This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: Making Espresso Espresso is a coffee beverage made by forcing steam through finely ground coffee beans. Modern espresso makers generate steam at very high pressures and temperatures, but in this problem we'll consider a low-tech espresso machine that only generates steam at 100C and atomospheric pressure--not much good for making your favorite coffee beverage. The amount of heat Q needed to turn a mass m of room temperature (T1) water into steam at 100C (T2) can be found using the specific heat c of water and the heat of vaporization Hv of water at 1 atmosphere of pressure. Suppose that a commercial espresso machine in a coffee shop turns 1.50 Kg of water at 22.0 C into steam at 100C . If and, how much heat Q is absorbed by the water from the heating resistor inside the machine? Assume that this is a closed and isolated system. C(water) = 4187J/Kg C, Hv = 2258 KJ/Kg. PartA : Q = 4187 ( J/Kg C) (100-22) C 1.5Kg + 2258 10 3 J/Kg 1.5 Kg = 3.8810 6 J PartB: Pt = 1200W (time) = Q = 3.8810 6 J So t = 3233 s = 54 minutes PartC Suppose the mass of propane is m, so that the number of mole of propane gas is m/44.1 It can release the heat m/44.1 2219 KJ / mol Solve equation m/44.1 2219 KJ / mol = 3.8810 6 J Get m = 77g 17.44. Model: There are two interacting systems: coffee (i.e., water) and ice. Changing the coffee temperature from 90 C to 60 C requires four steps: (1) raise the temperature of ice from - 20 C to 0 C, (2) change ice at 0 C to water at C, (c) raise the water temperature from 0...
View Full Document
This note was uploaded on 04/18/2010 for the course PHYS ? taught by Professor Zhou during the Spring '10 term at Georgia State.
- Spring '10