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**Part 3** 

**Helical Coils and Finned Surfaces** 


**Part 3** 

**Helical Coils and Finned Surfaces** 

308 Heat Exchangers – Basics Design Applications

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**12** 

*India* 

.

J. S. Jayakumar

**Helically Coiled Heat Exchangers** 

It has been widely reported in literature that heat transfer rates in helical coils are higher as compared to those in straight tubes. Due to the compact structure and high heat transfer coefficient, helical coil heat exchangers find extensive use in industrial applications such as power generation, nuclear industry, process plants, heat recovery systems, refrigeration, food industry, etc. (Abdulla 1994; Bai et al. 1999; Futagami and Aoyama 1988; Jensen and Bergles 1981; Patankar et al. 1974; Xin et al., 1996). Heat exchanger with helical coils is used for residual heat removal systems in islanded or barge mounted nuclear reactor systems, wherein nuclear energy is utilised for desalination of seawater (Manna et al., 1998). The performance of the residual heat removal system, which uses a helically coiled heat exchanger, for various process parameters was investigated by Jayakumar and Grover (1997). The work had been extended to find out the stability of operation of such a system when the barge on which it is mounted is moving (Jayakumar, 1999; Jayakumar et al., 2002).

Fig. 1 gives the schematic of the helical coil. The pipe has an inner diameter *2r*. The coil diameter is represented by *2RC* (measured between the centres of the pipes). The distance between two adjacent turns, called pitch is *H*. The coil diameter is also called as pitch circle diameter (*PCD*). The ratio of pipe diameter to coil diameter (*r/Rc*) is called curvature ratio,

The angle, which projection of one turn of the coil makes with a plane perpendicular to the

passing through the coil axis. The side of pipe wall nearest to the coil axis is termed inner side of the coil and the farthest side is termed as outer side of the coil. Similar to Reynolds number for flow in pipes, Dean number is used to characterise the flow in a helical pipe.

Heat transfer and flow through a curved tube is comprehensively first reviewed by Berger et al. (1983) and subsequently by Shah and Joshi (1987). The latest review of flow and heat transfer characteristics is provided by Naphon & Wongwises (2006). The characteristics of

. Consider the projection of the coil on a plane passing through the axis of the coil.

. Consider any cross section of the pipe created by a plane

**1. Introduction** 

pitch, 

**1.1 Terminology of helically coiled pipes** 

axis, is called the helix angle,

The ratio of pitch to developed length of one turn (*H/2*

**1.2 Review of single-phase flow and heat transfer** 

*Professor, Dept. of Mechanical Engineering,* 

*Amrita School of Engineering, Amritapuri, Kollam,* 

*Amrita Vishwa Vidyapeetham,* 

 *Rc*) is termed non-dimensional
