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This paper considers the age of air in a ventilated space with multiple supply inlets; the local mean age (LMA) of air is different from one inlet to another in multiple supply inlet situations. The purpose of this paper is to investigate theoretically the relations between the LMAs arising from each supply inlet and the overall combined LMA for all inlets. Transient concentration distributions are calculated using a CFD package in a simple room configuration with two inlets and one outlet, to verify the relations. Tracer gases are injected with a step-up method at each supply inlet individually, and at both inlets simultaneously. As a result, it can be found that the steady state concentration, with a continuous tracer injection at each supply inlet, works as a weighting factor for the corresponding LMA in calculating the overall combined LMA for the multiple inlet situations.

The cultural heritage left by the Egyptian pharaohs in the tombs of the Valley of the Kings represents some of the key elements of the Egyptian cultural wealth and standing monuments demonstrating the wealth and technology of the pharaohs. As the pharaohnic civilization is one of the oldest civilizations, the dedicated preservation of its remaining monuments and collections should be the focus of sincere international efforts. A major heritage of this civilization, i.e., the tombs of the Kings, is intact in the Valley of the Kings, Luxor, Egypt. These tombs were prepared to bury the Kings' mummies and artifacts for eternal life. Many of the wall paintings identifying the various ancient rituals and life style are in good conditions as the tombs were only recently opened to the public. However, tourists' activities in these tombs have resulted, in many instances, in the dramatic deterioration of wall paintings due in part to excessive humidity. The current indoor air flow conditions and air quality in the tombs are quite alarming; hence, appropriate measures should be taken to preserve the tombs and their contents. This dilemma invokes the need for a proper ventilation system that stabilizes the air conditioning as well as addresses comfort levels of visitors. Deterioration can be from lighting effects, high temperature and relative humidity. Pest infections, shock and vibration are also potential causes among pollution and visitors' traffic.

For an automobile air-conditioning system, performance improvement of the heat exchanger is needed to fit in the change of refrigerant and heat pump system. In this study, the heat transfer and pressure drop characteristic of air flow between parallel plates with concavity and convexity is grasped, and the possibility of using a fin-less heat exchanger is considered analytically. And it has been shown that a fin-less heat exchanger has the possibility of increasing performance compared to a conventional heat exchanger, which uses a corrugated louver fin.

Vapor Jet Refrigeration (VJR) system is attractive among various heat operated refrigeration systems, because it has the potential of utilizing low grade thermal energy with source temperature as low as 60°C, which could be harnessed from renewable energy, waste heat, automobile-exhaust, etc. Also absence of moving parts in this system resulted in lesser maintenance costs. In addition to that this system causes very low environmental pollution due to almost negligible consumption of high grade energy from fossil fuels for running a small liquid pump of the system. Although VJR was invented very long back, still performance improvement to compete with vapor compression refrigeration system is in progress. Plenty of research has been carried out in different aspects for enhancing the efficiency of this technology. The present work/paper gives an overview of VJR system and its progression in the aspect of performance improvement. The developmental progress of the VJR technology presented in this paper has been categorized into the following groups, namely (a) general performance of an ejector, (b) numerical analysis, viz., classical one-dimensional analysis and Computational Fluid Dynamics (CFD) analysis, (c) experimental studies, (d) flow visualization studies, (e) performance enhancement techniques, and (f) two-phase ejector. And also presented a glimpse of some of the review papers from literature on VJR system.

In order to obtain a higher heat transfer coefficient of refrigerant flow, the diameter of tubes tends to be smaller and smaller, which leads to large pressure drop of the refrigerant flow. Therefore, multiple numbers of parallel refrigerant passages are employed by using distributors. It is very important to distribute the two-phase refrigerant evenly into each tube, otherwise the thermal performance is significantly deteriorated. The performance reduction by flow mal-distribution could be as large as 20–25%. The goal of this paper is to investigate the influence of different configurations to the performance of refrigerant distributors by experiments and computational fluid dynamic code. The effects of mass flow rate and quality of distributor inlet on the characteristics were also quantitatively considered. In this study, an experiment test rig was built to measure the mass flow rate and quality of four circuits after using distributors under different conditions respectively. Refrigerant R410A was used as working fluids. Three classic types (jet, cyclone and reservoir) of distributors with four paths were manufactured and tested under relevant operating conditions. The inlet temperature was 4°C, mass flow rate range was 50–100 kg/h and the quality range was 0.1–0.3. Experimental results show that the maximum deviation of mass flow rate for jet, cyclone and reservoir type is 13.0%, 21.6% and 10.9%, respectively; the maximum deviation of quality was 0.08, 0.10 and 0.05, respectively. In addition, the standard deviation of mass flow rate and quality over four paths were selected to evaluate the performance of different type distributors. The results show that the performance of jet and reservoir are better than cyclone. The flow behavior of two-phase refrigerant such as phase distribution and separation phenomena was studied by Computational Fluid Dynamics (CFD). The flow pattern of inlet for R410A was investigated and used in the present model. The results in the present model show good and reasonable approximation with experimental data which validate the CFD simulation. CFD simulation analysis elucidates the mechanics which shows how the configuration and operation conditions affect the refrigerant distribution.

The present work aims to investigate the accurate method of performing computational fluid dynamics (CFD) — Acoustic analysis for axial flow fans in split air conditioner system. A comprehensive simulation procedure is developed to predict flow-induced noise in a system. The three-dimensional domain using k–ε turbulence model and Ffowcs Williams and Hawkings (FW-H) acoustic model is considered to predict noise generated by the fan blade surface. The acoustic and flow performances of the fan are predicted simultaneously using a computational aero-acoustic technique (combining steady flow and noise propagation analysis). The different cases are simulated by varying the blade angle, blade depth, blade width and serrations at trailing edge of fan blade. An impact of each of these parameter on A-weighted sound pressure level (SPL) and mass flow rate at outlet is determined. The numeric value of obtained A-weighted SPL by CFD simulation is found to be in close agreement with the experimental result within 5.4%. Finally, above mentioned parameters are varied in simulation and optimized design is proposed based on A-weighted SPL and cubic feet per minute (CFM). All simulations are carried out in commercially available CFD solver; ANSYS FLUENT 13.

In this paper, the heat pump system has been developed by CFD simulation and experimental investigation. It studies the thermal behavior of a thermobank and COP on heat pump system and cold storage. The thermobank stores the waste heat of during refrigeration cycles and this energy is used for defrosting process and heating room. It also reduces defrosting time and condensation load so that the temperature regulation in the cold storage is constant. The system is investigated experimentally and CFD simulated under thermobank. The dimension $L\times W\times H$ of cold storage is $3\times 1.6\times 1.4$m, thermobank is $600\times 300\times 400$mm. The temperature of ambient on CFD simulation process is 20${}^{\circ }$C. This heat pump system can be used to keep preservation of agricultural products in cold storage warehouse together with floor panel heating for room in winter. The ejector is used in system with the aim of increasing coefficient of performance (COP) and decrease in compressor displacement. As the experimental results, its COP is increased about 38.57% when using thermobank and ejector in heat pump system.

R-502, which had long been used as the refrigerant of a unitary ice maker, has been replaced by R-404A due to ozone depletion. In this study, the refrigeration cycle of a unitary ice maker was optimized using R-404A. The optimization was accomplished through a search for the proper refrigerant charge amount and the opening of the expansion valve. For the present ice maker having 24 ice cups, the optimum charge amount was 580g and the optimum valve opening was “0”. At this configuration, the ice making time was 12min 55sec, ice production was 4.46kg/h and COP was 0.439. After the initial start-up period, both condensation and evaporation temperature gradually decrease with time. As ice builds up in the cup, the heat transfer performance of the evaporator decreases, which results in the decrease of the evaporation and condensation temperature. Through CFD and relevant experiments, optimum nozzle slit width and nozzle to cup distance were obtained.

Recent concerns raised by the World Health Organization over the Coronavirus raised a worldwide reaction. Governments are racing to contain and stop the Coronavirus from reaching an epidemic/pandemic status. This research presents a way in tracking such a virus or any contagious germ capable of transferring through air specifically where such a transfer can be assisted by a mechanical room ventilation system. Tracking the spread of such a virus is a complicated process, as they can exist in a variety of forms, shapes, sizes, and can change with time. However, a beginning has to be made at some point. Assumptions had to be made based on published scientific data, and standards. The tracking of airborne viruses was carried out on the following assumption (for illustrative purposes); one person with one sneeze in a period of 600 s. The presence of viruses was tracked with curves plotted indicating how long it could take to remove the sneezed viruses from the mechanically ventilated room space. Results gave an indication of what time span is required to remove airborne viruses. Thus, we propose the following: (a) utilizing CFD software as a possible tool in optimizing a mechanical ventilation system in removing contagious viruses. This will track the dispersion of viruses and their removal. The numerical solution revealed that with one typical adult human sneeze, it can take approximately 640 s to reduce an average sneeze of 20,000 droplets to a fifth; (b) upscaling the status of human comfort to a “must have” with regards to the 50% relative humidity, and the use of Ultraviolet germicidal irradiation (UVGI) air disinfection in an epidemic/pandemic condition. A recommendation can be presented to the local authorities of jurisdiction in enforcing the above proposals partially/fully as seen fit as “prevention is better than cure”. This will preclude the spread of highly infectious viruses in mechanically ventilated buildings.

Although thermoacoustic devices comprise simple components, the design of these machines is very challenging. In order to predict the behavior and optimize the performance of a thermoacoustic refrigerator driven by a standing-wave thermoacoustic engine, considering the changes in geometrical parameters, two analogies have been presented in this paper. The first analogy is based on CFD analysis where a 2D model is implemented to investigate the influence of stack parameters on the refrigerator performance, to analyze the time variation of the temperature gradient across the stack, and to examine the refrigerator performance in terms of refrigeration temperature. The second analogy is based on the use of an optimization algorithm based on the simplified linear thermoacoustic theory applied for designing thermoacoustic refrigerators with different stack parameters and operating conditions. Simulation results show that the engine produced a high-powered acoustic wave with a pressure amplitude of 23kPa and a frequency of 584Hz and this wave applies a temperature difference across the refrigeration stack with a cooling temperature of 292.8K when the stacks are positioned next to the pressure antinode. The results from the algorithm give the ability to design any thermoacoustic refrigerator with high performance by picking the appropriate parameters.

A 3-D Eulerian-Eulerian multiphase Computational Fluid Dynamics (CFD) model combined with Population Balance Modeling (PBM) were presented for two phase bubbly flow in vertical pipes. The discrete bubble sizes prescribed in the dispersed phase were tracked by solving an additional set of transport equations, which these equations were progressively coupled with the flow equations during the simulations. Important flow quantities such as local void fraction, liquid velocity and normal turbulent stresses were calculated and compared against experimental data from literature. Good agreement with the experimental data was obtained. It was found that void fraction profile exhibited a sharp peak near the wall. The liquid velocity profile was flattened by the presence of the vapor phase (i.e. the bubbles), and all three normal fluctuations were affected by the presence of the vapor phase. These fluctuations do not increase monotonically as the void fraction increases. Thus this CFD-PBM modeling can be used for prediction of wall peaking and coring phenomena, and radial void distribution.

Heat pipes are devices of very high heat transfer capability and have been widely used in many thermal management applications. An experimental investigation and CFD simulation of thermal characteristics of heat pipe was presented in this paper. It can be found that UDF in FLUENT can simulate the evaporation and condensation in heat pipe. Phase change happened in evaporation section of heat pipe is boiling. In steady state, the fluctuation of axial velocity is very small in the most area (without evaporation section) in heat pipe. In general, the magnitudes of velocity vary from 0 to maximum from the end of both evaporation section and condenser, and the maximum value was maintained in the adiabatic section.