MODELING OF THE DYNAMICS OF R-11 BLOWN POLYURETHANE FOAM FORMATION
MODELING OF THE DYNAMICS OF R-11 BLOWN POLYURETHANE FOAM FORMATION
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DOI：
10.1002/pen.760340804
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发表时间：
1994-04-01
影响因子：
3.2
通讯作者：
KHAKHAR, DV
中科院分区：
文献类型：
--
作者：
BASER, SA;KHAKHAR, DV
R-11发泡聚氨酯泡沫形成的动力学取决于反应混合物的粘度增加速率和R-11蒸发速率，并且两者都由聚合过程控制。进行了详细的实验来研究发泡的动力学，并且所做的测量包括奶油和上升时间、膨胀泡沫的密度随时间的变化以及反应期间的温度升高。还进行了发泡混合物中不同点处的动态温度测量，以研究泡沫中温度的空间变化。实验结果表明，随着R-11浓度的增加，发泡速率、最终密度和最高温度均降低。当密度较低时，泡沫的热损失在发泡的后期阶段也很显着。理论模型被开发来预测温度和密度随着时间和空间变化的温度在泡沫中由于热损失，通过考虑发泡动力学是热生成控制或传热和传质控制。在前者中，假设泡沫为假均相，方法与Rojas等人的方法相似（5）。新的功能占在模型中的反应物浓度的稀释，由于液体发泡剂的存在和热损失的泡沫由于辐射。虽然理论预测和实验结果之间的良好协议，获得了温度随时间的变化在不同的位置在泡沫，该模型给出了一个更尖锐的密度随时间的减少相比，实验数据。在第二个模型中，假设发泡速率由向泡沫中单个气泡的传热和传质速率控制。假设一个膜模型的热量和质量传递，温度和密度的理论预测被发现是在非常好的协议与实验数据。
The dynamics of R-11 blown polyurethane foam formation depend on the rates of viscosity increase of the reacting mixture and R-11 evaporation, and both are controlled by the polymerization process. Detailed experiments were carried out to study the dynamics of foaming and the measurements made included the cream and rise times, the density change of the expanding foam with time, and the temperature rise during reaction. Dynamic temperature measurements at different points in the foaming mixture were also made to study the spatial variation of the temperature in the foam. The experimental results showed the rate of foaming, the final density, and the maximum temperature decreased with increasing R-11 concentration. The heat losses from the foam were also found to be significant towards the later stages of foaming when density was low. Theoretical models were developed to predict the temperature and density change with time and spatial variation of temperature in the foam due to heat losses, by considering the foaming dynamics to be either heat generation controlled or heat and mass transfer controlled. In the former, the foam was assumed to be a pseudo-homogeneous phase and the approach was similar to that of Rojas, et al. (5). New features accounted for in the model were dilution of the reactant concentration due to the presence of liquid blowing agent and heat loss from the foam due to radiation. While excellent agreement between theoretical predictions and experimental results was obtained for temperature variation with time at different locations in the foam, the model gave a much sharper reduction in density with time as compared to the experimental data. Iii the second model, the rate of foaming was assumed to be controlled by the rate of heat and mass transfer to a single bubble in the foam. Assuming a film model for heat and mass transfer, the theoretical predictions for both temperature and density were found to be in very good agreement with experimental data.