Mechanical Vapor Compression Research Articles

Theoretical performance analysis of a new hybrid air conditioning system with two-stage energy recovery in cold winter

Abstract Energy recovery technologies can effectively improve the energy efficiency of air-conditioning systems and significantly reduce building energy consumption. In this paper, a parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) is carried out theoretically based on developed models. The proposed HAC incorporates into a conventional mechanical vapor compression air conditioning system with an independent fresh air conditioner which is composed of a network of heat exchangers, including a packed bed and three air-water finned coils. Under cold winter climate, in the fresh air conditioner, a packed bed is coupled with a water-air heat exchange coil to form a total energy recovery loop. A run-around sensible energy recovery loop is also integrated in the system to produce a two-stage energy recovery effect. Moreover, a sprayer is installed upstream of the two-stage energy recovery process for fresh air humidification, and a fresh air recirculation duct is equipped for frost-free operation. In the parametric analysis, four independent affecting parameters are included: the air-to-water heat capacity ratio, the indoor temperature, the ambient temperature, and the ratio of recirculation fresh air. The energy-saving potential of the HAC is also evaluated for applications in seven typical cities located in middle-lower Yangtze River region of China over the winter period (December, January and February). The results show that compared with the conventional system with electric humidification, the HAC has an average energy saving rate of 44.0%, and its average power saving per hour is 13.41 W m−2.

Membrane Distillation of Butanol from Aqueous Solution with Polytetrafluoroethylene Membrane

AbstractNowadays, butanol is considered as biofuel. In this work, separation of butanol from aqueous solution was carried out by vacuum membrane distillation with polytetrafluoroethylene membrane, using mechanical vapor compression on the downstream. Higher flow rates could promote membrane separation with higher total flux and higher separation factor, thus influencing butanol separation. Membrane fouling was observed which exerted a substantial effect on the membrane separation performance with a real fermentation broth. Compared to the traditional distillation process, this procedure is more cost‐effective due to ∼ 50 % reduced energy consumption.

Experimental analysis of a multistage direct-indirect evaporative cooler using a straight heat pipe

Mechanical vapour compression air conditioning has advantages and drawbacks. The compressor used in this system increases energy consumption. In addition, the refrigerant used in this system harms the environment and contribute to ozone layer depletion. However, keeping a building at a comfortable temperature is still necessary and cannot be neglected. An evaporative cooler can be an alternative for overcoming this drawback because evaporative coolers are environment-friendly and have low operation costs. However, the evaporative cooler disadvantageous for producing air with a high relative humidity. The objective of this experiment is to evaluate the performance of a multistage direct–indirect evaporative cooler using a heat pipe in terms of saturation efficiency, the output air humidity, and sump water consumption. In this experiment, heat pipes are used as a pre-cooler in the first stage and for indirect cooling in the third stage. Tests are performed under different inlet temperatures ranging from 36 to 45 °C and an air flow rate ranging from 0.4 to 1.4 m/s. Thermocouple and humidity sensors are used to obtain the temperature and relative humidity values, respectively. The largest decrease in temperature is obtained when evaporation occurs during the first stage heat pipe at a 0.8 m/s air flow rate and 45 °C. The saturation efficiency and the output humidity are calculated and evaluated. The experiment shows that the first and second stages together can increase the saturation efficiency, but this process also increases the relative humidity of the outlet air and consumes more water than a single stage does. All three stages together produce a smaller decrease in temperature and relative humidity.

Performance analysis of an integrated cooling system consisted of earth-to-air heat exchanger (EAHE) and water spray channel

This study evaluates the cooling performance of a new hybrid system composing of an earth-to-air heat exchanger (EAHE) and a water spray channel to provide thermal comfort in Tehran, Iran. The inlet air temperature passing through the EAHE dissipates its heat to the surrounding soil and become slightly colder. To reach thermal comfort, the pre-cooled air flows upward through a channel spraying water downward and enters the living space. Considering the evaporative thermal comfort zone, the results showed that this system can meet comfort conditions for summer season Tehran. Moreover, according to the results, the cooling effectiveness of the proposed hybrid system is more than 100%, which means that the integrated system is capable of decreasing the air dry-bulb temperature below the inlet ambient wet-bulb temperature. Employing ground as a reliable source of alternative energy, the proposed cooling system can be considered an eco-friendly and energy-efficient system. Therefore, the introduced cooling system can be utilized as an alternative to conventional evaporative coolers or mechanical vapor compression systems while it can be considered an eco-friendly and energy-efficient system.

Використання технологій опріснення морської води для попереднього упарювання рідких радіоактивних відходів

Processing of liquid radioactive waste (LRW) includes evaporation followed by vitrification. Reducing the energy consumption of evaporation of LRW is an urgent task. In the article, an attention is paid to the fact that similar technical and economic problems are solved with the desalination of seawater. It is proposed to use well-developed seawater desalination technologies for preliminary evaporation of LRW. For a detailed analysis, desalination technology with mechanical vapor compression (MVC) was selected. This technology is energy-saving because it implements the heat pump principle. MVC technology is highly efficient, simple, and does not lead to the generation of secondary radioactive waste. A mathematical model of a single-stage desalination plant with MVC has been developed, taking into account that the thermodynamic cycle of this process is open. Since there are no data on the physical properties of LRW in the literature, the properties of sea water were used. The design and operational parameters were optimized in order to reduce the cost of 1 m3 of evaporated water. It has been established that the main design parameters affecting the cost of evaporated water are the degree of vapor compression in the compressor and the heat exchange surface area of the evaporatorcondenser. The influence of these parameters on capital and operating costs is shown. The optimal combinations of these parameters are determined. To ensure the optimal operating mode of the installation, it is necessary to maintain the optimum salt content of boiling brine, which is determined by the rate of consumption of the source water. The optimal values of these parameters are calculated in a wide range of salt content of the source water. It is shown that, at low salinity of the initial LRW, evaporation is advisable to be carried out in a multi-stage installation. As a result of the calculations, it was found that the specific cost of evaporation of liquid radioactive waste with an initial salt concentration of 10% to a salt content of 20% using the desalination technology with mechanical vapor compression is 0.843 USD/m3.

Parameter optimization and economic analysis of a single-effect mechanical vapor compression (MVC) distillation system

Parameter optimization and economic analysis of a single-effect mechanical vapor compression (MVC) distillation system

Exergy, exergoeconomic and exergy-based emission cost analyses of a coconut husk-fired power and desalination plant

A renewable-based energy system is proposed herein, which employs coconut husk briquettes and produces electricity and fresh water for a small municipality. The system is constituted by a Rankine-based steam power plant and a set of mechanical vapour compression desalination modules. Exergy-based cost allocation methodology is applied to the system, where exergy, economic, and emission costs are allocated to both electricity and fresh water. The energy system satisfied more than 70% of the water demand of the municipality - however, despite technically and socially viable, there are still margins for improvement.

Análisis de la generación de las irreversibilidades a partir del Coeficiente de Operación en un sistema de refrigeración por compresión mecánica de vapor con R-134a

This paper presents the development of individual contributions, in the generation of irreversibilities, of a refrigeration system based on the Coefficient of Operation (COP). The generation of irreversibilities has been widely analyzed using the principles of the first and second laws of thermodynamics. This analysis uses the parameters of enthalpy, entropy as well as the temperature and heat generated in each component. The method proposed in this work improves the accuracy of the calculations due to the use of the COP in the mathematical process, which includes the processes of heat transfer and pressure drops developed in the evaporator, suction line, compressor, discharge line, condenser, liquid line and expansion valve of the mechanical vapor compression refrigeration system. The mathematical analyzes and the experimental results are shown, with these it is concluded that the exposed procedure is closer to the real conditions than those traditional procedures found in the text books.

Performance enhancement of a conventional multi-effect desalination (MED) system by heat pump cycles

Multi-effect desalination (MED) systems are highly promising for high salinity seawaters at large scales, and hence are used broadly in desalination plants. Despite the fact that the MED systems can be driven by various renewable or waste heat energies, many of the available renewable technologies are expensive in some parts of the globe. Hence, proposing and developing high-efficient mechanical-based MED units can be an encouraging alternative. In pursuance of this objective, two innovative mechanical-driven MED units are devised, simulated and the results are compared with those of the conventional MED-MVC (mechanical vapor compression) unit. For this aim, absorption-compression heat pump (ACHP) and vapor compression heat pump (VCHP) systems are used for integrating with the MED unit. Under a constant input power of 1845 kW it is found that proposing the MED-VCHP system instead of the conventional MED-MVC system improves gain-output-ratio (GOR), performance ratio (PR), freshwater rate, specific work consumption (SWC), exergy efficiency, exergy destruction rate, and exergy of loss by 1%, 12.86%, 12.64%, 11.45%, 10.78%, 3.3%, and 10.86% respectively. However, the unit cost of distilled water (UCDW) of the MED-VCHP system is around 6.7% higher than that of the MED-MVC system. Also, the MED-VCHP system uses less exergy of fuel than the MED-MVC system due to its high seawater exergy. Furthermore, it is found that one can decrease the overall exergy loss rate from 145.4 kW to 129.6 kW when the MED-VCHP system is used instead of the MED-MVC system.

Thermal Energy Storage Technology for Application in Transport Refrigeration

This paper reviews the use of an alternative refrigeration system in refrigerated vehicles by using thermal energy storage systems. The application of thermal energy storage systems in transport refrigeration focusing particularly on latent heat phase change materials PCMs that have been used in recent years is reviewed. The majority of PCMs are found in building applications for space heating and cooling, greenhouse heating applications, solar cookers, and storage of solar energy for water heating. The focus of this work is on latent heat storage (LHS) materials for road transport refrigeration and their benefits in the refrigeration of perishable foodstuffs for short- and long-distance transportation. The benefits of using LHS materials over a conventional mechanical vapour compression system are explored. This paper also centres on the need to develop new PCMs with high thermal cycles and minimal degradation to ensure effective performance in the transport refrigeration industry. Criteria for selecting suitable PCMs for different applications were summarised, and classification of PCMs based on their melting temperature and latent heat were tabulated. Heat transfer materials for increasing PCM performance were analysed as well as the effect of container material corrosion on PCM stability. The different thermal techniques for determining the properties of PCMs were summarised, and the accuracy of each technique was explored based on similar research work by other researchers. The PCMs that have been used in transport refrigeration as well as the thermo-physical criteria that are needed for different applications were analysed.

Minimal and zero liquid discharge with reverse osmosis using low-salt-rejection membranes

Minimal and zero liquid discharge (MLD/ZLD) are wastewater management strategies that are attracting heightened attention worldwide. While conventional reverse osmosis (RO) has been proposed as a promising technology in desalination and MLD/ZLD processes, its application is limited by the maximum hydraulic pressures that current RO membranes and modules can withstand. In this study, we develop low-salt-rejection RO (LSRRO), a novel staged RO process, that employs low-salt-rejection membranes to desalinate or concentrate highly saline feed streams, requiring only moderate hydraulic pressures. Based on process modeling, we demonstrate that LSRRO can overcome the hydraulic pressure limitations of conventional RO, achieving hypersaline brine salinities (>4.0 M NaCl or 234 g L−1 NaCl) that are required for MLD/ZLD applications, without using excessively high hydraulic pressures (≤70 bar). In addition, we show that the energy efficiency of LSSRO is substantially higher than traditional thermally-driven phase-change-based technologies, such as mechanical vapor compressor (MVC). For example, to concentrate a saline feed stream from 0.1 to 1.0 M NaCl, the specific energy consumption (SEC) of 4-stage LSRRO ranges from 2.4 to 8.0 kWh of electrical energy per m3 of feedwater treated, around four times less than that of MVC, which requires 20–25 kWhe m−3. Furthermore, compared to osmotically mediated RO technologies that require bilateral countercurrent stages to treat hypersaline brines, LSRRO is eminently more practical as it can be readily implemented by using ‘loose’ RO or nanofiltration membranes in conventional RO. Our study highlights LSRRO’s potential for energy efficient brine concentration using moderate hydraulic pressures, which would drastically improve the energetic and economic performance of MLD/ZLD processes.

Green solvents-based fractionation process for kraft lignin with controlled dispersity and molecular weight

The aim of this work is to develop a novel green solvent based sustainable process to refine lignin into low molecular weight (LMW) and high molecular weight (HMW) fractions. Lignin dispersity reduction were experimentally determined using four solvent mixtures, and benchmarked against eight pure solvents. Data outputs were used for modelling the integrated fractionation process. Dispersity reduction of up to 73% was achieved for the high value LMW fraction. Also, a 90% reduction of energy requirement was achieved with an optimized process incorporating a mechanical vapor compression system. This study showed that solvent mixtures involving water can significantly reduce the cost, environment, health and safety impacts of lignin fractionation. Techno-economic evaluation confirmed the economic viability of a large-scale process processing 50 tonne/day of lignin.

Study of the thermal performance of a novel dew point evaporative cooler

Evaporative cooling has been proven to have higher efficiency than does mechanical vapor compression refrigeration. It has great energy saving potential, and it is also an environmentally friendly solution for air cooling systems. To improve its performance, a small size counter-cross-flow cooler coated with nylon fibers on the wet channel surface was proposed. Then, the impacts of the operating parameters on its thermal performance were analyzed. The results showed that the cooler coated with nylon fibers demonstrated better cooling performance. The dew point effectiveness of the polystyrene + nylon fiber (PS + NL) varied from 46.7% to 78.6%. Compared with previous studies, the effectiveness of the counter-cross-flow PS + NL evaporative cooler was close to that of counter-flow evaporative coolers and higher than that of cross-flow evaporative coolers. In addition, the counter-cross-flow PS + NL evaporative cooler may reduce the size and weight of the cooler while providing the same air flow rate. It would be a good solution for residential building precooling or air conditioning, improving the energy efficiency of the cooling system.

Cálculo de la generación de entropía a partir del Proceso de Temperatura Promedio en un sistema de refrigeración por compresión mecánica de vapor con R-134a

The Average Temperature Process (PAT) is modeled by an equation that is used to calculate the increase in energy needed for the refrigeration cycle, which is equivalent to the energy degradation that corresponds to the production of entropy. This work shows experimentally that the increase in entropy, taking into account the processes of heat transfer that occur in the condensation temperature and in the evaporation temperature between the mechanical vapor compression refrigeration system and the environment, is directly related to the falls of pressure presented in the suction pipe and in the compression process, as well as the heat losses that exist between the main components (evaporator, compressor, condenser and expansion throttling) and the environment. From this development, the behavior of the refrigeration cycle is evaluated in order to obtain a minimum entropy generation criterion in the main components. Analytical as well as experimental results are shown using R-134a refrigerant.

Membrane-based treatment of shale oil and gas wastewater: The current state of knowledge

Shale oil and gas exploitation not only consumes substantial amounts of freshwater but also generates large quantities of hazardous wastewater. Tremendous research efforts have been invested in developing membrane-based technologies for the treatment of shale oil and gas wastewater. Despite their success at the laboratory scale, membrane processes have not been implemented at full scale in the oil and gas fields. In this article, we analyze the growing demands of wastewater treatment in shale oil and gas production, and then critically review the current stage of membrane technologies applied to the treatment of shale oil and gas wastewater. We focus on the unique niche of those technologies due to their advantages and limitations, and use mechanical vapor compression as the benchmark for comparison. We also highlight the importance of pretreatment as a key component of integrated treatment trains, in order to improve the performance of downstream membrane processes and water product quality. We emphasize the lack of sufficient efforts to scale up existing membrane technologies, and suggest that a stronger collaboration between academia and industry is of paramount importance to translate membrane technologies developed in the laboratory to the practical applications by the shale oil and gas industry.

Energetic, entropic and economic analysis of a heat pump coupled humidification dehumidification desalination system using a packed bed dehumidifier

In this paper, the humidification dehumidification (HD) desalination system, driven by a mechanical vapor compression heat pump (MVCHP), is proposed. The direct contact dehumidifier, with packings filled, is applied to condense the humid air for water producing. On the basis of the thermodynamic laws, the energetic and entropic analysis, with the modified effectiveness to describe the heat and mass transfer characteristics of humidification, are first achieved to assess the desalination performance of the combined system. The influence laws from the terminal temperature difference (TTD) of the evaporator, the pressure ratio (PR) during compression and pinch temperature difference (PTD) of the condenser on the desalination performance are also explored and presented. The research results presented that the top thermodynamic performance of the MVCHP coupled HD desalination system arises as 71.56 kg h−1 for the water production, 5.28 for the gained-output-ratio (GOR) and 1.73 kJ kg−1 K−1 for the specific entropy generation rate, while two fully coupled cases at 1.21 and 1.96 for the mass flow rate ratio will emerge. It is found that water production can be elevated effectively through increasing the pressure ratio, while the peak value of GOR keeps at the design conditions. Furthermore, the positive effects from lower values both for the TTDe and PTDcon on the performance of the MVCHP coupled HD desalination system are proved. After the economic analysis, it is calculated that the cost of fresh water is about 0.018 $ L−1 with a lifetime of 10 years. According to the performance comparison, the great potential of energy conservation for the MVCHP coupled HD desalination system are validated, although the water production will be reduced after the integration of the MVCHP.

Determination of the Criteria for Comparative Analysis of Desalination Plant

The problem of fresh water lack can be solved my desalination of the seawater. Desalination of the seawater can be accomplished by several methods. Distillation of the seawater is one of the most promising among them. Comparative analysis of distillation desalination plant requires certain criteria. This criterion must take into account both energy consumption and seawater salinity. Relation of the minimal work required for seawater desalination to energy consumption was selected as such criterion. Four types of the distillation plants were considered: Multi-effect distillation plants (MED), multi-effect distillation plants with mechanical vapor compression (MVC) plants, MVC desalination plants have the best multi-effect distillation plant with thermal vapor compression (TVC) plants and Multistage flash distillation plants (MSF). MSF plants gave dependency that their efficiency rise along the gain ratio. That may be explained by the fact that its steam consumption does not depend on seawater consumption. TVC plants have slightly higher efficiency than MED plants. Thus, MVC plants can be recommended to use if there is no heat source, MSF plants - if there is heat source and plant must have a high gain ratio and TVC plant in the rest cases.

Determination of the Required Power of Tube Electric Heater for Distillation Desalination Plant

This article deals with the determination of tube electric heater for a distillation desalination plant. Tube electric heater is required for the distillation process because it prepares input water for the working process on the start regime of the desalination plant. Depending on its power, a time consumed for start regime will vary. Meanwhile, technical requirements for distillation desalination plants with mechanical vapor compression demands that plant must reach design operational regime within a certain time limit. Correspondingly, selection of the power for tube electric heater became an important task during distillation desalination plant designing. Amount of energy, which is necessary to add during heating, depends on the amount of water inside, mass-dimensional characteristics of the desalination plant and heat transfer with the environment. Algorithm for power selection is developed. This model allows determining the time required for the plant to reach a design operation regime. This time varies dependently on the power of the heater. Both analytical and numerical models of this dependencies were developed. A numerical model was used utilized to estimate the influence of the heat exchange with the environment on starting operation time. For the described plant, required power of TEH is equal to 24 kW.

A novel inlet air cooling system based on liquefied natural gas cold energy utilization for improving power plant performance

The performance of gas turbine-based power plants decreases significantly as ambient temperature increases. For improving power plant performance, this paper proposes a novel inlet air cooling system based on liquefied natural gas cold energy utilization. The novel system consists of two organic Rankine cycles in series and a mechanical vapor compression chiller. A simulation-based optimization method is developed to optimize its design parameters for maximizing the power plant performance. Moreover, the off-design performances of the proposed system and the power plant with and without inlet air cooling are evaluated under different ambient conditions. The results show that the novel inlet air cooling system gives larger air temperature drop (2.1–5.3 °C) and higher cooling duty (6.9–7.3 MW) than a literature design. Furthermore, for 28–40 °C ambient temperatures, the power plant with the novel inlet air cooling produces 1.83–14.4% (6.4–52.6 MW) higher power output than that without inlet air cooling. Importantly, the novel cooling system improves the plant power output by 0.79–3.04% (2.8–11.1 MW) when compared with the literature design. Finally, the economic analysis shows that the proposed system is economically viable with a net present value of $1.6–34.4 million higher than the literature design.

Bioethanol production in membrane distillation bioreactor with permeate fractional condensation and mechanical vapor compression

A membrane distillation bioreactor with permeate fractional condensation and mechanical vapor compression was developed for bioethanol production. Enhanced ethanol fermentation was achieved with ethanol in situ removal from the fermentation broth. Compared with the batch fermentation, the cell concentration in membrane bioreactor could be increased 26%. The deposited cells on the surface of the PTFE membrane led to membrane fouling. The membrane separation performance could be resumed by water rinse. High ethanol concentration of 421 g/L could be obtained by permeate fractional condensation with the process separation factor increased to 19.2. Mechanical vapor compression made the process energy efficient.