Simple Flat Plate Research Articles

Experimental results of a solar powered cooling system at low temperature

A solar thermochemical prototype producing low-temperature cold has been built and tested during the summer and autumn 2005 in Perpignan, France. It cools a 560 L cold box down to about −25 °C using only low-grade heat produced by two simple flat plate solar collectors. The process involves two cascaded thermochemical systems using BaCl 2 salt reacting with ammonia. Its working mode is discontinuous, as it alternates between one decomposition mode at high pressure (daytime) and one cold production mode at low pressure (nighttime). Experimental results prove the feasibility of this new concept of solar cold production, with temperatures as low as −30 °C, demonstrate its potential use in housing, by the acceptable size and weight of the system and show the system performances during the sunniest months of the year, with a rough solar coefficient of performance (COP) of about 0.031 over the test period. The major meteorological parameters influencing the process efficiency are the solar irradiation and the outside temperature.

Design of a thermochemical process for deep freezing using solar low-grade heat

A deep-freezing process has been designed and experimented to cool a cold box down to about −30 °C using only low-grade heat produced by simple flat plate solar collectors operating at 70 °C. The original process involves two cascaded thermochemical systems using BaCl 2 salt reacting with ammonia. It works discontinuously, with one day phase of regeneration at high pressure and one night phase of cold production at low pressure. A global dynamic model allows the simulation of the different system components functioning depending on the hourly weather conditions. It takes into account the transient periods and shows the temperature changes of the components, the chemical reactions in the system and its performances. This system will cover the cooling needs of a 560 L cold box at −20 °C during the 3 sunniest months of the year and provide more than 60% of the total yearly cooling needs of this box for the weather conditions of Perpignan (South of France). The prototype is expected to show a system coefficient of performance (COP) of about 0.07 over the 10 sunniest months of the year, and a net solar COP of 0.05, taking into account the collectors efficiencies.

Modelling and performances of a deep-freezing process using low-grade solar heat

A solar deep-freezing process has been designed. It aims at cooling down a cold box to about −20 °C, using simple flat plate solar collectors operating at 70 °C. This original process involves two cascaded thermochemical systems based on the BaCl 2/ammonia reaction. Its working mode is discontinuous as it alternates between a regeneration mode during daytime and a cold production mode during nighttime. A global dynamic model involving the various system components allows the simulation of the process; it predicts the evolution of the components temperatures and the rates of chemical reactions of the system. It also allows the dimensioning of the system components to maintain a 500 l cold box at −20 °C during the 6 sunniest months of the year under typical Mediterranean weather conditions and provide over 80% of the total yearly cooling needs of this box. This requires a solar collector area of 5.8 m 2 and 39 kg of reactive salt. The predicted coefficient of performance (COP) is about 0.1 over the year, and the net solar COP, taking into account the collector efficiencies, is 0.05.

Numerical simulation of flow in a circular duct fitted with air‐jet vortex generators

AbstractMost of the fundamental studies of the use of air‐jet vortex generators (AJVGs) have concentrated on their potential ability to inhibit boundary layer separation on aerofoils. However, AJVGs may be of use in controlling or enhancing certain features of internal duct flows. For example, they may be of use in controlling the boundary layer at the entrance to engine air intakes, or as a means of increasing mixing and heat transfer. The objective of this paper is to analyse the flow field in the proximity of an air‐jet vortex generator array in a duct by using two local numerical models, i.e. a simple flat plate model and a more geometrically faithful sector model. The sector model mirrors the circular nature of the duct's cross‐section and the centre line conditions on the upper boundary. The flow was assumed fully turbulent and was solved using the finite volume, Navier–Stokes Code CFX 4 (CFDS, AEA Technology, Harwell) on a non‐orthogonal, body‐fitted, grid using the k–ε turbulence model and standard wall functions. Streamwise, vertical and cross‐stream velocity profiles, circulation and peak vorticity decay, peak vorticity paths in cross‐stream and streamwise direction, cross‐stream vorticity profiles and cross‐stream wall shear stress distributions were predicted. Negligible difference in results was observed between the flat plate and the sector model, since the produced vortices were small relative to the duct diameter and close to the surface. The flow field was most enhanced, i.e. maximum thinning of the boundary layer, with a configuration of 30° pitch and 75° skew angle. No significant difference in results could be observed between co‐ and counter‐rotating vortex arrays. Copyright © 2002 John Wiley & Sons, Ltd.

The design and performance results of simple flat plate low solidity vaned diffusers

Vaned diffusers for centrifugal compressors have decades of development history, but most of it is of a proprietary and empirical nature. Centrifugal compressor designers are continuously searching for a diffuser system that combines the good qualities of vaneless and vaned diffuser systems. Vaneless diffusers are known to possess wide operating range with relatively low efficiency while current conventional vaned diffusers have narrow range and high efficiency. The low solidity vaned diffuser (LSVD) has shown good performance from both range and efficiency standpoints. Its relatively high efficiency and wide flow range potentials are strong current factors, leading the compressor manufacturer to seriously consider it as the best compromise diffuser that has been sought through the years. This paper discusses the design and experimental performance results of eight flat plate LSVDs. These diffusers had a solidity of 0.9, 0.8, 0.7 and 0.6. Eight low solidity vaned diffusers (LSVD1 to LSVD8) and for comparison purposes two vaneless diffusers (VNL1 and VNL2) and a conventional vaned diffuser (CVND) were all tested downstream of the same impeller at three speeds.

A theoretical investigation of enhanced lift in the presence of thin aerofoil stall

AbstractA theoretical study is presented for the investigation of a potential-flow model for enhancing lift over a flat-plate aerofoil experiencing thin aerofoil stall. Rather than suppressing the leading-edge separation, flow is assumed to separate tangentially at the leading edge and made to reattach smoothly at the tip of a forward-facing fence joining the plate tangentially on its upper surface to avoid any unnecessary stagnated flow. The length of the fence and its location from the leading edge form two geometrical parameters. At any positive angle of attack, the resulting bounding streamline emanating from the leading edge and terminating at the tip of the fence is simulated by using suitable mathematical singularities subject to boundary conditions such as attaining a finite velocity at each critical point of the conformal mapping involved, and the condition of finite pressure gradient at reattachment, when applicable. Computational results from varying these two geometrical parameters indicate that the lift from each model is enhanced, as compared with the attached flow model around a simple flat plate and the original separated flow model by Kirchhoff.

Head and Neck Compensation for Total Body Irradiation Using Opposed Laterals

Using shaped brass compensators that follow the coronal profile of a patient’s head and neck, we confirm that adequate compensation can be made to prevent overdosing in these regions when delivering total body irradiation using opposed lateral fields. Initially, these compensators were custom made for each patient, but we have shown that the variation from patient to patient is sufficiently small that individual compensators can be used for a number of different patients without compromising the dose distribution. In a subgroup of 35 patients on whom diode measurements were made, 20 used compensators from the library of ∼40 compensators made for previous patients and 15 required new compensators to be fabricated. No significant difference (3.4% on average) was observed in the dose distribution. By examining the profiles accumulated from 81 patients, we have shown that the primary difference between patients is not in the shape of the head and neck, but in the distance from the top of the head to the suprasternal notch and in the slope of the shoulders; thus, shaped compensators are not necessary and the same quality of dose homogeneity can be achieved using simple flat brass plates. Further, if the arms are supported so that the slope of the shoulders is constant, a relatively small number (15) of square-ended plates of thickness ranging from 4.0 to 11.0 mm would be sufficient to treat all 81 patients in our sample.

Steady-state nonlinear heat transfer in stiffened composite plates and shells by an exactly integrated facet triangular element

The present research work expands a previously developed study which was primarily concerned with the development of a multilayered composite triangular element for the steady-state analysis of the temperature fields in laminated shells (see J. Argyris, L. Tenek and F. Oberg. A multilayer composite triangular element for steady-state conduction, convection, radiation heat transfer in complex shells, Comput. Methods Appl. Mech. Engrg. 120 (1995) 271–301). These temperature fields included the linear effects of conduction and convection and the nonlinear effects of radiation. Here we augment the basic formulation with quadratically time-dependent thermal conductivities thus achieving together with the previously included radiation effects a high degree of nonlinearity in our steady-state heat transfer formulation. A distinct characteristic of the study is the exact integration of all matrices which is accomplished by employing advanced symbolic computation techniques as well as delicate programming. Comparison is made with available analytical results for various panels of different complexity; simple flat unstiffened plates to stiffened cylindrical shells are studied. The 3-node triangular element can be applied to any geometry thus ensuring generality. As we shall show in a subsequent study it can be made also compatible with structural elements.

Thwaites' Method In Laminar Boundary Layer

Thwaites' method can be applied to find the boundary layer characteristics for either similar or nonsimilar flow for a variety of boundaries ranging from a simple flat plate (Blasius's Solution(1)) to a symmetrical airfoil. The flow properties to be determined include potential flow velocity distribution, displacement thickness, momentum thickness and coefficient of friction. Furthermore,the location of flow separation is readily obtainable from the numeric value of local coefficient of friction. Thwaites' Method is able to provide satisfactory approximate solution to different types of simple boundary as long as the flow is laminar and not separated. For a complex curvature such a an airfoil Thwaite' Method is yet to be tested. In this context, we will look into the applicability of Thwaites' Method for a particular symmetrical airfoil, NACA 0012.

Performance of a simple flat plate solar collector at an equatorial location

Abstract The performance of a solar flat-plate collector installed at an equatorial location, Port Harcourt (latitude 4°51′N, longitude 7°01′E), Nigeria, has been investigate. It is found that the variation of fluid stagnation temperature wit local time is similar for a tracking collector as for a horizontal one whose longer axis is oriented in a north-south direction. It is observed that a tracking collector gives a higher ratio of fluid stagnation temperature to ambient temperature than either a horizontal or tilted collector. In the case of a tilted collector, it is found that the stagnation fluid temperature for an east-facing collector reaches a peak value earlier for larger angles of tilt (with respect to the horizontal) while for a west-facing collector, peak temperature is reached later for larger angles of tilt. Finally, the working efficiency of the collector is found to be highest (about 62%) when the collector is placed horizontally with its longer axis oriented in the east-west direction as against a north-south orientation or when the collector tracks the sun's daily east-west movement.

The performance of marine anchors with planar flukes in sand

The problem of determining the holding capacity of flat plates and marine anchors in cohesionless soils is briefly reviewed and the reasons for the difference in the performance of marine anchors and that of simple flat plates are identified. The role which each anchor component plays during the embedment process is discussed.An analytical procedure to estimate the holding capacity of anchors with planar flukes, such as the Danforth anchor, as a function of soil properties and the depth of penetration into the soil is presented and checked against data from laboratory and published field tests.Factors such as anchor stability and characteristics of the pulling cable which can affect both anchor orientation and the maximum depth to which a particular anchor can penetrate the soil have not been included in the analysis. Consequently, it is not yet possible to predict the ultimate holding capacity that a particular anchor may achieve if pulled through an adequate distance.

Application of ADINA and ADINAT in the creep analysis of heated concrete structures

ADINA and ADINAT have been used in the analysis of time-dependent changes of stress and strain occurring in heated concrete structures. The problems tackled include a simple concrete flat plate and a fast breeder reactor containment vessel. A direct method of solution, based on a variational principle, which does not require intermediate solutions at many small intervals of time, has been developed. This paper describes how ADINA can be used in conjunction with this method to predict time-varying stresses.

Gravity Survey of a Deep Buried Valley

ABSTRACTA gravity survey was conducted as part of a ground‐water investigation covering 400 mi2 (1,000 km2) in Outagamie County, northeastern Wisconsin. The objective of the gravity survey was to supplement bedrock topography data obtained from well logs and seismic refraction profiles. The gravity method was chosen as it is a rapid and low‐cost reconnaissance technique, and conditions in the study area were favorable for a successful gravimetric survey. The simple Bouguer gravity values were referenced to a local base station as only relative gravity values were required. The data were interpolated to a regular grid by an inverse‐distance weighted average algorithm. The gravity residual was derived using a five‐ring inverse weighted filtering routine. The residual map accurately reflects the major topographic features of the bedrock surface. A two‐dimensional geologic model fitted to the residual data agrees well with the simple flat plate approximation used to obtain quantitative estimates of glacial drift thickness. Estimates of drift thickness from the gravity data also agree well with bedrock depths obtained from well logs. The most productive drift aquifers are restricted to the major bedrock valleys. Gravity data were coupled with seismic refraction and well data to produce a bedrock elevation map, from which it is possible to predict the extent and distribution of the major drift aquifers.

Effect of off-south orientation on optimum conditions for maximum solar energy absorbed by flat plate collector augmented by plane reflector

A complete analysis of the off-south oriented, simple flat plate collector, augmented by flat sheet specular reflector, is developed. The enhancement of heat flux absorbed by solar collector due to the use of reflector is calculated as a funciton of solar altitude and azimuth angles, off-south orientation angle of collector and relative sizes and tilt angles of both collector. The shading effect due to the presence of the reflector is considered in the analysis. The collector and reflector variables are optimized for maximum solar energy flux absorbed by the collector during a pre-specified period of time. The Hooke and Jeeves optimization technique has been used in the analysis.

Contamination Flashover, Part II: Flat Plate Model Tests

In order to study some of the processes occurring during flashover, wet contaminant tests were done on a simple flat plate insulator. The effects of such factors as contaminant surface resistivity, the amount of inert binder (bentonite), the use of a different binder (kaolinite), and insulator orientation were studied. Additional data was obtained on time to flashover and the drying effect of the preliminary discharging. Some interesting polarity effects were noted.

Load support capability of flat plates of various shapes in soils

Abstract : A fundamental problem in soil-vehicle mechanics is the ability to predict accurately the load-sinkage characteristics of simple flat plates in homogeneous soils. This paper attempts to develop a more general theory of plate sinkage which will be applicable to a wide variety of soils, sinkages, plate sizes, and plate shapes. In a study to determine the strength characteristics of soils, many carefully performed tests must be conducted to eliminate the effects of the natural variability of the soil which can easily mask out the parameters being measured. (Author)

Evaluation of new couplers for circumaural earphones.

An experimental investigation of three couplers, suitable for testing circumaural earphones, was made to determine the limitations on their use. Two of these couplers were modified forms of standard U.S. couplers, the ASA-type 1 and the NBS-9A, while the third was a simple flat plate with a hole in which the test microphone is flush mounted. Results presented are based on tests made using the Telephonics TDH-39 earphone with NAF-48490-1 cushion and the Philips model HA-10 circumaural earphones. Below 2000 Hz, all three couplers are reliable and useful for measuring the responses of circumaural earphones. Above 2000 Hz, small variations in the electroacoustic system, defined by the earphone, cushion, coupler, and measurement microphone, cause large variations in the measured response. Variations in earphone responses are shown to be caused by variations in (1) earphones of a particular type, (2) cushions of a particular type, (3) applied force on the earphone, and (4) placement of the earphone on the coupler. These variations are in addition to the expected variations in the measured responses of different types of earphones when used with different types of cushions and when measured on different types of couplers.

Local heat-transfer coefficients in a nozzle with high-speed laminarflow.

Abstract : An experimental investigation of the local heattransfer coefficient in the throat region of a nozzle operating under conditions of cold wall, thick laminar boundary-layer, low-density, highspeed flow has been conducted. The experimental results have been compared with several analytic procedures for predicting the heat-transfer coefficient in laminar flow. The simple flat plate equation is shown to underestimate the heat-transfer coefficient, while the method of Cohen and Reshotko predicts coefficients which are too large. The incremental flat plate method of Pasqua and Stevens and a modification of a solution of Beckwith and Cohen exhibit good results downstream of the nozzle throat when reference to the value calculated by the simple flat plate equation at the nozzle exit. The effects of thermal raiation upstream of the nozzle throat are indicated.