A novel cryogenic insulation system of hollow glass microspheres and self-evaporation vapor-cooled shield for liquid hydrogen storage

Abstract

Liquid hydrogen (LH₂) attracts widespread attention because of its highest energy storage density. However, evaporation loss is a serious problem in LH₂ storage due to the low boiling point (20 K). Efficient insulation technology is an important issue in the study of LH₂ storage. Hollow glass microspheres (HGMs) is a potential promising thermal insulation material because of its low apparent thermal conductivity, fast installation (Compared with multi-layer insulation, it can be injected in a short time.), and easy maintenance. A novel cryogenic insulation system consisting of HGMs and a self-evaporating vapor-cooled shield (VCS) is proposed for storage of LH₂. A thermodynamic model has been established to analyze the coupled heat transfer characteristics of HGMs and VCS in the composite insulation system. The results show that the combination of HGMs and VCS can effectively reduce heat flux into the LH₂ tank. With the increase of VCS number from 1 to 3, the minimum heat flux through HGMs decreases by 57.36%, 65.29%, and 68.21%, respectively. Another significant advantage of HGMs is that their thermal insulation properties are not sensitive to ambient vacuum change. When ambient vacuum rises from 10⁻³ Pa to 1 Pa, the heat flux into the LH₂ tank increases by approximately 20%. When the vacuum rises from 10⁻³ Pa to 100 Pa, the combination of VCS and HGMs reduces the heat flux into the tank by 58.08%–69.84% compared with pure HGMs.

Keywords

liquid hydrogen storage / hollow glass microspheres (HGMs) / self-evaporation vapor-cooled shield (VCS) / thermodynamic optimization

Introduction

Hydrogen energy is regarded as the most promising energy due to its advantages of no pollution, high calorific value [¹], a wide range of sources [²,³], various forms of utilization, and excellent energy storage medium [⁴]. Efficient storage of hydrogen energy is an important concern in current hydrogen energy applications [⁵]. Compared with gaseous storage and metal hydride storage, liquid hydrogen (LH₂) attracts wide spread attention because of its highest energy storage density [⁶,⁷]. However, due to the low boiling point (20 K), the evaporation loss is a serious problem in LH₂ storage, and efficient insulation technology is an important issue in the study of LH₂ storage.

The main insulation forms for cryogenic fluid storage are the spray on foam insulation (SOFI), multilayer insulation (MLI), and powder insulation [⁸,⁹]. The advantage of SOFI is that it can be used under non-vacuum conditions, but the thermal insulation performance is relatively poor (0.005–0.03 W/(m·K)) [¹⁰]. The advantage of MLI is that it has better thermal insulation properties (10⁻⁶–10⁻⁵ W/(m·K)), but the vacuum deterioration will lead to a dramatic deterioration of the MLI performance [¹¹]. Powder insulation, usually referred to as perlite, is a relatively inexpensive insulation material with a moderate thermal insulation performance (10⁻³–10⁻² W/(m·K)), but its disadvantage is that it absorbs moisture and causes thermal insulation properties to gradually deteriorate [¹²,¹³]. Hollow glass microspheres (HGMs) are a new type of non-metallic spherical powder material composed of spherical thin-walled (0.5–2.0 mm) glass particles with a diameter of 10–120 mm, which attributes to low solid conductivity (point contact between particles) and low radiation heat transfer (the micron-sized particle scatters the radiation heat transfer) [¹⁴,¹⁵]. In addition, HGMs has excellent properties such as spherical shape, controllable size, low density, free-flowing, high strength, and noncombustible. Therefore, HGMs can provide a lightweight, durability, and low-maintenance cryogenic insulation system [¹⁶,¹⁷].

At present, relatively few studies on insulation performance of HGMs have been conducted. Some scholars from NASA have preliminarily explored the application of HGMs in LH₂ storage. Sass and Fesmire have carried out experimental work on the application of HGMs in cryogenic insulation field, and concluded that HGMs has obvious advantages over perlite in LH₂ tanks [¹⁸]. Wang et al. have measured the apparent thermal conductivity of HGM with different particle sizes under different vacuum conditions. The measured apparent thermal conductivity of HGMs (77–300 K, 10⁻³ Pa) can be up to 5 × 10⁻⁴ W/(m·K), which shows the superiority of HGMs as cryogenic insulation material [¹⁹]. These studies laid a good foundation for the application of HGMs in cryogenic fluid storage [²⁰,²¹].

A novel insulation system consisting of HGMs and a self-evaporation vapor-cooled shield (VCS) has been proposed for LH₂ storage in this paper. The reason for the use of VCS to recover the cold energy of cryogenic gaseous hydrogen (GH₂) in HGMs is that the sensible heat of hydrogen (3509 kJ/kg at 0.1 MPa, 20 to 300 K) is significantly higher than its evaporation heat (449 kJ/kg at 0.1 MPa) [²²,²³]. Besides, a thermodynamic model has been established to analyze the coupled heat transfer characteristics of HGMs and VCS in the composite insulation system. Based on the self-established model, the mechanism of VCS improving HGMs insulation performance has been quantitatively analyzed, and VCS position and configuration optimized to reduce the heat flux into the tank. In addition, the effects of hot boundary temperature, LH₂ storage pressure, and ambient vacuum on the performance of composite insulation system have also been analyzed.

Composite insulation system and thermodynamic model

Insulation system

The LH₂ tank is 18 m³, whose outside is filled with HGMs with a thickness of 100 mm and the VCS is installed inside the HGMs. Figure 1 shows the schematic of the proposed composite insulation system While Fig. 2 illustrates the heat transfer flowchart of the proposed composite insulation system.

For a particular VCS, the heat flux through it consists of the heat from the external HGMs, the heat to the internal HGMs, and the heat recovered from the cryogenic GH₂. The sensible heat recovered by VCS from the cryogenic GH₂ can be expressed in Eqs. (1) and (2).

(1)Q_i+Q_{\mathrm{r}i}=Q_{i+\mathrm{1}},

in which Q_i is the heat leak from VCS-i to HGMs(i); Q_ri is the sensible heat recovered by VCS-i, and Q_i+1 is the heat leak from HGMs (i + 1) to VCS-i.

(2)Q_{\mathrm{r}i}=\dot{m}(h_i-h_{i-\mathrm{1}}),

in which, \dot{m} is the GH₂ mass flow through VCS, kg/s; h_i and h_i–1 are the enthalpies of GH₂ flow in and out VCS, kJ/kg.

(3)\dot{m}={\displaystyle \frac{Q_{\mathrm{0}}}{q_{\mathrm{v}}}},

in which Q₀ is the total heat into the LH₂ tank, W; and q_v is the vaporization latent heat of H₂, kJ/kg.

The heat flux through the HGMs layer can be calculated according to classical Fourier heat conduction law.

(4)Q_i={\displaystyle \frac{A_i{K}_i(T_{\mathrm{H}i}-T_{\mathrm{C}i})}{L_i}},

in which A_i is the effective area of HGMs(i); K_i is the thermal conductivity of HGMs(i); T_Hi and T_Ci are the hot and cold boundary temperature of HGMs(i), respectively; and L_i is the thickness of HGMs(i).

Apparent thermal conductivity of HGMs

The heat transfer through the HGMs can be divided into solid conduction, gas conduction, and radiation. The inner diameter of the HGMs is usually only tens to hundreds of microns. Therefore, there exists almost no gas convection inside the HGMs [²⁴,²⁵]. The combined effects of different heat transfer forms mentioned above can be expressed by the apparent thermal conductivity [²⁶]. Eqs. (5) and (6) show the thermal conductivity of the HGMs with different temperatures and ambient vacuum degrees [¹⁹,²⁷,²⁸]. In the thermodynamics model, the apparent thermal conductivity of the HGMs is an important thermophysical property for calculation. In the model, the apparent thermal conductivity of the HGMs varies with temperature and vacuum.

The unit of the apparent thermal conductivity is mW/(m·K).

(5)K(T)=a_1{T}^{b_{\mathrm{1}}}+c_{\mathrm{1}},

(6)K(P)=a_2{P}^{b_{\mathrm{2}}}+c_{\mathrm{2}},

in which K(T) and K(P) are the apparent thermal conductivity of HGMs at different temperatures and pressures, respectively; and a1, b1, a2, b2, c1, and c2 are the empirical coefficients fitted through experimental data, and the value of a₁, b₁, c₁, a₂, b₂, c₂ are 4.399E-7, 2.611E0, 5.215E-2, 2.040E-1, 6.078E-1, 4.817E-1, respectively.

The heat transfer between the composite insulation system and the ambient environment can be obtained by

(7)Q_{\mathrm{total}}=\sigma \epsilon (T_A^{\mathrm{4}}-T_{\mathrm{2}n+\mathrm{2}}^{\mathrm{4}})A_{\mathrm{2}n+\mathrm{2}}\phi +h(T_A-T_{\mathrm{2}n+\mathrm{2}})A_{\mathrm{2}n+\mathrm{2}},

in which Q_total is the heat leak into HGMs(N + 1); ε is the reflectivity of the external surface of insulation system; T_2n+2 is the external surface temperature of HGMs(N + 1); A_2n+2 is the external surface area of HGMs(N + 1); σ is the Stefan Boltzmann constant, 5.675 × 10⁻⁸ W/(m²·K⁴); φ is the radiation angle coefficient; and h is the free convection heat transfer coefficient.

Thermodynamic model

In long-term storage of LH₂, both the storage tank and the composite insulation system are in a thermal steady-state. The following assumptions have been made in establishing the thermodynamic model: The tank wall temperature is uniform and consistent with internal LH₂ temperature; the ambient temperature (300 K) and pressure (1 × 10⁻³ Pa) remain constant; the temperature profile on VCS keeps uniform and has a good heat transferability with the adjacent HGMs layer; and the VCS is made of light material, whose thickness can be neglected in calculation.

Calculation results and discussion

Optimization of VCS in HGMs

HGMs with one VCS

The mechanism of VCS to improve insulation performance is to recover cryogenic GH₂ cold energy to cool adjacent HGMs. For HGMs between cold boundary and VCS, the decrease of hot boundary leads to a better material insulation performance and a smaller temperature difference, which reduces the heat flux through the very HGMs. Figure 3 depicts the heat flux through HGMs with one VCS. In Fig. 3, q_out refers to the heat transfer from the outer HGMs to VCS; q_c refers to the cold energy recovered by VCS from cryogenic GH₂; and q_in refers to the heat transfer into the LH₂ tank. As VCS moves through HGMs (from the inside to the outside), both heat flux through the outer HGMs and cold energy recovered by the VCS increase. At the same time, the heat flux through the inter HGMs (i.e., the heat flux into the LH₂ tank) decreases first and then increases. When VCS moves from 10% to 90%, HGMs between VCS and the ambient environment become thinner and the heat flux (q_out) increases. Meanwhile, the temperature of VCS increases, and the cold energy recovery by VCS keeps increasing (q_c). The optimization objective is the heat flux into the LH₂ tank-q_in, which equals q_out minus q_c. In the position of 30%, the heat flux into the tank (q_in) has the minimum value, indicating that the tank has the minimum value of the LH₂ evaporation rate.

Figure 4 demonstrates the results of position optimization in HGMs with one VCS. As VCS moves from the inside to the outside through HGMs, the VCS temperature rises continuously, which indicates that the recovered cold energy from cryogenic GH₂ increases. Aiming at the minimum heat flux into the tank, the optimal position of VCS is about 30% in HGMs (from the inside to the outside), and the corresponding temperature of VCS is approximately 140 K. Compared with the initial heat flux through HGMs without VCS, the maximum decrease with one VCS is 57.36% (from 0.896 W/m² to 0.382 W/m²).

HGMs with more than one VCS

Figure 5 displays the optimized insulation performance of HGMs with different VCSs. When VCS exceeds 3, the insulation performance does not improve markedly if VCS is added continuously. By setting different VCSs, the maximum limit of heat flux reduction should be around 70%. This very limit is mainly determined by the sensible/latent heat value of H₂ and the performance of HGMs. In practical applications, it is necessary to balance the effects of VCS on insulation performance improvement and equipment complexity. In Section 3.2, composite insulation systems with 3 or fewer VCSs will be discussed and optimized.

Insulation performance of composite insulation system

Figure 6 presents the insulation performance of HGMs with different thickness. As the thickness of HGMs increases, the heat flux into the LH₂ tank decreases gradually, but the decreasing range decreases continuously. When the HGMs thickness increases from 50 mm to 500 mm, the heat flux into the LH₂ tank decreases by 87.45% without VCS. Under conditions with VCS, the decreases are 87.99% (1 VCS), 88.18% (2 VCSs) and 88.27% (3 VCSs), respectively. To achieve a considerable insulation performance, the thickness of composite insulation system with VCS can be greatly reduced compared with that without VCS.

Figure 7 exhibits the temperature profile through HGMs under different conditions. After installing VCS, the temperature profile through HGMs changes obviously, which indicates the redistribution of cold energy from cryogenic GH₂ by VCS. As can be seen from the curves in Fig. 7, when the number of VCS increases, the temperature tends to increase to an extreme value. Assuming that the number of VCS is infinite, the insulation performance is the best, that is, the cold energy of cryogenic GH₂ is fully utilized. However, this infinite number of VCS schemes is uneconomical in practical applications due to the complexity of hardware. When the number of VCS exceeds 3, the insulation performance does not improve apparently if VCS is added continuously.

Effect of hot/cold boundary temperature

Overall, the increase of hot boundary temperature worsens the insulation performance of the HGMs material. Figure 8 shows the insulation performance under different hot boundary temperatures. With the increase of hot boundary temperature, the heat flux into the LH₂ tank increases. When the hot boundary temperature rises from 260 K to 340 K, the heat flux into the LH₂ tank increases by 128.96% (from 0.581 W/m² to 1.330 W/m²) without VCS. Under conditions with VCS, the decreases compared with pure HGMs are 86.75% (1 VCS, from 0.275 W/m² to 0.514 W/m²), 81.95% (2 VCSs, from 0.227 W/m² to 0.413 W/m²) and 79.70% (3 VCSs, from 0.209 W/m² to 0.376 W/m²), respectively. The above results suggest that the composite insulation system with VCS has advantages under higher hot boundary temperature conditions.

Figure 9 shows the saturation temperature, liquid density, vaporization heat, and sensible heat (from boiling point to 300 K) of LH₂ at different pressures. When the storage pressure increases from 0.1 MPa to 1.0 MPa, the LH₂ density decreases from 70.90 kg/m³ to 49.89 kg/m³ with a reduction rate of 29.63%. Meanwhile, the vaporization heat of H₂ decreases dramatically (from 448.90 kJ/kg to 242.13 kJ/kg) and the sensible heat from the boiling point to 300 K increases slightly (from 3509.30 kJ/kg to 3719.97 kJ/kg). As mentioned above, the ratio of sensible heat to vaporization heat has an important influence on the performance of VCS in the thermodynamic model.

Figure 10 shows the insulation performance at different LH₂ pressures. Obviously, the effect of increasing LH₂ pressure on insulation systems with VCS is more apparent than that without VCS. With the increase of storage pressure, the sensible/vaporization heat of hydrogen is more significant. When the storage pressure increases from 0.1 MPa to 1.0 MPa, the sensible heat/vaporization heat of hydrogen changes from 7.82 to 15.36, which means that VCS can recover more cold energy from cryogenic GH₂.

To analyze the influence of LH₂ pressure on insulation system, the change of daily evaporation rate of LH₂ tank is more intuitive.

(8)\eta ={\displaystyle \frac{Q_{\mathrm{0}}\cdot \mathrm{24}\cdot \mathrm{3600}}{q_{\mathrm{V}}{\rho }_{\mathrm{L}}{V}_{\tan \mathrm{k}}}},

in which η is the daily evaporation rate of the LH₂ tank; Q₀ is the total heat into the LH₂ tank, and Q₀ = q₀A_tank; q₀ is net heat flux into the LH₂ tank; A_tank and V_tank are the surface area and volume of the LH₂ tank, respectively; and q_V and ρ_L are the evaporative heat and liquid density of LH₂.

For the proposed insulation system, the LH₂ evaporation loss is determined by the heat flux into tank and the thermophysical properties of hydrogen (evaporation latent heat, sensible heat and liquid density). It can be found from Fig. 10 (b) that when storage pressure increases, the daily evaporation rate of LH₂ increases significantly with or without VCS, which is certainly not economical. Obviously, with the increase of pressure, the LH₂ density decreases continuously, which will undoubtedly weaken the advantage of high energy density of LH₂ storage [²⁹,³⁰].

In practical application, tank volume is also an important factor affecting the daily evaporation rate of LH₂. Figure 11 gives the insulation performance of the LH₂ tank at different volumes (from 18 m³ to 5000 m³). With the increase of volume, the specific surface area of the LH₂ tank decreases continuously, which is beneficial to the performance of the insulation system. When the tank volume increases from 18 m³ to 1000 m³, the LH₂ daily evaporation rate decreases by 73.72% without VCS, and 5000 m³ by 84.68%. Under the conditions with different numbers of VCS, the influence of the tank volume or specific surface area on insulation performance is similar to the former.

Effect of ambient vacuum

Another significant advantage of the HGMs and VCS composite insulation system is that they are insensitive to vacuum changes. Compared with MLI, the effect of vacuum deterioration on HGMs insulation performance is relatively small [¹³,¹⁹]. Figure 12 and Table 1 show the insulation performance of HGMs at different vacuum degrees. With the vacuum deteriorating, the heat flux through HGMs increases. At this time, VCS can still play an effective role. The insulation performance of HGMs is insensitive to vacuum changes compared with MLI. When ambient vacuum rises from 10⁻³ Pa to 1 Pa, the heat flux with HGMs into the LH₂ tank increases by only about 20% (The increase of MLI is more than 2000% [³¹].). When the vacuum rises from 10⁻³ Pa to 100 Pa, the insulation performance of pure HGMs worsens and the heat flux into the LH₂ tank increases by 658.48%. At an ambient vacuum of 100 Pa, the heat flux into the tank of pure HGMs is 6.796 W, and those with 1–3 VCSs are 2.849 W, 2.333 W and 2.160 W, respectively. Under this condition, the combination of VCS and HGMs reduces the heat flux into the tank by 58.08%–69.84% compared with that of pure HGMs [³²–³⁴].

Conclusions

A novel insulation system consisting of HGMs and self-evaporation VCS has been proposed for LH₂ storage, which has the advantages of excellent insulation performance, fast installation, and easy maintenance, which is especially suitable for large-scale and long-term LH₂ storage. A thermodynamic model has been established to analyze the coupled heat transfer characteristics of HGMs and VCS in the composite insulation system. It has obvious application advantages in the field of cryogenic insulation for LH₂ storage.

Compared with initial heat flux of 100 mm HGMs without VCS, the maximum decrease with one VCS is 57.36% (from 0.896 W/m² to 0.382 W/m²). The optimal position of VCS is about 30% in HGMs (from the inside to the outside), and the corresponding temperature of VCS is around 140 K.

When the number of VCS exceeds three, the insulation performance does not improve obviously if VCS is added continuously. By setting different numbers of VCS, the maximum limit of heat flux reduction is around 70%.

When the tank storage pressure increases, the daily evaporation rate of LH₂ increases significantly with or without VCS, which is certainly not economical. For the LH₂ tank, it is not feasible to reduce the heat flux through the composite insulation system by increasing the cold boundary temperature, i.e., increasing the storage pressure of LH₂.

The HGMs and VCS composite insulation system is insensitive to vacuum changes. When the vacuum rises from 10⁻³ Pa to 100 Pa, the combination of VCS and HGMs reduces the heat flux into the tank by 58.08%–69.84% compared with that of pure HGMs.

References

[1] Yan X H, Zhang X, Gu C H, Li F. Power to gas: addressing renewable curtailment by converting to hydrogen. Frontiers in Energy, 2018, 12(4): 560–568

[2] Khosravi A, Koury R N N, Machado L, Pabon J J G. Energy, exergy and economic analysis of a hybrid renewable energy with hydrogen storage system. Energy, 2018, 148: 1087–1102

[3] Mostafaeipour A, Qolipour M, Goudarzi H. Feasibility of using wind turbines for renewable hydrogen production in Firuzkuh, Iran. Frontiers in Energy, 2018: 1–12

[4] Pachapur V L, Sarma S J, Brar S K, Bihan Y L, Buelna G, Verma M. Energy balance of hydrogen production from wastes of biodiesel production. Biofuels, 2018, 9(2): 129–138

[5] Chen X P, Shangguan W F. Hydrogen production from water splitting on CdS-based photocatalysts using solar light. Frontiers in Energy, 2013, 7(1): 111–118

[6] Ozarslan A. Large-scale hydrogen energy storage in salt caverns. International Journal of Hydrogen Energy, 2012, 37(19): 14265–14277

[7] Abdalla A M, Hossain S, Petra P M, Ghasemi M, Azad A K.Achievements and trends of solid oxide fuel cells in clean energy field: a perspective review. Frontiers in Energy, 2018: 1–24

[8] Hastings L J, Hedayat A, Brown T M. Analytical modeling and test correlation of variable density multilayer insulation for cryogenic storage. Technical Report, NASA/TM-2004-213175, 2004

[9] Martin J J, Hastings L. Large-scale liquid hydrogen testing of variable density multilayer insulation with a foam substrate. Technical Report, NASA/TM-2001–211089, 2001

[10] Tseng C J, Yamaguchi M, Ohmori T. Thermal conductivity of polyurethane foams from room temperature to 20 K. Cryogenics, 1997, 37(6): 305–312

[11] Liu Z, Li Y Z, Xie F S, Zhou K. Thermal performance of foam/MLI for cryogenic liquid hydrogen tank during the ascent and on orbit period. Applied Thermal Engineering, 2016, 98(5): 430–439

[12] Wang Q, Chen J, Gui B Q, Zhai T, Yang D. Fabrication and properties of thermal insulating material using hollow glass microspheres bonded by aluminum-chrome-phosphate and tetraethyl orthosilicate. Ceramics International, 2016, 42(4): 4886–4892

[13] Fesmire J E, Sass J P. Aerogel insulation applications for liquid hydrogen launch vehicle tanks. Cryogenics, 2008, 48(5–6): 223–231

[14] Zhang J S, Fisher T S, Ramachandran P V, Gore J P, Mudawar I. A review of heat transfer issues in hydrogen storage technologies. Journal of Heat Transfer, 2005, 127(12): 1391–1399

[15] Wang F, Liang J S, Tang Q G, Wang N, Li L W. Preparation and properties of thermal insulation latex paint for exterior wall based on defibred sepiolite and hollow glass microspheres. Advanced Materials Research, 2009, 58: 103–108

[16] Li C D, Li B H, Pan N, Chen Z, Saeed M U, Xu T, Yang Y. Thermo-physical properties of polyester fiber reinforced fumed silica/hollow glass microsphere composite core and resulted vacuum insulation panel. Energy and Building, 2016, 125: 298–309

[17] Yan K Q, Wang P, Zhang J J. Progress in the cryogenic insulation of hollow glass microspheres. Vacuum and Cryogenics, 2016, 22(2): 63–69

[18] Sass J P, Cyr W W S, Barrett T M, Baumgartner R G, Lott J W, Fesmire J E, Weisend J G. Glass bubbles insulation for liquid hydrogen storage tanks. AIP Conference Proceedings, 2010, 1218: 772–779

[19] Wang P, Liao B, An Z G, Yan K, Zhang J. Measurement and calculation of cryogenic thermal conductivity of HGMs. International Journal of Heat and Mass Transfer, 2019, 129: 591–598

[20] Allen M S, Baumgartner R G, Fesmire J E, Augustynowicz S D.Advances in microsphere insulation systems. AIP Conference Proceedings, 2004, 710: 619–626

[21] Yuan J, An Z, Li B, Zhang J. Facile aqueous synthesis and thermal insulating properties of low-density glass/TiO₂ core/shell composite hollow spheres. Particuology, 2012, 10(4): 475–479

[22] Zheng J P, Chen L B, Wang J, Zhou Y, Wang J. Thermodynamic modelling and optimization of self-evaporation vapor cooled shield for liquid hydrogen storage tank. Energy Conversion and Management, 2019, 184: 74–82

[23] Jiang W B, Zuo Z Q, Huang Y H, Wang B, Sun P J, Li P. Coupling optimization of composite insulation and vapor-cooled shield for on-orbit cryogenic storage tank. Cryogenics, 2018, 96: 90–98

[24] Skochdopole R E. The thermal conductivity of foamed plastics. Chemical Engineering Progress, 1961, 57(10): 55–59

[25] Wang P. Research and application of vacuum thermal insulation performance of hollow glass microspheres. Dissertation for the Doctoral Degree. Beijing: University of Chinese Academy of Sciences, 2018 (in Chinese)

[26] Yung K C, Zhu B L, Yue T M, Xie C. Preparation and properties of hollow glass microsphere-filled epoxy-matrix composites. Composites Science and Technology, 2009, 69(2): 260–264

[27] Fesmire J E, Augustynowicz S D. Thermal performance testing of glass microspheres under cryogenic vacuum conditions. AIP Conference Proceedings, 2004, 710(1): 612–618

[28] Cunnington G R, Tien C L. Apparent thermal conductivity of uncoated microsphere cryogenic insulation. Advances in Cryogenic Engineering, 1977, 22: 263–271

[29] Zhu Q, Lee H, Zhang Z M. Radiative properties of materials with surface scattering or volume scattering: a review. Frontiers of Energy and Power Engineering in China, 2009, 3(1): 60–79

[30] Schlapbach L, Züttel A. Hydrogen-storage materials for mobile applications. Nature, 2001, 414(6861): 353–358

[31] Zheng J P, Chen L B, Wang J, Xi X, Zhu H, Zhou Y, Wang J. Thermodynamic analysis and comparison of four insulation schemes for liquid hydrogen storage tank. Energy Conversion and Management, 2019, 186: 526–534

[32] Yang J L, Tang J B. Influence of envelope insulation materials on building energy consumption. Frontiers in Energy, 2017, 11(4): 575–581

[33] Lim C L, Adam N M, Ahmad K A. Cryogenic pipe flow simulation for liquid nitrogen with vacuum insulated pipe (VIP) and Polyurethane (PU) foam insulation under steady-state conditions. Thermal Science and Engineering Progress, 2018, 7: 302–310

[34] Zheng J P, Chen L B, Cui C, Guo J, Zhu W, Zhou Y, Wang J. Experimental study on composite insulation system of spray on foam insulation and variable density multilayer insulation. Applied Thermal Engineering, 2018, 130: 161–168

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