Performance enhancement of a humidification–dehumidification desalination system (original) (raw)
Related papers
Journal of Thermal Analysis and Calorimetry, 2019
The purpose of the present work is to investigate humidification-dehumidification desalination system and to explore the effect of pertinent parameters on the overall performance of the process taking in account the irreversibilities and energy losses. The system has been inspected using first and second laws of thermodynamics, and an optimization of the performance along with design development has been performed based on mathematical calculation and modeling for the fundamental equations associated with mass, energy, exergy and salinity balance incorporating the effects of irre-versibilities and thermal losses which in turn helps in establishing an efficient desalination system by reducing these losses. The results show a good improvement compared to previous studies. The model target is to increase heat exchange in humidifier and dehumidifier compartment as well as augmenting pure water capacity and lessening energy consumption. Results expose that the inlet water temperature and flow rate represent the main factors affecting the system performance. It is found that the heater has the main part of exergy losses. Increasing the temperature of the water in the dehumidifier outlet allows minimizing the exergy losses in the dehumidifier.
Optimum thermal design of humidification dehumidification desalination systems
• Humidification dehumidification (HDH) cycles are investigated. • Theoretical analysis of water heated and air-heated HDH cycles are presented. • Practical design aspects of HDH cycles are given. • Humidifier and dehumidifier design models are provided. a b s t r a c t Humidification dehumidification (HDH) process is used for producing fresh water from saline water at sub-boiling temperature. This process uses a low-temperature source such as solar energy or waste heat source. Although these heat sources are available with minimal operating cost, an optimum thermal design is required to maximize the water production rate for a given heat input. In this paper, the main design and performance parameters are investigated for two HDH cycles namely, water-heated and air-heated cycles. First-law based thermal analyses are provided and performance charts are presented by considering assumptions. The design details of both the humidifier and dehumidifier are presented to determine their sizes under different design conditions. It has been demonstrated that optimum mass flow rate ratios exist for each cycle such that the gained-output ratio (GOR) is maximized. In addition, it is demonstrated that higher GOR can be obtained by using large-size hu-midifiers and dehumidifiers due to increasing their effectiveness. Moreover, increasing the temperature of water entering the humidifier reduces GOR for the water-heated cycle whereas it increases for the air-heated cycle. A comparison is also carried out between the two cycles to provide guidelines for designers in terms of, power requirements and components size.
2020
The humidification-dehumidification system is one of the desalination technologies that can utilize non-fossil thermal sources and requires insignificant input energy. This system is usually suitable for rural areas and places far from the main sources of energy. The purpose of this study is to obtain the most suitable working conditions and dimensions of this system. In this research, thermodynamic modeling was first performed for a simple type of the system (water-heated); then, the effect of parameters on the system performance was investigated. Modeling was conducted through a numerical simulation; furthermore, the assumption of the saturation of exhaust air from the humidifier was also considered in the mentioned code. Afterward, a comparison was made between two different forms of the system, and the proper form was chosen for the rest of the research. Moreover, through heat transfer equations, the dimensions of the two main parts of the system, i.e., humidifier and dehumidifi...
International Journal of Heat and Mass Transfer, 2013
Humidification dehumidification (HDH) is a promising technology for small-scale seawater desalination and has widespread application in drinking and industrial water treatment systems. This paper demonstrates the significance of a novel parameter known as the 'modified heat capacity rate ratio' (HCR) in the thermal design of HDH systems and in simultaneous heat and mass exchange (HME) devices. HCR is of particular importance in developing a fundamental understanding of the concept of thermodynamic balancing. A pilot-scale HDH unit (with a peak production capacity of 700 l/day) has been constructed and detailed experiments have been performed on this unit. Based on these experiments, the recently developed theories behind the design of HDH systems with or without mass extraction and injection are validated. Furthermore, important concepts with regard to design and optimization of HME devices have been studied in the present experiments.
Humidification dehumidification desalination process: Design and performance evaluation
Chemical Engineering Journal, 2008
This paper focuses on the design and modeling of the humidification dehumidification desalination (HDH) process. The process is only found on experimental or very small pilot scale. Literature studies are rather limited and it includes a number of experimental investigations, performance evaluation, and measurements of the heat and mass transfer coefficients. This study includes useful and new data on the evaluation of the heat transfer coefficient of the humid air stream in the condenser unit. The analysis develops a correlation for the heat transfer coefficient for the humid air stream as a function of the Reynolds and Prandtl numbers. Also, detailed evaluation of the system performance is presented as a function of the system temperatures and the inlet relative humidity of the air stream. Results are presented for variations in the humidifier height, heat transfer area of the condenser, flow rate of cooling water, performance ratio (defined as kg of product water per 1 kg of heating steam), and flow rates of the air and water streams. Results show the need for further system optimization through experimental measurements and mathematical modeling to determine the design and operating conditions that provides the lowest unit product cost.
Humidificaton-Dehumidification Desalination System -An Overview
This article reports about the recent researches and modifications carried out in the humidification-dehumidification desalination system using renewable energy sources, waste heat recovery and combined desalination systems for improving the fresh water production rate. Major desalination processes consume a large amount of energy derived from oil and natural gas for heat and electricity, while emitting harmful gases. Solar desalination has emerged as a promising renewable energy-powered technology for producing fresh water. Also, recovering waste heat from various heat sources is considered an economical one. Combining the principle of humidification-dehumidification with solar desalination results in an increase in the overall efficiency of the desalination plant. A brief study of the mechanism of various advancement in the humidification-dehumidification desalination system is presented in this report, along with an economical evaluation of the process. Comparison of the efficiencies and costs of currently available various humidification-dehumidification desalination processes presented in this report. The three major components such as humidifier, dehumidifier, and heater of the humidification–dehumidification desalination unit are undergone simulation verification and design optimization.
Desalination 436 (2018) 161–175, 2018
Humidification dehumidification (HDH) desalination system is a thermal-based desalination technology that is suitable for small-scale water desalination applications. In this paper, we present an experimental and ther-modynamic analysis of the energetic performance of two HDH cycles. The HDH cycles considered are the basic open-air open-water (OAOW) cycle and the modified closed-water open-air (CWOA) cycle with the options of brine recirculation. An experimental investigation is performed on the modified cycle to validate the theoretical model that is used to assess the energetic performance of both the basic and modified cycles. The theoretical model is found to be in a good agreement with the experimental data with a maximum percentage deviation of 5% from the experimental data. Furthermore, limiting cases of the system are explored. Within the limiting cases, the modified cycle recorded about 100% improvement in the energy performance over the basic cycle due to heat recovery process associated with the modified cycle. Additionally, a cost analysis was performed to determine the cost of freshwater production by the presented desalination cycles. Results show that the freshwater price varied from 4.10 to 6.55 /m3and0.79to2.25/m 3 and 0.79 to 2.25 /m3and0.79to2.25/m 3 for the basic OAOW HDH cycle and the modified CWOA HDH cycle, respectively.
MODELING AND OPTIMIZATION OF A DESALINATION UNIT USING HUMIDIFICATION-DEHUMIDIFICATION HDH PRINCIPLE
IAEME PUBLICATION, 2021
Humidification-Dehumidification desalination (HDH) process is an existing, widely-spread and developing technology. This technology has high potential to serve people who suf er lack of water in undeveloped, poor countries as it could be built and operated using locally available natural resources. HDH cycle is considered man-made rain cycle. It utilizes vaporization of water from saline solution into a carrier gas (usually air). Then this saturated air with water vapor passes over a cold surface, leading to condensation process obtaining fresh potable water suitable for human usage. This paper focuses on the heat and mass transfer processes inside each of the humidifier and the dehumidifier sections. In the humidifier section, counter flow between air and water at atmospheric pressure, where direct contact between air and water occurs. In the dehumidifier section, air flows over a coil containing flowing water in opposite direction. Based on mass balance and rate equations, the mathematical modeling equations of both humidifier and dehumidifier sections are established. Output results of simulation process depend on liquid-gas ratio, entering temperature of air in addition to water temperature entering both sections as well as the geometry of both humidifier and dehumidifier. These design parameters can provide great reference significance for the design, optimization and regulation of humidifiers and dehumidifiers sections.
Desalination, 2009
In this paper the humidification–dehumidification desalination process is studied and its performance optimized using mathematical programming. An advantage of this method is consideration of the simultaneous effect of various parameters on process performance. An NLP system model is solved for three objective functions: minimization of specific thermal energy consumption, maximization of productivity and maximization of condenser heat recovery. The solutions have been improved especially from a productivity point of view in comparison with previous studies. The productivity objective function leads to the best solution if there is no limitation for the humidifier inlet water temperature. Otherwise, the specific energy objective function seems to be better than others. In the next step the effect of important parameters on optimum operation point of the HD process is analyzed and related variation curves are presented. Results reveal that the water to air mass flow rate ratio (L/G) is the most effective parameter and has an optimum value. Also the humidifier inlet water temperature will be an important parameter. The upper temperature results in more productivity and a smaller heat transfer area. But minimum specific thermal energy consumption of the system occurs at an optimum temperature. Finally, the analysis of the dehumidifier inlet water temperature shows that if the humidifier inlet water temperature is high, the specific thermal energy consumption can be decreased more through recycling of the outlet humidifier water into the dehumidifier.
• Experimental demonstration of two stage desalination and cooling • Use of chilled water for condensation of humid air • Simulation of experimental results • Comparative study on conventional condensation and improved condensation • Improved design of proposed integrated plant a b s t r a c t Humidification–dehumidification (HDH) desalination is a simple and cost effective solution to convert the saline water into desalinated water. In current work, desalination yield has been augmented with two stage HDH integrated cooling plant. A pilot plant has been developed and analyzed with experimental and simulation studies. The identified operational variants are hot saline water supply to humidifiers and its inlet temperature. The saline water is heated in a solar water heater (SWH) and supplied to two humidifiers and two air preheaters. The simulated results developed for subsystems are validated with the experimental readings. Desalination yield is not satisfactory level at lower water temperature in the first stage plant but there is no such limitation in the second stage operation. Nearly 1.5 LPH of desalinated water is resulted at 15 m 3 /h of air. The energy utilization factor (EUF) of two stage plant is concentrated at higher side compared to the single stage plant's EUF. The increased flow of saline water in humidifiers and its high temperature is favoring the desalination output but with a penalty in cooling effect.