Vertical Evaporator Research Articles

Experimental investigation of a 10 kW-class flat-type loop heat pipe for waste heat recovery

A flat-type 10 kW-class loop heat pipe (LHP) with a box-type wick was designed and developed to handle the higher heat loads in waste heat recovery applications, such as industrial processing and internal combustion engines. Additionally, a numerical model was developed to predict the overall thermal performance of the LHP. The LHP used a stainless steel wick with a pore diameter of 2.0 µm and pure water as the working fluid. The LHP was tested using two types of cooling for the condenser (forced and natural convection), two types of evaporator orientations (horizontal and vertical), and with and without gravity assist (0.3 m and 0 m). For all the tests, the maximum heat load ranged from 5 kW to 10 kW, with the test with a gravity assist of 0.3 m, vertical evaporator orientation, and natural convection performing the best. This test sustained a 10 kW heat load at a steady-state temperature of 182 °C for the evaporator. During the same test, a maximum evaporative heat transfer coefficient of 92,000 W/m2/K at 4.5 kW and a thermal resistance between the evaporator and condenser value of less than 0.007 K/W was achieved. A numerical model was developed to compare the experimental results with the numerical temperature results for the heater block, evaporator, vapor line, condenser, liquid line, and compensation chamber. Overall, the average temperature difference for all components ranged from 7.1 °C to 10.6 °C, with the horizontal orientation without gravity assist and natural convection test predicting the best. The findings demonstrate that LHPs can handle the higher heat loads that are found in waste heat recovery applications for industrial processing and internal combustion engines.

Research of boiling flow parameters in vertical evaporators of marine refrigeration machines

In this work, the subject of research is hydrodynamics, and in particular, the hydraulic resistance of a boiling two-phase flow moving in vertical and inclined pipes of evaporators of ship refrigeration units. Such movement is typical for various types of industrial heat exchange equipment, including the development of promising types of evaporators, for example, vertical devices for ships in which in-tube boiling of liquid refrigerant occurs. Experiments were carried out to study hydraulic resistance in vertical pipes with different channel diameters and lengths. The main dependencies of the various components of hydraulic resistance that arise during the movement of a boiling two-phase flow are presented. Based on the data obtained, the prospects of transitioning ship evaporators of refrigeration units to a vertical arrangement of heat exchange tubes are shown. When applied to ship refrigeration machines, we can say that the transition to vertical units has its advantages, primarily in reducing pressure losses. The resulting set of data allows us to recommend the design of vertical evaporators for auxiliary ship installations.

Flow boiling heat transfer performance of R245fa in a vertical enhanced evaporator tube with sintering and electroplating composite coats

The R245fa flow boiling performance was investigated in a vertical evaporator tube of which inner wall surface is coated by a composite sintering and electroplating technology. The effects of vapor quality, heat flux, mass flux, and flow direction were compared and analyzed in the bare tube (BT) and the sintering and electroplating treated tube (SET). The results showed that the heat transfer coefficient increased and then decreased with the rise of vapor quality and heat flux. The heat transfer performance in downward flow was better than that in upward flow, while an opposite trend was observed for frictional pressure drop. With the increased of vapor quality, the frictional pressure drop increased and then decreased, but it monotonically increased with the increasing mass flux. The heat transfer enhancement mechanism was explored through flow pattern visualization. The annular flow pattern conversion line of SET was earlier than that of BT. Due to the strong wettability of SET, the thickness of liquid film was thinner in downward and the mother bubble was bigger in upward, which had a positive effect on flow boiling heat transfer. The maximum the heat transfer enhancement factor (EF) and the performance evaluation parameter (PEC) were 1.83 and 1.75, respectively.

Investigation of the inlet useful temperature difference effect on the distribution of hydrodynamic characteristics of the vapor-liquid flow inside the falling-film evaporator heating tube designed for a nitric acid solutions evaporation

We present the results of mathematical modeling of effect of inlet useful temperature difference on the vapor- liquid flow in the heat exchange tube of a vertical evaporating film apparatus, which is designed for evaporation of nitric acid solutions. Distributions obtained along the heat exchange tube length of local values of the: mass flow rate of the fluid and secondary steam, the velocity of the fluid film, the velocity of the secondary steam, the Reynolds criterion of the liquid and vapor phases, the absolute pressure depending on the values of this useful temperature difference. The study was carried out using numerical simulation. To study the effect of the initial useful temperature difference on the hydrodynamics of the vapor-liquid flow, the vertical evaporator equipped with the tube ø38x3 mm and length of L = 4 m was adopted. The linear nature of the distribution of hydrodynamic parameters along the length of the heat exchange tube is established. The absolute pressure in the tube space decreases along the heating tube due to pressure drop. The limiting factor in reducing the absolute pressure is the friction losses of the secondary vapor on the solution film surface. A decrease in the pressure in the tube space leads to decrease in the boiling point of the solution. This leads to increase useful temperature. This has a positive effect on the evaporation efficiency The obtained data should be used in the design of evaporation plants, which are designed for evaporation of nitric acid solutions.

Effect of a static magnetic field on the falling-film evaporation on a vertical plate evaporator by mixed convection

The application of a magnetic field to a falling-film evaporation system can have several effects. The magnetic field can alter the liquid film's flow behavior and modify the system's heat transfer characteristics. The numerical study of falling film evaporation by mixed convection on a vertical channel under a static magnetic field has been investigated. The vertical channel is composed of two parallel plates. The right plate is dry and isothermal, while the left plate is wetted by a falling liquid film and exposed to a static, uniform heat flux from the outside. Water film makes up the liquid, while dry air and water vapor make up the gas mixture. The results relate to the effects of the magnetic field on heat and mass transfer and on liquid film evaporation. The results demonstrate that the static magnetic field has a weak effect on heat and mass transfer and water film evaporation. In fact, it is shown that an increase in the static magnetic field weakly enhances heat and mass transfer as well as liquid film evaporation.

Comparison between Calculated, Simulated and Actual Plant Data of Multiple Effect Evaporators to Concentrate Sugarcane Juice

Multiple effect evaporators systems operating at steady state can be described by a series of nonlinear algebraic equations that include total and solute mass balances, energy balances, heat transfer rate equations, and the composition and temperature dependence of related thermodynamic properties such as vapor pressures and enthalpies. The main objective is to compare between the manual calculations, simulation and real data collected from Asalaya plant for validation the best design of multiple effect evaporators system in forward feed used in Asalaya Sugar Factory. In this design a short tube vertical evaporator, Calandria type has been used. The models include overall equations of materials balance, equations of energy balance and equations of heat transfer rate for measurement area for all the effects. These equations were solved using manual calculations methods and MATLAB coded program. The results of the present investigations have been compared with the data obtained from the Asalaya Sugar Factory with five evaporators. The results showed that the concentration of sugar cane juice at the final stage is equal to 60 Brix for the manual calculations, simulation and actual plant data with zero error. The temperature of solution in the pre- effect evaporator was found to be about (114.94, 114.94, 115)ºC, with a relative error equal to 0.05% and the steam temperature in the pre effect was found about (120)ºC for the manual calculations, simulation and actual plant data, with zero error. The area and number of tubes in the (pre, second, third and fourth) effect, are in a good agreement, with the standard value (Er=3.26%). The above results show great similarity with the real behavior of evaporator unit. This can be used as a reliable tool\for the simulation of different operating conditions.

Исследование потерь напора при движении кипящего двухфазного потока в наклонных трубах испарителя судовой холодильной машины

The study of pressure losses at boiling two-phase flow movement in vertical and inclined pipes of evaporators of ship refrigeration units is carried out. The study of the ascending two-phase flow is promising from the point of view of practical application. Such a movement is typical for various types of industrial heat exchange equipment, including for the development of promising types of evaporators, for example, vertical apparatuses for ships in which internal boiling of the refrigerant occurs. A methodology has been developed and an experiment has been set up to study the processes in the steam generating channels of refrigeration units at various angles of inclination with a fixed height. At the same time, the length of the channel changed, it became possible to analyze friction losses. A new approach has been applied that brings the model as close as possible to the actual boiling process, taking into account the constant increase of steam in the channel. Experimental studies have been carried out and data on pressure losses have been revealed when the angle of inclination of the steam generating channel changes. The main dependences and various components of hydraulic resistances during the movement of a boiling two-phase flow are presented. Based on the data obtained, the justification of ship evaporators transition of refrigeration units to the vertical arrangement of the heat exchange steam generating beam is proved. The results obtained indicate that an increase in the slope of the pipe, provided that the height is maintained, leads to an increase in pressure losses. Applicability to marine refrigerating machines has been determined – the transition to vertical apparatuses has advantages, primarily in reducing pressure losses. The obtained set of data allows to recommend the design of vertical evaporators for auxiliary ship installations.

Design and modeling of vertical tube evaporator in a thermal-driven multiple effect distillation system

Abstract The scarcity of freshwater is one of the biggest issues in the world, as a result of which more attention is given to the thermal distillation process for seawater and as well as brackish water distillation which removes almost all types of contaminants. Multiple effect distillation makes the process economical by recycling the latent heat of vaporization. In this paper a vertical tube evaporator is designed for a small scale thermal driven MED system comprising six effects and one condenser and a boiler that can produce 20–25 kg/hr of steam. VTE dimensions are calculated by estimating the outside diameter for different configurations. Heat transfer coefficient was estimated by using the developed correlations of the Bell method, Kandlikar and Kutateladze, compared with previous experiments and then used for calculating the heat transfer area for different distillate flow rates. An appropriate vertical tube evaporator is designed with the developed model to condense 25–30 kg/hr steam for producing 50–75 lt/hr freshwater. The result shows good agreement with previous work and reliability in design. The Developed model can also be used to design the vertical tube evaporator for different sizes (micro scale to large scale) MED plant.

Evaporation of CuO/H2O nanofluid film liquid flow downward in a vertical parallel plate evaporator by mixed convection

Evaporation of CuO/H2O nanofluid film liquid flow downward in a vertical parallel plate evaporator by mixed convection

Janus composite membranes enable efficient solar-powered desalination and soil remediation

Solar-driven water evaporation offers a sustainable pathway for energy-efficient seawater desalination. However, its further practical performance is limited by salt accumulation during solar saline evaporation. Herein, a novel Janus composite membrane based on the assembly of hydrophilic vermiculite (VMT), multi-walled carbon nanotubes (MWCNTs), and hydrophobic polydimethylsiloxane (PDMS) is designed to function cooperatively for efficient solar absorption and long-term salt-rejection. The unique heterostructure endows the sandwich-like membrane with the capability of decoupling the steam generation process from the solar absorption surface to avoid the mutual interaction between the escaped steam and the incident light. Moreover, the tailorable hydrophilic/hydrophobic channels weaken the interaction between water molecules and layers, as well as reduce interlayer friction and water molecules viscosity to accelerate the flow rate. Benefiting from the above merits, the constructed vertical evaporator exhibits a high solar evaporation rate of 1.48 kg m−2 h−1 and an energy efficiency of 92% in saline water (3.5 wt% NaCl). Solar evaporation-induced soil remediation strategy on the basis of efficient removal of heavy metals and organic pollutants is further proposed, implying its potential applications in sustainable freshwater generation and environmental remediation.

Heat transfer coefficient correlations of water subatmospheric vaporization in a channel of a smooth plate heat exchanger, based on Vaschy-Buckingham theorem

Water as an environmentally friendly, safe and cheap natural refrigerant (R-718) requires vaporization conditions at sub-atmospheric pressures (∼1 kPa). At these pressure ranges, studies on the specific vaporization of water are scarce and insufficient. For this reason, the engineering of heat exchangers using R-718 as working fluid remains empirical. The aim of this paper is thus to provide correlations to estimate water pool boiling and falling film evaporation heat transfer coefficient under subatmospheric pressure. Correlations developed are believed to be more widely used by providing dimensionless numbers consistent with phase-change phenomena occurring at sub and at-mospheric pressure. To develop these correlations, heat transfer phenomena during water vaporization at pressures ranging from 0.7 to 1.7 kPa in a scale-lab size (0.2 m wide × 0.5 m high) vertical smooth plate evaporator channel are studied. Filling ratio vary from 1/2 to 1/10 of the total channel height, canal thicknesses are set to 2 mm, 4 mm or 6 mm. Thus, raw experimental data from 139 tests performed under various operating conditions of a thermosyphon loop mimicking a sorption system are exploited. Each test consists of more than 1200 values. A graphical and statistical comparison between the heat transfer coefficient (HTC) obtained from the experimental database and the HTC estimated by empirical correlations from the literature is made, calculating the percentage of predicted data within an error band of ±30% (τ30), the mean absolute error (MAE), the mean relative error (MRE) and the correlation coefficient (r). Two methodical correlations for predicting the HTC of pool boiling and liquid film evaporation, are developed. They predict 86% (with MAE = 19%, MRE = 3%, r=0.79) and 83% (with MAE = 18%, MRE = 2%, r=0.84) of the experimental data in τ30 respectively. To extend their validity domains, the proposed correlations are evaluated using independent experimental data from the literature. Giving satisfactory results, it constitutes a first step towards the development of tools used for the sizing and the optimization of the design of two-phase heat exchangers.

CFD simulation of conjugated heat transfer with full boiling in OpenFOAM(R)

The Computational Fluid Dynamics (CFD) simulation of subcooled and saturated boiling flow with multi-domain thermal coupling is a challenge, and the current methods to solve the exchange of mass, momentum, and energy still require further development and validation. This work addresses the implementation and assessment of a new solver (CHT-2FM) in OpenFOAM(R), which includes the Conjugated Heat Transfer (CHT) model into the two-phase Eulerian method (2FM) in order to solve wall boiling. This solver allows applying the wall heat flux partitioning model (Rensselaer Polytechnic Institute) to solve subcooled and saturated boiling flows coupling two fluid circuits through a solid domain, without impose the heat flux at the heater wall. The solver is experimentally and numerically validated against three tests; First the well-known vertical heated pipe with homogeneous heat flux proposed by Bartolomej et al. (1982) was solved to assess the RPI model, and the interfacial momentum exchange. The test was also solved with RELAPMod3 in order to assess the boiling model implemented in this code. Second, a numerical low-pressure benchmark of a vertical double-pipe evaporator proposed by Abishek et al. (2017) was solved. This allow comparing some RPI model parameters, and the CHT implementation. The third test was proposed by the authors in order to evaluate the CHT-2FM implementation for water operation conditions relevant for nuclear engineering. The test was also solved with RELAPMod3. Based on the first test, the RPI model in OpenFOAM correctly solved the Bartolomej test in terms of void fraction. On the contrary, RELAPMod3 overestimated boiling at the end of the pipe. From the second test it was concluded that the CHT-2FM coupling was correctly implemented. Finally, the use of the developed tool to solve heat coupled fluid systems led to very acceptable solutions compared with RELAPMod3 estimations.

Heat transfer of flow boiling carbon dioxide in vertical upward direction

Heat transfer measurements of flow boiling Carbon Dioxide (CO2) in vertical upward direction have been carried out with a dedicated test facility at the European Organization for Nuclear Research (CERN). The investigation covers saturation temperatures within a range of −25∘C≤Tsat≤+5∘C, mass velocities from 100kgm−2s−1≤G≤450kgm−2s−1 and heat fluxes of 5.3kWm−2 and 11.4kWm−2. The experiments have been conducted in a vertical upward evaporator of 8 mm inner diameter and 8 m length and a database of more than 1900 measurements has been compiled within the present study. The heat transfer mechanism is dominated by the nucleate boiling contribution and dryout is observed as a function of saturation temperature, mass velocity and heat flux. A correlation is proposed to predict the dryout inception within the experimental range where the onset of dryout has been observed. The results suggest that most commonly used heat transfer prediction models underpredict the heat transfer mechanisms of CO2. Moreover, the heat transfer coefficients of CO2 increase in vertical upward direction, compared to the data of horizontal studies. For that reason, a vertical multiplier is suggested to capture the trends of vertical upflow with two existing prediction models.

Characteristics of phase-change flow and heat transfer in loop thermosyphon: Three-dimension CFD modeling and experimentation

Two-phase loop thermosyphon (TPLT) shows an oscillation phenomenon since the complex phase-change heat transfer and flow behaviors, decreases the system reliability in practice. A combined three-dimension CFD simulating/experimental investigation was carried out to investigate the phase-change flow inside TPLT. Results of the 3D-CFD model show good agreement with the experiments, with a maximum deviation of 2.86% and 3.98% for temperature distribution and pressure, respectively. In the vertical evaporator heating mode, the filling ratio of 23.3% produced the lowest total thermal resistance of 0.28–0.22K/W since the dominant heat transfer mechanism of phase-change in the loop. With the increasing FR, from 48.0 to 84.1%, the dominant heat transfer mechanism might be transformed to single-phase convection. Thermal performance with the horizontal evaporator heating mode is better than that with the vertical evaporator heating mode since the good flowability at high FR = 84.1%. In the horizontal evaporator heating mode, a bidirectional flow was observed in the loop with the horizontal evaporator even at low FR = 23.3%, which caused pressure fluctuation and reduced thermal performance. But the flow stability could increase by 90% with the auxiliary of a porous media in the horizontal evaporator, indicating that the porous media had a positive effect on avoiding bidirectional flow.

Hybrid heat transfer with falling film and pool boiling using R-134a outside a vertical tube

In this study, falling liquid film, pool boiling and hybrid heat transfer with refrigerant R-134a outside a vertical tube were experimentally investigated. A smooth tube and an enhanced tube specially designed for falling film were adopted for the tests. The results revealed that the heat transfer ratio of falling film to pool boiling gradually decreased as the heat flux increased for the two tubes. The heat transfer coefficients (HTCs) of falling film were smaller than those of pool boiling at a heat flux of 25 and 40 kW m−2 for the smooth and enhanced tubes, respectively. In the hybrid heat transfer mode analysis, it was observed that at a low heat flux, the HTCs of a completed falling film were higher than those of other heat transfer modes; moreover, the proportion increase of pool boiling led to a slight decrease in performance. However, at a high heat flux, a modest increase in the submerged height of the tubes in the refrigerant was beneficial for improving the performance, and the heat transfer had an optimal effect at the height of 800 mm and 600 mm for the smooth and enhanced tubes, respectively. Based on the experimental data, the heat transfer correlations of falling film combined with pool boiling at different submerged heights were obtained according to a dimensional analysis. The findings of the study serve as a guide for the design of vertical evaporators.

Investigation on detachable vertical tube evaporator for small scale multi effect distillation system: Design, modelling, fabrication and experimental analysis

Investigation on detachable vertical tube evaporator for small scale multi effect distillation system: Design, modelling, fabrication and experimental analysis

Dynamic modeling of a multi-effect vertical falling-film evaporator for water reuse in CSP plants

This work presents the dynamic modeling of a vertical multi-effect evaporator plant designed and manufactured for its installation at a commercial concentrating solar power (CSP) plant, within the framework of EU H2020 project SOLWARIS (Solving Water Issues for CSP plants). The model has been developed using Modelica computational language and implemented in Dymola® software environment. The results from the validation show a good agreement against the design data, obtaining relative errors lower than 5%. The dynamic response of the plant against external disturbances of the motive steam mass flow rate, feedwater mass flow rate and condenser pressure has been investigated. The main results reveal that increasing the motive steam flow rate by 5% produces a similar increment of the water recovered (5.2%), although the concentrate salinity is raised to an unsafe operation zone (106%) that could lead to scaling issues in the evaporators. The same effect occurs when the feedwater is decreased by 5% from its nominal value, causing a significant rise in the concentrate salinity (163%). In those cases, the simultaneous and proportional variation of the motive steam and feedwater mass flow rates allows maintaining the outlet concentrate salinity far from scale formation limits.

Experimental study of ammonia flow boiling in a vertical tube bundle: Part 1 – Enhanced dimple tube

• Boiling of ammonia in a vertical shell and tube evaporator with enhanced dimpled tube bundle. • Study of wide range of experimental parameters. • Enhanced heat transfer coefficient compared to previous studies. This paper presents the experimental results of saturated two-phase flow ammonia in a vertical shell and tube heat exchanger comprising of seven dimpled enhanced tubes. The tests were conducted for a wide range of parameters. The heat load was provided by hot ethylene glycol/water solution flowing on the shell side. Saturation temperature of ammonia was -20°C ≤ T sat ≤ 2°C, heat flux range 5 kW m −2 ≤ q ˙ ≤ 45 kW m −2 , exit vapor quality range 0.1 ≤ x ≤ 0.9 and a mass flux range of 34.99 kg m −2 s −1 ≤ G ≤ 66.32 kg m −2 s −1 . For each saturation temperature, the effects of heat flux and mass flux were studied for the saturated temperature range while the exit vapor quality at each mass flux was varied between 0.2 and 0.9. Two phase heat transfer coefficient increased with saturation temperature and heat flux. For all experimental conditions, performance showed initial increase and then a classic drop at the onset of dry out. The dimple tube showed better heat transfer coefficient compared to the previous studies performed on plain tubes with ammonia.

Evaporation of refrigerant R134a, R404A and R407C with low mass flux in smooth vertical tube

This experimental study analysis the low mass flux of refrigerant R134a, R404A, and R407C in the smooth vertical evaporator tube with an inner diameter of 32 mm. This downward-flow refrigerant with a mass flux of about 9 kg⋅m−2⋅s−1 in the parallel/counter flow of heating water shows suppressed heat transfer by convective boiling and dominant heat transfer by nucleate boiling. This dominant heat transfer by nucleate boiling is dependent on the superheated wall of evaporator tube. The experimentally obtained Nusselt number correlates 92.2 % for R134a, 92.4 % for R404A, and 83.2 % for R407C with the predicted Nusselt number for mass flux over 10 kg⋅m−2⋅s−1. In summary, the untypically low mass flux of refrigerant about 9 kg⋅m−2⋅s−1 is comparable with the current state of knowledge for low mass flux over 10 kg⋅m−2⋅s−1.

Heat Transfer Performance in a Vertical Grooved Thermosyphon

The performance of a grooved copper-water thermosyphon with a modest bend between a vertical evaporator section and inclined condenser section was characterized for a moderate fluid loading. The time-averaged temperature varied significantly along the evaporator for heat fluxes up to 10 W/cm 2 before becoming more uniform at higher heat fluxes. Transients of the measured temperatures show evidence of different flow regimes that were compared to existing flow pattern maps. The evaporator performance for both the pool region, which had the highest temperature, and the film region were not well predicted for heat fluxes up to 10 W/cm 2 . The local evaporator performance changed with the change in flow regime, suggesting the need for a flow regime-based performance model. The performance of the condenser appeared to depend on the reduced pressure and was significantly overpredicted by the standard condensation models. A modified model for the condenser was proposed.