Investigation of a new helical flow distributor design to extract thermal energy from hot water storage tanksby András Zachár

International Journal of Heat and Mass Transfer

About

Year
2015
DOI
10.1016/j.ijheatmasstransfer.2014.09.055
Subject
Condensed Matter Physics / Mechanical Engineering / Fluid Flow and Transfer Processes

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Text

uy

Received 19 May 2014

Received in revised form 21 September 2014

Accepted 24 September 2014

Keywords:

Temperature stratification

Heat exchanger coil

Flow distributor

Entrainment phenomenon tanks have been studied with a helical tube-in-tube flow distributor. The primary purpose of the study icant impact on the vertical transport of nutrients investigated by

Ruardij et al. [2]. Local temperature stratification can increase the fatigue of pipelines and serious mechanical damages such as cracks and plastic deformations due to excessive thermal stress caused by thermal stratification have been experienced in several nuclear power plants reported by Kang et al. [3]. Periodic occurrences of thermal transients lead to fatigue and may induce undesirable tribution of therlso important to ase the pos fluid cont

The reason behind this process is that the upper region waste or dangerous fluid container became hotter because stratification process and the boiling start earlier. Some c earlier boiling can lead to an emergency situation.

In the other hand temperature stratification is an important and useful physical phenomenon of hot water storage tanks, especially in solar systems (Duffie and Beckman [6]). The thermal efficiency of a hot water solar system with a thermally stratified storage tank can be significantly improved in comparison to a system operating with a fully mixed tank investigated by Hollands and Lightstone ⇑ Tel.: +36 25 551 618; fax: +36 25 551 231.

E-mail addresses: zachar.andras@mail.duf.hu, zachar.andras@gek.szie.hu

International Journal of Heat and Mass Transfer 80 (2015) 844–857

Contents lists availab

H .edangerous phenomenon depending on the thermo hydraulic application. For example temperature stratification is an important factor that affects significantly the nutrient dynamics in the North Sea as studied by Warrach [1]. Temperature stratification has a signifstress intensity due to nonlinear temperature dis mal stratification in a pipe cross-section. It is a note that the temperature stratification can incre of earlier boiling of dangerous fluids inside wastehttp://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.09.055 0017-9310/ 2014 Elsevier Ltd. All rights reserved.sibility ainers. of the of the ase the1. Introduction

Temperature stratification is an important phenomenon of several different area of thermal fluid engineering and other non engineering fields of natural science like marine biology. Temperature stratification can be useful or less useful or even in some cases a failures and deformations to the piping as studied by Rezende et al. [4]. Kweon et al. [5] has studied parameters which have significant effect on the fatigue of different structural elements of a piping system. These parameters are the boundary layer thickness, temperature difference, stratification length, wall thickness, inner diameter and material properties on peak temperature and peakis to improve the temperature stratification in hot water storage tanks operated with coiled-tube heat exchangers. The investigated operating mode is the extraction of thermal energy from hot water storage tanks. The studied flow distributor consists of two helically coiled pipes. The inner pipe is a common helically coiled tube heat exchanger and the outer pipe is a helically coiled flow distributor which separates the colder water from the significantly hotter bulk fluid of the tank to decrease the entrainment effect induced by natural convection. The flow distributor drives the cooling tank fluid to a helical flow path along the tube axis which induces additional secondary flow pattern in planes normal to the main flow direction over the outer surface of the inner coiled tube. Different inlet temperatures have been investigated to describe the impact for the developed velocity and temperature field. Comparison of the flow and temperature fields of hot water storage tank with common helical tube and the tube-in-tube flow distributor configuration are discussed. Numerical calculations have been carried out to examine different flow and temperature fields in laminar flow regimes. The proposed helical flow distributor ensures a highly stratified temperature field of storage tanks operating with helically coiled heat exchangers. In addition to this the suggested flow distributor geometry makes it possible to apply different heat transfer enhancement tools like spiral tape inserts, different kind of corrugations further improve if it is possible the poor outer side heat transfer rate of common helically coiled tube heat exchangers.  2014 Elsevier Ltd. All rights reserved.Article history: Unsteady heat transfer process and the developed flow and temperature field inside hot water storageInvestigation of a new helical flow distrib energy from hot water storage tanks

András Zachár ⇑

Institute of Informatics, College of Dunaújváros, Táncsics M. u. 1., Dunaújváros, Hungar a r t i c l e i n f o a b s t r a c t

International Journal of journal homepage: wwwtor design to extract thermal le at ScienceDirect eat and Mass Transfer l sevier .com/locate / i jhmt at an[7], Kleinbach et al. [8]. Many authors investigated experimentally and numerically several different aspect of the temperature stratification of different fluids inside different kind of enclosures.

Numerical study of transient mixed convection in a cylindrical cavity has been carried out by Bouhdjar et al. [9]. Mo and Miyatake [10] investigated numerically the transient turbulent flow field in a thermally stratified thermal storage water tank. Transient natural convection from a finned surface for thermal storage has been studied by Benmadda and Lacroix [11]. The effect of inlet geometry on stratification in thermal energy storage has been investigated

Nomenclature cP(T) temperature dependent specific heat function of the fluid (J kg1 K1) dc, dtank diameter of the coil and of the tank (m) din, dout inner and outer side diameter of the coiled pipe (m) ds inner side diameter of the helical flow distributor (m) dgap distance between the inner surface of the helical flow distributor and outer surface of the coil (m)