Evaporators and Metering Devices

Table of Contents

Chapter 1: Introduction to Evaporators

Topics: Evaporator operation; Latent and sensible heat; Evaporator capacity; Temperature differential; Circulation velocity

Learning Objectives:

• Explain the function of the evaporator in a refrigeration system.
• List five main factors affecting evaporator capacity, and explain how each can be optimized to gain the greatest possible evaporator capacity.
• Describe the basic evaporator configurations.
• Explain the function of headers and distributors in multiple-circuit evaporators.
• Explain how comfort coolers reduce both air temperature and humidity.

Chapter 2: Direct Expansion Evaporators and Secondary Refrigeration Systems

Topics: Dry and flooded evaporators; Evaporator configurations; Secondary-refrigeration systems; Multiple staging; Cascade systems

Learning Objectives:

• Compare and contrast dry-expansion and flooded evaporators.
• List the main types of flooded evaporators.
• Explain the process of secondary refrigeration.
• Define eutectic solution and eutectic temperature.
• Describe three types of multiple-evaporator systems.
• Identify cascade and multiple-staging refrigeration systems.

Chapter 3: Improving Evaporator Performance

Topics: Net refrigeration effect; Superheating; Subcooling; Accumulators; Heat exchangers; Headers; Oil separation

Learning Objectives:

• Explain how the laws of thermodynamics apply to refrigeration.
• Describe how to increase the net refrigerating effect of an evaporator.
• Demonstrate-using simple arithmetic-the amount of increase in net refrigerating effect caused by subcooling.
• List several advantages of using a heat exchanger in a refrigeration system.
• Describe three ways of keeping oil out of an evaporator.
• Explain why the circulation of air or water through an evaporator coil improves evaporator performance.

Chapter 4: Defrosting, Mainaining, and Troubleshooting Evaporators

Topics: Manual, ambient air, heated air, water, brine, hot-gas, reverse-cycle, and electric defrost methods; Cleaning coils; Frost problems; Troubleshooting

Learning Objectives:

• Explain why periodic defrosting of evaporator coils is necessary.
• List and describe at least five different methods of defrosting an evaporator.
• Explain the differences between the hot-gas and reverse-cycle defrost methods.
• Explain how to clean an evaporator coil, drain pan, and drain line.
• Describe how to remove rust, scale, and sludge from shell-and-tube evaporators.
• List two ways evaporator coils can be winterized.
• Tell how low airflow and excessive moisture increase frost buildup on coil surfaces.
• Explain how dirty coils and damaged fins reduce an evaporator's cooling capacity.

Chapter 5: Metering Device Types, Maintenance and Troubleshooting

Topics: Hand-operated, automatic, thermostatic, and thermal-electric expansion valves; Capillary tubes; Float valves; Maintenance and troubleshooting

Learning Objectives:

• Explain the primary function of a metering device.
• Name the five main types of expansion valve, and describe the operation of each.
• Contrast the operation of an internally equalized and an externally equalized TXV.
• Explain how to adjust the superheat on a TXV.
• Describe the structure, operation, and application of high- and low-side float valves.
• Identify three causes of floodback and describe the corrective action for each.
• List the common problems of TXVs along with their solutions.

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