Increase In Inlet Air Temperature Research Articles

Revealing and optimizing the design of cover installation for outdoor units of air conditioners through CFD simulations and thermodynamic modeling

When renewing building facades in most Chinese cities, covers are often designed and installed to conceal the outdoor units of residential split air conditioners for congruousness of building facades. However, how those covers impact airflow and energy efficiency should be thoroughly examined. This study investigates two popular designs of cover (louver and circular-hole) and selects Nanjing, renowned for its hot summers, as the case city. This study employs Computational Fluid Dynamics models to simulate airflow obstruction caused by the covers surrounding the outdoor units. Grey Model, trained from the CFD results, quantifies interactions between design of cover and inlet air temperature. Additionally, a thermodynamic model assesses the covers' impact on the coefficient of performance of air conditioners. The findings reveal that the primary cause of outdoor unit overheating is warm air backflow from the outlet to the inlet. A mere 1 °C increase in inlet air temperature can reduce COP by 4.1%–8.7%. The maximum temperature differences caused by different designs of cover are 4.5 °C for the louver type and 4.4 °C for the circular-hole type. To mitigate these negative impacts, optimal design recommendations are provided: a minimum distance between the cover and outdoor unit of 0.29 m for louver type and 0.1 m for circular-hole type, both feasible in most installations. These findings can help designers, manufacturers, installers and policymakers, to facilitate the design and installation of optimal covers for outdoor air-conditioning units, thus minimizing energy efficiency losses.

Reduction of maillard browning in spray dried low-lactose milk powders due to protein polysaccharide interactions

Lactose hydrolysed concentrated milk was prepared using β-galactosidase enzyme (4.76U/mL) with a reaction period of 12 h at 4 °C. Addition of polysaccharides (5 % maltodextrin/β-cyclodextrin) to concentrated milk either before or after lactose hydrolysis did not result in significant differences (p > 0.05) in degree of hydrolysis (% DH) of lactose and residual lactose content (%). Three different inlet temperatures (165 °C, 175 °C and 185 °C) were used for the preparation of powders which were later characterised based on physico-chemical and maillard browning characteristics. Moisture content, solubility and available lysine content of the powders decreased significantly, whereas, browning parameters i.e., browning index, 5-hydroxymethylfurfural, furosine content increased significantly (p < 0.05) with an increase in inlet air temperature. The powder was finally prepared with 5 % polysaccharide and an inlet air temperature of 185 °C which reduced maillard browning. Protein-polysaccharide interactions were identified using Fourier Transform infrared spectroscopy, fluorescence spectroscopy and determination of free amino groups in the powder samples. Maltodextrin and β-cyclodextrin containing powder samples exhibited lower free amino groups and higher degree of graft value as compared to control sample which indicated protein-polysaccharide interactions. Results obtained from Fourier Transform infrared spectroscopy also confirmed strong protein-polysaccharide interactions, moreover a significant decrease in fluorescence intensity was also observed in the powder samples. These interactions between the proteins and polysaccharides reduced the maillard browning in powders.

Experimental study and performance evaluation of an air source heat pump (ASHP) system with a frost-free evaporator

The air source heat pump (ASHP) is operated in a low temperature and high humidity working environment. There is always a lot of frost forming on the outdoor heat exchanger, which hinders the heat transfer rate of the heat exchange surface, leading to the decrease of performance of the ASHP system. This paper presents a new type of frost-free evaporator for ASHP system. The heat transfer zone of the evaporator is composed of three parts: non-packing zone, plain finned-tube falling film zone and horizontal smooth tube bundle falling film zone. The experimental system of the frost-free evaporator is established, and the reliability of the experimental data is verified. The effects of refrigerant flow rate, inlet air temperature, fan frequency and solution spray mode on energy efficiency ratio, heat transfer expansion coefficient, air side pressure drop and exergy loss of the evaporator are studied. The performance of the evaporator is evaluated. The results show that with the increase of inlet air flow and temperature, the energy efficiency ratio of frost-free evaporator increases by about 8%–12%, and the air side pressure drop also increases. As the inlet air temperature increases from −10 to 15 °C, the heat transfer expansion coefficient of evaporator decreases by about 3%–6%, indicating that the increase of inlet air temperature will lead to an increase of sensible heat transfer ratio and a decrease of latent heat transfer ratio. The results also show that compared with no spray mode and continuous spray mode, the intermittent spray mode is more recommended as a feasible operation scheme to realize the continuous, efficient and stable operation of the new evaporator.

Energy and exergy analyses of a hybrid adsorption refrigeration system for simultaneous production of cold water and dry air

Current adsorption refrigeration systems are limited by dehumidification methods and produce either cold water or cold dry air. The single cooling product greatly hinders their application into situations where multiple cooling outputs are needed. In order to address this issue, this paper introduces a hybrid adsorption refrigeration system using efficient desiccant coated heat exchangers to provide both cold water and dry air via the deep utilization of input heat sources. In this study, the performance of the hybrid system is experimentally investigated from a combined perspective of energy and exergy. Results show that the hybrid system can simultaneously output cold water and dry air with a heat source of 50–80 °C. A low-temperature cooling water is beneficial to system performance, while an optimum input hot water temperature exists. At a coolant-side temperature of 25 °C, the COP reaches its maximum of 0.238 under a heat source temperature of 60 °C, and the highest exergetic efficiency is quantified as 13.9% when powered by 50 °C hot water. Increasing inlet air temperature or relative humidity facilitates the COP improvement but has a negligible effect on the exergetic efficiency. In comparison with a traditional adsorption air conditioning system, the hybrid system has a wider range of input hot water temperatures and is more advantageous in terms of cooling exergy and exergetic efficiency. This hybrid system firstly enables adsorption refrigeration to export dual cooling products of cold water and dry air, which is expected to extend adsorption refrigeration into fully automatic industrial fields.

Effect of pressure on heat and mass transfer performance in spray drying tower with low inlet temperature

• Pressure effect on spray-drying tower used in wastewater treatment is studied. • A three-stage single droplet model is developed and used in spray drying simulation. • Wastewater treatment using spray-drying tower under low pressure is tested. • Guidance on selection of optimal operating pressure for spray drying is provided. • The optimum pressure is due to increased mass transfer and reduced residence time. The spray drying tower is an important device of the air circulation evaporation-separation electroplating wastewater treatment system based on Brayton refrigeration cycle, which can acquire the optimum system performance by controlling the operational pressure. In order to explore the optimum pressure in the tower, the heat and mass transfer performances of the spray drying tower under different pressures are investigated. The experimental results show that the evaporation rate increases with the decrease of the pressure. The effect of pressure on tower height and inlet air temperature required for droplet to be completely dried is simulated to use the model verified by experimental data. A three-stage heat and mass transfer model for single-droplet is developed in the simulation. The simulation results show that there is an optimal pressure corresponding to the lowest required tower height. The optimal pressure is increased with the increase of inlet air temperature. When the tower height is fixed, the inlet air temperature required for drying droplet firstly decreases and then increases with the increase of pressure. In addition, through analyzing heat and mass transfer, it is found that the decrease of pressure results in the increase of not only the mass transfer driving force but also the air velocity, thus the droplet residence time is decreased, which leads to the existence of optimal pressure. It is feasible to achieve complete drying in spray drying process by reducing the pressure in the tower with low inlet temperature.

Investigation of a novel combustion stabilization mechanism and combustion characteristics of a multi-nozzle array model combustor

Short and uniformly dispersed flames in multi-nozzle array combustors allow for shorter flue gas residence time, resulting in less NOx emissions at high combustor outlet temperature. A new combustion stabilization mechanism based on high-speed jet induced flue gas recirculation has been utilized in an array model combustor. The stabilization mechanism allows for stable combustion at higher nozzle outlet velocity. The flame stabilization mechanism and combustion characteristics for the model combustor fueled methane have been investigated by using the combination of experiments and numerical simulations. The parameters studied include nozzle outlet velocity, inlet air temperature, and heat loss ratio. The combustion characteristics include NOx/CO emissions and reaction zone distribution. The results show that the flame stabilization mechanism is a result of the combined effects of the inner and outer recirculation zone. Under atmospheric conditions within the adiabatic temperature range from 1500 K to 2100 K, the NOx emissions are less than 20 ppm@15%O2 and the CO emissions are less than 30 ppm@15%O2. As the heat loss ratio decreases, the NOx emissions for the model combustor increase. When the nozzle outlet velocity increases, the lean blowout (LBO) for the model combustor increases. With increasing inlet air temperature, the equivalent ratio range of combustion stability expands. The downstream of the reaction zone is mostly affected by the nozzle outlet velocity and inlet air temperature, while the root of the reaction zone is essentially unaffected due to the role of inner recirculation zone. The unique stabilization mechanism of the multi-nozzle array combustion is beneficial for fuel flexibility.

Two-stage evaporative cooling system with composite activated carbon fiber dehumidification

A two-stage evaporative cooling system with composite activated carbon fiber dehumidification is proposed. After the first evaporative cooling, the high humidity air is dehumidified in the internally cooled desiccant bed, then sent to the second evaporative cooling unit for further cooling. The evaporative cooling unit adopts the fiber wet curtain as the cooling medium. In the internally cooled desiccant bed, composite activated carbon fiber (ASL) is filled, and copper tubes are arranged for cooling/heating. ASL is prepared of activated carbon fiber (ACF) impregnated with silica sol and LiCl, with an equilibrium dehumidification capacity can increase 3.1 times higher than ACF. The average dehumidification capacity of the desiccant bed reaches 5.59 g/g, and the relative humidity of the outlet air decreased to below 50% in 46 min. In the two-stage evaporative cooling system performance experiments, the supply air temperature is 3.1–4.8 °C lower than the single-stage, and the humidity ratio is 0.42–2.66 g/kg lower. The cooling capacity Qc,e, cooling efficiency ղTwo-stage, and coefficient of performance (COP) increases with increasing inlet air temperature and decreasing inlet air relative humidity, air velocity, and cooling water temperature. Qc,e, ղTwo-stage, and COP of the two-stage evaporative cooling system can reach up to 3757.5 W, 1.78, and 10.8, 808.8 W, 0.64, and 2.33 larger than these in the single-stage.

Simulation investigation on a novel open-loop air cycle heat pump drying system

Different from conventional drying technology, the novel technology of an air cycle heat pump drying (ACHPD) system, using air as its working medium, is proposed to solve the problems of low energy efficiency, HCFC refrigerant use, and so on. A mathematical simulation model is constructed to evaluate system performance under various working conditions, and its verification via experimental results from a constructed test bench produced errors of temperature within ±1.6%, of drying rate within ±0.01%, and of system power within ±7%. Compared with a conventional electric heater drying (EHD) system, the energy-saving rate of the ACHPD system reaches about 15–27% when the mass evaporation rate increases from 0.75 kg h−1 to 3.45 kg h−1. Under set working conditions, an increase of inlet air flow rate (150–400 kg h−1) improved the dehumidification energy efficiency ratio (MER) by about 1%. However, the increase of inlet air temperature (10–40 °C) and relative humidity (30–80%) reduced MER by about 7% and 21% respectively. The efficiency improvements of heat exchanger (0.3–0.8) can improve the energy efficiency of system by 20%; however, the efficiency improvements of expander (0.55–0.8) and compressor (0.4–0.9) can deteriorate the energy efficiency of system by 17% and 36% respectively. These results would provide new technical references for the application of heat pump technology in drying field from a different perspective.

Performance study of heat and mass transfer in a counterflow liquid to air membrane-based parallel-plate dehumidifier

Liquid to air membrane energy exchanger (LAMEE) is the most important component in a liquid desiccant air conditioning system. Three main configurations of LAMEE are presented in the literature: co-current, counterflow, and cross-counter flow. In this paper, we evaluated the performance of a counterflow LAMEE dehumidifier in terms of its cooling capacity (CC) and moisture removal rate (MRR). A numerical model was developed and validated with experimental results. The impact of solution properties and inlet air characteristics on the LAMEE’s performance were investigated. Simulation results show that CC and MRR are enhanced by decreasing the temperature and increasing the concentration of the liquid desiccant simultaneously. In order to obtain an optimal performance of the LAMEE, the solution mass flow rate should be equal to or slightly higher than the inlet air mass flow rate. On the other hand, we found that both CC and MRR increase with increasing inlet air temperature and relative humidity. Even though solution properties and inlet air characteristics affect the MRR and the CC, they have a negligible effect on the required air sensible cooling to meet the supply air condition (Qsen). The characteristics of outlet air provided by the LAMEE are in a stable state condition, which proves that the LAMEE has a wide range of adaptability in different operating conditions.

Influence of processing conditions on quality of Indian small grey donkey milk powder by spray drying.

The study was carried out to know the quality of small grey donkey milk powder by spray dryer. Donkey milk powder moisture, fat, protein, carbohydrate and ash were 4.12 (d.b), 5.97, 22.84, 4.64 and 62.43 (%). Donkey milk powder was produced at milk total solids of 20, 25 and 30% concentration at 160, 170 and 180°C inlet air temperature using two fluid flow nozzle type atomizer of 0.84mm diameter, pressure of 1.75kg.cm-2, flow rate of 0.5 L.h-1, blower speed of 2100rpm. L * , a * , b * and aw values decreased with increasing concentrated milk feed as well as inlet air temperature. Density decreased as increase of inlet air temperature and increased as increase milk concentration. Flowability was fair according to Hausner ratio (1.25) and Carr's index (20%) values. The heat utilization efficiency increased as increase of concentration and decreased as increase of inlet air temperature. Solubility decreased as increase of concentration and inlet air temperature. Dispersibility decreased as increase of inlet air temperature and increased as increase of concentration. Wetting time increased as increase of concentration and inlet air temperature. Structure of the donkey milk powder was spherical and minerals were abundant.

Photochromic Microcapsules for Textile Materials by Spray Drying—Part 1: Production and Characterization of Photochromic Microcapsules

This study, which is the first in a three-part series, deals with the encapsulation of photochromic dyes by spray drying. An aqueous ethyl cellulose dispersion and a spirooxazine-based photochromic dye were used as a shell and core material, respectively. The effects of main encapsulation parameters, such as solvent type, inlet temperature, feed rate, solid content, and aspirator rate were investigated. The encapsulation results were evaluated by scanning electron microscopy (SEM) images, particle size measurements, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The microcapsules obtained from a water-ethanol mixture exhibited photochromic properties. For microcapsule production, the optimum feed rate, total solid content, and aspirator rate were determined. Capsule formation improved with increased inlet air temperature. Spray drying to produce photochromic microcapsules could be a practical method for production of photochromic smart textiles.

Study of Parameters Affecting Thermal Drying Process. (Dept. M)

Parameters affecting drying process has been studied experimentally as it associated with heat and mass transfer between porous bed to be dried and air which flows through the porous bed. To perform this study, a test rig is designed and constructed as it consists of vertical circular duct packed with wet porous bed which is made from clay balls of 20 mm in diameter. Drying process occurs as a result of forcing hot air vertically to pass through the wet porous bed, evaporation of moisture is existed in the bed due to the simultaneous heat and mass transfer. The studied operating parameters are inlet air temperature, inlet air mass flux, porous bed depth and porosity of balls. The average heat and mass transfer coefficients are estimated for flow of hot air through the wet porous bed. The results indicated that, the drying rate is directly proportional to inlet air temperature, mass flux of air, dimensionless bed depth and ball porosity. So, Drying process can be achieved in lower time as increasing both air mass flux and or inlet air temperature and decreasing bed depth. Also, heat transfer coefficient and mass transfer coefficient increase with increasing inlet air temperature, inlet air mass flux, and ball porosity, but they decrease with increasing bed depth. Comparison between the obtained experimental results and the previous work gave the same trend.

Study on combustion control of a methanol SICI engine

Spark induced compression ignition (SICI) combined mode combustion can effectively solve the problems existing in homogeneous charge compression ignition (HCCI) combustion, and expand its operation range. The SICI combined combustion of methanol is divided into two combustion stages and has the characteristics of spark ignition (SI) and compression ignition (CI) combustion modes at the same time. This paper studies the SICI combustion mode of methanol from two aspects: simulation and experiment. The simulation results show that with the increase of the wall temperature, it indirectly affected the SICI combined mode combustion by affecting the hot atmosphere in the cylinder, which shortened the whole combustion duration, the SI and CI duration, it had little effect on the combustion ratio of SI and CI. The bench test results show that the methanol engine can obtain stable SICI combined mode combustion mode under the conditions of appropriate intake temperature and suitable ignition timing. From the comparison of three combustion modes of methanol, the results show that the cyclic variability of SICI combustion is the smallest. With the increase of inlet air temperature and the delay of ignition, the BP of SICI combustion at methanol starting point moves backward, the CI combustion rate decreases, but the SI combustion duration changes slightly, and the compression ignition ratio decreases. In the SICI combustion mode of methanol engine, with the increase of intake temperature, NOx emission increases, HC and CO emission decreases. With the advance of ignition timing, CO emission decreases, HC and NOx emission increases.

The thermal and auto-ignition performance of a homogeneous charge compression ignition engine fuelled with diethyl ether and ethanol blends

Abstract This study aims to numerically investigate the thermal and auto-ignition performance of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with diethyl ether and ethanol blends at different inlet air temperatures and lambda values. In this study, DEE and DEE/ethanol blends with different volume percentages, such as 85% DEE/15% ethanol (D85E15) and 70% DEE/30% ethanol (D70E30) was used as test fuels. A four-stroke single-cylinder HCCI engine was designed to use reduced fuel chemistry to create a zero-dimensional single-zone model. The single-zone combustion model was developed with the first law of thermodynamics as a differential form. The inlet air temperature ranged from 360 K to 420 K at 15 K intervals, and the lambda ranged from 1.5 to 2.5 at 0.25 intervals to evaluate the combustion control in the HCCI engine. A numerical study was carried out at an engine speed of 1200 rpm. The numerical validation model results were well agreed with reported experimental results, and the significant trends of the combustion phases were varied with a minimum error of 5%. The numerical results show that the in-cylinder pressure and heat release rate are decreased for all test fuels with the increasing lambda. The combustion phase was found to be advanced, and the combustion duration was expanded with increasing inlet air temperature. Increasing the ethanol proportion in the test fuel delayed the start of combustion. For D85E15 and D70E30 at lambda of 2 and inlet air temperature of 420 K, the indicated mean effective pressure was increased by about 12.6% and 6.10 bar. Furthermore, with DEE and D85E15 at a lambda of 2, the indicated thermal efficiency was increased by approximately 11.4% and 49.17%. It is concluded that the combustion and performances characteristics for the HCCI engine are significantly affected by DEE and ethanol fuel blends.

Three-dimensional modelling of two-phase flow and transport in a pilot centrifugal spray dryer

Understanding of droplet evaporation and motion is of great value in optimizing the spray drying process. A numerical study based on the Euler-Lagrange approach was performed with experimental verification in a pilot centrifugal spray dryer. Predicted temperatures agreed well with measured values with a maximum relative error of 2.76%. Gas multiphysics distributions and droplet trajectories were visualized. Air backflow phenomena and droplet vortex motions were observed during drying. Increasing inlet air temperature could accelerate the drying rate and increasing disc rotational speed might cause the wall adherence. The results can help guide the future design and operation of spray dryers.

The research on the influence of boiler operating parameters on thermal efficiency

The influence of operating parameters on thermal efficiency was analyzed by thermal balance experiment of the boiler. The mathematical model of thermal efficiency was obtained by thermal balance equation. The results showed that the thermal efficiency decreased with the increase of exhaust gas temperature. The excess air coefficient had an important effect on thermal efficiency of the boiler. The thermal efficiency decreased with the increase of excess air coefficient. The increase of inlet air temperature leaded to the increase of thermal efficiency when other operating parameters remained unchanged. The thermal efficiency increased with the increase of fuel calorific value. As a result, in order to improve thermal efficiency, the optimum excess air coefficient should be adjusted as much as possible to ensure combustion condition of the boiler. For running boiler, the economizer should be installed on heated surface at the end of boiler.

Transformation between 2-Threityl-thiazolidine-4-carboxylic Acid and Xylose-Cysteine Amadori Rearrangement Product Regulated by pH Adjustment during High-Temperature Instantaneous Dehydration.

2-Threityl-thiazolidine-4-carboxylic acid (TTCA) was found to be the predominant product rather than the Amadori rearrangement product (ARP) during the formation of xylose-cysteine-derived (Xyl-Cys-derived) Maillard reaction intermediates (MRIs) through a thermal reaction coupled with vacuum dehydration. To regulate the existence forms of Xyl-Cys-derived MRIs, an effective method carried out by pH adjustment during high-temperature instantaneous dehydration through spray-drying was proposed in this research to promote the conversion from TTCA to ARP. The increased inlet air temperature of spray-drying could properly facilitate the shift of chemical equilibrium between the MRIs and promote the transformation from TTCA to ARP while raising the total yield of TA (TTCA + ARP). The conversion to ARP was increased to 20.83% at 190 °C of hot blast compared to the product without spray-drying (6.03%). The conversion from TTCA to ARP was further facilitated in the pH range of 7.5-9.5. When the pH of the aqueous reactants was adjusted to 9.5, the equilibrium conversion to ARP was improved to 47.23% after spray-drying, which accounted for 59.48% of the TA formation. Accordingly, MRIs with different TTCA/ARP proportions could be selectively obtained by pH adjustment of the stock solution during high-temperature instantaneous dehydration of spray-drying.

Experimental and model investigation on agglomeration of aluminized fuel-rich propellant in solid fuel ramjet

In order to gain insight into aluminum agglomeration behaviors and agglomeration processes, the aluminized fuel-rich propellants in solid fuel ramjet are investigated by using sampling method followed by scanning electron microscopy and laser scattering experimental technique on the small-scale combustion experimental system and connected-pipe experimental system. It is observed that the aluminum particles would break away from the burning surface after agglomeration, and interpocket agglomeration occurred. Under different ambient pressures, the microstructure of the combustion products and the aggregation behavior of aluminum particles are further analyzed. Based on the classical pocket theory and particle size analysis experiments, a new agglomeration size prediction model is established. It can be used to predict the agglomeration size on the burning surface. Compared with the empirical model and the typical pocket model, this model is in good agreement with the experimental results. A connected-pipe experimental system for solid fuel ramjet is established. The effects of inlet air temperatures on the combustion performance of ramjet, the microstructure and agglomeration size are studied. With the increase of inlet air temperature, the agglomeration size decreases, the pressure, temperature and thrust in the combustion chamber increase, which makes the propellant burn more fully. The characteristic velocity, specific impulse and combustion efficiency of the solid fuel ramjet increase.

Effect of Inlet Air Temperature on the Properties of Spray Dried San-sakng (Albertisia papuana Becc.) Leaf

Free glutamic acid is a flavor enhancer compound that provided umami taste. San-sakng (Albertisia papuana Becc.) leaf has been used as a seasoning in the Dayaks tribe, West Kalimantan, Indonesia. The aim of this study was evaluated the effect of different drying inlet air temperature on physico-chemical of the spray dried san-sakng leaf. San-sakng leaf powders was produced using spray drying and maltodextrin as raw material. Completely randomized design was used with one factor, namely drying inlet air temperature on the spray drying process (130°C, 140°C, and 150°C). The results showed that moisture, solubility, bulk density, particle size, and encapsulation efficiency on the San-sakng leaf powders presented significantly affected by the drying inlet air temperature. Increasing inlet air temperature led to reduced moisture, bulk density, and particle size, whereas enhancing the solubility and encapsulation efficiency.

ДОСЛІДЖЕННЯ ПРОЦЕСУ ПРИГОТУВАННЯ СУШИЛЬНОГО АГЕНТУ У СОНЯЧНОМУ ТЕПЛОВОМУ КОЛЕКТОРІ

У статті описано конструкцію сонячного теплового колектору. Наведено результати дослідження впливу геометричних і технологічних параметрів колектору та температури зовнішнього середовища на температуру приготованого сушильного агенту.