scholarly journals Heat Transfer Limitations in Supercritical Water Gasification

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 177
Author(s):  
Francisco Javier Gutiérrez Gutiérrez Ortiz ◽  
Francisco López-Guirao ◽  
Francisco José Jiménez-Espadafor ◽  
José Manuel Benjumea
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Experimental Studies ◽  
High Water ◽  
Conventional Heating ◽  
Slow Heating ◽  
High Water Content ◽  
Fluid Temperature ◽  
Factors Affecting ◽  
Supercritical Water Gasification

Supercritical water gasification (SCWG) is a promising technology for the valorization of wet biomass with a high-water content, which has attracted increasing interest. Many experimental studies have been carried out using conventional heating equipment at lab scale, where researchers try to obtain insight into the process. However, heat transfer from the energy source to the fluid stream entering the reactor may be ineffective, so slow heating occurs that produces a series of undesirable reactions, especially char formation and tar formation. This paper reviews the limitations due to different factors affecting heat transfer, such as low Reynolds numbers or laminar flow regimes, unknown real fluid temperature as this is usually measured on the tubing surface, the strong change in physical properties of water from subcritical to supercritical that boosts a deterioration in heat transfer, and the insufficient mixing, among others. In addition, some troubleshooting and new perspectives in the design of efficient and effective devices are described and proposed to enhance heat transfer, which is an essential aspect in the experimental studies of SCWG to move it forward to a larger scale.

scholarly journals A Model for the Spacing of Quicklime Pile to Treat High Water Content Loess

2020 ◽  
Vol 2020 ◽  
pp. 1-7
Author(s):  
Hong Guo ◽  
Yalin Nan ◽  
Rui Guo ◽  
Jiangtao Fu
Keyword(s):  
Water Content ◽  
Reference Value ◽  
High Water ◽  
High Water Content ◽  
Oxide Content ◽  
Factors Affecting ◽  
New Model ◽  
Pile Spacing ◽  
Construction Methods ◽  
Foundation Treatment

There has been a long history for foundation treatment by quicklime pile, but as for establishing a more precise model formula used by actual construction, further research is needed to be done at present. Therefore, how to quantitate the factors affecting pile spacing is of great reference value for both actual constructions and theoretical studies. Based on the reference formula for handling weak foundation by lime pile and the practical problems in the western region, mathematical model analysis method is used to get a new model for high water content loess foundation treatment after considering the factors such as pile expanding, construction method, piles arrangement, and calcium oxide content. In this model, pile spacing coefficient is created and the model formula for different construction methods and different pile arrangements is also given. As a result, the reference formula used in high water content loess is somewhat conservative. The new model is also verified to be rational by the actual works at the end of the paper.

Analysis of the Heat Transfer of Ginkgo Biloba Seeds during Radio-Frequency Heating

2019 ◽  
Vol 16 (1-2) ◽  
Author(s):  
Chunfang Song ◽  
Yao Chen ◽  
Jingke Wu ◽  
Zhenfeng Li ◽  
Haiying Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Radio Frequency ◽  
Electric Fields ◽  
Ginkgo Biloba ◽  
Simulation Method ◽  
High Water ◽  
High Water Content ◽  
Rf Heating ◽  
Distribution Law ◽  
Simulated Temperature

AbstractFresh ginkgo biloba (GB) seeds are seasonal and susceptible to microbial spoilage, especially the growth of mold owing to GB seeds’ high-water content, which greatly limits their shelf life. As an efficient and special heating method, radio-frequency (RF) heating can be used to dehydrate ginkgo to preserve its nutritional value and reduce postharvest losses. However, the non-uniformity of RF heating restricts the development in industrialized application. In this study, the RF drying of GB seeds was performed to investigate the effect of RF heating on temperature. The distribution law of the entire temperature field was also observed. Using numerical simulation method, the coupling model of electromagnetic and heat transfer was established. The model was validated by the 6-min heating profile of GB seeds in a 12 kw and 27.12 MHz RF system. The model was also qualitatively validated by comparing the simulated temperature profiles on the three planes in the GB seeds with the corresponding thermal images. Quantitative validation was performed by comparing the simulated temperature of GB seeds on the three planes with experimental temperature acquired at places using thermocouples. Furthermore, the model can be effectively used to identify the distribution of electric fields in different positions and to achieve satisfactory heating uniformity.

Effect of Inlet Fluid Temperature on the Buoyancy Induced Flow in Circular Tube Inserted With Twisted Strip

2005 ◽  
Author(s):  
S. B. Thombre ◽  
S. V. Prayagi ◽  
N. V. Deshpande
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Rate ◽  
Experimental Studies ◽  
Transfer Characteristic ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Induced Flow ◽  
Buoyancy Induced Flow

The present work deals with experimental studies on heat transfer characteristic for buoyancy induced flow through inclined tubes inserted with twisted strips. The parameters varied during the experimetation are; tube inclination, heat supply twist pitch and fluid inlet temperature. It was found that the percentage enhancement in heat transfer coefficient decreases with increase in pitch and tube inclination. The flow rate is found to decrease with decrease in the pitch and increase in the tube inclination. It was also observed that the heat transfer coefficient and flow rate decreases with the increase in the inlet fluid temperature. This may be due to reduction in Rayleigh number caused because of higher heat loss at the tube surface.

Investigation of Characteristic-Temperature Approaches for Heat-Transfer Correlations at Supercritical Conditions

2013 ◽  
Author(s):  
Sarah Mokry ◽  
Igor Pioro
Keyword(s):  
Heat Transfer ◽  
Supercritical Water ◽  
Wall Temperature ◽  
Characteristic Temperature ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Supercritical Conditions ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients ◽  
Bare Tube

It is expected that the next generation of water-cooled nuclear reactors will operate at supercritical pressures (∼25 MPa) and high coolant temperatures (350–625°C). In support of the development of SuperCritical Water-cooled Reactors (SCWRs), research is currently being conducted for heat-transfer at supercritical conditions. Currently, there are no experimental datasets for heat transfer from power reactor fuel bundles to the fuel coolant (water) available in open literature. Therefore, for preliminary calculations, heat-transfer correlations obtained with bare-tube data can be used as a conservative approach. A number of empirical generalized correlations, based on experimentally obtained datasets, have been proposed to calculate Heat Transfer Coefficients (HTCs) in forced convective heat transfer for various fluids, including water, at supercritical pressures. These bare-tube-based correlations are available in various literature sources. There have been a number of methods applied to correlate heat transfer data. The most conventional approach, which accounts for property variations in the data, is to modify the classical Dittus-Boelter equation for forced convection. However, analysis and comparison of these correlations has shown that differences in HTC values can be up to several hundred percent. In general, the familiar correlations of Dittus-Boelter and Bishop et al. have used the bulk-fluid temperature approach for characteristic temperature properties evaluations. However, at high heat fluxes, fluid near the tube-wall will have a temperature close to that of the wall temperature. This might be significantly different from the bulk-fluid temperature. Therefore, another approach can be used based on the wall temperature as the characteristic temperature. The Swenson et al. correlation is based upon this approach. Finally, a third approach has been considered in which the film-temperature is used as the characteristic temperature (Tf = (Tw+Tb) / 2). McAdams et al. based their correlation for annuli on this approach. Therefore, the objective of this paper is to evaluate the three characteristic temperature approaches, (1) Bulk-fluid temperature approach; (2) Wall-temperature approach; and (3) Film-temperature approach, and determine which characteristic temperature method can most accurately predict supercritical water heat transfer coefficients. Both classical correlations and more recently developed correlations are considered in this investigation.

Development of Supercritical Water Heat-Transfer Correlation for Vertically-Upward Internally-Ribbed Tubes

2014 ◽  
Author(s):  
Weiqiang Zhang ◽  
Huixiong Li ◽  
Qing Zhang ◽  
Yifang Zhang ◽  
Tai Wang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Supercritical Water ◽  
Nuclear Reactor ◽  
Large Deviation ◽  
Experimental Studies ◽  
Great Influence ◽  
Dimensionless Numbers ◽  
Experimental Database ◽  
Heat Transfer Correlations

The investigation on the heat transfer characteristics for supercritical pressure water (SCW) is of value for the development of the supercritical water-cooled nuclear reactor (SCWR). As an important heat transfer enhancement element, heat transfer for SCW in internally-ribbed tubes was still not solved, though lots of experimental studies have been published and a great many heat transfer correlations were proposed. This paper presented an analysis of heat transfer in the internally-ribbed tubes, through comparing heat transfer correlations for SCW gained from different internally-ribbed tubes under the same operating condition. It was found that all existing heat transfer correlations reported could not been well applied for various internally-ribbed tubes with large deviation between prediction results and experimental values, because rib geometry had a great influence on heat transfer of internally-ribbed tubes. On the basis of experimental data collected from open literature for internally-ribbed tubes, a new general calculation correlation of heat transfer coefficient for SCW was developed for various internally-ribbed tubes by combining an optimized empirical correlation for vertically-upward smooth tubes and four dimensionless numbers of rib geometry. The results show that the calculated values of the new present correlation is in reasonable agreement with available experimental data collected. Moreover, the new correlation was verified well by experiment data of two new-type internally-ribbed tubes performed beyond the above experimental database.

Lipids Extraction from Wet and Unbroken Microalgae Chlorella vulgaris Using Subcritical Water

2019 ◽  
Vol 964 ◽  
pp. 103-108 ◽  
Author(s):  
Siti Zullaikah ◽  
Maria Christy P. Jessinia ◽  
Rinaldi ◽  
Medina Yasmin ◽  
M. Rachimoellah ◽  
...  
Keyword(s):  
Ethyl Acetate ◽  
Chlorella Vulgaris ◽  
Subcritical Water ◽  
Dry Weight ◽  
High Water ◽  
Extraction Time ◽  
High Water Content ◽  
Subcritical Water Extraction ◽  
Factors Affecting ◽  
Polarity Index

Lipids extraction from wet and unbroken microalgae (Chlorella vulgaris) using subcritical water with aid of co-solvents has been investigated. Lipids extraction from wet and unbroken microalgae has a crucial role in order to eliminate dewatering and drying steps. Subcritical water is able to extract lipids from feedstock with high water content. This work was conducted to study several factors affecting in subcritical water extraction (SWE) from wet and unbroken microalgae. In this study, effect of co-solvent types (without co-solvent, chloroform, methanol, ethanol, ethyl acetate, and n-hexane) under subcritical water (microalgae = 5g (dry weight), moisture content= 94.12%, T= 160°C, P = 80 bar, t= 30 min), extraction time (15 min, 30 min, 1 h, 3 h, and 5 h), and temperature (160o C, 180o C and 200o C) on yield of lipids were investigated orderly. Yield of lipids obtained without co-solvent (water polarity index = 10.2) and with co-solvents of methanol (PI=5.1), ethanol (PI=5.2), chloroform (PI=4.1), ethyl acetate (PI=4.4), and n-hexane (PI=0.1) were 38.73%, 26.47%, 26.12%, 51.93%, 53.40%, and 25.59%, respectively compared to the yield of lipids extracted using Bligh and Dyer method. Ethyl acetate is solvent with moderate PI, therefore can extract more lipids that is also have moderate polarity. Ethyl acetate shows a good performance to extract lipids from wet and unbroken microalgae because ethyl acetate can extract broader range of lipids including neutral and polar lipids. This study also found that increasing of extraction time and temperature to extract lipids in subcritical water condition can increase yield of lipids.

Computational Fluid Dynamics Investigation of Supercritical Water Flow and Heat Transfer in a Rod Bundle With Grid Spacers

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Malwina Gradecka ◽  
Roman Thiele ◽  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Flow ◽  
Supercritical Water ◽  
Complex Geometry ◽  
Inlet Section ◽  
Fluid Temperature ◽  
Rod Bundle ◽  
Flow And Heat Transfer

This paper presents a steady-state computational fluid dynamics approach to supercritical water flow and heat transfer in a rod bundle with grid spacers. The current model was developed using the ANSYS Workbench 15.0 software (CFX solver) and was first applied to supercritical water flow and heat transfer in circular tubes. The predicted wall temperature was in good agreement with the measured data. Next, a similar approach was used to investigate three-dimensional (3D) vertical upward flow of water at supercritical pressure of about 25 MPa in a rod bundle with grid spacers. This work aimed at understanding thermo- and hydrodynamic behavior of fluid flow in a complex geometry at specified boundary conditions. The modeled geometry consisted of a 1.5-m heated section in the rod bundle, a 0.2-m nonheated inlet section, and five grid spacers. The computational mesh was prepared using two cell types. The sections of the rods with spacers were meshed using tetrahedral cells due to the complex geometry of the spacer, whereas sections without spacers were meshed with hexahedral cells resulting in a total of 28 million cells. Three different sets of experimental conditions were investigated in this study: a nonheated case and two heated cases. The nonheated case, A1, is calculated to extract the pressure drop across the rod bundle. For cases B1 and B2, a heat flux is applied on the surface of the rods causing a rise in fluid temperature along the bundle. While the temperature of the fluid increases along with the flow, heat deterioration effects can be present near the heated surface. Outputs from both B cases are temperatures at preselected locations on the rods surfaces.

scholarly journals Study of Nutrition Content Food Drop in Deer in PT. Gunung Madu Plantations

2018 ◽  
Vol 6 (1) ◽  
pp. 32
Author(s):  
Jumayanti Boru Hombing ◽  
Bainah Sari Dewi ◽  
Syahrio Tantalo ◽  
Sugeng Prayitno Harianto
Keyword(s):  
Nutritional Value ◽  
Nutrient Content ◽  
High Water ◽  
Proximate Analysis ◽  
High Water Content ◽  
Factors Affecting ◽  
Deer Population ◽  
In Captivity ◽  
Good Nutrition

Increasing the number of individual deer in captivity indicates an increase in the deer population. One of the factors affecting the increase in the deer population is a drop in the quality of feed and nutritional value adequate for deer. Therefore it is necessary to investigate the type of feed and feed nutrient content in captive deer drop in PT Gunung Madu Plantations (GMP). Nutrient content of feed drop in deer obtained through the proximate analysis by taking a sample of 100 grams per sample feed. This type of feed given drop in manager consists of the main feed forage consisting of grass and leaves, in the form of rice bran concentrate feed, and feed the tubers were given every month. Based on proximate analysis that has been made known that the feed drop-in provided by the organizer captivity contains good nutrition, as seen in the high water content, extract ingredients without nitrogen (BETN) high, protein and fibers that do not differ greatly in value and fat content is not excessive. Keywords: Drop in Feed Nutrition, Feeding Deer, Captive Deer PT. GMP

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