Search

Highlights • Ultrasonic is firstly used to enhance heat transfer of PA-SA in a cylindrical unit. • Heat transfer of PA-SA increases with the increasing of ultrasonic power and time. • The time of PA-SA from 30 °C to 70 °C reduces 46.81% with ultrasonic (150 W, 30 min). • Optimal effect of ultrasonic on heat transfer is obtained by intermittence action. Abstract In this work, ultrasonic is firstly used to enhance the heat transfer rate of palmitic acid-stearic acid eutectic mixture (PA-SA) in a cylindrical stainless-steel unit. The heating boundary condition of the phase change material (PCM) is constant wall temperature condition in this work. The effects of ultrasonic parameters including ultrasonic power and operation time on heat transfer enhancement of PA-SA are experimentally studied. The results show that the heat transfer rate in melting process of PA-SA increases with the increasing of ultrasonic power, Specifically, heat transfer rate is increased by 10.64%, 23.40% and 31.91% at the ultrasonic power of 60 W, 105 W and 150 W respectively. The heat transfer rate of PA-SA is also increased with the increasing of ultrasonic action time. Effect of ultrasonic on heat transfer enhancement varies in terms of different ultrasonic action stage of the charging process. Therefore, the optimal effect of ultrasonic on heat transfer enhancement can be obtained by using intermittence ultrasonic. In conclusion, it is an effective way to enhance the heat transfer of PCM used in the latent heat storage system by intruding ultrasonic. [ABSTRACT FROM AUTHOR]

Abstract: The solution for steady-periodic heat transfer of attached underground engineering can be expressed by complex temperature. The solution involves two parts: steady temperature and complex amplitude of the annual temperature fluctuations. Using a mathematical model of heat transfer of attached underground engineering, the calculation area is divided into eight rectangular blocks according to the interzone temperature profile estimation (ITPE) technology, and the solutions are obtained for all the parts using the separation of variables method. During the solution, the Fourier coefficients are determined based on the continuity of the heat flux and boundary conditions; as a result, a system of 14N linear equations with 14N unknowns is obtained, where N is the truncation point of the Fourier series. The linear equations can be easily solved with a standard method (e.g. Gauss–Jordan elimination). The semi-analytical solution obtained by the ITPE can provide rapid and accurate solution for calculation of heat transfer as well as the basis for analysis of the influential factors of the heat transfer. [Copyright &y& Elsevier]

Abstract: Using a mathematical model of heat transfer of attached underground Engineering Envelope, the calculation area is divided into 13 rectangular blocks according to the Interzone Temperature Profile Estimation (ITPE) technology, and the solutions are obtained for all the parts using the technique of variable separation. During the solution, the Fourier coefficients are determined based on the continuity of the heat flux and boundary conditions. The influences of the temperature of earth surface and the heat transfer coefficient between air and wall on heat flow through the envelope has been quantitatively analyzed. The results show that the heat flux through the envelope is no longer monotonously increase or decrease with increase of the influencing factors. By analyzing the curve of r-value (the ratio of the flux through the roof to the overall flux through the engineering section including the floor and walls), it can be concluded that the heat flow between the first floor of the building and the engineering is the major reason and the shape of the engineering is another one. [Copyright &y& Elsevier]

Abstract: Using a mathematical model of heat transfer of basement, the calculation area is divided into eight rectangles according to the interzone temperature profile estimation (ITPE) technology, and the solution obtained for all the parts by the separation of variables technique. During the solution, the Fourier coefficients are determined by the continuity of the heat flux and boundary conditions, as a result, a system of linear equation group including equations has been obtained. The effect of building materials on the temperature and heat flux for the building envelope has been evaluated by calculating the temperature and heat flux for three buildings built with different building materials. The results show that the highest relative error in heat flux among the three envelopes built with various non-insulation material is 27.8%, which indicates the thermal conductivity of the building materials is an important factor of the heat transfer of the envelope. [Copyright &y& Elsevier]