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Question 1 of 5
1. Question1 pointsCategory: HEAT TRANSFER
A composite wall is made of four different materials of construction in the fashion shown below.The resistance (in K/W) of each of the sections of the wall is indicated in the diagram.
The overall resistance (in K/W, rounded off to the first decimal place) of the composite wall, in the direction of heat flow, is________Correct
⇒ R23 = 0.3
Rtotal = 3+0.2+0.7 = 3.9 KWIncorrect
⇒ R23 = 0.3
Rtotal = 3+0.2+0.7 = 3.9 KW
Question 2 of 5
2. Question1 pointsCategory: HEAT TRANSFER
Steam at 100ºC is condensing on a vertical steel plate. The condensate flow is laminar. The average Nusselt numbers are Nu1 and Nu2, when the plate temperatures are 10ºC and 55ºC, respectively. Assume the physical properties of the fluid and steel to remain constant within the temperature range of interest. Using Nusselt equations for film-type condensation, what is the value of the ratio Nu2/Nu1 ?Correct
Question 3 of 5
3. Question2 points
In a 1-1 pass shell and tube exchanger, steam in condensing in the shell side at a temperature (Ts) of 135ºC and the cold fluid is heated from a temperature (T1) of 20ºC to a temperature (T2) of 90ºC. The energy balance equation for this heat exchanger is
Where U is the overall heat transfer coefficient, A is the heat transfer area, m² is the mass flow rate of the cold fluid and cp is the its specific heat. Tube side fluid is in a turbulent flow and the heat transfer coefficient can be estimated from the following equation:
where Nu is the Nusselt number, Re is the Reynolds number and Pr is the Prandtl number. The condensing heat transfer coefficient in the shell side is significantly higher than the tube side heat transfer coefficient. The resistance of the wall to heat transfer is negligible. If only the mass flow rate of the cold fluid is doubled, what is the outlet temperature (in oC) of the cold fluid at steady state?Correct
Question 4 of 5
4. Question2 pointsCategory: HEAT TRANSFER
In an experimental setup, mineral oil is filled in between the narrow gap of two horizontal smooth plates. The setup has arrangements to maintain the plates at desired uniform temperatures. At these temperatures, ONLY the radiative heat flux is negligible. The thermal conductivity of the oil does not vary perceptibly in this temperature range. Consider four experiments at steady state under different experimental conditions, as shown in the figure below. The figure shows plate temperatures and the heat fluxes in the vertical direction.
What is the steady state heat flux (in W m‒2) with the top plate at 70ºC and the bottom plate at 40ºC?Correct
Question 5 of 5
5. Question2 pointsCategory: HEAT TRANSFER
The space between two hollow concentric spheres of radii 0.1 m and 0.2 m is under vacuum.Exchange of radiation (uniform in all directions) occurs only between the outer surface (S1) of the smaller sphere and the inner surface (S2) of the larger sphere. The fraction (rounded off to the second decimal place) of the radiation energy leaving S2, which reaches S1 is ___________.Correct