Solar photovoltaic and thermal systems are potential solutions for current energy needs. One of the most important difficulties in using photovoltaic systems is the low energy conversion efficiency of PV cells and, furthermore, this efficiency decreases further during the operational period by increasing the cells temperature above a certain limit. In addition, reflection of the sun's irradiance from the panel typically reduces the electrical yield of PV modules by 8-15%. To increase the efficiency of PV systems one way is cooling them during operation period. In this experimental study combination of a PV system cooled by a thin film of water with an additional system to use the heat transferred to the water has been considered. Experimental measurements for both combined system and conventional panel indicate that the temperature of the photovoltaic panel for combined system is lower compared to the conventional panel. The results show that the power and the electrical efficiency of the combined system are higher than the traditional one. Also since the heat removed from the PV panel by water film is not wasted, the overall efficiency of the combined system is higher than the conventional system.

The interplays between acoustic and intrinsic modes in a model of a Rijke burner are revealed and their influence on the prediction of thermoacoustic instabilities is demonstrated. To this end, the system is examined for a range of time delays, temperature ratios and reflection coefficients as adjustable parameters. A linear acoustic network model is used and all modes with frequency below the cut-on frequency for non-planar acoustic waves are considered. The results show that when reflection coefficients are reduced, the presence of a pure ITA mode limits the reduction in the growth rate that usually results from a reduction of the reflection coefficients. In certain conditions, the growth rates can even increase by decreasing reflections. As the time delay of the flame and thus the ITA frequency decreases, the acoustic modes couple to and subsequently decouple from the pure ITA modes. These effects cause the maximum growth rate to alternate between the modes. This investigation draws a broad picture of acoustic and intrinsic modes, which is crucial to accurate prediction and interpretation of thermoacoustic instabilities.

One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we explore whether a heat exchanger, an integral component of a domestic boiler, can be made to act as a passive controller that suppresses combustion instabilities. The combustor is modelled as a quarterwave resonator (1-D, open at one end, closed at the other) with a compact heat source inside, which is modelled by a time-lag law. The heat exchanger is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the heat exchanger as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the heat exchanger is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function, which is the response of the heat transfer at heat exchanger to upstream velocity perturbations. Combining the aeroacoustic response and the heat exchanger transfer function, in the limit of the distance between these processes tending to zero, gives the net influence of the heat exchanger. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Our model predicts that stability can be achieved for a wide range of parameters.

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A large number of rubber products are formed into their final shape by vulcanization. In particular, curing process of rubber is the final step in manufacturing many rubber products and determines both the quality of the resulting product as well as production costs. This paper is devoted to the simulation of rubber curing process in a three-dimensional model. The effects of final temperature of mold are investigated on curing process and quality of final product. The results were compared with the experimentally measured data, which confirmed the accuracy and applicability of the method.