• Energy Research

Abstract High-temperature exhaust gas generated from turbines is a common issue among industrial applications. A wet system, e.g., spray cooling, can be an effective way to decrease the temperature, especially in limited spaces when ventilation can be ineffective. In this paper, the performance of water spray cooling on high-temperature (above 450 °C) exhaust gas using a 4 × 4 nozzle array, which consists of eight pressure-type spiral nozzles (PN) and eight impinging-type nozzles (IN), in a confined chamber was investigated. A standard procedure was developed to perform spray cooling tests at three back pressures (BPs), i.e., 0.5 MPa, 1.0 MPa and 1.5 MPa. Four cross-sections were dedicated to measure dry-bulb temperature and one of them can report wet-bulb temperature, all in real time. The results show that, first, spray cooling can decrease the temperature of exhaust at the four sections by approximately 10–100 °C, depending on working nozzles’ row and flowrate. The position of working nozzles has a significant impact on the cooling effects near the exhaust outlet, but not for the distant sections since the air and the exhaust can be better mixed. Second, both types of nozzles have similar correlations between BPs and flowrates. However, it is easier for IN to contribute to humidity ratio increment due to better atomization at higher BPs. As a result, the moist air during IN tests was prone to get saturated and significantly compromised the ability of evaporative cooling. Third, an analytical model was developed and validated using experimental data to predict cooling capacity at the near-exhaust cross-section. Furthermore, linear empirical models were also proposed and obtained to predict cooling effects using dry- and wet-bulb temperature difference and total flow rate at the sampling section.

Abstract High temperature impinging jet and the corresponding thermal protection is a common issue among industrial applications. This paper investigated the heat transfer of high temperature jet impinging a cross-shaped plate, by the following steps. First, a theoretical model was proposed to predict the temperature increment of the back-side surface(s) that opposed to the impinging surface, by simplifying and assuming the heat transfer process can be governed by convection. Second, an experimental mockup was used to produce high temperature (~ 500 °C) impinging gas jet with high speed (~56 m/s) near the exhaust nozzle (150 mm in diameter). In addition, three types of insulation materials are selected and tested. Third, the optimal thermal protecting solution was obtained by comparing back-side temperature increments. The model predictions were also compared and discussed with the experimental data.

Abstract In a passive nuclear plant, the main control room must provide self-support functions for 72 h after an accident occurs. In this isolation mode, the heat generated by indoor occupants and equipment should be removed by using concrete walls that are 610 mm thick, and the finned ceiling made of concrete should maintain thermal habitability. However, the finned ceiling design has not been studied in normal buildings, and the cooling storage effect of plate-shaped fins is usually ignored during the design phase. In this study, a novel parametric resistance–capacitance thermal network is proposed to simulate the thermal performance of different fin-plate layout forms in the case of an accident. An experiment was conducted on a 1200 mm × 1200 mm × 610 mm fin-concrete module for 72 h to validate the model under constant air temperature conditions. Based on the model, multi-objective optimization was conducted to obtain optimal solution sets by using a radial basis function approximation model. The results show that the optimal performance indicators can be classified into unsteady and quasi-steady states, in which the dominant factors for heat transfer include the heat transfer area and the thickness of the finned plate, respectively. Further, the optimal solution sets for different convection and heating conditions obtained through an optimization process are used to design a fin layout based on actual temperature control demands and cooling storage.

This paper investigated the heat transfer of high temperature jet impinging a cross-shaped plate. An experimental mockup was designed and used to produce high temperature (∼500 °C) impinging gas je...

Abstract The emission standards of non-methane total hydrocarbon were tightened from 120 mg/m3 to 10 mg/m3 for Chinese industries in 2012. Despite the investment into environmental treatment, many factories have since been struggling to hit the emission reduction target. Emissions from various production processes have the characteristics of low concentration and intermittency, so the conventional ventilation systems relying on high flow rates to collect and exhaust the low-concentration pollutants often result in large scale, high economic and energy consequences, but poor performance. In this study, a novel circulating system was proposed to concentrate pollutants and reduce the exhaust air volume using a rubber refining process as an example. Firstly, a circulating ventilation model based on the mass balance was established to predict the variation of pollutant concentration within the system, and two control strategies (i.e. continuous or intermittent exhaust scheme) were developed to improve the pollutant capture efficiency of the system. Secondly, the emission intensity of pollutants in the rubber refining process was measured and further used as boundary conditions in the subsequent simulation. Thirdly, the CFD simulation was adopted to optimize the circulating air volume, return air jet angle, and exhaust air volume of the circulation system. Results showed that the optimized design of the circulation system with the continuous/intermittent exhaust scheme can achieve a 14.5/32.6 fold increase in the exhaust concentration of VOCs and a 75.8%/53.8% reduction in exhaust air volume.

When an accident occurs in a nuclear power plant, the main control room (MCR) is isolated while initiating emergency measures. To keep the indoor temperature from increasing to dangerous levels, heating loads need to be mitigated by heavy concrete insulation, on which rectangular fins are installed to improve the heat transfer. However, the effect of optimized fins for the thermal environment has not been investigated. In this study, a parametric model based on COMSOL Multiphysics is proposed to describe the dynamic heat transfer process of a fin-concrete heat sink and validated by an experiment on a 1200 mm × 1200 mm × 610 mm module. A COBYLA algorithm has been implemented to optimize the fin parameters combination with different steel consumption. Results show that both steel consumption and fin structure parameters need to be taken into consideration when optimizing. The optimal heat transfer increases by 2.84%, 7.33%, and 9.26%. The maximum indoor temperature is 0.77, 1.85, and 2.39 °C lower than the prototype when the steel consumption is 100, 150, and 200 kg/m2, respectively. Furthermore, the heat storage will improve as increasing the steel consumption if the fin structure is optimized. And it does not necessarily so without optimization. Finally, the optimization potential increases with the decrease in fins space, the increase in fin height, and the increase in fin thickness. In the case of only taking reducing the maximum indoor temperature into account, reducing fins space and increasing fin height are the superior choices for the optimal design of heat sink.

A large-scale sphere-shaped experimental facility for neutrino detection is designed as a 23-latitudinal layer composite by using organic glass as the major raw material and is assembled via mass polymerization through a top-to-bottom approach. Heating belts at 4200 W/m2 are used to anneal the bonding joints of external and internal spherical surfaces and produce high-temperature thermal plumes. Buoyancy-driven plumes should be effectively mitigated using ventilation to ensure the near-surface air temperatures above the finished layers can be delicately controlled within 21±1 °C to minimize the deformation of the facility. Schemes to control plumes on both surfaces were investigated using Computational Fluid Dynamics (CFD) method by following a performance-based approach. First, an independent field study was conducted to measure surface temperature and heat flux of mass polymerization and provide references for simulations. Second, dynamic buoyancy-driven plumes produced along the external and internal spherical surfaces were simulated under a no-ventilation scenario. After contacting with the plumes, three periods, in which buoyancy, convection, and advection, were dominating, can be observed according to the changes of near-surface air temperature. Moreover, the temperature and Ra number of the surface-attached plumes were used as indicators to assess the intensity of the plumes quantitatively. Third, three major ventilation schemes, i.e., general, push-pull, and sphere-attached ventilations (with three subdesigns), were compared under the same air change rate level on the basis of the following perspectives: (1) air temperature distributions above the polymerizing layer, (2) overall heat exhaust efficiency, and (3) total spaces where temperature was higher than 22 °C. Results indicated that the combination of push-pull and side-supply ventilations, by which the heat exhaust efficiencies were up to 1.87–3.24, was found to be most effective to control thermal plumes, with approximately 0.1% of the total surrounding air exceeding 22 °C.