Engineering Answers

A project specifies a concrete strength of at least 3000 psi. Materials engineers will design

the mix for a strength higher than that. Calculate the required average compressive strength of

the mix design if the standard deviation is s = 350 psi. Estimate the modulus of elasticity of the

concrete at the required average compressive strength.

The design engineer specifies a concrete strength of 5500 psi. Determine the required

average compressive strength for:

a. A new plant where s is unknows

b. A plant where s = 500 psi for 22 test results

c. A plant with extensive history of producing concrete with s = 400 psi

d. A plant with extensive history of producing concrete with s = 600 psi

If the pressure in container A in Fig. P2.38 is 150 kPa,

compute the pressure in container B.

We are running out of resources. What practical ways would you recommend for packaging milk and other canned foods

A boiler produces 6 tonnes/hour of steam at a pressure of 1.8 MPa and a temperature of 250ºC. Feedwater enters at a temperature of 39ºC. At exit from the economizer part of the boiler the temperature is 72ºC. At exit from the evaporator part of the boiler the steam is 90 % dry. Energy is supplied by 650 kg of coal per hour, which has a calorific value of 36 MJ/kg. The A/F ratio is 25 : 1. The temperature of the flue gas at entry to the economizer part of the boiler is 430ºC. The average specific heat at constant pressure of the flue gas in the economizer is 1045 J/kg.K. 4.1 Calculate the efficiency of the boiler. 

A rectangular box with a square base and no top is to have a volume of 108 cubic inches. Find the dimensions for the box that require the least amount of material.

What is the temperature of 2 liters of water at 30°C after 3,500 calories of heat have been added?Use: Cp=4.187 KJ/Kg.-°K, 1 Kg. = 1 liter, 1 Kcal = 4.18 KJ

During a test on a boiler the following data were recorded: Pressure = 1.7 MPa Steam temperature at exit = 240ºC Steam flow rate = 5.4 tonnes/hour Fuel consumption = 400 kg/hour Lower calorific value of fuel = 40 MJ/kg Temperature of feedwater = 38ºC Specific heat capacity of superheated steam = 2100 J/kg.K Specific heat capacity of liquid water = 4200 J/kg.K. Calculate: 5.1 Efficiency of the boiler. 5.2 Equivalent evaporation (EE) of the boiler [91 %; 16.1] 

A boiler produces 6 tonnes/hour of steam at a pressure of 1.8 MPa and a temperature of 250ºC. Feedwater enters at a temperature of 39ºC. At exit from the economizer part of the boiler the temperature is 72ºC. At exit from the evaporator part of the boiler the steam is 90 % dry. Energy is supplied by 650 kg of coal per hour, which has a calorific value of 36 MJ/kg. The A/F ratio is 25 : 1. The temperature of the flue gas at entry to the economizer part of the boiler is 430ºC. The average specific heat at constant pressure of the flue gas in the economizer is 1045 J/kg.K. 4.1 Calculate the efficiency of the boiler. [70.5 %] 4.2 Draw up an energy balance, on a kJ/kg coal basis, with percentages of the total energy supplied. [economizer 3.6 %, evaporator 59 %, superheater 8 %, other 29.4 %] 

A vibration damper unit is composed of a rubber cylinder of diameter d compressed inside of a wrought-iron cylinder by a force F applied to the steel rod. Develop, in terms of d, F, and Poisson’s ratio ν for the rubber, the following expression for the lateral pressure p between the rubber and the wrought-iron cylinder. Compute the value of 𝑝 for the following data:

𝑑 = 63.5 𝑚𝑚, 𝜈 =0.5, 𝑎𝑛𝑑 𝐹 = 9 𝑘𝑁.