Design of a Transient, Temperature Control System for a Low-Temperature Infrared Optical Telescope Utilizing a Ramai R-Cooled Thermoelectric Assembly as the Condenser of a Two-Phase Cooling System

2005 ◽  
Author(s):  
Donald C. Price ◽  
W. Gerald Wyatt ◽  
Pete Townsend ◽  
Mark C. Woods ◽  
Brad W. Fennell
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Thermal Management ◽  
Constant Temperature ◽  
Heat Sink ◽  
Cooling System ◽  
Ambient Air ◽  
Temperature Gradients ◽  
Two Phase ◽  
Optical Elements

The design of a thermal management system for an airborne, infrared, optical telescope system is described. This system provides transient thermal management for the optical elements of the system beginning at a high-temperature soak condition of 71°C (159.8°F) on the ground to a low-temperature operating condition of −30°C (−22°F) to −40°C (−40° F) within 45 min after aircraft takeoff. An active cooling system is employed to enable this rapid cooldown. In addition to the low-temperature requirement, the mirrors and lenses must be cooled so that temperature gradients across the optical elements are on the order of 1°C (33.8 °F) to 2°C (35.6 °F). The ambient air available for ground cooling is specified by the military environment to be 55°C (131.0 °F). As the aircraft takes off and climbs to an altitude of 11,582.4 m (38 kft), the ambient air temperature decreases to a low-temperature of −22°C (−7.6 °F) for steady, level flight at at Mach 0.9, this ambient air temperature results in a ram air inlet temperature on the order of 13.5°C (56.3 °F), after the air is captured and diffused to Mach 0.2 prior to entry into a ram air heat exchanger. This ram air heat sink is used to provide a chilled liquid for cooling of optical elements and the turret housing the system. The low temperatures required for this system, which are on the order of −30°C (−22 °F) to −40°C (−40 °F), make the use of forced-convection, liquid-cooling problematic because of the tendancy of liquids to become quite viscous as they approach these low temperature levels. Furthermore, the use of a single-phase heat transfer process will result in temperature gradients within the system. For these reasons, cooling concepts employing single-phase cooling using chilled-liquids have been eliminated from consideration. A low-temperature, low-pressure refrigerant, R-404a, is used as the working fluid. The themal management system uses the optical elements as the evaporator of a two-phase cooling system. The liquid refrigerant is introduced into the optical elements at the saturation temperature and saturation pressure of the liquid. The flow rate of the refrigerant will be controlled in such a manner that all of the heat transfer takes place in the liquid-vapor mixture region of the thermodynamic diagram for R-404a with the refrigerant exiting the elements at an arbitraily determned quality of approximately 0.8. This will assure that all of the heat transfer will be by boiling heat transfer and will take place at a constant temperature and essentially a constant pressure. Since the heat transfer coefficients are large and the process takes place at essentially a constant temperature, the optical elements will be controlled at the saturation temperature of the refrigerant and will be essentially a constant temperature across the expanse of the optical surface. The thermal management system is comprised of an array of TECs configured as a condenser HX. This TEC HX uses ram air as the eventual heat sink and will provide chilled-liquid produced by a liquid-to-ram air HX as the heat sink for the hot side of the TEC array. This system utilizes the system mass as the evaporator and a TEC HX as the condenser in a two-phase heat transfer process to provide rapid cooldown of the system mass to low temperatures in a short period of time and maintain that mass at proper operating temperatures with essentially zero temperature gradients throughout the system.

Performance Assessment of Single and Multiple Jet Impingement Configurations in a Refrigeration-Based Compact Heat Sink for Electronics Cooling

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Pablo A. de Oliveira ◽  
Jader R. Barbosa
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Cooling System ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Small Scale ◽  
Two Phase ◽  
R 134A ◽  
Steady State Heat Transfer ◽  
Vapor Compression Cooling

The performance of a novel impinging two-phase jet heat sink operating with single and multiple jets is presented and the influence of the following parameters is quantified: (i) thermal load applied on the heat sink and (ii) geometrical arrangement of the orifices (jets). The heat sink is part of a vapor compression cooling system equipped with an R-134a small-scale oil-free linear motor compressor. The evaporator and the expansion device are integrated into a single cooling unit. The expansion device can be a single orifice or an array of orifices responsible for the generation of two-phase jet(s) impinging on a surface where a concentrated heat load is applied. The analysis is based on the thermodynamic performance and steady-state heat transfer parameters associated with the impinging jet(s) for single and multiple orifice tests. The two-phase jet heat sink was capable of dissipating cooling loads of up to 160 W and 200 W from a 6.36 cm2 surface for single and multiple orifice configurations, respectively. For these cases, the temperature of the impingement surface was kept below 40 °C and the average heat transfer coefficient reached values between 14,000 and 16,000 W/(m2 K).

Experimental Characterization of a Carbon Fiber Composite Material Heat Sink in Boiling Heat Transfer Using FC-72

2006 ◽  
Author(s):  
Venugopal Gandikota ◽  
Harish Chengalvala ◽  
Amy S. Fleischer ◽  
G. F. Jones
Keyword(s):  
Heat Transfer ◽  
Composite Material ◽  
Carbon Fiber ◽  
Thermal Management ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Fluxes ◽  
Two Phase ◽  
Operating Temperatures ◽  
Power Densities

The on-going trend towards increasing device performance while shrinking device size often results in escalating power densities and high operating temperatures. High operating temperatures may lead to reduced reliability and induced thermal stresses. Therefore, it is necessary to employ new and innovative thermal management techniques to maintain a suitable junction temperature at high power densities. For this reason, there is interest in a variety of liquid cooling techniques. This study analyzes a composite material heat sink. The heat sink consists of a very large number of small cross-section fins fabricated from carbon pitch fibers and epoxy. These carbon pitch fibers have a high thermal conductivity along the length of the fin. It is expected that the longer length will result in more heat transfer surface area and a more effective heat sink. This experimental study characterizes the thermal performance of the carbon-fiber heat sink in a two-phase closed loop thermosyphon using FC-72 as the operating fluid. The influence of heat load, thermosyphon fill volume, and condenser operating temperature on the overall thermal performance is examined. The results of this experiment provide significant insight into the possible implementation and benefits of carbon fiber heat sink technology in two-phase flow leading to significant improvements in thermal management strategies for advanced electronics. The carbon fiber heat sink yielded heat transfer coefficients in the range of 1300-1500 W/m2 K for heat fluxes in the range up to 3.2 W/cm2. Resistances in the range of 0.20 K/W – 0.23 K/W were achieved for the same heat fluxes. Condenser temperature and fill ratio did not show a significant effect on any of the results.

Experimental Characterization of a Unique Carbon Fiber Brush Heat Sink in Two-Phase Heat Transfer

2005 ◽  
Author(s):  
Harish Chengalvala ◽  
Amy S. Fleischer ◽  
G. F. Jones
Keyword(s):  
Heat Transfer ◽  
Carbon Fiber ◽  
Thermal Management ◽  
Thermal Performance ◽  
Heat Sink ◽  
Management Strategies ◽  
Liquid Cooling ◽  
Two Phase ◽  
Two Phase Heat Transfer ◽  
Power Densities

The performance enhancements and footprint decreases of advanced electronic devices result in soaring power densities which may in turn lead to elevated operating temperatures. As elevated device temperatures lead to decreased device reliability and increased thermal stresses, it is necessary to employ aggressive thermal management techniques to maintain an acceptable junction temperature at high power densities. For this reason, interest is growing in a variety of liquid cooling techniques This study analyzes an advanced engineered-material heat sink which provides significant improvements in thermal management strategies for advanced electronics. The heat sink consists of a very large number of small cross-section fins fabricated from carbon pitch fibers. For these carbon pitch fibers, the high thermal conductivity reduces the temperature drop along the length of the fin creating a longer effective fin length than for copper fins. The longer length results in more heat transfer surface area and a more effective heat sink. In liquid cooling, the rough surface of the fin will provide multiple bubble nucleation sites, strongly promoting active two-phase heat transfer over the entire fin surface. This surface enhancement is expected to lead to significant increases in performance over conventional heat sinks. This experimental analysis characterizes the thermal performance of the carbon-fiber heat sink in two-phase closed loop thermosyphon operation using FC72 as the operating fluid. The influence of power load, thermosyphon fill volume and condenser operating temperature on the overall thermal performance is examined. The results of this experiment provide significant insight into the possible implementation and benefits of carbon fiber heat sink technology in two-phase flow leading to significant improvements in thermal management strategies for advanced electronics.

Experimental Validation of PRHR System for Low Temperature and Low Pressure Pool-Type LWR Using Thermosyphon

2014 ◽  
Author(s):  
Jangsik Moon ◽  
Byung-Hyun You ◽  
Yong Hun Jung ◽  
Yong Hoon Jeong
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Experimental Validation ◽  
Cooling System ◽  
Low Pressure ◽  
Calculation Model ◽  
Working Fluid ◽  
Primary System ◽  
Two Phase ◽  
Pool Type

PRHR system for low temperature and low pressure pool-type LWR, AHR400 is designed by two-phase closed thermosyphon and experimental validation is conducted. AHR400 is dedicated only to heat generation used in seawater desalination and operation temperature and pressure. LBLOCA is not considered as DBA due to no pipeline in primary system. There are LOHS and SBO for DBAs and PRHR system reduces damage during DBAs. Design of the PRHR system follows Direct Reactor Auxiliary Cooling System (DRACS) type. Two-phase closed thermosyphon, which uses phase change of working fluid, is applied to the PRHR system and the heat transfer in thermosyphon are analyzed by thermal resistance calculation model. Experimental thermosyphon that has similar thermal condition with the thermosyphon in designed PRHR system was explored for validation. The results show that the evaporation model overestimates heat transfer rate on the evaporator region.

Thermal Design and Optimization of Harsh Environment Power Electronics in Natural Convection Heat Transfer

2003 ◽  
Author(s):  
Mehmet Arik ◽  
Manoj Nagulapally ◽  
Steven Brzozowski ◽  
John Glaser
Keyword(s):  
Heat Transfer ◽  
Power Electronics ◽  
Thermal Management ◽  
Heat Sink ◽  
Performance Enhancement ◽  
Cooling System ◽  
Thermal Design ◽  
Harsh Environment ◽  
Air Cooling ◽  
Heat Spreader

A study of thermal management of a harsh environment power electronics system is presented. The thermal environments were found to be between 65 °C and 90 °C that is considerably higher than many traditional electronics applications. A modular, low cost, and passive air-cooling system was desired. An analytical model was developed to obtain the heat transfer characteristics. Further performance verification of the thermal management solution was completed using a commercially available CFD tool. A small footprint area for thermal design of the power electronics connected with an electrically isolating low-conductivity material to the heat sink increased the challenge. A further thermal performance enhancement was achieved with the addition of a heat spreader between power electronics and the heat sink, and optimization of the heat spreader was achieved by utilizing FEM technique.

scholarly journals Analysis and Comparison of Some Low-Temperature Heat Sources for Heat Pumps

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1853 ◽  
Author(s):  
Pavel Neuberger ◽  
Radomír Adamovský
Keyword(s):  
Heat Transfer ◽  
Low Temperature ◽  
Heat Source ◽  
Heat Pump ◽  
Heat Exchangers ◽  
Ambient Air ◽  
Heat Transfer Fluid ◽  
Heat Sources ◽  
Ground Heat Exchangers ◽  
Temperature Heat

The efficiency of a heat pump energy system is significantly influenced by its low-temperature heat source. This paper presents the results of operational monitoring, analysis and comparison of heat transfer fluid temperatures, outputs and extracted energies at the most widely used low temperature heat sources within 218 days of a heating period. The monitoring involved horizontal ground heat exchangers (HGHEs) of linear and Slinky type, vertical ground heat exchangers (VGHEs) with single and double U-tube exchanger as well as the ambient air. The results of the verification indicated that it was not possible to specify clearly the most advantageous low-temperature heat source that meets the requirements of the efficiency of the heat pump operation. The highest average heat transfer fluid temperatures were achieved at linear HGHE (8.13 ± 4.50 °C) and double U-tube VGHE (8.13 ± 3.12 °C). The highest average specific heat output 59.97 ± 41.80 W/m2 and specific energy extracted from the ground mass 2723.40 ± 1785.58 kJ/m2·day were recorded at single U-tube VGHE. The lowest thermal resistance value of 0.07 K·m2/W, specifying the efficiency of the heat transfer process between the ground mass and the heat transfer fluid, was monitored at linear HGHE. The use of ambient air as a low-temperature heat pump source was considered to be the least advantageous in terms of its temperature parameters.

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