Absorption Chiller Components

Technical Overview

Absorption chiller components enable thermal compression refrigeration through chemical affinity between refrigerant and absorbent. The lithium bromide-water system employs specialized pumps, heat exchangers, spray distribution devices, and chemical treatment maintaining reliable operation. Understanding component functions, materials, and design considerations ensures proper selection, installation, and maintenance of absorption cooling systems.

Solution Pump Design and Operation

Solution pumps circulate concentrated lithium bromide solution from the absorber to the generator, driving the absorption refrigeration cycle. Hermetic centrifugal pumps eliminate shaft seals, preventing solution leakage and air infiltration. Pump materials resist corrosion from concentrated salt solutions, typically employing stainless steel or special alloys. Flow rates range from 5 to 50 GPM (19 to 189 L/min) depending on chiller capacity. Multiple solution circuits in larger chillers employ individual pumps enabling circuit isolation.

Solution Heat Exchanger Function

Solution heat exchangers recover thermal energy between hot concentrated solution leaving the generator and cool dilute solution returning from the absorber. This regenerative heat exchange improves cycle efficiency by 20-30% through internal heat recovery. Shell-and-tube or plate-and-frame designs accommodate the corrosive solution. Effectiveness typically ranges from 60% to 80%, determined by surface area and flow arrangement. Fouling resistance in the design accounts for scale formation over operating life.

Refrigerant Pump Optional Systems

Refrigerant pumps in flooded evaporator designs circulate water refrigerant over evaporator tube bundles, enhancing heat transfer coefficients. Pumped evaporators achieve superior performance compared to gravity-fed spray designs, particularly at reduced capacity. Hermetic pump construction prevents air ingress into vacuum conditions. Materials compatible with pure water and potential treatment chemicals ensure longevity. Some designs eliminate refrigerant pumps through thermosiphon or spray distribution.

Spray Nozzle Design - Absorber

Absorber spray nozzles distribute dilute solution uniformly over absorber tube bundles, maximizing surface area for water vapor absorption. Proper distribution ensures complete tube wetting and prevents dry spots reducing absorption effectiveness. Nozzle materials resist corrosion and scale buildup. Distribution headers feed multiple nozzles achieving uniform coverage. Nozzle orifice sizing balances pressure drop against distribution uniformity. Clogged nozzles reduce capacity, requiring periodic inspection and cleaning.

Spray Nozzle Design - Generator

Generator spray nozzles distribute concentrated solution over heated generator tubes, promoting refrigerant vapor evolution through enhanced surface area. High-temperature operation demands materials resisting thermal stress and corrosion. Proper distribution prevents tube dryout and localized overheating damaging heat exchanger surfaces. Multiple distribution levels in multi-effect generators ensure adequate coverage of each stage. Maintenance access enables nozzle inspection and replacement.

Corrosion Inhibitor Chemistry

Corrosion inhibitor packages protect steel and copper components from lithium bromide solution attack, particularly at elevated generator temperatures. Chromate-based inhibitors dominated historically but face environmental restrictions. Modern inhibitors employ lithium chromate, lithium molybdate, or organic compounds. Inhibitor concentrations typically range from 0.1% to 0.5% by weight. Annual solution analysis verifies adequate levels. Inhibitor depletion accelerates corrosion, requiring replenishment during maintenance.

Heat Exchanger Tube Materials

Tube materials balance heat transfer, corrosion resistance, and cost. Carbon steel suffices for absorber and condenser tubes at moderate temperatures. Generator tubes demand superior corrosion resistance, employing copper-nickel alloys, stainless steel, or specially treated carbon steel. Tube wall thickness and enhancement features (internal grooves or fins) optimize heat transfer. Material compatibility with solution chemistry and operating temperatures determines selection.

Vacuum Purge System

Non-condensable gases (air and hydrogen) accumulate in absorption chillers, reducing performance and accelerating corrosion. Vacuum purge systems extract these gases maintaining proper vacuum levels. Purge chambers cool mixed gas streams, condensing water vapor while venting non-condensables. Automatic purge operation triggered by pressure sensors maintains optimal conditions. Excessive purge operation indicates air leaks requiring investigation and repair.

Crystallization Prevention Features

Solution crystallization occurs when lithium bromide concentration and temperature combinations exceed solubility limits. Prevention features include solution dilution systems adding refrigerant water during abnormal conditions, electric heaters warming stagnant solution during shutdown, and control algorithms preventing operation outside safe concentration-temperature envelopes. Crystallization events block solution passages, requiring heat application and dilution for recovery.

Control and Instrumentation

Temperature sensors, pressure transducers, concentration sensors, and flow switches monitor system status. Microprocessor controllers manage solution pump speeds, heat input rates, and safety interlocks. Alarms warn of abnormal conditions including high pressure, low vacuum, high solution temperature, and low solution level. Data logging supports performance analysis and predictive maintenance.

Access Ports and Serviceability

Proper access enables solution sampling, heat exchanger inspection, and component maintenance. Isolation valves allow chamber opening without complete system evacuation. Inspection ports with replaceable gaskets facilitate periodic internal examination. Tube bundle removal systems enable cleaning and replacement. Lifting provisions support major component handling during installation and service.

Maintenance Considerations

Regular maintenance includes solution analysis, inhibitor replenishment, tube bundle cleaning, nozzle inspection, pump bearing verification, and seal condition checks. Solution samples analyzed annually verify concentration, inhibitor levels, and contaminant presence. Tube cleaning removes scale and sediment restoring heat transfer. Proper procedures maintain system vacuum and prevent air infiltration during service activities.