M. S. Youssef

A two-equation heat transfer model for predicting turbulent thermal fields under arbitrary wall thermal conditions

Abstract A new proposal for the P 2 -e 2 heat transfer model is presented along with an accurate prediction of wall turbulent thermal fields. The proposed model reproduces the correct wall limiting behavior of velocity and temperature under arbitrary wall thermal conditions. Assessment of the model constants and functions are made to generalize applicability of the P 2 -e 2 model. The proposed model is tested with five different typical thermal fields, which often occur in engineering applications, in wall turbulent shear flows. The predicted results are compared with the available experimental and full simulation data, together with the previous model predictions. It is shown that the present model works much better than the previous models.

Characteristics of Mean Droplet Size Produced by Spinning Disk Atomizers

Characteristics of mean droplet size of spray produced by spinning disk atomizers were experimentally investigated. The phase-doppler particle analyzer (PDPA) was used to measure the droplet size of water spray in the downstream distance along the spray trajectory. Effects of various operating conditions on the mean diameter had been studied. The studied variables were: the rotational speed in the range of 838 to 1677 rad/s (8,000–16,000 rpm), the liquid flow rate in the range of 0.56 to 2.8 × 10−6 m3 /s (2–10 L/h), the disk diameter in the range of 0.04 to 0.12 m, and the downstream tangential distance along the spray trajectory of up to 0. 24 m. The Sauter mean diameter (d32 ) was used to represent the mean of generated spray droplet sizes. The results indicated that the Sauter mean diameter can be correlated with dimensionless groups, such as the Reynolds number, Weber number, flow coefficient, and the ratio of downstream distance to disk diameter. Based on this correlation, it was found that the Sauter mean diameter (d32 ) increases as the downstream tangential distance, and liquid flow rate increase. Similarly, a decrease of rotational speed and disk diameter results in an increase in the Sauter mean diameter (d32 ). A comparison between the developed correlation and correlations obtained by other researchers has been presented and discussed in detail.

Study of Heat Transfer and Fluid Flow in Transitional Regime Inside a Channel With Offset Plates Heated by Radiation for Photovoltaic/Thermal System

This study investigates experimentally and theoretically both the effects of operating and configuration parameters on convection heat transfer process and fluid flow characteristics for air flowing in transitional regime through parallel plate channel with offset plate segments heated by a radiation heat flux. This configuration is intended to be applied into air heater solar collectors and/or a combined photovoltaic and air heater solar collector system (PV/T). In the experimental measurements, the operating parameters tested were Re values ranging from 2580 to 4650 with combination of incident radiation heat flux (qinc ) values of 400, 700, and 1000 W/m2 , respectively. The experimental results show that the local Nusselt number (Nux ) is not unique function in the axial distance. In addition, a linear relationship between Re and apparent friction factor is observed. Moreover, in case of Re = 2600, increasing the incident radiation flux values by 175% and 250% leads to an increase in Nux values by 20% and 35%, respectively. The theoretical results indicate that, combinations of Re values inside the channel falling within the laminar regime with selections of both the plate’s length and thickness can lead to the convection heat transfer enhancement with avoiding of additional pumping power penalty when the channel flow falls in transitional regime.Copyright