In commercial nuclear power plants spent fuel assemblies are usually stored in actively cooled water pools. The continuous decay heat release represents a potential risk in case of a station black out scenario. Thus two-phase passive heat removal systems are a key technology to enhance the safety of nuclear power plants. Such systems work only by the energy provided from the heat source, e.g. by the maintenance of a natural convection cooling. A heat transfer loop using air as an unlimited heat sink consists of a primary heat exchanger in the spent fuel pool water and a secondary heat exchanger located in ambient air. Thus the measurement of the heat flux, which gets transferred from the pool to the ambient air, is an important task. If one would measure heat flux, flow rates and temperatures in many positions by help of local probes, the natural flow would get strongly disturbed. For that reason we introduce a heat flux measurement around the secondary heat exchanger located in ambient air, which applies temperature and velocity measurement by an anemometric principle.

A $6.5m$ long flow channel with an electrical heated finned tube heat exchanger was set up at the TOPFLOW facility at HZDR. Since the tubes of a heat exchanger would be tilted in a passive heat removal system, i.e. to allow drainage of the condensed heat transfer medium, different tiled angles were adjusted to $0^{°}$ (horizontal), ${20}^{°},{30}^{°}$ and ${40}^{°}$. The frontal velocity was varied between $0.5\frac{m}{s}$ and $4\frac{m}{s}$ and three thermocouples were placed up- and downstream of the heat exchanger respectively. A Temperature Anemometry Grind Sensor (TAGS) was located downstream the heat exchanger. It consists of a wire grid with platinum resistance elements, which are placed in the small sub-channels of a flow straightener to generate laminar flow profiles. Two methods were used to calculate the heat flux: arithmetical average and weighting of the flow area. The results of velocity was compared with the average velocity measured by the volume flow control and out of the velocity and temperature the heat flux was calculated and compared with electrical supplied heat flux. The calculated average velocity measured by the TAGS corresponds well with the velocity measured by the volume flow controller up to approximately $3\frac{m}{s}$ with a maximum deviation of $\pm 5\%$, but underestimates the velocity measured by the volume flow controller at higher velocities. The heat flux was calculated by five methods, 1.) from the three thermocouples up- and downstream of the heat exchanger, 2.) from the average temperatures measured by the TAGS, 3.) from the weighted temperature measured by the TAGS, 4.) from the average temperature and velocity measured by the TAGS and 5.) from the weighted temperature and velocity measured by the TAGS. In this order the accuracy of methods increases compared to the electrical supplied heat flux. For the last method the maximum deviation was $6.5\%$ for all tilt angles. This measurement concept determines the heat flux without disturbing the flow in the loop.

在商业核电厂中，乏燃料组件通常存储在主动冷却的水池中。在站点停电的情况下，连续的衰减热量释放代表了潜在的风险。因此，两相无源排热系统是提高核电厂安全性的关键技术。这样的系统仅通过从热源提供的能量来工作，例如通过维持自然对流冷却来工作。使用空气作为无限散热片的传热环路由废燃料池水中的一级热交换器和位于环境空气中的二级热交换器组成。因此，从池传递到周围空气的热通量的测量是一项重要的任务。如果要借助本地探头来测量许多位置的热通量，流量和温度，自然流量会受到强烈干扰。因此，我们在周围空气中的二级热交换器周围引入了热通量测量，该测量通过风速原理应用了温度和速度测量。

一种 $6.5米$在HZDR的TOPFLOW设施中建立了带有电加热翅片管热交换器的长流道。由于换热器的管子会在被动排热系统中倾斜，即为了排出冷凝的传热介质，因此需要调整不同的平铺角度以适应$0^{°}$ （水平的）， ${20}^{°}，{30}^{°}$ 和 ${40}^{°}$。额叶速度在$0.5\frac{米}{s}$ 和 $4\frac{米}{s}$三个热电偶分别放置在热交换器的上下游。温度风速计研磨传感器（TAGS）位于热交换器的下游。它由带有铂电阻元件的线栅组成，将其放置在整流器的小子通道中以生成层流轮廓。两种方法用于计算热通量：算术平均值和流动面积权重。将速度结果与通过体积流量控制测得的平均速度进行比较，并从速度和温度中计算出热通量，并将其与供电热通量进行比较。TAGS测得的计算出的平均速度与体积流量控制器测得的速度非常吻合，直至大约$3\frac{米}{s}$ 最大偏差为 $\pm 5％$，但低估了体积流量控制器在较高速度下测得的速度。通过以下五种方法计算热通量：1.）从换热器上下的三个热电偶； 2.）由TAGS测量的平均温度； 3.）由TAGS测量的加权温度； 4） 。）根据TAGS测得的平均温度和速度，以及5.）根据TAGS测得的加权温度和速度。与供电的热通量相​​比，此方法的准确性得以提高。对于最后一种方法，最大偏差为$6.5％$适用于所有倾斜角度。此测量概念确定了热通量，而不会干扰环路中的流量。