Recent Progress on High Temperature and High Pressure Heat Exchangers for Supercritical CO₂ Power Generation and Conversion Systems

Figures & data

Figure 1. A supercritical CO₂ Brayton cycle developed at Brunel University London, UK. (a) Test facility, and (b) Cycle design conditions.

Figure 2. Potential applications relevant to supercritical CO₂ Brayton cycle (a) operating temperature range and (b) required operating pressure range. Source data from Reference [10], ARD (advanced reactor designs), ASMR (advanced small modular reactors), GTB (gas turbine bottoming), SP (shipboard propulsion), SHP (shipboard house power), WHR (waste heat recovery), CSP (concentrated solar power), GT (geothermal), IHFF (indirect heating fossil fuel), DHFF (direct heating fossil fuel).

Table 1. Developed high temperature and pressure heat exchangers for supercritical CO₂ applications.

Type of heat exchanger	Maximum temperature (°C)	Maximum pressure (bars)	Maximum compactness (m^2/m^3)
Printed circuit	900	400	5000
Diffusion-bonded plate-fin	500	200	800
Micro shell and tube or microtube	650	400	2000

Figure 3. Typical PCHE (a) flow paths and (b) diffusion-bonded core (courtesy of Heatric Meggitt UK).

Figure 4. Etched flow paths of PCHEs: (a) straight channel, (b) zigzag (or wavy) channel, (c) channel with S-shaped fins, and (d) channel with airfoil fins.

Table 2. Representative studies of thermohydraulic characteristics of supercritical CO₂ in printed circuit heat exchanger.

Reference	Geometry	Type	Methodology	Measurement
Liu et al. [23, 24]	PCHE-SC	Cooler	Experiment	Local temperature, local heat transfer, average friction factor, average heat transfer
Park et al. [25]	PCHE-SC	Cooler	Experiment	Local temperature, local heat transfer, average heat transfer
Zhang et al. [26]	PCHE-SC	Recuperator	CFD	Velocity contour, temperature distribution, local heat transfer, average heat transfer, Buoyancy effects
Chai and Tassou [27]	PCHE-SC	Recuperator	CFD	Local heat transfer, local friction factor, average heat transfer, average friction factor
Sarmiento et al. [28]	PCHE-SC	Recuperator	Theoretical model	Overall heat transfer, average friction factor
Chu et al. [30]	PCHE-ZC	Cooler	Experiment	Average friction factor, average heat transfer
Li et al. [31]	PCHE-ZC	Cooler	Experiment	Overall heat transfer
Cheng et al. [32]	PCHE-ZC	Recuperator	Experiment	Average friction factor, average heat transfer
Zhou et al. [33]	PCHE-ZC	Recuperator	Experiment	Average friction factor, average heat transfer
Ren et al. [34]	PCHE-ZC	Cooler	CFD	Velocity contour, temperature distribution, local heat transfer, average heat transfer, average friction factor
Saeed et al. [35]	PCHE-ZC	Cooler	CFD	Average heat transfer, average friction factor
Zhang et al. [36]	PCHE-ZC	Recuperator	CFD	Velocity contour, temperature distribution, local heat transfer, overall flow and heat transfer
Wen et al. [37]	PCHE-ZC	Recuperator	CFD	Velocity contour, average heat transfer, average friction factor
Marchionni et al. [38]	PCHE-ZC	Recuperator	1D dynamic model	Transit flow and heat transfer
Yang et al. [39]	PCHE-ZC	Recuperator	CFD	Heat flux distribution, average heat transfer, average friction factor
Saeed and Kim [42]	PCHE-SF	Recuperator	CFD	Average heat transfer, average friction factor
Chu et al. [43]	PCHE-AF		CFD	Velocity contour, average heat transfer, average friction factor, overall flow and heat transfer
Shi et al. [44]	PCHE-AF	Heater	CFD	Velocity contour, average heat transfer, average friction factor, overall flow and heat transfer

Table 3. Correlations of friction factor and heat transfer during supercritical CO₂ flowing in PCHEs.

Reference	Geometry	Correlations
Liu et al. [23]	PCHE-SC	$Nu=0.1229R{e}^{0.6021}P{r}^{0.3}{\left(c_{p,\mathrm{w}}/c_{p,b }\right)}^{0.1310}$ $\text{where}\mathrm{ }3600<Re<36500$
Liu et al. [24]	PCHE-SC	$f=\{\begin{array}{c}15.08/Re,\mathrm{ }2100<Re\\ 6.34\times 10^{-5}R{e}^{0.6373},\mathrm{ }2100\le Re<2700\\ 0.0557R{e}^{-0.2137},\mathrm{ }2100\le Re<7.1\times 10^5\end{array}$
Chu et al. [30]	PCHE-ZC	$Nu=0.0183R{e}^{0.82}P{r}^{0.5}{\left({\rho }_{\mathrm{b}}/{\rho }_w\right)}^{-0.3}\left[(c_1+c_2(\frac{Gr}{R{e}^{c_3}})\right]$ $f=c_{4}R{e}^{c_5}$ $\text{where}\mathrm{ }25000<Re<70000, \text{coefficients}\mathrm{ }{c}_1\mathrm{–}\mathrm{ }{c}_5\mathrm{ }\text{dependent}\mathrm{ }\text{on}\mathrm{ }\text{zigzag}\mathrm{ }\text{angles}$
Cheng et al. [32]	PCHE-ZC	$Nu=\left(0.02475\pm 0.002657\right)R{e}^{0.76214\pm 0.03899}$ $f=\left(0.7510\pm 0.09037\right)R{e}^{0.2834\pm 0.08859}$ $\text{where}\mathrm{ }4897\le Re\le 23888,\mathrm{ }0.765\le Pr\le 0.784$ $Nu=\left(0.02063\pm 0.002562\right)R{e}^{0.7678\pm 0.04928}$ $f=\left(12.74\pm 3.815\right)R{e}^{0.4806\pm 0.07792}$ $\text{where}\mathrm{ }3213\le Re\le 15631,\mathrm{ }1.01\le Pr\le 1.10$
Ren et al. [34]	PCHE-ZC	$Nu=6.3943R{e}^{0.4611}P{r}^{0.4759}{\left({\rho }_{\mathrm{b}}/{\rho }_{\mathrm{w}}\right)}^{1.027}{\left({\mu }_{\mathrm{b}}/{\mu }_{\mathrm{w}}\right)}^{-0.3428}{\left(\overline{c_{\mathrm{p},\mathrm{b}}}\mathrm{ }/c_{\mathrm{p},\mathrm{b}}\right)}^{0.7601}{\left(L_{\mathrm{p}}/D_{\mathrm{h}}\right)}^{-0.2121}{\left(\beta \cdot \pi /180\right)}^{0.4735}$ $f=15.78/Re+5.366\times 10^{-4}R{e}^{0.1182}{e}^{14.597\cdot \beta \cdot \pi /180}{{\left(L_{c,p}/D_h\right)}^{-3.6154}}^{\cdot \beta \cdot \pi /180}$ $\text{where}\mathrm{ }2.1\times 10^4<Re<4.8\times 10^4,\mathrm{ }0.9<Pr<12,$ $25^o<\beta <40^o, 6\text{mm}<L_p<12\text{mm},\mathrm{ }$ $L_{c,p}=L_p/\cos \hspace{0.17em}(\beta \cdot \pi /180)$
Saeed et al. [35]	PCHE-ZC	$Nu=0.475R{e}^{0.61}P{r}^{0.17}$ $f=0.13R{e}^{-0.044}$ $\text{where}\mathrm{ }3000<Re<60000, 2.0\le Pr\le 13$
Shi et al. [44]	PCHE-AF	$Nu=0.0986R{e}^{0.687}P{r}^{0.4}{\left({\mu }_{\text{b}}/{\mu }_{\text{w }}\right)}^{0.14}$ $f=0.513R{e}^{-0.667}$ $\text{where}\mathrm{ }11671<Re<123483,\mathrm{ }0.73<Pr<0.75$

Figure 5. Microtube heater (courtesy of Reaction Engines Ltd).

Table 4. Main advantages and drawbacks of developed heat exchangers for supercritical CO₂ applications.

Type of heat exchanger	Manufacturing techniques	Advantages	Drawbacks
Printed circuit heat exchanger	Photochemical machining; Diffusion bonding.	Compact footprint and reduced weight; Flexible flow passage design; High heat transfer efficiency; Withstand extremely high pressures and temperatures; Wide operating parameters and performance.	Equipment and manufacturing are still quite expensive; Fabricated parts require some post-processing and not installation-ready once complete; Limits of thermal fatigue; High pressure loss; High capital cost.
Diffusion-bonded plate-fin heat exchanger	Diffusion bonding.	Compact footprint and reduced weight; High heat transfer efficiency; High thermal stresses.	Fabricated parts require some post-processing and not installation-ready once complete; Limits of operating pressures and temperatures; Issue occurs in the joining of plate and fin.
Micro shell and tube or microtube heat exchanger	Vacuum brazing; Diffusion bonding.	High heat transfer efficiency; High thermal stresses; Easy maintenance; Meeting the high temperature and high differential pressure criteria.	High pressure loss; Issue occurs in the joining of microtube and header.

Table 5. Main advantages and drawbacks of potential heat exchangers for supercritical CO₂ applications.

Type of heat exchanger	Manufacturing techniques	Advantages	Drawbacks
3D printed heat exchanger	Additive manufacturing	Versatile, flexible, highly customizable fabrication method; More freedom for design of complex structures; Custom parts are easy to prototype; Less material, reduced volume.	Equipment and raw materials are still quite expensive; Fabricated parts require some post-processing and not installation-ready once complete; Quality of the fabricated parts are difficult to control; Infeasible mass production for most products and components; Issues related to surface roughness and powder removal; Size limitation.
Casted metal heat exchanger	Investment casting	Practically any metal can be investment cast; Many intricate forms with undercuts can be cast; Smooth surface can be obtained with no parting line; Allows high dimensional accuracy; Very thin sections can be produced by this process.	Limited to small casting, and present some difficulties where cores are involved; Quality of the fabricated parts are difficult to control; Difficulty to cast objects requiring large size, or holes and cores; The whole parts cannot be made totally for hollow parts, the finished piece will need no welding or assembling.
Ceramic heat exchanger	Laminated-object-manufacturing; Additive manufacturing	Resistance to high-temperature corrosion and oxidation; Stability at elevated temperature; Good thermal shock resistance; Low coefficient of thermal expansion; Ability to be fabricated in practical geometries; Chemical durability.	Brittleness; Permeability; Unsuitable for fabrication by joining techniques; Difficulty of joining of ceramics to metals; Require reliable high temperature, high pressure seals; Irreparability; Mass production and size limitations.

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