Heat transfer characteristics and thermal insulation optimization of buried ductile iron heat-supply pipeline

Figures & data

Figure 1. Schematic of central heating system.

Figure 2. Directly buried steel hot water pipe.

Figure 3. (a) Structure of directly buried ductile iron heat-supply pipeline (b) socket connection structure.

Figure 4. Model building system diagram.

Figure 5. Geometrical dimensions of ductile iron pipe.

Table 1. Pipe geometry of each pipe diameter.

DN	DE	D	Lu	e
80	98	140	85	6
100	118	163	88	6
125	144	190	91	6
150	170	217	94	6
200	222	278	100	6.3
250	274	336	105	6.8
300	326	393	110	7.2
350	378	448	110	7.7
400	429	500	110	8.1
450	480	540	120	8.6
500	532	604	120	9
600	635	713	120	9.9
700	738	824	150	10.8
800	842	943	160	11.7
900	945	1052	175	12.6
1000	1048	1158	185	13.5
1100	1152	1270	202	14.4
1200	1255	1378	217	15.3
1400	1462	1600	242	17.1
1500	1565	1710	253	18
1600	1668	1821	266	18.9
1700	1875	2043	297	18.9
1800	2082	2262	319	18.9

Figure 6. Pipe geometry model.

Figure 7. Three-dimensional model.

Figure 8. Boundary conditions for the heat transfer analysis of two-line heat-supply pipeline buried directly under the soil.

Figure 9. (a) Layer-wise temperature distribution of soil in different months (b) Monthly distribution of temperature at different burial depths.

Figure 10. (a) Position diagram of adiabatic surface (b) Temperature distribution along x-axis with different burial depths; (c) simulation of temperature field in the calculation domain.

Figure 11. Grid independence check result curve.

Figure 12. ANSYS simulation model of pipe main body part.

Figure 13. Testing section at the interface.

Figure 14. Experimental line experimental platform.

Figure 15. Experimental data module Settings.

Figure 16. Temperature sensor.

Table 2. Temperature of water supply and return pipes under 11 specific working conditions.

working condition	1	2	3	4	5	6
water supply (°C)	100.00	93.81	90.00	86.40	80.00	77.51
back water (°C)	50.00	43.11	45.00	41.61	40.00	39.64
working condition	7	8	9	10	11
water supply (°C)	72.71	70.00	67.11	60.00	58.74
back water (°C)	40.38	35.00	42.33	30.00	30.63

Figure 17. Temperature numerical solution and experimental value of main body of water supply pipeline.

Figure 18. Temperature distribution on outer wall of outer protective tube under a thermal-insulating layer thickness of 40 mm.

Figure 19. Temperature distribution of outer surface of the DN300 outer protective pipe.

Figure 20. Economic thickness of thermal-insulating layer (in absence of thermal bridge effect).

Figure 21. Economic thickness of thermal-insulating layer (in presence of thermal bridge effect).