ABSTRACT Schematic diagram of a cartridge-type humidification–dehumidification (HDH) desalination system consisting of a vertical cylindrical tower divided into humidification and dehumidification sections. The column contains multiple sieve trays and chimney trays arranged in a removable cartridge assembly. Heated saltwater flows downward across lower trays while air flows upward through perforations, forming bubbles. The humid air rises to the upper section, where cooler freshwater flows across trays and condensation occurs. Arrows indicate air, saltwater, and freshwater circulation loops between the tower, heater, pumps, and cooling unit. The system achieves up to 15.56 L/h freshwater production with a gain output ratio (GOR) of 3.17. In this study, a new and unique structure is used for the humidification and dehumidification chamber. A tray cartridge tower consisting of four sieves and two chimney trays has been utilized. The performance of this humidification–dehumidification system has been investigated experimentally. In addition to the humidifier and dehumidifier tray tower, this device includes saltwater heating and freshwater cooling systems, along with fresh and saltwater pumps and tanks. The tray tower offers various advantages for gas and liquid two-phase contact, including reasonable pricing, simplicity, and ease of maintenance and cleaning. These trays also address the problems caused by sedimentation in packing. The tower has a diameter of 25 cm and a height of 1.5 m. The effects of air flow rate, saltwater flow rate, freshwater flow rate, saltwater temperature, and freshwater temperature on the exit temperature of the humidification tower, dehumidification, freshwater production, and gain output ratio (GOR) will be investigated. Maximum freshwater production occurs when the inlet freshwater temperature is at its minimum, while the saltwater temperature, air flow rate, and freshwater flow rate are at their highest values. With this system, freshwater production and GOR can reach up to 15.56 L/h and 3.17, respectively.

In this research, the pool boiling process on the surface structures from hundreds of nanometers to several micrometers is studied. Ten different surface structures, consisting of bare, nanostructured coatings, microchannel geometries, and multiscale surfaces, were specifically created on the copper substrates. By combining the optimal nanostructured surface on various microchannels, multiscale structures were created. During pool boiling of saturated water at the atmospheric pressure, all surfaces were examined up to CHF. By significantly enhancing bubble dynamics and increasing the density of active nucleation sites at low heat fluxes, microchannel surfaces were found to promote HTC and CHF. By delaying bubble mergence and preventing the vapor film from spreading at high heat fluxes, the nanostructured coatings enhanced HTC and CHF through the nucleation process and surface wicking. It was shown that multiscale surfaces display the distinct enhancement mechanisms at each length scale, wicking-enhanced CHF from the nanostructures, as well as elevated bubble dynamics and nucleation from the microchannel surfaces. The performance of the multiscale surfaces proved promising, both CHF and HTC showed remarkable improvements in comparison to the bare surface.

Humidification-dehumidification (HDH) technology is an inventive desalination method that is dependable and reasonably priced for small-scale applications. In this study, a novel tray cartridge structure significantly enhances the efficiency of the HDH desalination process. A tray cartridge tower consisting of 4 sieves and 2 chimney trays has been used. In addition to the humidifier and dehumidifier tray tower, this device has saltwater heating and freshwater cooling systems, fresh and saltwater pumps and tanks. The tray tower has various advantages for gas and liquid two-phase contact, including a more reasonable price, simplicity, maintenance, and cleaning. Tower's diameter 25 cm and its height is 1.5 m. The performance of this HDH system has been investigated experimentally. Due to the wide range of parameters and variables, this research uses the experimental design method with the response surface method (RSM) to check the effective parameters and optimize the process. The variations in two system responses, freshwater production, and gain output ratio (GOR), were examined. Analysis of variance (ANOVA) using a Box-Behnken design (BBD) technique was used to assess the experimental data. The recommended empirical model can predict freshwater production and GOR. The results showed that the optimized values of responses were predicted for freshwater production at 14.35 L/hr and GOR at 2.91.

This paper presents a numerical analysis of subcooled flow boiling in a vertical pipe through CFD simulation. The study is aimed to investigate the effect of variable heat flux profiles on CHF. To achieve this, a two-phase Eulerian-Eulerian model coupled with the RPI and CHF boiling models is employed for numerical solutions. The variable heat flux profiles examined include linear-increasing, exponential-increasing, and three sinusoidal-shaped profiles. The results highlight that when variable heat flux profiles are utilized, the RPI model lacks reliability, and the CHF boiling model proves to be a more suitable choice. Among the profiles studied, the sinusoidal-shaped profile with a peak in the middle of the tube exhibits the highest CHF value, while the lowest CHF value corresponds to the exponential-increasing heat flux profile. In sinusoidal profiles, as the number of thermal peaks increases, the CHF value decreases, its location shifts towards the pipe's end, and augments the risk of approaching CHF. By illuminating the intricacies of subcooled flow boiling under variable heat flux, this study provides valuable insights for the development of more efficient and reliable heat transfer designs.

The efficient heat transfer mechanism is crucial for the operation of power generation, refrigeration, and advanced electronic systems to achieve high power density and optimal efficiency. Several investigations have been carried out on enhancing critical heat flux (CHF) and heat transfer coefficient (HTC) through surface modifications on heat transfer of pool boiling. This study focused on examining the pool boiling behavior of a graphene oxide (GO)-coated copper surface utilizing the spin coating deposition method under atmospheric pressure. Three different GO solution concentrations (4, 6, and 8 mg mL−1) were utilized. The thin films’ morphology, wettability, and thickness were analyzed using contact angle measurements, an energy-dispersive X-ray spectrometer, and a scanning electron microscope. The study revealed that the coated surfaces exhibited enhanced wettability, nucleation sites, and porosity characteristics, leading to swift rewetting and cooling of the surface’s hot and dry spots. For HTC and CHF optimization, various concentrations were experimented. In the sample with a 4 mg mL−1 concentration of GO, both CHF and HTC showed remarkable improvements of 59

In this study, the oscillation of walls in a Y-shaped active micromixer is considered to improve fluid mixing. Applying oscillation to the wall fortifies lateral convection and, consequently, improves mixing performance. Two-dimensional unsteady laminar flow simulations were conducted by COMSOL Multiphysics, and the effects of vibration amplitude, inlet fluid velocity, diffusion coefficient, actuator position, and two opposite oscillating parts’ settlement to one another and their phase difference on the mixing efficiency are evaluated. The results indicate the mixing performance improves by increasing the diffusion coefficient and oscillation amplitude of the moving walls as well as the proximity of the moving wall to the junction. The mixing efficiency increased from 25.4 to 90 2900 m from the junction compared with consecutive oscillation.

Forced heat transfer of Al 2 O 3 -water, CuO-water, and TiO 2 -water nanofluids, Al 2 O 3 -CuO-water, Al 2 O 3 -TiO 2 -water, and CuO-TiO 2 -water nanoparticles in volumetric concentrations of 0.5%, 0.9%, and 2% were studied in a flat tube car radiator. In this work, the thermal performance of hybrid nanofluid will be compared with mono nanofluid and pure water base fluid. These nanoparticles were combined in ratios of (75:25), (50:50), and (25:75) in pure water. Mono and hybrid nanofluids with an inlet temperature of 90 °C, and in different Reynolds numbers (272–816) were studied and numerically simulated. The heat transfer performances of mono and hybrid nanofluids were determined using Nusselt number (Nu), overall heat transfer coefficient ( U), convective heat transfer coefficient ( h), and heat transfer rate ( Qa). The results show an enhancement in the thermal performances of the radiator with an increase in Reynolds number and volume concentration as follows: (Al 2 O 3 -water > Al 2 O 3 -CuO-water (75:25) > Al 2 O 3 -CuO-water (50:50) >Al 2 O 3 -CuO-water (25:75) > Al 2 O 3 -TiO 2 -water (75:25) > CuO-TiO 2 -water (75:25) > Al 2 O 3 -TiO 2 -water (50:50) > CuO-TiO 2 -water (50:50) > CuO-water > Al 2 O 3 -TiO 2 -water (25:75) > CuO-TiO 2 -water (25:75) > TiO 2 -water).

This paper presents the pool boiling process of argon atoms on the copper surface by employing molecular dynamics simulation. Through the application of molecular dynamics simulation, this study explores three cases: the plain surface, and adding platinum and aluminum nanoparticles to the argon fluid. The main objective is to offer a comprehensive comparative analysis to highlight the significance and innovation of this research. The investigation aims to assess the effectiveness of two methods for improving heat transfer: the addition of nanoparticles to the base fluid and the creation of porous nanostructure. By subjecting these approaches to identical simulation conditions, an enthralling evaluation unfolds. The simulation framework is first validated, and then the results are presented and compared with the case of creating porous geometry. The results reveal that while the evaporation rate has a similar impact in both cases, creating porous geometry results in a 3.68% higher argon temperature compared to adding nanoparticles. On the other hand, adding nanoparticles enhances the maximum heat flux by approximately 15% more than creating porous geometry. This research compares two approaches to offer valuable investigations and insights into enhancing heat transfer efficiency due to the growing demand for strategies that promote heat transfer.

This paper is aimed to investigate the effectiveness of innovative nanostructured surfaces in terms of heat transfer and evaporation rate enhancement during the pool boiling process of argon atoms by employing molecular dynamics simulation. LAMMPS software and Lennard-Jones potential are used for the simulation and determination of the force field. The fundamental thought of creating these novel geometries (tree-root type nanostructures) is to use the branches as a barrier against liquid cluster separation, which leads to fluid temperature enhancement. First, the framework of simulation is validated, and then the results of creating two types of copper tree-root nanostructures are presented and compared with three cases which include: adding platinum, aluminum, and copper nanoparticles to the argon fluid on the plain copper substrate. The results revealed that creating tree-root type nanostructures postponed the separation of the liquid cluster in comparison with adding nanoparticles. In addition, the tree-root type nanostructures can enhance the evaporation rate and the argon temperature up to 60.05% and 17.13% more than adding nanoparticles, respectively. On the other hand, these nanostructures improve the maximum heat flux and corresponding convective heat transfer coefficient by 15.46% and 26.86% compared to the cases of adding nanoparticles, respectively.

This study examined the effect of surface roughness on the pool boiling heat transfer coefficient of pure water and water-alumina nanofluid with 0.1% and 0.01% volume concentration using computational fluid dynamics on the surface of a stainless-steel cylinder. The effect of nanoparticles was checked by averaging the thermophysical properties in the equations of the flow field with boiling. Simulations were performed for initial surface roughnesses from 0.1 to 0.8 µm. Furthermore, the presence of nanoparticles would make their deposition on the heated surface and change the surface properties. Thus, once again simulations were performed for roughness with the same values but because of the deposition of nanoparticles. In doing so, two separate equations were used for the nucleation site density parameter. Ultimately, the results obtained from both types of roughness were compared. The results indicated that with an increase in the roughness, the boiling heat transfer coefficient increased. Further, at the same roughness, the boiling heat transfer rate of the deposited surface decreased for nanofluid of 0.01% vol and increased for nanofluid of 0.1% vol compared to the non-deposited surface. For pure water at 0.8 µm roughness, the sediment improved heat transfer but it reduced heat transfer for 0.4 µm and lower roughness.

The purpose of this study is to obtain the optimal desalination system with economic approach and the least production pollution for the conditions of Bandar Abbas power plant. For optimal use of the returns of desalination units, five different arrangements of the combination of multi-effect desalination with thermal vapor compression (MED_TVC) and reverse osmosis (RO) desalination units were defined and using thermoeconomic equations and genetic algorithms to optimize different states, the final product cost associated with each arrangement was determined by modeling in engineering equation solver (EES), which is highly accurate according to the validation. The motive steam is provided to fuel the heating units from the steam generated in the heat recovery steam generator (HRSG), which increased the exergy efficiency to 2.53% compared to the exergy efficiency of 2.16% in the current state of the power plant that uses an auxiliary boiler. Two approaches are considered to evaluate the final cost of producing 7600 cubic meters per day of water required by the power plant for each of the arrangements. The first approach is for the current capacity of the power plant, and the second approach is for the case where most of the water capacity is produced by RO. The final results show that the second and fourth arrangements in both approaches have the lowest cost of water production with a slight difference. Also, these two arrangements have higher exergy efficiency than the other arrangements. The second approach showed the higher share of water production by RO, the lower final cost of production, and the best mode is when all the water is supplied by the RO unit, so that the final cost of the product is reduced from 2.59 to 0.59 dollars per cubic meter.

In this paper, a three-dimensional mathematical model is used to investigate the distribution of the temperature and moisture content in the shrimp through two different approaches as two modes of simulation. The governing equations, including heat and mass transfer, are discretized utilizing the finite element method and solved numerically by applying initial as well as boundary conditions and employing COMSOL Multiphysics (R) software (version 5.4). At the beginning of the drying, the heat is transferred from the hot air to the shrimp quickly, then follows a slower trend, leading to only moisture transfer. The numerical results of the two modes are presented and compared against experimental data from a natural convection type of shrimp dryer. The simulation results in the first and second modes show 39.7% and 4.41% deviation compared to the experimental results, respec-tively. In addition, the effect of the moisture diffusion coefficient on the moisture content is investigated.

This paper presents the design and performance evaluation of a cabinet hybrid shrimp dryer. The required energy of the hybrid dryer is provided through solar and an auxiliary infrared source by the solar collector and drying chamber. Three types of pre-treatments and four drying modes are applied in the hybrid dryer. The results of different cases are presented, compared, and evaluated in terms of drying time, amount of received energy, drying efficiency, and appearance of dried shrimp meat. The results reveal that using 2% (w/v) water-salt so-lution pre-treatment and hybrid drying without shade provide the best drying process and appearance of dried shrimp meat. Also, to use the dryer in the optimal condition with the highest mass of shrimp and dryer efficiency, the dryer capacity is determined. According to the results, the maximum capacity of the dryer is 2500 g, which has an efficiency of 16.37% in this capacity. In addition, the effect of using the infrared lamp as an auxiliary source on the drying process and the final quality of dried shrimp are investigated.

Pool boiling is used in various industries and play a significant role in heat transfer. So far, multiple studies have been carried out on investigating boiling and applying heat flux on the wire. In the present paper, the boiling of the coiled wire under atmospheric pressure conditions has been investigated. The fluid temperature inside the pool is considered under both constant (equal to saturation temperature) and variable temperature conditions. The value of the ring density in the coiled wire is considered to be variable. Based on the results, changing the pool liquid temperature changes bubble departure diameter and frequency. Also, increasing the density of the coil ring increases the diameter of bubbles. It has been observed that the bubbles are usually formed inside the coil, and after moving to the two ends of the coil, they leave the coil. However, by increasing the amount of heat flux and the pool liquid temperature, the size of bubbles will be larger; therefore, the bubbles must leave the coil from the empty spaces between the rings. By increasing the amount of applied heat flux, the coil was enclosed in a layer of vapor, which results in a decrease in the amount of heat transfer coefficient, and finally, a sudden increase in temperature on the wire will occur, which indicates the critical heat flux. Also, it has been observed that the critical heat flux always arises in the coil region of wire and not in the straight part of the wire.

In the present study numerical simulation of flow boiling process has been conducted for evaluation of critical heat flux conditions under the effect of different parameters (mass flux, heat flux, channel length and surface roughness). Comparison between the results of the present study and previous researches were done. The comparison shows a good agreement between the present study and previous researches. The three different turbulence models (k-epsilon, k-omega and Reynolds Stress) are considered for simulation of boiling heat transfer and CHF phenomenon. The highest accuracy of simulation is obtained by k-epsilon model. The results express that the wall temperature value of tube with adiabatic and heated boundary conditions for first and second half of the tube is lower than the wall temperature when the fluid flows only in the heated wall section. Reduction of velocity value also leads to reduction of maximum wall temperature value and CHF value. Decreasing Roughness value as an effective parameter leads to an increase in wall temperature. Maximum value of the wall temperature, after CHF point, also increases with increase in heat flux value. CHF depends on the surface roughness and rises with increasing roughness value.

One of the essential industry problems is the critical heat flux (CHF) phenomenon in the flow boiling regime which leads to the temperature jumping and damaging to the systems. Increasing the vapour volume fraction decreases the heat transfer coefficient, and finally, temperature jump will occur. Also, the existence of the bumps and indent in the flow domain changes the flow pattern. In this study, by considering bumps and indent in the tube, the boiling of fluid flow in the vertical tube is discussed. For modelling and simulating the problems, the Euler-Euler model for studying the interaction of the liquid-vapour phases was used. Some models and material specifications are declared using the user-defined function (UDF) codes to the ANSYS Fluent program. The results show that the existence of bumps and indent inside the tube causes the flow of liquid phase to be less redirected in comparison to vapour phase flow due to having more momentum; therefore, at the end of the bumps in the tube, the amount of vapour volume fraction near the wall rises sharply. By increasing the flow mass flux, the vapour volume fraction at the end of bumps increases which lead to decreasing CHF value. It has also observed that if there are bumps and indents inside the tube, there will be no significant change in the liquid flow and vapour volume fraction in the other parts of the tube, as compared to the regular tube.

The numerical simulation of subcooled flow boiling of R-113 working fluid has been done for two different nanofluids (R-113/Al2O3, R-113/TiO2) under different volume concentrations (0.5%, 1%, and 3%). The numerical results were compared with experimental results obtained by previous researchers, and the comparison shows that the numerical results are in good accordance. Nucleation site density, bubble departure frequency, and bubble departure diameter, which are three key parameters, are investigated in this study. The results express that these three parameters have the highest variation at low Reynolds numbers. The influence of different nanoparticles concentrations on the variation of the heat transfer coefficient is studied. The results indicate there is an insignificant difference between the effect of 1% and 3% concentrations on the heat transfer coefficient that means an increase of nanoparticles more than 1% concentration cannot improve heat transfer. The effect of different non-drag forces such as lubrication force, turbulent dispersion force, and lift force is also studied. Two correlations are proposed for predicting the convective heat transfer coefficient.

One of the major industry problems is the flow boiling, where reaching to the critical heat flux (CHF) condition can lead to a temperature jump and damage of the systems. In the present study, the effects of a uniform change in tube diameter on subcooled flow boiling and CHF was numerically investigated. The Euler-Euler model was used to investigate the relationship between the two liquid and vapor phases. The ANSYS Fluent code was used for simulation. According to the results, a linear increase in the tube diameter leads to increase of vapor volume fraction adjacent to the tube wall, as compared to a regular tube with a fixed-diameter, which leads to increase of the tube wall temperature due to the low value of the heat transfer coefficient. At CHF conditions, where the tube wall temperature is much higher than that in subcooled flow boiling, an increase in tube diameter may lead to higher tube wall temperature before the temperature jump, as compared to the post-jump temperature of a tube with a constant diameter. The best approach for decreasing the tube wall temperature was found to be a linear decrease in tube diameter. For the tube diameter change angles of theta < - 0.0383 degrees, tube wall temperature exhibited a decreasing trend from the inlet of the tube to its end.

Heat transfer occurs in flow boiling; as a result, the amount of heat between the tube wall surface and the fluid at different points of the tube may vary depending on the volume percent of vapor at those points. If the flow is fully vaporized, it does not allow for perfect heat transfer at that point; this significantly increases the temperature there; in this case the applied heat flux is called critical heat flux (CHF). The present paper has focused its attentions on simulating a twophase fluid flow within the CHF range using ANSYS Fluent. The simulation results indicated an average error below 7%, which is more than those obtained by the experimental results. The maximum temperature of the tube surface when applying CHF could range between 200 and 500 K degrees more than that of fluid saturation according to the fluid working conditions. It also should be noted that both CHF and maximum temperature increase as the input pressure and mass flux do increase.

Due to the different parameters affecting critical heat flux (CHF), four models were proposed in this study to estimate this parameter. The presented models were validated for mass fluxes of 100 < G [kg/m(2) s] < 2500 and working pressures of 100, 400, and 800 kPa. The nanoparticles used in this study are Alumina, Diamond, ZnO, and Graphene-Oxide. Based on the correlation coefficients, the mass flux and length of the tube have the greatest effect on the increasing and decreasing of the CHF, respectively. Also, the volume fraction and the thermal conductivity of the nanoparticle have the lowest impact on the CHF. It is observed that the most M.A.E. of previous studies is to estimate the CHF in microchannels. For the convenience of using the correlations, there is no need to calculate the nanofluid properties and the critical heat flux can be predicted only based on nanoparticle properties and volume concentration of nanoparticles in the nanofluid. Furthermore, a model was also proposed, in which there is no need for nanoparticle properties and is tuned according to the type of the nanoparticles (innovative parameter: Nanoparticle Number NO. In this study, two types of general and binary models were presented. Based on all existing experimental data, the general model has a mean absolute error (M.A.E.) of about 13%, and the binary model has an M.A.E. of 9%. The M.A.E. of the best model was observed for CHF < 400 [kW/m(2)] (M.A.E = 11%), and the M.A.E. for CHF > 400 [kW/m(2)] was 4.5%. Using the unique correlation for microchannels instead of using the Webber number coefficient, the model accuracy significantly increased. (C) 2019 Elsevier Ltd. All rights reserved.