Superheated Vapor Research Articles

The Heat Transfer Characteristics of Vapor Condensation in a Plate Heat Exchanger

Abstract The model of a single flow channel of a plate heat exchanger (PHE) has been established, and the condensation characteristics of vapor with different saturation temperatures and vapor superheating levels have been investigated. The results show that with a higher vapor saturation temperature, the average surface heat transfer coefficient (HTC) increases. The HTC of saturated steam at a saturation temperature of 348.15 K is about 104.1% higher than that at a saturation temperature of 323.15 K. The influence of vapor superheating is weaker compared to that of the saturation temperature. With the increase of vapor superheat, the surface average HTC first increased and then decreased. The HTC of superheated vapor with a vapor superheating of 10 °C is about 0.72% higher than that of saturated vapor. In industrial applications, it is appropriate to control the vapor inlet superheating to be between 5-10°C.

Application of Torrefaction for Improved Fuel Properties of Sunflower Husks

Sunflower husk (SFH) contributes 45–60% of the total sunflower seed weight and is a by-product of the sunflower oil industry. Among other elements, SFH ash contains K, Na, Ca and Mg. These elements cause rapid growth of ash deposits on convective heating surfaces of the boiler, resulting in reduced efficiency. The aim of this paper is to examine the possibility of producing quality fuel from SFH by its pretreatment with the technique of torrefaction in a fluidized bed in superheated water vapor. Continuous monitoring of the innovative SFH torrefaction process allowed for the determination of optimal process durations. SFH could be converted into a biofuel, having high calorific value and suitable characteristics for co-combustion with coal. Furthermore, the torrefaction in a fluidized bed of superheated water vapor allowed for a 6-fold reduction in the required process duration in comparison with data reported from the literature for the process of torrefaction in a dense bed, along with a 3-fold reduction in the chlorine content in SFH ash. These effects are beneficial to resolve the problem of corrosion on convective heating surfaces of boilers. However, torrefaction in superheated water vapor did not significantly reduce the content of alkaline and alkaline-earth elements in SFH ash. Still, this issue may be alleviated by significantly increasing the duration of SFH pretreatment.

Exploring the Potential of High-Fatty Acid Content Oils for Biodiesel Production: A Catalyst-Free Approach

Abstract The adoption of biofuels has been recognized as one of the key approaches to strive towards achieving net zero emissions, particularly through the utilization of biodiesel derived from oils or fatty acids. To further optimize the utilization of biodiesel, it becomes crucial to explore alternative non-food resources, such as oils with a high content of fatty acids, to serve as biodiesel feedstock. This paper examines the potential use of oil with high fatty acid content, specifically palm fatty acid distillate (PFAD), as a biodiesel feedstock. Typically, the biodiesel production process from PFAD involves a two-step catalytic process that requires a strong acid catalyst, known for its corrosiveness, that needs costly equipment materials. This research explores a catalyst-free production process ensuring a non-corrosive process with reduced capital expenses and fewer chemicals, thereby lowering operational costs. The results demonstrate that biodiesel from PFAD can be obtained in concentration of 83.9% using a one-step non-catalytic process with superheated methanol vapor at a temperature of 210°C under atmospheric pressure. This highlights the significant potential of catalyst-free technology in the production of biodiesel from PFAD.

Parametric analysis of the Charge-Hold-Vent method for cryogenic propellant tank chilldown

In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems.

A Novel Designation of Solid Oxide Fuel Cell-Integrated System Using LPG as Fuel for Marine Vessels

A Novel Designation of Solid Oxide Fuel Cell-Integrated System Using LPG as Fuel for Marine Vessels

Influence of heat flux profile on two-phase flow instability in parallel channels of helical coil once-through steam generator

To enhance the heat transfer capability, the helical coil once-through steam generator (HCOTSG) has been widely utilized in the small modular reactor (SMR). There are hundreds of parallel helical channels in the HCOTSG, and the coolant undergoes the phase change from subcooled liquid to superheated vapor in the helical tube. The flow oscillation between parallel channels may be triggered during the phase change. In present study, the two-phase flow instability is investigated with different heat flux profiles under many operating conditions. The thermal–hydraulic model for parallel channels of HCOTSG is established based on our previous work, while the local heat transfer phenomenon such as subcooled boiling, critical heat flux, and wall conduction are considered in detail. The heat flux profile along the tube is ascertained by the steady-state analysis of HCOTSG under different operating conditions and applied to the outside surface of the helical channel. The heat flux value is increased step by step to trigger the out-of-phase oscillation between parallel helical channels. The thermal–hydraulic model and analysis method are validated against experimental results. The characteristics of flow instability in the helical channel are also analyzed. It is observed that the delay effect causing the flow instability is more obvious if the void fraction exceeds 0.7 in the starting stage. Then the boundary of flow instability is compared under different heat flux profiles for various operating conditions of HCOTSG. The results suggest that the distribution of heat flux in the two-phase region plays a more significant role in the occurrence of flow instability in the parallel helical channel system. The thermal–hydraulic characteristics during flow instability are governed by the combined effects of void propagation and delayed feedback in the system. In conclusion, the thermal–hydraulic condition of HCOTSG undergoes the unstable region to achieve the normal operating point, which can be avoided by adjusting the operating parameters.

High-pressure liquid refrigerant injection for reciprocating compressors

Isentropic (adiabatic) compression of superheated vapor in vapor compression refrigeration cycles usually results in some discharge superheat, i.e. the discharge temperature exceeding the condensing temperature. Large discharge superheat reduces both operating range and compression efficiency. Sub-isentropic compression with heat rejection to the heat sink is therefore superior to adiabatic compression, as it results in lower discharge superheat and improved efficiency. However, significant temperature reduction by heat transfer through the working chamber walls is difficult to facilitate in common refrigeration compressors, particularly reciprocating compressors. Refrigerant and oil injection is a well-established method for reducing temperatures and increasing efficiency in screw and scroll compressors, as well as multi-stage systems. In comparison, effective methods for temperature reduction in single-stage reciprocating compressors are fairly limited. Therefore, a concept for high-pressure liquid injection is proposed. By means of a pump and injection valve, high-pressure liquid refrigerant is injected into the working chamber and atomized. The compressed gas is cooled through the evaporation of the injected liquid. The injection valve allows for control over the injection timing and quantity, enabling adjustment of the temperature profile, which is a major distinction from existing refrigerant injection methods. The coupled compression-injection process is evaluated for various refrigerants using an energetic chamber model. The injection is found to be particularly suitable for refrigerants with a large evaporation heat and a shallow dew line slope. For the example of ammonia, a theoretical reduction in compression work of 8.9% at an evaporation temperature of −10 °C and a condensing temperature of 45 °C is found.

A novel designation of LNG solid oxide fuel cells combined system for marine application

This paper presents a pioneering multigeneration system for marine vessel applications, involving the integration of solid oxide fuel cells (SOFCs) fueled by liquefied natural gas (LNG), coupled with LNG cold energy utilization cycles and exhaust gas heat recovery systems. The system comprises a tandem arrangement of organic Rankine cycle (ORC) and trans-critical carbon dioxide cycle (TCO2), specifically engineered to harness the cold energy released during LNG regasification process. The elevated temperature exhaust gases emanating from the SOFC are efficiently recuperated through a series of components including a gas turbine (GT), regenerative, steam Rankine cycle (SRC), and waste heat boiler (WHB). The proton exchange membrane fuel cells (PEMFC) is designed to enhance the overall operational flexibility and responsiveness of the multigeneration system. The Aspen Hysys V12.1 is used to simulate the propose system and numerical method is employed to parameter optimize of system. The first and second laws of thermodynamics are applied to establish the thermodynamics equations and calculated the system performances. The described system is estimated to obtain energy efficiency of 69.32 % and exergy efficiency of 33.85 %. The high-temperature exhaust gas harvesting integrated systems are sufficiently generated 2091.24 kW which accounted 35.49 % of entire power generate. Furthermore, the parametric researches are implemented to examine the influence of current density, β values to the performance indicators of systems. The WHB is designed to generate 1081 kg/h of superheated vapor at 170 °C and 405 kPa for various purposes of seafarers and equipment's onboard ship. The economic feasibility is performed to view the possibility of investment, maintenance cost and payback period for the described system.

An Evaluation of Correlations for Predicting the Heat Transfer Coefficient during the Condensation of Saturated and Superheated Vapors Inside Channels

Condensation heat transfer is involved in many industrial applications. Therefore, it is important to know the relative accuracy of the available methods for predicting heat transfer. Condensation can occur with saturated as well as superheated vapors. Predictive methods for both conditions were evaluated using a wide range of data. Twelve well-known correlations for the condensation of saturated vapor, including the most recent ones, were compared with data for 51 pure fluids and mixtures from 132 sources in horizontal and vertical channels of many shapes. Channel hydraulic diameters were 0.08–49 mm, the mass flux was 1.1–1400 kg/m2s, and the reduced pressure range was 0.0006–0.949. The fluids included water, CO2, ammonia, hydrocarbons, halocarbon refrigerants, various chemicals, and heat transfer fluids. The best predictive technique was identified. The three most commonly used models for heat transfer during the condensation of superheated vapors were studied. They were first compared with test data using measured saturated condensation and forced convection heat transfer coefficients to select the best model. The selected model was then compared with test data using various correlations for heat transfer coefficients needed in the model. The best correlations to use in the model were identified. The results of this research are presented, as are recommendations for use in design.

Exergy efficiency and heat transfer from the condenser in heat pump systems

In cooling systems, the thermal energy transfer capability of the condensers used for the condensation of the refrigerant is very important for the efficient operation of the systems. A heat pump assembly was installed and R134a was used as the fluid. During operation, the temperature of the refrigerant compressed in the condenser increases and reaches the superheated vapor phase. Heat is transferred from the surface of the condenser, whose temperature is increasing, to the environment with the help of a fan. The exergy efficiency of the condenser was determined based on the inlet and outlet temperature of the refrigerant to the condenser, the temperature of the air flow to and from the condenser surface, its masses and thermodynamic properties. It was observed that the exergy efficiency (ψ) increased and the irreversibility (İ) decreased with the increase of the air temperature difference (ΔT) passing over the condenser surface. In addition, it was determined that the exergy efficiency (ψ) and surface temperature of the condenser decreased with the increase in the amount of air passing through (ma) the condenser surface.

Investigation of operational limit of a pulsating heat pipe by estimating local heat transfer

How pulsating heat pipes (PHPs) reach their operational limit has not yet been fully understood. This study aims to provide a complete picture of the termination mechanism of the self-oscillation of vapor and liquid. Experimental studies on a 10-turn PHP with HFC-134a were conducted and the filling ratio (FR) was from 20% to 80%. The thermo-fluid behavior in the PHP was investigated by temperature measurements with a high-resolution and high-speed infrared camera and estimation of fluid-to-wall heat flux distributions by solving inverse heat conduction problems. The results suggested that the PHP, increasing heat load, reached the operational limit due to different mechanisms depending on the filling ratio: at a high FR (80%), the liquid volume ratio increased with the increase of the operating temperature, resulting in the compressed liquid phase. At a low FR (20%), when a large amount of heat was applied, the fluid in the evaporator dried out and became a superheated vapor. The PHP with an optimum FR (50%) transferred the maximum heat under the same evaporator temperature, as the fluid in the PHP was able to keep the saturated two-phase state until the evaporator temperature exceeded the critical temperature.

CFD simulation on droplet behaviour in post-dryout region

Abstract The investigation on heat transfer in post-dryout region is of great significance to determine the maximum wall temperature when dryout occurs. In this paper, the superheated vapor is considered as Eulerian continuous phase. With DPM (Discrete Particle Method) in the ASNSYS Fluent, droplets will be tracked with Lagrangian method. Heat, momentum and mass are exchanged between the two phases inside Eulerian control volumes. The stochastic tracking is included to investigate the effect of turbulence in the continuous phase on the droplet motion. The results show that the wall temperature profile differs a lot under different initial droplet sizes. By summary of the droplet evaporation rate, it’s found that less than 2 % evaporation happens directly on the wall surface, while evaporation mostly happens in the vapor layer near the wall.

THERMAL PROCESSING OF OIL FLAX BONES INTO ACTIVATED CARBON

Flax shives – waste generated during the primary processing of flax in the textile industry, make up 70% of the total mass of oil flax stalks. The results of an experimental study of the thermal processing of oil flax bonfires by the method of slow conductive pyrolysis in the temperature range of 400–650 °C are presented. An experimental bench for thermal decomposition of flax fire and activation of carbon residue by superheated water vapor is presented. The required temperature regimes of pyrogenetic decomposition were established, which are in the range of 500–600 °C. An analysis of the physicochemical properties of experimental samples of biochar obtained by pyrogenetic decomposition of flax fires has been carried out. At low temperatures of 400–430 °C, the specific gravity of carbon is in the range of 80–82%. Under temperature conditions of 500–600 °C, the specific gravity of carbon was 91–93%. At higher temperature conditions, the yield of gaseous products increases, and the ash content in the solid carbonaceous residue increases. The modes of steam activation of biochar from flax fires have been established, so to achieve the best sorption values, water vapor should be at a temperature of 900 °C. A comparative analysis of the sorption abilities of experimentally obtained activated carbon with BAU-A activated carbon is given. Based on the data obtained, it was concluded that the activated carbon from the fire of flax corresponds to the parameters of GOST 6217-74.

Thermal and Viscous Irreversibilities Analysis in a Liquid Metal Phase Change Counter Flow Heat Exchanger

Sodium, a liquid metal, is utilized in a heat exchanger system coupled to a nuclear reactor to produce hydrogen. The subcooled liquid metal enters a counterflow heat exchanger, undergoes a phase change, and exits as superheated vapor. The sodium heating process occurs through heat exchange with superheated helium vapor in three phases: subcooled liquid, saturated vapor, and superheated vapor. This article analyzes the thermal and hydraulic performance of the three stages of the heat exchanger through thermal and viscous irreversibilities using analytical simulation. The solution obtained is based on applying the thermal efficiency method and the second law of thermodynamics. The thermodynamic Bejan number, the relationship between thermal irreversibility and total irreversibility, allows a cost-benefit analysis when determining thermal performance and viscous dissipation. The essential physical quantities used in the analysis are the lengths and internal diameters of the three segments of the heat exchanger. The results are analyzed and compared with previous analytical work published in the literature. Numerical and graphical results are obtained for temperature profiles, thermal effectiveness, heat transfer rate, thermal irreversibilities, pressure drops, viscous irreversibilities, entropy generation rate, and Bejan numbers. It is demonstrated that the cost-benefit is highly advantageous when the diameter used for the internal tubes of the three segments is equal to the diameter of the saturated sodium vapor section, corresponding to ¼ of the speed of sound in the tube.

Study of the combustion process of liquid off-design fuel in a spray burner device with a controlled supply of primary air

This work studies the process of combustion of liquid off-design fuel (using waste oil as an example) in a jet of superheated water vapor in a spray burner device with a controlled supply of primary air. The average temperature along the vertical axis of the burner device was measured, the composition of intermediate and final combustion products, and heat release were studied when the parameters in the gas generation chamber were varied. It has been shown that changing the primary air flow rate when spraying liquid off-design fuel with a jet of superheated water vapor can additionally influence the flame structure and the level of emissions. And the technology itself can be used to create low-emission burner devices.

Control of CO2 evaporation in an integrated photovoltaic module: experiments and modelling

The use of environmentally friendly refrigerants and the improvement of the system performance are two main topics in the research on heat pump technology. Given the recent limitations imposed on the usage of high global warming potential refrigerants, there is a growing demand in the market for the adoption of natural refrigerants, like CO2. Nevertheless, CO2 heat pumps operate under transcritical conditions, which can adversely affect its efficiency. Therefore, incorporating a solar heat source into a CO2 heat pump can offer a solution to mitigate low system performance issues. In the present study, a photovoltaic module integrated with the evaporator of a CO2 heat pump is experimentally studied. The PV-T evaporator exploits solar radiation to both generate electricity in the PV cells and ensure the evaporation of CO2 in the collector’s tubes. Simultaneously, the PV conversion efficiency is improved by the cooling effect of the evaporation. The present evaporator works in dry expansion mode, thus the refrigerant flow after the expansion device is sent to the solar collectors, where it evaporates before returning to the compressor. When using a PV-T evaporator, it is necessary to prevent superheating in the evaporator to keep a uniform and efficient cooling of the PV cells. The current heat pump design prevents the occurrence of superheated vapor at the PV-T evaporator’s outlet. Beside the experimental activity a dynamic numerical model of the system has been developed and validated.

Condensation of refrigerant R450A inside a mini-channel of rectangular cross section with an internal longitudinal groove

The increase in jeopardizing the natural life and environmental resources together with high rates of energy consumption are still in focus of international agencies and scientific communities. For this issue, global awareness has been oriented to uncover alternatives to harmful species and to magnify effectiveness of thermal systems. For the present study, the refrigerant R450A was investigated as a potential substitute to R134a during condensation inside two mini-channels which are rectangular cross section channel (SRC) and a modified channel (MRC). The latter was characterized by an internal longitudinal groove. Wall subcooling, vapor superheat, and mass velocity were considered while the condensing temperature was kept constant. Numerical CFD simulation was realized for the condensation inside the channel using ANSYS-CFX 15.0 with additional user defined expressions to describe condensate layer thickness inside the channel, which in turn was utilized for the condensation heat transfer coefficient (HTC). Predicted data was compared with experimental one in terms of HTC and flow patterns. The predicted data of HTC showed an average deviation by about 6.6% compared to experimental data for R134a.The refrigerant R450A resulted in lower condensation HTC than R134a. The MRC resulted in an average enhancement in the HTC by about 55.7% and a reduction in the pressure drop by about 10.4% compared to the SRC. The enhancement of the MRC in HTC was remarkable at high degree of superheat, low mass velocity, and low wall subcooling. Accordingly, the novel MRC represents a successful potential design for condensation of refrigerants in mini-channels.

Functional Activated Biocarbons Based on Biomass Waste for CO2 Capture and Heavy Metal Sorption.

Inexpensive porous activated biocarbons were prepared from biomass and agriculture waste following the method of thermal and hydrothermal carbonization and activation with superheated water vapor. The activated biocarbons were characterized by nitrogen adsorption-desorption at 77 K, SEM, XRD, Raman spectrometry, FTIR spectroscopy, determination of particle size, and elemental composition by XRF. The specific surface area was in the range of 240-709 m2/g, and the total pore volume was from 0.12 to 0.43 cm3/g. The percentage of microporosity in activated biocarbons was 89-92%. These activated biocarbons have been used for CO2 and heavy metal sorption. Activated biocarbons based on pine cones and birch prepared by thermal carbonization and activation with superheated water vapor had the highest ability to capture CO2 and amounted to 6.43 and 6.00 mmol/g at 273 K, as well as 4.57 and 4.22 mmol/g at 298 K, respectively. The best activated biocarbon was characterized by unchanged stability after 30 adsorption and desorption cycles. It was proved that the adsorption of CO2 depends on narrow micropores (<1 nm). Activated biocarbons have also been analyzed as effective adsorbents for removing Cu2+, Zn2+, Fe2+, Ni2+, Co2+, and Pb2+ ions from aqueous solutions. Activated biocarbons are effective adsorbents for the removal of lead and zinc ions from aqueous solutions.

Analysis of prediction methods for non-equilibrium internal flow condensation heat transfer

Due to the climate crisis, there is a need to improve the performance of energy conversion systems and increase the use of renewable energy sources. In this context, accurate performance prediction methods for heat exchangers, including condensers, are of crucial importance. In the heat transfer process in a condenser including desuperheating and subcooling, both sensible and latent heat transfer may occur simultaneously due to thermal non-equilibrium effects. Liquid condensate may form close to the vapor saturation point of the bulk flow in the desuperheating region, while superheated vapor may penetrate beyond the liquid saturation point far into the two-phase region, and gas bubbles and subcooled mixture may exist in the subcooled region. These are complex phenomena that to a large extent affect the performance of the condenser. This paper presents an analysis of the prediction methods for non-equilibrium condensation heat transfer. First, the heat transfer mechanisms of non-equilibrium condensation are discussed. Next, state-of-the-art prediction methods developed for the target heat transfer processes are analyzed. Moreover, a database containing all data available in the open literature is built to evaluate the predictive performance of the prediction methods. Finally, a new prediction method is proposed for the subcooled condensation based on the identified heat transfer mechanisms. The results suggest that the Jacob correlation has the best predictive performance, followed by the Kondou correlation. The mean absolute percentage errors of both the Jacob and Kondou prediction methods are lower than 15 %, and more than 85 % of the experimental data points are predicted with a deviation within ± 30 %. The new prediction method proposed for the subcooled condensation is in good agreement with the experimental data, with a mean absolute percentage error of 12 %.

Micro-explosion of emulsion droplets with nanoparticles at high temperature

Compared with traditional fuels, emulsified fuels can improve fuel atomization and combustion, and nanoparticles as additives have the potential to enhance combustion and reduce emissions. Previous studies on micro-explosion mainly considered emulsion droplets, but the role of nanoparticles in emulsion droplets is still unclear. In this study, we experimentally investigate the micro-explosion of emulsion droplets with nanoparticles via high-speed photography, digital image processing, optical microscopy, and scanning electron microscopy. The results show that the presence of nanoparticles can greatly improve the strength and probability of micro-explosion, particularly for carbon nanoparticles. This is mainly because nanoparticles can agglomerate during the evaporation of emulsion droplets, facilitate the absorption of radiation energy, inhibit the diffusion of superheated vapor, and ultimately promote micro-explosion. The effects of nanoparticle mass fraction and water content are also investigated, and the results show that the increase of nanoparticles and water can facilitate micro-explosion.