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Unformatted text preview: EB Example 1. If someone is running and is covered with 0.1 mm of sweat, how much will they cool down when that sweat evaporates? Assume that the runner has a surface area of 1.3 m2 and a weight of 150 lbs. Assume that the specific heat of a person is the same as that for beef (3.43 kJ/kgK). Assume that sweat has the heat of vaporization (2443.9 kJ/kg) for water at the sweat temperature of 25 C. The density of sweat is 1000 kg/m3. EB Example 2. Twothirds of the energy content of fuel entering a 1000 MW nuclear power plant is removed by condenser cooling water that is withdrawn from a local river (no stack losses). The river has an upstream flow of 100 m3/s and a temperature of 20 C. If cooling water is only allowed to rise by 10C, what flow rate is required? How much would the river temperature rise as it receives the heated water? EB example 3. You have been hired to assess the fuel requirements of an incinerator. The incinerator burns 1000 lb/day hazardous waste that contains primarily benzene (C6H6, a carcinogen) and also contains 20% inert material and 15% water. The Environmental Protection Agency requires the incinerator stack gas to reach a temperature of 2912F in order to meet the regulations for a hazardous waste incinerator. If the incinerator cannot meet this requirement by burning the hazardous waste, they will add methane (CH4). They would like you to tell them how much CH4 (lb/day), if any, they need to add to be in compliance. Of course, you are well aware that first you need to determine the stack gas composition first so that you can know the energy of mass leaving the system (assuming air is added to burn the waste and the combustion is completeignore methane contributions to the stack gas composition). You find the following information in a handbook: Combustion heating value of C6H6 = 7790 Btu/lb Combustion heating value of CH4 = 802 kJ/mol Cash = 0.20 Btu/lb/F Lvapwater = 1060 Btu/lb (from 60F) HCO2at 2912F = 817 Btu/lb HN2at 2912F = 699 Btu/lb HH2Oat 2912F = 1398 Btu/lb CH2Ovapor 10 Btu/lb/F (C is actually a complicated function of temperature for water vapor) You also know that: Ash exits the incinerator at a temperature of 1650F There is a 5% energy loss from radiation. ...
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 Spring '08
 HILL

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