17 Ice Cube Machine, Ice Cream Plants

Ice Cube Machine

An ice cube machine is a specialized refrigeration system designed to produce clear, solid ice cubes for commercial and domestic use.

Core Components & Operation

• Evaporator (Freezing Plate): Typically a vertical or horizontal nickel-plated copper grid. Water is sprayed or flowed over it.

• Water Sump & Pump: Circulates water over the evaporator until it freezes layer by layer, ensuring clear ice (air bubbles are washed away).

• Hot Gas Defrost (Harvesting): To release the ice, a solenoid valve diverts hot refrigerant vapor directly from the compressor to the evaporator, slightly melting the interface so cubes fall into the bin.

• Thickness Sensor: A probe or float switch that detects when the ice has reached the desired thickness to trigger the harvest cycle.

Key Technical Facts for Exams

• Refrigerants: Commonly uses R-134a or R-404A.

• Cycle Stages: Water Filling $\rightarrow$ Freezing $\rightarrow$ Harvesting (Defrost) $\rightarrow$ Bin Full (Stop).

• Water Quality: Requires a filter to prevent scale buildup on the evaporator, which reduces heat transfer efficiency.

Ice Cream Plants

Ice cream production requires two distinct stages of refrigeration: Freezing (forming the mix) and Hardening (storage).

1. The Instant Freezer (Continuous/Batch)

• Scraped Surface Heat Exchanger (SSHE): The “heart” of the plant. A jacketed cylinder where refrigerant evaporates outside, while internal blades (dashers) scrape the freezing mix off the walls.

• Overrun: The air whipped into the ice cream to increase volume and provide a smooth texture.

  • Formula: $Overrun \% = \frac{Volume\ of\ Ice\ Cream – Volume\ of\ Mix}{Volume\ of\ Mix} \times 100$

• Temperature: Mix enters at 4°C and leaves the freezer at approximately -5°C.

2. Hardening Room

• Purpose: Rapidly cools the “soft” ice cream to stabilize the structure.

• Temperature: Maintained between -25°C to -30°C.

• Method: Uses high-velocity cold air (Blast Freezing) to ensure small ice crystal formation, preventing a “gritty” texture.

Key Technical Facts for Exams

• Refrigerant: Large-scale plants typically use Ammonia (R-717) due to high latent heat, while smaller units use R-404A.

• Secondary Coolants: In some designs, Brine (Calcium Chloride) is used as a secondary refrigerant to cool the freezing cylinders.

• Heat Load: Includes sensible heat (cooling the mix), latent heat (freezing water in the mix), and heat of agitation (from the scraper motor).

Comparison for RAC Mechanics