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The widescale adoption of most solar water-heating systems in colder climates is hampered by the fact that they require freeze protection, which inevitably leads to an increase in the unit cost. Integrated collector/storage solar water heaters (ICSSWH), due to their large thermal masses and simple compact structures, give good resistances to freezing in most climates. The experimentally determined performance of two full-size ICSSWHs for the winter period in Northern Ireland is reported. The ICSSWHs tested incorporated a novel heat-retaining storage vessel. Details of the performance of the two designs tested for 3 months over the winter period are presented in this paper.

The coupling between unsteady heat release and acoustic perturbations can lead to self-sustained thermoacoustic oscillations, also known as combustion instability. When such combustion instability occurs, the pressure oscillations may become so intense that they can cause engine structural damage and costly mission failure. Thus there is a need to understand the coupling physics between acoustic waves and unsteady combustion and to identify a measure to quantify the interaction between the flame and acoustics. The present work studies linear and nonlinear response of a conical premixed laminar flame to oncoming acoustic disturbances. Unsteady heat release from the flame is assumed to be caused by its surface area variations, which results from the fluctuations of the oncoming flow velocity. The classical G-equation is used to track the flame front variation in real-time. Second-order finite difference method is then used to expand the flame model. Time evolution of the flame surface distortions is successfully captured. To quantify the dynamic response of the flame to the acoustic disturbances, system identification is then conducted to estimate the linear and nonlinear flame transfer function. Good agreement is obtained. Finally, transfer function of an actuated open–open thermoacoustic system is experimentally measured by injecting a broad-band white noise. The present work opens up new applicable way to measure heat-driven acoustics transfer function in a thermoacoustic system by simply implementing white noise.

Abstract The conventional vapor-compression air-conditioner operates with low efficiency because of the intrinsic coupling between sensible and latent cooling. Its efficiency can be improved via employing solid desiccant coated heat exchangers (DCHEs). Dehumidification performance of a DCHE is influenced by the nature of the selected desiccant material. The key attributes of a desiccating material include higher sorption capacity and faster kinetics coupled with its ability to regenerate at a low temperature. In this paper, we developed different concentrations of composite polymer desiccant with polyvinyl alcohol (PVA) and lithium chloride (LiCl). Experiments on isotherms indicated that the composite PVA with a greater concentration of LiCl displayed superior sorption capacity; however, due to the occurrence of deliquescence phenomenon, the most effective concentration of LiCl was observed to be 50w%. The equilibrium sorption capacity of PVA-LiCl (50w%) was 177.2% in contrast to only 28% for silica gel. Further, kinetics revealed that silica gel would take twice the time to adsorb an equivalent amount of water vapor as absorbed by composite polymer desiccant. Our experimental findings on dehumidification performance and process efficacy revealed that the use of composite PVA on DCHEs yielded about 20–60% improvement in moisture removal capacity and thermal coefficient of performance. Lastly, energy analysis indicated that the novel composite polymer DCHE enabled high moisture removal rate even at lower regeneration temperature and recorded a significant saving of 54% in specific power consumption.

Abstract The dynamic behaviour of opaque components of the building envelope in steady periodic regime is investigated using parameters defined by the fluctuating heat flux that is transferred in the wall. The use of the heat flux allows for the joint action of the loadings that characterise both the outdoor environment and the indoor air-conditioned environment to be taken into account. The analysis was developed in sinusoidal conditions to determine the frequency response of the wall and in non-sinusoidal conditions to identify the actual dynamic behaviour of the wall. The use of non-dimensional periodic thermal transmittance is proposed for the sinusoidal analysis in order to evaluate the decrement factor and the time lag that the heat flux undergoes in crossing the wall as well as the efficiency of heat storage. In the presence of non-sinusoidal loadings, the identification of the dynamic behaviour of the wall is obtained using several dynamic parameters: the decrement factor in terms of energy, defined as the ratio between the energy in a semi-period entering and exiting the wall; the decrement factor and the time lag in terms of heat flux, considering the maximum peak and the minimum peak. These parameters allow for the identification of how the form of the heat flux trend crossing the wall is modified. The number of harmonics to be considered for an accurate representation of heat fluxes is determined by means of the introduction of the Total Harmonic Distortion (THD), which quantifies the distortion of a non-sinusoidal periodic trend compared to a sinusoidal trend. The methodology developed was used to evaluate the influence of external and internal loadings on the dynamic characteristics of two commonly used walls on a monthly and seasonal basis. The external loadings were changed considering two climatically different locations and different orientations of the walls; the internal loadings were changed by varying the operating mode of the plant and the shortwave radiative heat fluxes contributions on the inner surface.