Question

Page 2 of 3 Part II-Trivia (40%): check more than one if applicable Convective heat transfer at a surface is affected by the air speed. Which of the following statements is true () Increasing the air speed increases convective heat transfer () the thickness of the air film (coefficient) increases with air speed a) ) the air film (coefficient) is like an insulating blanket over the surface () the air film (coefficient) offers resistance against heat transfer The Reynolds number is used to distinguish between is true: () very low Reynolds numbers imply laminar flow () the type of flow is independent of the Reynolds number ) very low Reynolds numbers imply turbulent flow The Bernoulli equation is a statement of the conservation () th b) laminar and turbulent flow. W hich of the following statements c) of energy. Which of the following statements is true: e static, dynamic, and potential energy terms consider surface friction forces on the fluid ) for flow in pipes and ducts, surface shear force s are accounted for as friction losses ing Bernoulli principle in flow through pipes and ducts as cross-section area decreases, flow pressure increases and speed decreases house with continuous fan-driven exhaust ventilation is expected to operate at-4 Pa. The air-tightness curve from a multi-point blower door test on a leaky house indicates a leakage flow of 30 Ls at - 4Pa (extrapolated from the curve). The test was conducted with the passive vents sealed. If there are 6 passive vents with Cd- 0.65, and an area of 1000 mm2, what percentage of ventilation air is expected from the passive vents'? ( ) 15% ( )25% ( ) 45% ( ) 50% m2, what percentage of the e) If the house air leakage is halved and the passive vents opening is adjustedt500mm2, what percentage of the ventilation air is expected from the passive vents? ()10% ( )25% ( ) 45% ( ) 50% Estimate the expected ventilation energy and e), for a day in which the average outdoor temperature is 0°C and the indoor temperature is 21°C? (consider only sensible heat transfer). Round to zero decimal places. () d) 24 kwh/day and e) 12 kwh/day the expected ventilation energy consumption (including air leakage and passive vents) for questions d) ) d) 24 kwh/day and e) 18 kwh/day () d) 24 kwh/day and e) 8 kwh/day g) Considering moisture evaporation from a surface, which of the following statements is C) is a function of the vapour pressure gradient between the surface and the surrounding air ) is function of the air speed, as represented by the Lewis ratio C) the moisture film coefficient is independent of the convective heat transfer coefficient O. 1.. WG is approximately equal to )5 Pa h) 10 Pa )25 Pa ) 50 Pa

Answer 1

a) Convective heat surface at the surface is affectedby the air speed . the true statements are:

• Increasing the air speedincreases the convective heat transfer.

The air film (coefficient) is like an insulating blanket over the surface.

b) The Reynolds number is used to distinguish netween laminar flow and turbulent flow. The true statement:

• very low Reynolds number implies laminar flow