An inverse design method is proposed to achieve the pre-set control objectives of the aircraft cabin environment. The method combines the artificial neural network and the genetic algorithm, and the training and testing data of the artificial neural network is obtained by computational fluid dynamics analysis. Both of the thermal comfort and energy consumption are considered in the inverse design. The artificial neural network is used to identify the relationship between the thermal comfort and the air supply parameters (inlet velocity magnitude and angle, inlet air temperature). The genetic algorithm coupled with the well-trained artificial neural network is used to design the aircraft cabin environment. Numerical results show that the Bayesian regularization algorithm is proved to have better generalization capability than the other training algorithms for the artificial neural network. The increase of training data quantity improves the generalization capability of the artificial neural network, while it spends more simulation time. A computational fluid dynamics database with 60 datasets is shown to be suitable to the present inverse design, and the testing error of the artificial neural network is below 8.2%. Several groups of optimal air supply parameters are found with different trade-offs between the thermal comfort and energy consumption. The best solution of thermal comfort, i.e., the percentage of zone with |PMV| >0.5 in all cabin control domains, is less than 7.8%.

Engine oil migrating into the bleed air stream of aircraft environmental control systems occurs with enough frequency and deleterious effects to generate significant public interest. While previous work has explored the chemical makeup of the contaminants in the aircraft cabin during these events, little is known about the characteristics of the aerosol resulting from oil contamination of bleed air. This article presents particle counter data (giving both size distributions and concentration information) of the oil droplets from simulated jet engine bleed air. Four particle counters—a scanning mobility analyzer, an aerodynamic particle-sizer, an optical particle counter, and a water-based condensation particle counter—were used in the study encompassing a size range from 13 nm to 20 μm. The aerosol characterization is given for different bleed air temperatures and pressures. The data show a substantial increase of ultrafine particles as the temperature is increased to the maximum temperatures expected during normal aircraft operation. This increase in ultrafine particles is consistent with smoke generated from the oil. The pressure of the bleed air had little discernible effect on the particle size and concentration.

Transient thermal events in air-cooled data centers may lead to undesirable operating conditions such as the formation of hot spots and associated degradation of equipment reliability. These transients may be caused by cooling equipment failures, server load changes, or other time-dependent scenarios in data center operations. This paper introduces a fast-executing hybrid computational fluid dynamics (CFD)/Lumped-Capacitance model for predicting server inlet temperatures resulting from common transient events such as server shutdown, partial or total chilled water interruption, or partial or total failure of the computer room air handlers (CRAH). The model uses initial steady-state CFD or experimental data in combination with several lumped-capacitance models of the various thermal masses in the data center, including the servers, the room enclosure, the CRAHs and the underfloor plenum. The inclusion of these thermal capacitances and their associated thermal conductance was found to be an important contributor to the overall transient response of the data center air-space. The model predictions have been compared with experimental data obtained in a three-rack data-center test cell and found to agree well with the experimental measurements. Examples of the application of the model to more realistic data center configurations are also given.

One of the most influential factors of the performance of a finned-tube heat exchanger is the distribution of the air passing through it; therefore, it must be known in order to produce a highly efficient design. We examined two different common style air-to-refrigerant, finned-tube heat exchangers: a single-slab coil oriented at an angle of 65° to the duct wall and an A-shaped coil with an apex angle of 34°. We used particle image velocimetry (PIV) to measure their in-situ airflow distributions. The results show that the airflow distributions for both heat exchangers are highly nonuniform with different sections being subject to vastly different air velocities. We also used a momentum resistance-based computational fluid dynamics (CFD) approach to model the airflow distributions through these heat exchangers. The modeled results agreed with the measured values, with most of the simulated velocities falling within +/-10% of the measured velocities. The results of this study show that the velocity profile for any configuration is strongly influenced by the geometry of the heat exchanger and other features in its proximity and, therefore, each installation configuration will have its own unique velocity distribution. The information presented in this paper documents the maldistribution of airflowing through finned-tube heat exchangers and highlights the sources and magnitude of the nonuniformities.

The Imanta district heating plant began operation in 1974 as one of the main heating plants for the Riga district heating system. Until now, it has undergone several reconstructions. First, the ordinary boiler plant with steam and hot water boilers was reconstructed to be a natural gas-fueled combined cycle cogeneration plant supported with hot water boilers. Then, one of the cooling towers of the cogeneration section was replaced by an absorption heat pump/chiller, thus providing the closed cooling water circulation system and recovering 2 MWth (7 MMBTU/h) low-grade heat otherwise lost in the atmosphere. The driving force for the absorption heat pump is steam produced by the steam boiler (3 MWth = 10 MMBTU/h) already located at the boiler plant. The efficiency of the absorption heat pump is closely related to the operation of the cogeneration unit, outside temperature, and district heating water temperature regimes. The case study confirms that a more efficient energy production system reduces the fuel consumption with the same amount of the produced energy, thus lowering the expenses on energy production and reducing the amount of the polluting emissions into the atmosphere.

Blade passing frequency (BPF) noise is the dominating component of the flow induced noise of centrifugal fans. The numerical methods for BPF noise prediction, based on the computational aeroacoustics (CAA), have been published for decades. However, there are a couple of challenges for accurately predicting noise for industrial centrifugal fans. The first arises from the fact that the free field hypothesis, adopted in the numerical model, has not yet been carefully studied. The second challenge stems from the current criteria for which the prediction results are compared to the measurement data. Because the test conditions do not always satisfy the requirements of the numerical model, inaccurate predictions occasionally resulted. Therefore, since the prediction results may deviate largely from the test data, the applicability of these methods is severely limited.

Solar energy systems in combination with thermal driven sorption chillers for air conditioning are gaining increasing attention. Since solar energy is available only during daytime and solar cooling systems are usually intermittent and susceptible to the weather, applying cold storage methods to solar air-conditioning systems is favorable to utilize renewable energy and enhance the system stability. A self-developed phase change material (PCM) providing a suitable phase change temperature of 14.97°C and a reasonable phase transition latent heat of 115.1 kJ/kg is used to fabricate a cold storage tank. The aim of this article is to experimentally investigate the performance of the cold storage tank for solar air-conditioning application. The experiment includes a small-scale steady-state testing of a single spherical capsule and a solar air-conditioning system integrated with the PCM cold storage tank. The temperature distribution and phase change interface movement of the capsule are theoretically predicted. Main parameters of the cold storage tank, namely the inlet and outlet water temperature, internal temperature variation of capsules, charging/discharging capacity and charging/discharging rate are analyzed. The experimental results show that the charging and discharging process completed in 230 min and 220 min under steady states. While under unsteady states of a solar air-conditioning system, the charging and discharging process of the phase change cold storage tank completed within 320 min and 110 min with the total amount of charging and discharging capacity of 1016.1 kJ and 942.8 kJ, respectively. The phase change cold storage tank manifests good feasibility and stability for solar air-conditioning application.

A computational fluid dynamics (CFD) numerical simulation method was used in this study to simulate the indoor thermal environment affected by three air-supply modes, upper-supply bottom-return mode, upper-supply top-return mode, and bottom-supply top-return mode, in the condition of the fixed point heat source, and explored the change rule of the predicted percentage dissatisfied (PPD) affected by the three air-supply modes. A suitable air-conditioning supply mode might better meet the requirements of human to the indoor thermal environment. The results, based on the calculation and analysis of indoor air distribution, temperature field, and thermal comfort, showed that the mixing degree of supply air and indoor air of upper-supply mode was better than that of bottom-supply mode, and the uniformity of temperature distribution of upper-supply top-return pattern was better. Moreover, in the personal breathing zone (0.8–1.6 m), the pattern of upper-supply top-return obtained the lowest PPD value. It can be seen that the mode of upper-supply top-return is more comfortable according to the evaluation index of human thermal comfort.

Desiccant cooling and drying systems have attracted considerable attention in recent years because they can enhance the quality of dried products and reduce the use of conventional source of energy. Calcium chloride (CaCl2) aqueous solution is the cheapest and most readily available liquid desiccant that could be used in desiccant cooling and drying systems, but it has the disadvantage of being instable depending on the inlet air conditions and the concentration of the desiccant in the solution. CaCl2 + LiCl (1:1 mass) and CaCl2 + Ca(NO3)2 (5:2 mass) mixtures are thought to be the two most potential liquid desiccants with their relatively high performance and high economic efficiency. The main purpose of this research is to obtain the basic thermodynamic properties (isobaric heat capacities) of the aqueous solutions of CaCl2 and its two specially composed mixtures. The measurements were carried out at temperatures range from 308 to 348 K and different concentrations determined under consideration of the working conditions of the liquids in systems. Scanning calorimetry was applied and a specialized experimental unit for heat capacity measurements of liquids was used in this research. Based on the results, semiempirical equations as functions of temperature and solute concentration were obtained. The deviation between the equations and experiment values showed good agreements, which confirmed the capability of these equations to be used in engineering applications.