Absorption Refrigerator Part-Load Performance Control

Overview of Technical Issues:

During part-load operation, the absorption refrigerator's control mechanisms insufficiently modulate heat input and refrigerant flow to match reduced cooling demand, while the heat source continues supplying excessive thermal energy relative to actual load requirements. This mismatch causes the generator to produce excess refrigerant vapor, creates solution concentration imbalances, and forces all components to operate far from optimal conditions, resulting in significantly degraded coefficient of performance and wasted energy. The goal is to achieve proportional performance control that maintains high efficiency across the full range of part-load conditions.

Solution directions generated for this problem

Problem Direction 1 :

ImproveHeat input modulation range
VS
ConstraintSystem control complexity

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
E-cigarette personal vaporizer
Innovative Solution Refine solution

Solution-concentration-driven vapor production control via generator inlet dilution ratio adjustment

Control vapor output by adjusting solution concentration rather than heat input
How to solve :
  • Install a three-way mixing valve at generator inlet to blend strong solution from absorber with weak solution return—concentration ratio directly determines vapor production rate without heat modulation
  • Operate heat source at constant 100% output with simple on/off control—at 20% load inject 25% strong/75% weak solution (dilution ratio 1:3), at 100% load use pure strong solution (ratio 1:0), eliminating proportional valve and feedback loops
  • Use passive density-based flow divider with calibrated orifices (strong solution port 0.8-3.2mm variable aperture, weak solution port fixed 3.2mm)—buoyancy difference between solutions (density gap 50-150 kg/m³) naturally meters mixing ratio based on generator pressure, requiring only manual pre-set for load range
Expected Effect : Modulation range 20-100% with single mixing valve; control complexity reduced 60% (from 3 coordinated loops to 1 manual adjustment); COP maintained ≥0.65 across full range
Risk Control :
  • Solution crystallization at high dilution ratios
  • density-based divider accuracy ±8% affecting vapor output
  • mixing valve corrosion in LiBr environment

Problem Direction 2 :

ImproveControl response precision to load changes
VS
ConstraintEnergy consumption by control mechanisms

Inspiration 1 : Cross-domain reference

Application Principle: #28 Mechanics substitution
Cross-domain applicability Assess applicability
Breast pump system
Innovative Solution Refine solution

Optical solution concentration monitor with passive flow regulation

Optical concentration sensing eliminates powered sensors
How to solve :
  • Install optical refractometer using LED light source (0.5W) and photodetector array to measure solution concentration via refractive index — replaces powered density sensors (50W) and flow meters (30W)
  • Couple optical signal to passive thermostatic valve that mechanically adjusts solution bypass flow based on concentration-dependent light refraction angle, eliminating variable-speed pump control
  • Integrate pressure-differential ejector driven by generator-absorber pressure gap (15-25 kPa) to circulate solution — replaces electric circulation pump (120W), achieving self-regulating flow proportional to vapor production
Expected Effect : Control power reduced 85% (200W→30W); response time ≤15s for ±10% load variation; maintains COP within 3% of optimal across 20-100% load
Risk Control :
  • optical window fouling by crystallization
  • refraction calibration drift over temperature range
  • ejector performance degradation at <25% load

Problem Direction 3 :

ImproveRefrigerant flow regulation capability
VS
ConstraintSystem control complexity

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
System and method for providing cryptographically secured digital assets
Innovative Solution Refine solution

Solution-concentration-driven refrigerant flow self-regulation system

Control vapor production via solution concentration instead of adding flow valves
How to solve :
  • Install a weak solution dilution loop from absorber to generator inlet with thermostatic mixing valve (opening range 0–100% at 80–120°C) — higher load triggers higher generator temperature, valve opens wider, dilutes incoming strong solution to 45–52% LiBr concentration, directly reducing vapor generation rate without feedback control
  • Use concentration-dependent vapor pressure relationship (每1% concentration change yields 8–12% vapor production change) as the physical control mechanism — dilution ratio automatically matches load via generator temperature signal alone
  • Implement gravity-driven weak solution return with 0.5–1.5m height difference and passive check valve — eliminates powered pump, weak solution flows naturally when absorber pressure exceeds generator pressure by ≥2 kPa
Expected Effect : Refrigerant flow regulation 20–100% load; control components reduced from 5 to 2; parasitic power <15W; response time 3–8 min
Risk Control :
  • solution crystallization risk at high dilution
  • thermostatic valve calibration drift
  • concentration stratification in generator

Problem Direction 4 :

ImproveHeat input modulation range
VS
ConstraintEnergy consumption by control mechanisms

Inspiration 1 : Cross-domain reference

Application Principle: #2 Taking out
Cross-domain applicability Assess applicability
Display device and operating method thereof
Innovative Solution Refine solution

Passive thermostatic bypass valve for heat input modulation without control power

Eliminate powered control valve and modulation
How to solve :
  • Install a passive thermostatic bypass valve at generator inlet that diverts excess heat based on generator temperature — at low load (20-40%), high temperature (≥95°C) opens bypass to 60-80%, routing heat to absorber preheating
  • at high load (70-100%), low temperature (≤85°C) closes bypass to 0-20%, delivering full heat to generator
  • Wax-element actuator (melting point 88-92°C, stroke 8-12mm) mechanically modulates bypass opening proportional to temperature without electrical power, response time 45-90 seconds matches thermal inertia of absorption cycle
  • Bypass heat recovery loop preheats weak solution entering absorber, recovering 15-25% of diverted thermal energy and maintaining absorber efficiency, with counterflow heat exchanger (effectiveness ≥0.65) sized for 20-50% heat capacity flow
Expected Effect : Control power reduced from 120W to 0W; modulation range 20-100% load; COP maintained ≥0.65 across full range; payback period 8-14 months
Risk Control :
  • wax element response hysteresis ±3°C causing oscillation
  • bypass valve seat leakage at high temperature >100°C
  • heat recovery exchanger fouling reducing effectiveness below 0.5

Problem Direction 5 :

ImproveHeat input modulation range
VS
ConstraintMust not deteriorate

Inspiration 1 : Cross-domain reference

Application Principle: #10 Preliminary action
Cross-domain applicability Assess applicability
Heat exchanger
Innovative Solution Refine solution

Pre-concentrated solution reservoir with load-anticipatory injection system

Pre-concentrate solution during high-load periods and inject it during low-load operation
How to solve :
  • Install a dual-chamber solution reservoir (50L capacity, 316L stainless steel) with strong solution (≥55% LiBr) pre-concentrated during 70-100% load operation and stored at 60-80°C with electric trace heating (200W)
  • Implement load-anticipatory injection logic—when cooling demand drops below 50%, inject pre-concentrated strong solution at 2-8 L/min via solenoid valve into absorber inlet, maintaining optimal concentration (52-54% LiBr) without forcing generator into inefficient low-temperature regime
  • Operate generator in binary mode: high-load mode (70-100%) with heat input 180-250 kW for solution production and reservoir charging
  • low-load mode (20-50%) with reduced heat input 40-90 kW while pre-stored strong solution sustains absorption capacity, decoupling instantaneous heat input from refrigeration output
Expected Effect : COP maintained ≥0.65 across 20-100% load (vs 0.45 at 30% load baseline); crystallization risk eliminated below 50% load; control complexity reduced to binary heat input + timed injection
Risk Control :
  • solution stratification in reservoir during storage
  • concentration drift beyond 52-54% LiBr tolerance causing crystallization
  • trace heating failure leading to solution viscosity increase
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