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The photovoltaic thermal (PV/T) systems are promising techniques for cooling photovoltaic modules and performance improvement. The heat-exchanging fluid removes the heat from the PV module, which c...

This research work presents the thermal performance of a packed bed solar air heater under the combined effect of recyclic flow and fractional total mass flow rate. The investigated solar air heater consists of three air flow ducts and the fraction of total mass flow rate serves as an input to first and second ducts of the solar air heater. Based on the inputs, the first duct consists of single air pass whereas the second and third ducts are operated under recyclic air flow. In order to produce the recyclic effect, air exiting from the outlet of the second duct is recycled back through the third duct to the inlet of the second duct and gets mixed with inlet fraction of the total mass flow rate of the air. In order to predict the effect of fractional total mass flow rate two cases are considered i.e. when two streams of i) equal fraction ii) unequal fraction of mass flow rate flowing through the first and second duct of solar air heater by dividing the total mass flow rate. Moreover, results of this solar air heater are compared with another recyclic type solar air heater under similar geometric and operational flow parameters. The results indicate that the thermo-hydraulic efficiency of the proposed solar air heater is significantly higher at lower recycle ratio and the equal fraction of total mass flow rate.

Benzodiazepines (BZDs) represent a diverse class of bicyclic heterocyclic molecules. In the last few years, benzodiazepines have emerged as potential therapeutic agents. As a result, several mild, efficient and high yielding protocols have been developed that offer access to various functionalized benzodiazepines (BZDs). They are known to possess a wide array of biological activities such as anxiolytic, anticancer, anticonvulsant, antipsychotics, muscle relaxant, anti-tuberculosis, and antimicrobial activities. The fascinating spectrum of biological activities exhibited by BZDs in various fields has prompted the medicinal chemist to design and discover novel benzodiazepine-based analogs as potential therapeutic candidates with the desired biological profile. In this review, an attempt has been made by to summarize (1) Recent advances in the synthetic chemistry of benzodiazepines which enable their synthesis with desired substitution pattern; (2) Medicinal chemistry of BZDs as therapeutic candidates with promising biological profile including insight of mechanistic studies; (3) The correlation of biological data with the structure i.e. structure-activity relationship studies were also included to provide an insight into the rational design of more active agents.

This paper presents investigations related to the heat-transfer performance improvement of double-pass finned and finned with baffles solar air heaters. The analytical study has been carried out to see the effects of parameters such as mass flow rate, recycle ratio, fins thickness, number of fins, and baffles width on the heaters’ efficiencies. It is indicated that the mass flow rate and the recycle ratio are the most significant factors, which considerably increase the heaters’ efficiencies by increasing the fluid velocity. The theoretical results showed that the device with fins plus baffles can enhance the heat transfer rate compared with the device with fins under the same flow rate and working dimensions. The effect of the depth of the first channel on the thermal and thermohydraulic efficiency improvement is also delineated. To validate the proposed theoretical models, comparisons of the results are performed with those obtained from previous studies and show that good agreement is achieved.

In the present investigation, the energy and exergy efficiencies of double pass packed bed solar air heater under external recycle have been investigated, theoretically and experimentally. An analytical model capable of predicting the energy and exergy efficiencies is presented. The thermohydraulic efficiency criterion is also used to optimize the input parameters. It is observed that the energy efficiency of the heater increases with increasing mass flow rate and recycle ratio whereas, the exergy efficiency increases with an increase in the mass flow rate and the recycle ratio, but attains a maximum value and subsequently decreases with further increase in the mass flow rate and the recycle ratio. The optimum values of the mass flow rate to yield the maximum value of the energy and exergy efficiencies are found to be 0.025 kg/s and 0.006 kg/s, respectively, while the recycle ratio is found to be about 1.5 for both. In addition, the cost per unit energy delivered by the heater is also calculated. At the optimum value of input parameters; the heater's cost per unit energy delivery is 0.78 Rs/kWh and Rs. 0.58 Rs/kWh, respectively, on the basis of both energy and exergy gain.

The present work intended to conduct a comprehensive review on the thermal performance of double pass packed bed solar air heaters. Various aspects that govern the thermal performance of such solar air heaters has been highlighted and discussed in detail. A comprehensive review of reported studies indicate that the use of porous packed bed material in the upper channel of double pass solar air heaters significantly increases the thermal performance as compared to solar air heaters without packed bed and with packed bed when porous material is provided in the lower channel. Moreover, studies revealed that employment of parallel, counter and recyclic double air pass increases the thermal performance of the packed bed solar air heater as well by increasing the heat extraction rate of the flowing air through the packed bed duct. Although, it has been obtained that sufficient work using parallel and counter double air pass has been reported on packed bed solar air heaters, only few studies were reported using recyclic double air pass. However, results show that employment of recycle operation to the double pass packed bed solar air heaters momentously increases the thermal performance and can be used as an alternative thermal performance enhancement technique. Therefore, more investigations are required to be conducted using recyclic double pass packed bed solar air heaters.

In the present investigation, finite volume method is applied for the thermal performance prediction of a hybrid earth to air tunnel heat exchanger whereas process parameters are optimized using response surface methodology. A commercial CFD based software-ANSYS Fluent is used to simulate the heat exchanger. RNG k – ɛ turbulence model was selected to carry out a two-dimensional simulation modelling. Moreover, response surface methodology is applied to analyse the results of finite volume method and to optimize the process parameters of hybrid earth to air tunnel heat exchanger (HEAHX). The numerical results obtained from HEAHX are compared with that of individual EAHX. It is found that performance of HEAHX is about three times higher than as compared to individual EAHX. In addition, the theoretical results of present study are validated with theoretical results obtained from previous works and a good agreement is achieved. The maximum difference between the outlet and inlet air temperatures of hybrid and individual earth to air heat exchangers at the optimum value of input parameters are found to be 49.83 K and 14.4 K, respectively.

In the present work, analytical models to predict the thermal and thermohydraulic efficiencies of two different designs of double pass packed bed solar air heater under external recycle have been proposed. It is predicted that Model A with the single air pass through the first channel as well as the recycle of the air exiting from the second channel through the third channel can enhance the heat transfer rate more as compared to Model B. The wire mesh screen as an absorbing media above the absorber plate is used in both of the solar air heater models. The recycle ratio and the mass flow rate are varied from 0.1 to 1 and 0.01–0.025 kg/s, respectively. The results of the study depict that the recycle ratio and the mass flow rate substantially increases the heaters efficiencies by increasing the fluid velocity. The maximum value of the thermal efficiency of Model A is found to be about 6.6% higher than that of Model B. The optimum values of the recycle ratio and the mass flow rate, at which the heaters yield maximum values of thermo-hydraulic efficiencies, are identified and presented. In addition, the effect of the channel depth ratio on the thermal performance improvement is also delineated.

In the present study, an analytical and RSM (response surface methodology) combined approach has been applied to investigate the thermal and thermohydraulic performances of a novel type double pass packed bed solar air heater under external recycle with wire mesh screen as a packed bed material. An analytical model describing the various temperatures and heat transfer characteristics of such a double pass packed bed solar air heater under external recycle has been developed and employed to study the effects of mass flow rate, recycle ratio and varying channel depth between the top (upper and lower) glass covers for a fixed 95% porosity of the packed material on its thermal and thermohydraulic performances. The analytical model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass transfer involved. Furthermore, RSM is then applied for developing mathematical models based on simulation results obtained from analytical study. The effect of parameters and their interactions on the responses are studied using RSM. The results obtained from RSM revealed that proposed mathematical model is significant and good agreement is achieved with reasonable accuracy.

In the modern scenario, the quinolone scaffold has emerged as a very potent motif considering its clinical significance. Quinolones possess wide range of pharmacological activities such as anticancer, antibacterial, antifungal, antiprotozoal, antiviral, anti-inflammatory, carbonic anhydrase inhibitory and diuretic activity etc. The versatile synthetic approaches have been successfully applied and several of the resulted synthesized compounds exhibit fascinating biological activities in numerous fields. This has prompted to discover quinolone-based analogues among the researchers due to its great diversity in biological activities. In the past few years, various new, efficient and convenient synthetic approaches (including green chemistry and microwave-assisted synthesis) have been designed and developed to synthesize diverse quinolone-based scaffolds which represent a growing area of interest in academic and industry as well as to explore their biological activities. In this review, an attempt has been made by the authors to summarize (1) One of the most comprehensive listings of quinolone-based drugs or agents in the market or under various stages of clinical development; (2) Recent advances in the synthetic strategies for quinolone derivatives as well as their biological implications including insight of mechanistic studies. (3) Further, the biological data is correlated with structure-activity relationship studies to provide an insight into the rational design of more active agents.

In this paper, the thermal performance of double-pass packed-bed solar air heaters is investigated theoretically. A suitable computer program is developed for the analytical solution of the mathematical model which involves the energy balance equations for the different components of the air heaters. Three different characteristics of the double-pass packed-bed solar air heaters are considered for the analysis. The results obtained from the analytical models are compared with the experimental model data obtained from the previous works and showed that good agreement is achieved.

In this paper, the counter and parallel flow packed bed solar air heaters are investigated theoretically and experimentally. Analytical model for these air heaters is presented. Numerical calculations have been performed under Hamirpur ( latitude, 31° 40′ 47" N ) prevailing weather conditions. The effect of air mass flow rates and bed porosity on the thermal and thermohydraulic efficiencies of the counter and parallel flow packed bed solar air heaters are investigated. The theoretical predictions indicated that the agreement with the measured performance is fairly good. The results showed that the thermal efficiency of the counter flow packed bed solar air heater is 11–17% more compared to the parallel flow packed bed solar air heater whereas, parallel flow system achieved a 10% higher thermohydraulic efficiency when air steadily flowed at differential mass rates in its upper and lower ducts compared to the counter flow system. Range of bed porosities and air flow rates over which the parallel flow system yields higher thermohydraulic efficiency than the counter flow have been identified and presented. It is also indicated that the peak values of the thermohydraulic efficiencies of counter and parallel flow packed bed solar air heater are obtained when the mass flow rate of air of flowing in each duct is 0.03 kg/s.

Water flow over carbon nanotubes has been shown to generate an induced voltage in the flow direction due to coupling of ions present in water with free charge carriers in the nanotubes. However, the induced voltages are typically of the order of a few millivolts, too small for significant power generation. Here we perform tests involving water flow with various molarities of hydrochloric acid (HCl) over few-layered graphene and report order of magnitude higher induced voltages for graphene as compared to nanotubes. The power generated by the flow of ∼0.6 M HCl solution at ∼0.01 m/sec was measured to be ∼85 nW for a ∼30 × 16 μm size graphene film, which equates to a power per unit area of ∼175 W/m(2). Molecular dynamics simulations indicate that the power generation is primarily caused by a net drift velocity of adsorbed Cl(-) ions on the continuous graphene film surface.

A design of a parallel flow solar air heater with packed material in its upper channel and capable of providing a higher heat flux compared to the conventional non-porous bed double flow systems is presented. An analytical model describing the various temperatures and heat transfer characteristics of such a parallel flow packed bed solar air heater (PFPBSAH) has been developed and employed to study the effects of the mass flow rate and varying porosities of the packed material on its thermal performance. The model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass exchanges involved. To validate the proposed analytical model, comparisons between theoretical and experimental results showed that good agreement is achieved with reasonable accuracy. Also, PFPBSAH is found to perform more efficiently than the conventional non-porous double flow solar air heaters with 10–20% increase in its thermal efficiency. Furthermore, the effect of the fraction of mass flow rate in the upper or lower flow channel of PFPBSAH device on its performance, has also investigated theoretically. The fraction of the mass flow rate in the respective channels of the PFPBSAH is shown to be dominant parameter in determining the effective thermal efficiency of the heater.

The present work intended to investigate thermal and thermohydraulic efficiencies of two different models of recyclic double pass packed bed solar air heaters experimentally. Model-I consists of single air pass through two glass covers as well as double air pass caused due to recycle of the air exiting from the packed bed duct formed between the absorber plate and the glass cover through another duct integrated between the absorber and back plates to inlet of the packed bed duct. On the other hand, model-II consists of only double air pass originated due to recycle operation constituted between the similar solar air heater elements as that of model-I. Twelve numbers of wire mesh screens to form 95% bed porosity were used. Both solar air heater models were tested under the range of packed bed Reynolds number from 300 to 1500 for air mass flow rate and recycle ratio of 0.01 kg/s to 0.025 kg/s and 0.3 to 1.8, respectively. Results revealed that thermal performance of model-I is found to be 15% higher than that of model-II. The optimum value of the recycle ratio for model-I and model-II are obtained as 0.9 and 1.2, respectively, at a mass flow rate of 0.025 kg/s that yields the best thermohydraulic efficiency of 77% and 67%, respectively. Moreover, optimum solution for recycle ratio and air mass flow rate during off sun shine hours are also obtained and presented in the current work.

Thermal performance of a single-pass single-glass cover solar air heater consisting of semicircular absorber plate finned with rectangular longitudinal fins is investigated. The analysis is carried out for different hydraulic diameters, which were obtained by varying the diameter of the duct from 0.3–0.5 m. One to five numbers of fins are considered. Reynolds number ranges from 1600–4300. Analytical solutions for energy balance equations of different elements and duct flow of the solar air heater are presented; results are compared with finite-volume methodology based numerical solutions obtained from ansys fluent commercial software, and a fairly good agreement is achieved. Moreover, analysis is extended to check the effect of double-glass cover and the recycle of the exiting air. Results revealed that the use of double-glass cover and recycle operation improves the thermal performance of solar air heater.

In the present study, the thermal and effective thermal efficiencies of a double-flow packed-bed solar air heater with an external recycle are investigated theoretically. An analytical model capable of predicting the thermal and effective thermal performances of the heater is presented. The effects of the mass flow rate, the recycle ratio, and the bed porosity on the thermal and effective thermal efficiencies of the heater are investigated. It is indicated that the recycle ratio significantly improves the thermal performance of a double-pass packed-bed solar air heater. The results revealed that the thermal and effective thermal efficiencies of the heater are about 21.3 and 25.4% higher when compared to a conventional-type solar air collector of the same size with an external recycle. The optimum values of the recycle ratio, the mass flow rate, and the bed porosity, at which the heater yields the maximum value of effective thermal efficiency, are identified and presented. The results of the therma...

Different manifold shapes of microchannel device are investigated for the pressure drop characteristics under the effect of varying microchannel depth, width and spacing. The response surface methodology is applied to optimise the operating conditions of different microchannel systems. Four operating parameters, the channel width, depth, spacing and the inlet Reynolds number are considered in this study. The individual effects of these operating parameters and the combined effects of multiple operating conditions on pressure drop characteristics are examined using CFD. The semi-elliptical manifold shapes results the high level of fluid flow uniformity within microchannels and lower pressure drop. The maximum percentage reduction in the pressure drop across the microchannel device is 70%, obtained for semi-elliptical manifold shape as compared to other. The heat transfer analysis is also carried out in the extent of the study.

In this paper, double flow packed bed solar air heater was investigated theoretically and experimentally. A numerical model for the air heater was presented. Numerical calculations had been performed under Hamirpur (latitude, 31o25’ to 31o52’North) prevailing weather conditions. A mathematical models based on the volumetric heat transfer coefficient have been developed. To solve this model and to provide an iterative approach, forward difference method of finite difference scheme is employed. The theoretical predictions indicated that the agreement with the measured performance is fairly good. The effect of mass flow rates of air on thermal and effective thermal efficiencies of the double flow with and without packed bed solar air heaters were also investigated. The results showed that the double flow packed bed solar air heater is about 78.8% more efficient compared to the double flow without packed bed solar air heater.