use of twin pipes for the construction of pre-insulated quadruple networks has contributed to a significant reduction in heat loss in relation to the existing single pre-insulated network (up to 57.1%), while reducing the thermal insulation field of the cross-section of the pre-insulated pipe by 21.4%.

Thermal and economic analysis of preinsulated and twin-pipe heat network operation

This study focuses on the economic analysis of the heating network modernization by using preinsulated pipes and twin-pipes. The cost analysis is based on different type, diameter, and technological diagrams of different heating network pipe variants (from DN25to DN100) and various types of insulation. Net present value (NPV) analysis comparing a five variants of the heating network pipes (Case 0: Pipes with insulation PUR standard; Case 1: Pipes with insulation PUR plus; Case 2: Pipes with insulation PEX standard; Case 3: Twin-Pipes with insulation PUR; Case 4: Twin-Pipes with insulation PEX). The value of NPV, which is the highest (NPV = 7000 €, DN65, case 2 and NPV = 5200 €, DN50, case 4) among presented variants is the best choose to consider during the investment. Despite the higher prices of Twin Pipe system, they are more profitable due to shallow heat transfer losses. Heat losses are calculated for various heating networks, including preinsulated and twin-pipe heating networks. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined using the pipe dimensions and materials. It is found that the most cost-effective from an economic point of view is the use of TwinPipe system. These pipes are more expensive, but the heat losses that occurs during their use are much smaller compared to preinsulated pipes. Short return time of such an investment (6–7 years) with 100 m of pipe installed and positive NPV causes that this type of pipes is the best investment in the case of district heating networks. The results shown that Case 3 (PEX insulation) is more economicaly beneficial than Case 4 (PUR insulation).

Thermal performance analysis of triple pipes for district heating systems

There are a large number of proposals coming every day for the future district heating designs. One of these solutions has been the use of two different supply temperatures, i.e., a high-temperature supply for domestic hot water supply and a low-temperature supply for space heating. For this, apart from the use of two pairs of pipes that was an unreasonable solution economically, employing triple pipes is an interesting idea. Although specific designs of triple pipes are in use for specific district heating applications at some points in Europe, there is not any detailed thermal performance analysis of such pipes yet. This study, by the use of computational fluid dynamic methods, numerically investigates the thermal performance of triple pipes in various configurations. The obtained results are first thoroughly compared with the results obtained for twin pipes when working in the same operating conditions and heat loads and then are compared with those available for specific triple pipe designs used for specific district heating applications in the literature. The results show that a triple pipe for a separate supply of space heating and domestic hot water is better than twin pipes (no matter in which configuration it comes) and more efficient than the triple pipe application already proposed and investigated in the literature.

Numerical determination of temperature distribution in heating network

This paper presents the determination of the heat losses of the pre-insulated pipe and twin pipe in the heating network. The paper compares the heat losses calculated by using the analytical solution (1D model) and numerical model (2D model) based on the Finite Element Method. The developed numerical model considered undisturbed ground temperature at various depths. Therefore, it allowed to study the effect of temperature distribution at various ground depths on heat losses in heating network. Various variants of insulation are considered including standard, plus and plus-plus types for pre-insulated tubes. The remaining heat loss calculation is based merely on temperature levels and thermal resistance factors (in the ground), determined by the pipe dimensions and materials. The differences in calculated heat losses by analytical and numerical model do not exceed 10%.

Pipe Sizing for Novel Heat Distribution Technology

This paper assesses pipe sizing aspects for previously proposed, novel, low heat distribution technology with three pipes. Assessment issues include heat loss, pressure loss, and pipe sizing for different typical pipe configurations. This assessment has been provided by the analysis of a case area with single-family houses. Concerning heat loss, the proposed three-pipe solutions have the same magnitude of heat loss as conventional twin pipes, since lower return temperatures compensate for the larger heat loss area from the third pipe. Regarding pressure loss, the main restriction on the size of the third pipe is limited to the pressure loss in the third pipe. Thermostatic valves to manage the flow rate of the third pipe are advocated, since alternative small pumps have not been found to be commercially available. The pipe sizing recommendation is that the third pipe for recirculation purposes can be two to three standard pipe sizes smaller than the corresponding supply and return pipe, if no prosumer is connected in the heat distribution network.

Development of an empirical method for determination of thermal conductivity and heat loss for pre-insulated plastic bonded twin pipe systems

Pre-insulated twin pipe systems (PTPS) for heat distribution offer advantages for heat supply companies. Trench dimensions for heat supply systems of District Heating (DH) networks might be reduced using these pipe systems. This reduces costs in civil engineering. Additionally heat loss of the DH network may be reduced, that decreases operational costs of these systems. On the other hand, operational heat losses of PTPS significantly differ in many cases from theoretical heat loss of PTPS. This may inhibit the application of this technology in DH networks.Against this background, a standard measurement procedure of thermal properties of PTPS shall be developed, validated and tested at FFI. These tests shall be based on standard measurement procedures for single pipe systems described in EN ISO 8497 and modified for PTPS. Within this context, preliminary tests are done at FFI. Numerical simulations of heat loss are done at IGTH and iteratively fitted to data generated from measurements at the same time.Numerical simulations of stresses occurring due to operational temperatures for PTPS are done in a second step. Internal stresses due to temperature gradients within PTPS as well as external stresses due to interactions of PTPS with the bedding material and ground will be examined. In addition, interactions of bedding materials, operational conditions and heat losses in situ will be assessed.First results obtained are presented in this paper. Focus of this paper is on development of a standard measurement procedure for thermal properties of PTPS, as well as results of numerical calculations regarding heat loss of these systems. One goal of this project funded by the “BMWi – Federal Ministry for Economic Affairs and Energy”, is to discuss and mirror project results in order to modify existing standards, e.g. EN 15698, EN 15632 and EN 13941. Defined quality standards for PTPS, verified by standardized measurement procedures for PTPS, will increase the acceptance of PTPS in the DH sector. This supports small and medium sized enterprises (SME) using and producing PTPS.

Assessment of extinguishing efficiency of hybrid system using water mist and inert gas during class A fires

Fixed hybrid fire extinguishing system, a new technology used in fire protection all over the world in the last years, was discussed. A four-head twin pipe system supplied with water mist and inert gas (air or nitrogen) was applied. A pile of 50 pine wood boards was used as a combustible material (class A fire). It was located in the corner of the compartment while the nozzles were mounted symmetrically in the centre (volume suppression). The extinguishing processes differing in the proportion of water mist to gas were analysed. The extinguishing time was taken as the most important parameter indicating the extinguishing efficiency. The impact of water flow on extinguishing process was discussed. The clear dependence of extinguishing time on the water/gas ratio was proven. The best performance of the hybrid system at water flow 3 dm3/min and nitrogen as inert gas was observed. The results obtained during experiments can be useful in developing new international standards e.g. NFPA.

Modelling steady-state thermal behaviour of double thermal network pipes

Optimal design and operation of district heating networks require accurate, but simple models to allow fast simulation. This paper describes the analytical derivation of such a model based on existing work regarding heat loss and dynamic temperature profile calculations in literature. The most important addition from this work is the incorporation and investigation of heat transfer from supply to return side in double pipes, something which is often (over)simplified in more commonly used models.The paper presents the mathematical derivations and the assumptions made in detail for the case of steady-state heat losses in double pipes. The resulting model is carefully examined in a parameter study, from which a number of interesting conclusions can be drawn. Firstly, the heat losses are found to be nearly independent of the mass flow rate in the range of mass flow rates usually encountered in thermal network pipes. The remaining heat loss calculation is simply based on temperature levels and thermal resistance factors, determined by the pipe dimensions and materials. Furthermore, it is found that heat losses from supply to return side should be incorporated in the analysis for better accuracy of the results, even more so with the increasing popularity of twin pipes with common insulation.

Record Setting 3,300-m Distance by Horizontal Directional Drilling of a 711-mm-Diameter Pipeline Crossing the Yangtze River

AbstractThis paper describes a record setting project in the horizontal directional drilling field involving twin pipes with a diameter of 711 mm and a length of 3,300 m. The Yangtze River is the longest river in China. The Jiangdu-Rudong gas pipeline, which is part of the Chinese gas pipeline trunk network, was constructed to transport gas from the north side to the south side of the River. The width of the river surface is 3,000 m, and the length of the crossing is 3,300 m. It was recommended by engineers that twin pipes with a diameter of 711 mm be used instead of the existing pipe with a diameter of 1,016 mm. The required depth of penetration for the crossing was determined by an analysis of 43 years of historical river scour data from 1966 to 2009 combined with a calculated result using a river scour depth formula. The recommended construction scheme included arranging two drilling rigs, laying magnetic-signal submarine cable, using the intersect method, and designing a new flat-barrel combination-ty...

Assessing the Thermal Performance of District Heating Twin Pipes with Vacuum Insulation Panels

In Sweden, around 10% of the energy supplied to the district heating networks are lost through heat losses from the distribution pipes. In cylindrical geometries it is preferable to improve the insulation as close to the center as possible. This has resulted in a hybrid insulation district heating pipe concept with a combination of vacuum insulation panels at the center, held in place by polyurethane foam. In the twin pipe concept, the vacuum insulation panel cover the supply pipe. This creates a complex temperature profile over the section and measured results on single pipes might not be applicable. Therefore, there is a need for a method to evaluate the improvement of hybrid insulation twin pipes in the laboratory. This paper presents a method where two guarded hot pipe apparatuses is used, one heating rod for each pipe, to measure the heat losses from hybrid pipes and compare to a conventional polyurethane pipe. The measurements indicate an improvement in thermal performance by 12%-18% for the total losses and by 29% -39% for the supply pipe losses.

Strategic techno-economic assessment of heat network options for distributed energy systems in the UK

Distributed energy systems facilitated by heat networks are rising in the UK as a viable option to decarbonise the heating sector, particularly at a community level (up to several MW). However, in this respect there is lack of suitable modelling tools and studies to assess the techno-economic performance of heat network options in different areas at a strategic level. Therefore, this paper presents a generic and comprehensive model to perform heat network design and assessment according to specified input criteria and assess operational, capital, and overall costs of multiple alternatives. More specifically, the model developed can provide strategic information on the feasibility and performance of heat network options with different operational temperatures, load densities, network lengths, cost parameters, pipe types, dwelling connection types, etc. (which are key to address the utilisation of different local supply sources in distributed energy systems). Generic test networks were used for strategic analysis, which resemble typical topologies used for electrical networks in the UK in urban, sub-urban, semi-rural, and rural areas. Numerical case studies and sensitivity analyses were carried out to assess different options and the main drivers in different scenarios. As a general result, twin pipes emerge as the most viable alternative.

Modeling Transient Heat Transfer in Small-Size Twin Pipes for End-User Connections to Low-Energy District Heating Networks

The low-energy district heating concept has the potential of increasing the energy and exergy efficiencies of heat supply systems and of exploiting renewable energy, provided that technical solutions for its wide application can be developed and implemented. This article investigates the dynamic behavior of district heating branch pipes in low-temperature operation (supply temperature 50–55°C and return temperature 20–25°C). We looked at state-of-the-art district heating branch pipes, suitable for the connection of a typical single-family house to a substation equipped with a heat exchanger for domestic hot water preparation. Experimental measurements of the supply temperature profiles at the outlet of the pipe, that is, at the inlet to the substation, were compared with detailed simulations based on the finite-volume (FV) method. A programming code was developed to model these profiles, and this was validated against experimental measurements and compared to the results of an analytical formula and the FV simulations. The model proved accurate, since it gives results that represent well the outlet temperature profiles measured in the experiments and calculated in the FV simulations, both where there was a step change of the inlet temperature and where there was a sinusoidal inlet temperature profile. The model could be used for the development of improved substation concepts and enhanced control strategies.