AMIE Study Circle Blog

An air-conditioning system involves the mixing of cold air and warm outdoor air before the mixture is routed to the conditioned room in steady operation. Cold air enters the mixing chamber at 7°C and 105 kPa at a rate of 0.55 m3/s while warm air enters at 34°C and 105 kPa. The air leaves the room at 24°C. The ratio of the mass flow rates of the hot to cold airstreams is 1.6. Using variable specific heats, determine (a) the mixture temperature at the inlet of the room and (b) the rate of heat gain of the room.  (AMIE Summer 2024, 10 marks)

Choose the correct answers (1 x 20) 1. In the absence of an unbalanced force within the system itself and also between the system and the surroundings, the system is said to be in (a) Thermal equilibrium (b) Mechanical equilibrium (c) Chemical equilibrium (d) Phase equilibrium 2. First law is based on (a) Law of conservation of mass (b) Law of conservation of energy (c) Law of conservation of momentum (d) None of the above 3. When a liquid flows through a tube with subcooled or saturated boiling, the process is called (a) Pool boiling (b) Bulk boiling (c) Convection boiling (d) None of the above 4. A system comprising a single phase is called a (a) Closed system (b) Open system (c) Isolated system (d) Homogeneous system (e) Heterogeneous system 5. Throttling process is (a) A reversible and constant entropy process (b) A reversible and constant enthalpy process (c) An irreversible and constant enthalpy process (d) Reversible and isothermal process 6. In a psychrometric chart, the vertic...

Choose the correct answer: (1 x 20) 1. Which one of the following represents an open thermodynamics system? (a) Manual ice cream freezer (b) Centrifugal pump (c) Pressure cooker (d) Bomb calorimeter 2. A small container has gas at a higher pressure. It is placed in an evacuated space. If the container is punctured, work done by the gas is (a) Positive (b) Negative (c) Zero (d) infinite 3. The transition from laminar flow to turbulent flow in a forced convection situation is determined by which one of the following dimensionless numbers?  (a) Grashoff  (b) Nusselt  (c) Reynolds  (d) Stanton  (e) Mach 4. Air is at 15 °C is compressed steadily and isothermally from 100 kPa to 700 kPa at a rate of 0.12 kgs. The minimum power input to the compressor is (a) 11.2 kW (b) 25.8 kW (c) 19.3 kW (d) 161 kW 5. Heat cannot be transported from a low-temperature reservoir to a high-temperature reservoir without the aid of external work input. This is (a) Kelvin Planck statement ...

1. The fin efficiency is defined as the ratio of the actual heat transfer from the fin to (a) The heat transfer from the same fin with an adiabatic tip. (b) The heat transfer from an equivalent fin which is infinitely long. (c) The heat transfer from the same fin if the temperature along the entire length of the fin is the same as the base temperature. (d) None of the above. 2. A cylindrical pin fin of diameter 0.6 cm and length of .3 cm with negligible heat loss from the tip has an efficiency of 0.7. The effectiveness of the fin is (a) 0.3 (b) 0.7 (c) 2 (d) 8 (e) 14 3. For the same initial conditions, one can expect the laminar thermal and momentum boundary layers on a flat plate to have the same thickness when the Prandtl number of the flowing fluid is (a) close to zero (b) small (c) approximately one (d) large (e) very large 4. The transition from laminar flow to turbulent flow in a forced convection situation is determined by which one of the following dimensionless numbers? (a)...

Explain the following in brief Clausius inequality The following equation is known as the inequality of Clausius. It provides the criterion of the reversibility of a cycle. ∮(dQ/T) ≤ 0 If ∮(dQ/T) = 0 then the cycle is reversible If ∮(dQ/T) < 0 then the cycle is irreversible and possible If ∮(dQ/T) > 0 the cycle is irreversible and possible Nucleate boiling In nucleate boiling, steam bubbles form at the heat transfer surface and then break away and are carried into the mainstream of the fluid. It is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux.  Entropy principle All heat is not equally valuable for converting into work. The heat that is supplied to a substance at a high temperature has a greater possibility of conversion into work than heat supplied to a substance at a lower temperature. “Entropy is a ...

Write a short note on any four.   Natural Convection Vs Forced convection Free or natural convection. Free or natural convection occurs where the fluid circulates by virtue of the natural differences in densities of hot and cold fluids; the denser portions of the fluid move downward because of the greater force of gravity, as compared with the force on the less dense. Forced convection. When the work is done to blow or pump the fluid, it is said to be forced convection. Clapeyran equation       Clausius-Claperyon equation is a relationship between the saturation pressure, temperature, the enthalpy of evaporation, and the specific volume of the two phases involved. This equation provides a basis for calculations of properties hi a two-phase region.  This is known as Clausius-Claperyon or Claperyon equation for evaporation of liquids. The derivative dp/dT is the slope of vapour pressure versus temperature curve. where, s g  = Specific entropy of sat...

Multiple choice questions choose the correct answer (20 marks) 1. Measurement of temperature is based on ⸺ (a) thermodynamic properties (b) zeroth law of thermodynamics (c) the first law of thermodynamics (d) the second law of thermodynamics 2. Carnot cycle efficiency depends upon ⸺ (a) properties of the medium/substance use (b) condition of engine (c) working condition (d) temperature range of operation 3. In a Rankine Cycle, heat output is obtained from (a) Condenser (b) Boiler (c) Turbine (d) Pump 4. The ideal gas-refrigeration cycle is similar to (a) Brayton cycle (b) Reversed Brayton cycle (c) Rankine cycle (d) Reversed Rankine cycle 5. When humidity ratio of air------air is said to be dehumidified. (a) increases (b) decreases (c) remains constant (d) None of the mentioned 6. Heat transfer deals with the rate of (a) work transfer (b) temperature transfer (c) energy transfer (d) None of the above 7. Aluminium is used as a fin material because (a) it has a higher convection heat tr...