Testing of Rectangular Channels With Perturbed Entrances for Temperature Difference Under Constant Heat Flux

2011 ◽  
Author(s):  
Jacek Marek Matyja ◽  
Tunde Bello-Ochende
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Cold Water ◽  
Constant Heat Flux ◽  
Entrance Region ◽  
Average Error ◽  
Transfer Performance ◽  
Rectangular Duct ◽  
Constant Heat

In this paper convective heat transfer performance of various duct geometries are compared using theoretical and experimental analyses. The experiments stretch further by perturbing the entrance region of the 2:1 rectangular duct (both inwards and outwards) and to obtain the effect on heat transfer performance. The cross-sectional area and length of the ducts are fixed and constant heat flux is applied to the ducts while cold water is used as the flow stream. The laminar flow regime is analysed. The theoretical and experimental cases are in agreement, with slight deviances attributed to certain assumptions made during the theoretical analysis and non-ideal testing conditions. The analyses concludes that perturbing the entrance region of a standard rectangular duct, both inwards and outwards, has a visible increase in heat transfer performance. The inward perturbed duct shows the highest increase in performance. The average variation between the theoretical and experimental case is about 18% for constant heat flux. The average error imposed on the results due experimental equipment is about 3% for constant heat flux experiments.

Laminar Slug Flow: Heat Transfer Characteristics With Constant Heat Flux Boundary

2009 ◽  
Author(s):  
P. A. Walsh ◽  
E. J. Walsh ◽  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Heat Transfer Performance ◽  
Constant Heat Flux ◽  
Transfer Performance ◽  
Segmented Flow ◽  
Constant Heat ◽  
Flux Boundary Condition ◽  
Flow Heat

The problem of elevated heat flux in modern electronics has led to the development of numerous liquid cooling devices which yield superior heat transfer coefficients over their air based counterparts. This study investigates the use of liquid/gas slug flows where a liquid coolant is segregated into discrete slugs, resulting in a segmented flow, and heat transfer rates are enhanced by an internal circulation within slugs. This circulation directs cooler fluid from the center of the slug towards the heated surface and elevates the temperature difference at the wall. An experimental facility is built to examine this problem in circular tube flow with a constant wall heat flux boundary condition. This was attained by Joule heating a thin walled stainless steel tube. Water was used as the coolant and air as the segregating phase. The flow rates of each were controlled using high precision syringe pumps and a slug producing mechanism was introduced for segmenting the flow into slugs of various lengths at any particular flow rate. Tube flows with Reynolds numbers in the range 10 to 1500 were examined ensuring a well ordered segmented flow throughout. Heat transfer performance was calculated by measuring the exterior temperature of the thin tube wall at various locations using an Infrared camera. Nusselt number results are presented for inverse Graetz numbers over four decades, which spans both the thermally developing and developed regions. The results show that Nu in the early thermally developing region are slightly inferior to single phase flows for heat transfer performance but become far superior at higher values of inverse Gr. Additionally, the slug length plays an important role in maximizing Nusselt number in the fully developed region as Nu plateaus at different levels for slugs of differing lengths. Overall, this paper provides a new body of experimental findings relating to segmented flow heat transfer in constant heat flux tubes without boiling. Put abstract text here.

scholarly journals Laminar convective heat transfer for in-plane spiral coils of noncircular cross sections ducts: A computational fluid dynamics study

2012 ◽  
Vol 16 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jundika Kurnia ◽  
Agus Sasmito ◽  
Arun Mujumdar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Cross Sections ◽  
Wall Temperature ◽  
Heat Transfer Performance ◽  
Constant Heat Flux ◽  
Uniform Heat Flux ◽  
Transfer Performance ◽  
Constant Wall Temperature ◽  
Flux Boundary Condition

The objective of this study was to carry out a parametric study of laminar flow and heat transfer characteristics of coils made of tubes of several different cross-sections e.g. square, rectangular, half-circle, rectangular and trapezoidal. For the purpose of ease of comparison, numerical experiments were carried out base on a square-tube Reynolds number of 1000 and a fixed fluid flow rate while length of the tube used to make coils of different diameter and pitch was held constant. A figure of merit was defined to compare the heat transfer performance of different geometry coils; essentially it is defined as total heat transferred from the wall to the surroundings per unit pumping power required. Simulations were carried out for the case of constant wall temperature as well as constant heat flux. In order to allow reasonable comparison between the two different boundary conditions - constant wall temperature and constant wall heat flux - are tested; the uniform heat flux boundary condition was computed by averaging the heat transferred per unit area of the tube for the corresponding constant wall temperature case. Results are presented and discussed in the light of the geometric effects which have a significant effect on heat transfer performance of coils.

EXPERIMENTAL STUDY ON THERMAL TRANSPORT PHENOMENON OF NANOFLUIDS AS WORKING FLUID IN HEAT EXCHANGER

2014 ◽  
Vol 22 (01) ◽  
pp. 1450005 ◽  
Author(s):  
SHUICHI TORII
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Horizontal Tube ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Transfer Performance ◽  
Nanoparticles Concentration ◽  
Transfer Behavior

This paper aims to study the convective heat transfer behavior of aqueous suspensions of nanoparticles flowing through a horizontal tube heated under constant heat flux condition. Consideration is given to the effects of particle concentration and Reynolds number on heat transfer enhancement and the possibility of nanofluids as the working fluid in various heat exchangers. It is found that (i) significant enhancement of heat transfer performance due to suspension of nanoparticles in the circular tube flow is observed in comparison with pure water as the working fluid, (ii) enhancement is intensified with an increase in the Reynolds number and the nanoparticles concentration, and (iii) substantial amplification of heat transfer performance is not attributed purely to the enhancement of thermal conductivity due to suspension of nanoparticles.

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