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The water vapour in the atmosphere has the potential to fulfil the need for potable water. Solar powered atmospheric water generation system (SPAWG) is an emerging and renewable approach to obtain potable water from atmospheric air. But, the productivity of these systems is limited, which needs improvement. Therefore, a new SPAWG system is proposed in the present study, which consists of desiccant wheel, both ends open evacuated tube solar air heater, and heat exchanger. Initially, a numerical model of the desiccant wheel is developed and the recommended operating parameters are: regeneration temperature range of 80–150 °C, rotational speed of 15 RPH, facial area ratio of 3, and 8 m/s & 2 m/s air velocities at adsorption and regeneration sectors, respectively. A double-ended open evacuated tube solar air heater with the collector area of 9.37 m2 has been used to regenerate desiccant wheel, which produces the hot air up to 155.2 °C at a mass flow rate of 117 m3/h. This results in the regeneration air having a humidity ratio of 53.5 g/kg da with a dew point temperature of 41.5 °C, allowing the available water vapour to be easily condensed by an air cooled heat exchanger. The proposed SPAWG system produces 10.39 L of water throughout the day with thermal efficiency of 10.19 %. The cost of water produced by the system is estimated at 0.2 $/L. [Display omitted] • AWH system integrating desiccant wheel and solar air heater has been proposed. • Hot air up to 150 °C generated using evacuated tube solar air heater. • Air-to-air heat exchanger is used to condense water vapour present in humid air. • This system produced 10.39 L of fresh potable water for a small nuclear family. [ABSTRACT FROM AUTHOR]

Metal foams have gained popularity in the renewable energy industry due to their superior thermo-physical properties. In the present study, a coupled finite volume and discrete element numerical method is used to numerically investigate the mechanisms that govern particle-laden gas flows and particulate fouling in idealized metal foam air-cooled heat exchangers. This paper provides a systematic analysis of the foulant distribution and the pressure drop due to the metal foam structure and the presence of fouling. The idealized Weaire-Phelan metal foam geometry serves as a good approximation to a real metal foam geometry. The pressure drop and deposition fraction follows a linear relation for sandstone cases, whereas for the sawdust cases, the pressure drop is sensibly invariant with time although a noticeable increase in deposition fraction with time is realized. The foulant residence time in addition to the correlations between pressure drop, deposition fraction, and inlet velocity can be used to optimize metal foam heat exchanger designs. Optimum heat exchanger performance is achieved by keeping the same fiber thickness of 0.17 mm at a high porosity at 97.87%. An increase in fluid carrier velocity promotes particle transport by means of particle interception thereby reducing the deposition fraction irrespective of foam geometry. [ABSTRACT FROM AUTHOR]

In the present study, air-side entropy generation rate for an evaporative air-cooled heat exchanger has been investigated using thermodynamic second-law analysis. For this purpose, entropy generations due to heat transfer, friction loss and evaporation were taken into consideration. From the results of this study, it was observed that the total air-side entropy generation was increased by increasing the air-side Reynolds number. Actually, increasing of air mass flow rate, increases irreversibilities due to both evaporation and friction. Stepping up of ambient temperature leads to increasing of irreversibility due to water evaporation. The results showed when the ambient temperature approaches to inlet process fluid temperature, the contribution of the entropy generation rate due to water evaporation becomes the dominant term in the total entropy generation rate. Moreover, it was seen that the effect of deluge water mass flow rate changes on entropy generation rate is slight.

Numerical study was conducted to investigate the water spray cooling effect in an air cooled heat exchanger. A k-ε turbulence model, discrete phase model, and species transport equations were solved simultaneously along with heat-mass exchange model to capture heat and mass transfer effects. The simulation result was compared to an available real scale test data. Using the real scale operating condition, the effect of spray water droplet diameter (10 to 100 pm), spray system configuration (horizontal, vertical, inclined), evaporative time (vertical location of spray system), wind speed (0 to 4.47 m/s), ambient air relative humidity, and spray water amount were investigated. A non-dimensional spray cooling parameter was introduced to evaluate various effects. A parametric study reveals that the vertical location of the water spray system is critical to the evaporative performance and the minimization of adverse wind effects. Securing enough evaporative time by increasing liquid droplet flow path is required to enhance spray cooling effects. It is also found that proper spray nozzle selection (i.e. liquid water droplet size) is critical to achieve desired spray cooling capacity. The spray cooling system design should consider the interactive relationship between the heat exchanger configuration and the local climate condition. [ABSTRACT FROM AUTHOR]

In this paper, a review is presented on the experimental investigations and the numerical simulations performed to analyze the thermal-hydraulic performance of the air-cooled heat exchangers. The air-cooled heat exchangers mostly consist of the finned-tube bundles. The primary role of the extended surfaces (fins) is to provide more heat transfer area to enhance the rate of heat transfer on the air side. The secondary role of the fins is to generate vortices, which help in enhancing the mixing and the heat transfer coefficient. In this study, the annular and plate fins are considered, the annular fins are further divided into four categories: (1) plane annular fins, (2) serrated fins, (3) crimped spiral fins, (4) perforated fins, and similarly for the plate fins, the fin types are: (1) plain plate fins, (2)wavy plate fins, (3) plate fins withDWP, and (4) slit and strip fins. In Section 4, the performance of the various types of fins is presented with respect to the parameters: (1) Reynolds number, (2) fin pitch, (3) fin height, (4) fin thickness, (5) tube diameter, (6) tube pitch, (7) tube type, (8) number of tube rows, and (9) effect of dehumidifying conditions. In Section 5, the conclusions and the recommendations for the future work have been given. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims at developing a novel air-cooled condenser for concentrated solar power plants. The condenser offers two significant advantages over the existing state of the art. Firstly, it can be installed in a modular format where pre-assembled condenser modules reduce installation costs. Secondly, instead of using large, fixed speed fans, smaller speed controlled fans are incorporated into the individual modules. This facility allows the operating point of the condenser to change in order to maximise plant efficiency at all times. Two condenser designs were proposed and full-scale prototype modules were manufactured for experimental testing. Both designs comprise a bank of circular finned tubes, coupled to an array of axial fans. The air-side thermal and aerodynamic characteristics were measured using a purpose built steady-state test facility. The measurements were correlated and compared well with existing correlations in the relevant literature, thus validating their use in thermodynamic models to predict power plant performance. A plant performance analysis was conducted combing the experimental measurements with output data from a 50MW concentrated solar power plant. This analysis firstly verified that the plant efficiency can be continually maximised by altering the condenser fan speed. Furthermore, under certain conditions plant output can be increased by over 10% by varying fan speed by 10% of the full speed. The study also provides a comparison of the two designs in terms of their effect on the plant output power. With respect to the thermodynamic efficiency and cost-efficiency, the four row condenser substantially outperforms the initial six row design. [Copyright &y& Elsevier]

Abstract: In this paper a novel optimization algorithm based on Imperialist Competitive Algorithm (ICA) is used to optimize the heat transfer in an air cooled heat exchanger equipped with the classic twisted tape inserts. This algorithm has some advantages such as simplicity, accuracy, and time saving. Experiments included the twist ratio ranging from 1.76 to 3.53. Also, the Reynolds number varied from 4021 to 16,118. After data reduction, the regression equation of average Nusselt number was obtained as a function of Reynolds number and the twist ratio. Then the cost function was optimized by the use of ICA. One can be sure that the Nusselt number will be optimized due to the optimization of the cost function. Computational results indicate that the proposed optimization algorithm is quite effective and powerful in optimizing the cost function. According to the results, in order to obtain maximum heat transfer, the twist ratio must be at the lowest level. [Copyright &y& Elsevier]

Abstract: This paper highlights the application of fuzzy logic to predict the heat transfer in an air cooled heat exchanger equipped with three types of tube inserts including; butterfly, classic and jagged twisted tape. In the study which was carried out in the range of Reynolds number, the maximum heat transfer was obtained by the butterfly insert with an inclined angle of 90°. The results have also revealed that the heat transfer rates obtained by employing the classic and jagged inserts, reduced by increasing twist ratio. Moreover, it has been also shown that, fuzzy logic is a powerful technique used for predicting the heat transfer due to its low error rate. The average error of fuzzy technique as compared with experimental data was found to be 0.68% for this study. [Copyright &y& Elsevier]

Abstract: This paper reports the experimental and Computational Fluid Dynamics (CFD) modeling studies on heat transfer, friction factor and thermal performance of an air cooled heat exchanger equipped with three types of tube insert including butterfly, classic and jagged twisted tape. In the studied range of Reynolds number the maximum thermal performance factor was obtained by the butterfly insert with an inclined angle of 90°. The results have also revealed that the difference between the heat transfer rates obtained from employing the classic and jagged inserts reduces by decreasing the twist ratio. The CFD predicted results were used to explain the observed results in terms of turbulence intensity. In addition, good agreements between the predicted and measured Nu number as well as friction factor values were obtained. [Copyright &y& Elsevier]

Abstract: This study investigates the use of global sensitivity analysis (GSA) and harmony search (HS) algorithm for design optimization of air cooled heat exchangers (ACHEs) from the economic viewpoint. In order to reduce the size of the optimization problem, GSA is performed to examine the effect of the design parameters and to identify the non-influential parameters. Then HS is applied to optimize influential parameters. To demonstrate the ability of the HS algorithm a case study is considered and for validation purpose, genetic algorithm (GA) is also applied to this case study. Results reveal that the HS algorithm converges to optimum solution with higher accuracy in comparison with GA. [Copyright &y& Elsevier]

Direct reduction of iron process in steel industry has special production conditions. Low quality cooling water, low cold and high hot cooling water temperature, space limitation for new equipment installation, high value-added of product and severe effect of cooling water temperature on production rate are of these conditions. Considering technical and economic constraints and limitations, this situation makes this process an attractive case study for converting the existing wet cooling tower to hybrid cooling system. In this paper, based on integration of process, dry and wet cooling system and ambient conditions profiles, a new method for designing hybrid cooling system has been proposed. The calculation program has been developed as a MATLAB code and resulted: 1) Calculation of annual water saving and energy consumption with reasonable accuracy, 2) Control system of dry and wet cooling blocks to maximize water saving under various ambient conditions, 3) Closed loop simulation of cooling system considering thermal feedback of process to cooling system and 4) Obtaining optimum values for 16 design parameters of dry block cooling (consisting air cooled heat exchanger and plate heat exchanger). The optimization has been done via genetic algorithm, considering annual response of each design under various ambient temperature and relative humidity. Considering design standards for new equipment and operational and technical constraints, made the optimization model reliable as well as checking the design parameters with process equipment constructors. In optimum point, converting existing wet cooling tower to hybrid cooling system in direct reduction of iron plant of Mobarakeh Steel Complex located in Isfahan province in Iran, will decrease the annual water consumption by 70.15% and production loss by 98% with payback period of 1 years and 10 months. [ABSTRACT FROM AUTHOR]

• Evaluation of Brayton cycle layouts at higher temperature operating conditions. • Critical temperature enrichment using binary mixture. • Provide solution to the integration problems at higher temperatures. • Suggest best supercritical cycle configuration for arid climate conditions. In this study, the globally known supercritical Brayton cycles have been evaluated for their ability to accommodate dry cooling. Dry cooling is the most favourable choice for concentrated solar power plants, since these plants are more productive in drought areas. The performance of six Brayton cycle layouts (regenerative, recompression, intercooling, partial cooling, pre-compression, and split expansion) has been determined by developing complete mathematical models. Key parameters, such as, cycle efficiency, specific work requirement and incorporation ability of the cycle with solar receiver have been investigated for arid climate conditions. In addition, an effort has been made to enhance the cycle performance by increasing the critical temperature of the working fluid by using a mixture of carbon dioxide and benzene. The computed results revealed that cycles using binary mixture offer high efficiency in drought areas in combination with air cooling. Moreover, binary mixture showed higher integration ability with solar power plant because of expanded temperature difference across the solar receiver. [ABSTRACT FROM AUTHOR]