Short Questions with Answers APPLIED THERMODYNAMICS(5 TH MECHANICAL) Chapter No-1 1. Define mechanical efficiency in case of an IC engine? [2015w] Ans. Mechanical efficiency of an I.C. engine is defined as the ratio of brake power and indicated power. BP mech FP 2. Define brake specific fuel consumption. Ans. Brake specific fuel consumption is defined as the ratio of the mass of fuel consumed per hour per unit mf power output. bsfc BP 3. Define volumetric efficiency of an I.C Engine. Ans. Volumetric efficiency of an I.C. engine is defined as the ratio between volume of actual charge inducted into the cylinder and the volume of charge corresponding to the swept volume. Vol Vactual V 4. What is meant by I.P and B.P. Ans. I. P Indicated power B. P. Brake power s IP is defined as the rate of work done on the piston by burning of charge inside the cylinder. B. P. is the net power available at the engine shaft for external use. 5. Define calorific value of fuel? Ans. Calorific value of fuel is defined as the amount of heat energy liberated by complete combustion of unit mass of a fuel. 6. Define air-standard efficiency of an I.C Engine. Ans. Air standard efficiency is defined as the thermal efficiency of the internal combustion engine while working under appropriate air-standard cycles 7. Define mean effective pressure. Ans. Mean effective pressure is defined as the ratio between net work and the swept volume of the cycle. 8. A rope- brake dynamometer was used to measure the brake power of a single cylinder, 4-stroke cycle petrol engine. It was found that the torque due to brake load was 175Nm and the engine makes 500 rpm. Determine the brake power developed by the engine. [Ex. 24.1, M. Rathore] Ans. Given, K=1, T=175Nm, N=500rpm BP = 2NT 2x500x175 9.16KW 60,000 60,000 {50}
Chapter No 2 1 Write advantages of multistage compressor? [2016s] Ans. Advantages of multistage compressor 1) Gas can be compressed to a sufficiently high pressure. 2) It improves volumetric efficiency of each cylinder. 2. Classify the Air Compressor. Ans. Classification of air compressor Compressor Positive displacement type Dynamic Compressor Reciprocating Rotary Centrifugal Axial Single acting Double Root Vane Acting Blower type 3. Mention 4 industrial usage of compressed air? [2015w] Ans. 1. Air refrigeration 2. Driving pneumatic tools 3. Cleaning purposes. 4. Starting of heavy-duty diesel engines. 4. State the main parts of reciprocating air compressor. Ans. Main parts of reciprocating air compressor use cylinder, piston, connecting rod, crank, inlet and delivery valves. 5. Define FAD. Ans. It is the volume of compressed air corresponding to atmospheric conditions. 6. Why is the clearance volume provided in each reciprocating compressor? Ans. In reciprocating compressor, clearance volume is provided. i) to avoid piston striking cylinder head. ii) To let the valves freely actuate inside the cylinder. 7. What is the use of intercooler in a 2-stage air compressor? Ans. The use of intercooler is to cool the compressed air from the first stage compressor. 8 Define volumetric efficiency of a reciprocating compressor. Ans. Volumetric efficiency of a reciprocating compressor is defined as the ratio of actual volume of air sucked into the compressor and the piston-displacement volume. 9. What do you mean by air compressor? Ans. Air compressor is a machine which compresses atmospheric air with the help of mechanical energy to a high pressure. {51}
Chapter - 3 Name of the Chapter: Refrigeration 1. Define tone of refrigeration. [2016s] Ans. It is defined as the amount of heat required for uniform melting of 1 ton of ice from and at 0ºC in 24 hours. 2. State properties of a good refrigerant [2016S] Ans. Properties of a good refrigerant 1) High critical temperature 2) Low boiling print 3) High latent heat of vaporization 4) Non-flammable, Non-toxic 3. What do you mean by refrigeration? [2015w] Ans. Refrigeration is the process of continuous removal of heat from a system to keep its temperature below that of the surrounding. 4. What are the chemical formula of refrigerants R-11, R-12, R-21 and R-22 [2015w] Ans. Refrigerant R-11 C Cl 3 F R-12 CCl 2 F 2 R-21 CHCl 2 F R-22 CHClF 2 Chemical Formula 5. Name the refrigerant commonly used in domestic refrigerator. Ans. Refrigerant commonly used in domestic refrigerator are R-12, R-134a 6. Define refrigerant. Ans. Refrigerant is a heat carrying medium which transfers heat from a low temperature system to a high temperature surrounding. 7. List out the components of vapour compression refrigeration system. Ans. Components of vapour compression refrigeration system are compressor, condenser, expansion valve, evaporator. 8. Define COP. Ans. Cop is defined as the ratio of refrigerating effect to work done in compressor. 9. Write down the properties of R-12. Ans. i) It is non-toxic, non-corrosive, non-irritating non-flammable. ii) It has relatively low latent heat valve. 10. State two advantages of vapour absorption system over vapour compression system. Ans. Two advantages are 1) Less noisy 2) It uses low grade energy. So, waste heat can be utilized. 11. State the function of an analyzer in a vapour absorption refrigeration system. Ans. Analyzer is used to remove water vapour from ammonia vapour leaving the generator. {52}
12. What is the function of rectifier of a vapour absorption refrigeration system. Ans. Rectifier is used to further check for the water vapour which is not removed in analyzer. 13. Draw the flow diagram of simple vapour absorption system Ans. Chapter - 4 Name of the Chapter : Psychrometry 1 Define psychrometry. [2015w] Ans. Psychrometry is defined as the study of properties & behavior of moist air. 2 What is saturated air? Ans. Saturated air is the condition of air when it has dissolved maximum amount of water vapour into it. 3 Define relative humidity [2016s] Ans. It is the ratio between actual mass of water vapour present in air and the mass of water vapour present in saturated air at same temperature and pressure. 4 Define specific humidity or humidity ratio. Ans. It is the ratio between mass of water vapour to the mass of dry air in a given mass of moist air. 5 Define dew Pt. temperature. Ans. It is defined as the temperature at which atmospheric water vapour starts to condense. 6 What is the difference between dry bulb temperature and wet bulb temperature? [2016s] Ans. Dry bulb temperature is the temperature of air when it is not affected by temp. of air when it is affected by moisture. 7 What is the function of Psychrometer? Ans. Psychrometre is an instrument used to measure the dry bulb temperature and wet bulb temperature of air. 8 Define sensible heat Ans. Sensible heat is defined as the heat which causes rise or fall in temperature of a body. 9 What is by-pass factor? Ans. It is defined as the fraction of air which doesn t come in contact with heating or cooling coil. 10 What is ADP? Ans. ADP is defined as surface temperature of cooling coil. 11. What is humid specific heat? Ans. It is the specific heat of the mixture of dry air & water vapour. {53}
Chapter - 5 Name of the Chapter: Physiological Factors 1. What is effective Temp? [2016s] Ans. Effective temperature is a measure of feeling warmth or cold to the human 2. What is optimum effective temperature? Ans. It is the effective temperature at which majority of the people feel comportable. 3. Define comfort. [2016s] Ans. Human comfort is that condition of mind, which expresses satisfaction with the thermal environment. 4. What is comfort chart? Ans. It is a graphical representation showing the effective temperatures &number of people feeling comfortable at various effective temperature. 5. Define sensible heat. Ans. Sensible heat is the heat which causes a rise or fall is temperature of a body. 6. What factors are taken care of in any air-conditioning system? Ans. The factors to be taken care of is air-condition system are Oxygen supply, carbon dioxide removal, Body heat & moisture removal, Infiltration heat Chapter - 6 Name of the Chapter: Air Conditioning System 1. State why ducts are used in air conditioning system. Ans. Ducts are used to transmit conditioned air from a/c equipment to different parts of the room. 2. What is the use of air filter and blower in air conditioning system? [2015w] Ans. Air filter removes dirt, smoke, bacteria from entering air blower is used to circulate air over the evaporator coil. 3. What do you understand by static & velocity pressure in a duct? Ans. Static pressure : -It s the pressure that exists in a duct system always which is independent of movement. Velocity Pressure :- It is the drop is static pressure necessary to produce a given velocity of flow. 4. What is the function of a fan in an air-conditioning system? Ans. Fan is used to circulate atmospheric air over the condenser coil which removes heat from refrigerant. 5. Classify Air conditioning system. Ans. Based on arrangement of equipments, 1. Summer a/c, 2.Window a/c Based on psychrometric processes involved, 1. Summer a/c 2. Winter a/c 3. Year round a/c Based on number of outlets, 1. Unitary a/c 2. Central a/c {54}