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This article presents the heat transfer augmentation in a solar air heater (SAH) using arc-shaped ribs with multiple gaps. Multiple gaps in arc-shaped ribs are used to enhance the heat transfer by interrupting the growth of the boundary layer. Thermal performance analysis of a SAH has been carried out experimentally for the roughness parameters: number of gaps (Ng) ranging from 2 to 5 and flow parameters; Reynolds number (Re) ranging from 3000 to 18000 at a constant heat flux of 1000 W/m2. The data obtained from the experimental investigation are validated and compared with the smooth duct under similar conditions. For roughened SAH duct, the heat transfer and pressure drop are found to be 274% and 169% higher than that for smooth SAH duct at Ng = 3. Thermo-hydraulic performance is determined for considered parameters and maximum value is observed to be 2.75. [ABSTRACT FROM AUTHOR]

Earth air tunnel heat exchanger (EATHE) is a promising passive technique to provide thermal comfort condition in buildings. EATHE system uses undisturbed temperature of the ground for heating/cooling of air. Despite the several advantages, this technique has not become much popular owing to its high capital cost (mainly pipe cost and trench excavation cost) and large land area requirements. The primary objective of this study is to present a comprehensive review of different EATHE pipe layouts, pipe properties and positioning of the pipe with their advantages and limitations. It is observed that the ring pipe layout is the most cost-effective pipe-layout for small size EATHE system because it saves excavation cost by using a trench of the existing foundation of the building. However, Grid pipe-layout is an ideal layout for a large size EATHE system. Multi-layer pipe layouts should be used to reduce the land area requirement significantly. Moreover, EATHE system can be installed beneath the building (under building foot-print) to eliminate extra land area requirement for the installation of EATHE system. This review article shows that the Initial capital cost and land area requirement for the EATHE system can be substantially reduced by using appropriate pipe layout. It can be concluded that if EATHE system is installed with proper design strategies, it will be a clean and cost-effective method for building heating/cooling with significant power savings. [ABSTRACT FROM AUTHOR]

A comparative experimental study of two box-type solar cookers with different cooking environments was conducted. The first one with natural convection heat transfer-based and the second one with forced convection heat transfer (fan for flow augmentation)-based environment. The experimental results show that the forced convection-based environment remarkably improves the thermal performance of box-type solar cooker. Forced convection-based cooker is able to cook food at much faster rates compared with natural convection-based cooker. This reduces the cooking time considerably. Results of thermal performance tests show (i) stagnation absorber plate temperatures of 133.9°C and 119.3°C and (ii) boiling times of 52 min (3120 s) and 75 min (4500 s) for heating 1 kg of water, for the cooker with and without fan, respectively. The solar cooker performance has been rated using the first figure of merit (F1) on the no-load test and the second figure of merit (F2) on the sensible heat tests. The cooking time was considerably reduced by 30.6%. The tests were carried out on the research unit in Government Engineering College Ajmer, Rajasthan located at 26°27′ N latitude and 74°42′ E longitude in India. [ABSTRACT FROM PUBLISHER]

Nanosized C-doped TiO2 was prepared by a new method based on resorcinol-formaldehyde (RF) gel formation in situ during hydrolysis of Ti precursor (TTIP, titanium tetraisopropoxide). XRD, DRS, EDX, SEM and HRTEM results confirmed that the carbon in the sample existed as free carbon (C-C), carbonate carbon (-CO3) and doped into lattice of TiO2(Ti-C), resulting in red shift of optical adsorption edge and band gap narrowing. The photo activity of the C-doped TiO2, tested on 2-chlorophenol, revealed that it was more active under visible light (kvis= 3.50 × 10-3 min-1). [ABSTRACT FROM AUTHOR]