Mechanical Engineering Answers

A standard cast from pipe inner diameter = 50mm and outer diameter is insulated with 85% magnesium insulation (k = 0.02w/mc) temperature at interface between the pipe and insulation is 300 degree celcius, the allowable heat loss through pipe is 600w/m length of pipe

In order to reduce cooling electricity consumption in an industrial plant, it is proposed to install an absorption refrigeration system running on solar energy. The absorption system costs $300,000 and the operating and maintenance expenses are $8000 per year. It is estimated that this absorption system will save $27,500 per year from the electricity they save. The lifetime of the system is expected to be 20 years with an average annual inflation-adjusted interest rate of 4 percent. The system will have no salvage value after 20 years of its lifetime. Would you support this project from an economic point of view? How would you evaluate this project if the inflation-adjusted interest rate is 2 percent?

Springbok (South Africa) City or Windhoek (Namibia) are considered for the installation of a solar power plant utilizing parabolic trough collectors. The total area of the collectors is 6000 m2 and the average efficiency of the plant is estimated to be 15 percent. Using the average daily solar radiation values on a horizontal surface available online, determine the amount of electricity that can be produced in each city.

Compare the amount of solar energy input to a horizontal surface for winter and summer months in Cairo (Egypt) and Upington (South Africa). Determine the ratio of solar energy input in summer to that in winter for each city.

As a consulting engineer, you are tasked to advise on an installation of solar panels for the purpose of supplying a household that contains 1 double-door fridge, 1 x 150 L deep freezer, 1 x 65” TV, 1 x desktop computer (with 2 screens), 1 x combo internet rooter-modem and 1 water-pump used to supply a water tank (2 occupants). The above appliances should be able to operate off-grid. Please advise on what it would cost and payback period (Desired storage autonomy 36 hrs).

The absorber surface of a solar collector is made of aluminum coated with black nickel oxide (α1 = 0.92 and ε = 0.08). The collector is to be installed in Stellenbosch (South Africa). The air and the effective sky temperatures are 20 and 7°C, respectively, and the convection heat transfer coefficient is 15 W/m2·K. For an absorber surface temperature of 60°C, determine the net rate of solar energy delivered by the absorber plate to the water circulating behind it.

The beam shown is under the action of a uniformly distributed load w of 3kN/m between the supports and a point load of 2k/N at the end point. Determine the bending moment in kNm at point A situated 4 m to the right of the left support Round off your answer to one decimal place and use the standard sign convection for the bending moment

Water is pumped to a height of 150 m at a rate of 300 litres per minute. The efficiencies of the pump and the 200 V driving motor are 73 % and 82 % respectively.

Determine:

The current of the motor

The cost of running the motor for 14 hours per day  (Note: 1kWh cost 35c)

A dc shunt motor after running for several hours on constant mains of 350 V takes a field current of 1,6 A. If the temperature rise is known to be 40°C, what value of extra circuit resistance is required to adjust the field current to 1,6 A when starting from cold at 20°C?

The temperature coefficient of the motor’s armature material is 0,0043/K at 20°C.

Prove that for closed thermodynamic system, change of energy of the system is

independent of path, it is function of state only.