Practical mechanical refrigeration dates back to 1855 with the invention of the ammonia-absorption machine by Carré and the Perkins ether-compression machine. Both systems have been used in direct expansion and brine systems for medium and extremely low temperatures. The absorption system is more economical at producing extremely low temperatures, while compression systems are more common today due to advancements in prime mover efficiency. Since both systems share many parts, this chapter focuses on the details of construction of the compression machine first.
Ice Bunker System: Bunkers for ice or cooling means are usually constructed as a tank with one side removed to allow air circulation freely between sides and room walls. Ice is stored on a water-tight floor over the compartment to be cooled, where cooling occurs through natural air circulation up over the ice and down through the cold-storage compartment.
<Callout type="important" title="Historical Context">The development of both absorption and compression systems began in 1855, marking a significant milestone in mechanical refrigeration history.</Callout>
Natural circulation of air in a cold storage compartment can be compared to natural draft in a chimney. In the case of chimneys, heated air rises due to expansion; in cold storage compartments, cooled air sinks due to contraction.
Bunker Insulation: To ensure maximum 'draft' or 'air circulation', it is necessary to maintain a liberal difference in temperature and a reasonable 'head'. Proper insulation prevents cooling of rising warm air and maintains the difference in temperatures for effective circulation. Exceptionally well-insulated coolers can achieve temperatures as low as 38°-40°F without salt.
Gravity Brine System: This system consists of a tank holding ice and salt, and a continuous pipe circuit where brine absorbs heat from the cold storage compartment and releases it to the ice or freezing mixture. The brine in the coil located in the tank becomes heavier as it is cooled by surrounding ice and salt, flowing down into the coil in the cold-storage compartment.
Elementary Mechanical Systems: When the refrigerating fluid is a condensable gas like anhydrous ammonia, heat passes from the air into the refrigerant; the former is refrigerated while the latter heats up to boiling point. This cooling effect is hastened by marked circulation of air around the flask due to specific gravity differences.
<Callout type="tip" title="Efficiency Tip">Using a brine solution instead of ice can prevent contamination and maintain lower temperatures without salt, enhancing system efficiency.</Callout>
Brine Circulation System: The boiling refrigerating medium absorbs heat from surrounding brine, which does not freeze at the temperature of the evaporating refrigerant. This cooling effect is hastened by circulation within the solution itself due to specific gravity differences.
Ice Freezing System: If ammonia were immersed in water instead of brine, the water would give up its specific and latent heat to the anhydrous ammonia, freezing at 32°F and then being cooled further if sufficient ammonia remains.
Key Takeaways
- Both absorption and compression systems were developed in the mid-19th century for commercial refrigeration.
- Proper insulation is crucial for maintaining effective air circulation and temperature control in cold storage compartments.
- Brine solutions offer advantages over ice bunkers, including preventing contamination and allowing lower temperatures without salt.
Practical Tips
- Ensure proper insulation around the coolers to maintain efficient air circulation and prevent moisture buildup.
- Consider using brine systems for their ability to maintain lower temperatures without salt and reduce contamination risks.
Warnings & Risks
- Improper insulation can lead to reduced efficiency in cold storage compartments due to insufficient temperature differences.
- Using ice bunkers without proper precautions may result in air contamination from melting ice and unsanitary conditions.
Modern Application
While the historical context of refrigeration systems has evolved, understanding these early methods provides valuable insights into system design principles. Modern survival preparedness can benefit from this knowledge by applying efficient insulation techniques and considering brine solutions for maintaining low temperatures without salt.
Frequently Asked Questions
Q: What are the main differences between absorption and compression refrigeration systems?
The absorption system is more economical at producing extremely low temperatures, while the compression system is more common today due to advancements in prime mover efficiency.
Q: Why is insulation important for cold storage compartments?
Proper insulation maintains a liberal difference in temperature and ensures effective air circulation by preventing cooling of rising warm air.
Q: How does the gravity brine system work?
The gravity brine system uses a tank holding ice and salt, with a continuous pipe circuit where brine absorbs heat from the cold storage compartment and releases it to the ice or freezing mixture of ice and salt.