相变蓄冷保温箱的模拟仿真与实验Numerical Simulation and Experimental Investigation of Storage Box Using Phase Change Materials

DOI: 10.12677/MOS.2021.101018, PDF, HTML, XML, 下载: 49  浏览: 91

Abstract: An insulated box was made from a new type of low temperature phase change material (PCM)., which is to test the thermal performance of this new type PCM and find the melting law of the PCM in this box . The no-load experiment was carried out with the self-made box. The results show that the proportion of the PCM in the upper layer can be increased because of the rapid melting of the PCM in the upper layer. The heat transfer model can ensure the cold storage time to meet people’s needs and also can be applied to the cold chain logistics system. ANSYS Fluent software was used to simulate the temperature variation of the box. The simulation results show that the bottom tem-perature curves are in agreement with the experimental results and consistent. There is a big dif-ference in the intermediate temperature because there is natural convection of hot air in the reali-ty rising so that the intermediate temperature is higher than the bottom temperature. The PCM’s melting inside the storage box usually starts from the corner and the corner structure needs to be optimized. Due to the presence of heat leakage, the experimental temperature is seriously strati-fied. However, in the simulation, the temperature distribution is uniform and there is basically no stratification because of idealized conditions and no heat leakage.

1. 引言

2. 保温箱设计与实验

2.1. 保温箱的设计计算

Table 1. Coefficient of insulation material

Figure 1. Section of box (vertical section)

${S}_{o}=2\ast \left({a}_{o}\ast {b}_{o}+{a}_{o}\ast {b}_{o}+{b}_{o}\ast {h}_{o}\right)$ (1)

${S}_{i}=2\ast \left({a}_{i}\ast {b}_{i}+{a}_{i}\ast {b}_{i}+{b}_{i}\ast {h}_{i}\right)$ (2)

$S=\sqrt{{S}_{o}\ast {S}_{i}}$ (3)

${k}_{2}=1/\left(\frac{{\delta }_{1}}{{\lambda }_{1}}+\frac{{\delta }_{2}}{{\lambda }_{2}}\right)$ (4)

${\delta }_{1}$${\delta }_{2}$ 分别为泡沫层和保温棉的厚度 m， ${\lambda }_{1}$${\lambda }_{2}$ 分别为泡沫层和保温棉层的导热系数， w/(m·k)。

${k}_{o}=1/\left(\frac{1}{{k}_{1}}+\frac{1}{{k}_{2}}+\frac{1}{{k}_{3}}\right)$ (5)

$\Delta T={T}_{o}-{T}_{i}$ (6)

${T}_{o}$ , ${T}_{i}$ 分别为箱外环境温度和箱内冷藏温度，℃。

$Q=3600t{K}_{o}A\Delta T$ (7)

Q为散热量J； ${K}_{o}$ 为传热系数w/(m2·k) ；t为保冷时间h；A为传热面积m2$\Delta T$ 为传热温差℃；

$m=\frac{Q}{H}$ (8)

m——蓄冷剂质量g；

H——相变蓄冷材料相变潜热J/g；本实验所用蓄冷剂的相变潜热为222.7 J/g。

2.2. 实验过程

2.2.1. 实验仪器

2.2.2. 实验步骤

3. 模拟

3.1. 模型的建立

Figure 2. The diagram of numerical model

Figure 3. The diagram of grid

3.2. 数学模型及基本假设

$\frac{\partial \left(\rho \varphi \right)}{\partial t}+div\left(\rho V\varphi \right)=div\left({\Gamma }_{\varphi }grad\varphi \right)+{S}_{\varphi }$ (9)

3.3. 边界条件与求解

${G}_{r}=\frac{g{\alpha }_{v}\Delta t{l}^{2}}{{v}^{2}}$ (10)

(10)式中， ${\alpha }_{v}$ 为体胀系数，本材料体胀系数为0.84 m3/kg；l表示长度特征尺度，本例为0.14 m； $\Delta t$ 温差，本例最大温差不超过20℃；g重力加速度，9.81 m/s2$\nu$ 运动粘度系数，取15 * 10−6

$\beta =\left\{\begin{array}{l}0,\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{\hspace{0.17em}}\text{ }T<{T}_{S}\\ \frac{T-{T}_{S}}{{T}_{L}-{T}_{S}},\text{\hspace{0.17em}}\text{\hspace{0.17em}}{T}_{S}{T}_{L}\end{array}$ (11)

4. 结果与分析

4.1. 实验结果分析

Figure 4. Temperature curve of no load experiment with 0.836 kg PCM

4.2. 模拟结果分析

(a) (b)

Figure 5. Experiment and simulation’s temperature contrast diagram

Figure 6. Simulation liquid fraction diagram

Figure 7. Actual change diagram of liquid fraction

Figure 8. Temperature change diagram of simulation

5. 结语

1) 加装蓄冷材料会延长保冷时间，用传热模型计算所得的蓄冷剂质量将保温箱蓄冷时间维持在8小时左右，能够满足人们日常所需。

2) 经试验验证，保温箱底面保冷实验的温度模拟值与试验值随时间变化规律基本吻合，说明所建立的模型比较可靠。但有2℃左右的温差，这是因为实验环境温度不能完全稳定，实验一开始不能达到密封性要求，其次因为模型的简化，忽略掉了自封袋的不均匀性。

3) 通过对蓄冷式冷藏箱降温过程的数值模拟发现：相变材料从边角开始相变，分层可以优化边角。模拟与实验都验证蓄冷材料对保温箱的保冷具有主要的作用，可以将食品储存在保温箱环形区域内。采用fluent对蓄冷式冷藏箱降温过程中温度场的数值模拟具有一定的科学性，有助于认清温度场分布规律，为蓄冷式冷藏箱降温过程的参数优化提供参考。