Design of supporting devices for large diameter thin pipes

When an analysis is made in accordance with ASME Code Class 1 for piping by the stress indices method (NB 3650), the stresses induced locally in the piping by the supports are not taken into account. For piping whose thickness is small in relation to its diameter, which is subject to sudden temperature changes and to seismic shocks and which also operates at high temperature, it is undesirable to ignore these effects. This is particularly the case with piping carrying liquid sodium since the classic solutions do not provide a satisfactory answer to the thermomechanical problems and cannot resolve many uncertainties in the analysis. The design finally selected must meet the double requirement of permitting free radial expansion of the piping whilst enabling it to withstand considerable loads with minimal deformation. The design must also be justifiable by easily verified hypotheses.The design adopted consists of a rigid collar connected to the piping by blades which are flexible radially in relation to the pipe and rigid tangentially. These blades are attached to very short ring lugs welded on to the piping. In this way, the outside forces acting on the piping are reduced almost exclusively to circumferential forces which, combined with the circumferential shearing flux due to the adjacent sections, constitute a distribution of forces which is particularly favourable for limiting the circumferential bending moments in the pipe. The resulting deformation of the circular section is thus sufficiently small not to affect the longitudinal bending strength, and particularly the buckling strength.The most significant stresses prove to be those due to the moment on the lug; these are well known and are limited due to the small height of the lug. The thermal stresses due to the presence of the lug were calculated by the finite element method. The thermal and mechanical disturbance created by the lug has the effect of multiplying by about a factor of 2 the maximum total stresses occurring during thermal transients in the straight part; they thus remain limited and less than those developed in other straight discontinuities affecting the piping; for instance, the changes in thickness between straight parts and bends. To back up these calculations, a series of tests was performed to check that the technological requirements of manufacture did not question the load distribution hypotheses taken into account in the calculations.     

热管微槽蒸发器薄液膜蒸发的径向干点预测分析

假设热量全部通过蒸发扩展液膜区传递,联立能量守恒方程和动量守恒方程,考虑了脱离压力和粘性力的影响,建立了热管微槽蒸发器槽道侧壁面上薄液膜蒸发的径向干点位置的解析解。讨论了接触角、加热热流密度、运行温度、槽道几何对干点位置的影响。分析结果有助于更好地理解薄液膜蒸发理论和高效率热管的设计。     

A comparison of methods of calculating stress intensity factors for cracks in pipes and thin walled cylinders

This paper presents results of a study undertaken to compare stress intensity factor solutions for various crack geometries in pipes and thin walled cylinders against the equivalent flat plate K solutions. The exercise was restricted to cylinders and pipes with wall thickness to radius ratios (t/R) of 0·1.

The results of the exercise indicate that structural integrity assessments of pipes and thin walled cylinders which contain flaws should ideally incorporate representative stress intensity factor solutions. Nevertheless there are a number of crack geometries for which flat plate K solutions can provide reasonable estimates of the stress intensity factor.     

Materials for internally lining pipes

Internal lining is a well established practice for inhibiting corrosion and/or erosion within pipelines. This brief survey of protective lining materials and their properties indicates those liners which will probably be suitable for the internal thermal insulation of pipes.     

Gravitational heat pipes for discontinuous applications

Gravitational heat pipes or thermosiphons (TS) are simple and efficient heat exchangers. This paper deals with the adaptation of these exchangers to discontinuous or cyclic processes such as chemical heat pumps. Such TS must fulfil a two-mode working too: the TS working must be active/inactive according to the successive endothermal/exothermal phases of the cyclic process. Two kinds of TS blockage processes have been successfully experimented: they act either on the liquid or on the vapor phase inside the TS. A simple model demonstrates that realistic configurations of TS and reactor can easily reduce the energy and duration required by the blockage process itself on the performances of the coupling.     

Internally insulated pipes for district-cooling systems

A method is presented whereby, for any set of prescribed conditions, an optimal thickness of a thermally insulating internal lining may be determined for pipes to be used for the conveyance of chilled water. The optimum investigated in this paper corresponds with the minimum total rate off energy dissipation costs as a result of refrigeration and pumping. The overall optimal design cannot be decided at this juncture without a knowledge of such unknowns as the capital cost of internally lining the pipe.     

Exact solutions for a longitudinal steady mixed convection flow over a permeable vertical thin cylinder in a porous medium

The title problem is considered under the assumption that both the surface temperature of the cylinder and the mainstream velocity at the outer edge of the boundary layer vary linearly with the axial distance x from the leading edge. Self-similar solutions are given in exact analytic form. Their domain of existence in the plane (f_w, λ) of the suction/injection parameter f_w and the mixed convection parameter λ is determined. It is shown that in general for both the aiding (λ > 0) as well as the opposing (λ < 0) flow regimes multiple solutions bifurcating from certain branching curves of the plane (f_w, λ) occur. The particular case of the dual solutions is discussed in the paper in detail.     

Miniature loop heat pipes for electronics cooling

The paper is devoted to the development of miniature loop heat pipes (mLHPs) with a nominal capacity of 25–30 W and a heat-transfer distance up to 250 mm intended for cooling electronics components and CPU of mobile PC. It gives the results of investigating several prototypes of mLHPs incorporated into remote heat exchanger (RHE) systems in different conditions. It has been established that in the nominal range of heat loads orientation does not practically affect the mLHPs operating characteristics. Under air cooling the total thermal resistance of such a system is 1.7–4.0 °C/W and depends strongly on the cooling conditions and the radiator efficiency. In this case the mLHP’s own thermal resistance is in the limits from 0.3 to 1.2 °C/W, and the maximum capacity reaches 80–120 Bt. The obtained results make it possible to regard mLHPs as quite promising devices for RHE systems providing thermal regimes for electronics components and personal computers.     

Multilayer fabric stratification pipes for solar tanks

The thermal performance of solar heating systems is strongly influenced by the thermal stratification in the heat storage. The higher the degree of thermal stratification is, the higher the thermal performance of the solar heating systems. Thermal stratification in water storage can for instance be achieved by use of inlet stratifiers combined with low flow operation in the solar collector loop. In this paper, investigation of a number of different fabric stratification pipes is presented and compared to a non-flexible inlet stratifier. Additional, detailed investigation of the flow structure close to two fabric stratification pipes is presented for one set of operating conditions by means of the optical PIV (Particle Image Velocimetry) method.     

Probabilistic design factors for pipes used for hydrogen transport

Probabilistic design factors for pipes used for hydrogen transport are proposed for 3 locations: urban, peri-urban and rural areas.The used method involves a risk equation defined as the product of probability of leakage after failure, probability to have a gas flow greater than a prescribed value, probability of ignition, probability of lethal effects greater than a threshold value and probability of the presence of a person corrected by an environment factor and a risk reduction coefficient. The results obtained are less conservative than the deterministic values provided by ASME code.     

Refrigerating heat pipes

The concept of novel heat pipe application, called refrigerating heat pipes (RHPs) is discussed. Thermodynamic classification of the RHPs is proposed. The possibilities of using classical driving forces for the RHP analysis (osmotic, inertial, capillary, gravitational, electrohydrodynamical, etc.) are firmly established. The cycles of absorption, vapour-ejector and mixed RHP with respect to their thermodynamic performance are considered.     

Development of heat pipes for solar water heaters

Numerous heat pipes were designed, manufactured, and filled on a specially developed filling rig. Each heat pipe was incorporated into a prototype solar water heater developed for this purpose, and was tested under actual insolation condition. An extensive testing program lasting for more than a year revealed that the heat pipes perform satisfactorily as heat transfer elements in solar water heaters.A special heat pipe featuring a compact and effective condenser configuration was also tested. It was observed to likewise exhibit isothermal behavior and hence promised potential for large scale solar applications.     

Ductile fracture theories for pressurised pipes and containers

The probable mechanisms of fracture which may be encountered in various components may generally be classified in two main groups. In the first the fracture is of ‘plane strain’ type which may occur in components (e.g. thick walled pressure vessels and other heavy section components) where prior to and during a possible fracture propagation the material is not expected to undergo large scale plastic deformations. In this case the underlying fracture theory is rather well-understood, and a criterion based on K_IC usually provides a highly reliable tool to deal with the problem.

The second type of fracture failure falls into the general category of ‘plane stress’ or ‘high energy’ fracture. In a great variety of tubings and containers, due to relatively small wall thickness, large defect size, high material toughness, and high temperature, prior to and during a possible rupture process, around the defect region the material would be expected to undergo large scale plastic deformations. In this case the standard theories of fracture based on the concept of plane strain fracture toughness are not applicable. This type of fracture which is generally accompanied by large inelastic deformations is (somewhat loosely) termed the plane stress fracture for which currently there does not seem to be a universally accepted criterion. In some components an additional complicating factor arises where one is dealing essentially with a shell of given curvature rather than a flat plate.

The theories which are currently in use in practice to analyse plane stress type of fracture are those which are based on the concepts of critical crack opening stretch, K_R-characterisation, J-integral, and the recently proposed plastic instability. In this paper the application of the fracture criteria based on these concepts to the fracture of shells will be discussed and the concept of plastic instability will be developed in some detail. Since there is no widely accepted standard criterion to deal with this type of fracture, one of the aims of the paper will be to provide an up-to-date critical appraisal of the current theories.     

Heat pipes thermoelectric solar collectors for energy applications

This study investigates the load characteristics of heat pipe thermoelectric solar collector (HPTSC) in practice. Heat pipe thermoelectric solar collector converts the heat generated by the Sun directly into electrical energy and produces hot water as well. The maximum power in HPTSC is obtained when the internal resistance of the thermoelectric module is equal to the load resistance. It has been observed to be possible to produce both hot water and electricity by improving available solar collectors or producing new generation HPTSC. While it is possible to generate an electrical power of 160 W from a HPTSC of one square meter using the thermoelectric method, the power produced with an average photovoltaic panel with the same area is only 132 W. Accordingly, HPTSC is a superior alternative not only to available solar collectors, but also to available PV panels. HPTSC, involving three different technologies, is environmentally friendly and certainly a product that allows for more efficient use of solar energy.     

Exact non-similarity solutions for laminar jet flows

Exact analytical solutions are obtained for the problems concerning the propagation of submerged free (plane and fan) jets with “symmetric” and “asymmetric”, relative to the jet axis, temperature distribution in the surrounding space and of semi-bounded (plane and fan) jets for four types of surface temperature boundary conditions (the wall temperature and that of the quiescent medium are the same, the wall temperature,is fixed and different from the ambient temperature, the heat flux at the surface is prescribed) for different values of Prandtl number.     

Splayed mirror light pipes

An expression is given for the transmission of the rectangular-section mirror light pipe. The expression is used to model throughputs for simulated solar conditions over a calender year. It is found that the splaying of a mirror light pipe results in a significant increase in throughputs particularly in winter months.     

Limit loads and fracture mechanics parameters for thick-walled pipes

In this paper, information on plastic limit loads and both elastic and elastic-plastic fracture mechanics parameters is given for cracked thick-walled pipes with mean radius-to-thickness ratios ranging from two to five. It is found that existing limit load expressions for thin-walled pipes can be applied to thick-walled pipes, provided that they are normalized with respect to the corresponding un-cracked thick-walled pipe values. For elastic fracture mechanics parameters, FE values of the influence functions for the stress intensity factor and the crack opening displacement are tabulated. For elastic-plastic J, it is shown that existing reference stress based J estimates can be applied, provided that a proper limit load for thick-walled pipes is used.