Transient thermodynamic response and boiling heat transfer limit of dielectric liquids in a two-phase closed direct immersion cooling system

2021 ◽  
pp. 100986
Author(s):  
Xingping Li ◽  
Lucang Lv ◽  
Xinyue Wang ◽  
Ji Li
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Cooling System ◽  
Two Phase ◽  
Dielectric Liquids ◽  
Immersion Cooling ◽  
Heat Transfer Limit ◽  
Direct Immersion Cooling ◽  
Direct Immersion

Two Phase Flow Simulation for Nucleate Boiling Heat Transfer Calculation in Waterjacket of Diesel Engine

2011 ◽  
Author(s):  
Arash Mohammadi ◽  
Hossein Hashemi ◽  
Ali Jazayeri ◽  
Mahdi Ahmadi
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Diesel Engine ◽  
Transfer Coefficient ◽  
Cylinder Head ◽  
Boiling Heat Transfer ◽  
Cooling System ◽  
Nucleate Boiling ◽  
Two Phase ◽  
Phase Mixture

Basic understanding of the process of coolant heat transfer inside an engine is an indispensable prerequisite to devise an infallible cooling strategy. Coolant flow and its heat transfer affect the cooling efficiency, thermal load of heated components, and thermal efficiency of a diesel engine. An efficient approach to study cooling system for diesel engine is a 3D computational fluid dynamics (CFD) calculation for coolant jacket. Therefore, computer simulation can analyze and consequently optimize cooling system performance, including complex cooling jacket. In this paper a computational model for boiling heat transfer based on two-phase Mixture model flow is established. Furthermore, the phenomenon of nucleate boiling, its mathematical modeling, and its effect on heat transfer is discussed. Besides, the static, total and absolute pressure, velocity and stream lines of the flow field, heat flux, heat transfer coefficient and volume fraction of vapor distribution in the coolant jacket of a four-cylinder diesel engine is computed. Also, comparison between experimental equation (Pflaum/Mollenhauer) and two-phase Mixture model for boiling hat transfer coefficient is done and good agreement is seen. In conclusion, it is observed that at high operating temperatures, nucleate boiling occurs in regions around the exhaust port. Numerical simulation of boiling heat transfer process of cooling water jacket and temperature field in the cylinder head of the diesel engine is compared with the data measured on the engine test bench. The calculated results indicate that this method can reflect the impact of boiling heat transfer on water jacket rather accurate. Therefore, this method is benefit to improve the computational precision in the temperature field computation of a cylinder head.

Design and Performance of Novel Low-Profile Heat Sinks Created Through Additive Manufacturing

2016 ◽  
Author(s):  
Pratik KC ◽  
Sangeet Shrestha ◽  
Adarsh Radadia ◽  
Leland Weiss ◽  
Arden Moore
Keyword(s):  
Additive Manufacturing ◽  
Heat Sink ◽  
Heat Sinks ◽  
Two Phase ◽  
Printed Circuit ◽  
Immersion Cooling ◽  
Low Profile ◽  
Direct Immersion Cooling ◽  
Power Densities ◽  
Direct Immersion

Traditional thermal management techniques such as air-cooled plate- and pin-fin heat sinks are today being pushed to their limits by the increasing power densities of computing hardware (power supplies, controllers, processors, and integrated circuits). In comparison, direct immersion cooling within an alternative cooling medium such as commercial dielectric fluids offers the ability to handle high power densities while also accommodating tighter printed circuit board spacing. Together, these attributes are critical to facilitating higher computing densities. However, this type of high density setup also requires that any heat sink present be low profile so as to not obstruct adjacent printed circuit boards. Such a stringent limit on heat sink height can make achieving cooling targets challenging with existing designs. In this work, the performance of several low profile (height less than 6 mm) heat sinks of varying design are evaluated within a carefully controlled direct immersion cooling environment. Commercial copper heat sinks fabricated through conventional manufacturing (CM) approaches serve as baselines for these performance tests. These same heat sink designs are also replicated via additive manufacturing (AM) utilizing a conductive, carbon-filled printable polylactic acid (PLA) composite material. The performance of these AM heat sinks are then compared to the CM heat sinks, with special emphasis on differences in thermal conductivity between the constituent materials. Finally, novel bio-inspired heat sink designs are developed which would be difficult or impossible to achieve using CM approaches. The most promising of these designs were then created using AM and their performance evaluated for comparison. The overall goal of this is to ascertain whether the design and fabrication flexibility offered by AM can facilitate low profile heat sink designs that can meet or exceed the performance of conventional heat sinks even with perceived deficiencies in material properties for AM parts. Experiments were carried out within Novec 7100 dielectric fluid for single-phase natural convection scenarios as well as two-phase subcooled boiling conditions at atmospheric pressure. A custom test rig was constructed consisting of mirror-polished stainless steel plates and polycarbonate viewing ports to allow visual access. A rotating sample stage allows for data to be obtained at varying heat sink orientation angles from 0° to 90°. For two-phase experiments, multi-angle video capture allows for analysis of the two-phase dynamics occurring at the heat sink samples to be visualized and temporally linked to the associated temperature and heat flux data.

Cooling Characteristics of Ultrafine Cryoprobe Utilizing Convective Boiling Heat Transfer in Microchannel

2010 ◽  
Author(s):  
Junnosuke Okajima ◽  
Shigenao Maruyama ◽  
Hiroki Takeda ◽  
Atsuki Komiya ◽  
Sangkwon Jeong
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Cooling System ◽  
Capillary Tube ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling

This paper describes a novel cooling system to be applied in cryosurgery. An ultrafine cryoprobe has been developed to treat small lesions which cannot be treated by conventional cryoprobes. The main problem of the ultrafine cryoprobe is the reduction of the heat transfer rate by the small flow rate due to the large pressure drop in a microchannel and the large ratio of the surface area to the volume. In order to overcome these problems, we utilized boiling heat transfer in a microchannel as the heat transfer mechanism in the ultrafine cryoprobe. The objectives of this paper are to develop an ultrafine cryoprobe and evaluate its cooling characteristics. The ultrafine cryoprobe has a co-axial double tube structure which consists of inner and outer stainless steel tubes. The outer and inner diameters of the outer tube are 0.55mm and 0.3mm, respectively. The outer and inner diameters of the inner tube are 0.15mm and 0.07mm, respectively. The inner tube serves as a capillary tube to change the refrigerant from liquid state to two-phase flow. Furthermore, two-phase flow passes through the annular passage between the inner and out tube. The hydraulic diameter of the annular passage is 0.15mm. Furthermore, HFC-23 (Boiling point is −82.1°C at 1atm) is used as the refrigerants. The temperature of the ultrafine cryoprobe was measured. The lowest temperatures were −45°C in the insulated condition and −35°C in the agar at 37°C (which simulates in vivo condition). Furthermore, the frozen region which is generated around the ultrafine cryoprobe was measured 5mm from the tip of cryoprobe at 120s, and resulted to be 3mm in diameter. Moreover, the change of the refrigerant state is calculated by using the energy conservation equation and the empirical correlations of two-phase pressure drop and boiling heat transfer. As a result, the refrigerant state in the ultrafine cryoprobe depends on the external heat flux. Finally, the required geometry of the ultrafine cryoprobe to make high cooling performance is evaluated.

Pool Boiling of HFE 7200–C4H4F6O Mixture on Hybrid Micro-Nanostructured Surface

2012 ◽  
Vol 3 (4) ◽  
Author(s):  
Aravind Sathyanarayana ◽  
Pramod Warrier ◽  
Yunhyeok Im ◽  
Yogendra Joshi ◽  
Amyn S. Teja
Keyword(s):  
Heat Transfer ◽  
Heat Dissipation ◽  
Molecular Design ◽  
Pool Boiling ◽  
Dielectric Constants ◽  
Heat Transfer Fluid ◽  
Fluid Mixture ◽  
Immersion Cooling ◽  
Direct Immersion Cooling ◽  
Direct Immersion

Steadily increasing heat dissipation in electronic devices has generated renewed interest in direct immersion cooling. The ideal heat transfer fluid for direct immersion cooling applications should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by poor thermal properties like low thermal conductivity (about twice that of air) and low specific heat (same as that of air). These factors necessitate the development of new heat transfer fluids with improved heat transfer properties and applicability. C4H4F6O is a new heat transfer fluid which has been identified using computer-aided molecular design (CAMD) and knowledge-based approaches. A mixture of Novec fluid (HFE 7200) with C4H4F6O is evaluated in this study. Pool boiling experiments are performed at saturated condition on a 10 mm × 10 mm silicon test chip with CuO nanostructures on a microgrooved surface, to investigate the thermal performance of this new fluid mixture. The mixture increased the critical heat flux moderately by 8.4% over pure HFE 7200. Additional investigation is necessary before C4H4F6O can be considered for immersion cooling applications.

Visualization of Boiling Heat Transfer on Micro Porous Coated Surface in Confined Space

2013 ◽  
Author(s):  
Chien-Yuh Yang ◽  
Chien-Fu Liu
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Confined Space ◽  
Two Phase ◽  
Nucleate Boiling Heat Transfer ◽  
Coated Surface

Numerous researches have been developed for pool boiling on microporous coated surface in the past decade. The nucleate boiling heat transfer was found to be increased by up to 4.5 times than that on uncoated surface. Recently, the two-phase micro heat exchangers have been considered for high flux electronic devices cooling. The enhancement techniques for improving the nucleate boiling heat transfer performance in the micro heat exchangers have gotten more importance. Previous studies of microporous coatings, however, have been restricted to boiling in unconfined space. No studies have been made on the feasibility of using microporous coatings for enhancing boiling in confined spaces. This study provides an experimental observation of the vapor generation and leaving processes on microporous coatings surface in a 1-mm confined space. It would be helpful for understanding the mechanism of boiling heat transfer and improving the design of two-phase micro heat exchangers. Aluminum particles of average diameter 20 μm were mixed with a binder and a carrier to develop a 150 μm thickness boiling enhancement paint on a 3.0 cm by 3.0 cm copper heating surface. The heating surface was covered by a thin glass plate with a 1 mm spacer to form a 1 mm vertical narrow space for the test section. The boiling phenomenon was recorded by a high speed camera. In addition to the three boiling regimes observed by Bonjour and Lallemand [1], i.e., isolated deformed bubbles, coalesced bubbles and partial dryout at low, moderate and high heat fluxes respectively in unconfined space, a suction and blowing process was observed at the highest heat flux condition. Owing to the space confinement, liquid was sucked and vapor was expelled periodically during the bubble generation process. This mechanism significantly enhanced the boiling heat transfer performance in confined space.

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