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Experimental study on water separation process in a novel spray flash vacuum evaporator with heat-pipe
Abstract
Based on the high heat transfer performance of heat pipe (HP) and large specific surface area of small diameter droplets, HP and spray technologies are combined in a novel single stage vacuum evaporator and artificial seawater with 3% saltness is studied experimentally. Parametric studies are carried out, such as cold source and heat source temperature, spray temperature, and spray flow. The results show that: the maximum heat flux density reaches 32 W cm− 2 on evaporator bland plate; HPs absorb energy effectively from low grade heat source (40–80 °C) then transfer the energy to the droplets already flashed, so as to maintain or even increase the superheat degree of droplets during evaporating process; This method can significantly improve the water separation rate (quality of condensed water / quality of dilute solution ∗ 100%); Changing the parameters can regulate water separation from 0% to 65%. Thus it has important significance for utilizing lower grade heat source effectively, gaining brine, and promoting the fresh water yield per unit volume and adaptability to variable load in desalination project.
... Experimentation was carried on the process of separation of water in a spray flash vacuum evaporator with heat pipe. It was reported that heat pipe absorbed more low-grade energy and transferred to droplets already evaporated thereby increased or maintained the superheat during evaporation thereby improving the water separation rate [7]. The fundamental principles to size and design of vapor separator applied to industrial refrigeration were studied. ...
... Hence, water droplets stay on the plate surface and gas escapes through the gaps in between the angle plates. The contour plot shows that the velocity is high at the outlet and in separator outer (1) In the case of modification and (2) by increasing the distance between the angle plates, velocity is found to be more in outer wall of separator than former [5,7,9]. Table 3 shows the outlet velocity in the vapor separator models studied and the values are almost similar. ...
... In order to overcome this pressure drop, the second modification was proposed by increasing the distance between the angle plates. The pressure drop of 817.68 N m −2 in the vapor separator was observed by increasing the distance between the angle plates [7,14]. This is very much less than that of the existing separator design as shown in Fig. 5b. ...
Vapor separator is a vital component in liquid-dominated steam field equipment. While various designs exist, the currently employed separator design was not so effective on separation and there is limitation in understanding the fluid behavior within the separator. Challenges arise from the difficulties in predicting the pressure distribution, flow regime and separation efficiency inside the separator vessel. Owing to this complexity, computational fluid dynamics (CFD) simulation of two-phase fluid movement inside a vapor separator was carried out using Cosmos Express software package. The modifications made to the existing vapor separator were done considering the major mechanisms such as gravity separation, inertial separation, centrifugal separation and surface tension force. This paper describes the CFD analysis of a modified vapor separator model. The design modification made in this vapor separator was to increase the efficiency of the system by reducing its drawbacks. The effect of turbulence and pressure drop on the existing vapor separator design was studied while improving their efficiency to 100% and 99.5% in two different designs. The separator efficiency was calculated by injecting water droplets after a converged solution was achieved. Though, pressure drop inside the vapor chamber is higher (1344.91 N m−2) for the first design compared to later having a lower value of 817.68 N m−2. CFD simulation results demonstrated a promising method to optimize the separator design.
... The condenser evaporator [4], the effect of thickening honey by using a vacuum evaporator on the quality of honey produced, and to increase the variant of honey products [5]. The energy performance of vacuum evaporators for liquid digestate treatment [6], scale up production indonesian liquid propolis from raw propolis and wild beehive using bubbling vacuum evaporator [7], experimental study on water separation process in a novel spray flash vacuum evaporator with heat-pipe [8], analysis of the residual gases in several types of high-vacuum evaporators [9] and changes in properties of palm sugar syrup produced by an open pan and a vacuum evaporator during storage [10] are some other recent examples of research on vacuum evaporators that can be used as a reference for this research. ...
Riau still has many protected forests and nature reserves. One of the wealth of protected debt is the forest’s Honey. One of the weaknesses of forest honey is the high water content in honey. The permissible water content in honey is 22% based on SNI 01-3545-2004. This paper presents a vacuum evaporator of control system design as a tool for reducing the water content in Honey. The control system design is made such that the honey temperature in the evaporation process is no more than 40°C. There are three quantities that are controlled in this process, namely vacuum chamber pressure, temperature and screw rotation. Temperature control system and pressure control system use close loop system, while the control system for screw rotation uses open loop system. The three main components of this control system are the VE 115N vacuum pump, the stirring screw motor with 1 HP power, 2 heaters with 250 watts of power each, Temperature Control (Eliwell IC901 thermostat and thermistor sensor), 35x25 panel box. To meet the quality of honey, the control system is set with a maximum temperature of heating water 40°C and vacuum pressure at 7.4 kPa and screw rotation at 60 rpm
... Lin et al. [2] studied a research focusing on heat transfer of R141b and multiphase flow in a tube. Gao et al. [3] developed high efficiency in small heat pipes for high heat flux cooling. Ma et al. [4,5] investigated the pulsating heat pipe charged with diamond nanofluids. ...
This paper represents an experimental study about the effect of curves related to thermosyphons and heat pipes with different active fluids and inclination angle at the thermal efficiency. The nanofluid utilized in this work is an aqueous soluble of Al2O3 nanoparticles with 35 nm diameter in pure water. The test saturation level of nanoparticles is 0%, 1%, and 3%wt. All the experiments were conducted and repeated at inclination angle of 30°, 60°, and 90° (vertical). The article presents the gravity impacts on the heat transfer characteristics in different angles and the effects of working fluids and tilt angle of heat pipe tube by the addition of nanoparticles and weight fractions on the thermal efficiency of heat pipe at different inclination. According to the experimental results, the heat pipe at the tilt angle of 60° generates the superior results. At a particle volume concentration of 1%, the use of Al2O3/water nanofluid gives significantly higher heat transfer.
... Lin et al. [2] studied a research focusing on heat transfer of R141b and multiphase flow in a tube. Gao et al. [3] developed high efficiency in small heat pipes for high heat flux cooling. Ma et al. [4,5] investigated the pulsating heat pipe charged with diamond nanofluids. ...
This paper represents an experimental study about the effect of curves related to thermosyphons and heat pipes with different active fluids and inclination angle at the thermal efficiency. The nanofluid utilized in this work is an aqueous soluble of Al 2 O 3 nanoparticles with 35 nm diameter in pure water. The test saturation level of nanoparticles is 0%, 1%, and 3%wt. All the experiments were conducted and repeated at inclination angle of 30°, 60°, and 90° (vertical). The article presents the gravity impacts on the heat transfer characteristics in different angles and the effects of working fluids and tilt angle of heat pipe tube by the addition of nanoparticles and weight fractions on the thermal efficiency of heat pipe at different inclination. According to the experimental results, the heat pipe at the tilt angle of 60° generates the superior results. At a particle volume concentration of 1%, the use of Al 2 O 3 /water nanofluid gives significantly higher heat transfer.
... Experimental testing remains the most important means of evaluating the actual performance of a thermal transfer device, whether the objective is cooling [1], waste heat recovery [2], or even desalination [3]. However, it has been observed that large discrepancies exist within reported experimental results for microscale heat sinks and heat exchangers, leading to difficulty in comparison between studies, or with existing devices in industry [4]. ...
There exist numerous methods of experimentally testing designs for heat sinks in the laboratory, especially for microscale fluidic devices, which can lead to a problem for comparison between new studies and those in the literature. To explore this issue, laboratory-based experiments on the heat transfer and flow impedance properties of a sample microchannel heat sink were repeated over a varying range of equipment. Three types of heat source (hot plate, film heater and copper block with cartridge heaters), two types of piping (polymer and metal), and the presence or absence of manifolds were investigated and the differences in heat sink performance were noted.
Overall, especially in terms of achieving consistent, repeatable results, it was found that the arrangement of copper block heater, metal piping and the inclusion of manifolds was superior for this particular microchannel device. Hence, it is suggested that future testing of heat sinks and heat exchanger devices employ a similar arrangement of equipment for greater accuracy and comparability. In particular, the plastic tubing and hot plate configurations were found to have relatively poor consistency when testing the heat sink, and the film heater produced non-uniform heating, even over a small surface area.
... However in term of desalination, the proposed system produces more fresh water. Gao et al [8] performed an experimental study on water separation process in a novel spray flash vacuum evaporator with heat-pipe (HP). ...
In the present work characteristics and performance of a natural vacuum desalination system using low grade heat source is studied numerically and experimentally. In the numerical work, a program to solve the governing equations in forward time step marching technique is developed. In the experimental work a lab scale natural vacuum system using electric heater as a heat source is designed and tested. The surface area of seawater in the evaporator is 0.5 m. The numerical and experimental results show a good agreement. By using numerical simulations effect operating conditions such as heat source temperature, condenser temperature, heating coil surface area, and the present of heat recovery unit are explored. The simulation showed that, the present system with evaporator surface area of 0.2 m², operation time of 9 hours and source temperature of 80 °C will produce 6.63 L of fresh water ant thermal efficiency is 70.4%. The main conclusion can be drawn here is that the performance of the natural vacuum desalination system is mainly affected by maximum temperature in evaporator and minimum temperature in condenser. On the other hand, the surface area of heating coil and the heat recovery unit showed only a small effect.
Spray flash evaporation is an effective desalination method, which increases specific surface area of salty water by liquid atomization, thereby improving desalination performance and maximising low-grade heat source utilization. During evaporation, explosive boiling phenomenon occurs inside superheated droplets on a heated surface. In order to understand the mechanism of explosive boiling, spray flash evaporation of distilled water and 3.5 wt% salty water in a high vacuum vessel was observed visually. Meanwhile, a parametric study was carried out to scrutinize the impacts of the variation of ambient pressure, heat flux, and surface superheat degree. The experiment data indicates that nucleate site is located in the upper layer of a droplet due to internal superheated liquid and Marangoni convection. In different operating conditions, bubble fragmentation process or crown fragmentation process happens at nucleate site. The fragmentation time of pure water, which is mainly influenced by heat flux and surface superheat degree, shrinks with higher heat flux and higher surface superheat degree. The fragmentation time of 3.5 wt% salty water decreases with ambient pressure drops and superheat degree increments.
A novel microwave flash evaporation (MFE) system is presented in this paper for the first time, which is expected to solve the inherent problems of conventional flash evaporation (CFE) system, such as high energy consumption, scaling, and long stages etc. In order to demonstrate the performance of such a novel system, some single factor experiments have been carried out by using water as experimental material, and the influence of parameters such as microwave power, initial temperature, and liquid flow rate have been studied. The results show that the evaporation quantity increases with the increase of microwave power, flow rate, and initial temperature. Under experimental conditions, the better operation condition is achieved at flow-rate of 40 L/h, initial liquid temperature of 50 °C, and microwave power of 1.35 kW, the evaporation quantity in the case of MFE is as high as 1.35 L in 20 min, but it is only 0.74 L in 20 min for CFE. The enhanced performance of MFE system is shown by comparing with the CFE system under the same conditions. Moreover, the energy efficiency is calculated and represented by a dimensionless parameter Gain Output Ratio (GOR), and the maximum energy efficiency for MSF system is about 79.38% at the better operation condition.
In the sugar industry, the problems that occur not only in the factory but also in sugar cane land, namely a decrease in factory load because the age of the developing factory needs maintenance and replacement of the machine that must be adjusted. Therefore, it is necessary to make a breakthrough to maximize operations from land to factories. The breakthrough was made in the form of making a mobile evaporator that can support the business process of reengineering the production of sugar cane juice on the land. In addition, the problem encountered in the functional evaporator itself is the steam pressure setting that is not in accordance with the SOP, the results of brix are difficult to predict, cleaning of hard sugar juice catchers, cleaning of difficult heating bodies and too long evaporation process. The problem- solving process is conduct using the TRIZ method to get design specifications that are expected by the user. Improving and worsening contradiction matrix in the form of 3 attributes that are used, namely an effective process, easier temperature settings, and portable. The results from TRIZ provide several specific solutions for functional tools such as adopting the sugar juice input method into the heating body using spray and cyclone to create a more effective process, adding additional blowers to maintain heating temperature and evaporator dimensions that are suitable for mobile application. The solution obtained from TRIZ was applied in the manufacture of evaporators and experiments on these devices to produce sugarcane juice that meets quality standards. The initial volume of this experiment was 15 liters of sugar cane juice and the final volume was 7 liters. The initial Brix sugar cane juice is 23% and the final brix is 40%
A novel single stage vacuum evaporator, as a salt-water separator, is developed to fully use ultra-low grade heat source as low as 50 °C. The novel design incorporates several technologies, including heat pipes (HPs), spray flashing and solid adsorption. Its performance is evaluated by separating water from NaCl solution with 3%concentration. The results of the experiment study show that HPs transfer heat to the droplets rapidly to assist a second evaporation and maintain the superheat degree for the salt-water separation process after the flash evaporation. It is also found that, when the adsorbent beds are applied, the evaporation pressure decreases by 0.4–1 kPa compared to the early experiment results, which results in an increase of the superheat degree. The introduction of solid adsorption in the salt-water separator provides a new way to utilize ultra-low grade heat source, although it brings a mixed success to the whole device while the separation ratio is slightly lower than expected due to the fact that there are both improved and impaired effects of heat transfer during the whole adsorption process. The lower cooling water temperature of the adsorption process, leads to better desorption effect, which improves the overall performance of the salt-water separator.
A novel solar still with spiral-shape multiple-effect diffusion unit is developed in the present study. The test results of a 14-effect unit coupled with vacuum-tube solar collector (absorber area 1.08 m2) show that the highest daily pure water production is 40.6 kg d−1. The measured highest productivity based on the area of glass cover, solar absorber, and evaporating surface is 34.7, 40.6, and 7.96 kg m−2d−1, respectively, which are much higher than the published results. The measured solar distillation efficiency is 2.0–3.5. The performance enhancement results mainly from the lateral diffusion process in the spiraled still cell. The vapor flow generated by heat input can flow freely and laterally through the spiral channel down to the end when solar heat input is high. Besides, the larger evaporating and condensing area at the outer cell may increase heat and mass transfer at the outer cell.
A seawater distiller utilizing the thermal energy of waste gas from a portable electric generator by means of heat pipe was constructed and tested with actual waste gas from a small portable electric generator. The distiller tested is a vertical single-effect diffusion still, whose structure is equivalent to the first distilling cell of a vertical multiple-effect diffusion still, consisting of a series of closely spaced parallel partitions in contact with saline-soaked wicks. Evaporation and condensation processes were repeated on all partitions by recycling thermal energy to increase the distillate productivity in the still. All of the experiments were performed in steady-state conditions. Experimental results for the distillate productivity are in good agreement with theoretical predictions, and show that 40 to 50% of thermal energy of waste gas can be transported by heat pipe and about 35% of thermal energy of waste gas can be utilized for the distillation of saline water.
A vapor diffusion model, which takes into account the reduction of droplet temperature during the evaporation process, was used to determine the achievable targets for desalination of seawater at temperatures between 26°C and 32°C when the saline water was injected as fine droplets in a low-pressure vaporizer. The temperatures between 26°C and 32°C correspond to the warm temperatures of the ocean surface in the tropics. The predictions from the model were verified by a large number of experiments at vacuum pressures between 10mm and 18mm mercury. The upper bound of the rate of flow of the saline water in the experiments was 1000l/h. Typical evaporation time of the droplets was a few hundred milliseconds and this was less than the residence time of the spray provided for in the vaporizer. The yield of fresh water measured in the experiments was between 3% and 4% and matched well with the predictions. Small values of water injection pressures of about 0.1MPa were found to be adequate when a swirl nozzle, used for garden sprays, was employed. Changes in the height of water injection in the vaporizer did not significantly influence the yield of fresh water.
This article is about heat transport limitation standard-used construction wick heat pipes with various working fluids operating at temperatures from −30 °C to 140 °C. In this paper is the proposal and verification of a mathematical model for calculating heat transport limitations of heat pipe. The calculations of the various variants of the wick structure of heat pipe and working fluid are presented in diagrams as a dependency of the heat transport limitations on the working temperature. In the conclusion, the effect of these limits on the cooling power of the heat pipe is evaluated.
An experimental study has been made of a spray flash evaporation occurring in a superheated water jet injected through a circular nozzle into a low-pressure vapour zone. The effects of nozzle diameter, flow rate and superheat on the rate of spray flash evaporation are shown. From the experimental results an empirical equation useful for predicting the variation of liquid temperature in the center of jet cross section with residence time is deduced. The rate of flash evaporation of water jet, that is, spray flash evaporation is considerably faster than that of a flowing liquid in a conventional multistage flash evaporator and that of pool water exposed to a sudden pressure drop in a container. (A)
The application of the solar energy in thermal desalination devices is one of the most beneficial applications of the renewable energies. In this study, a novel solar desalination system is introduced, which is benefited from the undeniable advantages of pulsating heat pipe (PHP) as a fast responding, flexible and high performance thermal conducting device. Results show a remarkable increase in the rate of desalinated water production and the maximum production reaches up to 875 mL/(m 2 .h). However, the optimum water depth in basin and the filling ratio of the PHP are measured 1 cm and 40%, respectively.
This paper presents the preliminary field test data of a two-stage low temperature phase-change desalination process. The process under development operates at low temperatures and low pressures generated by local barometric head. A two-stage configuration of this process was developed and tested at a field site in the Puget Sound bay area of the State of Washington. The field test results proved that the two-stage desalination process has potential for standalone small to large scale applications in water and energy scarce rural areas with specific energy consumption of 1500 kJ/kg of freshwater. Economical analysis conducted on the desalination system results in desalination costs around $3/m3 using a cheap waste heat source purchased at $0.5/GJ. Since, most small scale domestic desalination systems are designed in combination with a renewable energy source; when this desalination system is powered by a low grade flat plate solar collector heat source, the desalination costs are less than $7/m3 which falls in acceptable range for small scale desalination systems of similar capacity.Highlights► Feasibility of a new 2-stage low temperature desalination process was investigated. ► Low temperature evaporation was caused by natural vacuum generation in the process. ► Technical performance and energy recovery options of the process were presented. ► Economic analysis shows that the freshwater from this process costs around $3–7/m3. ► The process saves mechanical energy and competitive to other desalination processes.
This paper describes the design and performance evaluation of swirl injectors which find application in the spray flash desalination system at low pressures and temperatures. Water was sprayed into the vaporizer through a swirl injector as fine droplets. The vaporizer was maintained at low pressure. The maximum flow rate was 1 l/s. The injector performance was determined at different feed water temperatures, vacuum and water injection pressures. The effects of injector dimensions and flow parameters on droplet production were studied and analyzed. Droplet size of 0.7–0.9 mm from the theory compared with the experiments estimates. From this study, it is established that the droplet diameter in the range of 0.7–0.9 mm is optimum for flashing.