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In this article, thermal performance of a solar air heater (SAH) having broken arc-shaped ribs has been investigated experimentally, and then, performance parameters have been optimized. Study reveals that the use of artificial roughness enhances both heat transfer rate and pumping power requirement, and hence, the overall performance of solar air heater increases. Thus, it is imperative to optimize the performance-defining criteria viz. Nusselt number enhancement ratio, friction factor enhancement ratio, and thermohydraulic performance parameter, to propose an optimal set of flow and roughness parameters. The hybrid entropy-VIKOR technique has been employed to outline the optimal set of parameters using performance-defining criterions, to obtain maximum profit with the minimum incurred cost. The optimal set of parameters attained using entropy-VIKOR approach among all the alternatives is as follows: relative gap width = 4, relative roughness pitch = 10, and arc angle = 45 deg at Reynolds number = 9000. [ABSTRACT FROM AUTHOR]

In the present experimental work, two identical real field experimental setups (with dry soil and wet soil) of ground-air heat exchanger (GAHE) have been developed in order to evaluate the influence of change in inlet air temperature, airflow velocity, diameter of pipe and soil moisture content on the thermal performance of GAHE system. Influence of these parameters on the required pipe length to produce a specified drop in air temperature has also been investigated. Results reveal that the drop in air temperature achieved from GAHE having dry soil is 11.2 °C at 60 m pipe length, whereas, for GAHE with wet soil having 20% moisture, the same amount of drop in air temperature is obtained at a pipe length of 28 m only. Moreover, upon increasing the airflow velocity from 2 m/s to 10 m/s, cooling capacity of GAHE with dry soil, wet soil with 5% moisture and wet soil with 20% moisture increases by 122%, 185% and 220%, respectively, after 6 h of operation, but the effectiveness of the GAHE system with dry soil, wet soil with 5% moisture and wet soil with 20% moisture decreases by 55.4%, 42.5% and 36.2%, respectively. • Development of an outfield experimental set up for GAHE system with dry and wet soil. • 53% length of GAHE pipe can be reduced by using wet soil with 20% moisture. • By increasing air flow velocity 2 m/s to 10 m/s, cooling capacity increases 220% in wet soil. • By increasing air flow velocity 2 m/s to 10 m/s, effectiveness decreases 36.2% in wet soil. • Required length of GAHE pipe highly depends on soil moisture, air velocity and pipe diameter. [ABSTRACT FROM AUTHOR]

Thermal performance of ground-air heat exchanger (GAHE) depends on the rate of heat transfer between air and soil, which is governed by thermal properties of soil surrounding the GAHE pipe. Soil thermal properties around GAHE pipe can be improved either by increasing its moisture contents or by using some thermally enhanced backfilling materials. In the present study experimentally investigates the thermal performance of ground-air heat exchanger system using a sand-bentonite mixture (dry as well as wet) and compare their performance with the ground air heat exchanger system having native soil (dry as well as wet) as backfilling material. The study acknowledges the highest cooling capacity (125 W) for GAHE with wet sand-bentonite as backfilling material, and after 6 h of continuous operation, it is 38.4%, 18.4% and 11.1% higher than that obtained with dry native soil, dry sand-bentonite and wet native soil, respectively. The study also revealed that thermal performance deterioration factor (TPDF) increases with the duration of the operation. At airflow velocity of 5 m/s, after 6 h of continuous operation highest TPDF is noticed for ground-air heat exchanger with dry soil (0.22); whereas, lowest TPDF is observed for ground-air heat exchanger system with wet sand-bentonite (0.07). Schematic of laboratory experimental setup of GAHE system. Image 1 • Development of a laboratory scale experimental set up for GAHE system. • To evaluate the effect of sand-bentonite backfilling material (dry as well as wet) on performance of GAHE system. • Maintaining a certain level of moisture into the soil in the close vicinity of GAHE pipe. • Better thermal performance of GAHE due to BFM resulting reduction in required pipe length. [ABSTRACT FROM AUTHOR]

• Earth air heat exchanger system is one of the promising passive techniques for building heating and cooling application. • Efficiency and utility of the EAHE system increase by coupling it with other active/passive systems. • EAHE system may be a good option for pre-heating and pre-cooling of air in industrial applications. • Large land area required to install EAHE is a major constraint for the adaptability of EAHE system in urban areas. • The required pipe length of EAHE can also be reduced by using soil of high thermal conductivity at the vicinity of the pipe. Earth air heat exchager (EAHE) is a promising passive technique that utilises the constant temperature of the underground soil for heating/cooling of air. The EAHE system possesses several advantages and can be used stand-alone as well as in hybrid mode for heating/cooling of air for building and commercial/ industrial applications. This article reviews the available literature pertaining to technology integration and applications of earth air heat exchanger system in the last four decades and also account for the recent significant developments in EAHE to indicate the emerging trends in the domain. The comprehensive review of the literature suggests that a standalone EAHE system can does not cater the requirements of thermal loads entirely and therefore has not grown much popular and still vying for commercial/ industrial applications, worldwide. The requirement of auxiliary devices so as to supplement the standalone EAHE system to achieve thermal comfort conditions entailing huge expenses conflicts the economics of the hybrid EAHE systems. The exorbitantly increasing costs of pipes, land and labour necessitate the paradigm-shift in the major thrust of the research associated with thermal comfort so as to incorporate the economics of system as a whole to enhance the acceptability of EAHE system. [ABSTRACT FROM AUTHOR]

Earth air tunnel heat exchanger (EATHE) systems are inadequate to meet the thermal comfort requirements in semi-arid regions as they require large pipe lengths. The effectiveness and performance of such system can be increased by increasing soil moisture content, making as wet soil configuration. In the present work, the thermal performance of the EATHE system with dry and wet soil has been evaluated during the peak summer season. Further, the thermal behavior of these two EATHE systems has been compared on the basis of temperature of air flowing through buried pipes at different sections along the length. For the same a theoretical model is developed and validated with experimental results and found in good agreement with an error ranging from 2.44% to 10.85%. Moreover, the exergetic analysis has been carried outto investigate the work potential and scope of maximum utilization of energy. Results reveal that thepipe length can be reduced by 12–14 m with wet EATHE system as compared to dry EATHE system for the same cooling performance. The second law analysis shows that the maximum exergetic efficiency is 52.25% and 53.18% for dry and wet soil EATHE systems respectively. [ABSTRACT FROM AUTHOR]

An EATHE system performs well for short periods but its thermal performance gets deteriorated during long continuous operation due to sub-soil thermal saturation in the vicinity of buried pipe. Effect of soil thermal saturation can be reduced to some extent in longer EATHE pipe but it is uneconomical. In the present study sub-soil moisture content is increased to enhance soil thermal properties and its effect on EATHE thermal performance and pipe length requirement for certain temperature drop has been investigated experimentally for summer cooling in hot and arid climate. In the study, two identical experimental set-ups have been developed at Ajmer city (India). A water impregnation system has been introduced to maintain different soil moisture contents in the close proximity of EATHE pipe. Knee point is obtained at a length of 29 m, 28 m, 27 m and 26 m from pipe inlet section with 5%, 10%, 15% and 20% moisture in sub-soil respectively, as compared to 41 m length in dry soil, after 10 h of continuous operation. The average heat transfer rate and COP increased by 24.1% and 24.0% respectively for 20% moisture content at 30 m EATHE pipe length as compared to dry system. [ABSTRACT FROM AUTHOR]

In the present research thermal performance of earth air tunnel heat exchanger (EATHE) coupled with a solar air heating duct has been experimentally evaluated for arid climate of Ajmer city of northwestern India, during winter season. An attempt has been made to enhance the heating capacity of EATHE system by coupling it with a solar air heating duct at the exit end. Results show that the air which comes out of coupled EATHE system is relatively hotter than the air supplied by the stand alone EATHE system. It was found that the heating capacity of EATHE system got increased by 1217.625–1280.753 kWh when it was coupled with solar air heating duct with a substantial increase in room temperature by 1.1–3.5 °C. The COP of the system also increased up to 4.57 when assisted with solar air heating duct. Therefore, the heating capacity of EATHE can be significantly increased by coupling it with solar air heating duct. [ABSTRACT FROM AUTHOR]

Microalgal biodiesel has to overcome a cost incurring harvesting bottleneck for its commercial scale production. In this study electrochemical harvesting (ECH) using Chlorella sorokiniana and Scenedesmus obliquus was investigated. Nonsacrificial carbon electrodes were used to overcome the cost and metallic contamination implications. The effect of applied current and addition of electrolyte on harvesting efficiency was investigated. Addition of electrolyte (NaCl) increased the recovery efficiency of C. sorokiniana from 65.99% to 94.52%. ECH process has not shown any deteriorating effect on the lipid extraction process as well as fatty acid composition. ECH process for C. sorokiniana with optimum conditions showed 94.52% recovery efficiency with energy consumption of 1.6 kWh kg-1. This study for the first time validates application of nonsacrificial carbon electrodes in ECH process of microalgae. Attractive high recovery efficiency, low energy consumption and use of nonsacrificial electrodes could make ECH a possible step in commercial microalgal biomass and biodiesel production. [ABSTRACT FROM AUTHOR]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics modeling. Effects of time duration of continuous operation, thermal conductivity of soil pipe diameter and flow velocity on thermal performance of EATHE under transient conditions have been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of EATHE. Study reveals that the effect of pipe diameter due to prolonged use of EATHE system on its thermal performance is least in case of soil with higher value of thermal conductivity. Results show that the increase in flow velocity leads to deterioration in thermal performance of EATHE system. Under steady state condition, drop of 18.8°C in air temperature is obtained, whereas, under transient conditions cooling of air reduces from 18.7°C to 16.6°C for soil thermal conductivity of 0.52Wm−1 K−1, after 24h of continuous operation. [Copyright &y& Elsevier]

Abstract: Effect of soil thermal conductivity and time period of continuous operation of EATHE on thermal performance has been carried out for different pipe length of EATHE using experimentally validated CFD simulation. In this paper, the authors aim to study the underground temperature characteristics of the soil surrounding the EATHE pipe and the effect of duration of operation of EATHE on its thermal performance. Maximum air temperature drop of 15.6, 17.0 and 17.3K are observed for soil thermal conductivities of 0.52, 2 and 4Wm−1 K−1 respectively. Maximum deterioration in the performance in terms of temperature drop obtained during continuous operation of 24h is recorded as 2.9K for soil with thermal conductivity of 0.52Wm−1 K−1. Thickness of soil annulus surrounding the pipe up to which the thermal influence is observed depends on the thermal conductivity of the soil and period of continuous running of EATHE system. The thickness of the soil annulus beyond which no significant rise in temperature of soil is observed is equal to the pipe diameter. [Copyright &y& Elsevier]

Abstract: Thermal performance of earth air tunnel heat exchanger (EATHE) under transient operating conditions has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and computational fluid dynamics modeling. Effect of time duration of continuous operation and thermal conductivity of soil on thermal performance of EATHE under transient conditions has been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. Under steady state condition, a drop of 18.8°C is obtained in air passing through EATHE having 0.1m diameter and 60m length, at 5ms−1 flow velocity, whereas, the transient analysis shows that for soil having thermal conductivity of 0.52Wm−1 K−1, the cooling of air reduces from 18.7°C to 16.6°C, after 24h of continuous operation. Change in cooling effect after 24h of operation for soil thermal conductivity of 2.0Wm−1 K−1 and 4.0Wm−1 K−1, reduced from 18.8°C to 18.5°C and 18.8°C to 18.7°C respectively. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of earth air heat exchangers. [Copyright &y& Elsevier]

Abstract: Thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions in winter season has been evaluated for predominantly hot and dry climate of Ajmer (India) using experimental and Computational Fluid Dynamics (CFD) modeling. Effect of time duration of continuous operation and thermal conductivity of soil on thermal performance of EATHE under transient conditions has been analyzed. Results show that the transient thermal performance of EATHE is significantly dependent on thermal conductivity of the soil and duration of its continuous operation. Under steady state condition, a rise of 19.6°C is obtained in air passing through EATHE having 0.1m diameter and 60m length, at 5m/s flow velocity, whereas, the transient analysis shows that for soil having thermal conductivity of 0.52Wm−1 K−1, the heating of air reduces from 19.4°C to 17.2°C, after 24h of continuous operation. Heating effect after 24h of operation for soil thermal conductivity of 2.0Wm−1 K−1 and 4.0Wm−1 K−1, reduced from 19.6°C to 19.2°C and 19.6°C to 19.5°C, respectively. The analyzed cases have shown the range of derating to be as minimal as 0% to as high as 64%, which if ignored while designing may lead to poor performance of earth air heat exchangers. [Copyright &y& Elsevier]

Abstract: A new term ‘Derating Factor’ is devised for evaluating deterioration in thermal performance of Earth Air Tunnel Heat Exchanger (EATHE) under transient operating conditions in predominantly hot and dry climate of Ajmer (India) using experimental and computational fluid dynamics modeling with FLUENT software. Maximum air temperature drop obtained using steady state approach for EATHE of pipe length 100m, pipe diameter 0.2m and at air velocity of 5ms−1 is 18.4°C, 18.7°C and 18.4°C for soil thermal conductivity of 0.52, 2.0 and 4.0Wm−1 K−1 respectively. However, the maximum air temperature drop obtained using transient approach during 24h of operation vary between 18.3°C and 14.0°C, 18.3°C and 17.2°C and 18.6°C and 18.0°C for soil thermal conductivity of 0.52, 2.0 and 4.0Wm−1 K−1 respectively. The derating factor is found to be a function of thermal conductivity of soil, duration of continuous operation of EATHE and length of pipe. The analyzed cases have shown the range of derating to be as minimal as 0.2% to as high as 68%, which if ignored while designing may lead to poor performance of earth air heat exchangers. Maximum value of derating factor is observed after continuous operation of EATHE for 24h. [Copyright &y& Elsevier]

Abstract: Earth–air–tunnel heat exchanger (EATHE) systems are insufficient to meet the thermal comfort requirements in summer conditions. Therefore, evaporating cooling has been integrated with EATHE to enhance the thermal comfort hours. Economics of integrated EATHE–evaporative cooling system to reduce/avoid the use of air-conditioner and electric heater is analyzed by evaluating simple Internal Rate of Return (IRR) on investment. For this analysis a transient and implicit model based on computational fluid dynamics has been used for evaluating the energy saving obtained by the use of EATHE system integrated with evaporative cooling. Four base cases of existing systems, i.e. air-conditioner and electric heater have been considered for carrying out the economic analysis. Moreover, three different types of blower (i.e. energy efficient blower, standard blower and inefficient blower) have been considered for evaluating the energy saving and financial viability of the proposed system. These results of IRR calculation shows that wherever, the existing air conditioner and heaters are efficient, their replacement with proposed EATHE system is not a technically and economically viable option. It is observed that the IRR value is greatly dependent on the electric tariff and the energy efficiency of the blower used in the proposed EATHE system. [Copyright &y& Elsevier]

This paper presents the theoretical investigation of CDM opportunity in a township at Jaipur, India. The purpose of study is to identify and analyze the various opportunities viz., installation of solar water heater, energy efficient lighting, energy efficient air conditioners, and energy efficient submersible water pumps in desert coolers and thus achieve a considerable (65.7 %) reduction in GHG emissions. Out of the various opportunities considered, the retrofitting with solar water heater can be recommended for CDM. Though, the retrofitting with energy efficient lighting, energy efficient air conditioners and energy efficient submersible water pumps in desert coolers claimed CO emission reduction of 104.84, 25.92, and 36.94 tons per annum, respectively, but the only opportunity which got through CDM was retrofitting with solar water heater claiming 115.70 tCO (100 %) emission reductions per annum which could result into net earnings of 115.70 CERs. The simple and discounted payback period for all four project activities are also calculated with and without CDM and tax benefits. [ABSTRACT FROM AUTHOR]

Abstract: Increasing the coefficient of performance of air-conditioner with air-cooled condenser is a challenging task especially in areas where weather conditions are quite hot. The performance of conventional vapour compression system based air-conditioners can substantially be improved by coupling these active cooling systems with less energy intense passive cooling systems. In the present research, an attempt has been made to enhance the performance of active cooling system by coupling it with EATHE in four different hybrid modes and thermal performance of the developed hybrid cooling system has been investigated experimentally. The power consumption of conventional 1.5 TR window type air conditioner is found to be reduced by 18.1% when cold air from EATHE is completely used for condenser cooling of the air-conditioner. [Copyright &y& Elsevier]

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]

A fixed bed electrochemical reactor comprising stainless steel cathode/granular activated carbon (GAC) bed//Carbon anode//GAC bed//stainless steel cathode configuration was fabricated and tested for degradation of Reactive Blue 4 aqueous solutions (RB4). On the basis of measured concentrations of residual RB4 dye and total organic carbon (TOC), approximately 80–90% of RB4 dye was found to be degraded at 0.30–0.90A and 13.4±0.1V in 6 h under recirculation batch mode of operation (flow rate, 1.8Lh−1). The dye removal due to adsorption on carbon was ∼9–10% under the same experimental conditions but excluding applied current. The apparent Faradic efficiency and electrical energy consumption were estimated to be 2.8% and 16.0kWh kg−1 RB4 at the optimum current and voltage (0.6 A, 13.3 V). Further, the adsorption of the dye on GAC bed, cyclic voltammetric response of RB4, SEM and FT-IR characterization of original and spent carbon and ion chromatographic analysis of inorganic intermediates were carried out to elucidate the mechanism of dye degradation. It appears that the dye degradation takes place by ready scission of SO3H groups, and oxidation of mainframe chromophore (anthraquinone group). The chlorotriazine group resists to the electrooxidation and remains as the final reaction product. [Copyright &y& Elsevier]

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]

Abstract: Earth–pipe–air heat exchanger (EPAHE) systems can be used to reduce the cooling load of buildings in summer. A transient and implicit model based on computational fluid dynamics was developed to predict the thermal performance and cooling capacity of earth–air–pipe heat exchanger systems. The model was developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth–air–pipe heat exchanger systems are studied. The 23.42m long EPAHE system discussed in this paper gives cooling in the range of 8.0–12.7°C for the flow velocities 2–5m/s. Investigations on steel and PVC pipes have shown that the performance of the EPAHE system is not significantly affected by the material of the buried pipe (pipe). Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. The COP of the EPAHE system discussed in this paper varies from 1.9 to 2.9 for increase in velocity from 2.0 to 5.0m/s. [Copyright &y& Elsevier]

Abstract: Earth–pipe–air heat exchanger (EPAHE) systems can be used to reduce the heating load of buildings in winter. A transient and implicit model based on computational fluid dynamics is developed to predict the thermal performance and heating capacity of earth–air–pipe heat exchanger systems. The model is developed inside the FLUENT simulation program. The model developed is validated against experimental investigations on an experimental set-up in Ajmer (Western India). Good agreement between simulated results and experimental data is obtained. Effects of the operating parameters (i.e. the pipe material, air velocity) on the thermal performance of earth–air–pipe heat exchanger systems are studied. The 23.42m long EPAHE system discussed in this paper gives heating in the range of 4.1–4.8°C for the flow velocities 2–5m/s. Investigations on steel and PVC pipes have shown that performance of the EPAHE system is not significantly affected by the material of the buried pipe. Velocity of air through the pipe is found to greatly affect the performance of EPAHE system. [Copyright &y& Elsevier]

• Evaluated economic feasibility of backfilling materials for GAHE system. • Developed a CFD simulation model for GAHE system with backfilling materials. • Use of backfilling materials to improve the overall economics of GAHE system. • Required length of GAHE pipe is determined with different BFMs. The ground-air heat exchanger (GAHE) system is an energy-efficient system for building cooling/ heating, but its initial cost is higher due to the requirement of longer pipes to achieve the desired heat exchange between air and soil. To reduce required pipe length, secondary soil (i.e. soil of high thermal conductivity) can be used as backfilling material in the vicinity of GAHE pipe. However, due to the use of secondary soil, the installation cost of the GAHE system may increase. Therefore, the key objective of this study is to explore the economic feasibility of using backfilling materials in the vicinity of GAHE pipe. For this, a three-dimensional CFD simulation model of GAHE system with backfilling material has been developed using FLUENT 15.0, and the required length of GAHE pipe to achieve a specified drop in air temperature with backfilling materials has been determined. Based on this, the initial installation cost of the GAHE system (i.e. pipe cost, trench excavation cost, backfilling material cost) has been estimated. The study revealed that the initial installation cost of a GAHE system could be reduced by 25.7%, 32%, and 38% using dry sand-bentonite, wet sand-bentonite, and wet native soil respectively, as backfilling materials in place of dry native soil. [ABSTRACT FROM AUTHOR]

• A rigorous CFD simulation has been conducted to determine the outcomes of V-down rib with multiple gaps and turbulence promoters as artificial roughness on the thermo-hydraulic response of an equilateral triangular passage air heating duct. • Proposed roughness proves its worth as its attachment over the absorber leads to an improvement in heat transfer and fluid flow behavior both, because of enhanced level of interaction among the fluid particles. • Friction characteristics have been discussed in terms of Eddy viscosity and Helicity. • As compared to smooth SAH duct, friction factor for SAH duct roughened with proposed roughness is found to be utmost at P/e = 10, α = 60⁰ and Re = 20,000. In the current study, duct of equilateral triangular cross section having V-down ribs with multiple gaps and turbulence promoters as artificial roughness is analyzed and thermo-hydraulic response of duct is measured. For in depth analysis computational fluid dynamics analysis has been carried out using ANSYS FLUENT 19.0. Under the parametric variation part, effect of change in roughness parameters, viz., relative roughness pitch and angle of attack on thermohydraulic performance has been explored. Flow Reynolds number (Re) is systematically varied from 4,000 to 20,000. Proposed roughness proves its worth as its attachment over the absorber leads to an enhancement in Nusselt number and friction factor both, because of enhanced level of interaction among the fluid particles. Study reveals that upon varying the relative roughness pitch (P/e) from 8 to 14 and angle of attack from 45⁰ to 60⁰, maximum heat transfer rate is attained at P/e = 10 and α = 45⁰, respectively, irrespective of Reynolds number. Performance of the SAH with proposed roughness is found to be better than other type of roughness elements studied in recent past. [ABSTRACT FROM AUTHOR]

• Development of a laboratory scale experimental set up with slinky-coil pipe layout. • Use of sand–bentonite mixture as backfilling material for GAHE system. • Required length of the trench is reduced by using slinky-coil pipe layout. • Substantial saving in terms of excavation cost and piping cost. The ground-air heat exchanger (GAHE) is the promising passive technique for building heating/cooling, but due to its high installation cost (mainly pipe cost and excavation cost), it could not become popular. The required length of pipe can be reduced by using thermally enhanced backfilling material (BFM), while, the length of the trench can be reduced by using slinky-coil pipe layout. In the present study, an experimental laboratory setup of GAHE system has been developed with a slinky-coil pipe layout and sand-bentonite as BFM. For this, a flexible PVC pipe of 75 mm diameter and 30 m length, has been arranged in slinky-coil pattern and installed horizontally in a soil box of 10.2 m length. For the study, variation in soil temperature (23 °C–27 °C), inlet air temperature (38 °C–46 °C), air flow velocity (5 m/s–20 m/s) and soil conditions (dry and wet), have been considered. Study reveals that a drop-in air temperature as high as 18.7 °C at 30 m pipe length (trench length of 10.2 m) can be achieved with soil at a temperature of 27 °C and inlet air temperature of 46 °C. The study also revealed that the pipe length could be reduced by 20% with wet sand-bentonite as compared to dry sand-bentonite. [ABSTRACT FROM AUTHOR]

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]

Solar air heater (SAH) is a popular and economical device which collects the solar energy and is employed for space heating, drying of agricultural products, food items, and leather, seasoning of timber, etc. Attachment of artificial roughness on the absorber surface is an appropriate method to augment the heat transfer from the heated surface to the air flowing through SAH duct. Use of artificial roughness has been an area of great interest for researchers as far as the cooling of turbine blades, and combustion chambers are concerned. This technique is effective in enhancing the heat transfer in a micro-channel heating/cooling system. Present paper holistically furnishes concise information about various kinds of V-shaped roughness geometries used in SAHs for improving its performance covering experimental, analytical, numerical and computational fluid dynamics (CFD) approaches. In this paper, 124 research articles have been referred, which provide a detailed comprehensive and comparative study revealing the effect of various geometrical parameters and different V-shaped roughness patterns on the performance of SAH. This article also brings in the information about the correlation developed by researchers for heat transfer and friction factor. This comprehensive review will be quite useful for technical persons and researchers working in the area of SAH. [ABSTRACT FROM AUTHOR]

Large-scale adaptation of solar air heating in industries and agro-processing will lead to clean energy processing as well as reducing the production cost for these industries. The solar air heater uses the principle of the greenhouse effect to heat air through the collected heat in the absorber. Among the various techniques employed by the researchers to augment heat transfer, the addition of artificial roughness elements/fins/corrugations on the heated surface is the promising one for heat transfer augmentation. In the present work, the effect of broken inclined ribs with rectangular cross-section on heat transfer and friction characteristics of the equilateral triangular passage duct has been analyzed using computational fluid dynamics. The effect of roughness parameters, viz., relative gap position and relative gap width, is being investigated for the Reynolds number (Re) ranging from 4000 to 18,000. The values of relative gap position (d/W) and relative gap width (g/e) are varied from 0.16 to 0.67 and 0.5 to 2, respectively, while a constant heat flux is supplied on the absorber side, other surfaces being insulated. The Nusselt number increased up to 2.16 times by using broken ribs than that of the smooth duct at d/W = 0.25 and g/e = 1. [ABSTRACT FROM AUTHOR]

Highlights • Fabrication of a unique sub-soil water trickling system (SWTS) integrated with EAPHE system. • Three soil moisture content values viz. 5%, 10%, and 15% have been considered for wet EAPHE system. • Investigation of the effect of soil moisture variation on thermal performance of EAPHE system. • Comparison of thermal performance of dry and wet EAPHE system for winter heating. • Estimation of heat transfer rate, COP and knee point position for dry and wet EAPHE systems. Abstract Earth-air-pipe heat exchanger (EAPHE) system is a passive system but requires long pipes for heat transfer and its performance also gets deteriorated during continuous operation. In this study, the moisture content of sub-soil is increased in the close vicinity of EAPHE pipe and its influence on thermal performance and pipe length requisite for certain temperature rise in winter season have been determined. The system comprises of two identical set-ups of EAPHE system buried at a depth of 3.7 m (one for dry soil, other for wet soil). A unique water impregnation system is presented to maintain different soil moisture content levels in the close vicinity of EAPHE pipe. The knee point for dry EAPHE system is obtained at a pipe length of 40 m from inlet section while in wet EAPHE system knee point is obtained at 28 m, 27 m and 26 m with 5%, 10%, and 15% soil moisture levels respectively, after 12 h of continuous operation. The average heat transfer rate and coefficient of performance increase up to 26.0% and 26.1% respectively, for 15% moisture content at 30 m length of EAPHE pipe as compared to dry system. [ABSTRACT FROM AUTHOR]

Highlights • The Earth air tunnel heat exchanger system is capable to provide sufficient heating and cooling in buildings with significant energy savings. • The knowledge of thermo-physical properties of soil is crucial for the design of an EATHE system. • In multiple pipe system, the distance between the pipes should be reduced gradually along the length of pipe. • Too deeper excavation of soil does not result in any appreciable change in soil temperature. • EATHE should be used during daytime in summer and during night time in winter season. Abstract The principal drivers that led to the high growth rate in the renewable energy market in developing countries over the past twenty years include not only the dwindling fossil reserves, exorbitant increase in the price of crude oil, widening energy deficit, but also the extravagant lifestyle of profligate consumers of energy. Nearly one-third of total primary energy is consumed for the purpose of space cooling and heating. Renewable and passive systems can reduce the building cooling and heating energy demand. Earth air tunnel heat exchanger system is one of the promising technique used for space cooling and heating nowadays, thus reduce fossil fuel based energy demand as well as greenhouse gas emission, but its use has been restrained owing to its poor performance, land area requirement and financial viability. Various experimental, analytical and simulation studies have been conducted in last few decades to investigate the various parameters that may enhance its performance. In this article, the effect of thermo-physical parameters of soil, thermal and flow parameters of air, geometrical and material properties of pipe, different modes of operation on the performance of earth air tunnel heat exchanger systems have been critically reviewed. Following thorough review of the articles, it is concluded that if EATHE system is developed with proper design guidelines, then it may facilitate sufficient space heating and cooling with significant energy savings. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents results of a theoretical study carried out to investigate the effect of flow maldistribution, caused by the manufacturing imperfections and tolerances, on the thermal efficiency of a solar air heater array with subcollectors in parallel. The air mass flow rate, ambient temperature, solar insolation and wind heat transfer coefficient have been systematically varied to study the effect under a wide range of these parameters. The collector length, duct height, and plate emissivity were also changed to study their effect. It has been found that the maximum reduction in thermal efficiency due to flow maldistribution is less than about 3% for an array with a commercial grade finish of duct surfaces and ±10% manufacturing tolerance for the duct height. [Copyright &y& Elsevier]

The plants of Spinacia oleracea L. grown on contaminated soil (CS) and different amendments of tannery sludge (TS) have shown high accumulation of metals in its edible part. The accumulation of toxic metal (Cr) in the leaves of the plants grown on CS was recorded as 40.67μgg−1 dw. However, the leaves of the plants grown on 100% TS have accumulated about two times (70.80μgg−1 dw) higher Cr than the 10% TS (31.21μgg−1 dw). Among growth parameters, the root length was more affected at 90d than the shoot length, number of leaves and leaf area. The study of scanning electron micrographs showed 29.31% increase in stomatal length in the leaves of the plants grown on CS as compared to garden soil (GS), which served as control, however it decreased in the plants grown on higher amendments of TS. The decrease in MDA content at initial period of exposure and lower amendment was recorded in the leaves, whereas, significant increase (>10% TS onward) was observed with increase in tannery sludge ratio at 90d as compared to GS. A coordinated increase in all the studied antioxidants (cysteine, non-protein thiol, ascorbic acid, carotenoid contents) was found up to 75d of growth. At 90d, most of the antioxidant decreased as compared to 75d causing oxidative stress as evidenced by increased level of lipid peroxidation and decreased chlorophyll and protein contents. Maximum increase of 181.43% in MDA content and maximum decrease of 53.69% in total chlorophyll content was recorded in the leaves of the plants grown on 100% TS after 90d of growth. The plants grown on CS have shown an increase in shoot length, number of leaves, leaf area, photosynthetic pigments and protein contents and in all the studied antioxidants. Thus, these plants are able to combat stress involving defense mechanism, resulting in healthy growth of the plants. The results are well coordinated as there is no change in the MDA content as compared to the plants grown on GS. In view of high Cr accumulation in edible part of S. oleracea grown on CS after irrigation with tap water, it is not advisable to use these plants for edible purposes. Summing up, it is recommended that the level of metals in the edible part should be checked instead of healthy growth as deciding parameter for consumption. It is demonstrated through this study that metal enriched plants have detoxification mechanism and grow well on organic matter enriched contaminated soil. [Copyright &y& Elsevier]

Abstract: Industrial wastewaters containing high concentrations of organics, particularly of recalcitrant nature, demand a unique type of treatment approaches often requiring two or more processes operated in tandem. In this paper, the effectiveness of combined treatment processes viz., coagulation/flocculation (C/F), electrooxidation (EO) and membrane (M) processes for tackling organic load in a segregated chemical industry wastewater is reported. The wastewater is characterized by strong color, high concentrations of salinity, total kjeldhal nitrogen (TKN) and chemical oxygen demand (COD). Three different combined process; i) UF–RO (CP-I); ii) C/F–EO–UF–RO (CP-II) and iii) C/F–EO1–EO2–UF–RO (CP-III) were investigated. The overall COD and TDS removal efficiencies in that order were: CP-I, 73% and 82%; CP-II, 84% and 85%, and CP-III, 93% and 87%. The percent COD and TDS removals at each stage of the combined process were evaluated and the impact of EO process on the overall performance of the process schemes was discussed. It emerged that intermediate level EO process considerably reduces organic load in the effluent, while large part of TDS removal can be attributed to final RO treatment. Thus, the combined treatment processes appear to be promising for obtaining greater efficiency of organic and salinity load removals. [Copyright &y& Elsevier]

Abstract: For the first time, a new carbon–carbon composite electrode material for supercapacitors is prepared by simple KOH activation of waste newspaper. The amorphous nature and surface morphology of the carbon composite are investigated by X-ray diffraction (XRD), N2 adsorption/desorption and scanning electron microscopy. The surface area and pore diameter are 416m2 g−1 and 5.9nm, respectively. Electrochemical characteristics are evaluated by cyclic voltammetry (CV) and charge–discharge tests in 6.0M KOH at a 1mAcm−2 current density. The CV results reveal a maximum specific capacitance of 180Fg−1 at a 2mVs−1 scan rate and the data explore a development of new use for waste paper into a valuable energy storage material. [Copyright &y& Elsevier]

Abstract: Photocatalytic decoloration kinetics of triazine (Reactive Red 11, Reactive Red 2, and Reactive Orange 84) and vinylsulfone type (Reactive Orange 16 and Reactive Black 5) of reactive dyes have been studied spectrophotometrically by following the decrease in dye concentration with time. At ambient conditions, over 90–95% decoloration of above dyes have been observed upon prolonged illumination (15h) of the reacting system with a 150W xenon lamp. It was found that the decoloration reaction followed first-order kinetics. The values of observed rate constants were found to be dependent of the structure of dyes at low dye concentration, but independent at higher concentration. It also reports for the first time the decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO2 photocatalyst. Rate of decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO2 photocatalyst is governed by the adsorptivity of the particular dye onto the surface of the TiO2 photocatalyst. [Copyright &y& Elsevier]