The Effect of Swirl, Inlet Conditions, Flow Direction, and Tube Diameter on the Heat Transfer to Fluids at Supercritical Pressure

1970 ◽  
Vol 92 (3) ◽  
pp. 465-471 ◽  
Author(s):  
B. Shiralkar ◽  
P. Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Tube Diameter ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

An investigation has been made of the factors governing the heat transfer coefficient to supercritical pressure fluids, particularly at high heat fluxes. The deterioration in heat transfer to supercritical carbon dioxide has been experimentally studied with reference to the operating conditions of mass velocity and heat flux, tube diameter, orientation, tape induced swirl, inlet temperature, and pressure. A detailed comparison has been made with the apparently contradictory results of other investigators, and operating regions, in which the heat transfer coefficient behaves differently, have been defined. The terms used to describe these regions are the Reynolds number, a heat-flux parameter, and a free-convection parameter.

scholarly journals Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

1969 ◽  
Vol 91 (1) ◽  
pp. 27-36 ◽  
Author(s):  
B. S. Shiralkar ◽  
Peter Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Bulk Temperature ◽  
Operating Pressure ◽  
The Heat Transfer Coefficient

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.

scholarly journals Distributed parameter modeling and thermal analysis of a spiral water wall in a supercritical boiler

2013 ◽  
Vol 17 (5) ◽  
pp. 1337-1342 ◽  
Author(s):  
Shu Zheng ◽  
Zixue Luo ◽  
Huaichun Zhou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Supercritical Pressure ◽  
Distributed Parameter ◽  
Water Wall ◽  
Coefficient Distribution ◽  
Distributed Parameter Model ◽  
The Heat Transfer Coefficient

In this paper, a distributed parameter model for the evaporation system of a supercritical spiral water wall boiler is developed based on a 3-D temperature field. The mathematical method is formulated for predicting the heat flux and the metal-surface temperature. The results show that the influence of the heat flux distribution is more obvious than that of the heat transfer coefficient distribution in the spiral water wall tube, and the peak of the heat transfer coefficient decreases with an increment of supercritical pressure. This distributed parameter model can be used for a 600 MW supercritical-pressure power plant.

Local Heat Transfer Coefficient During Condensation in a 0.8 mm Diameter Pipe

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Local Heat Transfer Coefficient ◽  
Wide Range ◽  
The Heat Transfer Coefficient

The first preliminary tests carried on a new experimental rig for measurement of the local heat transfer coefficient inside a circular 0.8 mm diameter minichannel are presented in this paper. The heat transfer coefficient is measured during condensation of R134a and is obtained from the measurement of the heat flux and the direct gauge of the saturation and wall temperatures. The heat flux is derived from the water temperature profile along the channel, in order to get local values for the heat transfer coefficient. The test section has been designed so as to reduce thermal disturbances and experimental uncertainty. A brief insight into the design and the construction of the test rig is reported in the paper. The apparatus has been designed for experimental tests both in condensation and vaporization, in a wide range of operating conditions and for a wide selection of refrigerants.

Experimental Study on Flow Boiling of HFE-7100 in Wavy Copper Microchannels

2020 ◽  
Author(s):  
Peilin Cui ◽  
Zhenyu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Thin Liquid Film ◽  
Bubbly Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

Abstract This study experimentally investigated the flow boiling of HFE-7100 in wavy copper microchannel heat sink (20 mm × 10 mm), which was fabricated with the ultrafast laser micromachining approach, consisting of 20 wavy microchannels with wavelength of 2000 μm and wave amplitude of 100 μm with triangular cross section (200 μm × 573 μm). The experiment was conducted with the mass fluxes of 330.07–550.11 kg/(m2·s) and heat flux of 14.5–411.3 kW/m2 at an inlet temperature of 15°C. Four flow patterns including bubbly flow, slug flow, churn flow and annular flow were captured with the visualization technique. Several confined bubbles with irregular shape were observed. In the low heat flux region, the dominant flow regime of heat transfer in the microchannels is the nucleate boiling and the heat transfer coefficient increases with increasing heat flux. With the nucleate boiling suppressed gradually, the evaporation of thin liquid film begins to dominate and the heat transfer coefficient decreases with the increase of heat flux. The heat flux has a significant effect on heat transfer coefficient compared with the mass flux and vapor quality.

Flow Boiling of Refrigerants Inside a Single Circular Minichannel

2008 ◽  
Author(s):  
Stefano Bortolin ◽  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Test Tube ◽  
Inlet Temperature ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

The present paper reports the heat transfer coefficients measured during flow boiling of HFC-32 and HFC-134a in a 0.96 mm diameter single circular channel. The test runs have been performed during vaporization at around 30°C saturation temperature, correspondent to 19.3 bar for R32 and 7.7 bar for R134a. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. The quality of the inner surface of the test tube has been measured to check the influence of surface roughness on the heat transfer coefficient. The flow boiling data taken in the present test section is presented and discussed, with particular regard to the effect of heat flux, mass velocity, vapor quality and fluid properties.

Study on the Influence Factors of Heat Transfer Coefficient of Supercritical Water Under Different Circulation Modes

2020 ◽  
Author(s):  
Peng Xu ◽  
Tao Zhou ◽  
Jialei Zhang ◽  
Juan Chen ◽  
Zhongguan Fu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Flow Rate ◽  
Supercritical Water ◽  
Natural Circulation ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

Abstract There are many factors that can affect the heat transfer coefficient (HTC) of supercritical water in forced and natural circulation. The correlation between the factors with the HTC under different circulation modes has an important influence on the reactor core design. By extracting the experimental data of supercritical water in forced circulation and natural circulation, the grey correlation model was used to analyze the relational degree between these factors with HTC. The results show that: Under the condition of forced circulation, there is a positive correlation between the inlet temperature, mass flow velocity, the thickness of the grid body with the HTC of supercritical water, and the order is: mass flow velocity > inlet temperature > the thickness of the grid body; there is a negative correlation between the pressure, heat flux with the heat transfer coefficient of supercritical water, and the order is: pressure > heat flux. Under the condition of natural circulation, there is a positively correlation between heating power, inlet temperature and circulation flow rate with HTC, and the order of magnitude is: circulation flow rate > heating power > inlet temperature; diameter and pressure are negatively correlated with heat transfer coefficient, and the order of magnitude is: pressure > diameter. In the two circulation modes, mass flow rate is an important factor affecting the heat transfer capacity of supercritical water, while the effect of heat flux on the heat transfer coefficient is contrary.

Novel Arrangement of Rough Tubes for Heat Flux Improvement

2012 ◽  
Vol 326-328 ◽  
pp. 81-86
Author(s):  
Farshad Farahbod ◽  
Sara Farahmand ◽  
Farzaneh Farahbod
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Crude Oil ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Set Up ◽  
The Heat Transfer Coefficient

The objective of the research is to represent a novel arrangement of conical three dimensional rough tubes (FS3D) for heat transfer coefficient enhancement. Experiments were performed with 316 stainless steel tubes of FS3D roughness and hot crude oil was circulated in constant heat flux condition in the related set up. The pressure drop is measured in this set up and compared with the pressure drop in a smooth tube with the same operating conditions. The heat transfer coefficient is one of essential parameters for design of heat transfer equipments and in this experimental work this is investigated for an Iranian crude oil in the FS3D rough tube. The heat transfer coefficient in FS3D rough tubes is higher than in other commercial enhanced tubes. FS3D rough tubes improve the performance of heat transfer equipments and also optimize the size of the mentioned devices. Consequently this type, the FS3D rough tube, is advantageous in energy and cost saving.

Influence of the operating conditions on the heat transfer coefficient during agitated sludge drying

2002 ◽  
Author(s):  
Jean Henry Ferrasse ◽  
Sofia Chavez ◽  
Patricia Arlabosse ◽  
C. Prévot ◽  
Didier Lecomte
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Operating Conditions ◽  
Sludge Drying ◽  
The Heat Transfer Coefficient

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

Effect of Open Micro-Channels on External Condensation Heat Transfer

2016 ◽  
Author(s):  
Brandon Hulet ◽  
Andres Martinez ◽  
Melanie Derby ◽  
Amy Rachel Betz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Heat Fluxes ◽  
Condensation Heat Transfer ◽  
Dropwise Condensation ◽  
Micro Channels ◽  
Lower Heat ◽  
The Heat Transfer Coefficient

This research experimentally investigates the heat transfer performance of open-micro channels under filmwise condensation conditions. Filmwise condensation is an important factor in the design of steam condensers used in thermoelectric power generation, desalination, and other industrial applications. Filmwise condensation averages five times lower heat transfer coefficients than those present in dropwise condensation, and filmwise condensation is the dominant condensation regime in the steam condensers due to a lack of a durable dropwise condensation surface. Film thickness is also of concern because it is directly proportional to the condenser’s overall thermal resistance. This research focuses on optimizing the channel size to inhibit the creation of a water film and/or to reduce its overall thickness in order to maximize the heat transfer coefficient of the surface. Condensation heat transfer was measured in three square channels and a plane surface as a control. The sizes of the square fins were 0.25 mm; 0.5 mm; and 1 mm, and tests were done at a constant pressure of 6.2 kPa. At lower heat fluxes, the 0.25mm fins perform better, whereas at larger heat fluxes a smooth surface offers better performance. At lower heat fluxes, droplets are swept away by gravity before the channels are flooded. Whereas, at higher heat fluxes, the channels are flooded increasing the total film thickness, thereby reducing the heat transfer coefficient.

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