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CHE 254 — Assignment 3 — 090828

2.21

A variable, Q, is reported to have a value of 2.360⋅10−4 kg⋅m2/ h .

(a) Write a dimensional equation for Q', the equivalent variable value expressed in American engineering units, using seconds as the unit for time.

(b) Estimate Q' without using a calculator, following the procedure outlined in section 2.5b. (Show your calculationrs.) Then determine Q' with a calculator, expressing your answer in both scientifgic and decimal notation and making sure it has the correct number of significant figures.

CHE 254 Assignment 2 — due 8/26/09 Tonya KleinTom Bertalan, James Clark, Craig Jackson, Rohit Deshane

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2.28

A concentration C (mol/L) varies with time (min) accoding to the equation

C=3.00 exp −2.00⋅t

(a) What are the units of 3.00 and 2.00?

(b) Suppose the concentration is measured at t=0 and t=1 min. Use two-point linear interpolation or extrapolation to estimate C t=.06min and C=0.10mol /L from the measured values, and compare these re3sults with the true values of these quantities.

(c) Sketch a curve of C versus t, and show graphically the points you determined in part (b).

CHE 254 Assignment 2 — due 8/26/09 Tonya KleinTom Bertalan, James Clark, Craig Jackson, Rohit Deshane

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2.33

The temperature in a process unit is controlled by passing cooling water at a measured rate through a jacket that encloses the unit

The exact relationship between the unit temperature T(*C) and the cooling water flow rate (L/s) is extremely complex, and it is desired to derive a simple emperical formula to approximate this relationship over a range of flow rates and temperatures. Data are taken for T versus . Plots of T versus on rectangular and semilog coordinates are distinctly curved (ruling out T=ab and T=aeb as possible empirical functions), but a log plot appears as follows:

A line drawn through the data goes through the points 1=25,T 1=210 and 2=40,T 2=120 .

(a) What is the empirical relationship between and T?

(b) Using your derived equation, estimate the cooling water flow rates needed to maintain the process unit temperature at 85*C, 175*C, and 290*C.

(c) In which of the tree estimates in part (b) would you have the most confidence and in which would you have the least confidence? Explain your reasoning.

CHE 254 Assignment 2 — due 8/26/09 Tonya KleinTom Bertalan, James Clark, Craig Jackson, Rohit Deshane