Refrigerants and Refrigerant Oils Textbook
Prepared as part of ACRC Project Saturation Pressure-Temperature Relationships for. Refrigerant-Oil Combinations. A. M. Jacobi, Principal Investigator. Refrigerants and Refrigerant Oils training covers the physical properties of refrigerants, including pressure-temperature relationships. Discusses various kinds of. Correlation of Experimental Pressure Drop Results. Summary. Saturation temperature of refrigerant-oil mixtures as a function. 10 of vapor quality.
List the reports you should keep concerning refrigerant purchase and use. Explain the levels of technician certification. Refrigerant Filters and Driers Topics: System contaminants; Types of filters, driers, and filter-driers; Desiccants; Strainers; Suction filters; Installation precautions Learning Objectives: List the contaminants that can infiltrate or form within a refrigeration system.
Describe the various types of filters, driers, filter-driers, and strainers used in mechanical refrigeration systems. Distinguish between absorption-type and adsorption-type desiccants.
Explain the importance of proper location when installing filters, filter-driers, and strainers. List the important factors to consider when selecting a filter-drier. List several safety precautions to follow when working with filter-driers. Describe the various methods of locating leaks in a refrigeration system. Explain how to connect a gauge manifold to a system and how to remove air from the manifold.
Explain how to check the refrigerant charge in a system. Name and describe the two methods of evacuating and dehydrating a refrigeration system. Describe the procedures for vapor charging and liquid charging a system. Identify and explain the various methods of adding the correct amount of refrigerant to a system. Contrast active and passive refrigerant recovery.
Oil properties; Compressor lubrication; Oil-related problems; Oil separators; Contaminants; Maintenance and servicing; Adding and removing oil Learning Objectives: Explain the purposes oil serves in a refrigeration system. It is still an effective refrigerant in industrial applications. It could not be used in air conditioning applications because it is toxic so if there was a substantial leak, toxic gas could enter the conditioned space and cause casualties.
Likewise, hydrocarbon refrigerants like propane or butane were good refrigerants but could not be used due to their flammability.
Incidentally, butane and propane are now used in Europe to replace CFCs in small units. Refrigerants like methyl chloride and sulfur dioxide were excellent refrigerants but they are poisonous. For a number of years there was no safe refrigerant for air conditioning. In the s the CFCs were developed.
Of these, we found 3 to be of the best efficiency and price. They were used for many decades. The first common use for CFCs was movie theaters. They were both nonflammable, nontoxic, efficient and miscible with mineral oil.
R was used in autos, household refrigerators, commercial coolers and some air conditioning. It was cheap, highly efficient and operated at low pressures. R was used in mostly low temperature freezers and ice machines. R was used mostly in air conditioners. R and R were also CFCs. These chemicals have been determined to be harming the ozone layer in the atmosphere. All CFCs were phased out beginning in Taxes were added and limits were placed on production accelerating each year.
By they were essentially banned.
It was not considered as damaging to the ozone as CFCs. Its phaseout was started in These refrigerants cause no damage to the ozone layer. Saturated temperature pressure The concept of saturated is a hard one to understand. To be saturated a refrigerant must be in an enclosed container.
It also must have enough of the refrigerant in the container to be a mixture of liquid and gas. So lets start putting gas into a container by pressurizing the gas. As I increase the pressure, at some point part of the gas will condense into a liquid. As it does this, it releases heat. The latent heat was absorbed when the gas first became a gas from a liquid. Well when the gas becomes a liquid again it releases the latent heat.
If the container was insulated to the point that it could not release the heat it would not condense. Table 1 shows all cases simulated in the present work, and lists the main input and output parameters of the model. These were observed to be the minimum values that produced numerical results independent from the number of discrete points of time and spatial grids. Tolerances for the secondary and main loops were and In order to verify the validity of the results, Table 1 presents the material balance error represented in terms of the relative difference between the bubble mass gain and the refrigerant depletion in the liquid layer during the whole growth period.
Also, the error tends to increase for cases where smaller quantities of refrigerant are transferred to the bubble, i. Figure 4 shows the behavior of the bubble and liquid layer radii for Simulation 1.
The model computes the liquid layer growth due to bubble expansion depressurization.
The results show that the bubble growth process is characterized by three distinct periods Proussevitch et al. The first period is marked by a slow growth of the bubble and liquid layer radii, which is generally attributed to the high interfacial tension.
In this period, growth is controlled by the interfacial tension and normal viscous stresses that offer a resistance to growth associated with displacing the body of liquid around the bubble. This marks the second period of bubble growth, which is called here the effective growth period.
This period is controlled by mass diffusion, as the excess dissolved refrigerant that existed in the first period is transported into the bubble. The bubble and liquid layer reach stable radii in the third period, when the concentration gradient in the liquid layer vanishes. At the end of the process, the bubble and the liquid layer reach, respectively, around and 5 times their initial radii.
An analysis of the forces that affect the bubble growth for Simulation 1 is presented in Fig. All forces are depicted in normalized form, as presented in Eq. As can be verified for this case, the main opposing force for bubble growth is generated by the interfacial tension; almost no difference is observed between the pressure difference and interfacial tension curves at any given instant.
Thus, the small resultant force associated with the pressure difference, interfacial tension and viscous forces is the net force that drives the bubble growth. This small difference is due to the small initial radius chosen for the bubble, which, in turn, determines the slow growth rate period pointed out previously.
Figure 6 analyzes the refrigerant transport by diffusion in the liquid layer by comparing the refrigerant concentration profiles in liquid layer at different instants for Simulation 1.
This period of time is also characterized by high concentration gradients near the interface. Then, as the bubble growth speed increases, refrigerant solubility at the interface decreases due to the decrease in gas pressure, and the gradient at the interface becomes smoother as the refrigerant in the liquid layer is transported towards the interface, thus reducing the total amount of refrigerant available in the liquid layer.
The terms on the right side of Eq. The first term represents the growth induced by refrigerant molecular diffusion from the liquid layer towards the bubble, while the second term is the portion of the growth due to expansion of the gas inside the bubble as the pressure in the liquid layer decreases.
The effect of both terms on total bubble growth rate along the time for Simulation 1 is shown in Fig. Right after the beginning of the bubble growth process, the growth rate is governed exclusively by bubble expansion, which decreases as the interfacial force acting on the bubble remains large.
This behavior is consistent with the period of slow growth described earlier in Fig. When the bubble reaches a sufficiently large size to overcome the opposing interfacial force, both gas expansion and refrigerant molecular diffusion effects increase rapidly and contribute equally to the growth rate that reaches its maximum value.
Then, a sudden decrease of the molecular diffusion growth rate takes place indicating that the amount of excess refrigerant present in the liquid layer has extinguished, and the growth process is again governed by gas expansion effect, which vanishes slowly as the bubble reaches its final size. Figure 8 shows the effect of variation of the initial bubble radius on the bubble growth behavior. It can be observed that the smaller the initial radius, the longer the slow growth period will be due to the large interfacial force at the initial instants of bubble growth.
Additionally, there is almost no difference between the bubble growth curves when the initial bubble radii were smaller than 9. It is believed that this has to do with the fact that for these initial bubble diameters, the interfacial tension force is still quite large and, because the sizes of the bubbles are small, the amount of volatile material refrigerant in the liquid layer is very similar in both cases.
Nevertheless, when the initial radius was set to 0. The result presented in Fig. This is a consequence of the smaller amount of refrigerant initially in the liquid layer for the smallest liquid layer radii.
IDEALS @ Illinois: Refrigerant-Oil Mixtures and Local Composition Modeling
Moreover, the influence of interfacial tension was more important as the liquid layer radius was decreased. This is clearly noticed in the result for Simulation 6, where bubble growth is slow for most of the time, until the stable radius is reached more abruptly. The effect of the initial refrigerant concentration is shown in Fig.