Search results

This paper aims to focus on the fabrication and characterization of mixed thin-/thick-film thermoelectric microgenerators, based on magnetron sputtered constantan (copper–nickel alloy) and screen-printed silver. To improve the adhesion of the constantan layer to the applied substrates, the additional chromium sublayer was used. The aim of the study was to investigate the influence of chromium sublayer on the electrical and thermoelectric properties of such hybrid microgenerators.

Fabrication of such structures consisted of several steps – magnetron sputtering of the chromium and then constantan layer, exposing the first arms of thermocouples, applying the second arms by screen-printing technology and firing the prepared structures in a belt furnace. The structures were made both on Al₂O₃ (alumina) and low temperature co-fired ceramics (LTCC) substrates.

To the best of the authors’ knowledge, for the first time, laser ablation process was applied to fabricate the first arms of thermocouples from a layer of constantan only or constantan with a chromium sublayer. Geometric measurements have shown that the mapping of mask pattern by laser ablation technique is very accurate.

The determined Seebeck coefficient of the realized structures was about 40.4 µV/K. After firing the exemplary structures at 850°C peak temperature, Seebeck coefficient is increased to an average value of 51 µV/K.

GENERALLY speaking, the demand for thermo‐electric pyrometer equipment is such that individual calibration of each instrument and its couple is possible. For the measurement of aircraft temperatures thermo‐electric pyrometers are employed but the following conditions render individual calibration impracticable:

IN research or development work on aero engines there are many occasions when it is desirable, or sometimes essential, to obtain temperature readings under somewhat difficult conditions. In many cases it is possible for serious errors to arise, under conditions which make their detection difficult, and the writer, therefore, thinks that the information he has gained in dealing with these problems may be of value to others.

The purpose of this paper is to study the statistics of thermal conductivity and resistivity tensors in two-phase random checkerboard microstructures at finite mesoscales.

Microstructures at finite scales are generated by randomly sampling an infinite checkerboard at 50 percent nominal fraction. Boundary conditions that stem from the Hill-Mandel homogenization condition are then applied as thermal loadings on these microstructures.

It is observed that the thermal response of the sampled microstructures is in general anisotropic at finite mesoscales. Based on 1,728 boundary value problems, the statistics of the tensor invariants (trace and determinant) are obtained as a function of material contrast, mesoscale and applied boundary conditions. The histograms as well as the moments (mean, variance, skewness and kurtosis) of the invariants are computed and discussed. A simple analytical form for the variance of the trace of mesoscale conductivity tensor is proposed as a function of individual phase conductivities and the mesoscale.

A rigorous methodology to determine the evolution of the invariants of thermal conductivity (and resistivity) tensors across a variety of length scales (microscale to macroscale) is presented. The objective is to enable setting up of constitutive equations applicable to heat conduction that are valid across all length scales.

This paper presents a new multi‐channel temperature measurement system (MCTMS) with small size, light weight and low power consumption for the microgravity fluid experiment of drop Marangoni migration on SZ‐4 spaceship, a test module of the manned space mission of China.

The MCTMS, with a commercial‐off‐the‐shelf (COTS) component monolithic thermocouple amplifier with cold junction compensation AD595, is designed to measure temperature gradient field of up to 6 type T thermocouples Cu‐Constantan for microgravity fluid experiment. Through an analog multiplexer, the very small signal amplitude of the six‐channel temperatures can be acquired and amplified by the same monolithic thermocouple amplifier to retain the consistency of the six channels. A fully mission analysis and evaluation on the COTS component was taken into account before it was used in the thermal and radiation environment of space.

Using the COTS component in space can increase the system performance and considerably reduce the size, weight, power consumption and the overall complexity of the system. The measurement resolution of the MCTMS reaches 0.1°C because of the utilization of the COTS with high performance. In addition, the transfer function of the AD595 was deduced for type T thermocouples.

This paper suggests an easy way of measuring temperature for microgravity fluid experiment on spacecraft. Using a COTS component on spacecraft, also, is a new practical case study, which is more suitable for on‐board implementation. The MCTMS, presented in this work, has run in‐orbit successfully on SZ‐4 spaceship and the experiment result in space is reported.

Grinding may generate high temperature along the arc of grinding zone, especially during the grinding process of difficult‐to‐machine materials. It can cause thermal damage to the ground surface and poor surface integrity. Conventional cooling methods based on large amounts of water‐oil emulsions can be both ineffective and environmentally unacceptable. The purpose of this paper is to offer a new high efficiency cooling method – cryogenic pneumatic mist jet cooling (CPMJ) to enhance heat transfer in the grinding zone during grinding of difficult‐to‐machine materials.

CPMJ equipment is a set up, which can produce water mist of −5°C with jet velocity above 150 m/s and mean particle size below 20 μm at the impingement distance of 10‐40 mm on the symmetry axis. To validate the cooling efficiency of CPMJ equipment, heat transfer experiments were carrying out on it. Finally, CPMJ was applied to the grinding of titanium alloy to verify its cooling effects.

With high penetrative power and water mist of −5°C, CPMJ can greatly improve heat transfer efficiency in the grinding zone. Experimental results, including heat transfer experiments and grinding experiments, indicate that CPMJ has strong cooling ability and can offer better cooling effects compared with cold air jet and traditional flood cooling method. With CPMJ cooling method, grinding zone temperature can be effectively reduced and good surface quality can be achieved during grinding of titanium alloy.

CPMJ cooling method is an effective and pollution‐free way to solve the thermal problems during grinding of difficult‐to‐machine materials.

This is a further contribution from our correspondent who is a maintenance engineer in South Africa and whose forthright opinions and practical experiences are always of interest to our readers.

Periods spent in various industries are essential in all applied science courses, and enable the student to keep his academic studies, especially experimentation, in perspective. The type of sandwich course consisting of six‐monthly periods spent alternately in college and industry for three years followed by a final year completely in college provides the wisest combination of industrial training and academic studies. This sandwich course is a headache for administrators but offers the students a very wide range of experience; the scheme also permits two end‐on streams per year to be accommodated by our universities, so enabling existing academic facilities to be used more efficiently, as well as producing an even demand on industrial training facilities (Probert, 1964).

Presently there exists no way to directly measure strain at high temperatures in engine components such as the combustion chamber, exhaust nozzle, propellant lines, and turbine blades and shaft. The purpose of this paper is to address this issue.

Thermomechanical fatigue (TMF) prediction, which is a critical element for a blade design, is a strong function of the temperature and strain profiles. Major uncertainties arise from the inability of current instrumentation to measure temperature and strain at critical locations. This prevents the structural designer from optimizing the blade design for high temperature environments, which is a significantly challenging problem in engine design.

Being able to directly measure strains in different high temperature zones would deeply enhance the effectiveness of aircraft propulsion systems for fatigue damage assessment and life prediction. The state of the art for harsh environment, high temperature sensors has improved considerably over the past few years.

This paper lays down specifications for high temperature sensors and provides a technological assessment of these new sensing technologies. The paper also reviews recent advances made in harsh environment sensing systems and takes a peek at the future of such technologies.

Modular ac to dc Sorensen power supply units have built‐in over voltage protection. They offer voltage regulation to within 0·05 per cent in six voltage levels to 100W and operate within a temperature range of 0° to 71°C. They are capable of automatic adjustable current limiting and remote sensing and programming.