Henrik Bjurström

An exergy analysis of sensible and latent heat storage

An analysis of sensible and latent heat storage units is performed in both energy and exergy terms. The stores are compared, through variation of design parameters for both charging and discharging ...

Thermal conductivity of a microporous particulate medium: moist silica gel

A systematic study of the thermal conductivity of beds of moist silica gel is presented. The influence of porosity, water content, total gas pressure and temperature is determined through measurements under transient conditions with the transient hot-strip (THS) method and under static conditions in a bench-scale reactor. The predictions of the effective thermal conductivity of the beds from four different simple models (Russell, geometric mean value, unit-cell model and stochastic model) agree reasonably well with the experimental results. The unit-cell model is extended in order to account for the water sorbed in the micropores and describes satisfactorily the dependency of the effective thermal conductivity on the water content.

Experimental and theoretical investigation of the kinetics of the sorption of water vapour by silica gel

The kinetics and mechanism of the sorption reaction between water vapour and silica gel have been investigated in the pressure range 1–50 Torr using thermogravimetry under controlled temperature and water-vapour pressure. Measurements at equilibrium were carried out in order to determine the pertinent equilibrium parameters and the extent of hysteresis. The influence of particle radius and temperature on the kinetics in the whole of the pressure range investigated are well described by theoretical curves fitted to experimental data by taking into account simultaneous mass- and heat-transfer. Calculations yield a diffusivity of 8 × 10–10 m2 s–1. The sorption kinetics in the pressure range 15–40 Torr are shown to be controlled by heat transfer.

Detecting the thickness mode frequency in a concrete plate using backward wave propagation

Material stiffness and plate thickness are the two key parameters when performing quality assurance/quality control on pavement structures. In order to estimate the plate thickness non-destructively, the Impact Echo (IE) method can be utilized to extract the thickness resonance frequency. An alternative to IE for estimating the thickness resonance frequency of a concrete plate, and to subsequently enable thickness determination, is presented in this paper. The thickness resonance is often revealed as a sharp peak in the frequency spectrum when contact receivers are used in seismic testing. Due to a low signal-to-noise ratio, IE is not ideal when using non-contact microphone receivers. In studying the complex Lamb wave dispersion curves at a frequency infinitesimally higher than the thickness frequency, it is seen that two counter-directed waves occur at the same frequency but with phase velocities in opposite directions. Results show that it is possible to detect the wave traveling with a negative phase velocity using both accelerometers and air-coupled microphones as receivers. This alternative technique can possibly be used in non-contact scanning measurements based on air-coupled microphones.

Air-coupled detection of the S1-ZGV lamb mode in a concrete plate based on backward wave propagation

Impact Echo is commonly used to determine thickness of concrete plate like structures. The method is based on the generation and detection of the plate thickness resonance frequency, where the group velocity of the first higher symmetric Lamb mode goes to zero (S1-ZGV). When using air-coupled microphones as receivers it is hard to determine the correct resonance frequency due to low signal to noise ratio. In this study multichannel signal processing is used to identify the S1-ZGV frequency, based on backward wave propagation instead of the conventional amplitude spectrum approach.The original PDF file of this article, as supplied to AIP Publishing, contained some minor font problems within Figures 1, 4, 7, 8, and 9. An updated PDF file using the correct font within those figures was issued on June 3, 2013. There are no other changes to the scientific content.

Non-contact rolling surface wave measurements on asphalt concrete

Rolling surface wave measurements on a single, thin asphalt concrete (AC) layer are presented to investigate their use in rapid nondestructive field tests. An array of 47 micro-electro-mechanical sensor (MEMS) microphones is mounted on a trailer together with an automated impact source. Multichannel recordings from single impacts are obtained at 80 equally spaced array positions as the trailer moves at a constant speed. The complete battery-powered data acquisition system enables large-scale testing of newly built pavements. Multiple sets of test results show good repeatability for the assessed shear wave velocity and demonstrate the strong temperature dependency of AC. The presented results indicate a possible application for quality assurance of AC using rolling surface wave measurements.

Effect of surface unevenness on non-contact surface wave measurements using a rolling microphone array

Surface wave velocity is measured and evaluated along a straight survey line in order to compare two different data acquisition methods. Results from a rolling microphone array are compared to data acquired using a conventional accelerometer. Results from the two different data acquisition methods are shown to be similar. However, it is demonstrated that the results are very sensitive to misalignments between the microphone array and the measured surface. Practices to overcome problems with misalignments are discussed and demonstrated.