Expansion Devices I. Introduction
Expansion devices are basic components of a refrigeration system which carry out two major purposes: (1) the pressure reduction from the condenser to evaporator pressure and (2) the regulation of refrigerant flow into the evaporator. These expansion devices can be generally classified into two types which are namely the fixed opening type (flow area is fixed) and the variable opening type (flow area changes correspondingly with a change in mass flow rates). There are about seven basic types of expansion devices for a refrigerant in a refrigeration system. These include capillary tubes and orifice which are under the fixed opening type and the manual expansion valves, automatic expansion valve (AEV), thermostatic expansion valve (TEV), electronic expansion valve and float type expansion valve which are all under the variable opening type. The float type expansion valve is further classified into high side float valve and low side float valve (Arora, 2006). One of the most commonly used expansion device is the capillary tube. For the purpose of this exercise, a computation related to it will be performed. In a lesson guide on expansion devices prepared by Prof. R.C. Arora in 2006, he/she defined a capillary tube as “…a long, narrow tube of constant diameter. The word „capillary‟ is a misnomer since surface tension is not important in refrigeration application of capillary tubes. Typical tube diameters of refrigerant capillary tubes range from 0.5 mm to 3 mm and the lengths range from 1.0 m to 6 m.” II. Objectives The exercise was conducted to familiarize the students with expansion devices, its functions and its importance. Specifically, the objectives were: 1.) to examine the construction of some commonly-used expansion devices; and 2.) to assess the performance of some commonly-used expansion devices.
Methodology A. Lab-Scale Refrigeration System A lab-scale set-up for a refrigeration system in the...