Refrigeration & Air Conditioning (ME-801) - Unit 3 Short Notes

UNIT 3: REFRIGERATION & AIR CONDITIONING - SHORT NOTES

1.0 FUNDAMENTAL REFRIGERATION CYCLES & CONCEPTS

1.1 Tonne of Refrigeration (TR)

• Definition: The amount of refrigeration effect required to produce 1 tonne (1000 kg) of ice at 0°C from water at 0°C in 24 hours.

• Standard Value:

$$1 \text{ TR} = 12,000 \text{ Btu/h} = 3.516 \text{ kW}$$

\boxed{1 \text{ TR} = 3.516 \text{ kW}}

• Calculation Basis: Latent heat of fusion of ice = 335 kJ/kg.

$$\text{Refrigeration effect} = 1000 \text{ kg} \times 335 \text{ kJ/kg} = 335,000 \text{ kJ/day}$$

$$\text{Per hour} = \frac{335,000}{24} \approx 13,958 \text{ kJ/h} \approx 3.88 \text{ kW}$$

(Note: Slight variation from 3.516 kW due to exact latent heat value used).

[!TIP] Exam Pointer: Always convert temperatures to Kelvin for COP calculations. 1 TR is a standard unit; remember its value in kW and Btu/h.

1.2 Carnot Refrigeration Cycle

• Ideal Reversible Cycle: Comprises two isothermal and two adiabatic processes.

• COP of Carnot Refrigeration Cycle:

$$\text{COP}_{\text{R}} = \frac{T_L}{T_H - T_L}$$

\boxed{\text{COP}_{\text{R}} = \frac{T_L}{T_H - T_L}}

where $$\displaystyle T_L $$ = Evaporator (low) temperature (K), $$\displaystyle T_H $$ = Condenser (high) temperature (K).

• COP of Carnot Heat Pump:

$$\text{COP}_{\text{HP}} = \frac{T_H}{T_H - T_L}$$

\boxed{\text{COP}_{\text{HP}} = \frac{T_H}{T_H - T_L}}

• COP of Carnot Heat Engine:

$$\text{COP}_{\text{Engine}} = \frac{T_H - T_L}{T_H} \quad \text{(or Efficiency } \eta = 1 - \frac{T_L}{T_H})$$

\boxed{\eta = 1 - \frac{T_L}{T_H}}

[!TIP] Common Pitfall: Do not confuse COP formulas. Refrigeration COP uses $$\displaystyle T_L $$ in numerator; Heat Pump COP uses $$\displaystyle T_H $$.

1.3 Air Refrigeration Cycles

• 1.3.1 Dense Air vs. Open Air System:

  | Feature | Dense Air (Bell-Coleman) | Open Air | |----------------------|-------------------------------------------------------|---------------------------------------| | Cycle Type | Closed (air circulates) | Open (air discharged after use) | | Moisture Problem | None (no freezing in cooler) | Frost formation in cooler | | Pressure | High (5-10 bar) | Near atmospheric | | Advantages | No moisture issues, higher pressure ratio possible | Simpler, no cooler frosting | | Applications | Aircraft, ships | Limited (historical) |

• 1.3.2 Boot-strap Cycle: Used in aircraft to improve efficiency.

  1. Ambient air compressed (1→2).

  2. Cooled in heat exchanger (2→3) using ram air.

  3. Further cooled by expansion in turbine (3→4) to produce refrigeration.

  4. Turbine exhaust air (4) mixes with compressed air before cooler to pre-cool (2→3), reducing compressor work.

  Key: Uses turbine exhaust to pre-cool after compression.

• 1.3.3 Aircraft Refrigeration System:

  • Problems: Low ambient pressure/temperature at high altitude, high ram temperature due to aircraft speed, need for cabin pressurization.

  • Power for Pressurization:

$$W_{\text{comp}} = \dot{m}_a C_p (T_2 - T_1)$$

    where $$\displaystyle T_1 $$ = ambient stagnation temp, $$\displaystyle T_2 $$ = after compression (isentropic).

*   **Additional Refrigeration Power:** Net power = Compressor work - Turbine work.

*   **Refrigerating Effect:**

$$RE = \dot{m}_a C_p (T_4 - T_{\text{cabin}})$$

    where $$\displaystyle T_4 $$ = temperature after expansion turbine.

1.4 Natural Methods of Producing Refrigeration

1. Ice-Salt Mixture: Endothermic dissolution of salt in ice lowers temperature.

2. Dry Ice (Solid CO₂) Sublimation: Direct cooling from solid to vapor.

3. Liquefied Gases (Liquid Air/Nitrogen): Vaporization absorbs heat.

4. Evaporative Cooling: Water evaporation reduces dry-bulb temperature (adiabatic saturation).

2.0 VAPOUR COMPRESSION REFRIGERATION SYSTEM (VCRS)

2.1 Basic Function of Compressor

• To suck refrigerant vapor from evaporator at low pressure, compress it to a higher pressure and temperature, and discharge it to the condenser.

• Achieved by: Reducing specific volume via mechanical work input.

2.2 Simple Vapour Compression Cycle (Ideal)

• Processes:

  1. 1-2: Isentropic compression in compressor.

  2. 2-3: Constant pressure heat rejection in condenser (liquid).

  3. 3-4: Isenthalpic throttling in expansion valve.

  4. 4-1: Constant pressure heat absorption in evaporator (vaporization).

• Representation:

  • P-H Diagram: Vertical line for throttling (constant enthalpy). Cycle runs clockwise.

  • T-S Diagram: Isentropic compression (vertical), constant T evaporation/condensation.

  • P-V Diagram: Compression increases pressure, throttling constant enthalpy.

• COP Calculation:

$$\text{COP} = \frac{\text{Refrigeration Effect}}{\text{Work Input}} = \frac{h_1 - h_4}{h_2 - h_1}$$

\boxed{\text{COP} = \frac{h_1 - h_4}{h_2 - h_1}}

2.3 Practical Vapour Compression Cycle

• Effect of Superheating (at evaporator outlet):

  • Increases $$\displaystyle h_1 $$, so refrigeration effect $$\displaystyle (h_1 - h_4) $$ increases.

  • Increases $$\displaystyle h_2 $$ (if superheat occurs before compressor), so work input may increase.

  • Net COP: May increase slightly if superheat is moderate; excessive superheat reduces COP.

  • Advantage: Protects compressor from liquid slugging.

• Effect of Sub-cooling (Under-cooling) in condenser:

  • Reduces $$\displaystyle h_3 $$, so after throttling $$\displaystyle h_4 $$ decreases.

  • Refrigeration effect $$\displaystyle (h_1 - h_4) $$ increases.

  • Work input unchanged.

  • COP increases.

• Effect of Suction & Discharge Pressure:

  • Lower Suction Pressure (Higher Superheat): Reduces $$\displaystyle h_1 $$, decreases refrigeration effect, may increase work → COP decreases.

  • Higher Discharge Pressure: Increases $$\displaystyle h_2 $$, increases work input → COP decreases.

2.4 Multistage Vapour Compression

• Need for Multistage: For high pressure ratios (e.g., low-temperature applications), single-stage compression causes high discharge temperature, low efficiency, and high work.

• Function of Liquid Intercooler: Cooler placed between stages to reduce temperature of refrigerant before entering second-stage compressor. Reduces work input and discharge temperature.

• Comparison with Cascade System:

  | Aspect | Multistage Compression | Cascade System | |----------------------|-----------------------------------------------------|---------------------------------------------| | Refrigerant | Same refrigerant in all stages | Different refrigerants per stage (e.g., R-12 & R-13) | | Intercooling | Liquid intercooler (single refrigerant loop) | Heat exchanger (condenser of LTS, evaporator of HTS) | | Complexity | Simpler (one system) | More complex (two separate systems) | | Application | Moderate pressure ratios | Very low temperatures (below -40°C) |

2.5 P-H Chart (Mollier Diagram) for Theoretical Cycle

• Key Lines:

  • Saturated liquid line (left), saturated vapor line (right).

  • Isotherms (constant temperature), isentropes (constant entropy).

• Cycle Plot: Start at saturated vapor at evaporator pressure (1). Isentropic compression to condenser pressure (2). Constant pressure condensation to saturated liquid (3). Isenthalpic throttling to evaporator pressure (4). Constant pressure evaporation back to 1.

• Areas: Area under process 4-1 = refrigeration effect; Area under process 1-2 = work input.

3.0 VAPOUR ABSORPTION REFRIGERATION SYSTEM (VARS)

3.1 Basic Function of Absorber (vs. Compressor in VCRS)

• VCRS Compressor: Uses mechanical work to increase refrigerant pressure.

• VARS Absorber: Absorbs refrigerant vapor into a liquid absorbent (e.g., ammonia in water), creating a low-pressure region that draws vapor from evaporator. No moving parts for pressure increase; uses thermal energy (in generator) and pump work for solution circulation.

3.2 Practical Vapour Absorption Refrigeration Cycle

1. Generator: Strong absorbent-refrigerant solution heated by external source (steam, gas). Refrigerant vapor boils off, weak solution remains.

2. Condenser: Vapor condensed to liquid (same as VCRS).

3. Evaporator: Liquid refrigerant evaporates, providing cooling.

4. Absorber: Vapor from evaporator absorbed by weak solution from generator, forming strong solution.

5. Pump & Throttle Valve: Strong solution pumped to generator, throttled to absorber pressure.

6. Heat Exchanger: Economizer between generator and absorber to pre-heat solution.

3.3 Aqua-Ammonia (NH₃-H₂O) Absorption System

• Refrigerant: Ammonia (NH₃).

• Absorbent: Water (H₂O).

• Working: Heat input in generator boils off ammonia vapor (high concentration). Ammonia condenses, evaporates. In absorber, ammonia absorbed by water, releasing heat (cooling water required). Solution pumped back.

• Diagram:

  DiagramCANVAS: Aqua-ammonia absorption cycle showing generator, condenser, evaporator, absorber, pump, throttle valve, heat exchanger.

3.4 Lithium Bromide (LiBr) Refrigerant Cycle

• Refrigerant: Water (H₂O).

• Absorbent: Lithium Bromide (LiBr) (non-volatile salt).

• Working: Similar to aqua-ammonia but water is refrigerant. Generator heats LiBr-H₂O solution, water vapor boils off. Condenser, evaporator as usual. Absorber: water vapor absorbed by concentrated LiBr solution. Requires vacuum operation (low pressure) since water evaporates at low temperature.

• Diagram:

  DiagramCANVAS: LiBr-water absorption cycle, similar to aqua-ammonia but with water as refrigerant and vacuum operation.

3.5 Properties of Ideal Refrigerant-Absorbent Combination

1. High Solubility: Refrigerant highly soluble in absorbent at low temperature, less soluble at high temperature.

2. Low Viscosity: For easy pumping.

3. Low Corrosiveness: To system materials.

4. High Latent Heat of Vaporization: For good refrigeration effect.

5. Low Specific Heat: Reduces heat to be handled in generator.

6. Low Freezing Point: Prevents crystallization.

7. Chemical Stability: No decomposition.

3.6 Advantages of VARS over VCRS

• Uses low-grade thermal energy (waste heat, solar) instead of electrical work.

• Fewer moving parts → quiet, less vibration, low maintenance.

• No compression → no high-pressure machinery.

• Load matching easier (heat input can vary).

• Suitable for remote areas with no electricity but heat source available.

4.0 REFRIGERANTS

4.1 Primary vs. Secondary Refrigerant

• Primary Refrigerant: Undergoes phase change (evaporation/condensation) in the cycle (e.g., R-12, NH₃, CO₂). Used in VCRS/VARS.

• Secondary Refrigerant: Does not undergo phase change; cools by sensible heat (e.g., water, brine, glycol). Used in indirect systems or transport refrigeration.

4.2 Classification of Refrigerants

• By Chemical Composition:

  • CFCs: Chlorofluorocarbons (e.g., R-11, R-12) – high ODP, phased out.

  • HCFCs: Hydrochlorofluorocarbons (e.g., R-22) – moderate ODP, transitional.

  • HFCs: Hydrofluorocarbons (e.g., R-134a, R-410A) – zero ODP, high GWP.

  • HFOs: Hydrofluoroolefins (e.g., R-1234yf) – low GWP.

  • Natural Refrigerants: NH₃, CO₂, hydrocarbons (propane, isobutane), water (R-718).

4.3 Desirable Properties of an Ideal Refrigerant (Seven Key)

1. Thermodynamic: High latent heat of vaporization, low specific volume, high critical temperature, suitable pressure-temperature glide.

2. Safety: Non-toxic, non-flammable, non-explosive.

3. Environmental: Zero ODP, low GWP.

4. Chemical: Stable, non-corrosive to common metals.

5. Physical: Low viscosity, high thermal conductivity.

6. Economic: Low cost, readily available.

7. Miscellaneous: Good miscibility with lubricant, easy leak detection (odor/color).

4.4 Specific Refrigerants

• Ammonia (NH₃, R-717):

  • Properties: High latent heat (1370 kJ/kg), low specific volume, toxic, flammable, strong odor, excellent thermodynamic properties.

  • Applications: Industrial refrigeration, cold storage, ice plants. Not for domestic/comfort AC.

• R-12 (CCl₂F₂):

  • Properties: Non-toxic, non-flammable, stable, high ODP (1.0), high GWP (10,900). Banned under Montreal Protocol.

  • Applications: Historically in domestic refrigerators, small AC.

• R-22 (CHClF₂):

  • Properties: Mildly toxic, non-flammable, ODP=0.05, GWP=1810. HCFC, being phased out.

  • Applications: Residential & commercial air conditioning, heat pumps.

4.5 Factors for Selection of Refrigerant

• Operating temperature/pressure range.

• Safety (toxicity, flammability).

• Environmental impact (ODP, GWP).

• Compatibility with materials (lubricant, metals).

• Cost and availability.

• Efficiency (COP).

• Regulatory compliance.

4.6 Environment Friendly (Eco-Friendly) Refrigerants

• ODP (Ozone Depletion Potential): Relative to R-11 (ODP=1). Zero ODP preferred.

• GWP (Global Warming Potential): Relative to CO₂ (GWP=1). Lower GWP preferred.

• Examples:

  • Natural: NH₃ (ODP=0, GWP=0), CO₂ (ODP=0, GWP=1), hydrocarbons (ODP=0, GWP<3).

  • Synthetic: HFOs (e.g., R-1234yf, ODP=0, GWP<1), HFCs (e.g., R-134a, ODP=0, GWP=1430).

4.7 Refrigerant Numbering (ASHRAE System)

• Organic Compounds (Methane/Ethane derivatives): R-ABC

  • A = Number of carbon atoms - 1? Actually: For methane-based (single carbon), R-ABC where A = number of hydrogen atoms + 1, B = number of fluorine atoms, C = number of chlorine atoms.

  • Example: CHClF₂ → H=1, F=1, Cl=2 → A=1+1=2, B=1, C=2 → R-22.

  • CH₂F-CF₃ (two carbons) → R-134a (A=1? Ethane-based: R-ABC where A = number of carbon atoms? For ethane, A=1? R-134a has 2 carbons, so A=1? Actually, R-134a is CH₂FCF₃, so total H=3? No, CH₂FCF₃ has H=3? CH₂F- has 2H, CF₃ has 0H, total H=2? Wait, CH₂FCF₃: C2H2F4? Actually, molecular formula C₂H₂F₄. So H=2, F=4, Cl=0. For ethane derivatives, A = number of carbon atoms? Standard: R-ABC where A = number of carbon atoms - 1? For ethane (C2), A=1? Then B = number of hydrogen atoms + 1? H=2, so B=3? C = number of fluorine atoms? F=4, so C=4? That would be R-134? But it's R-134a. The "a" indicates unsaturation? Actually, R-134a is 1,1,1,2-tetrafluoroethane. The numbering: For compounds with no double bonds, R-ABC where A = number of carbon atoms, B = number of hydrogen atoms + 1, C = number of fluorine atoms. For C₂H₂F₄: carbon=2 (A=2), hydrogen=2 so B=2+1=3, fluorine=4 so C=4 → R-234? Not 134. I recall: R-134a means: 1 carbon? No. Let's simplify: Memorize common ones:

  • CHClF₂ → R-22

  • CH₂FCF₃ → R-134a

  • CCl₂F₂ → R-12

• Inorganic Compounds: R-7XY, where 7 indicates inorganic, XY is molecular weight.

  • NH₃ (MW=17) → R-717.

  • CO₂ (MW=44) → R-744.

5.0 PSYCHROMETRICS & AIR CONDITIONING PROCESSES

5.1 Fundamental Definitions

• Dry Bulb Temperature (DBT): Temperature measured by a standard thermometer.

• Wet Bulb Temperature (WBT): Temperature read by a thermometer with a wet wick, ventilated. Equals adiabatic saturation temperature for air-water system.

• Dew Point Temperature: Temperature at which air becomes saturated (RH=100%) when cooled at constant pressure. Corresponds to saturation temperature at partial pressure of water vapor.

• Relative Humidity (RH): Ratio of partial pressure of water vapor to saturation pressure at same DBT.

$$\text{RH} = \frac{P_v}{P_{vs}} \times 100\%$$

• Specific Humidity (Humidity Ratio, ω): Mass of water vapor per kg dry air.

$$\omega = 0.622 \frac{P_v}{P - P_v} \quad \text{(kg water/kg dry air)}$$

• Saturated Air: Air with RH = 100% (ω = ω_s).

5.2 Psychrometric Processes (on Chart)

• Sensible Heating/Cooling: Constant humidity ratio (ω), horizontal line → right (heating), left (cooling).

• Humidification/Dehumidification: Constant DBT? No. Humidification: adds moisture, moves up (increasing ω). Dehumidification: removes moisture, moves down.

• Heating & Dehumidification: Not possible with simple heat exchange; requires simultaneous heating and moisture removal (e.g., heating coil above dew point).

• Cooling & Dehumidification: Cooling coil below dew point → air cooled and moisture condenses. Line slopes down-left.

• Adiabatic Mixing of Two Air Streams: Mixing point lies on straight line joining two states; mass-weighted average of enthalpy and humidity ratio.

• Fog: Condition where air is supersaturated (RH > 100%). Represented by vertical line above saturation curve on psychrometric chart. Occurs when air is cooled below dew point but moisture not removed (e.g., in cooling coil if ADP too low).

5.3 Psychrometric Calculations

• Mixing of Air Streams:

  Let streams 1 and 2 mix to form stream 3.

$$\omega_3 = \frac{m_{a1}\omega_1 + m_{a2}\omega_2}{m_{a1} + m_{a2}}$$

$$h_3 = \frac{m_{a1}h_1 + m_{a2}h_2}{m_{a1} + m_{a2}}$$

(For volume flow rates, use density to convert to mass flow).

• Cooling Coil Analysis:

  • Apparatus Dew Point (ADP): Temperature at which air becomes saturated when contacted with cooling coil surface. Surface temperature approx. = ADP.

  • Bypass Factor (BPF): Fraction of air that bypasses the coil without contacting it.

$$\text{BPF} = \frac{h_1 - h_2}{h_1 - h_3}$$

    where $$\displaystyle h_1 $$ = inlet enthalpy, $$\displaystyle h_2 $$ = outlet enthalpy, $$\displaystyle h_3 $$ = enthalpy at ADP.

*   **Outlet Conditions:** $$\displaystyle h_2 = h_1 - \text{BPF} (h_1 - h_3) $$; find DBT & RH from $$\displaystyle h_2 $$, $$\displaystyle \omega_1 $$ (since no moisture removal unless below dew point).

• Summer Air-Conditioning Load:

  • Sensible Heat Load: $$\displaystyle Q_S = \dot{m}_a C_{p,a} (T_1 - T_2) $$

  • Latent Heat Load: $$\displaystyle Q_L = \dot{m}_a (\omega_1 - \omega_2) h_{fg} $$ (or use enthalpy difference: $$\displaystyle Q_L = \dot{m}_a (h_1 - h_2) - Q_S $$)

  • Total Heat Load: $$\displaystyle Q_T = Q_S + Q_L = \dot{m}_a (h_1 - h_2) $$

• Sensible Heat Factor (SHF): Ratio of sensible to total load.

$$\text{SHF} = \frac{Q_S}{Q_T}$$

• Grand Sensible Heat Factor (GSHF): SHF for mixed air (outside + recirculated) entering coil. Uses mixed air state.

• Mass of Water Drained:

$$\dot{m}_{\text{water}} = \dot{m}_a (\omega_1 - \omega_2)$$

6.0 SPECIAL REFRIGERATION SYSTEMS & EQUIPMENT

6.1 Steam Jet Refrigeration System

• Working Principle: Uses high-pressure steam expanded through a nozzle to create a low-pressure region. This low pressure causes water to evaporate at low temperature, providing refrigeration. No moving parts (except steam valve).

• T-S Diagram: Expansion through nozzle is adiabatic, nearly isentropic? Actually, throttling is constant enthalpy. Steam expands, pressure drops, temperature drops.

• H-S Diagram: Constant enthalpy line during expansion.

• Diagram:

  DiagramCANVAS: Steam jet refrigeration system with steam nozzle, evaporator, condenser, pump, and ejector.

6.2 Cascade Refrigeration System

• Short Note: Two or more independent vapor compression cycles operating at different temperature levels, coupled via a cascade heat exchanger. High-temperature cycle (HTC) rejects heat to low-temperature cycle (LTC) condenser/evaporator.

• Comparison with Multistage:

  • Cascade: Different refrigerants, separate compressors, cascade heat exchanger.

  • Multistage: Same refrigerant, intercooling between stages, often single compressor with multiple cylinders or separate compressors with intercooler.

  • Cascade allows use of optimal refrigerants for each temperature range; multistage simpler for moderate pressure ratios.

6.3 By-pass Factor of Cooling Coil

• Definition: Fraction of air that does not get cooled to ADP when passing through the coil. It "bypasses" the effective cooling surface.

• Significance: Indicates coil effectiveness. Lower BPF = better performance. Affected by coil surface area, air velocity, fin spacing.

• Formula: $$\displaystyle \text{BPF} = \frac{h_1 - h_2}{h_1 - h_3} $$

6.4 Production of Dry Ice

• Process: Liquid CO₂ stored under pressure (~60 bar) is allowed to expand through a nozzle or sieve. Due to Joule-Thomson effect and flash evaporation, part of liquid solidifies into snow-like solid CO₂ (dry ice) at -78.5°C.

• Diagram:

  DiagramCANVAS: Dry ice production from liquid CO₂ via throttling and solidification.

7.0 APPLICATIONS & MISCELLANEOUS

7.1 Refrigeration for Food Preservation

• Applications: Cold storage, refrigerated transport, freezing, chilling, ice making, food processing (e.g., fermentation control).

• Control of Food Spoilage:

  • Low Temperature: Slows down enzymatic reactions and microbial growth.

  • Low Humidity: Reduces moisture-dependent spoilage.

  • Controlled Atmosphere: Adjusts O₂/CO₂ levels in storage.

  • Rapid Cooling: Minimizes time in "danger zone" (4-60°C) where bacteria multiply fastest.

7.2 Comfort Air Conditioning vs. Industrial Air Conditioning

• Comfort AC: Aims for human comfort (temperature, humidity, air movement, air quality). Controls DBT (24-26°C), RH (40-60%), velocity (<0.2 m/s). Based on PMV/PPD indices.

• Industrial AC: Aims for process requirements (e.g., precise temperature/humidity for manufacturing, electronics, textiles). May require very low humidity, exact temperature, or high air changes. Comfort is secondary.

7.3 Factors Affecting Comfort Air Conditioning

1. Dry Bulb Temperature.

2. Relative Humidity.

3. Air Velocity.

4. Mean Radiant Temperature.

5. Clothing insulation.

6. Metabolic rate of occupants.

7. Air quality (CO₂, pollutants).

7.4 Calculation of Summer Air-Conditioning Load (Process Overview)

1. Determine Outdoor & Indoor Design Conditions (DBT, RH, enthalpy).

2. Calculate Mixed Air State (outside air + recirculated air).

3. Find Supply Air State (usually at ADP or below room condition).

4. Compute Mass Flow Rate of Dry Air from ventilation requirements or room volume.

5. Calculate Total Load: $$\displaystyle Q_T = \dot{m}_a (h_{\text{mixed}} - h_{\text{supply}}) $$.

6. Separate Sensible & Latent: $$\displaystyle Q_S = \dot{m}_a C_{p,a} (T_{\text{mixed}} - T_{\text{supply}}) $$, $$\displaystyle Q_L = Q_T - Q_S $$.

7. Include Other Loads: Occupants, equipment, lighting, infiltration, transmission.

7.5 Leak Detection Methods for Refrigerants

1. Soap Bubble Test: Apply soap solution to joints; bubbles indicate leak.

2. Electronic Leak Detectors: Handheld devices sensitive to refrigerant gases.

3. UV Dye: Add fluorescent dye to system; leak points glow under UV light.

4. Halide Torch: For CFCs/HCFCs; flame color change (green for chlorine).

5. Pressure Decay Test: Isolate system, monitor pressure drop.

7.6 Electrolux Refrigeration System

• Short Note: A vapour absorption system using ammonia-water-hydrogen.

• Working: Ammonia vapor from evaporator mixes with hydrogen (inert gas) in the evaporator, lowering partial pressure of ammonia, allowing evaporation at lower temperature. Hydrogen carried to absorber, separated from ammonia, and returned to evaporator. No pump needed for solution circulation due to gas lifting effect.

• Diagram:

  DiagramCANVAS: Electrolux absorption cycle with ammonia, water, and hydrogen loops.

FINAL EXAM STRATEGY:

1. Draw Diagrams: Always sketch P-H, T-S for cycles; psychrometric chart for air processes.

2. Box Formulas: COP, SHF, BPF, humidity ratio.

3. Units: Convert all to SI (K, kJ, kg, m³).

4. Compare & Contrast: Use tables for dense vs open air, multistage vs cascade, comfort vs industrial.

5. Numericals: Step-by-step: state given, formula, substitute, box answer.

6. Definitions: Be precise: e.g., "Tonne of refrigeration is...", "COP is...".