Articulo tuberias

International Journal of Heat and Fluid Flow 29 (2008) 1029–1038

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International Journal of Heat and Fluid Flow
journal homepage: www.elsevier.com/locate/ijhff

Experimental study of heat transfer in pulsating turbulent flow in a pipe
Elsayed A.M. Elshafei, M. Safwat Mohamed, H. Mansour, M. Sakr *
Mechanical Engineering Department, MansouraUniversity, Faculty of Engineering, Mansoura 35516, Egypt

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Heat transfer characteristics of pulsating turbulent air flow in a pipe heated at uniform heat flux were experimentally investigated. The experiments were performed over a range of 104 < Re < 4 Â 104 and 6.6 6 f 6 68 Hz. This situation finds applications in modern power generation facilities andindustrial processes. With installing the oscillator downstream of the tested tube exit, results showed that Nu is strongly affected by both pulsation frequency and Reynolds number. Its local value either increases or decreases over the steady flow value. The variation is more pronounced in the entrance region than that in the downstream fully developed region. It is observed also that the relative meanNu either increases or decreases, depending on the frequency range. Although the deviations are small, it seems to be obvious at higher values of Reynolds number. The obtained heat transfer results are classified according to turbulent bursting model and looked to be qualitatively consistent with previous investigations. Ó 2008 Elsevier Inc. All rights reserved.

Article history: Received 5February 2007 Received in revised form 12 February 2008 Accepted 31 March 2008 Available online 21 May 2008 Keywords: Pulsating flow in a pipe Convective heat transfer Turbulent flow

1. Introduction There are many engineering practical situations where heat is being transferred under conditions of pulsating and reciprocating flows such as the operation of modern power producing facilities andindustrial equipment used in metallurgy, aviation, chemical and food technology. Cavitations in hydraulic pipelines, pressure surges and flow of blood are also some of familiar instance of such flows. The performance of this equipment in thermal engineering applications is affected by the pulsating flow parameters (Al-Haddad and Al-Binally, 1989). During the past few decades, numerous studies have beendevoted to this pulsating flow and its associated heat transfer problems. A review of these studies with emphases on the onset of turbulence, velocity distribution and pipe flow as well as the heat transfer characteristics including axial heat transfer enhancement and convective heat transfer are presented in the following sections. Pulsating flows can be produced by reciprocating pump or by steady flowpump together with some mechanical pulsating devices. It may normally be expected that the heat transfer to or from the flow would be changed since the pulsation would alter the thickness of the boundary layer and hence the thermal resistance. Pulsating flow is assumed to be consisted of a steady Poiseuille flow and purely oscillatory (Zhao and Cheng, 1998). The amplitude of the oscillatory velocity isless than the time mean velocity and flow direction never reverse. Pulsating flow is one of the unsteady

* Corresponding author. E-mail addresses: eelshafei@mans.edu.eg (E.A.M. Elshafei), msafwat@mans. edu.eg (M. Safwat Mohamed), moh_saker1981@yahoo.com (M. Sakr). 0142-727X/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.ijheatfluidflow.2008.03.018

flows that arecharacterized by periodic fluctuations of the mass flow rate and pressure. Most of investigators (Al-Haddad and Al-Binally, 1989; Zhao and Cheng, 1998; Hesham et al., 2005a; Habib et al., 1999; Gupa et al., 1982; Barid et al., 1996; Gbadebo et al., 1999; Zheng et al., 2004; Zohir et al., 2005; Erdal and Gainer, 1979; Habib et al., 2004, 2002) considered in their studies a small number of operating...