Sharif Digital Repository

The current study examines different arrangements of vortex tubes (VTs) to get higher performances for cooling and heating. The effects of thermo-physical parameters such as inlet feed temperature and inlet/outlet vortex tube pressure on generated temperature gradient are investigated. To estimate the cold outlet temperatures, the available equations in the literature are verified against our experimental data. Moreover, we propose a new equation to estimate the hot outlet temperature based on the upper limit of hot temperature (ULHT) and the lower limit of cold temperature (LLCT), verified with experimental data as well. Further, several arrangements are simulated to obtain the minimum cold... 

The overall heat transfer coefficient (OHTC) of air in a double-pipe helical heat exchanger is studied and experimentally investigated. In order to increase the rate of heat transfer in the annulus section, a copper-wire fin is soldered on the outside area of the internal tube. The literature correlations’ results are presented against the experimental data by changing mass flow rate and temperature, and consequently changing the Reynolds number. Further, a new method is suggested to obtain the heat transfer coefficients of double-pipe helical heat exchangers for the internal tube and the annulus section by combining two of the previously proposed approaches and making subsequent... 

In this paper, optimization on a two-tube helical heat exchanger with a fin is represented. The spiral pipes heat exchanger which is made of the cooper is adopted for investigation. The effects of three types of fins with the proposed geometric shapes on the overall heat transfer coefficient and pressure loss are investigated. The fins are located on the inner surface of the outer pipe. The obtained numerical results are compared with the experimental results, and a good agreement is observed between the results. The studies show that the total heat transfer coefficient has increased by 170% compared to an exchanger with no fin. Therefore, the best fin has been selected based on the...