Fundamentals of Mechanical Refrigeration Systems - a PDH Online Course for Engineers

Fundamentals of Mechanical Refrigeration Systems

Course Outline

In the big world of HVAC/R (heating ventilating air conditioning refrigeration) you can kind of divide refrigeration systems as either "air conditioning" or "refrigeration". Air conditioning refers to a system to cool air, and refrigeration systems cool your walk-ins, freezers, food processing etc. But both these rely on the same fundamental principle of refrigeration cycles.

This 4-hr course material provides a basic introduction to the principles of refrigeration and air-conditioning.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

Learning Objective

Following completion of the course readers will learn:

the four stages of closed loop mechanical refrigeration cycle;
the basic components of vapor compression refrigeration system;
the Pressure-enthalpy (P-h) and Temperature-Entropy (T-s) diagram;
how to calculate system parameters such as power input, system efficiency, and cooling capacity;
the factors affecting the refrigeration system coefficient of performance (COP);
Describe the different types of evaporators - Direct expansion (DX) systems and shell & tube evaporators;
the different techniques of evaporator defrosting;
the application of different refrigeration compressors -reciprocating, centrifugal, screw and scroll compressors;
the different types of condensers - Air cooled, water cooled and evaporative condensers;
the different types of metering devices - Capillary, thermostatic expansion valves and float valves;
how to choose a right refrigerant and learn the affects of certain refrigerant on ozone depletion; and
the basic thermodynamics theory and terms.

Intended Audience

This course is aimed at students, engineers, designers, architects, facility managers, energy auditors, environmentalists, H &S professionals, technical and sales representatives.

Course Introduction

Refrigeration is the removal of heat from a material or space, so that its temperature is lower than that of its surroundings. The most widely used refrigeration cycle is the vapor-compression refrigeration cycle, which uses a circulating liquid refrigerant as the medium to absorb heat from the space and reject that heat elsewhere. All such systems have four components: a compressor, a condenser, an expansion valve (also called a throttle valve) and an evaporator.

It is easy to understand refrigeration if you know the relationships among temperature, pressure, and volume, and how pressure affects liquids and gases.

This course reviews the above criteria in detail.

Course Content

The course content is in a PDF file Fundamentals of Mechanical Refrigeration Systems. You need to open or download this document to study this course.

Course Summary

Refrigeration means an artificial way of lowering the temperature. Most refrigeration systems use the vapor compression cycle. Heat is absorbed through a heat exchanger as the refrigerant evaporates and the heat is rejected through another heat exchanger as the refrigerant condenses.

Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor and is compressed to a higher pressure, resulting in a higher temperature as well.

The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor is condensed into a liquid by flowing through a condenser.

The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure.

That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.

The cold mixture is then routed through the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat which is subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser.

To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.