The Departure From Nucleate Boiling in Rod Bundles During Pressure Blowdown

1970 ◽  
Vol 92 (4) ◽  
pp. 621-627 ◽  
Author(s):  
J. O. Cermak ◽  
R. F. Farman ◽  
L. S. Tong ◽  
J. E. Casterline ◽  
S. Kokolis ◽  
...  
Keyword(s):  
Steady State ◽  
Flux Distribution ◽  
Cross Flow ◽  
Nucleate Boiling ◽  
Inlet Temperature ◽  
Local Velocity ◽  
Heat Flux Distribution ◽  
Rod Bundles ◽  
Rod Bundle ◽  
Proper Allowance

Tests were performed in a high pressure heat transfer loop to determine the behavior of transient DNB during pressure blowdown in rod bundles. Water flowed along a 21 rod, 5-ft-long electrically heated rod bundle with a radially nonuniform heat flux distribution. Both steady-state and transient DNB tests were conducted over the following range of operating parameters: 1 Pressure—750 to 1500 psia; 2 Inlet temperature—480 to 540 deg F; 3 Mass velocity—1 × 106 to 3 × 106 lb/hr ft2; 4 Grid configurations—2. The data were analyzed using calculated subchannel local velocity and enthalpy as a function of time with proper allowance for the mixing and cross flow within the bundle. Results show that the inception of transient DNB during pressure blowdown can be predicted on the basis of steady-state data.

Determination of Convective Heat Flux on Steady-State Heat Transfer Surfaces With Arbitrarily Specified Boundaries

1996 ◽  
Vol 118 (4) ◽  
pp. 850-856 ◽  
Author(s):  
B. G. Wiedner ◽  
C. Camci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Steady State ◽  
Film Cooling ◽  
Flux Distribution ◽  
Heat Flux Distribution ◽  
Steady State Heat ◽  
Steady State Heat Transfer ◽  
Film Cooling Holes

The present study focuses on the high-resolution determination of local heat flux distributions encountered in forced convection heat transfer studies. The specific method results in an uncertainty level less than 4 percent of the heat transfer coefficient on surfaces with arbitrarily defined geometric boundaries. Heat transfer surfaces constructed for use in steady-state techniques typically use rectangular thin foil electric heaters to generate a constant heat flux boundary condition. There are also past studies dealing with geometrically complex heating elements. Past studies have either omitted the nonuniform heat flux regions or applied correctional techniques that are approximate. The current study combines electric field theory and a finite element method to solve directly for a nonuniform surface heat flux distribution due to the specific shape of the heater boundary. Heat generation per unit volume of the surface heater element in the form of local Joule heating is accurately calculated using a finite element technique. The technique is shown to be applicable to many complex convective heat transfer configurations. These configurations often have complex geometric boundaries such as turbine endwall platforms, surfaces disturbed by film cooling holes, blade tip sections, etc. A complete high-resolution steady-state heat transfer technique using liquid crystal thermography is presented for the endwall surface of a 90 deg turning duct. The inlet flow is fully turbulent with an inlet Re number of 360,000. The solution of the surface heat flux distribution is also demonstrated for a heat transfer surface that contains an array of discrete film cooling holes. The current method can easily be extended to any heat transfer surface that has arbitrarily prescribed boundaries.

The Shape of an Enclosure With Uniform-Flux, Isothermal, Nonhorizontal Walls

1995 ◽  
Vol 117 (4) ◽  
pp. 936-941 ◽  
Author(s):  
R. A. Kuyper ◽  
C. J. Hoogendoorn
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Flux Distribution ◽  
Special Kind ◽  
Computational Procedure ◽  
Convection Flow ◽  
Heat Flux Distribution ◽  
Evolution Algorithm ◽  
Cold Walls ◽  
Rayleigh Numbers

This paper presents a computational procedure and results of a numerical quest for the shape of a special kind of differentially heated air-filled enclosure. The enclosure shape is such that the natural-convection flow in the enclosure gives rise to a uniform horizontal-heat-flux distribution at the isothermal hot and cold walls. By using an evolution algorithm, the isothermal walls are “consumed” according to the heat-flux distribution until a steady-state shape is reached. For both adiabatic and perfectly conducting horizontal walls, results of calculations are presented for Rayleigh numbers up to 8 × 104. The resulting flow and temperature distributions in the steady-state enclosures are presented and discussed.

Radiation heat transfer within a solar system considering nanofluid flow inside the absorber tube

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Zahra Ebrahimpour ◽  
Mohsen Sheikholeslami ◽  
Seyyed Ali Farshad ◽  
Ahmad Shafee
Keyword(s):  
Heat Flux ◽  
Thermal Treatment ◽  
Flux Distribution ◽  
Second Step ◽  
Inlet Temperature ◽  
Heat Flux Distribution ◽  
Optical Efficiency ◽  
Content Type ◽  
Carrier Fluid ◽  
Finite Volume Approach

Purpose This paper aims to model solar unit equipped with mirrors with numerical simulation. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Design/methodology/approach Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment. Findings Surface temperature decreases by 0.498, 0.07 and 0.017% with intensify of Re, HF and NF, respectively, when other factors were minimum. With augment of Tin, wall temperature increases about 9.87%. Given NF = 8, HF = 3 mmm, growth of Re makes Darcy factor to decrease about 28.28%, but it augments the Nu by 2.63%. Nu augments with rise of NF and HF about 2.63 and 7.66%. Irreversibility reduces about 29.5 and 11.65% with augment of NF and HF, respectively. Originality/value Numerical simulations for solar unit equipped with mirrors were reported in this modeling. To augment the efficiency of system, absorber pipe was equipped with fins and nanomaterial was used as carrier fluid. Existence of secondary reflector results in better optical efficiency. Finite volume approach is used for modeling which is done in two steps. The first one is done to achieve the heat flux distribution and second step to model turbulent flow inside the pipe. Verification has been presented for calculation of important functions (f and Nu). Outputs reveal the impacts of fin height (HF), number of fin (NF), inlet temperature (Tin) and velocity on irreversibility, thermal treatment.

Experimental investigation on repeatability of CHF in rod bundle with non-uniform axial heat flux distribution

2016 ◽  
Vol 90 ◽  
pp. 151-154 ◽  
Author(s):  
Shengjie Qin ◽  
Xuemei Lang ◽  
Shijie Xie ◽  
Pengzhou Li ◽  
Wenbin Zhuo ◽  
...  
Keyword(s):  
Heat Flux ◽  
Experimental Investigation ◽  
Flux Distribution ◽  
Heat Flux Distribution ◽  
Rod Bundle ◽  
Axial Heat

scholarly journals Comparative Analysis of CTF and Trace Thermal-Hydraulic Codes Using OECD/NRC PSBT Benchmark Void Distribution Database

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
M. Avramova ◽  
A. Velazquez-Lozada ◽  
A. Rubin
Keyword(s):  
Steady State ◽  
Nucleate Boiling ◽  
Test Bed ◽  
Rod Bundles ◽  
Distribution Models ◽  
Hydraulic Behavior ◽  
Void Distribution ◽  
The Us ◽  
Accident Scenarios ◽  
Transient And Steady State

The international OECD/NRC PSBT benchmark has been established to provide a test bed for assessing the capabilities of thermal-hydraulic codes and to encourage advancement in the analysis of fluid flow in rod bundles. The benchmark was based on one of the most valuable databases identified for the thermal-hydraulics modeling developed by NUPEC, Japan. The database includes void fraction and departure from nucleate boiling measurements in a representative PWR fuel assembly. On behalf of the benchmark team, PSU in collaboration with US NRC has performed supporting calculations using the PSU in-house advanced thermal-hydraulic subchannel code CTF and the US NRC system code TRACE. CTF is a version of COBRA-TF whose models have been continuously improved and validated by the RDFMG group at PSU. TRACE is a reactor systems code developed by US NRC to analyze transient and steady-state thermal-hydraulic behavior in LWRs and it has been designed to perform best-estimate analyses of LOCA, operational transients, and other accident scenarios in PWRs and BWRs. The paper presents CTF and TRACE models for the PSBT void distribution exercises. Code-to-code and code-to-data comparisons are provided along with a discussion of the void generation and void distribution models available in the two codes.

Study on the Prediction of DNB-Type Critical Heat Flux in Rod Bundle Under Motion Conditions

2018 ◽  
Author(s):  
Siyang Huang ◽  
Xiaoyan Wang ◽  
Wenxi Tian ◽  
Ronghua Chen ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Nuclear Reactor ◽  
Cross Flow ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Coupled Analysis ◽  
Flow Conditions ◽  
Local Flow ◽  
Rod Bundle

In the nuclear reactor design, the critical heat flux (CHF) is one of the most important parameters for the reactor safety analysis. The occurrence of CHF will cause a sharp increase in the fuel rod surface temperature, which will result in the failure of fuel claddings and damage of the core. The CHF depends on the local flow conditions and the geometry of the flow channels, which makes the prediction of CHF in a fuel assembly more difficult when considering the cross flow between neighboring channels, spacer grids and mixing vanes. In this paper, the departure from nucleate boiling (DNB) type CHF in rod bundles under motion conditions is investigated based on the coupled analysis of the subchannel method and a CHF mechanism model, namely the liquid sublayer dryout model. The liquid sublayer dryout model assumes that there is a thin liquid sublayer underneath a vapor blanket formed by the coalescence of small bubbles near the heated wall. The dryout of this sublayer is considered as the CHF occurrence. In the liquid sublayer dryout model, sublayer thickness, velocity and length of the vapor blanket are three crucial parameters. In present research, the subchannel code calculates the local flow conditions for the rod bundle and provides input parameters for the liquid sublayer dryout model to predict CHF. In order to verify the method above, the predicted results are compared with the CHF Look-Up Table 2006 (LUT-2006) and a reasonable agreement can be achieved. In addition, the effects of rod bundle inlet coolant mass flow rate, subcooling and motion conditions on the CHF are analyzed.

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