Thermal management is one of the major concern for modern miniaturised electronic devices dissipating high heat flux. The miniature loop heat pipes (mLHPs) are considered to be an efficient heat transfer device among the various cooling technologies available. The mLHPs are two-phase passive heat transfer devices that are an attractive solution for reliable and long-term maintenance-free thermal management. The flexible and compact nature of the loop heat pipe and its capillary driven abilities are important for its employment in terrestrial and space applications. In the current work, a mathematical model is developed for the proper understanding of the thermal performance during transient processes. The mathematical model is based on the one-dimensional time-dependent momentum and energy conservation equations for heat and fluid flow in each loop heat pipe components. The energy and momentum conservation equations for all the components of loop heat pipes are solved using ethanol as working fluid. The developed numerical code captures the transient thermal characteristics of the mLHP unit for different time-varying heat loads. The present model has been validated with the experimental results in the literatures and a reasonable match is obtained. A comparative numerical investigation is studied for different working fluids like ethanol, pentane, methanol, and water which is difficult to perform experimentally. A parametric study is conducted to predict the effects of varying heat load, sink temperature, on the transient thermal response of miniature loop heat pipe.