Server-Rack Air Flow and Heat Transfer Interactions in Data Centers

2007 ◽  
Author(s):  
S. P. Tan ◽  
K. C. Toh ◽  
Y. W. Wong
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Data Center ◽  
Vertical Plane ◽  
Pressure Profile ◽  
Design Data ◽  
Flow And Heat Transfer ◽  
Pressure Profiles

The current study focuses on modeling the server-rack airflow and heat transfer interaction in a data center. In a typical computing facility, the computing requirements are often gradually built-up. For example, in this instance, two servers are placed in a rack designed for a six-server stack. Each server will be separately modeled to the required specifications, and also so that their numbers and placement can be changed. The mass flow rate through the server is determined by examining how pressure profiles develop at the inlet and outlet. This mass flow rate then becomes the input into the rack model. The air inflow temperatures at the front and rear grills were obtained from experiments. The pressure profile into and out of the servers were extracted from the rack model and substituted back into the server model. Iteration continues till an acceptable level of convergence is obtained. To validate the models, experiments were carried out using thermocouples arranged in a 3 × 3 grid on a vertical plane between the exit of the server and the rear cabinet wall of the rack. The results showed that the modeling had captured the essence of the flow and heat transfer interaction. The temperature and pressure profile at the rack inlet and outlet, although in a segmented form, have performed adequately to obtain a good approximation of the flow and temperature distribution within the server/rack. The methodology of passing parameters at the server-rack level using a segmented pressure profile has been established. A similar rack-room level interaction will subsequently be developed. In essence, the methodology is equivalent to replacing the server in the rack and the rack in the room with combined flow network - thermal models. But because of the coupled nature of these two different length scale systems, the models are obtained through an iterative process. The approach enables various combinations of servers and racks to be studied quickly for any undesirable effects of off-design data center operation or layout.

Investigations on the Effect of Blade Angle on Ventilated Brake Disc Using CFD

2005 ◽  
Author(s):  
Kannan M. Munisamy ◽  
Hanan Mokhtar ◽  
Hasril Hasini ◽  
Mohd Zamri Yusof ◽  
Mohd Azree Idris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Linear Trend ◽  
Brake Disc ◽  
Blade Angle ◽  
Flow And Heat Transfer

This paper presents the investigation on the effect of blade angle to the mass flow and heat transfer coefficient of a ventilated brake disc. Six different blade angle configurations are simulated using commercial computational fluid dynamics code, FLUENT. Important parameters such as mass flow rate of air through the ventilated blade and surface heat transfer coefficient are predicted and analyzed. Prediction shows reasonable estimation of mass flow rate and heat transfer coefficient on the disc brake. Linear trend is achieved on the mass flow and heat transfer coefficient as the vehicle speed increases. It is also concluded that the optimum mass flow and heat transfer coefficient are predicted at blade angle of 15°. The prediction provides an insight into the behavior of the air flow through the restricted passage of the brake disc design.

A CFD technique to investigate the chocked flow and heat transfer characteristic in a micro-channel heat sink

2015 ◽  
Vol 04 (02) ◽  
pp. 1550007 ◽  
Author(s):  
Ahmad Azari ◽  
Abdorrasoul Bahraini ◽  
Saeideh Marhamati
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Relative Error ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Sink ◽  
Stanton Number ◽  
Micro Channel ◽  
Flow And Heat Transfer ◽  
Channel Exit

In this research, a Computational Fluid Dynamics (CFD) technique was used to investigate the effect of choking on the flow and heat transfer characteristics of a typical micro-channel heat sink. Numerical simulations have been carried out using Spalart–Allmaras model. Comparison of the numerical results for the heat transfer rate, mass flow rate and Stanton number with the experimental data were conducted. Relatively good agreement was achieved with maximum relative error 16%, and 8% for heat transfer and mass flow rate, respectively. Also, average relative error 9.2% was obtained for the Stanton number in comparison with the experimental values. Although, the results show that the majority of heat was transferred in the entrance region of the channel, but the heat transfer in micro-channels can also be affected by choking at channel exit. Moreover, the results clearly show that, the location where the flow is choked (at the vicinity of the channel exit) is especially important in determining the heat transfer phenomena. It was found that Spalart–Allmaras model is capable to capture the main features of the choked flow. Also, the effects of choking on the main characteristics of the flow was presented and discussed.

Effect of pre-swirl nozzle closure modes on unsteady flow and heat transfer characteristics in a pre-swirl system of aero-engine

2021 ◽  
pp. 095441002110191
Author(s):  
Gaowen Liu ◽  
Zhao Lei ◽  
Aqiang Lin ◽  
Qing Feng ◽  
Yan Chen
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Temperature Drop ◽  
Thermodynamic Characteristics ◽  
Circumferential Direction ◽  
Temperature Changes ◽  
Air Supply ◽  
Cooling Air

The pre-swirl system is of great importance for temperature drop and cooling air supply. This study aims to investigate the influencing mechanism of heat transfer, nonuniform thermodynamic characteristics, and cooling air supply sensitivity in a pre-swirl system by the application of the flow control method of the pre-swirl nozzle. A novel test rig was proposed to actively control the supplied cooling air mass flow rate by three adjustable pre-swirl nozzles. Then, the transient problem of the pre-swirl system was numerically conducted by comparison with 60°, 120°, and 180° rotating disk cavity cases, which were verified with the experiment results. Results show that the partial nozzle closure will aggravate the fluctuation of air supply mass flow rate and temperature. When three parts of nozzles are closed evenly at 120° in the circumferential direction, the maximum value of the nonuniformity coefficient of air supply mass flow rate changes to 3.1% and that of temperature changes to 0.25%. When six parts of nozzles are closed evenly at 60° in the circumferential direction, the maximum nonuniformity coefficient of air supply mass flow rate changes to 1.4% and that of temperature changes to 0.20%. However, different partial nozzle closure modes have little effect on the average air supply parameters. Closing 14.3% of the nozzle area will reduce the air supply mass flow rate by 9.9% and the average air supply temperature by about 1 K.

Heat Transfer and Flow Friction Characteristics for Compact Cold Plates

2003 ◽  
Vol 125 (1) ◽  
pp. 104-113 ◽  
Author(s):  
Chang-Yuan Liu ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Thermal Resistance ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Average Nusselt Number ◽  
Cold Plate ◽  
Air Mass

Both experimental and theoretical investigations on the heat transfer and flow friction characteristics of compact cold plates have been performed. From the results, the local and average temperature rises on the cold plate surface increase with increasing chip heat flux or decreasing air mass flow rate. Besides, the effect of chip heat flux on the thermal resistance of cold plate is insignificant; while the thermal resistance of cold plate decreases with increasing air mass flow rate. Three empirical correlations of thermal resistance in terms of air mass flow rate with a power of −0.228 are presented. As for average Nusselt number, the effect of chip heat flux on the average Nusselt number is insignificant; while the average Nusselt number of the cold plate increases with increasing Reynolds number. An empirical relationship between Nu¯cp and Re can be correlated. In the flow frictional aspect, the overall pressure drop of the cold plate increases with increasing air mass flow rate; while it is insignificantly affected by chip heat flux. An empirical correlation of the overall pressure drop in terms of air mass flow rate with a power of 1.265 is presented. Finally, both heat transfer performance factor “j” and pumping power factor “f” decrease with increasing Reynolds number in a power of 0.805; while they are independent of chip heat flux. The Colburn analogy can be adequately employed in the study.

scholarly journals Performance Evaluation of a Prototype Solar Collector Using Convex Lenses for Varying Mass Flow Rate of the Heat Transfer Fluid

2015 ◽  
Vol 2 (7) ◽  
pp. 40-43
Author(s):  
Pramod Kumar Trivedi ◽  
Jitendra Jayant ◽  
Kamal Kant Vashistha ◽  
Tiwari A C
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Solar Collector ◽  
Heat Transfer Fluid ◽  
Varying Mass

scholarly journals Thermal Characteristics Analysis on Multi- Heat Pipe Induced Heat Exchanger

2019 ◽  
Vol 9 (2S2) ◽  
pp. 143-147 ◽  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Pipe ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Cold Water ◽  
Hot Water ◽  
Working Fluid ◽  
Physical Parameters

In this investigation of multi heat pipe induced in heat exchanger shows the developments in heat transfer is to improve the efficiency of heat exchangers. Water is used as a heat transfer fluid and acetone is used as a working fluid. Rotameter is set to measure the flow rate of cold water and hot water. To maintain the parameter as experimental setup. Then set the mass flow rate of hot water as 40 LPH, 60LPH, 80 LPH, 100LPH, 120 LPH and mass flow rate of cold water as 20 LPH, 30 LPH, 40 LPH, 50 LPH, and 60 LPH. Then 40 C, 45 ºC, 50 ºC, 55 C, 60 ºC are the temperatures of hot water at inlet are maintained. To find some various physical parameters of Qc , hc , Re ,, Pr , Rth. The maximum effectiveness of the investigation obtained from condition of Thi 60 C, Tci 32 C and 100 LPH mhi, 60 LPH mci the maximum effectiveness attained as 57.25. Then the mhi as 100 LPH, mci as 60 LPH and Thi at 40 C as 37.6%. It shows the effectiveness get increased about 34.3 to the maximum conditions.

scholarly journals ANALYSIS OF EVAPORATOR EFFECTIVENESS ON 1/2 CYCLE REFRIGERATION SYSTEMS: A CASE STUDY ON LPG FUELED VEHICLES

2020 ◽  
Vol 82 (3) ◽  
Author(s):  
Muji Setiyo ◽  
Budi Waluyo ◽  
Nurkholis Hamidi
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Exchange Process ◽  
Cooling Curve ◽  
Heat Exchange Process ◽  
Heat Transfer Capacity ◽  
The Ideal

The ½ cycle refrigeration system on LPG fueled vehicles has a significant cooling effect. However, the cooling is very dependent on the heat exchange process in the evaporator. Therefore, this paper analyses the deviation of the actual cooling curve from the ideal scenario carried out on a laboratory scale. The analytical method used is the calculation of the effectiveness of the evaporator, which compares the actual to the potential heat transfer capacity. The LPG flow rate was varied from 1-6 g/s, while the evaporation pressure ranged between 0.05, 0.10, and 0.15 MPa, which applied to compact type evaporators with dimensions of 262 ´ 200 mm, with a thickness of 65 mm. The research results confirm that the higher the LPG mass flow rate, the lower the heat transfer effectiveness. At the higher LPG mass flow rate, heat transfer occurs less optimally,  due to incomplete evaporation of LPG in the evaporator.

Conjugate Heat Transfer Analysis on Generic Rim Seal Configurations in Rotor-Stator System

2018 ◽  
Author(s):  
Xingyun Jia ◽  
Liguo Wang ◽  
Qun Zheng ◽  
Hai Zhang ◽  
Yuting Jiang
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Conjugate Heat Transfer ◽  
Heat Transfer Analysis ◽  
Minimum Mass ◽  
Aerodynamic Efficiency ◽  
Axial Clearance ◽  
The Impact

Performance of generic rim seal configurations, axial-clearance rim seal (ACS), radial-clearance rim seal (RCS), radial-axial clearance rim seal (RACS) are compared under realistic working conditions. Conjugate heat transfer analysis on rim seal is performed in this paper to understand the impact of ingestion on disc temperature. Results show that seal effectiveness and cooling effectiveness of RACS are the best when compared with ACS and RCS, the minimum mass flow rate for seal of RACS is 75% of that of RCS, and 34.6% of ACS. Authors compare the disc temperature distribution between different generic rim seal configurations where the RACS seems to be favorable in terms of low disc temperature. In addition, RACS has higher air-cooled aerodynamic efficiency, minimizing the mainstream performance penalty when compared with ACS and RCS. Corresponding to the respective minimum mass flow rate for seal, the air-cooled aerodynamic efficiency of RACS is 23.71% higher than that of ACS, and 12.79% higher than the RCS.

An Experimental Study on Cryogenic Spray Quenching of a Circular Metal Disk II. Chilldown Efficiency and Effects of Coating and Flow Pulsing

2021 ◽  
Author(s):  
Jun Dong ◽  
Hao Wang ◽  
Samuel Darr ◽  
Jason Hartwig ◽  
Jacob Chung
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Liquid Nitrogen ◽  
Mass Flow ◽  
Flow Rate ◽  
Continuous Flow ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Teflon Coating ◽  
Bare Surface

Abstract This is the second part of a two-part series that presents the results of liquid nitrogen spray quenching of a Stainless Steel disc. The results of continuous-flow spray chilldown of a bare surface disc are summarized first that serves as the baseline information for evaluating the effects of disc surface coating and pulse flow. We found that for continuous-flow spray chilldown of a bare surface disc, the chilldown efficiency is mainly a function of the average mass flow rate with the trend of decreasing efficiency with increasing mass flow rate. Additional experiments were performed to evaluate the enhancement of cryogenic spray quenching by three techniques: 1. Using intermittent pulse sprays on SS bare surface, 2. Coating the SS surface with a layer of low thermal conductivity Teflon film, and 3. Spraying liquid nitrogen intermittently on the coated SS surface. In general, the results indicate that all three methods effectively produced higher spray thermal efficiencies and reduced liquid nitrogen mass consumption. However, it was also found that the Teflon coating was more effective than the flow pulsing due to that the Teflon coating induced a large surface temperature drop at the beginning of the chilldown that allowed the quenching to move quickly from poor heat transfer film boiling to efficient heat transfer transition and nucleate boiling regimes. This quick transition shortens the film boiling period, thus facilitates the switch to much higher heat transfer transition boiling and nucleate boiling periods earlier to complete the chilldown process faster.

scholarly journals Effect of nanofluid properties and mass-flow rate on heat transfer of parabolic-trough concentrating solar system

2019 ◽  
Vol 16 (1) ◽  
pp. 33-44 ◽  
Author(s):  
M.K. Islam ◽  
Md. Hasanuzzaman ◽  
N.A. Rahim ◽  
A. Nahar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Parabolic Trough ◽  
Concentrated Solar Energy

Sustainable power generation, energy security, and global warming are the big challenges to the world today. These issues may be addressed through the increased usage of renewable energy resources and concentrated solar energy can play a vital role in this regard. The performance of a parabolic-trough collector’s receiver is here investigated analytically and experimentally using water based and therminol-VP1based CuO, ZnO, Al2O3, TiO2, Cu, Al, and SiC nanofluids. The receiver size has been optimized by a simulation program written in MATLAB. Thus, numerical results have been validated by experimental outcomes under same conditions using the same nanofluids. Increased volumetric concentrations of nanoparticle is found to enhance heat transfer, with heat transfer coefficient the maximum in W-Cu and VP1-SiC, the minimum in W-TiO2 and VP1-ZnO at 0.8 kg/s flow rate. Changing the mass flow rate also affects heat transfer coefficient. It has been observed that heat transfer coefficient reaches its maximum of 23.30% with SiC-water and 23.51% with VP1-SiC when mass-flow rate is increased in laminar flow. Heat transfer enhancement drops during transitions of flow from laminar to turbulent. The maximum heat transfer enhancements of 9.49% and 10.14% were achieved with Cu-water and VP1-SiC nanofluids during turbulent flow. The heat transfer enhancements of nanofluids seem to remain constant when compared with base fluids during either laminar flow or turbulent flow.

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