Counterflow heat exchanger with core and plenums at both ends

doi:10.1016/j.ijheatmasstransfer.2016.03.117

International Journal of Heat and Mass Transfer

Volume 99, August 2016, Pages 622-629

https://doi.org/10.1016/j.ijheatmasstransfer.2016.03.117 Get rights and content

Highlights

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Architecture: two plenums and core (counterflow) between them.
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Two-objective design: low flow resistance and low thermal resistance.
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The two resistances are the lowest when the core is absent.
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These conclusions hold for laminar and turbulent flow.

Abstract

This paper illustrates the morphing of flow architecture toward greater performance in a counterflow heat exchanger. The architecture consists of two plenums with a core of counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the heat exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of heat transfer units (N_tu) is steeper (when N_tu < 1) than the classical curves for counterflow and crossflow.

Graphical abstract

Introduction

Heat exchangers are a central topic in thermal science and engineering because of their essential role across the landscape of technology, from geothermal and fossil power generation to refrigeration, desalination, and air conditioning [1], [2], [3], [4]. The literature on heat exchangers is voluminous and continues to be active today (e.g., Refs. [5], [6], [7], [8], [9], [10]). The field covers two main aspects of this class of flow systems: fluid flow and heat transfer performance, and ways (criteria) of evaluating performance [11], [12], [13], [14], [15]. The general trend in the field is to develop heat exchangers that offer better performance. This trend is universal in evolution [16], and unites heat exchangers with other evolutionary flow systems, bio, non bio, and manmade.

The starting point for the present paper is the observation that all performance criteria change, and hopefully improve, when one changes and chooses a better flowing architecture. This, the free evolution of the flow architecture is captured by the law of physics of evolution [17]: it is the essence of constructal design [18], and serves as unifying method for all evolutionary design phenomena. Here, we illustrate this approach by analyzing a morphing two-stream counterflow heat exchanger with one plenum at each end. The key architectural feature to be discovered is how much of the total volume is allocated to the counterflow core and the plenums.

Section snippets

Model

Two streams $({\dot{m}}_{1}, {\dot{m}}_{2})$ flow in counterflow through parallel tubes of diameter D, in a core situated between two plenums. As shown in Fig. 1, each stream arrives into a plenum (xL) by flowing across tubes that carry the second stream. At the other end, the second stream arrives into a plenum by flowing across tubes that carry the first stream.

The elemental volume of the heat exchanger has the longitudinal length L (one plenum + the flow length of one stream) and the width H = nD, shown in the

Pressure drop

The overall pressure drop experienced by one stream ${\dot{m}}_{1}$ is due to contributions from the plenum (p) and the core flow (c), through tubes of diameter D and length (1 − x) L, $Δ P = Δ P_{p} + Δ P_{c}$

The plenum has the flow cross section xLD, flow length H (vertical in Fig. 1), and average fluid velocity $U_{p} = {\dot{m}}_{1} / (ρ xLD)$ . The drag force experienced by each tube of length xL (or frontal area xLD) inside the plenum is $F_{1} = C_{D} xLD \frac{1}{2} ρ U_{p}^{2}$ , where we regard C_D as of order 1, based on the assumption that the Reynolds number

Thermal conductance

The thermal contact between the two streams in Fig. 1 is proportional to the overall thermal conductance $C_{th} \sim A_{p} h_{p,tot} + A_{c} h_{c,tot}$ where h_p_,tot and h_c_,tot are the overall heat transfer coefficients including htc on both sides of the tubes and conduction through the tube. A_p and A_c are the contact surfaces in the plenum and the core, $A_{p} \sim nxLD, A_{c} \sim n (1 - x) LD$ or using H ∼ nD: $A_{p} \sim HxL, A_{c} \sim H (1 - x) L$ where n is the number of tubes in cross flow in each plenum, and h_p and h_c are the respective scales (orders of

Numerical method

The pressure drop experienced by one stream ${\dot{m}}_{1}$ in the counterflow parallel tubes solved analytically in the previous section can be solved numerically using the software COMSOL [23]. Consider a fixed element volume of one stream ${\dot{m}}_{1}$ in the heat exchanger with a longitudinal length L = 1 m (one plenum + core), width H = 1 m and depth W = 0.1 m, as shown in Fig. 4. The number of parallel counterflow tubes in the element volume is n = 8. Each tube has the diameter D = 0.7 W. The fluid is water and the flow is

Effectiveness

In order to find the effectiveness of the heat exchanger, consider a fixed element volume of two streams ${\dot{m}}_{1}$ and ${\dot{m}}_{2}$ in a heat exchanger with a longitudinal length L = 2 m, transversal dimension H = 0.4 m and depth W = 0.1 m. As shown in Fig. 6, the hot stream enters the volume at one end with temperature T_h_,in = 330 K, and the cold stream enters the volume at the other end with temperature T_c_,in = 295 K. Each stream flows through a tube before exiting the volume. The tube diameter remains D = 0.7 W. The flow is

Conclusions

Correlations for laminar and turbulent flows were used to assess performance of a heat exchanger that consists of a core sandwiched between two plenums. The length of the core with respect to the length of the plenums is sought based on two objectives: low flow resistance and low thermal resistance. The analysis showed that both the pressure drop and thermal resistance monotonically decrease with decreasing the core length.

In order to verify the use of correlations to evaluate the pressure

Acknowledgements

This work was performed for the project “Freeform Heat Exchangers for Binary Geothermal Power Plants” sponsored by the Geothermal Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy under contract DE-AC05-00OR22725, Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC. Mr. Alalaimi’s work was supported by Kuwait University, Kuwait.

Notice: This submission was sponsored by a contractor of the United States Government under contract

References (23)

J. Yang et al.
Optimization of shell-and-tube heat exchangers using a general design approach motivated by constructal theory
Int. J. Heat Mass Transfer
(2014)
Y. You et al.
Numerical simulation and performance improvement for a small size shell-and-tube heat exchanger with trefoil-hold baffles
Appl. Therm. Eng.
(2015)
A.C. Caputo et al.
Heat exchanger design based on economic optimization
Appl. Therm. Eng.
(2008)
A. Singh et al.
Effects of heat exchanger design on the performance of a solid state hydrogen storage device
Int. J. Hydrogen Energy
(2015)
Jalaluddin et al.
Experimental study of several types of ground heat exchanger using a steel pile foundation
Renewable Energy
(2011)
A.E. Bergles et al.
Energy conservation via heat transfer enhancement
Energy
(1979)
A. Bejan et al.
The effect of size on efficiency: power plants and vascular designs
Int. J. Heat Mass Transfer
(2011)
W.M. Rohsenow et al.
Handbook of Heat Transfer Applications
(1985)
W.M. Kays et al.
Compact Heat Exchangers
(1984)
V. Ganapathy
Industrial Boilers and Heat Recovery Steam Generators: Design
(2002)

A.G. Bloch

Heat Transfer in Steam Boiler Furnaces

(1998)

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ReviewCounterflow heat exchanger with core and plenums at both ends

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Model

Pressure drop

Thermal conductance

Numerical method

Effectiveness

Conclusions

Acknowledgements

Int. J. Heat Mass Transfer

Appl. Therm. Eng.

Appl. Therm. Eng.

Int. J. Hydrogen Energy

Renewable Energy

Energy

Int. J. Heat Mass Transfer

Handbook of Heat Transfer Applications

Compact Heat Exchangers

Industrial Boilers and Heat Recovery Steam Generators: Design

Heat Transfer in Steam Boiler Furnaces

Review
Counterflow heat exchanger with core and plenums at both ends