This paper presents a detailed analysis of the thermodynamic performance of spiral plate heat exchangers (SPHEs) and their channels by considering the fluid friction effect and no heat leakage to the environment. An optimal design algorithm for SPHEs is developed to find higher compactness and the overall heat transfer coefficient by increasing channels pressure drops, maintaining the geometric aspect ratio, and minimizing total costs. To determine the internal temperature distributions and the rates of heat transfer, a mathematical model is proposed. Fluid friction effects are examined as viscous heating; for this purpose, new parameters of the viscous heating entransy number and viscous heating entransy resistance are defined. Finally, various single-phase countercurrent SPHEs assuming a constant heat transfer rate, are modeled and compared in terms of energy, entropy generation, and entransy criteria. The results show the fluid friction effects as pressure drop effects in entropy generation are insignificant when compared to those caused by heat transfer. However, fluid effects as viscous heating in entransy analysis show that these effects can be rather significant in SPHEs with large spiral turn numbers or small values of heat capacity rate ratios. The obtained data suggest the significant role of entransy methods and their reliability to entropy generation methods in thermodynamic performance evaluation of SPHEs.