- Author
- El-Iskandarani, B. M. K.
- Title
- Emergency Relief Venting Analysis for Flammable Liquid Storage Tanks.
- Coporate
- Worcester Polytechnic Inst., MA
- Report
- Thesis, May 1994, 160 p.
- Keywords
- storage tanks | flammable liquids | emergencies | relief valves | liquid fires | heat flux | codes | standards | entrainment | venting
- Identifiers
- two phase flow effects; flame heat fluxes and heights; emergency vent area for all vapor vent; liquid swell and void fraction calculation; emergency vent area for two-phase slip flow venting; emergency vent area for two-phase homogeneous flow venting; vent discharge coefficient; vent area calculations; liquid entrainment results; fire exposure effect
- Abstract
- This thesis investigates the emergency relief venting requirements of flammable liquid storage tanks immersed in liquid pool fires with a specified heat flux to the tank. Steady state conditions are assumed with the vapor volume generation rate equal to the vent flow rate of vapor. Liquid is assumed to be entrained in the vapor flow if the vapor velocity exceeds a critical entrainment velocity, and if the tank vapor space is sufficiently small. If liquid entrainment conditions are satisfied, the amount of liquid entrained in the vapor flow is calculated based on an assumed entrainment coefficient value. Two alternative two-phase flow vent flow models are used to calculate required vent areas. A computer code has been developed and sample calculations conducted for a few liquids. Results are compared to current fire code requirements which are based on all vapor venting. It was concluded that liquid is entrained in the vapor flow at fill levels equal to 87% and 94% for heptane and methanol tanks respectively. The homogeneous two-phase vent flow model suggests a larger area than the slip flow model because it takes into consideration the inter-phase friction between the liquid and the vapor as they exit the vent. As a result, for a heptane tank with an entrainment coefficient value of 0.01, the slip flow model suggest a vent size 2% larger than the one calculated for all vapor flow. On the other hand, the homogeneous flow model suggests a vent size 77% larger than the one calculated for all vapor flow. If the entrainment coefficient is increased to 0.1, then the slip flow model and the homogeneous flow model suggest areas that are 94% and 404% larger than the ones calculated by the all vapor model respectively.