# Study the Effect of Operating Temperature on Performance in Dry Scroll Vacuum Pump
## 1 Introduction  
The dry scroll vacuum pump is a kind of simple structure, small size, low vibration, quiet, and reliable positive displacement vacuum pump. The water-cooled horizontal dry scroll vacuum pump was originally developed by [PERSON] in 1990 [1]. In 1998, [PERSON] et al. [2] and [PERSON] et al. [3, 4] developed an air-cooled dry scroll vacuum pump. They established the model of lean gas flow leakage through the scroll clearance and also calculated the pumping performance. Their experiments show that the results coincided well with the calculation. To predict the scroll machine performance through theoretical simulation, some mathematical models were established by researchers. [PERSON] et al. [5] developed a three-dimensional mathematical model to simulate the flow condition in a scroll. [PERSON] [6] accomplished the numerical simulation of the operating process of the entire scroll compressor and provided the detailed physics of the unsteady flows inside the scroll compressors. [PERSON] [7] set up the general geometrical model of a scroll compression chamber which could demonstrate the deforming, opening, and vanishing process of all scroll chambers. [PERSON] et al. [8], [PERSON] et al. [9, 10], [PERSON] and [PERSON] [11], and [PERSON] et al. [12, 13] developed different mathematical models to predict compressor performance. [PERSON] and [PERSON] [14, 15], and [PERSON] et al. [16] used experimental research methods to study the flow characteristics in scroll compressors. Computational fluid dynamics (CFD) has also been applied to study the inner flow of scroll compressors and scroll expanders [17, 18, 19, 20, 21, 22, 23, 24, 25]. [PERSON] et al. [21] [PERSON] et al. [22], and [PERSON] et al. [25] all used the structured dynamic mesh method toachieve the motion of the scroll chambers. Compared with the structured dynamic mesh method, the spring smoothing method only needs one mesh file, and the mesh movement can be realized by controlling the coordinates of grids. The spring smoothing method is very efficient for calculation and can control the changes in overall nodes through the formulations of motion. In recent years, [PERSON] et al. [26; 27] analyzed the working process of the scroll pump, introduced the factors that can affect the performance such as the rotational speed and heat transfer, and improved the related pumping theory by combining experiments. In general, considering the special structure and operating condition of the scroll vacuum pump, it is difficult to obtain the internal flow characteristics. Experimental research is not the primary method to study the flow characteristics of the scroll vacuum pump. Our previous work once used the CFD method to numerically simulate the dry scroll vacuum pump [28] and analyzed the working process of \"under-compression\", \"over-compression\", and other phenomena. The author also simulated another dry scroll vacuum pump which has a more complicated structure and working process [29], compared the pumping speed at different suction pressure, and analyzed the working process of the scroll pump. With extensive application in chemical, pharmaceutical, semiconductor, and scientific instruments, dry scroll vacuum pumps will face more complex and demanding pumping conditions, and the requirements for the performance of the dry scroll vacuum pump are more stringent. As a kind of variable capacity dry vacuum pump, the dry scroll vacuum pump compresses the pumped gas to generate a large amount of heat during operation, which causes the temperature of the pump body to rise sharply, thereby affecting the working performance of the pump. When the component temperature rises seriously, the pump may get stuck or even be damaged. A theoretical model of the heat transfer rate between rarefied gas and the working chamber wall was developed by [PERSON] et al. [26]. This performance prediction model of the dry scroll vacuum pump considered the heat transfer between the gas and the working chamber wall.