Lower Bound Estimate for Droplet Size in Two-Phase Dispersed Flow

1980 ◽  
Vol 102 (3) ◽  
pp. 501-507 ◽  
Author(s):  
C. F. Delale
Keyword(s):  
Heat Transfer ◽  
Lower Bound ◽  
Droplet Diameter ◽  
Transfer Model ◽  
Two Phase ◽  
Dispersed Flow ◽  
One Dimensional ◽  
Droplet Sizes ◽  
Using Data ◽  
Lower Bound Estimate

A theoretical post-dryout heat transfer model is developed based on one-dimensional two-phase dispersed flow and is applied to calculate the wall temperatures in the post-CHF regime. The model is also applied to reason the existence of a lower bound for average droplet diameter in two-phase dispersed flow. Results obtained using data by Bennett, et al. show lower droplet sizes than the experimentally measured values.

Theoretical Post-Dryout Heat Transfer Model

2018 ◽  
Vol 1 (1) ◽  
pp. 142-150
Author(s):  
Murat Tunc ◽  
Ayse Nur Esen ◽  
Doruk Sen ◽  
Ahmet Karakas
Keyword(s):  
Heat Transfer ◽  
Droplet Diameter ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Operating Pressure ◽  
Vertical Pipe ◽  
Two Phase ◽  
Experimental Values ◽  
Reactor Operating ◽  
Coolant System

A theoretical post-dryout heat transfer model is developed for two-phase dispersed flow, one-dimensional vertical pipe in a post-CHF regime. Because of the presence of average droplet diameter lower bound in a two-phase sparse flow. Droplet diameter is also calculated. Obtained results are compared with experimental values. Experimental data is used two-phase flow steam-water in VVER-1200, reactor coolant system, reactor operating pressure is 16.2 MPa. On heater rod surface, dryout was detected as a result of jumping increase of the heater rod surface temperature. Results obtained display lower droplet dimensions than the experimentally obtained values.

RBHT Steam Cooling and Droplet Injection Pre-Test Analysis Using COBRA-TF

2001 ◽  
Author(s):  
C. Frepoli ◽  
A. J. Ireland ◽  
L. E. Hochreiter ◽  
F. B. Cheung
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Injection System ◽  
Test Facility ◽  
Film Boiling ◽  
Two Phase ◽  
Field Representation ◽  
Dispersed Flow ◽  
Spacer Grids ◽  
Flow Film Boiling

Abstract The droplet injection experiments to be performed in a 7 × 7 rod bundle heat transfer test facility are being simulated using an advanced thermal hydraulics computer code called COBRA-TF. A current version of the code, which provides a three-dimensional, two-fluid, three-field representation of the two-phase flow, is modified to facilitate the simulation of the droplet field produced by the injection system in the test facility. The liquid phase is split into a continuous liquid field and droplet field where a separate momentum and mass equation is solved for each field, with the effects of spacer grids being properly accounted for. Pre-test analyses using the modified COBRA-TF code have been conducted for different injection conditions. Results indicate that there are specific ranges of conditions that can be simulated within the facility constraints to provide for validation of the dispersed flow film boiling models. The numerical results also show important effects of the spacer grids on the local heat transfer in the dispersed flow film boiling regime.

One-Dimensional Zonal Model for the Unsteady Heat Transfer Analysis in an Open Volumetric Air Receiver

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Gurveer Singh ◽  
Vishwa Deepak Kumar ◽  
Laltu Chandra ◽  
R. Shekhar ◽  
P. S. Ghoshdastidar
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
High Heat Flux ◽  
Unsteady Heat Transfer ◽  
Volumetric Heating ◽  
One Dimensional ◽  
Zonal Model

Abstract The open volumetric air receiver (OVAR)-based central solar thermal systems provide air at a temperature > 1000 K. Such a receiver is comprised of porous absorbers, which are exposed to a high heat-flux > 800 Suns (1 Sun = 1 kW/m2). A reliable assessment of heat transfer in an OVAR is necessary to operate such a receiver under transient conditions. Based on a literature review, the need for developing a comprehensive, unsteady, heat transfer model is realized. In this paper, a seven-equations based, one-dimensional, zonal model is deduced. This includes heat transfer in porous absorber, primary-air, return-air, receiver casing, and their detailed interaction. The zonal model is validated with an inhouse experiment showing its predictive capability, for unsteady and steady conditions, within the reported uncertainty of ±7%. The validated model is used for investigating the effect of operating conditions and absorber geometry on the thermal performance of an absorber. Some of the salient observations are (a) the maximum absorber porosity of 70–90% may be preferred for non-volumetric and volumetric-heating conditions, (b) the minimum air-return ratio should be 0.7, and (c) the smallest gap to absorber-length ratio of 0.2 should suffice. Finally, suggestions are provided for extending the model.

An Analytical Model for Bubble Growth and Heat Transfer in Microchannels

2007 ◽  
Author(s):  
Martin Cerza ◽  
Sonia M. F. Garcia ◽  
Joshua L. Nickerson
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Bubble Growth ◽  
Leading Edge ◽  
Superior Performance ◽  
Transfer Model ◽  
Two Phase ◽  
Microchannel Cooling ◽  
Convection Schemes

Forced liquid convection microchannel cooling systems present an alternative to the forced air-convection schemes and offer higher thermal performance. With regard to forced liquid convection, two-phase convection offers superior performance to liquid only convection. This paper presents results developed from a bubble heat transfer growth model applied to microchannel geometry and incorporates these results into a model for the averaged bubble heat transfer coefficient. Results are shown for water and FC-72. The bubble heat transfer model shows that the bubble growth rates and subsequent averaged heat transfer coefficient are functions of the film thickness between the bubble and the microchannel wall, the slip velocity between the bubble and the fluid comprising the bubble base, the wall heat flux and the subsequent liquid superheat in the microchannel just upstream of the bubble leading edge.

Heat Conduction Analysis on the Evaporator in Gravity Heat Pipe of Heavy Oil Wellbore

2014 ◽  
Vol 608-609 ◽  
pp. 991-995
Author(s):  
Wei Li ◽  
Xin Yuan Tian
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Heat Pipe ◽  
Nucleate Boiling ◽  
Liquid Pool ◽  
Transfer Model ◽  
Two Phase ◽  
Extra Energy ◽  
Phase Change Heat Transfer ◽  
Bottom To Top

A technology for using petroleum deposit’s energy and the principle of medium’s phase change heat transfer to make hollow rod into heat pipe, which transferred heat from bottom to top in wellbore by using it without extra energy is proposed. It can improve the temprature distribution of the fluid at the upper part of wellbore; therefore paraffin deposition and flocculation are improved. In this paper, heat transfer model of liquid film and liquid pool is established by means of the equation of N-S.Based on the principle of micro unit in liquid film’s thermal equilibrium and liquid pool’s heat transfer.By analying the heat transfer coeffcients of this two part,it was found out that gravity heat pipe had better heat transfer performance with increasing the length of liquid film in evaporator,improving the flow rate of inner steam and strengthening nucleate boiling of liquid pool,when the requirement of the continuous circulation of two-phase flow was achieved.

Numerical Simulation of Heat Transfer in a Closed Two-Phase Thermosiphon

2017 ◽  
Vol 743 ◽  
pp. 449-453
Author(s):  
Vladimir Arkhipov ◽  
Alexander Nee ◽  
Lily Valieva
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Phase Transitions ◽  
Finite Difference ◽  
Finite Difference Method ◽  
Mathematical Modelling ◽  
Three Dimensional ◽  
Two Phase ◽  
One Dimensional ◽  
The Finite Difference Method

This paper presents the results of mathematical modelling of three–dimensional heat transfer in a closed two-phase thermosyphon taking into account phase transitions. Three-dimensional conduction equation was solved by means of the finite difference method (FDM). Locally one-dimensional scheme of Samarskiy was used to approximate the differential equations. The effect of the thermosyphon height and temperature of its bottom lid on the temperature difference in the vapor section was shown.

Flow Boiling in Horizontal Tubes: Part 3—Development of a New Heat Transfer Model Based on Flow Pattern

1998 ◽  
Vol 120 (1) ◽  
pp. 156-165 ◽  
Author(s):  
N. Kattan ◽  
J. R. Thome ◽  
D. Favrat
Keyword(s):  
Heat Transfer ◽  
Annular Flow ◽  
Flow Boiling ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Two Phase ◽  
Horizontal Tubes ◽  
High Vapor ◽  
Coefficient Versus ◽  
The Heat Transfer Coefficient

A new heat transfer model for intube flow boiling in horizontal plain tubes is proposed that incorporates the effects of local two-phase flow patterns, flow stratification, and partial dryout in annular flow. Significantly, the local peak in the heat transfer coefficient versus vapor quality can now be determined from the prediction of the location of onset of partial dryout in annular flow. The new method accurately predicts a large, new database of flow boiling data, and is particularly better than existing methods at high vapor qualities (x > 85 percent) and for stratified types of flows.

Two-Phase Flow Heat and Mass Transfer Model Construction and Experiment Study of the Fuel Evaporation Progress

2012 ◽  
Vol 614-615 ◽  
pp. 174-180
Author(s):  
Bo Yun Liu ◽  
Jin Yun Pu ◽  
Xiang Lie Yi
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Two Phase Flow ◽  
Time Dependent ◽  
Transfer Model ◽  
Phase Flow ◽  
Two Phase ◽  
Dependent Behavior ◽  
Mass Evaporation ◽  
Hot Surface

As for the time-dependent behavior of the fuel heat and mass evaporation transfer progress on hot surface,consider the convective mass transfer and heat transfer, the liquid-gas two-phase flow of continuous heat transfer model was studied. By the dimensionless transform, the time-dependent behavior of the concentration distribution and the temperature field was obtained. The result of n-Heptanes evaporation transfer progress on hot surface experiment is consistent with the academic model.

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