Heat Transfer, Refrigeration and Air Conditioning Questions

• At the suction of a refrigeration compressor, the working fluid should be in which state to avoid liquid slugging and ensure reliable operation?
• According to the Stefan–Boltzmann (Stefan’s) law of thermal radiation, the total emissive power of an ideal black body is proportional to which function of its absolute temperature?
• Psychrometrics — during sensible heating of moist air, which property remains unchanged? In heating, ventilation, and air-conditioning (HVAC) analysis, “sensible heating” means raising the dry-bulb temperature without adding or removing moisture. State whether the specific humidity (also called humidity ratio) stays constant in this process.
• Air-cycle refrigeration (Bell–Coleman) — typical applications Identify where the air refrigeration (reverse Brayton) cycle is commonly employed in practice.
• Electrolux (Platen–Munters) absorption refrigerator — working pair and inert gas In an Electrolux refrigerator, identify the correct description of the roles of ammonia, water, and hydrogen within the system.
• Psychrometry — when is wet-bulb depression zero? At what relative humidity does the wet-bulb temperature equal the dry-bulb temperature (i.e., zero wet-bulb depression)?
• Psychrometric relationships — select all correct statements Which of the following statements about moist-air properties and chart lines are correct?
• Refrigerant selection — desirable thermophysical properties Which combination best characterizes a good refrigerant for vapor-compression systems from a thermodynamic and practical standpoint?
• Definition check — dew-point temperature of moist air State whether the following is correct: “Dew-point temperature corresponds to the saturation temperature of the water vapor at its partial pressure in the air mixture.”
• Humidification energy split — does sensible heat always decrease? Evaluate the statement: “The sensible heat during humidification decreases.” Consider general humidification methods (evaporative and steam-injection).
• Thermal diffusivity — correct engineering units Select the correct unit for thermal diffusivity when time is measured in hours (h).
• Aircraft environmental control: In a boot-strap air-refrigeration system equipped with evaporative cooling, where is the evaporator (for the evaporative subcooling stage) installed relative to the main components (first heat exchanger, secondary compressor, second heat exchanger, cooling turbine)?
• Convective heat transfer correlations: The ratio of the Nusselt number to the product of Reynolds number and Prandtl number equals which dimensionless group?
• Condensers in refrigeration practice: In a shell-and-coil condenser, which fluid flows in the shell and which flows inside the coil?
• Vapour-compression basics: After passing through the expansion (throttle) valve, the refrigerant in a standard vapor-compression system is in which thermodynamic state?
• Vapour-compression basics: Just before entering the expansion (throttle) valve, the refrigerant in a standard vapor-compression system is typically in which state?
• Compressor discharge state: In a vapor-compression cycle, what is the most accurate description of the refrigerant state as it leaves the compressor and enters the condenser?
• Human thermal comfort and heat loss mechanisms: Which statement(s) correctly describe how the human body can lose heat to the environment?
• Radiation terminology: The thermal radiation emitted by an ideal blackbody is commonly referred to as what?
• Modes of heat transfer in fluids: In liquids and gases, the dominant mechanism of heat transfer under most engineering conditions is: