Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

A simple method for measuring the dielectric constant of solids

This paper presents a simple method for determining the dielectric constant of a solid material. The method consists of measuring the return loss due to a slab of such material inserted into a rectangular waveguide. The dielectric slab presents a discontinuity inside the waveguide, and the electric field at each interface of the slab is described as a summation of weighted sinusoidal basis functions. The scattered magnetic field on either side of the slab is determined using the modal expansion approach. These weights are solved by using the method of moments on the boundary conditions of continuity of the tangential magnetic field at the interfaces. The component of the electric field (scattered) for the dominant TE₁₀ mode can then be determined in terms of these weights, and from this result the reflection coefficient can be theoretically evaluated. A comparison between the experimentally obtained reflection/transmission coefficient and the theoretical values provide a figure for the dielectric constant of the material     

A nonstationary method for measuring heat fluxes

A nonstationary method for measuring heat fluxes using a hollow cylindrical probe placed in the critical cross section of a nozzle is proposed. The temperature at a fixed distance from the inner surface of the probe is measured as a function of time. The time variation of the heat flux is determined by solving the one-dimensional nonlinear heat-conduction equation.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 1, pp. 51–55, July, 1975.     

A simple graphical method for measuring inherent safety

Inherently safer design (ISD) concepts have been with us for over two decades since their elaboration by Kletz [Chem. Ind. 9 (1978) 124]. Interest has really taken off globally since the early nineties after several major mishaps occurred during the eighties (Bhopal, Mexico city, Piper-alfa, Philips Petroleum, to name a few). Academic and industrial research personnel have been actively involved into devising inherently safer ways of production. The regulatory bodies have also shown deep interest since ISD makes the production safer and hence their tasks easier. Research funding has also been forthcoming for new developments as well as for demonstration projects.A natural question that arises is as to how to measure ISD characteristics of a process? Several researchers have worked on this [Trans. IChemE, Process Safety Environ. Protect. B 71 (4) (1993) 252; Inherent safety in process plant design, Ph.D. Thesis, VTT Publication Number 384, Helsinki University of Technology, Espoo, Finland, 1999; Proceedings of the Mary Kay O'Connor Process Safety Center Symposium, 2001, p. 509]. Many of the proposed methods are very elegant, yet too involved for easy adoption by the industry which is scared of yet another safety analysis regime. In a recent survey [Trans. IChemE, Process Safety Environ. Prog. B 80 (2002) 115], companies desired a rather simple method to measure ISD. Simplification is also an important characteristic of ISD. It is therefore desirable to have a simple ISD measurement procedure. The ISD measurement procedure proposed in this paper can be used to differentiate between two or more processes for the same end product. The salient steps are: Consider each of the important parameters affecting the safety (e.g., temperature, pressure, toxicity, flammability, etc.) and the range of possible values these parameters can have for all the process routes under consideration for an end product. Plot these values for each step in each process route and compare. No addition of values for disparate hazards (temperature, pressure, inventory, toxicity, flammability, etc.) is being suggested to derive an overall ISD index value since that conceals the effects of different parameters. Further, addition of numbers with different units ( degrees C for temperature, atm/bar for pressure, t for inventory, etc.) is inappropriate in scientific sense. The proposed approach has a major advantage of expanding consideration in future to incorporate economic, regulatory, pollution control and worker health aspects, as well as factors such as the experience one has or 'the comfort level' one feels with each of the processes under consideration. Additionally, it would also guide the designers and decision makers into affecting specific changes in the processes to reduce the unsafe features. We demonstrate our simple approach by using the example of six routes to make methyl methacrylate as documented by Edwards and Lawrence [Trans. IChemE, Process Safety Environ. Protect. B 71 (4) (1993) 252; Quantifying inherent safety of chemical process routes, Ph.D. Thesis, Loughborough University, Loughborough, UK, 1996] and show that the decision could well have been different if addition of disparate hazards had not been done.     

A simple method for measuring thoron spatial distributions

A simple but effective method that allows the measurement of the 220Rn spatial distribution in working or living environments using a solid-state detector is presented in this paper. The method is based on measurements of the alpha particles emitted by 216Po (the first 220Rn progeny) directly deposited on the detector surface at different distances from a 220Rn exhalation source. The validity of the method is shown by comparing the results of an experiment, where the 220Rn activity concentration is measured under conditions of diffusion at constant temperature, with finite-element calculations.     

A transient hot-wire method for measuring the thermal conductivity of gases and liquids

In this paper we describe a version of a transient hot-wire apparatus which employs an integrating digital voltmeter to measure the bridge out-of-balance signal. The integrating period of the voltmeter is variable and is routinely set equal to one 60-Hz power-line cycle, 16.67 ms. Use of measurement or integration periods less than an integral multiple of the power-line period results in substantially more electronic noise and a significant degradation in experimental precision. A correction to the working equation which accounts for the integration of the out-of-balance signal is also presented. The precision of the digital voltmeter used with the apparatus is ±0.1 V, which translates into an ultimate precision of ±0.03 mK in the measured temperature rise. In practice the precision in the temperature rise is typically ±0.3 mK, which represents a moderate improvement over the precision generally obtained with transient techniques employing automatic bridge balancing schemes. Although the current apparatus is designed principally for measurements of the thermal conductivity of liquids, it can been used for gas-phase measurements, with some decrease in accuracy due to the somewhat larger heat capacity correction which must be applied to the temperature rise measurements. The operation of the instrument was verified by measuring the thermal conductivities of toluene and nitrogen. Preliminary data are presented for the new environmentally acceptable fluorocarbons such as R-134a (CF₃CH₂F), R-123 (CHCl₂CF₃), and R-141b (CCl₂FCH₃).Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Simple model for scanning calorimeter with pyroelectric heat sensor

The heat-conduction equation is solved for a simplified model of a scanning heat-conducting calorimeter with a working cell in the form of a spherical pyroelectric thermometer. The optimum material and dimensions for the pyroelectric sensors are determined by numerical analysis of the solution.     

A cryostat for measuring specific heats of absorbed gases at low temperatures

A cryostat was designed and built for specific heat measurements of adsorbed gases on low thermal conductivity surfaces at low temperatures, without the use of a thermal switch. The calorimeter consists of five copper disks assembled with long ribbons of exfoliated graphite wound between them. The thermal time constant between the calorimeter and the cryostat's shield is about five hours at 4 K and the calorimeter's time constant is better than two minutes.     

A simple framework of spherical indentation for measuring elastoplastic properties

Based on the indentation load–displacement curve, spherical indentation may deduce material elastoplastic properties from the measurements at several depths (which mimics the dual/plural sharp indentation method). The previous approaches, however, have very complex formulations and involve many fitting parameters that lack theoretical backgrounds; moreover, studies based on shallow indentation may not lead to unique solution. To close these gaps, we propose a simple framework of spherical indentation based on a new limit analysis-based representative strain analysis, which contains minimum number of fitting parameters. Two simple equations of the normalized loading work (at two different depths) are proposed, which can determine the material plastic properties accurately from the loading curve. In addition, by using either the established Fischer-Cripps method or an extra equation based on the contact stiffness, both the elastic and plastic properties are determined with reasonable accuracy. The simple framework may be useful for guiding the measurement of elastoplastic properties via spherical indentation.     

Portable calorimeter for measuring absorbed doses of x-rays and electrons from accelerators

Translated from Izmeritel'naya Tekhnika, No. 11, pp. 56–58, November, 1991.