Engineering Answers

Two large parallel planes having emissivities of 0.4 and 0.6 are maintained at temperatures of 846 K and 288 K, respectively. A radiation shield having an emissivity of 0.2 on both sides is placed between the two planes. Calculate (a) the heat-transfer rate per unit area if the shield were not present, (b) the heat-transfer rate per unit area with the shield present. If the emissivity of the shield is increased by 50%, how many shields are needed for the heat transfer rate per unit area as compared with the obtained results from (b)?

Two large parallel planes having emissivities of 0.4 and 0.6 are maintained at temperatures of 846 K and 288 K, respectively. A radiation shield having an emissivity of 0.2 on both sides is placed between the two planes. Calculate (a) the heat-transfer rate per unit area if the shield were not present, (b) the heat-transfer rate per unit area with the shield present. If the emissivity of the shield is increased by 50%, how many shields are needed for the heat transfer rate per unit area as compared with the obtained results from (b)?

6. A throttling calorimeter is connected to the superheated steam line supplying steam to the auxiliary feed pump on a ship. The line pressure measures 2.5 Mpa. The calorimeter pressure is 110 kpa and 150oC. Determine the entropy of the steam line. Please explain the answer.

Answer: a. 6.8 KJ/kg-oK c. 6.6 KJ/kg-oK

b. 6.2 KJ/kg-oK d. 7.5KJ/kg-oK

Design the concrete mix according to the following conditions:

Design Environment

Building frame

Required design strength = 27.6 MPa

Minimum dimension = 150 mm

Minimum space between rebar = 40 mm

Minimum cover over rebar = 40 mm

Maximum slump is required

Statistical data indicate a standard deviation of compressive strength of 2.1 MPa is

expected (more than 30 samples).

Only air entrainer is allowed.

Available Materials

Air entrainer: Manufacture specification 6.3 ml/1% air/100 kg cement. (Use maximum

or +2% air content)

Coarse aggregate: 19 mm nominal maximum size, river gravel (rounded)

Bulk oven-dry specific gravity = 2.55, Absorption = 0.3%

Oven-dry rodded density = 1761 kg/m³

Moisture content = 2%

Fine aggregate: Natural Sand

Bulk oven-dry specific gravity = 2.6

The design of a concrete mix requires 1173 kg/m3

of gravel in dry condition, 582 kg/m³ of sand in dry condition, and 157 kg/m³of free water. The gravel available at the job site has a moisture content of 0.8% and absorption of 1.5%, and the available sand has a moisture content of 1.1% and absorption of 1.3%. What are the masses of gravel, sand, and water per cubic meter that should be used at the job site?

What is your recommendation for the maximum size of coarse aggregate for the following situation? A continuously reinforced concrete pavement cross section contains a layer of No.6 reinforcing bars at 6-inch centers, such that the steel is just above mid-depth of a 10-inch￾thick slab. Cover over the top of the steel is therefore about 4 inches.