Experimental Investigation into Effect of Surface Roughness on Convective Heat Transfer of Concrete

doi:10.12141/j.issn.1000-565X.220638

Abstract

Abstract:

The convective heat transfer coefficient (CHTC) is one of the important thermal parameters of concrete. At present, there are great differences in the selection of CHTC in the temperature-related research and engineering applications of building energy efficiency, structural temperature loading and temperature effects of concrete structures, and the influence of material surface conditions is not considered, all these directly affect the accuracy and reliability of the analysis results. In this paper, based on Newton's law of cooling and the principle of heat balance, a set of experimental determination system of CHTC of concrete surface was designed and constructed, and an experimental study on the CHTC of concrete surfaces with different roughness was carried out with a quantitative and controllable method of parameters to further improve and refine the quantitative calculation method of CHTC of concrete. The results show that the designed test system and method can well determine the CHTC of concrete surface in the component scale, and that the surface roughness significantly affects the convective heat exchange on concrete surface. At the wind speed of less than 10 m/s, the relative difference in CHTC of concrete surfaces with different roughness varies from 40.1% to 77.4%. The CHTC increases with the increase of surface roughness, and the forced convection is more greatly influenced by surface roughness than the natural convection. Moreover, based on the regression analysis of experimental data, the formulae for the CHTC of concrete surfaces with four typical roughness are derived, and the formulae for the CHTC of concrete considering the effects of coupled wind speed and surface roughness are also given. Some suggestions are finally given on how to determine the value of CHTC of concrete with the consideration of surface roughness in engineering.

Key words: concrete, convective heat transfer coefficient, surface roughness, laser scanning, regression analysis

CLC Number:

TU502

ZHOU Linren, LI Shaoji, CHEN Lan. Experimental Investigation into Effect of Surface Roughness on Convective Heat Transfer of Concrete[J]. Journal of South China University of Technology(Natural Science Edition), 2023, 51(7): 81-89.

Figures/Tables 13

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参数	取值
参数	水	钢材	混凝土
密度/（kg·m^-3）	1 000	7 850	2 400
比热容/（J·kg^-1·K^-1）	4 200	460	960

试件编号	表面状况	表面积/mm²	表面最大深度/mm	表面平均深度/mm
CGJ1	光滑	150 988	2.33	0.79
CGJ2	些许凹凸不平	151 958	3.39	1.48
CGJ3	细小颗粒感	154 017	4.20	1.64
CGJ4	明显凹凸不平	155 059	4.94	2.50

T_a/℃	保温箱水温/℃			试件温度/℃			Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
T_a/℃	上	中	下	上	中	下	Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
22.7	50.3	50.2	50.3	40.2	42.8	45.0	—	—	—	—
22.5	50.0	50.0	50.0	40.4	42.8	45.1	25.00	4.07	7.51	5.04
22.5	49.7	49.7	49.8	40.3	42.8	45.0	26.60	4.06	7.58	5.57
22.5	49.4	49.6	49.5	40.2	42.7	44.8	23.80	4.05	7.50	4.59
22.4	49.2	49.3	49.4	40.1	42.5	44.6	24.28	4.03	7.50	4.79
22.5	49.0	49.0	49.2	39.8	42.3	44.4	25.20	3.99	7.41	5.24
22.3	48.7	48.8	49.0	39.7	42.2	44.3	23.61	3.98	7.34	4.70
21.1	48.5	48.6	48.7	39.5	42.0	44.1	24.57	3.91	7.54	4.87
21.2	48.4	48.4	48.4	39.2	41.8	43.8	25.20	3.85	7.63	5.01
20.7	48.1	48.3	48.2	38.9	41.4	43.4	22.95	3.81	7.59	4.24

T_a/℃	保温箱水温/℃			试件温度/℃			Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
T_a/℃	上	中	下	上	中	下	Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
22.7	50.2	50.2	50.4	39.7	43.1	45.8	—	—	—	—
22.5	49.9	49.9	50.1	40.0	43.2	46.0	26.98	4.08	7.54	5.92
22.5	49.7	49.6	49.7	40.0	43.1	45.8	28.21	4.07	7.58	6.29
22.5	49.3	49.5	49.5	39.8	42.8	45.5	28.15	4.06	7.53	6.32
22.4	49.1	49.2	49.2	39.6	42.5	45.5	27.49	4.03	7.46	6.16
22.5	48.9	48.9	48.9	39.6	42.4	45.4	26.50	3.99	7.41	5.85
22.3	48.6	48.7	48.6	39.4	42.3	45.2	27.49	3.98	7.39	6.27
21.1	48.3	48.3	48.5	39.2	42.1	45.0	28.18	3.92	7.57	6.31
21.2	48.0	48.0	47.2	39.1	41.8	44.8	27.87	3.86	7.76	6.02
20.7	47.8	47.8	47.9	39.0	41.2	44.2	27.87	3.84	7.76	5.58

T_a/℃	保温箱水温/℃			试件温度/℃			Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
T_a/℃	上	中	下	上	中	下	Q_t/W	Q₁/W	Q_R/W	h_c/（W·m^-2·K^-1）
22.7	50.9	50.9	51.1	40.0	43.5	46.0	—	—	—	—
22.5	50.6	50.6	50.7	40.5	44.0	46.1	28.55	4.12	7.83	6.25
22.5	50.3	50.3	50.3	40.6	43.9	46.0	30.12	4.09	8.01	6.64
22.5	50.0	49.9	50.0	40.6	44.0	45.8	31.52	4.08	8.04	7.09
22.4	49.7	49.6	49.7	40.3	43.8	45.6	31.08	4.07	7.99	7.02
22.5	49.3	49.4	49.4	40.3	43.6	45.4	30.41	4.06	7.92	6.87
22.3	49.1	49.1	49.1	40.0	43.4	45.1	28.51	4.03	7.86	6.22
21.1	48.7	48.8	48.9	39.8	43.1	44.8	28.51	3.99	7.97	7.09
21.2	48.5	48.5	48.6	39.5	42.9	44.5	28.51	3.96	8.14	6.24
20.7	48.2	48.3	48.3	39.2	42.6	44.1	29.14	3.90	8.06	5.86