A novel solar-driven direct contact membrane-based water desalination system

This study proposes a novel integrated solar membrane-based desalination system. The system includes vacuum glass tubes to increase absorbed solar energy and to decrease heat loss, heat pipes to transfer the absorbed energy efficiently, and a tubular direct contact membrane distillation module to use the absorbed energy more effectively. To improve the freshwater production rate and overall efficiency of the proposed system, a cooling unit was also added to the permeate loop of the desalination unit. The performance of the system was experimentally investigated without (Case I) and with (Case II) the cooling unit in summer and without the cooling unit in winter (Case III) under climatic conditions of Perth, Western Australia. The experimental results indicated that except a few minutes in the morning, the heat pipe solar system was able to provide all the required thermal energy for the desalination system. The maximum thermal efficiency of the solar system in summer reached ~78% and its exergy efficiency fluctuated between 4 and 5% for a noticeable amount of time from 10:30 AM to 3 PM. Moreover, the maximum freshwater production rate were 2.78, 3.81, and 2.1 L/m2h in Cases I, II, and III, respectively. The overall efficiency of the system improved from 46.6% in Case I to 61.8% in Case II showing the technical effectiveness of implementing the cooling unit in the permeate flow loop of the system. In addition, the daily averaged specific energy consumption in Cases I, II, and III were 407, 377, and 450 kWh/m3, respectively

Performance analysis of a thermal-driven tubular direct contact membrane distillation system

This paper examines the performance of a thermal-driven tubular direct contact membrane distillation (DCMD) system theoretically and experimentally. A multi-step mathematical model was developed to predict the freshwater productivity of the tubular DCMD module applicable for both small and large-scale applications by considering the changes in the operational variables along the membrane’s length. The proposed model was verified by building an experimental rig which was tested under different operational conditions. The results showed that keeping the mass flow rates in the hot and cold channels either near the end or beyond the transition range of the flows results in higher water production. In addition, heating up the feed stream is more efficient for enhancing water productivity than using the same amount of energy to cool the permeate stream down. Finally, the effects of operational and physical factors on the freshwater productivity were identified and discussed

Strategies to improve the thermal performance of heat pipe solar collectors in solar systems: A review

Invention of evacuated tube heat pipe solar collectors (HPSCs) was a huge step forward towards resolving the challenges of conventional solar systems due to their unique features and advantages. This has led to their utilization in a wide range of solar applications surpassing other conventional collectors. However, relatively low thermal efficiency of heat pipe solar (HPS) systems is still the major challenge of solar industry evidenced by numerous studies conducted mainly during the last decade to improve their efficiency. To date, several review papers have been published summarizing studies relevant to utilization of HPSCs in various thermal applications. However, to the authors\u27 knowledge, a comprehensive review which surveys and provides an overview of the studies undertaken to improve the thermal performance of HPS systems (mainly during the last decade) by implementing different strategies has not been published to date. This review paper summarizes all the proposed strategies to improve the thermal efficiency of different industrial, domestic, and innovative HPS systems. First, the concept, structure, and operational principles of HPSCs are introduced concisely. Then, novel structures and designs of HPSCs aiming to increase the thermal efficiency of the collector as the most important component of the solar system is reviewed. This is followed by a comprehensive review of various methods to store solar energy more efficiently, increase solar system’s operation time, increase overall efficiency by turning the solar system into a multi-purpose system, enhance heat transmission in the solar system, and implement new solar loop and heat pipe working fluids with better heat transfer characteristics. Finally, research gaps in this field are identified and some future research trends and directions are recommended

Thermal performance of an evacuated tube heat pipe solar water heating system in cold season

This study evaluates the performance of a heat pipe solar water heating system to meet a real residential hot water consumption pattern theoretically and experimentally under non-ideal climatic conditions during a cold day in Perth, Western Australia. A mathematical model was developed and used to calculate the optimum number of glass tubes of the heat pipe solar collector. Based on the obtained data, an experimental rig with 25 glass tubes was designed, built, and tested as the temperature changes after 25 tubes reached the insignificant value of 0.6%. The results showed that hot water extraction had significant impact on the thermal performance of solar water heating system by increasing the amount of the absorbed energy and overall efficiency and decreasing exergy destruction. This indicates the importance of considering hot water consumption pattern in design and analysis of these systems. Auxiliary heating element was a necessary component of the system and played an important role mainly at the beginning of the operation in early morning (operation time of 19 min) and partly during the cloudy and overcast periods (operation time of 8 min). Two empirical equations relating the thermal and exergetic efficiencies of the heat pipe solar collector to the operational and environmental parameters were proposed. Comparison of the theoretical and experimental outlet temperature of the collector showed very good agreement with the maximum absolute and standard errors being 5.6% and 1.77%, respectively

A review of latest developments, progress, and applications of heat pipe solar collectors

Among all the available solutions to the current high energy demand and consequent economic and environmental problems, solar energy, without any doubt, is one of the most promising and widespread solutions. However, conventional solar systems face some intractable challenges affecting their technical performance and economic feasibility. To overcome these challenges, increasing attention has been drawn towards the utilization of heat pipes, as an efficient heat transfer technology, in conventional solar systems. To the authors’ knowledge, despite many valuable studies on heat pipe solar collectors (mainly during the last decade), a comprehensive review which surveys and summarizes those studies and identifies the research gaps in this field has not been published to date. This review paper provides an overview of the recent studies on heat pipe solar collectors (HPSCs), their utilization in different domestic, industrial, and innovative applications, challenges, and future research potentials. The concept and principles of HPSCs are first introduced and a review of the previous studies to improve both energy efficiency and cost effectiveness of these collectors is presented. Moreover, a concise section is dedicated to mathematical modeling to demonstrate suitable methods for simulating the performance of HPSCs. Also, the latest applications of HPSCs in water heating, desalination, space heating, and electricity generation systems are reviewed, and finally, some recommendations for future research directions, regarding both development and new applications, are made

Theoretical modelling approaches of heat pipe solar collectors in solar systems: A comprehensive review

The invention of heat pipe solar collectors (HPSCs) is considered as an immense step forward towards solving the challenges of conventional solar thermal systems. Their unique qualities have acted as a great motivation for researchers to focus their studies on HPSCs and their applications. A considerable share of these studies has been allocated to theoretical studies due to several technical and economic reasons. However, to the authors’ knowledge and despite many valuable efforts in this field, there is no review paper available to summarise the relevant proposed and developed theoretical models to date and identifies the research gaps in this field. Therefore, in this review paper, the latest theoretical studies in the field of HPSCs along with their advantages, disadvantages, and contribution have been categorized, reviewed, and discussed. First, the operational principles and structure of HPSCs have been explained to create a background for readers. This is followed by a short section dedicated to the simulation of solar radiation as the most important input for all solar mathematical models. In addition, various mathematical approaches including steady state models (i.e. one-dimensional energy balance and thermal resistance network methods), dynamic models, and models for novel configurations and applications of HPSCs have been reviewed. Moreover, mathematical models to determine the exergy efficiency of HPSCs, which is an effective tool to evaluate the solar systems from a thermodynamic point of view, have been presented. Finally, the challenges, research gaps, and recommendations for future research directions have been provided