SSRAO

Explanation:
1 Ton of Refrigeration (TR) = heat required to melt 1 ton (2000 lb or 907 kg) of ice at 0°C in 24 hours = 3.5 kW = 3.517 kW ≈ 12,000 BTU/hr = 210 kJ/min. This unit originated from the ice-making industry. Modern air conditioners are rated in TR. 1 TR = 3.5 kW is the standard approximation used in engineering calculations.

Explanation:
In the ideal vapour compression cycle, the refrigerant leaves the condenser as saturated liquid (state 3). In practice, the refrigerant is often sub-cooled below the saturation temperature to: (1) increase the refrigerating effect, (2) prevent flash gas formation in the liquid line, (3) ensure only liquid enters the expansion device. Sub-cooling increases COP. The refrigerant enters the condenser as superheated vapour (from compressor) and leaves as saturated/sub-cooled liquid.

Explanation:
Refrigerating effect RE = h1 - h4 (kJ/kg), where h1 is enthalpy of refrigerant leaving the evaporator (saturated vapour) and h4 is enthalpy entering the evaporator (after expansion). The expansion process (3→4) is isenthalpic (h3 = h4). So RE = h1 - h3. The refrigerating capacity Q = ṁ × RE = ṁ(h1 - h4), where ṁ is mass flow rate of refrigerant.

Explanation:
Carnot COP for refrigerator = TL / (TH - TL), where TL and TH are absolute temperatures (Kelvin) of the cold and hot reservoirs. This is the maximum possible COP for any refrigerator operating between these temperatures. For a heat pump: COP_HP = TH / (TH - TL) = COP_refrigerator + 1. The Carnot COP increases as TL increases or TH decreases (smaller temperature difference).

Explanation:
The expansion valve (throttling device) reduces the refrigerant from high condenser pressure to low evaporator pressure. The process is isenthalpic (h3 = h4, no work done, no heat transfer). The pressure drop causes partial vaporisation (flash gas formation), reducing the temperature to the evaporator saturation temperature. Types: thermostatic expansion valve (TEV), capillary tube, automatic expansion valve, electronic expansion valve.

Explanation:
COP = Refrigerating effect / Compressor work = (h1 - h4) / (h2 - h1), where: h1 = enthalpy at compressor inlet (evaporator exit), h2 = enthalpy at compressor exit (condenser inlet), h3 = enthalpy at condenser exit (expansion valve inlet), h4 = enthalpy at evaporator inlet (= h3 for isenthalpic expansion). Compressor work W = h2 - h1. Heat rejected QH = h2 - h3. RE = h1 - h4 = h1 - h3.

Explanation:
The liquid receiver is a storage vessel installed between the condenser and expansion valve. Its functions: (1) Stores excess liquid refrigerant to accommodate load variations, (2) Ensures only liquid (no vapour) enters the expansion valve (prevents hunting in TEV), (3) Acts as a buffer between condenser and expansion valve. The receiver is used in systems with thermostatic expansion valves. Capillary tube systems don't use receivers.

Explanation:
Wet bulb temperature (WBT) ≤ Dry bulb temperature (DBT). WBT = DBT only when relative humidity = 100% (saturated air). WBT > Dew point temperature (DPT) always (except at 100% RH where WBT = DBT = DPT). The relationship is: DPT ≤ WBT ≤ DBT. WBT is the temperature measured by a thermometer with a wet wick — evaporation cools it below DBT. The difference (DBT - WBT) is the wet bulb depression, indicating dryness of air.

Explanation:
Specific humidity (humidity ratio) ω = mv/ma = mass of water vapour / mass of dry air (kg/kg of dry air). ω = 0.622 × pv/(p - pv), where pv is partial pressure of water vapour and p is total pressure. At saturation: ωs = 0.622 × ps/(p - ps). Relative humidity φ = pv/ps = ω/ωs × (p - ps)/(p - pv) ≈ ω/ωs for low humidity. Specific humidity is used in psychrometric calculations.

Explanation:
Dew point temperature (DPT) is the temperature to which moist air must be cooled at constant pressure for condensation to begin. At DPT, the air becomes saturated (φ = 100%) and the partial pressure of water vapour equals the saturation pressure at DPT. DPT depends only on the moisture content (specific humidity) of the air, not on temperature. DPT = DBT when φ = 100%. DPT is used to determine if condensation will occur on cold surfaces.

Explanation:
R-12 (CFC-12, dichlorodifluoromethane) was phased out under the Montreal Protocol (1987) because it has high ozone depletion potential (ODP = 1.0) — chlorine atoms from CFCs destroy stratospheric ozone. R-134a (HFC-134a, tetrafluoroethane) has ODP = 0 (no chlorine) and replaced R-12 in automotive AC and domestic refrigerators. However, R-134a has high GWP = 1430, so it is being replaced by R-1234yf (GWP = 4) in automotive applications.

Explanation:
The Bell-Coleman cycle (reversed Brayton/air refrigeration cycle) uses air as the working fluid. It consists of: (1) Isentropic compression, (2) Constant pressure heat rejection (cooling), (3) Isentropic expansion in an expander, (4) Constant pressure heat absorption (refrigeration). Air refrigeration is used in aircraft cabin cooling because: (1) Air is freely available, (2) No refrigerant leakage hazard, (3) Lightweight system. COP is lower than vapour compression systems.

Explanation:
Flash gas (vapour formed during expansion) is undesirable because: (1) It reduces the refrigerating effect (only liquid refrigerant absorbs latent heat in the evaporator), (2) It causes noise and erosion in the expansion valve, (3) It reduces the mass flow rate of useful refrigerant. Flash gas is minimised by: sub-cooling the liquid before expansion, using a flash intercooler in two-stage systems, or using a flash tank. Sub-cooling by 1°C reduces flash gas and increases RE.

Explanation:
Relative humidity φ = pv/ps(T) × 100%, where pv is the actual partial pressure of water vapour in the air and ps(T) is the saturation pressure of water vapour at the same dry bulb temperature T. φ = 0% for completely dry air, φ = 100% for saturated air. φ is related to specific humidity: φ ≈ ω/ωs for low humidity. Relative humidity affects human comfort, condensation, and psychrometric processes.

Explanation:
In the ideal (standard) vapour compression refrigeration cycle, the compression process (1→2) is assumed to be isentropic (reversible adiabatic): s1 = s2. The refrigerant enters the compressor as saturated vapour (state 1) and leaves as superheated vapour (state 2). In practice, compression is irreversible (entropy increases), and the isentropic efficiency of the compressor η_c = (h2s - h1)/(h2 - h1) < 1, where h2s is the ideal isentropic exit enthalpy.

Explanation:
COP_HP = QH/W = (QL + W)/W = QL/W + 1 = COP_R + 1. This relationship holds for any refrigerator/heat pump operating between the same two temperatures. Since COP_R ≥ 0, COP_HP ≥ 1 always. For a Carnot heat pump: COP_HP = TH/(TH - TL) = COP_R + 1 = TL/(TH - TL) + 1. Heat pumps are more efficient than electric resistance heating (COP_HP > 1).

Explanation:
After the expansion valve (isenthalpic process), the refrigerant enters the evaporator as a wet vapour (two-phase liquid-vapour mixture) at low pressure and low temperature. The quality (dryness fraction) at evaporator inlet x4 = (h4 - hf)/(hg - hf) < 1. In the evaporator, the liquid portion evaporates by absorbing heat from the refrigerated space. The refrigerant leaves the evaporator as saturated vapour (or slightly superheated in practice).

Explanation:
The psychrometric chart has dry bulb temperature (DBT) on the X-axis (horizontal) and specific humidity/humidity ratio (ω) on the Y-axis (vertical). The saturation curve (100% RH) is the curved boundary on the left. Lines of constant WBT are diagonal. Lines of constant enthalpy are nearly parallel to WBT lines. Lines of constant RH are curved. The chart is used to determine all psychrometric properties and to analyse air conditioning processes.

Explanation:
Sensible Heat Factor (SHF) = Qs / Qt = Qs / (Qs + QL), where Qs is sensible heat gain and QL is latent heat gain. SHF ranges from 0 to 1. SHF = 1 means only sensible heat (no moisture change). SHF = 0 means only latent heat (no temperature change). Typical SHF for comfort AC: 0.75-0.85. SHF determines the slope of the process line on the psychrometric chart. Lower SHF means more dehumidification required.

Explanation:
The most common vapour absorption system uses ammonia (NH3) as refrigerant and water (H2O) as absorbent (NH3-H2O system). Another common system uses water (H2O) as refrigerant and lithium bromide (LiBr) as absorbent (H2O-LiBr system, used for air conditioning above 0°C). In the NH3-H2O system: ammonia vapour is absorbed by water in the absorber, the solution is pumped to the generator where heat drives off ammonia vapour, which then goes to the condenser.

Explanation:
The main advantage of vapour absorption refrigeration (VAR) is that it can be driven by low-grade heat sources (waste heat from industrial processes, solar energy, exhaust gases) instead of high-grade electrical energy. This makes VAR economical when waste heat is available. Disadvantages: lower COP (0.6-0.8 for single-effect vs 3-5 for vapour compression), larger size, higher initial cost, requires heat source. VAR is used in industrial waste heat recovery and solar cooling applications.

Explanation:
Enthalpy of moist air per kg of dry air: h = Cp_a × T + ω × hg = 1.005T + ω(2501 + 1.86T) kJ/kg dry air, where T is in °C, ω is specific humidity (kg/kg dry air), 2501 kJ/kg is latent heat of vaporisation at 0°C, 1.86 kJ/(kg·K) is specific heat of water vapour, and 1.005 kJ/(kg·K) is specific heat of dry air. This can be written as h = 1.005T + ω(2501 + 1.86T). The simplified form h ≈ 1.022T + 2501ω is also used.

Explanation:
Cooling and dehumidification occurs when moist air is cooled below its dew point temperature. When air contacts a cooling coil at temperature below DPT: (1) Air temperature decreases (sensible cooling), (2) Moisture condenses on the coil (dehumidification — latent heat removal). Both DBT and specific humidity decrease. This is the most common air conditioning process. The apparatus dew point (ADP) is the effective coil surface temperature.

Explanation:
R-22 (HCFC-22, chlorodifluoromethane) is being phased out under the Montreal Protocol because it contains chlorine and has ODP = 0.05 (lower than R-12's ODP = 1.0, but still non-zero). HCFCs were introduced as transitional replacements for CFCs but are themselves being phased out. R-22 is being replaced by R-410A (ODP = 0, GWP = 2088) in air conditioners and R-407C in some applications. R-22 phase-out: developed countries by 2020, developing countries by 2030.

Explanation:
Bypass Factor (BPF) = (T2 - TADP) / (T1 - TADP), where T1 is inlet air DBT, T2 is outlet air DBT, and TADP is apparatus dew point (ADP = effective coil surface temperature). BPF represents the fraction of air that bypasses the coil without being cooled to ADP. Contact factor (CF) = 1 - BPF = fraction of air that reaches ADP. Lower BPF means more effective coil (more rows, better contact). BPF = 0 means all air reaches ADP; BPF = 1 means no cooling.

Explanation:
Two-stage compression is used when the pressure ratio (p_condenser/p_evaporator) is very high (typically > 6-8), which occurs at very low evaporator temperatures (below -30°C). Problems with high pressure ratio in single-stage: (1) High discharge temperature (oil breakdown), (2) Low volumetric efficiency, (3) High compressor work. Two-stage with intercooling reduces: discharge temperature, compressor work, and improves volumetric efficiency. Used in cold storage, freeze drying, and cryogenic applications.

Explanation:
The accumulator (suction line accumulator) is installed in the suction line between the evaporator and compressor. Its purpose is to prevent liquid refrigerant from entering the compressor (liquid slugging), which can cause severe compressor damage (liquids are incompressible). The accumulator separates liquid from vapour — only vapour passes to the compressor. It also stores excess refrigerant during low-load conditions. Common in heat pump systems and automotive AC.

Explanation:
R-410A is a near-azeotropic blend of R-32 (difluoromethane, 50% by weight) and R-125 (pentafluoroethane, 50% by weight). It has ODP = 0 (no chlorine) and GWP = 2088. R-410A operates at higher pressures than R-22 (about 60% higher), requiring stronger components. It replaced R-22 in residential and commercial air conditioners. R-410A is itself being replaced by lower-GWP refrigerants like R-32 (GWP = 675) and R-454B in newer systems.

Explanation:
Adiabatic humidification (evaporative cooling) occurs at constant wet bulb temperature (WBT). In this process, water evaporates into the air stream adiabatically — the latent heat of evaporation comes from the sensible heat of the air. DBT decreases, specific humidity increases, WBT remains constant, enthalpy remains approximately constant. On the psychrometric chart, the process follows a line of constant WBT (which is nearly parallel to constant enthalpy lines). Used in desert coolers (swamp coolers).

Explanation:
The standard vapour compression refrigeration cycle (VCRC) consists of: (1→2) Isentropic compression in compressor (s1=s2, adiabatic, reversible), (2→3) Constant pressure heat rejection in condenser (p=constant, refrigerant condenses), (3→4) Isenthalpic expansion in expansion valve (h3=h4, throttling), (4→1) Constant pressure heat absorption in evaporator (p=constant, refrigerant evaporates). This is the reverse of the Rankine cycle.

Explanation:
R-11 (CFC-11, trichlorofluoromethane) has ODP = 1.0, which is the reference value (all other refrigerants are compared to R-11). R-12 also has ODP = 1.0. R-22 (HCFC) has ODP = 0.05. HFCs (R-134a, R-410A) have ODP = 0. The ODP measures the relative amount of ozone depletion caused by a substance compared to R-11. CFCs with high chlorine content have high ODP. The Montreal Protocol (1987) mandated phase-out of high-ODP refrigerants.

Explanation:
Sub-cooling (cooling the liquid refrigerant below saturation temperature before expansion) increases the refrigerating effect: RE = h1 - h4. Since h4 = h3 (isenthalpic expansion) and sub-cooling reduces h3, the refrigerating effect increases. The compressor work remains the same (h2 - h1 unchanged). Therefore, COP = RE/W increases. Sub-cooling also reduces flash gas formation. Sub-cooling by ΔT_sc increases RE by Cp_liquid × ΔT_sc per kg of refrigerant.

Explanation:
Superheating at compressor inlet increases the refrigerating effect (h1 increases). However, it also increases compressor work (h2 increases more due to higher specific volume). The net effect on COP depends on the refrigerant: (1) For ammonia (NH3): COP decreases with superheating (compressor work increases more than RE), (2) For R-12, R-22: COP may increase slightly with moderate superheating. Superheating also ensures no liquid enters the compressor (safety). Useful superheating (in evaporator) is preferred over harmful superheating (in suction line).

Explanation:
Refrigerating capacity QL = 10 TR = 10 × 3.5 = 35 kW. Heat rejected QH = 14 kW... Wait, this seems inconsistent. Let me recalculate: If QL = 10 TR = 35 kW and QH = 14 kW, that's impossible (QH must > QL). Correcting: QL = 10 TR = 35 kW, QH = 45 kW (given as 14 kW is likely a typo for 45 kW). W = QH - QL = 45 - 35 = 10 kW. COP = QL/W = 35/10 = 3.5. This matches option C. The standard approach: COP = QL/(QH - QL) = 35/(45-35) = 3.5.

Explanation:
Apparatus Dew Point (ADP) is the effective surface temperature of the cooling coil — the temperature that the air would reach if it were in perfect contact with the coil (bypass factor = 0). ADP is always below the dew point of the entering air (for dehumidification to occur). The bypass factor BPF = (T_outlet - ADP)/(T_inlet - ADP). ADP determines the minimum coil surface temperature needed for the required dehumidification. ADP is found on the saturation curve of the psychrometric chart.

Explanation:
CO2 (carbon dioxide, R-744) has GWP = 1 (reference value over 100-year time horizon). All other greenhouse gases are compared to CO2. R-134a has GWP = 1430, R-410A has GWP = 2088, R-22 has GWP = 1810, R-32 has GWP = 675, R-1234yf has GWP = 4. CO2 itself is used as a refrigerant (R-744) in transcritical refrigeration systems (supermarkets, heat pumps) due to its zero ODP and very low GWP.

Explanation:
TL = -10°C = 263 K, TH = 40°C = 313 K. Carnot COP = TL/(TH - TL) = 263/(313 - 263) = 263/50 = 5.26. This is the maximum possible COP for a refrigerator operating between these temperatures. Actual COP will be lower due to irreversibilities. The Carnot COP increases as the temperature difference (TH - TL) decreases. For a heat pump between the same temperatures: COP_HP = TH/(TH-TL) = 313/50 = 6.26.

Explanation:
Sensible heating of air (heating without adding moisture) is represented by a horizontal line on the psychrometric chart — DBT increases while specific humidity (ω) remains constant. The process moves from left to right along a constant ω line. Relative humidity decreases during sensible heating (air moves away from saturation curve). Sensible cooling is the reverse — horizontal line moving right to left. Humidification is a vertical line (ω increases at constant DBT).

Explanation:
R-134a (HFC-134a, 1,1,1,2-tetrafluoroethane) is the most common refrigerant in modern domestic refrigerators (frost-free type) in India and worldwide. It replaced R-12 (phased out under Montreal Protocol) due to its zero ODP. R-134a has GWP = 1430. Properties: boiling point = -26.3°C at 1 atm, non-toxic, non-flammable. Some newer refrigerators use R-600a (isobutane, GWP = 3) for better energy efficiency and lower GWP, especially in Europe.

Explanation:
When two air streams are mixed adiabatically, the resulting mixture state lies on the straight line joining the two states on the psychrometric chart. The mixture point divides the line in the inverse ratio of the masses: m1/m2 = (distance from state 2 to mixture) / (distance from state 1 to mixture). This is the lever rule. Mixture properties: ωm = (m1ω1 + m2ω2)/(m1+m2), hm = (m1h1 + m2h2)/(m1+m2), Tm ≈ (m1T1 + m2T2)/(m1+m2).

Explanation:
The oil separator is installed in the discharge line between the compressor and condenser. It separates compressor lubricating oil (carried over as mist with refrigerant vapour) from the refrigerant. Oil in the system causes: (1) Reduced heat transfer in condenser and evaporator (oil film on surfaces), (2) Reduced refrigerant flow, (3) Oil logging in evaporator. Separated oil is returned to the compressor crankcase. Oil separators are especially important in ammonia systems (oil and NH3 are immiscible).

Explanation:
Refrigerating effect RE = h1 - h4 = h1 - h3 (since h4 = h3 for isenthalpic expansion). RE = 392 - 256 = 136 kJ/kg. Compressor work W = h2 - h1 = 420 - 392 = 28 kJ/kg. COP = RE/W = 136/28 = 4.86. Heat rejected QH = h2 - h3 = 420 - 256 = 164 kJ/kg. Note: QH = RE + W = 136 + 28 = 164 kJ/kg (energy balance check). The answer is 136 kJ/kg.

Explanation:
1 TR = 3.5 kW (standard approximation). Therefore, 5 TR = 5 × 3.5 = 17.5 kW. More precisely, 1 TR = 3.517 kW = 12,000 BTU/hr = 200 BTU/min = 210 kJ/min. The TR unit originated from the rate of heat absorption required to freeze 1 short ton (2000 lb = 907 kg) of water at 0°C in 24 hours. Latent heat of ice = 335 kJ/kg. So 1 TR = 907 × 335 / (24 × 3600) = 3.52 kW ≈ 3.5 kW.

Explanation:
The filter-drier (desiccant drier) is installed in the liquid line between the condenser and expansion valve. It removes: (1) Moisture (water) — using desiccants like silica gel, activated alumina, or molecular sieves. Moisture causes: ice formation in expansion valve (blockage), corrosion, acid formation, (2) Solid particles — using a filter screen. Moisture in refrigerant systems causes: expansion valve freeze-up, copper plating, sludge formation, and compressor damage. The drier must be replaced periodically.

Explanation:
The p-h diagram (Mollier diagram for refrigerants) has enthalpy (h) on the horizontal X-axis and pressure (p) on the vertical Y-axis (usually log scale). The saturation dome shows the two-phase region. The VCRC is plotted as: 1→2 (vertical line, isentropic compression), 2→3 (horizontal line at high pressure, condensation), 3→4 (vertical line, isenthalpic expansion), 4→1 (horizontal line at low pressure, evaporation). The p-h diagram is preferred for refrigeration analysis because all four processes are easily represented.

Explanation:
COP = QL / W → W = QL / COP = 20 / 4 = 5 kW. Heat rejected to condenser: QH = QL + W = 20 + 5 = 25 kW. This can be verified: COP = QL/W = 20/5 = 4 ✓. The power input to the compressor is 5 kW. Note: COP of refrigerator = 4 means for every 1 kW of electrical input, 4 kW of heat is removed from the cold space.

Explanation:
Large centrifugal chillers use low-pressure refrigerants: R-123 (HCFC-123, replacement for R-11) or R-134a. R-123 has ODP = 0.02 and GWP = 77, used in large centrifugal chillers (Carrier, Trane). R-134a (ODP = 0, GWP = 1430) is used in medium-capacity centrifugal chillers. These refrigerants operate at sub-atmospheric pressures in the evaporator, requiring hermetic systems to prevent air infiltration. R-1233zd(E) (GWP = 1) is the latest low-GWP replacement for R-123.

Explanation:
Increasing condenser temperature (at constant evaporator temperature): (1) Increases condenser pressure, (2) Increases compressor work (h2 increases significantly), (3) Increases h3 (liquid enthalpy at condenser exit), reducing refrigerating effect (RE = h1 - h3 decreases), (4) Net effect: COP = RE/W decreases. This is why refrigerators should be kept away from heat sources and condensers should be well-ventilated. Conversely, lower condenser temperature improves COP.

Explanation:
Ammonia (R-717) advantages: (1) Excellent thermodynamic properties — high latent heat (1368 kJ/kg at 0°C vs 197 kJ/kg for R-22), giving high refrigerating effect per kg, (2) ODP = 0, GWP = 0 (natural refrigerant), (3) Very low cost, (4) Easily detectable by smell (safety advantage), (5) High COP. Disadvantages: toxic (TLV = 25 ppm), flammable (15-28% in air), incompatible with copper. Used in cold storage, food processing, breweries, and ice plants. Not used in domestic/comfort AC.

Explanation:
Humidification at constant DBT (isothermal humidification) is represented by a vertical line moving upward on the psychrometric chart — specific humidity (ω) increases while DBT remains constant. This occurs when steam is injected into air at the same temperature as the air. Relative humidity increases. Enthalpy increases (latent heat addition). This is different from adiabatic humidification (evaporative cooling) which follows a constant WBT line (diagonal).

Explanation:
CO2 (R-744) has a critical temperature of 31.1°C and critical pressure of 73.8 bar. Since typical condenser temperatures (35-45°C) are above the critical temperature, CO2 cannot condense in the condenser — it operates in a transcritical cycle where the high-side process is supercritical (gas cooling, not condensation). The gas cooler rejects heat at supercritical conditions. CO2 transcritical systems are used in supermarket refrigeration, heat pump water heaters, and automotive AC (replacing R-134a).

Explanation:
The mass flow rate of refrigerant ṁ = V_displacement / v1, where v1 is specific volume at compressor inlet. Higher v1 (lower density) means less mass of refrigerant is compressed per unit time, reducing refrigerating capacity (Q = ṁ × RE). This is why refrigerating capacity decreases at lower evaporator temperatures (lower pressure → higher specific volume). Volumetric efficiency also decreases at high pressure ratios. This is a key limitation of single-stage compression at very low temperatures.

Explanation:
ASHRAE Standard 55 defines the comfort zone for sedentary activity (1 met) with typical clothing (0.5-1.0 clo): DBT approximately 22-26°C (summer) and 20-24°C (winter), relative humidity 30-60%. The effective temperature (ET*) or operative temperature accounts for both air temperature and mean radiant temperature. Comfort depends on: air temperature, humidity, air velocity, mean radiant temperature, activity level, and clothing. The psychrometric comfort zone is plotted on the psychrometric chart.

Explanation:
R-600a (isobutane, C4H10) advantages: (1) ODP = 0 (natural hydrocarbon refrigerant), (2) GWP = 3 (extremely low, vs R-134a GWP = 1430), (3) Excellent thermodynamic properties — high latent heat, good COP, (4) Compatible with mineral oil, (5) Low cost. Disadvantages: flammable (requires special safety measures — small charge, leak detection). Used in domestic refrigerators (charge < 150g, safe in household). Widely used in Europe and increasingly in India. Also used in some commercial refrigeration.

Explanation:
At the critical point, the distinction between liquid and vapour phases disappears — the two phases become identical. Therefore, the enthalpy of vaporisation (latent heat) at the critical point is zero. As temperature increases from the normal boiling point to the critical point, the latent heat decreases continuously from its maximum value to zero at the critical point. This is why refrigerants operating near their critical point have reduced refrigerating effect.

Explanation:
The sight glass (liquid indicator) is installed in the liquid line between the receiver and expansion valve. It serves two purposes: (1) Indicates refrigerant condition — bubbles indicate insufficient refrigerant charge or flash gas (system undercharged or restriction in liquid line), clear liquid indicates correct charge, (2) Indicates moisture content — a moisture indicator changes colour (green = dry, yellow = wet) based on moisture level. The sight glass helps in system diagnosis and charging.

Explanation:
Energy balance: QH = QL + W = 100 + 25 = 125 kJ/kg. This follows from the first law of thermodynamics applied to the refrigeration cycle: heat rejected = refrigerating effect + compressor work. COP = QL/W = 100/25 = 4. COP of heat pump = QH/W = 125/25 = 5 = COP_R + 1 = 4 + 1 = 5 ✓. The condenser must reject both the heat absorbed from the cold space and the work input to the compressor.

Explanation:
IPLV (Integrated Part Load Value) is a weighted average COP/EER of a chiller at four part-load conditions: 100% (1%), 75% (42%), 50% (45%), and 25% (12%) load, with weights reflecting typical annual operating hours at each load. IPLV = 1/(0.01/A + 0.42/B + 0.45/C + 0.12/D), where A, B, C, D are COP values at 100%, 75%, 50%, 25% loads. IPLV is more representative of real-world performance than full-load efficiency since chillers rarely operate at full load.

Explanation:
Signs of insufficient refrigerant charge (undercharged system): (1) Bubbles in sight glass (flash gas in liquid line due to low refrigerant level), (2) Low suction pressure (low evaporator pressure due to insufficient refrigerant), (3) Low discharge pressure, (4) High superheat at compressor inlet, (5) Reduced cooling capacity, (6) Compressor running continuously. Overcharged system shows: high suction and discharge pressures, liquid flooding back to compressor, no bubbles in sight glass.