A heat–fluid–solid coupling method was established to calculate the flow and stress fields, and the changes in temperature pressure fields and erosion stresses on aluminum surfaces under 100 MPa submerged water jets were studied. The results show that the impact temperature is the key factor affecting the aluminum erosion area and jet angle under viscous dissipation. The water jet can produce an impact temperature of 80 °C, and the area above 70 °C is more than ten times that of pressure above 80 MPa. The maximum tensile and shear stress under the temperature–pressure coupling field are 1.5 times and 6 times that under the pressure field, respectively. Under the pressure field, aluminum will not be destroyed, while under the temperature-pressure coupling field, aluminum will produce tensile and shear failure, and the damage radius is 4–6 times the nozzle diameter. With the jet angle increase, the impact pressure decreases, and there is no optimal non-zero jet angle for erosion stress under the pressure field. With the jet angle increase, the impact temperature increases, the 70 °C isotherm and 80 MPa isobar move close to each other, and the coupling effect of the temperature and pressure fields against erosion stress increases, and there is an optimal jet erosion angle. The optimal jet angle of maximum tensile and maximum shear stress varies from 35° to 0° and from 25° to 0°, respectively. The optimal jet angle of maximum tensile stress and shear failure area decreases with the increase in spray distance.

CO₂ is a potential fluid for absorbing and accumulating thermal energy; an accurate and fast calculation method for the heat capacity is essential for the study of the flow state near the critical point. However, the calculation of the heat capacity near the critical point by the equations suggested by NIST can easily be divergent, such as for CO₂, nitrogen, methane, etc. Therefore, an explicit fitting equation was studied. The fitting equation, which used density and temperature as variables and contained three constants, was derived from the nature of heat capacity change (molecular kinetic energy and potential energy). Based on the heat capacity data of the NIST WebBook, the heat capacity of CO₂ is taken as the example for the equation deduction and parameter fitting. The three constants were defined in order by Origin fitting software. By this new approach, it is found that the heat capacity at the critical point is below 1% deviant from that of the NIST WebBook. Moreover, the heat capacities that are difficult to be calculated in the NIST WebBook are well calculated. The study shows that the fitting equation is efficient for the prediction of heat capacity of gases near the critical point.