Evaporation Heat Transfer Research Articles

CO2 mitigation, energy matrices, and the performance analysis of N-evacuated tube collector (ETC)-integrated modified solar distiller for water/electricity co-generation using CQD nanoparticles

With advances in science and technology, nanofluids are the ultrafast heat transfer fluids which effectively empowers the distillation process. In this research article, N-evacuated tube collector (N-ETC)-coupled single slope solar still-equipped built-in-passive condenser and roof-top semitransparent photovoltaic (PV) module have been analyzed incorporating carbon quantum dot nanoparticles (CQD-NPs). The effect of volume concentration of nanoparticles (NPs) and packing factor ( βc) is tested to study the system performance (thermal and electrical). The use of CQD-NPs showed impressive enhancement in thermal conductivity (56.06%), Reynold's number ([Formula: see text]), evaporative (37.9%) and convective (76.94%) heat transfer coefficient even at moderate value of βc (0.67). Thermal energy efficiency and overall daily productivity is improved by 37.67% and 44.15%, respectively, using CQD-NPs. Moreover, thermal energy/exergy-based energy metrics and life cycle assessment has been performed for different lifespans ( n = 1 to 50 years) of the proposed system. Significant improvement in life cycle conversion efficiency [31.90% ( βc = 0), 28.91% ( βc = 0.67), 24.56% ( βc = 0.75), 32.02% ( βc = 0.85), 53.38% ( βc = 0.95)] is observed; also, enviro-economic analysis showed effective rise in annual CO2 mitigation (tons) [41.39 ( βc = 0), 104.85 ( βc = 0.67), 96.23 ( βc = 0.75), 85.14 ( βc = 0.85), 65.51 ( βc = 0.95)] and carbon credits earned using CQD-NPs. This renewable stand-alone two-in-one output system effectively meet the drinking water and electrical energy requirements of societies, and families living in arid/semiarid regions.

Thermal Performance Optimization of Nano-Enhanced Phase Change Material-Based Heat Pipe Using Combined Artificial Neural Network and Genetic Algorithm Approach

Abstract The present study focuses on the numerical investigation of nano-enhanced phase change material (Ne-PCM)-based heat pipes designed for electronic cooling applications. It uses both paraffin wax and n-eicosane as phase change materials (PCMs) that are combined with copper oxide (CuO) nanoparticles at different concentrations of 1%, 3%, 5%, and 7%. The heat input to the heat pipe ranges from 10 to 50 W in an increment of 10 W to simulate realistic operating conditions. The idea is to predict the heat pipe's thermal performance at various combinations of nanoparticles and PCMs and compare the same to the baseline case of deionized (DI) water (without PCM). The results show a constant drop in the evaporator temperature for the Ne-PCM-assisted heat pipes. Paraffin wax and n-eicosane exhibit maximum reductions of 2.86% and 1.94%, respectively, in evaporator wall temperature compared to using conventional DI water (without PCM). The thermal resistance of the heat pipe also decreases consistently with increasing the heat input for all cases, with the most significant reduction of 33.11% and 16.63% for paraffin wax–CuO- and n-eicosane–CuO-assisted heat pipes, respectively. The maximum evaporator heat transfer coefficients recorded are 257.79 W/m2K, 353 W/m2K, and 265.18 W/m2K for heat pipes using DI water (without PCM), paraffin wax–CuO, and n-eicosane–CuO, respectively. The nanoparticles act as a thermal conductivity enhancer and bring down the heat pipe's evaporator temperature with the addition of PCMs. Thus, the effective thermal conductivity of the Ne-PCM-based heat pipe is notably higher compared to heat pipes using DI water (without PCM). To understand the complex thermal behavior of the Ne-PCM-based heat pipes and to better predict their thermal performance, a predictive model has been developed using an artificial neural network (ANN). This model drives the genetic algorithm (GA) that considers the multivariable interaction of PCMs and nanoparticle concentrations to identify the optimal configuration and results in better thermal performance of the heat pipe. Thus, the combination of ANN and GA aids a useful approach for the effective prediction of the heat pipe's thermal performance. The outcomes of this study are useful for the development of sustainable solutions in electronic cooling applications.

Comparative Study of Different Machine Learning Models for Heat Transfer Performance Prediction of Evaporators in Modular Refrigerated Display Cabinets

This study explores the potential of machine learning models to predict evaporator heat transfer performance in Modular Refrigerated Display Cases (MRDCs). Six experimental datasets from MRDC systems were analyzed to compare the efficacy of six machine learning models: Linear Regression, Decision Tree Regression, Support Vector Machines (SVMs), Feedforward Neural Networks (FNNs), Random Forest (RF), and Light Gradient Boosting Machine (LightGBM). The findings indicate that the ensemble tree-based models, LightGBM and RF, are particularly effective in predicting evaporator heat transfer performance. These models demonstrate high accuracy and robustness, effectively capturing the nonlinear relationship between the evaporator temperature and heat transfer coefficient. Moreover, LightGBM and RF exhibit notable stability and adaptability in scenarios of limited data availability and elevated noise levels. Their consistent predictive accuracy across different experimental conditions highlights their suitability for complex refrigeration systems. This research provides essential insights for optimizing MRDC evaporator performance, establishing a theoretical and data-driven foundation for energy-efficient enhancements and intelligent management within cold chain systems.

Experimental investigations on simple and modified concatenated stepped solar still units for the extraction of clean water: A comparative study

In this experimental research work, a parallel comparison of a modified concatenated stepped solar still (MCSSS) unit was done with a simple concatenated stepped solar still (SCSSS) unit for the extraction of clean water, considering thermo-enviro-economic aspects. Each stepped solar still in these experimental units had 0.25 m2 heat absorbing area. The MCSSS unit was equipped with internal reflectors, external reflector and glass cover cooling arrangement. The experimental units were feed with a pre-optimized tap water flow rate of 50 ml/min for the extraction of clean water. The comparison revealed that the MCSSS unit produced 3.43 L/day of distillate which was 18.72 % higher than that of SCSSS unit. In the MCSSS unit, the convective and evaporative heat transfer coefficients were found to be 15.29 % and 11.50 % higher, respectively. The energy and exergy efficiencies of MCSSS unit were 41.58 % and 14.52 % which were found to be respectively 19.93 % and 25.93 % higher than that of SCSSS unit. The MCSSS unit had lower energy payback time and earned higher carbon credits as compared to SCSSS unit. The economic payback period of MCSSS unit was evaluated to be lower than SCSSS unit by 1.297 months.

Concentration of alumina nanofluid on stability and thermal behaviour of the hybrid solar thermal system

In the modern era, renewable solar energy has the potential for different energy applications, including domestic and industrial. With the excellence of high solar radiance and environmental sustainability, it is adopted for heat exchanger applications. This research involves enhancing the thermal behaviour of heat exchangers for space heating applications by implementing 0, 10, 20, and 30 vol% of alumina nanofluid under the flow rate of 0.05 kg/s. The nanofluid stability is evaluated by the Ultrasonication route with multiple days, and it was spotted that the 4-day preparation had better peaks with a mean diameter of 50 nm. Influences of alumina nanofluid of thermal behaviour, including thermal conductivity (k), heat transfer (Q), and thermal adsorption properties of solar operate heat exchanger was studied at 24 to 250 °C through simultaneous thermal analysis differential thermo-gravimetric apparatus Netzsch 409 model and its evaluated results were compared with conventional solar energy operated heat exchanger system contained water as a source. Test condition 4 (30 vol% concentration of alumina nanofluid) was offered a maximum k of 38.98 ± 0.91 W/m°C, a Q of 138 ± 1.52 kJ/Mol, and the thermal absorption system is directly proportional to the solar thermal energy temperature. Moreover, the evaporator heat transfer (0.69 ± 0.01 kW) and total heat dissipation across the condenser (0.98 ± 0.01 kW) were higher than the test condition one value.

Wetting dynamics and heat transfer of droplet evaporation around boiling point: Facile manipulation by surface roughness

The evaporation of water–ethanol droplets on solid surfaces has vast potential for applications in thermal management, microfluidics, and biomedical sciences, while the approach of manipulating wetting dynamics and heat transfer of droplet evaporation around the boiling point remains open for investigations. The present study proposes a facile approach: fabricating solid surfaces with diverse roughness by sandpaper milling with different grit densities, which can alter the wetting and heat transfer characteristics of droplet evaporation. We discover that when the temperature of the heated surface exceeds the droplet boiling point, the existence of bubbles affects the solid–liquid wetting state; surface roughness alters the ability of bubble departure, thus determining the solid–liquid contact and the contact line retraction time. Consequently, in this case, the solid–liquid contact area and the heat absorbed from heated surfaces for droplets changes with surface roughness, altering the droplet evaporation time and the average heat flux at the solid–liquid interface. Bridged by droplet wetting dynamics, the heat transfer of droplet evaporation above the boiling point can be manipulated by adjusting surface roughness, offering a facile approach to tuning the process of droplet evaporation in the related industrial applications.

Evaluation of evaporative heat transfer performance based on observation of Thermo-Fluid behavior in porous structures fabricated by additive manufacturing

This study focuses on improving the performance of Loop Heat Pipes (LHPs) by investigating the thermo-fluid behavior within the evaporator. Previous observations using infrared and visible techniques have revealed potential improvement methods, such as modifications to vapor groove dimensions and enhancements in evaporator wettability. In this research, additive manufacturing technology is employed to manufacture both porous media and evaporator casings, with the aim of enhancing performance. The study evaluates four types of evaporator structures, including samples fabricated separately for porous media and heating plate corresponding to the evaporator casing, samples fabricated integrally, and samples with a porous monolayer loaded onto the heating plate. Micro-scale infrared observation is utilized to assess evaporative heat transfer coefficients and maximum heat flux. The experimental results demonstrate a substantial increase in maximum heat flux in structures where the porous body and heating plate are integrated into a single unit. Moreover, the investigation reveals the influence of the contact area structure between the porous media and heating plate on performance. The presence of voids in this area, allowing for improved vapor release during nucleate boiling, was found to enhance heat transfer efficiency. These findings underscore the efficacy of employing additive manufacturing technology for optimized evaporator designs, offering a pathway toward structurally enhanced and more efficient evaporators.

Visualization and quantitative study on film boiling heat transfer of a salt droplet on the hydrophobic substrate

A droplet impacts on high temperature surface may lead to film boiling. Hydrophobic coating used for corrosion prevention is easy to cause film boiling at low temperature, which results in a remarkable decrease in evaporation efficiency and heat transfer coefficient. However, there is a lack of quantitative visual experimental data on the flow field around the droplet to understand the heat transfer characteristics during film boiling. In this study, schlieren photography combined with high-speed imaging technology is used to observe the evolution process of a droplet impact, rebound, oscillation, and stable boiling. The effects of temperature on lifetime, vapour velocity and heat transfer coefficient of a salt droplet with different concentrations are studied for aluminum and Teflon surfaces. The distribution characteristics of vapour velocity are quantitatively analyzed using cross-correlation algorithm, and the calculation formulas of heat transfer coefficient under nucleate and film boiling modes are proposed. It is found that increasing the concentration of a salt droplet can improve the heat transfer coefficient during film boiling. This work will provide a theoretical basis for the improvement of heat exchanger efficiency in areas such as sea water spray cooling.

Non-intrusive experiments on coupled bubble dynamics and heat transfer during nucleate boiling under varying pressure conditions

The experimental investigation is concerned with the dynamics of single vapor bubble and heat transfer during nucleate boiling under varying pressure conditions, encompassing both atmospheric and sub-atmospheric levels. Utilizing high-speed rainbow schlieren deflectometry, a non-intrusive imaging technique for visualizing and quantifying the flow field variables in the fluid medium, this research examines the influence of operating pressure on some of the important parameters pertaining to boiling phenomenon such as bubble size, shape, and detachment mechanisms. The observations show that a decrease in pressure leads to the formation of larger bubbles, which, in turn, alters their growth mechanism. These changes in bubble behavior have a significant influence on the various forces acting on the growing bubble as well as on the associated heat transfer rates. The analysis provides insights into the complex interplay between buoyancy, surface tension, growth and contact pressure forces. Change in pressure significantly impacts these forces, influencing bubble dynamics. Moreover, the study presents a quantitative analysis of the whole field temperature distribution and heat transfer rates throughout the boiling process. Results reveal a strong dependence of thermal field on the working pressure, with higher pressures leading to more uniform temperature distributions. Evaporative component of heat transfer from the bubble base and convective heat transfer from the superheated layer are identified as the dominant mechanisms. Natural convection initially dominates, decreases post-nucleation, and increases upon bubble departure due to the fluid quenching effects.

Experimental investigation of single slope solar still for culinary wastewater treatment

Solar still desalination (SD) offers a sustainable method for purifying contaminated water, despite its productivity limitations. This study proposes an effective treatment process for culinary wastewater (CWW), multilayer-filtered culinary wastewater (MFCWW), and borewell water. We conducted a comprehensive experimental analysis comparing key SD characteristics, including evaporative heat transfer, efficiency, productivity, exergy, and water quality parameters, across these water sources. Our findings reveal that integrating multilayer filtration with CWW significantly improves efficiency, productivity, turbidity reduction, and hardness removal compared with untreated CWW. Notably, MFCWW has emerged as the most promising modification, demonstrating enhanced solar still performance over conventional SD processes. This study highlights the potential of combining multilayer filtration with solar desalination as an innovative approach to improve water purification outcomes, particularly for culinary wastewater treatment.

Comparative thermal model analysis and experimental validation for predicting performance of a pyramidal solar still with integrated pulsating heat pipe

Developing nations face a dire situation as water scarcity and pollution significantly impact various aspects of life. It's crucial to take action now to address these pressing issues and ensure a sustainable future for all. Solar desalination processes emerge as a promising solution to these pressing problems in water purification technologies.This paper reports the thermal modeling and experimental results of two solar still designs, namely (i) Pyramidal solar still with pulsating heat pipe (PHP), Modified pyramidal solar still (MPSS), and (ii) conventional pyramidal solar still (CPSS). This study uses energy balance equations to focus on MPSS and CPSS thermal modeling. In the MPSS, a PHP, in conjunction with a solar collector, provides external heat to basin water. Several models, including Dunkel, Kumar and Tiwari, Chen, and Zheng Hongfei, are utilized to estimate the performance of both MPSS and CPSS. Extensive experiments have been conducted for validation purposes. Key parameters considered for prediction and comparison include evaporative heat transfer coefficient, convective heat transfer coefficient, total heat transfer coefficient, and hourly yield. It is noted that the Kumar and Tiwari model demonstrates a superior ability to predict cumulative yield, with a percentage error of 5.81 % and 5.9 % for MPSS and CPSS, respectively, compared to the experimental cumulative yield. The theoretical average basin water temperature observed in MPSS is 64.56 °C, and CPSS is 58.8 °C. The enhancement in temperature is attributed to the supplementary heat provided by the PHP.

Optimization of evaporation heat transfer in high-porosity porous columns

Compared to pool boiling or flow boiling, the evaporation within porous media can offer a higher heat transfer advantage. In this work, the numerical simulations were conducted on the application of porous columns at hot spots in heat exchanger and an analysis was performed on the transient evaporation of liquid within the porous medium. The thermal performance of porous columns with different porosities and pore sizes were investigated on the basis of the obtained data. It finds that the porous columns tend to experience vapor blockage during the phase change, which will hinder liquid replenishment and result in a deterioration of heat transfer. Moreover, the vapor blockage phenomenon is more pronounced in porous columns with lower porosity and smaller pore size. Six types of porous columns were compared, and it finds that inlet-optimized samples with a relief in vapor blockage exhibits a better thermal performance compared to the conventional ones. After an optimization of outlet, a rapid discharge of vapor within the porous medium column can be achieved, which reduces the difficulty of liquid replenishment and contributes to performance of evaporation heat transfer.

Effect of pin fins on heat transfer during condensation in minichannel heat exchanger

In this study, condensation heat transfer of water vapor in a minichannel heat exchanger on smooth and pin fins surfaces was investigated experimentally. The experimental study was carried out to evaluate heat transfer coefficient, overall heat transfer coefficient, and Nusselt number over different ranges of vapor mass flux from 0.0064 to 0.0368 kg m−2 s−1 and cold-water flow rate range between 0.0013 kg s−1 to 0.0057 kg s−1. The minichannel has a rectangular shape with a hydraulic diameter of 1.3 mm. The experimental testing is carried out on aluminum surface with a channel that has a length of 270, width of 30 mm, and height of 1.3 mm. The pin fins surface is on the bottom of the condensing channel and the fins are circular and have diameter, height, and spacing of 1 mm, and are in-inline arrangement. It is found that condensation heat transfer coefficient on pin fins surface is about 15 % higher than that on smooth surface. It is found that the condensation heat transfer coefficient increases significantly with increasing the vapor mass flux. In addition, the effect of increasing the cold fluid flow rate is lower than that of the hot vapor flow rate, but it becomes more significant for higher vapor flux.

Thin-film evaporation in microchannels: A combined analytical and computational fluid dynamics approach to assessing meniscus curvature impact

Computational fluid dynamics (CFD) is employed to investigate the effects of variation in bulk meniscus curvature on evaporative heat and mass transfer in microchannels. Evaporation in microchannels presents a classic multiscale problem, encompassing both microscopic and macroscopic length scales in the thin-film and bulk meniscus regions, respectively. Therefore, the liquid-vapor interface or meniscus shape is first determined through thin-film evaporation analysis using numerical approaches found in the literature. However, a new approach for establishing boundary conditions is also proposed, allowing for the representation of varying curvatures within the bulk meniscus region. Then, the obtained meniscus thickness profiles are exported to a two-dimensional CFD framework. The primary advantage of this developed CFD framework lies in its capability to simultaneously analyze evaporative heat and mass transfer from both microscopic and macroscopic regions, a feature that enhances research endeavors concerning micro and miniature heat pipes. The developed model is applied to various rectangular microchannel sizes, ranging from 10 to 100 μm in width, with wall superheats varying from 0.1 to 3.0 K. The aim is to quantify the effects of variations in bulk meniscus curvature on the evaporative characteristics of the extended meniscus (comprising both thin-film and bulk meniscus regions), using the concept of thermal resistance. Consequently, based on the CFD simulation results, multiple regression analysis is employed to formulate the total thermal resistance in terms of independent parameters, namely the microchannel width, wall superheat, and the radius of curvature (Rc). It is observed that the radius of curvature has a marginal impact on the total thermal resistance, allowing its influence to be expressed by a power-law function of (Rc/Rm)0.102, where Rm represents the minimum radius of curvature.

Carbon dioxide evaporation heat transfer coefficient prediction in porous media using Machine learning algorithms based on experimental data

The prediction of the internal heat transfer coefficient during evaporation is vital for vapor-compression refrigeration and closed-loop power cycles. Accurate measurements and understanding of CO2 heat transfer in porous evaporators are essential for optimal system design across various operating conditions. This study utilizes a reference dataset derived from previous experiments that investigated the impact of porous evaporators on CO2′s internal heat transfer coefficient under sub-critical conditions, employing gravel sand as the porous medium. The dataset encompasses key factors: gravel sand porosities ranging from 39.8 % to 44.5 %, evaporator inlet pressures between 3700 and 4300 kPa, CO2 mass flow rates from 10.7x10-5–18x10-5kg.s−1, and porous tube effective diameters spanning 1.53 x10-3–3.4x10-3m. Employing three machine learning techniques (SVM, GPR, OBEM), the study predicts the internal heat transfer coefficient using regression models. The models’ predictions are analyzed and compared to expected values for validation, evaluating their performance using four statistical criteria. Results indicate SVM, GPR, and OBEM models achieved RMSEs of 1.5471, 1.8212, and 3.6978, respectively, while MAE errors were 1.1479, 1.2418, and 2.9787, respectively. Comparison with the dimensional analysis method reveals the effectiveness of the proposed models in accurately predicting internal heat transfer coefficients. The models exhibit low uncertainty and maintain prediction quality on an extended dataset without overfitting concerns. Overall, this research contributes valuable insights for designing heat exchangers and systems in vapor-compression refrigeration and closed-loop power cycles.

Comparative study on productivity of double slope solar still using different wick and energy storage materials

The aim of the proposed study is to evaluate the efficiency of Double Slope Solar Still (DSS) using different wick and energy storage materials. In the study, wick materials such as jute, cotton and sponge were used in combination with energy storage materials such as mild steel, cast iron and copper. The experiments were conducted using DSS with different combinations of wick and energy storage materials to determine the efficient performance combination. The results show that sponge and copper have higher efficiency with wicks and energy storage materials. The results show that the maximum amount of water produced in a single day was 3147 ml when the DSS system was used with a combination of sponge and copper materials. This range shows an increase of 17.47 % and 12.44 % over the DSS with jute and copper and the DSS with the combination of cotton and copper respectively. The DSS showed the highest average energy efficiency when used in conjunction with a combination of sponge and copper, namely 51 % of the average efficiency. This corresponds to an increase of 18.60 % and 10.86 % compared to the combination of DSS with jute and copper and the combination of DSS with cotton and copper respectively. The best evaporation heat transfer coefficient of 345 W/m2K was determined for the combination of DSS with sponge and copper. Average exergy efficiency is also maximum of 3.076 % for the DSS with sponge and copper materials, which is higher than other investigated combinations. The proposed system has an energy payback period of 1.26 years, an energy production factor of 0.78, a life cycle efficiency of 6.9 % and a cost of $0.031 per litre of water produced in the environmental economic analysis.

Thermal performance analysis and optimization of a heat pipe-based electronic thermal management system using experimental data-driven neuro-genetic technique

Heat pipes are highly efficient heat transfer devices and are used widely to dissipate heat generated by electronic components, thereby maintaining their operating temperatures and preventing overheating. The present study deals with the thermal performance prediction of a cylindrical heat pipe (length 380 mm) based electronic thermal management system using steady-state experimental investigation. The experiments are conducted under varying operational conditions, including heat inputs (10–50 W), condenser cooling water inlet temperatures (288.15, 293.15, and 298.15 K), and flow rates (10, 25, and 40 LPH). The study shows that the evaporator temperature of the heat pipe consistently rises with the increase in heat inputs for all tested conditions. The lowest evaporator temperature (311.42 K) is noticed for the cooling water inlet temperature of 288.15 K across all heat inputs. Notably, at 10 LPH, the heat pipe supplied with cooling water at 288.15 K exhibits reductions of up to 1.47 % and 2.29 % compared to 293.15 K and 298.15 K, respectively. Similar trends are also observed at 25 LPH and 40 LPH. The heat pipe’s thermal resistance is lowest (0.95 K/W) at a cooling water inlet temperature of 298.15 K. At 10 LPH, there are reductions of 10.19 % and 5.62 % compared to 288.15 K and 293.15 K, and at 40 LPH, reductions are 15.66 % and 7.89 %. The heat pipe’s evaporator heat transfer coefficient also plays a significant role and is maximum for the cooling water inlet temperature of 288.15 K at a flow rate of 10 LPH. To understand the complex behavior of the heat pipe and for better prediction of its thermal performance, a neuro-genetic (experimental data-driven artificial neural network and genetic algorithm) optimization technique is considered in the study. This predicts the optimal combination of operating parameters (heat input, cooling water inlet temperature, and flow rate) to minimize the heat pipe’s evaporator wall temperature which is found to be 312.54 K at a heat input of 10 W, flow rate of 10 LPH, and cooling water inlet temperature of 289.14 K. These input combinations are further validated through the experiments and the error in the heat pipe’s evaporator temperature is found to be 0.66 % only. Overall, this neuro-genetic technique underscores the importance of optimizing operational parameters for enhanced heat pipe performance and offers valuable insights for electronic cooling systems.

Modeling the thermal and hydrodynamic performance of grooved wick flat heat pipes

A compact model is developed to predict the thermal and hydrodynamic performance of a flat heat pipe with a rectangular grooved wick. The present model relies on the analytical solution to the energy equation in the wall and an equivalent heat transfer coefficient predicted using a computationally efficient iterative method. This efficient iterative method can also provide a framework for modeling other grooved or porous wick heat pipes for which analytical or semi-analytical solutions to the wall conduction, fluid flow, and film equations exist. Compared to prior numerical tools, the present modeling approach is computationally efficient, making it compelling for use in parametric and optimization studies. Instead of numerically solving a set of coupled differential equations, the present model considers only analytical and semi-analytical solutions for evaporation and condensation heat transfer rates. The non-discretized nature of the present model allows computations on a typical workstation to be completed within seconds as opposed to the hours required for prevalent numerical tools. The present model accounts for varying liquid fill volumes, geometry, and interfacial properties, such as surface tension and contact angle. The present model closely agrees with published numerical and experimental results for wall temperatures and maximum heat transfer rates. Parametric studies, which vary wall thermal conductivity, water contact angle, and groove dimensions are conducted on a previously experimentally investigated heat pipe to demonstrate the present model’s capabilities. The present model found that the maximum heat transfer rate of the heat pipe can be enhanced by about 15 and 20% by varying its wetting angle and groove dimensions, respectively.

Single feed droplet–catalyst particle collision in a liquid containing gas–solid fluidized bed to convert fructose to value-added chemicals

Carbohydrates, comprising C6 sugars, dehydrate to form furfural (FUR) and 5- hydroxymethyl furfural (HMF). HMF is an intermediate for value-added specialty chemicals like 2,5-diformyl furan (DFF) and 2,5-furandi carboxylic acid, a monomer for polyethylene furaonate. Atomizing sugar solutions into catalytic fluidized beds operating beyond the caramelization temperature, Tcarm, accelerates reaction rates while avoiding humins, which are color forming agents characteristic of liquid phase processes. However, droplets partially coat particles in the spray zone and agglomerate due to liquid cohesive forces, which reduces heat transfer rates at the micro-scale and degrades reaction rates at the macro-scale. Here, we developed a CFD model to study the collision between a single feed droplet and a catalytic particle above Tcarm. We focused on evaluating the evaporation rate and heat transfer between the droplet and particle to promote vaporization the liquid feed, and assessing the impact of bed temperature, liquid feed rate, and superficial gas velocity. The highest DFF and furfural selectivity obtained are 17% and 24%, respectively, and these values are correlated to the maximum coke formation and agglomeration of 0.6% and 12g. However, the corresponding heat transfer and mass transfer are among the lowest values of 40% and 0.5W.

Experimental study on thermal performance of plate evaporator under yawing and heaving conditions

To elucidate the role of marine sloshing in thermal performance of plate evaporators, an experimental system of flow boiling in plate evaporator was constructed, integrating with a six-degree-of-freedom motion platform. The effects of sloshing modes (yawing and heaving), mass flow rate, sloshing frequency, amplitude, and intensity on the boiling performance of plate evaporator were examined and investigated. The experimental results indicate that, both yawing and heaving motions significantly enhance the boiling heat transfer performance of the R410A plate evaporator. In the yawing motion, the frequency and amplitude both play a role in bolstering the heat transfer capabilities of the evaporator. As the intensity of the sloshing increases, the heat transfer performance of the plate evaporator significantly improves compared to stable conditions, with enhancements ranging from 6% to 33%. As the intensity of the sloshing increases, the heat transfer performance of the plate evaporator significantly improves compared to stable conditions, with enhancements ranging from 7% to 84%. Notably, the impact of heaving motion on heat transfer enhancement surpasses that of the yawing motion. In addition, a heat transfer correlation for the R410A was introduced to evaluate the boiling heat transfer in plate evaporator under the yawing and heaving conditions.