محمد نظیفی فرد

Thermal energy is one of the most important issues in most industries, because conversion of energy from fossil fuels to thermal energy occurs in almost all conventional industries. Therefore, considering the lack of fossil resources and the increasing pollution of human environments, attention to the proper use of thermal energy should be considered by researchers. In recent years, attention has been focused on the use of new technologies to increase the efficiency of thermal systems, including heat exchangers. Among these technologies, which are considered in this paper, is the simultaneous use of nanofluids and torsion strips placed inside the heat exchanger tube. In the present numerical study, for the first time, a two-phase Euler-Lagrangian numerical simulation has been used in this geometry to overcome the shortcomings of previous monophasic studies. The effects of independent variables such as the volume fraction of nanoparticles and Reynolds number and the structural variables of the torsion bar, such as the shear and the torque ratio on heat transfer and the coefficient of friction, have been investigated. The results showed that other variables except Reynolds have the same qualitative effects on heat transfer and friction coefficient.

Today, increasing the efficiency and optimization of energy systems in terms of economic and environmental conditions is of particular importance. So far, several methods have been proposed to increase the heat transfer in thermal systems, including the use of nanofluids and types of fluid flow turbulators. In this research, the application of both nanofluid and twisted tape to improve the heat transfer coefficient were numerically investigated. Different turbulence models were used to simulate fluid turbulence. The results showed that increasing the nanoparticle volume fraction, reducing the twisting ratio, and increasing the Reynolds number resulted in an increase in heat transfer. By reducing the twisting ratio from 15 to 5, the heat transfer rate increases from 8-16%. With rising Reynolds number from 10,000 to 20,000, maximum temperature differences decreases by 4.5%. Moving downstream of the flow, the difference between the maximum temperature of the sections decreases. Increasing the heat transfer and intensifying the effects of the twisted tape to downward are the reasons for this decline.

Knowing patient exact dose during radiological activities is considered as one of the main principles to decrease radiation-induced dangers which are not really necessary and affect a great deal of people. In this respect, in recent years many extensive studies have been done on types of photodiodes and production of X-ray detectors using semiconductor elements. Since these elements are not very expensive and are too small in size and we can gain information of received dose immediately and without wasting time, they are mostly used. We aim to design a dosimeter using semiconductor elements for X-ray diagnostic radiation dosimetry. We used a typical silicon diode. Also, a stable circuit was applied to detect diagnostic X-ray radiations. To determine logical correlation between the electronic behavior of PIN sensor and specific parameters of X-ray (KV, mA.S), the designed circuit and calibrated ionization dosimeter were simultaneously irradiated by the diagnostic X-ray radiation with different energies and intensities. Finally, signal behavior was converted to digital amounts by the designed circuit. The amounts were then compared with received dose as recorded by ionization dosimetry. Results of the designed dosimetry behavior and ionization dosimetry simultaneously showed that the designed dosimetry responses are rather linear in different radiations whereas responses of the dosimetry under study is linear in low voltages while in high voltages no specific linear relation was found. It seems that used photodiode due to its availability, and low cost can be used as a dosimeter to measure diagnostic x-ray radiations in low energies.

Precise measurement of void coefficient in two phase flow is one of important parameters in thermal hydraulic parameters such as average density, two phase flow pressure drop and two phase flow pattern. In this study the void coefficient has been correlated experimentally based on attenuation coefficient gamma ray emitted form 137Cs source passing a rectangular channel. The average void fraction was reasonably measured for a two-phase flow in the rectangular channel

The ionizing radiations are able to make either a permanent or temporarily damage in the electronic circuits. The temporary effects during irradiation can be used to detect the ionizing radiation. In this study a diode in reverse bias has been used to investigate the effects of ionization radiation on semiconductors. The variation of reverse current of diode has been monitored due to interaction of gamma with semiconductor material. The commercially available diode N4001 was used in serial connection with resistant. Results show the major effect of irradiation on diodes is the increase in reverse current. The increase in reverse bias current is linked to the creation of mid-gap states. It is possible to detect the gamma radiation using a simple diode circuit in reverse bias. Thus, a silicon diode can be thought of as a solid-state equivalent to an ionization-chamber radiation detector.