Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

Geothermal Energy

Science – Society – Technology

Table 3 Overview of modified parameters and variation range for thermal calculations

Parameters	Units	Reference case (st.)	Range/variation	Abbreviations
\({r}_{{i}}\)	[m]	–	[0.01:0.99]
\({\text{SDR}}\)	\([-]\)	11	6
\({\text{SDR}}\)	\([-]\)	11	41
flow type	\([-]\)	Turbulent (turb.)	Laminar
flow type	\([-]\)	Turbulent (turb.)	Turb. r. r. (rough regime)
\({\lambda }\)	[W/(m K)]	Plastic/steel	Steel/plastic	\(\lambda _{\text{switch}}\)
		Plastic/steel	Steel / steel	\(\lambda _{\text{steel}}\)
		(Inner/outer pipe)	Plastic / plastic	\(\lambda _{\text{plast}}\)
\({r_a}\)	[mm]	75	39	\(r_{a,\min}\)
\({r_a}\)	[mm]	75	240	\(r_{a,\max}\)
\({r_o}\)	[mm]	85	45	\(r_{o,\min}\)
\({r_o}\)	[mm]	85	250	\(r_{o,\max}\)
\({L}\)	[m]	20	5	\(L_{\min}\)
\({L}\)	[m]	20	100	\(L_{\max}\)
\({Re}\)	\([-]\)	10000	1000	\(Re_{c,\text{lam}}\)
			4000	\(Re_{c,\min}\)
			100000	\(Re_{c,\max}\)