Understanding Engineering Calculations and Material Concentrations
Explore the concepts of density, specific gravity, and material concentration in engineering calculations. Learn how to calculate concentrations in water and understand the concept of residence time in water treatment processes.
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Presentation Transcript
Density It is defined as mass divided by unit volume. ? =? ? Where: = density (kg/m ) m = mass, kg V = volume, m Density of water (at 4 Co), w= 1000 kg/m = 1 g/cm Density of water (at 25 Co), w= 997 kg/m = 1 g/cm
Density can be expresses in terms of specific gravity. ??.??.=????????? ?????? Substances with specific gravity greater than 1 are heavier than water and those with a specific gravity less than 1 are lighter than water. Sp. Gr. Of water at 4 Cois 1.000.
Concentration of materials in water Usually expressed as: ????????????? =???? ?? ? ????????? ?????? ?? ????? Concentration could be expressed in: kg/m3 milligram/liter (mg/L) parts per million (PPM) PPM = mg/L
??=1000 ?? 1000 ?? 1000 ?= 1 kg/L = ?3 1 L = 1 kg 1 L = 1000 g 1 L = 1 000 000 mg Ex/ 35 ?? ? 35 ?? 106??= 35 ppm =
Ex/ Plastic droplets with a mass of 0.48 kg are placed into a 100 L container and the container filled with water. What is the concentration of plastic droplets in mg/L? Sol. ????????????? =???? ?? ? ????????? ?????? ?? ????? ????????????? =0.48 ?? 100 ?= 0.0048 kg/L = 0.0048 x 106= 4800 mg/L
Ex/ A wastewater treatment plant discharges a flow of 1.5 m3/s with a solids concentration of 20 mg/L (20 mg of solids per liter of flow). How much solid material is the plant discharging per day? Sol/ Solids = Concentration x flow Solids = 20 mg/L x 1.5 m3/sec = 20 mg/L x 1500 L/sec = 30 000 mg/sec = 30 000/ 106=0.03 kg/sec = 0.03 x 60 x 60 x 24 = 2592 kg/day
Residence time Residence time = detention time = retention time. Residence time is the time when the fluid is exposed to treatment or a reaction in water treatment process. Definitions: the time an average particle of the fluid spends in the container through which the fluid flows. the time it takes to fill the container.
When a fluid flows through a container, how long does the average particle of fluid stay in the container? The average residence time (t) is: ? =? ? V: volume of the tank. Q: flow rate.
Ex/ A tank has a volume of 150 m3and the flow into the tank is 30 m3/hour. What is the residence time in the tank? Sol/ ? =150 30 ? = 5 ?.
