A cooling plant adopted a two-stage cascade refrigeration system to meet the required cooling load. In both upper and lower cycles, the refrigerant leaves condenser as saturated liquid and enters compressor as saturated vapor. The isentropic efficiency of the upper cycle compressor is 80 %, while the lower cycle compressor is 70% efficient. The pressure limits of the upper and lower cycles are 1 MPa and 0.2 MPa with refrigerant-134a, respectively. Heat rejection from the lower cycle to the upper cycle takes place in an adiabatic counterflow heat exchanger where the lower cycle enters about at 0.5 MPa and the upper cycle enter about at 0.32MPa. If the mass flow rate of the refrigerant in the upper cycle is 0.28 kg/s, determine

i. the mass flow rate of the refrigerant in the lower cycle

ii. the rate of heat removal from the refrigerated space and the power input into the compressors

iii. the COP of the refrigerator

Evaluate the proportion of the heat of fuel carried away by the flue gases for the following data: Coal with Calorific Value of 30 MJ/kg has composition by mass as follow: C= 78%, H=5%, 02,=8%, S=2%, N2=2% and the remaining is ash. The coal is burnt in the furnace with 50% excess air. The flue gases leaving the chimney at 327°C and the atmospheric temperature is at 15 °C. Assume perfect combustion. Specific heat for dry product (Cp) is 1045J/kg. Heat is carried away per kilogram of moisture in the flue gas is 3000kJ/kg. The composition of air by mass is as follow: 02 = 23% and N2= 77 %.

Taichung thermal power station wants to change their steam generator with a new steam generator that has a better efficiency. The existing steam generator operating with Rankine cycle with reheat and has a thermal efficiency of 30%. Taichung thermal power station has been offered by Patron Company that supplies new steam generators that are more environmentally friendly. The specifications of the new steam generator are as follow: maximum pressure is 15MPa, minimum pressure is 10kPa Temperature entering the turbine is 500°C. Isentropic efficiency of the pump is 85%

Taichung thermal power station wants the new steam generator to have vapor content of the steam to exceed 90% and the steam mass flow rate is 12kg/s. Evaluate: i. the pressure at which the reheat cycles takes place (12 marks, C5) H. the total rate of heat in the boiler (4 marks, C5) Hi. Does the new steam generator have higher thermal efficiency of the cycle than the current generator? Justify your answer.

In an ideal standard dual cycle, the pressure and temperature at the beginning of compression are 1 bar and 47°C, respectively. The heat supplied in the cycle is 1250kJ/kg, two third of this heat is being added at constant volume and the remaining heat is added at constant pressure. If the compression ratio is 16, determine

i. the maximum temperature in cycle

ii. thermal efficiency of the cycle

iii. the mean effective pressure

A tractor is pulling a drawbar tillage implement at a ground speed of 1.6 m/s. The total rear axle static load is 35 kN, the wheelslip is 0.1, and the value of mobility number for the particular tyre and soil is 2.84. The driving tyre radius is 0.6 m, and the engine speed is 2100 rpm, and the overall gear transmission mechanical efficiency is 79%.

• Calculate the drawbar pull, drawbar power and the tractive efficiency

• Calculate the wheel axle power

• Calculate the overall transmission ratio

• Calculate the engine power

• Calculate the engine torque.

Taichung thermal power station wants to change their steam generator with a new steam generator that has a better efficiency. The existing steam generator operating with Rankine cycle with reheat and has a thermal efficiency of 30%. Taichung thermal power station has been offered by Patron Company that supplies new steam generators that are more environmentally friendly. The specifications of the new steam generator are as follow:

• maximum pressure is 15MPa,

• minimum pressure is 10kPa
• Temperature entering the turbine is 500°C.
• Isentropic efficiency of the pump is 85%

Taichung thermal power station wants the new steam generator to have vapor content of the steam to exceed 90% and the steam mass flow rate is 12kg/s. Evaluate:

i.                             the pressure at which the reheat cycles takes place

(12 marks, C5)

ii.                     the total rate of heat in the boiler

(4 marks, C5)

iii.                           Does the new steam generator have higher thermal efficiency of the cycle
than the current generator? Justify your answer.

It is often stated that the refrigerator door should be opened as few times as possible for the shortest duration of time to save energy. Consider a household refrigerator that have an average internal temperature of 4o C. Assume that one-third of the refrigerated space is occupied by food items, and the remaining is filled with air. Given that the moisture contents of the air in the kitchen and the refrigerator are 0.010 and 0.004 kg per kg of air, respectively, and thus 0.006 kg of water vapor is condensed and removed for each kg of air that enters. The refrigerator door is opened an average of 30 times a day, and each time half of the air volume in the refrigerator is replaced by the warmer kitchen air. The refrigerator has a coefficient of performance of 1.5 and the cost of electricity is RM0.218/kWh in Malaysia.

Design the interior volume of the refrigerator and assume the average temperature and pressure in the kitchen. From your design, assumptions and the information given above, determine the cost of the energy wasted per year as a result of opening the refrigerator door.

Explain the changes on your results if the kitchen air were very dry and thus a negligible amount of water vapor condensed in the refrigerator.

Explain and give your opinion on solidification process from nucleation until solidified metal.

A 10.8 kg of nickel initially at 202 ∘C is dropped into an insulated basin containing 23.6 kg of water initially at 27.8 ∘C. Assume that he water does not undergo any phase change when the hot metal was initially dropped into the water.

a) Assuming no heat losses from the container, what is the final equilibrium temperature between the water and the nickel? ∘C

b) What would the equilibrium temperature be if the nickel had lost 479 kJ of heat before being dropped in the water? ∘C

Explain the difference between the terms peak and residual shear strength in relation to loose sands and dense sands.

Understand the impact of professional engineering solutions in societal and environmental context and demonstrate knowledge of and need for sustainable development

Identify basics and opportunities in entrepreneurship related to engineering

Please type the working principles and application areas of a venturi tube in a few paragraphs (5 or 6) with examples. If there are any direct quotes from a resource, please use quotation marks. Thanks!

Solve Q1 and Q2 by matlab :

Q1: Based on what you learned about thermophysical

properties library, calculate the density of seawater at 25°C

and Pressure 1 MPa where the salinity is changed from 25,000

ppm to 55,000 ppm ?

02: Based on what you learned about thermophysical

properties library, calculate the density of seawater at

Pressure 1 MPa and has salinity of 42,000 ppm where the

temperature is changed from 25°C to 65°C ? If it changed why?

A 15kW electric motor, which is running at 43 rev/s, is used to drive a crusher which operates 24 hours per day. An engineer has specified 212 mm and 315 mm pitch diameters for small pulley and large pulley respectively; and C 3454 V-belt type.

a) What should be the conservative service factor for this belt and pulley system?

b) Calculate the center distance between the pulleys?

c) Calculate allowable power, design power and required number of belts. (Take design factor nd as 1.)

d) Calculate centrifugal tension, forces at tension side and loose side, initial tension and factor of safety. (Take friction coefficient including wedge effect as 0.5123.)