A two-shell-eight-pass heat exchanger is used to recoup heat from coolant water in a manufacturing plant. The heat exchanger has a rated area of 15 m^2 with an overall heat transfer coefficient of 900 W/m^2?K. The device has been used and has a fouling factor of 0.0001 m2?K/W. The coolant water enters at 85ºC and leaves at 55ºC whereas the cooling water enters at 15ºC and leaves at 45ºC. Determine (a) the mass flow of the coolant water and (b) the heat exchanger effectiveness.
What will be an ideal response?
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Photoelectric Effect: A photocathode having a work function of 2.8 eV is illuminated with monochromatic electromagnetic radiation whose photon energy is 4.0 eV. What is the threshold (cutoff) frequency for photoelectron production? (1 eV = 1.60 × 10-19 J, h = 6.626 × 10-34 J ? s)
A. 6.8 × 1014 Hz B. 2.9 × 1014 Hz C. 7.7 × 1014 Hz D. 8.6 × 1014 Hz E. 9.7 × 1014 Hz
Dielectrics: The square plates of a 3000-pF parallel-plate capacitor measure 40 mm by 40 mm and are separated by a dielectric that is 0.29 mm thick and completely fills the region between the plates. What is the dielectric constant of the dielectric? (?0 = 8.85 × 10-12 C2/N ? m2)
A. 61 B. 56 C. 50 D. 45 E. 67
What is the sign of these fields’ divergence at point P on each diagram? (Hint: Draw a cross-sectional view of a small div-meter centered on the point in question, and sketch the electric field vectors at the midpoint of each of the div-meter’s four sides in the drawing’s plane. Don’t worry about how we might create such a field. 
A. The divergence is positive. B. The divergence is negative. C. The divergence is zero.
When a hydrogen atom absorbs a photon that raises it to the n = 4 state, what is the least number of photons that can be emitted by that atom as it returns to the ground state?
a. 4 c. 5 b. 3 d. The correct value is not given.