Low frequency sound propagation in activated carbon

Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining the resonant frequencies of Helmholtz resonators with different backing materials. It was found that the addition of activated carbon increased the compliance of the backing volume. The effect was observed up to the highest frequency measured (500 Hz), but was most significant at lower frequencies (at higher frequencies another phenomenon can explain the behavior). An apparatus was constructed to measure the effective porosity of the activated carbon as well as the number of moles adsorbed at sound pressures between 104 and 118 dB and low frequencies between 20 and 55 Hz. Whilst the results were consistent with adsorption affecting sound propagation, other phenomena cannot be ruled out. Measurements of sorption isotherms showed that additional energy losses can be caused by water vapor condensing onto and then evaporating from the surface of the material. However, the excess absorption measured for low frequency sound waves is primarily caused by decreases in surface reactance rather than changes in surface resistance

The Intentional Use of Service Recovery Strategies to Influence Consumer Emotion, Cognition and Behaviour

Service recovery strategies have been identified as a critical factor in the success of. service organizations. This study develops a conceptual frame work to investigate how specific service recovery strategies influence the emotional, cognitive and negative behavioural responses of . consumers., as well as how emotion and cognition influence negative behavior. Understanding the impact of specific service recovery strategies will allow service providers' to more deliberately and intentionally engage in strategies that result in positive organizational outcomes. This study was conducted using a 2 x 2 between-subjects quasi-experimental design. The results suggest that service recovery has a significant impact on emotion, cognition and negative behavior. Similarly, satisfaction, negative emotion and positive emotion all influence negative behavior but distributive justice has no effect

Customer emotions in service failure and recovery encounters

Emotions play a significant role in the workplace, and considerable attention has been given to the study of employee emotions. Customers also play a central function in organizations, but much less is known about customer emotions. This chapter reviews the growing literature on customer emotions in employee–customer interfaces with a focus on service failure and recovery encounters, where emotions are heightened. It highlights emerging themes and key findings, addresses the measurement, modeling, and management of customer emotions, and identifies future research streams. Attention is given to emotional contagion, relationships between affective and cognitive processes, customer anger, customer rage, and individual differences

Acoustics of activated carbon

This thesis describes a study into how sound interacts with activated carbon, a material that exhibits adsorbing and desorbing properties. Adsorption is where molecules from the surrounding gas are attracted to the material microstructure and held in place by a weak physical attraction force named after the scientist van der Waals\ desorption is the opposite process. Activated carbons include a complex porous structure, with a large internal surface area, and a considerable adsorption capacity caused by free electrons in the deformed graphene layers. The process of adsorption and desorption is usually associated with energy exchanges, caused by transfers of heat between the adsorbate molecules and the adsorbent surface.The study of acoustic interactions with granular activated carbons at normal conditions makes the subject of this doctoral thesis. Two main physical phenomena were seen to accompany sound propagation through the material: (i) an increase in volume compliance which is assumed to be caused by a change in the density of the interacting gas, and (ii) excess absorption at low frequencies thought to be due to the energy lost in the adsorption/desorption hysteresis. For the former, measurements on the impedance of low frequency Helmholtz resonators reveal significant shifts in resonance when activated carbon is used as a porous liner in the backing volume. At constant aperture dimensions, these shifts are attributed to a larger apparent volume of the resonator as compared to an empty backing volume. This phenomenon is in direct contravention of the physical theory associated with Helmholtz resonators as the resonant frequency of a device increases slightly when a porous solid is placed in the backing volume. An upper frequency limit of SOOHz is also determined where sorption effects in activated carbon are assumed to become almost negligible in relation to sound propagation.For the latter, the excess absorption at low frequency, a series of experiments to reveal the physical cause of the phenomenon have been undertaken. Hysteresis was observed during the sorption of humid air onto activated carbon at room temperature. At such conditions, the different rates of adsorption and desorption lead to a disturbance in the system equilibrium and cause a change in entropy. The return of the system to equilibrium is an exothermic process hence involves energy losses between activated carbon and the surrounding gas. This is suggested as a possible cause of the excess attenuation. However,the relaxation times are rather long for acoustic propagation, and further work is needed to examine this.An experimental apparatus to explore sound propagation through the material was devised. Results showed a violation of the equation of state for the relationship between volume and pressure: as the volume in a sealed chamber was reduced at constant temperature, the measured pressure change was found to be lower for a sample of activated carbon than when the chamber was empty; a phenomenon assumed due to the differences between adsorption and desorption rates.A new method for determining the porosity of a material exhibiting adsorption at acoustic pressures has been devised and found to be 81 ±7% for the granular sample examined. BET analysis and examination of electron microscope pictures allowed the pore size distribution to be found. Although the activated carbon sample has many very small pores (0.7nm in width), the BET isotherm showed that these will be saturated with water vapour in normal conditions. Consequently, the pores that affect sound propagation are those between the grains of the activated carbon, and the macropores (>50nm) on the surface of the grains.A theoretical model is developed and outlined based on the Langmuir isotherm. This was used to predict the sound propagation within the material and is compared to acoustic impedance measured in a large low frequency impedance tube, which was constructed especially for this project. The match between theory and measurement is rather poor, thought to be due to the lack of modelling the hysteresis effects in the adsorption- desorption cycle.Two applications of the material are examined, within a Helmholtz resonator and the cups of hearing defenders. In both cases, improved performance is seen. For instance, the use of the material in hearing defenders showed that activated carbon could be used to improve the attenuation at low frequencies in comparison to conventional foam liners