6.76 A successful California engineer has installed a circular hot tub in his backyard and finds that, for the typical operating conditions shown in the sketch, water must be added at a rate of 0.001 kg/s to maintain a fixed water level in the tub. Air 三 Hot water T= 310 K T_=290 K -0.30 wwwww If the tub is well insulated on its sides and bottom and if the temperature of the makeup water is equal to that of the tub water, at what rate must electrical heaters supply energy to maintain the tub water at 310 K?

Problem -1 A tank is initially empty. A liquid with p = 62.4 Ibm/ft is poured into the tank at a constant mass flow rate of mi = 7 lbm/s. The tank has cross-sectional area A = 0.2 fe, and the fluid in the tank has a %3D variable height H(t). There is a hole at the bottom of the tank. The fluid flows out of the tank at a rate proportional to the fluid height: rme = kH, where k= 1.4 lbm/ft/s. Find H(t). A sketch is given in Fig. P.1. Figure.P.1: Sketch of tank filling problem

PROBLEM 2 Consider a firefighter who is standing on a ladder and spraying water with a hose into Chief Inspector Jacques Clouseau's (Figure 3a) third-story apartment. A diagram of the hose/nozzle used by the firefighter is shown in Figure 3b. Assume the nozzle has little effect on the flow in the hose and water in the hose/nozzle is incompressible. The temperature of the water in the hose is 15 °C. (a) Chief Inspector Jacques Clouseau investigating the cause of the fire in his apartment. water hose diameter=10cm outlet diameter=5cm Figure 3 个个个 outlet velocity=6ms¹ (b) Fire hose/nozzle used to extinguish the fire in Inspector Clouseau's apartment.

Given • 1 million people in Hong Kong using low-flush toilet and low-flow shower head.• 1 million leaky toilet and Faucet. Energy needed to treat waterAverage energy use for water treatment drawn from southern California studies is 652 kWh per acre-foot (AF), where one AF = 325,853 gallons.Thermal Energy in CoalThe thermal power plants consume about 0.45 kg of coal per kWh.Energy output/fire power plantA typical 500 megawatt coal power plant produces 3.5 billion kWh per year.CO2 EmissionTaking coal to contain 50 percent carbon, which combines with oxygen during burning to form CO2, we can arrive at 1.83 kg CO2 for every 1 kg of coal burned. Find 4. How many African children (1 liter/kid/day) we can support?