Heating Air Conditioning Research Articles

Comparison of a novel un-baffled and a conventional shell-and-tube dry-expansion evaporator

To overcome the disadvantage of the poor heat transfer performance of the conventional baffle shell-and-tube dry-expansion evaporator (BSTDEE), a novel un-baffled shell-and-tube dry-expansion evaporator (USTDEE), for use in air source heat pumps (ASHPs), was developed and investigated. An experimental platform was built to test the performance of the USTDEE-ASHP and BSTDEE-ASHP. Several parameters, including the overall heat transfer coefficient (U) of the USTDEE and BSTDEE, cooling capacity (Qe), heating capacity (Qc), and coefficient of performance (COP) of the ASHP were investigated. The results show that the COP of the USTDEE-ASHP is higher than that of the BSTDEE-ASHP. The refrigerant charge of the former unit is less than that of the latter, whereas the water pressure drop of the former is greater than that of the latter. With increasing evaporating temperature (Te), outside tube Reynolds number (Reo) and heat flux (qi), the heat transfer performance of the USTDEE is enhanced and is better than that of the BSTDEE. With an increase in condensing temperature (Tc), the heat transfer performance of the USTDEE and BSTDEE decreases, and the former is worse than the latter. This research indicates that the USTDEE has the advantages of higher heat transfer performance; compact volume and less heat transfer area and has broad prospects in air conditioning heat pump applications.

연결세경관을 이용한 휜관형 열교환기의 기계확관에 의한 전열특성

The fin and tube heat exchanger using a two-port tube has in air-conditioner heat exchanger because heat transfer performance. This study investigates the feasibility of a fin and tube heat exchanger using two-port copper tube by mechanical expansion. The optimum size of the tube-expanding bullet for the heat exchanger using two-port tube was through numerical calculation. The heat exchanger using a two-port tube was fabricated by mechanical expansion, and the heat exchanger performance was evaluated condensation and evaporation experiments. Compared to the heat exchanger of a conventional circular tube, the pressure drop per unit length of the heat exchanger with a two-port tube decreased. Compared to the heat exchanger using a conventional circular tube, the overall heat transfer coefficient of heat exchanger with a two-port tube increased up to 13% in the case of condensation, and up to 25% in the case of evaporation. The two-port tube heat exchanger outperforms conventional heat exchanger for air conditioner with a inner grooved circular tube.

Simplified model of finned-tube heat exchangers based on the effectiveness method and calibrated with manufacturer and experimental data

A simplified model for predicting the overall thermal performance of finned-tube heat exchangers considering water and air as hot and cold fluids, respectively, is investigated. The model is based on the classical ɛ-NTU method and the thermal convective resistance in each fluid is estimated after conventional-type (Nusselt number) empirical correlations. The model is calibrated with catalogue data of a heating coil. Calibrations of six families of model versions are performed by using different numbers of operating cases ranging from 2 to 320, some of them taking into account the influence of varying properties. The calibrated versions are tested for operating cases listed in the catalogue and the best performing versions are identified, such as the one calibrated with 24 cases and taking into account the effect of the fluid properties, which provided better accuracy than the versions calibrated in previous works. A test of the method robustness is conducted regarding the influence of the initial guessed values of the thermal resistances on the calibration procedure.The validity of the component model is further investigated by using a set of published experimental data for an automotive radiator covering ranges of practical interest of the mass flow rates of both air and water streams, and some versions providing excellent results are identified.The model based on a suitable version previously calibrated and tested is a promising procedure for the modular component simulation of finned-tube heat exchangers, when used as air conditioning heating coils or in other particular applications.

Heat stroke admissions during heat waves in 1,916 US counties for the period from 1999 to 2010 and their effect modifiers.

BackgroundHeat stroke is a serious heat-related illness, especially among older adults. However, little is known regarding the spatiotemporal variation of heat stroke admissions during heat waves and what factors modify the adverse effects.MethodsWe conducted a large-scale national study among 23.5 million Medicare fee-for-service beneficiaries per year residing in 1,916 US counties during 1999–2010. Heat wave days, defined as a period of at least two consecutive days with temperatures exceeding the 97th percentile of that county’s temperatures, were matched to non-heat wave days by county and week. We fitted random-effects Poisson regression models to estimate the relative risk (RR) of heat stroke admissions on a heat wave day as compared to a matched non-heat wave day. A variety of effect modifiers were tested including individual-level covariates, community-level covariates, meteorological conditions, and the intensity and duration of the heat wave event.ResultsThe RR declined substantially from 71.0 (21.3–236.2) in 1999 to 3.5 (1.9–6.5) in 2010, and was highest in the northeast and lowest in the west north central regions of the US. We found a lower RR among counties with higher central air conditioning (AC) prevalence. More severe and longer-lasting heat waves had higher RRs.ConclusionsHeat stroke hospitalizations associated with heat waves declined dramatically over time, indicating increased resilience to extreme heat among older adults. Considerable risks, however, still remain through 2010, which could be addressed through public health interventions at a regional scale to further increase central AC and monitoring heat waves.Electronic supplementary materialThe online version of this article (doi:10.1186/s12940-016-0167-3) contains supplementary material, which is available to authorized users.

Refrigerant and lubricant charge in air condition heat exchangers: Experimentally validated model

The paper presents a semi-empirical model to predict refrigerant and lubricant inventory in both microchannel condenser and plate-and-fin evaporator of an air conditioning system. Validated against experiments, where mass of refrigerant and lubricant are isolated under steady state and afterwards measured within ±1% and ±2.5% uncertainty, respectively, the model predicts refrigerant mass in both heat exchangers within 20%. As for lubricant, initial application of the model predicts mass well for evaporator but consistently under-predicts for condenser. Analysis shows that the lubricant might be separated in the condenser inlet header. Accumulated in the bottom, the lubricant-rich liquid may start to fill in the microchannel tubes. The temperature profile in the infrared image supports this hypothesis, as the temperature of the bottom channels is much lower. After modifying the model by counting in these liquid filled channels, both refrigerant and lubricant mass in the condenser can be modeled within 15% error.

Analysis of the Building Envelope Influence to Building Energy Consumption in the Cold Regions

Building envelope thermal conduction is dominant in the cold regions, the thermal performance of the building envelope plays a very important role in reducing building energy consumption. In cold areas, the annual air conditioning heating energy consumption of public buildings, there are about 50% consumed by the heat transfer of building envelope. Therefore, the study on energy saving building envelope is very important. This paper start from the building shape coefficient and the heat transfer coefficient of the building envelope, using DEST energy simulation software to analyze the office building energy consumption. Choosing the typical cold B region Shenyang, establishing the Office model, analysis the influence of office building envelope heat transfer coefficient to indoor equipment energy consumption. Pointing out that the architectural design and planning should try to select the building bottom shape close to a circle or a square, and try to select middle-high-rise buildings to reduce building shape coefficient. Generally, in cold B region the heat transfer coefficient K≤0.5W/m2 • K, the windows and roofs try to select low heat transfer coefficient material, by reducing the heat transfer coefficient to achieve an insulating effect.

Numerical Analysis of a Hygrothermal Environment During Hot and Humid Seasons Considering Room Hygroscopicity and Air Conditioner Driving Mode

This study aims to investigate the hygrothermal environment by estimating the room air conditioner (RAC) heat load in a room with hygroscopic materials. The sensible and latent heat capacity and the water retention quantity in the RAC indoor unit are tested in cooling and dehumidification operation modes. Then, a model is developed to predict their values and investigate room temperature and humidity. The RAC model numerical analysis estimates the heat load by taking into account indoor hygroscopicity. In particular, the water is retained from several hundred grams to approximately 1kg in the indoor unit. The RAC model is implemented considering the heat exchanger temperature distribution. In the weak cooling dehumidification mode, the room relative humidity is maintained between larger than 5% and 8% of the target value with and without hygroscopicity, respectively. Hygroscopicity does not affect the heat load in the bedroom during night time.

낮은 유량에서 외경 7.0 mm 마이크로핀 튜브 내 R-410A 증발 열전달 및 압력 손실

Microfin tubes having an outside diameter (O.D.) of 7.0 mm are widely used in residential air conditioning systems and heat pumps. It is known that the mass fluxes for air conditioners and heat pumps under partial load conditions are several tens of kg/ms. However, literature surveys reveal that previous investigations were limited to mass flux over 100 kg/ms. In this study, we conduct R-410A evaporation heat-transfer tests at low mass fluxes (50– 250 kg/ms) using a 7.0 mm O.D. microfin tube. During the test, the saturation temperature was maintained at 8C, and the heat flux was maintained at 4.0 kW/m. For comparison purposes, we also test a smooth tube with a 7.0 mm O.D. The results showed that the heat-transfer enhancement factor of the microfin tube increased as the mass flux decreased up to 150 kg/ms, which decreased as the mass flux further decreased. The reason for this was attributed to the change of the flow pattern from an annular flow to a stratified flow. Within the test range, the frictional pressure drops of the microfin tube were approximately the same as those of the smooth tube. We then compare experimental data obtained with the predictions obtained for the existing correlations. † Corresponding Author, knh0001@incheon.ac.kr C 2015 The Korean Society of Mechanical Engineers

Facile Fabrication of Anodic Alumina Rod-Capped Nanopore Films with Condensate Microdrop Self-Propelling Function.

We report that aluminum surfaces can be endowed with condensate microdrop self-propelling (CMDSP) function by one-step voltage-rising mild anodization in hot phosphoric acid solution followed by fluorosilane modification. Via regulating reaction parameters, we can achieve anodic alumina self-standing rod-capped nanopore films and minimize their solid-liquid interface adhesion. Such low-adhesive nanostructured film owns remarkable CMDSP function, especially to condensate microdrops with sizes below 50 μm, differing from usual gravity-driven dropwise condensation on flat aluminum surfaces. Clearly, this work offers a facile, efficient, and industry-compatible approach to processing CMDSP aluminum materials, which is significant for developing innovative energy-saving air-conditioner heat exchangers.

Study on Energy Saving of the Air-Conditioning Exhaust Heat Recovery System in Office Buildings

The study analyzed the thermal performance of a sensible heat recovery system in an office building in Beijing area. Based on proposing the basic evaluation index of the thermal performance, the study analyzed the effect of outdoor temperature and wind speed on the heat recovery efficiency and the reduction of fresh air load. The analysis results show that, the operation effect of the sensible heat recovery device in winter is better. In winter, the sensible heat efficiency η is higher than 60%, the system has higher EER, and the fresh air load can be reduced more than 50%. While the sensible heat efficiency η is lower than 60% in most time in summer. And in a hot, humid climate, the recovery effect of sensible heat recovery device is significantly reduced.

Application Analysis of the Recovery Fresh Air Heat Pump Units in Energy Saving Reform of Air Conditioning in the Severe Cold Regions

This article introduces the working principle of the recovery fresh air heat pump units,and analyzes the applications system which units apply in air-conditioning heat recovery system.By using the principle of regression analysis of mathematical statistics,the article measured data for statistical analysis.The regression equation is established, the established regression equation has a high prediction accuracy.

Pueden los pozos hidrotermales someros en pares de ciclo abierto ayudar a remediar la intrusión de agua de mar?

Recharge through injection wells is a well-established technique to remediate and protect coastal aquifers from saltwater intrusion. In this study, it is shown that hydrothermal doublet installations can also be used to protect coastal aquifers while producing heat or cold for air conditioning. Such a method could be extremely valuable for situations where there is both a need for freshwater and energy production in coastal regions. The efficiency of the proposed approach is tested using Strack’s analytical solution on a wide range of scenarios where the number of injection and pumping wells vary as well as the distance between these wells and the coast. The efficiency is evaluated through four control parameters: the relative freshwater volume, the maximum penetration distance of the saltwater toe, the thermal breakthrough time, and the percentage of injected water recycled. The analysis of these parameters computed for 343 scenarios confirms the efficiency of the method. Those results are extremely encouraging even if they still need to be confirmed through field experiments.

Study on Hot Air Distribution of Ship Cabin Air-Conditioning

This paper analyzes the ship cabin air-conditioning heating load characteristics, we pointed out the ship cabin air-conditioning air distribution form suitable for characteristics of variable air volume, big air volume and high air velocity. By Experimenting on interior temperature and air velocity of ship multi-function hall in high air velocity heating condition, we got the good temperature uniformity. But the area of the air velocity is large, which reduces the comfort. By simplifying the cabin geometry model, assuming the initial conditions and using computational fluid dynamic to simulate three supply air angles in heating condition, the comparison between simulation results and experimental results proved the accuracy of the simulation. And evaluating the air distribution of three supply air angles by air distribution evaluation index, we got the suitable supply air angle of ship cabin in high air velocity heating condition.

Stimmrehabilitation nach Laryngektomie

Laryngeal and hypopharyngeal carcinomas are among the most common malignant tumours of the head and neck region, accounting for about 3,000 new cases per year. Despite enormous advances in organ preservation surgery and chemoradiotherapy, total laryngectomy is still necessary in approximately one quarter of affected patients. The removal of the larynx results in the loss of 3 important functions, i. e., voice production, the air conditioning mechanism of the nose, and the ability to smell. Whereas voice rehabilitation has been a mainstay of treatment from the very beginning of laryngeal surgery, pulmonary and olfactory rehabilitation has received increasing attention only in the past 2 decades. Today every head and neck surgical oncologist should be familiar with the various methods of voice rehabilitation and the use of heat and moisture exchangers for air conditioning. The objective of this article is to provide an overview of current methods of rehabilitation after total laryngectomy and to introduce young surgeons with an interest in voice rehabilitation to available techniques.

Simulation on Building Energy Consumption for a Residential Building

A two floor residential building in Tianjin as the research object was studied in this paper. The software eQUEST was carried out to simulate residential buildings energy consumption, and to explore the annual total energy consumption of the residential building, which was influenced by air conditioning heating modes and the building orientations. The air conditioning and heating system modes used to simulate including the heat pump air conditioning, air conditioner & heat sink and radiant heating & heat sink. The simulated building orientations include east, west, south and north. The transformation of the sunshade direction could be obtained by changing the building orientation. The indoor design temperature in summer was set at 26°C, while winter design temperature was set at 18°C. As the result of the energy consumption simulation study showed that, the annual total energy consumption achieved the minimum when heat pump type air conditioning heating system was adopted. When the effected factors such as air conditioning heating system, indoor heat source condition, window size and some other factors which influenced energy consumption were constant, the simulation results might be found that the building orientation had a small influence on the building energy consumption.

Environmental Impact Evaluation and Economy Analysis of Air-Conditioning Cold and Heat Source Based on TEWI Index

TEWI (total equivalent warming impact) index, a comparatively scientific method to evaluate the environmental impact of air-conditioning cold and heat source, is introduced. Taking some engineering in Hunan Province for example, the TEWI analysis was performed on the environmental impact assessment of four air-conditioning cold and heat source plans. Also the first investment and energy consumption were analyzed. The results indicate that: water loop heat pump unit, due to investment recovery period with only 2.9 years and carbon emission reduction up to 22.68%, has significant economy and environmental protection, which is followed by water source heat pump; the screw chilled water units plus gas boiler is poor. Gas direct-fired machine has certain economic advantage, but its environmental performance is general. Among four schemes, the proportion of indirect effects of CO2emissions from fossil fuels used to generate energy to operate the equipment throughout its lifetime are all larger, respectively is 95.1%, 95.2%, 100% and 89.9%. It fully showed the importance of developing clean and renewable energy, reducing energy consumption and increasing performance coefficient of refrigeration and air conditioning device.

Effect of Ageing Treatment on the Microstructures of Ti-50.7at.%Ni Shape Memory Alloy

In this study, a commercial Ti-50.7at.%Ni was subjected to solution treatment at 800oC and 900oC for one hour followed by ageing at 300oC, 400oC, 500oC and 600oC for 1 hour, 2 hours and 4 hours respectively. Characterization of the material using optical microscope, XRD, FESEM and EDX has shown that the presence of Ti2Ni and Ti-rich precipitates in the as-received material remained unchanged even after heat treatment. The presence of oxygen in the air condition heat treatment has stabilized Ti2Ni since this condition causing the formation of Ti4Ni2O which is also determined as Ti2Ni due to their same crystal structure. The formation of Ti3Ni4 precipitates during ageing encouraged the establishment of R phase instead of martensite due to the depletion of Ni content in the matrix. Ageing treatment at 300oC generates two steps of R phase transformation due to the differences in Ni composition in the matrix at the grain boundary and grain interior region. However, for samples subjected to ageing at higher temperature, 400-500oC, only one step of R phase transformation occurred because Ni atomic diffusion was not forbidden in the high temperature. Hardness test performed on the samples revealed that increasing the ageing time will increase the hardness of material; however for the sample aged at 600oC, increasing the ageing time would reduce the hardness due to dissolution of Ti3Ni4 precipitaes into the matrix.

LCCP Evaluation on Environmental Impact of Air-Conditioning Cold and Heat Source

Several indexes for evaluating the global warming impact, including GWP (global warming potential), TEWI (total equivalent warming impact) and LCCP (life cycle climate performance), are analyzed and investigated from the concept, contents, difference and correlation among them. LCCP is a rigorous method to calculate the cradle-to-grave warming impact of different refrigeration and air conditioning systems. The LCCP index was therein used to analyze overall greenhouse effect of three air conditioning cold and heat source plans for a public building. The results show that the total amount of equivalent CO2 emission from air conditioning heat and cold sources is up to 50,000 tons throughout the life cycle. Indirect global warming impact dominated the LCCP values of cold and heat source systems, which accounts for >96% of overall impact and caused by energy consumption both for producing refrigerant and operating refrigeration and air conditioning equipment. Therefore, increasing the energy efficiency of air conditioning and refrigeration equipment to reduce indirect global warming impact is the key to lowering A/C’ total impact on climate change. The LCCP of water source heat pump is always lower than that of conventional electric water chillers plus gas direct-fired unit, and its carbon emission reduction rates up to 32.4% as compared to the latter. So the overall impact from air conditioning cold and heat source could be effectively reduced through using renewable energy technology.

Swimming pools as heat sinks for air conditioners: California feasibility analysis

Earlier studies used field testing of swimming pool temperatures to validate a mathematical model for predicting the temperature of an unheated pool. Combining those results with manufacturers’ data on the performance of vapor-compression air conditioners as a function of heat rejection temperature, the analyses in the paper suggest that rejecting air conditioning heat to a swimming pool can save approximately 25–30% of single-family residential cooling electricity use and reduce cooling electricity demand during peak conditions by 30–35%, as compared to using the same compressor to reject the heat to ambient air. The savings is expected to vary depending on the severity of the climate, as well as the pool temperature experienced during the summer. The original model was refined so as to accommodate air-conditioner heat rejection to predict pool temperatures based on weather data, pool size, shading of the pool, and air-conditioner heat rejection to the pool. The results of an experimental validation of the augmented pool thermal model are presented here. In addition, the model of a pool-coupled air conditioning system was used to develop a design tool for determining the pool size needed to absorb realistic heat rejection from air conditioners in various California climate zones.

CONTINUOUS CASTING OF THE CLADDING 3003/4004 ALUMINUM ALLOY CIRCULAR INGOT

Cladding metals have been widely applied to many fields because they have many excellent physical, chemical and mechanical properties that can not be obtained from the single metals. There are many conventional processes for manufacturing cladding metals, for example roll bonding, diffusion bonding, explosive welding, extrusion cladding and casting cladding. Among these processes, continuous casting is an ideal process to prepare cladding metals which has the advantages of high production efficiency, low production cost and good interface bonding. This process can make two metals contact directly by the ways of one liquid-one liquid, one liquid-one solid or one liquid-one semi- solid and then the good metallurgical bonding can be obtained. So, this process is extensively studied by researchers engaging in material processing. The process of the direct water-cooled continuous casting to fabricate cladding 3003/4004 aluminum alloy circular ingot is researched in this paper. The 3003 aluminum alloy has excellent corrosion resistance, low strength and high melting point, while the 4004 aluminum alloy has poor corrosion resistance, high strength and low melting point. The cladding 3003/4004 aluminum alloy material can combine the advantages of two metals and can be widely used in many fields, especially in car engine and air conditioning heat sink. To obtain the good interface bonding, a special inner mold with the single-side cooling capability was applied in this process. By the special inner mold, the two alloys can make the contact of one liquid-one solid or one liquid-one