A New Analytical Model for Calculating Transient Temperature Response of Vertical Ground Heat Exchangers with a Single U-Shaped Tube

The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient response. In comparison to the existing models, this proposed model can account for the fluid thermal storage effect and heat rate difference between the two legs of the single U-tube. With the aid of this proposed model, we conduct a thorough sensitivity analysis to investigate the effects of different influencing factors on the thermal transient response. The calculated results show that fluid thermal storage and the rate difference can significantly influence the thermal response during the early studied period. Therefore, the effect of fluid thermal storage should not be neglected when the early-time thermal response is investigated. The thermal interference between the two legs will reduce the heat capacity of GHEs. A large distance between these two legs can be favorable for practical use.

Rewetting of Vertical Pipes by Bottom Flooding Using Nanofluid as a Coolant

The present investigation reports the rewetting phenomenon by bottom flooding in vertical pipes using both water and nanofluid as coolant. The transient temperature response of rewetted surface indicates that rewetting takes place faster in nanofluids than in water. The effect of several parameters, including the coolant flow rate, distance from the inlet of fluid, concentration of nanoparticle loading on the rewetting characteristics, has been investigated. The rewetting velocity, for both water and nanofluid, is observed to depend strongly on the inlet coolant flow rate and initial wall temperature of the tube. The rewetting velocity is observed to follow the correlation for water proposed in an earlier work. Starting from the logic proposed in that previous report, the authors propose a correlation for predicting the rewetting velocity in nanofluids.

Experimental Study of Deicing Process in an Airfoil Application

A customized airfoil for deicing process was designed, built and tested in order to investigate the effect of icing on the airfoil and the process of removing it by heating processed. A numerical simulation was performed to provide more details of the fluid flow characteristics of the presence of the ice and the temperature distribution on the airfoil when it reached the steady state conditions. An experimental setup was developed to measure and record the transient temperature response on the trailing and leading edge respectively. The experimental results suggest that from a minimum temperature of −10°C on the trailing edge, and 0°C in the leading edge with ice on the surface, the time to reach the steady state temperature of 46°C in the leading edge and 38°C in the trailing edge was close to 8 minutes approximately.

Basic Study on Transient Temperature Response of Papers in a Thermal Transfer Printer

This study describes temperature response of papers in a thermal transfer printer. Thermal transfer printer produces an image by heating heat sensitive papers using a thermal head. The print quality of the thermal printing is highly dependent on a temperature response of the paper. Our research targets to develop a control technique of temperature of the printing paper to improve the print quality of the thermal transfer printer. In this report, our special attention is paid to investigate the temperature response of a paper when the heat is applied by the thermal head. The temperature transient in the paper is measured while changing the type of the paper. Moreover, in order to investigate a relationship between thermophysical properties of papers and the temperature response, the thermophysical properties are measured. A thermal network analysis is additionally performed and the effects of a contact resistance between the paper and the thermal head are also investigated. It is found that transient temperature response of the printing paper is strongly dependent on a type of the printing paper and the level of an input heat. A change of the temperature response is caused by the difference of thermophysical properties of the paper and a variation of a contact resistance between the paper and the thermal head.