One-dimensional Unsteady Heat Transfer Model Research Articles

Cylindrical Rotating Detonation Engine with Propellant Injection Cooling

A cylindrical rotating detonation engine (24 mm diameter) with multiple injector holes on the combustor side wall for both propellant injection and cooling by injector gas flow was designed and tested. As each set of injectors created its own detonations, the synchronized detonation waves propagated along the three injector rows. From the axial view, those detonation combustion regions stood off from the injector surface as the non-well-mixed propellant existed between the wall and the combustion zone. This combustion region tended to broaden in lateral and radial directions as the mass flow rate increased by pushing its region with the injected propellant. Wall heat flux and heat balance were evaluated by a one-dimensional unsteady heat transfer model with propellant injection cooling. Even when the flow rate was doubled, the increase in the wall heat flux was only 18–25%. This heat trend and the image of standoff self-chemiluminescence from the injector surface implied that a non-well-mixed unburned propellant acted as a heat-reduction layer to ease heat load into the combustor. Measurements and thermal analysis verified the flow structure near the injector and heat-exchange mechanism due to the propellant gas flow, which has a potential for thermal steady operation.

A transient composition tracking method for natural gas pipe networks

A transient composition tracking method is developed for natural gas pipe networks. It adopts the control volume method for hydraulic simulation and a one-dimensional unsteady heat transfer model for thermal simulation. In order to model the junction in the network, a special grid is proposed to connect all adjacent pipes together. Under this grid, the momentum equation could be discretized by the first-order upwind scheme while the mass equation could be discretized just like an ordinary pipe node. To track the composition, the advective concentration equation is given for each component. Therefore, the gas composition in the pipe network could be predicted in real time and its influence on the calculation of property parameters could be taken into consideration. Based on these models, a transient composition tracking algorithm is developed for natural gas pipe networks. It consists of three parts: transient flow simulation, composition tracking and parameters calculation. Case studies show that the proposed method can provide reliable results for transient flow simulation. Compared with the measured data, the composition outcomes given by this method are also very accurate. In addition, the impact of injecting LNG/H2 into the pipe network is quite complicated and should be treated with caution.

Determination of optimum insulation thicknesses for salinity gradient solar pond’s bottom wall under different climate conditions

The salinity gradient solar pond is one of the most efficient tools that can be used to collect, convert and store the solar energy. The performance of solar pond specially depends on heat losses from it. The performance of the solar pond could be improved by using the thermal insulation on the bottom and sides of the solar pond. Determination of insulation thickness is very important; it is commonly estimated based on the climate conditions, insulation materials and economic parameters. Therefore, in this study, the optimum insulation thickness, cost and energy savings were calculated for a salinity gradient solar pond under different climate conditions. An economic analysis was applied to obtain the optimum value of the insulation thickness when the polyurethane was used as the insulation material. For this purpose, the temperature of the lower layer of the solar pond was calculated using the one-dimensional unsteady heat transfer model inside the pond. The model and the literature experimental lower layer temperatures showed a good agreement, with the average deviation of 5%. They also had the same trend in all months of the year. The results revealed that the optimum insulation thickness strongly depended on the solar irradiance and the ambient temperature. This study also found that by introducing the optimum insulation thickness of 62–122 mm, according to the climate conditions, in the solar pond’s bottom wall, the energy saving could be enhanced by 36.7–55.2% as compared with the solar pond without insulation.

Investigation of a double-PCM-based thermoelectric energy-harvesting device using temperature fluctuations in an ambient environment

Energy-harvesting devices, consisting of thermoelectric modules and phase change materials (PCMs), can extract energy from the ambient environment for the self-power supply of many small electronic devices such as wireless sensors. However, due to the distinct temperature ranges of various seasons in different places, these devices’ power generation performance may be seriously impaired. In this paper, a new double-PCM-based thermoelectric energy-harvesting device based on temperature fluctuations in the ambient environment is proposed to improve device performance. A double-PCM-based device has been built and tested in an environment with a large temperature range (0–40°C) for three days. Experimental results show that the average output power of the double-PCM-based thermoelectric energy-harvesting device under matched load resistance outperforms that of the single-PCM device by 35.8%. A one-dimensional unsteady heat transfer model is established to describe the temperature variation of PCMs. The influence of phase change is considered through variations in PCMs’ specific heat capacity. This work demonstrates that the proposed double-PCM-based thermoelectric energy-harvesting device performs better over a large temperature range and is more suitable for small electronic devices operating at different times and in different places.

Performance analysis of capillary front-end heat exchanger for subway tunnel

The ground source heat pump system can remove the waste heat from the subway tunnel and supply heat to the above-ground building in winter at the same time, which not only alleviates the thermal accumulation of the tunnel surrounding rock, but also effectively utilizes renewable energy. In this study, the heat transfer performance of the capillary front-end heat exchanger for the subway tunnel ground source heat pump system was studied by simulation. The capillary heat exchanger was simplified as a surface heat source, and the one-dimensional unsteady heat transfer model was established by TRNSYS. The heat transfer process between the capillary, the surrounding rock and the tunnel air was simulated. The effect of inlet water temperature, water flow velocity, initial temperature of tunnel surrounding rock and tunnel air temperature on the performance of capillary heat exchanger was analyzed. Based on the actual conditions, the range of the capillary heat flux was given. Besides, the heat transfer performance of the capillary under intermittent operation was studied. It was found that, when the operating time ratio was 2/3, 1/2, 1/3, and 1/6, the heat flux increased by 10.6%, 21.8%, 28.3%, and 36.9% respectively compared with continuous operation.

Thermal Conductivity Simulation of High Temperature Overalls Materials

When workers work in high temperature environments, they need to wear high temperature work clothing to avoid burns. The garment is often composed of three layers of fabric material, which are referred to as layers I, II, and III from the outside to the inside, and there is a gap between the layer III and the skin. We refer to this void as the IV layer. In order to make the design of special clothing more efficient, reduce research and development costs, and shorten the development cycle, this paper uses mathematical models to determine the temperature changes outside the skin of the dummy. We assume that the body temperature of a dummy wearing a high temperature workwear can be controlled at 37 °C. We have established a set of thermal differential equations as a heat transfer model for the four layers of high temperature work clothing. First, we consider three heat transfer modes of heat conduction, heat radiation and heat convection, and analyze the heat conduction form of each layer to obtain a one-dimensional unsteady heat transfer model. Then, the numerical solution of all partial differential equations is obtained by the finite difference method of Crank-Nicolson format, and the temperature distribution outside the skin of the dummy is obtained. Finally, this paper gives a proposal for the design work of four-layer high temperature work clothing in combination with the actual situation.

Nonlinear response behavior of Fe/Bi2Te2.7Se0.3 artificially tilted multilayer thermoelectric devices to thermal contact

The response behavior of artificially tilted multilayer thermoelectric devices (ATMTDs) to thermal radiation has been intensely investigated for remote thermal detection; however, their response behavior to thermal contact is still not well understood. In this letter, Fe/Bi2Te2.7Se0.3 ATMTDs have been fabricated by alternately stacking metallic Fe layers and Bi2Te2.7Se0.3 layers to reveal the response behavior to thermal contact. It was found that the transverse thermoelectric voltages (ΔVx) of the ATMTDs once contacting heat source were rapidly raised in the first seconds and then nonlinearly attenuated after reaching maximum ΔVx. A one-dimensional unsteady heat transfer model was proposed to reveal the attenuation process, which obeys an exponential variation and strongly depends on the heat source temperature. Using the ATMTDs as temperature sensors, the detection uncertainty can be less than 1 K. This work has demonstrated great potential application of the ATMTDs in the field of contact-type temperature detection.

A novel building energy efficiency evaluation index: Establishment of calculation model and application

In current system of building energy efficiency, the building energy saving rate is calculated based on energy consumption per unit area on a certain past stage. The approach is restricted by the development of economy, progress of energy-saving technologies and climate change. In present work, a novel building energy efficiency evaluation index is developed to represent building energy saving performance. A building model can be first established according to architectural design scheme, current standards and operating conditions. Then, average daily indoor air temperature would be obtained using hourly outdoor air temperature as input conditions, with the one-dimensional unsteady heat transfer model. Finally, the calculation equations of energy saving of envelopes (ΔS) and building energy saving rate (BESR) are derived. In application, a building envelopes trade-off option is proposed and a target building in Western China is employed for case study. The results indicate that, about 19.3% of whole energy achieving indoor human thermal comfort is provided by building envelopes for the target building. The parametric analyses indicate that, BESRs of the standard building model in cold climate zone (2A) are much higher than those in cold climate zone (2B) in China. It is found that, the trade-off option can also be employed to select and optimize insulation materials and layer thicknesses. The approach can provide new thoughts for evaluation of energy saving performance of building envelopes in the design phase.

Investigation on the hot melting temperature field simulation of HDPE water supply pipeline in gymnasium pool

Abstract In view of the special needs of the water supply and drainage system of swimming pool in gymnasium, the correlation of high density polyethylene (HDPE) pipe and the temperature field distribution during welding was investigated. It showed that the temperature field distribution has significant influence on the quality of welding. Moreover, the mechanical properties of the welded joint were analyzed by the bending test of the weld joint, and the micro-structure of the welded joint was evaluated by scanning electron microscope (SEM). The one-dimensional unsteady heat transfer model of polyethylene pipe welding joints was established by MARC. The temperature field distribution during welding process was simulated, and the temperature field changes during welding were also detected and compared by the thermo-couple temperature automatic acquisition system. Results indicated that the temperature of the end surface of the pipe does not reach the maximum value, when it is at the end of welding heating. Instead, it reaches the maximum value at 300 sand latent heat occurs during the welding process. It concludes that the weld quality is the highest when the welding pressure is 0.2 MPa, and the heating temperature of HDPE heat fusion welding is in the range of 210 °C–230 °C.

Heat-Transfer Stability of Porous Fibrous Composition under Different Condition

In this paper, the influences of different conditions on heat-transfer stability of porous fibrous composition were analyzed by the one-dimensional unsteady heat transfer model. It was resulted that the surface condition of composition was key parameter for heat performance during different thermal process. Great humidity and thermal difference caused the heat transfer fluctuating of material covering, and then changed the thermal conductivity. For the insulation materials under low temperature, the heat performance was sharply fluctuated nearby 0°C.