Solar Engineering Of Thermal Processes

Solar and Terrestrial Radiation

Solar air heaters (SAHs) form the foremost component of solar energy utilization system. These air heaters absorb the irradiance and convert it into thermal energy at the absorbing surface and then transfer this energy to a fluid flowing through the collector. SAHs are inexpensive and most used collection devices because of their inherent simplicity. SAHs are found in several solar energy applications, especially for space heating, timber seasoning and agriculture drying. It has been observed by studying the previous literature that all the elements of a solar air heater such as; an absorber tray, the ducts, glazing, insulation, extended surfaces, as well as the tilt angle, have a significant effect on the thermal performance of the system. This review article focus on the developments that has followed round the globe in various aspects of solar air heating systems since 1877 up to now, with a glimpse of some novel patents of SAHs. The various methods that are used to improve the thermal performance of SAHs such as; optimizing the dimensions of the air heater construction elements, use of extended surfaces with different shapes and dimensions, use of sensible or latent storage media, use of concentrators to augment the available solar radiation, integrating photovoltaic elements with the heaters, etc, are also reported. Besides this, some benefits by using the SAHs has been discussed.

A thermodynamic review of solar air heaters

Experimental study of heat transfer and thermal performance with longitudinal fins of solar air heater.

This paper reviews various kinds of heat storage materials, their composites and applications investigated over the last two decades. It was found that sensible heat storage systems are bulkier in size as compared to the latent heat storage systems. Latent heat storage system using phase change materials (PCMs) stores energy at high density in isothermal way. Various geometries of PCM containers used for enhancement of heat transfer area, materials used for the construction of PCM containers and their interaction with heat storage materials are studied. The choice of storage material depends on the desired temperature range, application of thermal storage unit and size of thermal storage system. Low temperature heat storage system uses organic phase change materials while inorganic phase change materials are best suited for high temperature heat storage. Heat transfer within the PCM can be enhanced by preparing composite of high thermal conductivity as well as by altering the geometrical design like addition of fins, use of straight and helical tubes etc. Shell and tube configurations were mostly used for thermal storage systems. Heat transfer enhancement using PCM composite is a promising approach as it reduces cost and bulkiness to the system.

Heat storage materials, geometry and applications: A review

Transparent conducting Co doped ZnO thin films have been fabricated by Ultrasonic spray. The thin films were deposited at three different substrate temperatures of 300, 350 and 400 °C. The obtained films had a hexagonal wurtzite structure with a strong (002) preferred orientation. The maximum crystallite size value of the film deposited at 350 °C is 55.46 run. Spectrophotometer (UV-vis) of a Co doped ZnO film deposited at 350 °C shows an average transmittance of about 90%. The band gap energy increased from 3.351 to 3.362 eV when the substrate temperature increased from 300 to 350 °C. The electrical conductivity of the films deposited at 300, 350 and 400 °C were 7.424, 7.547 and 6.743 (Ω·cm)−1 respectively. The maximum activation energy value of the films at 350 °C was 1.28 eV, indicating that the films exhibit a n-type semiconducting nature.

https://iopscience.iop.org/article/10.1088/1674-4926/33/9/093001/pdf

Effect of substrate temperature on the stability of transparent conducting cobalt doped ZnO thin films

This paper examines the growth of ZnO thin films on glass substrate at 350 °C using an ultrasonic spray technique. We have investigated the influence of growth time ranging from 1 to 4 min on structural, optical and electrical properties of ZnO thin films. The as-grown films exhibit a hexagonal structure wurtzite and are (002) oriented. The maximum value of grain size G = 63.99 nm is attained for ZnO films grown at 2 min. The average transmittance is about 80%, thus the films are transparent in the visible region. The optical gap energy is found to increase from 3.26 to 3.37 eV with growth time increased from 1 to 2 min. The minimum value of electrical resistivity of the films is 0.13 Ωcm obtained at 2 min. A systematic study on the influence of growth time on the properties of ZnO thin films deposited by ultrasonic spray at 350 °C has been reported.

Influence of growth time on crystalline structure, conductivity and optical properties of ZnO thin films

A comparative study on the nanocrystalline ZnO thin films prepared by ultrasonic spray and solgel method

This paper presents a thermal performance of a single pass solar air heater with fins attached was investigated experimentally. Longitudinal fins were used inferior the absorber plate for an increase the heat exchange and uniform the flow fluid in the channel. The effects of mass flow rate of air on the outlet temperature, the heat transfer in a thickness of solar collector and thermal efficiency were studied. Experiments were performed for two air mass flow rates of 0.012 kg/s., Moreover; the maximum efficiency was obtained by using five longitudinal fins and without fins. The maximum efficiency obtained for the 0.012 kg/s with and without fins were 40.02 % and 34.92 %, respectively. Comparison of the results as an effect the solar collector’s with and without fins shows a substantial enhancement in the thermal efficiency.

https://papers.itc.pw.edu.pl/index.php/JPT/article/view/369/518

Foued Chabane

Papers

Experimental study of heat transfer and thermal performance with longitudinal fins of solar air heater.

Effect of substrate temperature on the stability of transparent conducting cobalt doped ZnO thin films

Influence of growth time on crystalline structure, conductivity and optical properties of ZnO thin films

A comparative study on the nanocrystalline ZnO thin films prepared by ultrasonic spray and solgel method

Experimental analysis on thermal performance of a solar air collector with longitudinal fins in a region of Biskra, Algeria