往復式壓縮機性能模擬

Abstract

本文目的在模擬往復式壓縮機運轉過程中冷媒的狀態與壓縮機的性能。模擬方法為利用能量平衡與質量平衡方程式來描述壓縮機內各控制容積的狀態，並配合氣體狀態方程式、流量方程式、汽缸容積方程式、熱交換方程式、閥片動態方程式，與有效流通面積、有效受力面積、熱對流係數等經驗公式數據，以及壓縮機的幾何尺寸、材料性質、馬達特性、工作流體、及操作條件等參數來模擬壓縮機的動態性能。由模擬結果可得各控制容積內冷媒在各種不同的曲柄轉角時的壓力、溫度、質量，進而掌握影響往復式壓縮機性能的各種現象，如：排氣時的過壓(over pressure)、吸氣時的低壓(under pressure)、閥片動態、閥片延遲關閉造成的閥座通道回流以及冷媒進入汽缸前的吸氣過熱等。除計算壓縮機性能動態外，本文還比較不同的控制容積數目、冷媒直接流入吸入消音器比例和理想氣體與實際氣體三種情況對模擬結果的影響。參數研究方面則包括：、出入口條件、馬達轉速、閥片彈性係數以及活塞與汽缸壁間隙的影響，對壓縮機整體性能的影響。

The main purpose of this thesis is to develop a simulation code to describe the performance of a reciprocating compressor, whose working fluid is refrigerant. The mass conservation and energy conservation equations are applied to solve pressure, mass, and temperature of refrigerant in the compressor. To solve mass and energy conservation equations, a set of equations is needed. They are equations of state, orifice flow, cylinder volume, heat transfer, valve motion equations. some semi-empirical relations, such as orifice coefficient, convection heat transfer coefficient, geometric size of the compressor, material properties of the compressor, working fluid and operating conditions, are required as well. From the simulation, it can obtain the pressure, temperature and mass of the refrigerant as a function of crank angle for each control volume. From these data, many situations affecting reciprocating compressor performance can be identified. Those include the over-pressure in discharge period, under-pressure in suction period, motion of valve, refrigerant back-flow through orifice, and pre-heat of refrigerant before flowing into cylinder. A set of parametric study is carried out to see their influence on the compressor performance. Those varying parameters are the number of control volumes, the ratio of refrigerant directly flowing into suction muffle, the applications of real- and ideal-gas equation of state, inlet and outlet conditions, rotational speed of motor, spring coefficient of valve, and gap between piston and cylinder wall.