Solid Heat Transfer Research Articles

Flash pyrolysis of wood in a cyclone reactor

This paper reports the first results of an experimental study of the continuous flash pyrolysis of wood sawdust in a cyclone reactor between 893 and 1330 K. The reaction produces low fractions of char (4%) and the gasification yield increases from 0% at about 800 K to 90% at around 1330 K with a constant volume fraction of CO and H 2 (≈73%) and an increasing fraction of light hydrocarbons (up to 50% mass fraction). The heating value of the gas reaches 19 000 kJ m −3 STP for the highest temperatures. The wood particles mainly heated by radiation and solid convection react in less than 1 s while the carrier gas (residence time of the order of 0.05 s) seems to be only weakly heated. The 46.2 × 10 −6 m 3 cyclone reactor can operate with excellent stability for wood flow rates up to 0.35 kg h −1 at a wall temperature of 1330 K. The cyclone seems to be very efficient for carrying out reactions of the solid → fluids type but more accurate determination of process parameters such as gas and solid residence times and heat transfer efficiencies are required to gain a better understanding of the behaviour of such a high temperature reactor.

Calculating the performance of sprinkler pipe exposed to fire conditions

A computer model for predicting the onset of yielding in pressurized plastic pipe exposed to fire conditions has been developed. The model couples the aspects of solid mechanics and heat transfer to simulate the pipe performance. The von Mises yield criterion from solid mechanics is applied to predict yielding resulting from the plane stress induced in the pipe wall from the internal water pressure. The heat transfer analysis is performed via a finite difference approach to estimate the temperature profile in the pipe wall resulting from exposure to a heated ceiling jet. Results are reported of estimates for the time to yielding for 1 and 1 1/4 in. (25 and 32 mm) SDR-11 polybutylene pipe at three selected locations relative to the fire considering a range of internal pressures and water flow rates inside the pipe.

Regeneration of activated carbons used in waste‐water treatment by a moving‐bed regenerator

AbstractA method was developed for calculating the distributions of weight loss and temperature of spent activated carbon in a moving‐bed regenerator in which the solid flow was regarded as being plug flow. A kinetic model developed earlier, which was based on regeneration consisting of many first‐order reactions each with different frequency factors and different activation energies, was successfully applied to a design method for the regenerator. The flow pattern of the solid particles and heat transfer characteristics in a small moving bed were clarified experimentally, and the information obtained was used to calculate the distributions of weight loss of the spent carbon and temperature in the moving‐bed regenerator by means of the design method. The calculated results were in fairly good agreement with the experimental data obtained in a small moving‐bed regenerator. The adsorption capacity of the regenerated carbon was comparable to or greater than that of the virigin carbon.

Study of the effects of wall conductance on natural convection in differently oriented square cavities

This paper reports experimental and numerical results on the effects of wall conductance on natural convection in a two-dimensional rectangular cavity. Three different configurations in which the external wall is heated from the side, top and bottom and cooled from the side, bottom and top respectively have been investigated. Experiments have been performed in a square enclosure with solid walls made from Lexan and forming a square air-filled cavity. A Mach–Zehnder interferometer was used to determine the temperature distributions in the fluid. Solutions for stationary two-dimensional equations of energy and motion governing heat conduction in the solid and natural convection flow and heat transfer of a Boussinesq fluid contained in the cavity have been obtained numerically. The coupled flow distributions, including the appearance of multicellular flow, temperature profiles and heat-transfer predictions compare favourably with experimental results. Heat conduction in the connecting (unheated) walls is shown to simultaneously stabilize and destabilize the fluid in the cavity.

Boundary element method in nonlinear transient heat transfer of reactor solids with convection and radiation on surfaces

This paper deals with the boundary (integral) element method for non-steady conduction problems of solids, subject to non-linear convective and radiation conditions on surfaces. Boundary integral equations for the mixed-type and non-linear boundary conditions, both for the case with constant and variable heat conductivity are derived, modelled by non-conforming boundary elements, while domain integrals are evaluated within triangular cells. A test case is included to illustrate the described procedure.

PE-II Scoping Test Results: Solid Breeder Heat Transfer and Stability

Two scoping test stands have been designed, built and installed at GA Technologies to perform single effect type testing to investigate specific thermomechanical and thermal-hydraulic data needs of typical solid breeder blanket designs. An initial test has been completed successfully yielding important information on the stability of Li2O breeder material at typical fusion reactor environmental conditions. Assembly of the second test rig and a pre-testing checkout of the equipment has been completed.

Drying wheat with solid heat transfer medium

AbstractLaboratory experiments have shown the feasibility of drying milling wheat from 17.0 to 14.5% moisture content using hot sand. The amount of moisture removed increased with the increase in residence time from 1 to 2 min but decreased when the residence time was increased to 3 min. Heated sand to wheat mass ratios ranging between 3:1 and 5:1 were found to be effective in removing moisture from wheat with sand temperatures ranging from 90 to 105°C.

Wirbelschicht‐Prozesse für die Chemieund Hütten‐Industrie, die Energieumwandlung und den Umweltschutz

AbstractFluidized bed processes for the chemical and metallurgical industries, energy conversion, and pollution control. This article presents a review of, and selection criteria for, gas/solids reactors with the aid of examples of industrially operating fluidized bed processes. The choice of optimum reactor design with regard to flow and reaction conditions, heat and mass transfer, grain size, and retention time of solids and gas is considered. In conclusion, various processes are described in terms of several process flowsheets.

The role of interfaces in heat transfer processes

An understanding of the role of interfaces between phases is essential to true understanding of many heat transfer processes. In the cases of evaporation ion and condensation in single component systems, the evaporation or condensation coefficient represents the transmitance of the vapor-liquid interface itself or the maximal possible rate of interfacial heat as well as mass transfer. Jet tensimetry is a simple but powerful technique for the study of the resistance of the interface in the evaporation and condensation processes, with or without chemical reaction, involving the interface between phases. This technique also eliminates most of the complications of the bulk phases on both sides of the interface. Get tensimetry and other recent experimental data verify that the evaporation coeffecients of water and other common liquids are unity or nearly unity; the interface does not constitute a significant resistance to the heat transfer processes.Boiling and condensation are two processes with very high heat transfer coefficients, especially in the cases of nucleate boiling and dropwise condensation. An examination of the vapor-liquid interface under equilibrium conditions shows that there are many similarities between these two processes from the thermodynamic point of view. However, since the creation of a new phase is a problem of stability, more attention should be paid to the dynamic rate of the nucleation of the vapor bubbles and condensate droplets. The solid heating and cooling surfaces introduce more complications because they are usually not smooth and homogeneous. Vapor bubbles and condensate droplets are often generated at the position of active sites. Because most of the solid heat transfer media are hydrophilic, the nucleation theory shows that from the point of view of interfacial phenomena: 1) nucleate boiling is usual but film boiling is exceptional: and 2) film condensation is usual but dropwise condensation is exceptional.Dropwise condensation can be realized by making the solid cooling surface hydrophobic with the help of promoters. Its mechnism is complicated but relactively well understood after the experimental studies and theoretical simulation carried out by many authors. Their conclusions are discussed with emphasis on the solid-liquid-vapor interfacial properties. The condensation on the surface of an immiscible liquid is also discussed because of its similarity to dropwise condensation. The treatment of dropwise condensation problems by nucleation theory and statistical methods is also introduced.

Thermally Symmetric Nonlinear Heat Transfer in Solids

Material thermal properties are temperature dependent, and this effect cannot be disregarded at elevated design temperatures. Based upon the principle of equivalent linearization, analytical solutions are developed for thermally symmetric planar solids. The solution method is, in turn, extended to a composite wall whose individual thermal conductivities are also temperature dependent. As a demonstration of the method’s accuracy several numerical examples are shown.

Solids Circulation in Turbulent Fluidized Beds and Heat Transfer to Immersed Tube Banks

In gas fluidized beds of large particles, a change in flow regime from bubbling flow to turbulent flow has been observed as the superficial gas velocity is increased. Solids flow and heat transfer models based on the bubbling flow regime are not generally adequate in the turbulent flow regime. A turbulent flow model is given here that is supported by limited solids flow measurements. A simplified model of the heat transfer to tube banks immersed in fluidized beds, that employs the solids flow model, is also given and is shown to be supported by data over a wide gas pressure and temperature range with particles in the 350μm to 2600μm size range.

Heat Transfer in Composite Solids with Heat Generation

Steady-state heat transfer problems have been considered in a composite solid comprising two materials, one, a slab, which forms the bulk of the interior and the other, a plate, which forms a thin layer around the boundary. Through the use of appropriate Green’s functions, it is shown that the boundary value problem can be converted into a Fredholm integral equation of the second kind. The integral operator in the integral equation is shown to be self-adjoint under an appropriate inner product. Solutions have been obtained for the integral equation by expansion in terms of eigenfunctions of the self-adjoint integral operator, from which the solution to the boundary value problem is constructed. Two problems have been considered, for the first of which the eigenvalues and eigenvectors of the self-adjoint operator were analytically obtained; for the second, the spectral decomposition was obtained numerically by expansion in a convenient basis set. Detailed numerical computations have been made for the second problem using various types of heat source functions. The calculations are relatively easy and inexpensive for the examples considered. These examples, we believe, are sufficiently diverse to constitute a rather stringent test of the numerical merits of the eigenvalue technique used.

Network analysis—a useful but underused tool for modelling of chemical engineering systems?

Network analysis may be used to model a number of chemical engineering systems such as; distribution problems, heat transfer in solids, simultaneous heat and mass transfer in catalyst pellets. Manipulation of simple network representation matrices requires a minimum of core store and generates rapid solutions to a variety of modelling problems. Using methods of tearing and decomposition such as diakoptics there is effectively no limit to the complexity of the network problem which can be solved.

Holdup of Solid Particles and Heat Transfer Coefficient between Bed and Vertically Inserted Tube Wall in Dense and Dilute Zone of Fluidized Bed

内径12cmの流動層を用い, 広い粒径分布を有するFCC粒子を流動化し, 局所重量平均粒径, 局所粒子ホールドアップおよび層と垂直挿入管壁間の伝熱係数を測定した.FCC粒子の重量平均粒径は65μm, 流動化開始速度は約0.25cm/secであった.気泡を含む濃厚領域の上方に形成される希薄な領域内の局所重量平均粒径および局所粒子ホールドアップは, 濃厚領域の上面からの距離とともに減少し, またガス流速の増加とともに増加する.ガス流速が50cm/secとなると, 層全体にわたり重量平均粒径の差異がなくなるが, 軸方向の粒子ホールドアップの分布は存在する.伝熱係数は, 粒子ホールドアップ, 重量平均粒径, ガス流速およびガスと固体の物性の関数であり, 管の直径には関係しない.伝熱係数に関する実験式が得られた.

Variational irreversible thermodynamics of heat and mass transfer in porous solids: new concepts and methods

A recently developed variational principle of virtual dissipation along with a new approach to the thermodynamics of open systems is applied to coupled mass and heat transfer in a porous solid containing a fluid. General differential field equations are derived directly from the variational principle. A general energy flux theorem is formulated. Vapor-liquid phase transition and capillary condensation are discussed. Field equations for nonequilibrium adsorption are also obtained. Lagrangian equations with generalized coordinates are derived directly from the variational principle without use of the field equations. They provide the foundation of finite-element methods as well as of many other techniques particularly suitable in geothermal systems analysis.

Multivalued differential equations in Banach space. An application to control theory

This paper is concerned with the study of existence theorems for multivalued differential systems in infinite-dimensional Banach space: the method used is based on techniques (extension theorem for linear operator, compactly convergent sequences) developed earlier by the authors for multivalued differential systems defined inn-dimensional vector spaces. As an application, the authors consider a distributed-parameter control problem arising in mathematical physics, more specifically, in the study of heat transfer in solids.

A Variational Principle for Non‐Conservative Dynamical Systems

AbstractThe purpose of the present paper is to establish a variational principle of Hamilton's type, for purely nonconservative mechanics according to Central Lagrangian Equation. The velocity of variation and the variation of velocity are not commutative as in conservative mechanics. The applications on the nonlinear heat transfer in solids are discussed in detail.

Effects of surface resistances on simultaneous heat and mass transfer in porous solids with phase change

The drying mechanism and the drying rate of porous solids in the usual hot air dryers have been widely analized, and also have been theoretically systematized. However, when the wet solids were dried in a fluidized bed making use of the fact that the heat-transfer coefficients between fluidized bed and solids were remarkably large, such unusual phenomena were found that the inner temperature dropped while drying. Such unusuality has never been expected from conventional theories of hot air dryer. In this report, the authors dried various solid spheres containing liquids in a fluidized bed, and tried to analize such unusual phenomena with application of the analytical method of drying rate previously presented by us.

The influence of diameter on the burning velocity of strands of solid propellant

A simple heat transfer model is coupled with an Archenius type pyrolysis law to investigate the effect of solid state heat transfer losses upon burning rates of strands of solid rocket propellant. Analysis shows that such heat transfer can materially affect these rates and that it can also give rise to extinction phenomena similar to some which have been observed experimentally. Strand diameter, composition, adiabatic burning rate, and the heat transfer film coefficient at the strand surface are all important variables.

Low-Temperature Thermal Conductivity ofn−Ge

The measurements of the lattice thermal conductivity of $n\ensuremath{-}\mathrm{Ge}$ from 0.3 to 4.2 \ifmmode^\circ\else\textdegree\fi{}K by Bird and Pearlman are explained satisfactorily by the nonlinear theory of heat transfer in solids given by Kazakov and Nagaev.