Heating value of crude benzene
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A spiral plate heat exchanger is now being designed to condense benzene vapor at 93 degrees Celsius into a liquid at 80 degrees Celsius. First, calculate the enthalpy value of 93-degree crude benzene vapor using i=103+ct; then, the heat Q1 is equal to flow rate multiplied by the enthalpy value. The heat Q2 at 80 degrees for the crude benzene condensate = flow rate * specific heat capacity * 80. Is this the correct way to calculate the heat transfer amount? The formula i=103+ct was written by a previous technician, and its source has not been found. Do you know if it’s right?
The enthalpy of steam is related to its vapor pressure; a simple simulation using ChemCAD shows that at 93°C, the saturated pressure is 148 kPa and the enthalpy is 1140 kJ/kg； At 101.325 kPa, it is superheated steam with a specific enthalpy of 1141 kJ/kg; the difference between the two values is not significant ； At 101.325 kPa, benzene at 80°C is a subcooled liquid with a enthalpy value of 730 kJ/kg.
At 101.325 kPa, the saturation temperature is 80.1°C, so it can be considered a saturated liquid. The specific enthalpy value is actually meaningless; what we need is the enthalpy difference, which in this case is 411 kJ/kg.