Influence of the switch -over period of an alternately active bi -heater on heat transfer enhancement inside a cavity Anish Pal1 Riddhideep Biswas1 Sourav Sarkar1 Aranyak Chakravarty 2

2025-04-27 0 0 1.02MB 29 页 10玖币

侵权投诉

Influence of the switch-over period of an alternately active bi-heater on

heat transfer enhancement inside a cavity

Anish Pal1,#, Riddhideep Biswas1, Sourav Sarkar1, Aranyak Chakravarty 2,*,

Achintya Mukhopadhyay1

1Department of Mechanical Engineering, Jadavpur University, Kolkata, India

2School of Nuclear Studies & Application, Jadavpur University, Kolkata, India

*Corresponding author: aranyak.chakravarty@jadavpuruniversity.in

#Present affiliation: Department of Mechanical Engineering, University of Illinois at Chicago,

Chicago, USA

Abstract

Increasing power demands on multicore processors necessitate effective thermal management.

The present study investigates natural convection heat transfer inside a square cavity with an

alternately active bi-heater that mimics two cores of a dual-core processor. Pulsating heat flux

condition is implemented on two discrete heaters with a certain switching frequency. The heat

transfer characteristics have been investigated for Prandtl number =0.71 and Rayleigh number

in the range of 103 - 106 using OpenFOAM. The results obtained for alternative active heaters

configuration have been compared with that of the steady single heater and steady double-

symmetric heaters subjected to the same heat flux. The alternately active heater configuration

showed better heat transfer characteristics than a single steady heater for all switchover periods,

and better than a double-symmetric heater for low switchover periods. However, it is found

that for higher values of the switchover period, the maximum temperature of alternately active

heaters configuration touches the temperature of steady single heater. This threshold

switchover period has been determined using a scale analysis. The threshold switchover periods

determined from scale analysis are consistent with the results obtained from numerical

simulations for different Rayleigh numbers and heater lengths.

INTRODUCTION

Technological improvements in computing systems have resulted in increasing usage of

systems with multi-core processors. Along with improvement in computing performance,

multi-core systems generate significantly larger amounts of heat which needs to be

continuously removed. This is only possible with the help of an effective thermal management

system which also ensures longevity of the system. One of the most effective means of ensuring

proper thermal management of such systems is through natural convection. Other means such

as liquid cooling and air-cooled heat sinks, although feasible, increase the cost as well as the

system weight which hinders optimisation [1]. On the other hand, the efficiency of passive heat

removal through natural convection needs to be improved in order to meet the requirements of

heat removal from high power-density electronic components.

A large number of studies are available in literature which investigated natural convective heat

transfer inside a rectangular cavity [2-16]. Several aspects of natural convection heat transfer,

such as heater position, cavity aspect ratio, and non-uniform heat flux, have been studied in

detail. However, many of these studies have considered the heaters at steady-state constant

temperature. A multi-core processor, however, involves switching of jobs between different

cores leading to localized pulsating heating depending on the core usage. Proper

characterization of such multi-core systems, therefore, requires consideration of the transient

pulsating heating of the cores. Studies on the effects of localized pulsed heating are, however,

limited [17]. The resonance effect between contained natural convection and pulsating wall

heating was described by Lage and Bejan [18]. Cheikh et al [19] reported the effect of aspect-

ratio on natural convection in a cavity due to pulsed heating. Bae and Hyun [20] reported heat

transfer enhancement due to implementation of pulsed heating in a vertical rectangular cavity

with three discrete heaters. It was found that transient-stage heating temperatures could exceed

corresponding steady-state values at higher Raleigh numbers. Mahapatra et al. [21] reported

and quantified heat transfer enhancement associated with pulsed heating employing constant

temperature conditions for the heater. Furthermore, the analysis shows that a decrease in time

period results in increased heat transfer.

In the present study, a pulsating heat flux boundary condition is imposed on the heaters (instead

of a constant temperature condition) inside a bottom heated square cavity. This emulates the

job scheduling between the cores of a dual core processor. Study has been conducted for a

range of Ra (104 to 106) for three different heater characteristics - alternately active heater,

steady asymmetric and steady double asymmetric heater. The major objective of this work is

to identify a suitable range of the switchover time period for the alternately active heaters for

which the heat transfer can be augmented. Furthermore, it is worth mentioning that the limited

studies that have reported heat transfer enhancement due to implementation of pulsed heating

have not mentioned the minimum switch-over frequency that needs to be maintained in order

to obtain the heat transfer augmentation. Proper quantification of the minimum switchover

frequency is imperative because not adhering to this minimum frequency of alteration will not

provide any heat-transfer augmentation. The work not only implements a pulsating heat flux

boundary, which is a more authentic representation of the heaters than studies involving a

temperature boundary condition, but also endeavours to enumerate the switchover frequency

that keeps the maximum system temperature below the permissible limit in the cavity for any

combination of Ra and heater length. A rigorous scale analysis has been carried out in this work

to ascertain this minimum switching frequency. This information allows the designer to

determine the cooling rate of the electronic equipment with an aim to estimate the optimum

switchover time for maximum possible heat transfer. The results of this analysis would provide

the necessary information for better scheduling of jobs on a multi-core processor to ensure

maximum heat transfer within the permissible junction temperature limit.

PROBLEM DESCRIPTION

Physical configuration and assumptions

The modelled system of heaters and the associated flow domain is depicted in Fig. 1 for the

various configurations studied. The heaters represent the cores of a dual core processor and are

assumed to be present on the bottom wall of a square cavity. The side walls of the cavity are

kept isothermal at a lower temperature, while the top and bottom walls of the cavity are

assumed to be adiabatic. All cavity walls are assumed to be rigid and impermeable.

Three different heater configurations are considered. The first configuration (Case 1, Fig. 1a)

pertains to the case of alternate switching of heaters. Two heaters (H1 and H2) of equal length

( & ) and placed apart at a distance  (  are alternatively subjected to uniform

heat flux i.e., at a particular instant of time, only a single heater is active. Active condition of a

heater corresponds to the imposition of uniform heat flux, while in inactive state the heater is

subjected to adiabatic boundary condition. The alternate activation and deactivation of the

heaters is shown in Fig. 2 as a pulse graph. The second configuration (Case 2, Fig. 1b)

corresponds to steady, double symmetric heaters with both heaters remaining active for the

entire duration. Besides the heaters, all other conditions remain similar to Case 1. In order to

ensure that equivalent thermal energy is supplied to the domain as that in Case 1, each of the

two heaters are considered to be half the length ( of that considered in the Case 1

( such that  



 . The third configuration (Case 3, Fig. 1c) considers

a single steady asymmetric heater with the heater length ( being same as that in Case

The working fluid is considered to be laminar and incompressible with constant isotropic and

homogenous thermo-physical properties. The contributions of radiative heat transfer and

viscous dissipation are neglected in the energy balance. Boussinesq approximation is utilised

for modelling the natural convective effects.

Governing Equations and Boundary conditions

The governing equations for conservation of mass, momentum and energy in the cavity are

formulated based on the assumptions made and are represented by Eqs. 1-4.





 (1)

















 (2)

















 (3)











 (4)

The following scaling parameters are used to obtain the dimensionless form of the equations

(Eqs. 6-9) –





 







 (5)

 



  







 (6)













 (7)













 (8)











 (9)

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

Influenceoftheswitch-overperiodofanalternatelyactivebi-heateronheattransferenhancementinsideacavityAnishPal1,#,RiddhideepBiswas1,SouravSarkar1,AranyakChakravarty2,*,AchintyaMukhopadhyay11DepartmentofMechanicalEngineering,JadavpurUniversity,Kolkata,India2SchoolofNuclearStudies&Application,JadavpurUni...

展开>> 收起<<

Influence of the switch -over period of an alternately active bi -heater on heat transfer enhancement inside a cavity Anish Pal1 Riddhideep Biswas1 Sourav Sarkar1 Aranyak Chakravarty 2.pdf

共29页,预览5页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Influence of the switch -over period of an alternately active bi -heater on heat transfer enhancement inside a cavity Anish Pal1 Riddhideep Biswas1 Sourav Sarkar1 Aranyak Chakravarty 2

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: