2025 Paper - II Mechanical Engineering

The percentage of incoming radiation energy reflected back to space by the earth is about

Consider the following statements regarding flat-plate collector : 1. One of the desirable characteristics of thermal insulating material is low thermal conductivity. 2. Copper is often chosen for absorber plates due to its high thermal conductivity and good corrosion resistance. 3. Absorber plate material should have low thermal conductivity. Which of the above statements are correct?

Consider the following statements regarding performance indices of a solar collector : 1. Temperature range is the range of temperature to which the heat transporting fluid is heated up by the collector. 2. Collector efficiency is defined as the ratio of the energy actually absorbed and transferred to heat transporting fluid by the collector to the energy incident on the collector. 3. Concentration ratio is defined as the ratio of the area of the receiver to the area of aperture of the system. Which of the above statements are correct?

Consider the following statements regarding solar thermal systems : 1. In cold climate regions, large amount of low-grade thermal energy is required for heating air for comfort. 2. Solar energy is best suited for low-grade thermal applications. 3. Solar thermal energy is not utilized in drying industries. Which of the above statements are correct?

Consider the following statements regarding chemical energy storage : 1. The chemical energy in hydrogen can be converted into thermal energy. 2. Hydrogen-fired steam turbine may also be used to obtain mechanical energy. 3. Electrical energy may also be obtained more efficiently directly from hydrogen by means of fuel cell. Which of the above statements are correct?

Consider the following statements regarding solar space heating system : 1. Passive systems do not require any mechanical device and make use of natural process of convection, radiation and conduction for transport of heat. 2. Uses of active heating systems put restrictions on the building design to make possible the flow of heat naturally. 3. Active heating systems employ mechanical devices to circulate the working fluid for transportation of heat. Which of the above statements are correct?