Heat Transfer Characteristics of a Train of Droplets Impinging Over a Hot Surface: From Film Evaporation to Leidenfrost Point

Author(s):  
Ganesh Guggilla ◽  
Arvind Pattamatta ◽  
Ramesh Narayanaswamy

Abstract Due to the advancements in computing services such as machine learning and artificial intelligence, high-performance computing systems are needed. Consequently, the increase in electron chip density results in high heat fluxes and required sufficient thermal management to maintain the servers. In recent times, the liquid cooling techniques become prominent over air cooling as it has significant advantages. Spray cooling is one such efficient cooling process which can be implemented in electronics cooling. To enhance the knowledge of the process, detailed studies of fundamental mechanisms involved in spray cooling such as single droplet and multiple droplet interactions are required. The present work focuses on the study of a train of droplets impinging over a heated surface using FC-72 liquid. The surface temperature is chosen as a parameter, and the Dynamic Leidenfrost point (DLP) for the present impact conditions is identified. Spread hydrodynamics and heat transfer characteristics of these consecutively impinging droplets till the Leidenfrost temperature, are studied and compared.

2021 ◽  
Author(s):  
Ganesh Guggilla ◽  
Ramesh Narayanaswamy ◽  
Peter Stephan ◽  
Arvind Pattamatta

Abstract High-performance computing systems are needed in advanced computing services such as machine learning and artificial intelligence. Consequently, the increase in electron chip density results in high heat fluxes and requires good thermal management to maintain the servers. Spray cooling using liquid offers higher heat transfer rates and is efficient when implemented in electronics cooling. Detailed studies of fundamental mechanisms involved in spray cooling, such as single droplet and multiple droplet interactions, are required to enhance the process's knowledge. The present work focuses on studying a train of two FC-72 droplets impinging over a heated surface. Experimental investigation using high-speed photography and infrared thermography is conducted. Simultaneously, numerical simulations using opensource CFD package, OpenFOAM are carried out, emphasizing the significance of contact angle hysteresis. The surface temperature is chosen as a parameter, and different boiling regimes along with Dynamic Leidenfrost point (DLP) for the present impact conditions are identified. Spreading hydrodynamics and heat transfer characteristics of these consecutively impinging droplets till the Leidenfrost temperature, are studied and compared.


Author(s):  
Ge Zhu ◽  
Qincheng Bi ◽  
Jianguo Yan ◽  
Qizheng Yuan ◽  
Haicai Lv ◽  
...  

Experiments of heat transfer characteristics of subcooled water flowing in vertical circular channels, which were off-center in rectangular blocks, were carried out under high heat fluxes up to the ITER requirements. The heating flux distributions of the channels were non-uniform in the circumferential direction, which were obtained by electrically heating the blocks directly. Two types of channels were used: smooth channel and twisted tapes channel. The surface temperature of the rectangular blocks was measured by infrared camera and thermocouples. Effect of the system pressure, mass flow rate, inlet subcooling, and equivalent heat fluxes on heat transfer were all investigated. The main attention was paid to the subcooled water heat transfer under non-uniform heating flux, and the effect of twisted tapes. Results show that subcooled boiling is more likely to become the dominant factor under the conditions of lower mass flow rates, higher heat fluxes and lower system pressures. Twisted tapes can enhance the heat transfer, which is more evident in high heat fluxes. The temperature fields in the block were calculated with a Computational Fluid Dynamics (CFD) method to obtain, which were consistent with the experimental results.


Volume 3 ◽  
2004 ◽  
Author(s):  
Ratnesh K. Sharma ◽  
Cullen E. Bash ◽  
Chandrakant D. Patel

Increases in microprocessor power density along with an accompanying spatial variation in power density has been well documented in recent years. These combined factors pose a severe challenge for the provisioning of cooling resources at the microprocessor level. The use of thermal inkjet technology to precisely supply coolant onto the surface of a microprocessor has the potential to address this problem in a chip-scale form factor. By providing coolant when and where it is needed on the surface of a chip or package, very high critical heat fluxes can be obtained in an energy efficient manner in a minimum of physical space. In this paper, the unique heat transfer characteristics of inkjet assisted spray cooling of a heated surface are investigated. Sprays of water are used to cool heated surfaces ranging from 281mm2 to 35mm2. Several experiments are conducted at different nozzle-to-surface distances to measure critical heat flux (CHF) at different flow rates and firing frequencies. The impact of volumetric flux variation on CHF is studied. CHF data, measured over broad range of operating conditions is correlated to volumetric flux and liquid properties. Flow visualization studies are also conducted to understand the vapor-liquid interaction at the heater surface and the intermediate region. Jet breakup length studies are carried out to understand the propagation of Rayleigh instabilities in the spray jets and, subsequent, formation of liquid drops. CHF data combined with fluid flow studies have been used to optimize the nozzle-to-surface clearance. Results obtained from these experiments are invaluable for the design of micro scale spray cooling devices for chips.


Author(s):  
U. Oh ◽  
Jun Ishimoto ◽  
Naoki Harada ◽  
Daisuke Tan

The fundamental characteristics of heat transfer and cooling performance of micro-solid nitrogen particulate spray impinging on a heated substrate were numerically investigated and experimentally measured by a new type of integrated computational-experimental technique. The employed CFD based on the Euler-Lagrange model is focused on the cryogenic spray behavior of atomized particulate micro-solid nitrogen and also on its ultra-high heat flux cooling characteristics. Based on the numerically predicted performance, a new type of cryogenic spray cooling technique for application to a ultra-high heat power density device was developed. In the present integrated computation, it is clarified that the cryogenic micro-solid spray cooling characteristics are affected by several factors of the heat transfer process of micro-solid spray which impinges on heated surface as well as by atomization behavior of micro-solid particles.


Metals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 61 ◽  
Author(s):  
Yazhu Zhang ◽  
Zhi Wen ◽  
Zengwu Zhao ◽  
Chunbao Bi ◽  
Yaxiang Guo ◽  
...  

Spray cooling is a key technology in the continuous casting process and has a marked influence on the product quality. In order to obtain the heat transfer characteristics, which are closer to the actual continuous casting to serve the design, prediction and simulation, we created an experimental laboratory setup to investigate heat transfer characteristics of air mist spray cooling during the continuous casting secondary cooling process. A 200-mm thick sample of carbon steel was heated above 1000 °C, and then cooled in a water flux range of 0.84 to 3.0 L/(m2∙s). Determination of the boundary conditions involved experimental work comprising an evaluation of the thermal history and the heat flux and heat transfer coefficient (HTC) at the casting surface using inverse heat conduction numerical schemes. The results show that the heat fluxes were characterized via boiling curves that were functions of the slab surface temperatures. The heat flux was determined to be 2.9 × 105 W/m2 in the range of 1100 to 800 °C with a water flux of 2.1 L/(m2∙s). The critical heat flux increased with the increase of water flux. The HTC was close to a linear function of water flux. We also obtained the relation between the HTC and the water flux in the transition boiling region for surface temperatures of 850 to 950 °C.


2015 ◽  
Vol 813-814 ◽  
pp. 782-786
Author(s):  
C. Anbumeenakshi ◽  
M.R. Thansekhar ◽  
M. Satheeshkumar ◽  
R. Vishnu Gayathri

The microchannel cooling technique appears to be a viable solution to high heat rejection requirements of today’s high-power electronic devices. The thermal design of the small electronics cooling devices is a key issue that needs to be optimized in order to keep the system temperatures at certain levels. Thus the need of microchannel became vital. This present work investigates the experimental work conducted in a coated rectangular microchannel heat sink of hydraulic diameter of 0.763 mm for a heat input of 250 to 1020 Watt with water to study the heat transfer characteristics with two types of header arrangement such as rectangular header and trapezoidal header. The header plays a significant role in distributing the water in to the channels. The uniform distribution of water leads to uniform heat transfer in microchannels. From the experimental results carried with two types of header arrangements, it was found that coated rectangular microchannel with trapezoidal header gives better heat transfer characteristics for the range of heat inputs.


2000 ◽  
Author(s):  
Jungho Lee ◽  
Jungho Kim ◽  
Kenneth T. Kiger ◽  
Bohumil Horacek

Abstract Heat transfer by phase change is an attractive method of cooling since large amounts of heat can be removed with relatively small temperature differences. Droplet cooling is one method whereby very high heat transfer rates coupled with good temperature uniformity across surfaces can be provided, which is important in microelectronics where even small temperature gradients across the chip can cause component failure. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. Significant time and space resolved variations in wall heat fluxes were exhibited during boiling and evaporation. The droplet behavior with wall interaction was simultaneously viewed using a high-speed digital video camera. Local heat transfer measurements can provide much needed information regarding the relevant wall heat transfer mechanisms by pinpointing when and where large amounts of heat are removed. This study should result in benchmark data against which numerical calculations can be compared.


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