Question

Liquid ethanol is a flammable fluid and can release vapors that form explosive mixtures at temperatures above its flashpoint at 16.6°C. In a chemical plant, liquid ethanol (c_p = 2.44 kJ/kg*K, rho = 789 kg/m^3) is being transported in a pipe with an inside diameter of 5 cm. The pipe is located in a hot area with the 20 kW of heat is added to the ethanol. Your task, as an engineer is to design a pumping system to transport the ethanol safely and to prevent fire hazard.
1. If the inlet temperature of the ethanol is 10°C, determine the volume flow rate that is necessary to keep the temperature of the ethanol in the pipe below its flashpoint.

Answer 1

Answer:

The volume flow rate necessary to keep the temperature of the ethanol in the pipe below its flashpoint should be greater than 1.574m^3/s

Explanation:

Q = MCp(T2 - T1)

Q (quantity of heat) = Power (P) × time (t)

Density (D) = Mass (M)/Volume (V)

M = DV

Therefore, Pt = DVCp(T2 - T1)

V/t (volume flow rate) = P/DCp(T2 - T1)

P = 20kW = 20×1000W = 20,000W, D(rho) = 789kg/m^3, Cp = 2.44J/kgK, T2 = 16.6°C = 16.6+273K = 289.6K, T1 = 10°C = 10+273K = 283K

Volume flow rate = 20,000/789×2.44(289.6-283) = 20,000/789×2.44×6.6 = 1.574m^3/s (this is the volume flow rate at the flashpoint temperature)

The volume flow rate necessary to keep the ethanol below its flashpoint temperature should be greater than 1.574m^3/s