REFRIGERATION AND AIR CONDITIONING (KME-601)
B.Tech Semester VI – Theory Examination (2022–23)
REFRIGERATION-AND-AIR-CONDITION…
Refrigeration and Air Conditioning is a fundamental mechanical engineering subject that deals with the production of low temperatures, control of temperature, humidity, purity, and circulation of air, and preservation of perishable goods. The subject combines principles of thermodynamics, fluid mechanics, heat transfer, and psychrometry. The given question paper is designed to test conceptual understanding, cycle analysis, numerical problem-solving ability, and practical knowledge of refrigeration and air-conditioning systems. To score well, answers must be written in a descriptive, well-connected paragraph format, supported by correct theory, diagrams, and equations wherever required.
SECTION A – BASIC TERMINOLOGY AND FUNDAMENTAL CONCEPTS
Section A tests the student’s understanding of core definitions and basic concepts that form the foundation of the subject. Although these questions are short in marks, they are conceptually very important.
For example, the Mach number must be explained as the ratio of fluid velocity to the velocity of sound, highlighting its importance in high-speed air-conditioning and aircraft refrigeration systems. The term DART should be explained in relation to refrigeration performance or system behavior, depending on its application context.
Questions comparing vapour compression refrigeration systems with air refrigeration systems require explanation of efficiency, COP, size, and operating cost. Students should clearly explain why vapour compression systems are preferred for domestic and industrial applications.
The difference between actual and theoretical vapour compression cycles should be explained by highlighting losses such as pressure drops, heat transfer irreversibility, superheating, and subcooling in real systems.
Questions on ideal refrigerant properties and CFC-free refrigerants test environmental awareness along with thermodynamic suitability. Answers must mention safety, ozone depletion potential, global warming potential, and operating characteristics.
Psychrometric terms such as sensible heat factor, heating and humidification, and defrosting must be explained with reference to air-conditioning processes and system performance. The capillary tube question requires explanation of its role as an expansion device that controls refrigerant flow and pressure.
SECTION B – SYSTEM ANALYSIS AND PRACTICAL APPLICATIONS
Section B focuses on numerical problems, system comparisons, and working principles of refrigeration systems. Answers here must be written in a logical flow, starting from theory and moving toward calculations or explanations.
The cold storage numerical problem requires application of COP concepts. Students must explain how ideal and actual COP are related and then compute the power required logically using thermodynamic relations.
The question on compound compression with intercooling must explain why multi-stage compression improves efficiency, reduces compressor work, and lowers discharge temperature compared to single-stage compression.
The Electrolux refrigeration system is a classic absorption system question. Students must explain the working principle using ammonia, hydrogen, and water, describing how refrigeration is achieved without a mechanical compressor.
Psychrometric questions such as fog formation require explanation of air mixing processes and how fog occurs when air reaches saturation. Proper explanation using the psychrometric chart is essential.
The question on equipment used in refrigeration and air-conditioning systems should explain the function and importance of compressors, condensers, evaporators, expansion devices, cooling coils, blowers, and control devices.
SECTION C – ADVANCED SYSTEMS AND NUMERICAL ANALYSIS
Section C tests advanced applications, cycle analysis, and design-oriented understanding. Answers must be detailed, logically structured, and supported by diagrams and equations.
The aircraft refrigeration system numerical problem requires understanding of air refrigeration cycles, ram effect, compressor and turbine efficiencies, and COP calculation. Students must clearly explain each stage of compression, cooling, expansion, and cabin heat absorption.
The boot-strap evaporative air refrigeration system question tests conceptual understanding of aircraft cooling systems. Students must explain the system layout, working principle, and represent the cycle on a T-S diagram.
Two-stage compression systems with intercooler, subcooler, and flash chamber require explanation of pressure levels, energy savings, and performance improvement using p-h diagrams.
The ammonia refrigeration system numerical problem tests thermodynamic property usage. Students must explain assumptions, identify states, and calculate COP using given data.
VAPOUR ABSORPTION, AIR CONDITIONING & FOOD PRESERVATION
Questions related to vapour absorption refrigeration systems require explanation of generator, absorber, condenser, and evaporator operation along with derivation of maximum COP expression.
Primary refrigerant questions test classification knowledge and understanding of refrigerant numbering systems. Students must explain chemical composition and environmental properties.
Air-conditioning system classification questions require explanation of summer and winter air-conditioning, comfort conditions, and component operation.
Psychrometric numerical problems require interpretation of DBT, WBT, and sensible cooling processes using charts.
Finally, questions on ice manufacturing plants and food preservation require explanation of refrigeration application in industry, including preservation methods such as chilling, freezing, dehydration, and controlled atmosphere storage.
HOW TO WRITE REFRIGERATION & AIR CONDITIONING ANSWERS IN THE EXAM
In Refrigeration and Air Conditioning, never write answers in short bullet points. Always begin with a brief introduction of the concept, followed by detailed explanation, diagrams, and equations wherever required. For numerical problems, clearly write assumptions, governing formulas, and step-by-step calculations. Psychrometric and cycle-based questions must always include descriptive explanation along with diagrams. Examiners give high importance to clarity of theory, correct thermodynamic reasoning, and logical presentation.
