SCALE MODELING OF THE TRANSIENT BEHAVIOR OF HEAT FLUX IN ENCLOSURE FIRES

A new scaling technique based on the hypothesis that flows in a compartment fire are buoyancy driven was introduced by Quintiere [4]. Based on this hypothesis, scaling relations for convective and radiative heat transfer within compartment fires is presented. A technique to measure and differentiate convective and radiative heat flux in compartment fires is presented which utilizes a newly developed metal plate sensor and Gardon heat flux gauge. Experiments conducted to test the scaling hypotheses were conducted at two scales. Wood cribs were used to model a fuel load. The repeatability of wood crib fires has been demonstrated. Experimental results indicate that radiation heat flux scales…

Contents

1. INTRODUCTION
1.1 Objectives
1.2 Thesis Outline
2. THEORY
2.1 Dimensionless Groups from Conservation Equations
2.1.1 Defining a Characteristic Time and Velocity
2.1.2 Dimensionless Groups from the Momentum Equation
2.1.3 Dimensionless Groups from the Energy Equation
2.1.4 Dimensionless Groups from Species Conservation Equation
2.1.5 Summary of π Groups
2.2 Scaling Relationships from π Groups
2.2.1 π1 – Reynolds Number
2.2.2 π2 – Scaling Fire Power
2.2.3 π3 and π4 – Wall Material Scaling
2.2.4 π5 – Convective Heat Flux Scaling
2.2.5 π6 – Radiation Scaling
2.2.6 Summary of Heat Flux Scaling
2.2.7 π8 – Species Concentration
2.2.8 Summary of Length Scaling Results
2.2.9 Preserved π Groups
2.3 Wood Crib Scaling
2.3.1 Wood Crib Theory
2.3.2 Derivation of Scaling for Crib Parameters
2.3.3 Derivation of Scaling for Crib Parameters – Croce and Heskestad
3. MEASURING HEAT FLUX
3.1 Previous Work on Convective Heat Flux Measurement
3.2 Novel Sensor Design and Approach
3.2.1 Calibrating Sensor Conduction Loss and Time Response
3.2.2 Corrected Sensor Output
3.2.3 Sensor Time Response in Compartment Fires
4. EXPERIMENT DESIGN AND METHODOLOGY
4.1 Design Requirements for Scaling Validation Experiments
4.1.1 Full Scale Crib and Vent Design
4.1.2 Compartment Wall Material Design
4.1.3 Proposed Testing Schedule
4.2 Compartments and Sensor Setup
4.2.1 Ignition of Wood Cribs
5. RESULTS
5.1 Prior Scaling Results and Data Comparisons
5.1.1 Free Burn Results
5.1.2 Compartment Burning Rate Data
5.1.3 Compartment Species Concentration
5.1.4 Gas Temperature Data Repeatability
5.1.5 Mass Loss Rate Repeatability
5.2 Compartment Measured Convective and Radiative Flux Data
5.1.1 Convective Heat Transfer Coefficient
5.3 Scaling Results
5.3.1 Gas Temperature
5.3.2 Wall Temperature
5.3.3 Radiation
5.3.4 Convection
5.3.5 Conduction / Total Heat Flux to Wall
5.4 Analysis of Convective Heat Transfer Coefficient Data
6. CONCLUSION
REFERENCES

Author: Veloo, Peter Surendran

Source: University of Maryland

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