Insulator Cylinder Research Articles

A New Spore Precipitator with Polarized Dielectric Insulators for Physical Control of Tomato Powdery Mildew

ABSTRACT In an attempt to physically protect greenhouse tomato plants from the powdery mildew fungus Oidium neolycopersici, we developed a new electrostatic spore precipitator in which a copper wire conductor is linked to an electrostatic generator and covered with a transparent acrylic cylinder (insulator). The conductor was negatively charged by the generator, and the electrostatic field created by the conductor was used to dielectrically polarize the insulator cylinder. The dielectrically polarized cylinder also produced an electrostatic force without a spark discharge. This force was directly proportional to the potential applied to the conductor and was used to attract conidia of the pathogen. The efficacy of this spore precipitator in protecting hydroponically cultured tomato plants from powdery mildew was evaluated in the greenhouse. The hydroponic culture troughs were covered with a cubic frame installed with the spore precipitator, and the disease progress on precipitator-guarded and unguarded seedlings was traced after the conidia were disseminated mechanically from inoculum on tomato plants. Seedlings in the guarded troughs remained uninfected during the entire experiment, in spite of rapid spread of the disease to all leaves of the unguarded seedlings.

CFD Analysis of Premixed Methane Chlorination Reactors with Detailed Chemistry

With the implementation of efficient algorithms for the accurate calculation of reaction source terms, computational fluid dynamics (CFD) is now a powerful tool for the simulation and design of chemical reactors with complex kinetic schemes. The example studied in this work is the methane chlorination reaction for which the detailed chemistry scheme has 152 reactions and 38 species. The adiabatic, jet-stirred chlorination reactor used for the CFD simulations is an insulated right cylinder with a coaxial premixed feed stream at one end. In order for this reactor to remain lit, recirculation of hot products is crucial, and hence, reactor stability is sensitive to both macroscale and microscale mixing. By neglecting density variations, a Lagrangian composition probability density function (PDF) code with a novel chemistry tabulation algorithm (in-situ adaptive tabulation or ISAT) for handling complex reactions is used to simulate the species concentrations and temperature field inside of the reactor. In addition, a reduced mechanism with 21 reactions and 15 species is tested for accuracy against the detailed chemistry scheme, a simplified CSTR model is used to illustrate the shortcomings of zero-dimensional models, and a pair-wise mixing stirred reactor (PMSR) model is used to show the stabilizing effect of micromixing on reactor stability. The CFD simulations are generally in good agreement with results from pilot-scale reactors for the outlet temperature and major species.

Improved concept of hydrogen on-board storage and supply for automotive applications

Hydrogen is a promising alternative to liquid hydrocarbon fuels. It has particular advantages when injected directly into the cylinder of an internal combustion engine. However, when using hydrogen for automotive applications, large and heavy tanks are required. This problem can be lessened by the proposed thermocontrolled tank concept which uses well insulated high pressure cylinders initially filled with liquid hydrogen which changes phase to compressed gas at a low temperature of 100 to 200 K and high pressure of 300 bar. The gas pressure is maintained during vehicle operation at over 100 bar by the heat transfer to the tank and used for direct hydrogen injection. To increase the heat transfer, the energy of the engine exhaust gases can be used. This concept requires an electronic control based on microprocessor technology with temperature and pressure sensors, as well as electronically actuated valves for the control of heat transfer from the engine exhaust gases to the tank.

Calculation of sensitivity derivatives in thermal problems by finite differences

AbstractThe transient thermal analysis of large aerospace vehicles such as the space shuttle requires models with thousands of degrees‐of‐freedom. The design of thermal protection systems for such vehicles requires the repetitive thermal analysis of the vehicle and the calculation of sensitivities—derivatives of the transient response with respect to design parameters. When the number of design parameters is large, the cost of the sensitivity calculations may become prohibitive. The present work is concerned with reducing the computational cost and errors in sensitivity calculations with one of the simplest available methods—the finite difference approach. A technique for calculating simultaneously the nominal and perturbed solutions required for the finite difference derivative is proposed. An expression for the optimum value of the perturbation parameter is obtained which permits reducing the computational error. An insulated cylinder is used as an example which demonstrates that significant improvements in accuracy and efficiency may be obtained.

Cylindrical antennas with constant capacitive loading

Experimental and theoretical values of admittance are presented for a monopole antenna made in the form of a row of identical conducting, mutually insulated cylinders. The influence of the number of cylinders making monopoles of equal length and with equal total gapwidths between the cylinders is analysed. It was found that such antennas exhibit broadband properties similar to those of antennas with tapered capacitive loading.

Magnetoaerodynamic boundary layer flow with pressure gradient and separation

This study considers the large interaction parameter magnetoaerodynamic boundary layer associated with the free stream flow of a conducting fluid over an infinitely long circular insulator cylinder with the applied magnetic field normal to the distant free stream flow. The investigation is conducted in two parts; a theoretical solution of the associated boundary layer equations and a qualitative experimental investigation to allow visualization of flow separation caused by the magnetic field. The general integral formulation of Galerkin-Kantorovich-Dorodnitsyn is used to determine the boundary layer thickness, momentum thickness, displacement thickness, approximate separation point, and velocity profiles.

Heat Transfer Rates and Temperature Fields for Underground Storage Tanks

Abstract A digital computer was used to obtain an exact numerical solution for the transient behavior of the insulation and earth adjacent to an isothermal, submerged flat surface for a single set of parametric values. Comparison of the computed results with analytical solutions for limiting conditions revealed that a complete and general solution for all parametric values could be constructed from these limiting solutions. Complete and general solutions for insulated spheres and cylinders can also be constructed for limiting solutions only. The procedure is illustrated in part for an insulated spherical tank. The heat flow was found to fall rapidly to a pseudo-steady state; after some time, it then decreased slowly to zero for a flat plate and cylinder, and to a low steady-state rate for a sphere. The accumulative heat flow during the initial falling-rate period may be a significant fraction of the heat flow during the entire first year. Introduction Underground storage of liquefied natural gas and liquefied petroleum gas has received considerable recent attention. The rate of heat flow from the earth to the storage cavity and the resulting temperature field in the earth are important factors in the technical and economic evaluation of such storage facilities. The objective of this paper is to indicate how complete solutions can be developed for the transient flux and temperature field for various geometrical configurations. The representative properties and dimensions, and the resulting parameters utilized in the illustrative results, are indicated in Table 1. The results presented herein are for dry earth. The effect of the latent heat of solidification of water in the soil will be described in a subsequent paper. The temperature field in the insulation and earth is determined by energy balances, boundary conditions and initial conditions. The physical problem can be described mathematically with virtually no idealizations insofar as physical properties are known. It appears possible to solve the equations by numerical integration on a high-speed digital computer for any geometrical configuration and conditions. For complex situations, however, the computations are expensive and the results are highly specific. Analytical solutions have been developed for a few simple but important geometrical configurations and conditions, including one- dimensional heat transfer from (or to) earth at an initially uniform temperature to (or from) isothermal flat plates, spheres and circular cylinders. The solution for an insulated flat plate has also been derived but is in the form of a slowly converging series involving tabulated functions. It was planned to use a computing machine to evaluate this series for a number of representative conditions. However, upon examination of the results of preliminary computations it was discovered that a complete, general and accurate solution could be developed by interpolation between several much simpler solutions for limiting conditions. This technique then was used to develop a complete solution for an insulated sphere. The equations presented herein are derived in Carslaw and Jaeger and other books on applied mathematics, or they are simple extensions of these previous results. Hence, all derivations are omitted. SPEJ P. 28^