Reduction of heat losses from greenhouses by means of internal blinds with low thermal emissivity

Heat losses in greenhouses may be substantially reduced by the use of heat reflecting blinds. Quantitative results are obtained solving a mathematical heat flow model by numerical methods. Special attention has been given to the emissivity and transmittance of the screen and the ventilation through screen and glass. The heat losses by condensation are obtained from a simultaneously solved moisture balance. In most cases condensation on the lower side of the screen influences the emissivity. An unexpectedly large part of the heat is transmitted by ventilation. The emissivity of the coated surface has been measured for a number of screen materials. The durability of the coatings is also taken into consideration. For greenhouse application it is always necessary to protect against corrosion

Optimization of Laser Beam Transformation Hardening by One Single Parameter

The process of laser beam transformation hardening is principally controlled by two independent parameters, the absorbed laser power on a given area and the interaction time. These parameters can be transformed into two functional parameters: the maximum surface temperature and the hardening depth.\ud \ud It has been proved that with a constant hardening depth the results hardness. residual stress. etc.) can be optimized easily with respect to only one independent parameter, the maximum surface temperature. which is applied directly in adaptive control strategies

Metal surface temperature induced by moving laser beams \ud

Whenever a metal is irradiated with a laser beam, electromagnetic energy is transformed into heat in a thin surface layer. The maximum surface temperature is the most important quantity which determines the processing result. Expressions for this maximum temperature are provided by the literature for stationary cases. In practice, however, moving beams are of more importance.\ud Based on a fast numerical algorithm which allows calculation of the induced temperature profile, the maximum surface temperature for stationary and moving laser beams is calculated. Next, two types of approximating functions are presented relating the scanning speed to the maximum surface temperature. Using dimensionless numbers, the results can be applied to different material

Accuracy of Surface Plate Measurements - General Purpose Software for Flatness Measurement

Flatness departures of surface plates are generally obtained from straightness measurements of lines on the surface. A computer program has been developed for on-line measurement and evaluation, based on the simultaneous coupling of measurements in all grid points. Statistical methods are used to determine the accuracy of the measurements. The program runs on standard personal computers and supports different types of measuring instruments like electronic levels, autocollimators, laser interferometers or straight edge based instruments. Apart from the given height map, some meaningful characteristic parameters: sphericity, torsion and waviness are obtained. They have been proven very valuable to record long term effects of surface plates. Reliable measurements with an accuracy of 0.1 μm/m demonstrate the capabilities of the method

Characteristic numbers to describe the detail transfer quality of electro-chemical machining

For reproducing processes such as electrochemical machining (ecm) the accuracy of the reproduction is an important process parameter. Characteristic numbers which are a measure of this accuracy are proposed in this paper. Due to the non-linearity of the process a detail transfer function, which is helpful in linear cases, cannot be used, as will be shown from experimental work. Based on the same experiments, a characteristic radius and the standard deviation of a normal profile are proposed to describe the quality of the detail transfer. These numbers, which are easily interpreted criteria for quality and accuracy, have been proved to be almost independent of the geometry. Although developed for optimizing the ecm process, these values are also valid for edm and other reproducing processes. The usefulness of the characteristic numbers is illustrated by a comparison of continuous and pulsed ecm processes

Analysis of Flatness Measurement and Form Stability of a Granite Surface Plate

It is rather difficult to compare quantitatively flatness measuring results of one and the same object (e.g. in case of a long-term stability investigation) or the results of a series of products (e.g. from the same machinetool in order to indicate machinetool-influences). An extension of a computerprogram applied to the evaluation of flatness measurement (as described in the CIRP-Annals, vol. 26 (1977), no.1), separates the form deviations of a surface into a geometrical part and a random part.\ud The geometric part consists of a best-fitting non-flat, reference plane, composed of the single curvature of a sphere and the double curvature of a real twisted plane. Three parameters (the dimensionless curvature parameters of sphericity and torsion, together with the direction of the torsionvector) are able to characterize the geometrical part of the surface; a fourth one is a measure for the random part.\ud Advantages of the method are demonstrated with the aid of a long-term investigation into the form stability of a granite surface plate.\ud Another extension of the program makes it now possible to measure surfaces with non-rectangular contours in the same way as it is being done in case of a rectangular surface plate.\u

The Base Engine for Solar Stirling Power

A new concept in Stirling engine technology is embodied in the base engine now being developed at Stirling Thermal Motors, Inc. This is a versatile energy conversion unit suitable for many different applications and heat sources. The base engine, rated 40 kW at 2800 RPM, is a four-cylinder, double-acting variable displacement Stirling engine with pressurized crankcase and rotating shaft seal. Remote-heating technology is incorporated with a stacked-heat-exchanger configuration and a liquid metal heat pipe connected to a distinctly separate combustor or other heat source. High efficiency over a wide range of operating conditions, long life, low manufacturing cost and low material cost are specifically emphasized. The base engine, its design philosophy and approach, its projected performance, and some of its more attractive applications are described

Integrated sensors for robotic laser welding

A welding head is under development with integrated sensory systems for robotic laser welding applications. Robotic laser welding requires sensory systems that are capable to accurately guide the welding head over a seam in three-dimensional space and provide information about the welding process as well as the quality of the welding result. In this paper the focus is on seam tracking. It is difficult to measure three-dimensional parameters of a ream during a robotic laser welding task, especially when sharp corners are present. The proposed sensory system is capable to provide the three dimensional parameters of a seam in one measurement and guide robots over sharp corners

Measuring welfare effects in models with random coefficients

In economic research, it is often important to express the marginal value of a variable in monetary terms. This marginal monetary value is the ratio of two partial derivatives of the conditional indirect utility function, which reduces to the ratio of two coefficients if the utility function is linear. Based on the overwhelming evidence of taste differences among people, random coefficient models have become increasingly more popular in recent years. In random coefficient models, the marginal monetary value is the ratio of two random coefficients and is thus random itself. In this paper, we study the distribution of this ratio and particularly the consequences of different distributional assumptions about the coefficients. It is shown both analytically and empirically that important characteristics of the distribution of the marginal monetary value may be sensitive to the distributional assumptions about the random coefficients. The median, however, is much less sensitive than the mean. The authors would like to thank Ton Steerneman for stimulating discussions and helpful comments.