Question

Saturated propane vapor at 2:00 102 psia is fed to a well-insulated heat exchanger at a rate of 3:00 103 scfh (standard cubic feet per hour). the propane leaves the exchanger as a saturated liquid (i.e., a liquid at its boiling point) at the same pressure. cooling water enters the exchanger at 70°f, flowing cocurrently (in the same direction) with the propane. the temperature difference between the outlet streams (liquid propane and water) is 15°f.

(a) what is the outlet temperature of the water stream? (use the antoine equation.) is the outlet water temperature less than or greater than the outlet propane temperature? briefly explain.
(b) estimate the rate (btu/h) at which heat must be transferred from the propane to the water in the heat exchangerand the requiredflowrate (lbm/h) ofthewater. (youwill need to write two separate energy balances.) assume the heat capacity ofliquid water is constant at 1.00 btu/(lbm°f) and neglect heat losses to the outside and the effects of pressure on the heat of vaporization of propane

Answer 1

To find the outlet temperature of cooling water and rate of heat transfer in a heat exchanger, the Antoine equation is used to find the temperature of saturated propane, and then energy balances are performed using given flow rates, heat of vaporization of propane, and heat capacities.

Step-by-step explanation:

The question is asking to solve two parts: (a) to find the outlet temperature of the water stream when propane enters a heat exchanger as a saturated vapor and leaves as a saturated liquid at the same pressure, and (b) to calculate the rate of heat transfer from the propane to the water and the flow rate of water required.

For part (a), the outlet temperature of the water stream will be 15°F less than the outlet temperature of the propane since the streams are in cocurrent flow and there is a given temperature difference of 15°F between them. The Antoine equation can be used to find the boiling point of propane at the given pressure, which will be the temperature of saturated liquid propane.

For part (b), the rate of heat transfer can be estimated by an energy balance using the heat of vaporization of propane and the mass flow rate of propane. To find the required flow rate of water, another energy balance should be performed, considering the inlet temperature of the water, the outlet temperature calculated in part (a), and assuming a constant heat capacity for liquid water. Since the heat losses to the surroundings and the effects of pressure on propane's heat of vaporization are neglected, the calculations should be straightforward.