Author: William Vance PaynePublisher:
ISBN:
Category :
Languages : en
Pages : 444
Book Description
A Universal Mass Flowrate Correlation for Refrigerants and Refrigerant/oil Mixtures Flowing Through Short Tube Orifices
Author: William Vance PayneDissertation Abstracts International
Author: Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 836
Book Description
Two-phase Flow of Two HFC Refrigerant Mixtures Through Short-tube Orifices
Author: American Doctoral Dissertations
Author: Publisher:
ISBN:
Category : Dissertation abstracts
Languages : en
Pages : 872
Book Description
Applied Mechanics Reviews
Author: Boiling and Condensation Heat-transfer-correlations for Flows of Refrigerant-oil Mixtures Inside Augmented Tubes
Author: Ghayyurul Iman UsmaniPublisher:
ISBN:
Category : Heat-transfer media
Languages : en
Pages : 116
Book Description
Two-phase Pressure Drop and Flow Regime of Refrigerants and Refrigerant-oil Mixtures in Small Channels
Author: Brandon S. FieldPublisher: ProQuest
ISBN: 9780549339977
Category :
Languages : en
Pages : 130
Book Description
As microchannel heat exchangers have become more sophisticated in their design, more exact understanding of the flow inside them is necessary. A decrease in diameter enhances the heat transfer (which takes place at the inner walls of the tubes), but also increases the pressure drop (as the diameter decreases, it becomes like drinking a milkshake through a coffee stirrer). The inclusion of even small amounts of oil in circulation can have a significant effect as well. Historical correlations and studies of two-phase flow have been shown to be insufficient for predicting pressure drops in the smaller channels, due to the different fluid physics that are relevant in flows of small diameter. This study is aimed at understanding the fluid property effects that contribute to pressure drop and flow regime. Two-phase pressure drop data for four refrigerants (R134a, R410A, R290 and R717) were measured in a channel with hydraulic diameter of 148 mum. These data were combined with previous two-phase data of R134a in small channels (hydraulic diameters ranging from 70 to 300 mum) to generate a separated flow model that spans a wide variety of fluid properties. Refrigerant was then mixed with two different viscosities of oil at concentrations ranging from 0.5 to 5% oil, and two-phase pressure drop measurements were taken of those mixtures. Flow visualizations of three of these refrigerants (R134a, R290 and R717) and several concentrations of a R134a-oil mixture were made in a channel with 500 mum hydraulic diameter, and flow regime classifications and comparisons with previous flow maps were made. Finally, a mechanistic description of the two-phase flow that occurs in small channels is put forth, based on the pressure drop measurements and the flow visualizations.
Flow Boiling of Pure Refrigerants and Binary Refrigerant Mixtures in a Horizontal Tube
Author: Ali A. RabahPublisher:
ISBN: 9783832218102
Category :
Languages : en
Pages : 187
Book Description
Experimental and Analytical Investigation of Refrigerant and Lubricant Migration
Author: Steffen PeukerPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
The off-cycle refrigerant mass migration has a direct influence on the on-cycle performance since compressor energy is necessary to redistribute the refrigerant mass. No studies, as of today, are available in the open literature which experimentally measured the lubricant migration within a refrigeration system during cycling or stop/start transients. Therefore, experimental procedures measuring the refrigerant and lubricant migration through the major components of a refrigeration system during stop/start transients were developed and implemented. Results identifying the underlying physics are presented. The refrigerant and lubricant migration of an R134a automotive A/C system-utilizing a fixed orifice tube, minichannel condenser, plate and fin evaporator, U-tube type accumulator and fixed displacement compressor-was measured across five sections divided by ball valves. Using the Quick-Closing Valve Technique (QCVT) combined with the Remove and Weigh Technique (RWT) using liquid nitrogen as the condensing agent resulted in a measurement uncertainty of 0.4 percent regarding the total refrigerant mass in the system. The determination of the lubricant mass distribution was achieved by employing three different techniques-Remove and Weigh, Mix and Sample, and Flushing. To employ the Mix and Sample Technique a device-called the Mix and Sample Device-was built. A method to separate the refrigerant and lubricant was developed with an accuracy-after separation-of 0.04 grams of refrigerant left in the lubricant. When applying the three techniques, the total amount of lubricant mass in the system was determined to within two percent. The combination of measurement results-infrared photography and high speed and real time videography-provide unprecedented insight into the mechanisms of refrigerant and lubricant migration during stop-start operation. During the compressor stop period, the primary refrigerant mass migration is caused by, and follows, the diminishing pressure difference across the expansion device. The secondary refrigerant migration is caused by a pressure gradient as a result of thermal nonequilibrium within the system and causes only vapor phase refrigerant migration. Lubricant migration is proportional to the refrigerant mass during the primary refrigerant mass migration. During the secondary refrigerant mass migration lubricant is not migrating. The start-up refrigerant mass migration is caused by an imbalance of the refrigerant mass flow rates across the compressor and expansion device. The higher compressor refrigerant mass flow rate was a result of the entrainment of foam into the U-tube of the accumulator. The lubricant mass migration during the start-up was not proportional to the refrigerant mass migration. The presence of water condensate on the evaporator affected the refrigerant mass migration during the compressor stop period. Caused by an evaporative cooling effect the evaporator held 56 percent of the total refrigerant mass in the system after three minutes of compressor stop time-compared to 25 percent when no water condensate was present on the evaporator coil. Foam entrainment led to a faster lubricant and refrigerant mass migration out of the accumulator than liquid entrainment through the hole at the bottom of the U-tube. The latter was observed for when water condensate was present on the evaporator coil because-as a result of the higher amount of refrigerant mass in the evaporator before start-up-the entrainment of foam into the U-tube of the accumulator ceased before the steady state refrigerant mass distribution was reached.
A Study of Metastability Effects for Refrigerant-12 Flowing in Small Bore Tubes
Author: Jon A. HoffmannPublisher:
ISBN:
Category : Fluid dynamics
Languages : en
Pages : 168
Book Description