Absorption Refrigerator Heat Rejection System Sizing

Overview of Technical Issues:

The heat rejection system in the absorption refrigerator provides insufficient cooling capacity when undersized, causing the condenser and absorber temperatures to rise excessively, which reduces the refrigerant circulation rate and degrades overall cooling performance; the goal is to properly size the heat rejection system to maintain optimal operating temperatures and achieve the target coefficient of performance.

Solution directions generated for this problem

Problem Direction 1 :

ImproveHeat rejection system heat transfer capacity
VS
ConstraintHeat rejection system size and weight

Inspiration 1 : Cross-domain reference

Application Principle: #17 Another dimension
Cross-domain applicability Assess applicability
Compact mode-locked laser module
Innovative Solution Refine solution

Vertical stacked plate heat exchanger for absorption refrigerator

Vertical multi-layer plate architecture
How to solve :
  • Stack 8–12 thin plate heat exchanger layers vertically with 15–20mm spacing, converting horizontal footprint expansion into vertical dimension utilization to achieve 3–4× heat transfer area within same floor space
  • Use 0.6mm thick aluminum plates with thermal conductivity ≥200 W/(m·K), vacuum-brazed assembly ensuring <0.05mm flatness tolerance per plate, enabling compact vertical integration without performance loss
  • Implement counter-flow coolant distribution manifold with flow velocity 0.8–1.2 m/s across all layers, maintaining uniform temperature distribution (±2°C layer-to-layer variation) and condenser/absorber temperatures within optimal range of 35–42°C
Expected Effect : Heat transfer capacity +180%, footprint unchanged, weight +15%, COP improvement 22–28%
Risk Control :
  • inter-layer flow maldistribution causing hotspots
  • brazing joint integrity under thermal cycling
  • vertical space constraint in existing installations

Problem Direction 2 :

ImproveHeat rejection system heat transfer capacity
VS
ConstraintCoolant circulation pumping power

Inspiration 1 : Cross-domain reference

Application Principle: #19 Periodic action
Cross-domain applicability Assess applicability
Method for operating a brake system
Innovative Solution Refine solution

Pulsed coolant flow control for enhanced heat rejection efficiency

Alternate high-low flow to boost heat transfer while cutting average pump power
How to solve :
  • Install solenoid flow modulator upstream of condenser/absorber — pulse cycle 2–5 seconds, high-flow phase at 150% nominal rate for 40% duty cycle, low-flow phase at 50% nominal rate
  • Implement boundary layer disruption through flow pulsation — instantaneous Reynolds number peaks create turbulence that increases heat transfer coefficient by 25–35% compared to steady flow at same average rate
  • Deploy variable-frequency drive pump with programmed pulse profile — square-wave modulation between 30 Hz and 75 Hz, synchronized with thermal load sensors to maintain condenser below 45°C and absorber below 40°C
Expected Effect : Heat transfer capacity +30%, pumping power −22%, COP improvement 12–18%
Risk Control :
  • solenoid valve fatigue under cyclic duty
  • flow oscillation inducing pipe vibration
  • control algorithm stability during transient loads

Problem Direction 3 :

ImproveCondenser and absorber temperature control
VS
ConstraintHeat rejection system size and weight

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
Apparatus for a resonance circuit
Innovative Solution Refine solution

Variable-temperature coolant supply for adaptive heat rejection

Adaptive coolant temperature control
How to solve :
  • Install variable-temperature coolant supply system that dynamically adjusts inlet temperature 15–30°C based on real-time condenser/absorber temperature feedback, increasing ΔT driving force by 40–60% without enlarging heat exchangers
  • Deploy modulating mixing valve (3-way proportional control, response time <5s) blending chilled water (10–15°C) with ambient return flow, controlled by PLC reading condenser outlet temperature with ±0.5°C accuracy and 10s sampling interval
  • Implement dual-setpoint control logic: condenser priority mode (coolant 12–18°C) during peak load, absorber priority mode (coolant 18–25°C) during part-load, switching threshold at 75% capacity to maintain both components within optimal range (condenser <45°C, absorber <40°C)
Expected Effect : Heat rejection capacity +45–55% with zero size increase; COP improvement 12–18%; payback period 8–14 months
Risk Control :
  • chilled water supply stability fluctuation
  • mixing valve precision degradation over time
  • sensor calibration drift affecting control accuracy
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