Current Search:   cryocooler (x)

View All Items

  • CSV Spreadsheet
(1 - 2 of 2)
NUMERICAL STUDY OF A HIGH-SPEED MINIATURE CENTRIFUGAL COMPRESSOR
Title
NUMERICAL STUDY OF A HIGH-SPEED MINIATURE CENTRIFUGAL COMPRESSOR.
Creator
Li, Xiaoyi, Kapat, Jayanta, University of Central Florida
Abstract / Description
A miniature centrifugal compressor is a key component of a reverse Brayton cycle cryogenic cooling system. The system is commonly used to generate a low cryogenic temperature environment for electronics to increase their efficiency, or generate, store and transport cryogenic liquids, such as liquid hydrogen and oxygen, where space limit is also an issue. Because of space limitation, the compressor is composed of a radial inlet guide vane, a radial impeller and an axial-direction diffuser ...
Show moreA miniature centrifugal compressor is a key component of a reverse Brayton cycle cryogenic cooling system. The system is commonly used to generate a low cryogenic temperature environment for electronics to increase their efficiency, or generate, store and transport cryogenic liquids, such as liquid hydrogen and oxygen, where space limit is also an issue. Because of space limitation, the compressor is composed of a radial inlet guide vane, a radial impeller and an axial-direction diffuser (which reduces the radial size because of smaller diameter). As a result of reduction in size, in order to obtain the required static pressure ratio/rise, the rotating speed of the impeller is as high as 313 KRPM, if Helium is used as the working fluid. Two main characteristics of the compressor – miniature and high-speed, make it distinct from conventional compressors. Higher compressor efficiency is required to obtain a higher COP (coefficient of performance) system. Even though miniature centrifugal compressors start to draw researchers' attention in recent years, understanding of the performance and loss mechanism is still lacking. Since current experimental techniques are not advanced enough to capture details of flow at miniature scale, numerical methods dominate miniature turbomachinery study. This work numerically studied a high speed miniature centrifugal compressor. The length and diameter are 7 cm and 6 cm, respectively. The study was done on the same physical compressor but with three different combinations of working fluid and operating speed combinations: air and 108 KRPM, helium and 313 KRPM, and neon and 141 KRPM. The overall performance of the compressor was predicted with consideration of interaction between blade rows by using a sliding mesh model. It was found that the specific heat ratio needs to be considered when similarity law is applied. But Reynolds number effect can be neglected. The maximum efficiency observed without any tip leakage was 70.2% for air 64.8% for helium 64.9% for neon. The loss mechanism of each component was analyzed. Loss due to turning bend was found to be significant in each component, even up to 30%. Tip leakage loss of small scale turbomachines has more impact on the impeller performance than that of large scale ones. Use of 10% tip gap was found to reduce impeller efficiency from 99% to 90%. Because the splitter was located downstream of the impeller leading edge, any incidence at the impeller leading edge leads to poorer splitter performance. Therefore, the impeller with twenty blades had higher isentropic efficiency than the impeller with ten blades and ten splitters. Based on numerical study, a four-row vaned diffuser was used to replace a two-row vaned diffuser. It was found that the four-row vaned diffuser had much higher pressure recovery coefficient than the two-row vaned diffuser. However, most of pressure is found to be recovered at the first two rows of diffuser vanes. Consequently, the following suggestions were given to further improve the performance of the miniature centrifugal compressor. 1. Redesign inlet guide vane based on the numerical simulation and experimental results. 2. Add de-swirl vanes in front of the diffuser and before the bend. 3. Replace the current impeller with a twenty-blade impeller. 4. Remove the last row of diffuser.
Show less
Date Issued
2005
Identifier
CFE0000702, ucf:46605
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000702
Large Scale Cryogenic Storage With Active Refrigeration
Title
Large Scale Cryogenic Storage With Active Refrigeration.
Creator
Swanger, Adam, Chow, Louis, Kapat, Jayanta, Notardonato, William, University of Central Florida
Abstract / Description
Storage and transfer of cryogenic liquefied gases on volume scales from under 10 liters for lab use, up to hundreds of millions of liters for industrial applications is of paramount importance across a vast range of industries. Traditionally, these commodities have been stored at or near the normal boiling point due to relative ease of operation and safety-related considerations; however, this also means that some percentage will always be lost due to environmental heat leaking into the...
Show moreStorage and transfer of cryogenic liquefied gases on volume scales from under 10 liters for lab use, up to hundreds of millions of liters for industrial applications is of paramount importance across a vast range of industries. Traditionally, these commodities have been stored at or near the normal boiling point due to relative ease of operation and safety-related considerations; however, this also means that some percentage will always be lost due to environmental heat leaking into the vessel and causing boiloff. These losses become more concerning as scales increase, and are of particular importance for high-cost commodities such helium and hydrogen. Additionally, the normal boiling point has typically marked the highest liquid density achievable, which became a strong driver of end-use system designs such as space launch vehicles. Recent development and testing of an Integrated Refrigeration and Storage (IRAS) system for liquid hydrogen has proven that next generation cryogenic storage operations such as zero boiloff and densification are feasible on a large scale. This IRAS system married an 850 Watt at 20 Kelvin reverse-Brayton cycle commercial cryogenic refrigerator with a 125,000 liter LH2 storage tank via an internal tubular heat exchanger; thereby allowing heat to be removed directly from the hydrogen, and by extension, providing a means to control the bulk thermodynamic state. Tests of zero boiloff, in-situ liquefaction, and densification down to the triple point were performed, and data including fluid temperature profiles and tank pressure were gathered. Details regarding the design, setup, and testing of the IRAS system are discussed herein, and the data are used to anchor various physics models created to predict the behavior of the system during both transient and steady state operations. Hopefully these efforts will provide a useful basis for the design and implementation of future large scale IRAS systems across numerous industries.
Show less
Date Issued
2018
Identifier
CFE0007588, ucf:52530
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007588