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The use of solar air heaters (SAH) for the collection and effective utilization of solar radiations for thermal applications is widely reported in the literature. The current article aimed to present a comprehensive literature review on history, fundamentals and the latest advancement reported in the field of solar thermal air heating systems. Various designs of solar collectors viz, evacuated tube, flat plate, multiple passages, a cross-section of the flow passage, etc. are reported and discussed. Techniques which are used for performance enhancement of SAHs such as artificial roughness, fins, baffles, vortex generators, etc. are discussed and a comparative performance assessment has been carried to identify thermohydraulic performance parameter to select the optimum configuration that can be further used for applications. A few key recommendations are also concluded from the literature for the effective design and implementation of the SAHs.

The bruchid, Callosobruchus maculatus is a serious pest of stored pulses. Four biophysical seed characteristics viz. Seed size, texture of seed surface, thickness of seed coat and seed hardness of 10 genotypes of rice bean, a wild pulse crop were investigated for assessing mechanism of resistance against C. maculatus. Oviposition preference and larval penetration in seed coat did not differ significantly among different test genotypes. Highest number of larvae which developed up to last larval/pupal instar were observed in susceptible check variety of mungbean, PAU 911 (30.00) and lowest in rice bean genotype, LRB 535 (0.83). Highest and lowest seed weight was noticed in rice bean genotype, LRB 529 (6.81 g) and PAU 911 (3.88 g), respectively. Almost similar seed coat thickness was recorded among different test genotypes. Maximum seed hardness was noted in genotype LRB 507 (6.45 kg) whereas minimum in PAU 911 (2.00 kg) among all test genotypes. Any remarkable correlation of biophysical seed characteristics of test genotypes with ovipositon, larval penetration and development of C. maculatus was not observed. Thus, biophysical seed characteristics of rice bean did not suggest to play a vital role in imparting resistance against C. maculatus.

A walk-in type solar greenhouse dryer supplemented with solar air heating system has been developed with an objective of sustainable development. One of its novel features is the use of an evacuated tube solar air heating system with the greenhouse dryer to achieve required drying temperature for different products in north India plains. This dryer was tested in laboratory in both batch and semi-continuous mode for turmeric (Curcuma longa). The open sun drying was used as control. The thermal efficiency of the dryer for batch and semi-continuous drying obtained are 18.5% and 22.5% respectively. Drying time in comparison to open sun drying has been found to be 55% approximately. The quality of dried turmeric obtained using this dryer is superior to open sun drying in terms of polishing loss, curcumic content, volatile oil content and colour. Its energy payback period and cost payback period were estimated as 2.95 and 1.10 years, respectively, which is very low as compared to its life of 20 years. In the entire lifetime, the CO2 mitigation was found to be 209.21 tons, which proves its suitability.

In present paper, solar air heater duct having aspect ratio 12 roughened with broken arc rib has been investigated. The broken arc is formed by creating symmetrical gap in continuous arc with gap width equal to roughness height. It has been planned to investigate the influence of position of gap in arc rib on Nusselt number as well as on friction factor. For this purpose, five broken arc rib roughened plates having relative gap position ranging 0.2–0.8 have been investigated for values of Reynolds number 2000–16000. The remaining roughness parameters like relative roughness height, arc angle, and relative roughness pitch were taken as 0.043, 30o and 8 respectively. The presence of broken arc ribs enhanced the Nusselt number, friction factor and thermo-hydraulic performance up to 2.37, 2.55 and 1.94 respectively, compared to smooth duct. The results of ducts roughened with broken arc rib and continuous arc rib have been compared under similar flow conditions. The effect of gap in continuous arc rib on the flow pattern has also been observed using ANSYS Academic Research CFD 15.0.

This paper presents an experimental investigation on heat transfer and friction factor characteristics of solar air heater duct whose absorber is roughened with “broken arc rib combined with staggered rib piece”. The duct has aspect ratio of 12 and the absorber is heated with uniform heat flux while others three walls are insulated. The rib roughness has fixed relative staggered rib position, relative roughness height, relative gap size, relative gap position, arc angle and relative roughness pitch of 0.4, 0.043, 1.0, 0.65, 30° and 10 respectively. The relative staggered rib size and Reynolds number were varied from 1 to 6 and 2000 to 16,000 respectively. The effect of staggered rib on the flow pattern has also been observed using ANSYS Academic Research CFD 15.0. The maximum enhancement in Nusselt number and friction factor over that of broken arc rib roughened duct under similar flow and boundary conditions has been found to be 2.60 and 2.27 times respectively. The corresponding enhancements over that of smooth duct are 3.06 and 2.50 times respectively. The thermo-hydraulic performance of duct roughened with present rib roughness has been considerably enhanced and was found to be highest for relative staggered rib size of 4.

The article presents experimental and computational investigation of solar air heater using hybrid configuration of broken arc and staggered rib for heat transfer enhancement. The performance of the solar air heater is investigated through a series of experimental trials by varying flow and geometrical parameters like non-dimensional staggered rib position (0.2–0.8), roughness pitch (4–12), gap width (0.5–2.5), gap position (0.2–0.8), roughness height (0.022–0.043), arc angle (15°-75°), staggered rib piece size (1–6), and Reynolds number(2000–16000). The impact of staggered rib on the fluid flow pattern has been observed using numerical approach based on Finite volume method. The proposed design increases the friction factor & Nusselt number by 2.57 and 3.16 times respectively in comparison with a smooth duct. Moreover, the Nusselt number augments by 1.22 times in comparison with broken arc rib. The optimum values of both the flow and geometric parameters are evaluated and empirical correlations for pressure loss & Nusselt number are also reported. It is concluded that the thermal–hydraulic performance of the proposed hybrid rib roughness (2.33) is found to be superior in comparison with similar rib roughness geometries.

This article presents a novel active-mode indirect solar dryer consisting of highly efficiency through-flow evacuated tube collector for air heating. A DC fan powered with solar photovoltaic (PV) module is provided for forced air flow through this dryer. The dehydration chamber is of tray type with loading capacity of 6 kg–45 kg depending on the drying product. The dryer was evaluated to dry fenugreek leaves (Trigonella foenum-graecum) and turmeric (Curcuma longa) in semi-continuous mode; and respective overall thermal efficiency was found to be 34.1% and 23.6%. The respective thermal efficiency in open sun drying (OSD) was 5.7% and 5.4%. The quality of dried fenugreek leaves and turmeric was found better than OSD. Economics of the solar dryer indicate the capital cost is negligible in comparison to cumulative present worth of life cycle savings. The values are 211,262 INR (1 US$ = 74.57 INR) and 229,152 INR respectively for fenugreek leaves and turmeric; and capital cost of the dryer is only 50,000 INR. The low value of payback period also confirms economic viability of this dryer. The generalized economic curves have also been plotted.

In present experimental investigation, solar air heater duct with aspect ratio 12 roughened with broken arc rib has been investigated. The broken arc was formed by creating symmetrical gap in continuous arc. To investigate the influence of roughness parameters of broken arc rib on Nusselt number as well as on friction factor, thirty-seven broken arc rib roughened plates having relative roughness pitch (P/e), relative gap width (g/e), relative gap position (d/w), relative roughness height (e/Dh) and arc angle (α) varying from 4 to 12, 0.5 to 2.5, 0.2 to 0.8, 0.022 to 0.043 and 15° to 75° respectively, have been investigated for Reynolds number range of 2000–16,000. Keeping similar flow conditions, results of broken arc rib roughened duct have been compared with smooth and continuous arc rib roughened ducts. The maximum increase in Nusselt number and friction factor over that of continuous arc rib roughened duct was 1.19 and 1.14 times respectively. The corresponding values over that of smooth duct were 2.63 and 2.44 times respectively. Experimental results of heat transfer and friction in flow have also been correlated in terms of flow and roughness geometry parameters.

A 3-dimensional CFD (computational fluid dynamics) investigation has been carried out to study the heat transfer and friction characteristics of solar air heater duct roughened with periodic transverse rib. The selected rib roughness is a new concept; it has non-uniform cross-section in the form of saw-tooth. For comparison, transverse ribs with uniform cross-section of circular, square and trapezoidal have also been investigated. The Nusselt number and friction factor have been determined for Reynolds number range of 3000–15,000. The k-e turbulence model was selected for analysis. The non-uniform cross-section saw-tooth rib was found to result in higher Nusselt number than uniform cross-section ribs for Reynolds number above 7000 due to reduced low heat transfer area downstream of the rib caused by disruption in re-circulations. The maximum enhancement in Nusselt number for duct roughened with saw-tooth rib and trapezoidal rib was 1.78 and 1.50 respectively. The friction factor was found to be lower for saw-tooth rib as compared to uniform cross-section ribs investigated. The maximum enhancement in friction factor for duct roughened with saw-tooth and trapezoidal rib was 2.49 and 3.58 respectively.

Two low cost solar air heaters viz. single glazed and double glazed were designed, fabricated and tested. Thermocole, ultraviolet stabilised plastic sheet, etc. were used for fabrication to reduce the fabrication cost. These were tested simultaneously at no load and with load both in summer and winter seasons along with packed bed solar air heater using iron chips for absorption of radiation. The initial costs of single glazed and double glazed are 22.8% and 26.8% of the initial cost of packed bed solar air heater of the same aperture area. It was found that on a given day at no load, the maximum stagnation temperatures of single glazed and double glazed solar air heater were 43.5 °C and 62.5 °C respectively. The efficiencies of single glazed, double glazed and packed bed solar air heaters corresponding to flow rate of 0.02 m3/s-m2 were 30.29%, 45.05% and 71.68% respectively in winter season. The collector efficiency factor, heat removal factor based on air outlet temperature and air inlet temperature for three solar air heaters were also determined.

Since the New York outbreak in 1999, West Nile Virus (WNV) has spread across the United States and North America. The spectrum of disease may range from asymptomatic to debilitating neuroinvasive. We present a case of a woman with myasthenia gravis on immunosuppressive therapy who developed WNV meningoencephalitis presenting as flaccid paralysis and severe bilateral hearing loss. To our knowledge this is the first reported case of WNV-associated hearing loss, and the first reported in a patient with previously diagnosed myasthenia gravis. Of epidemiologic interest was that her mother, 81 years old and in previous good health, developed a WNV infection shortly before the patient's infection.