Vapor Mass Flow Rate Research Articles

A novel model for evaporator structural design in the multi-effect evaporation plant

In this paper, a novel model called Evaporator Structural Design (ESD) model is introduced. The model not only predicts the three-dimensional distribution of heat transfer coefficient under different operation conditions but also guides the evaporator structural design. The results show that the heat transfer coefficient decreases with the decline of the spray density from 0.08 to 0.015 and with the increase of the tube length from 2 m to 10 m. The heat transfer coefficient exhibits higher values for the evaporation zone than the preheating zone, almost twice or more. Either in the preheating zone or in the evaporation zone, the heat transfer coefficient in different row positions have small differences. A forward-feed MEE (multi-effect evaporation) plant with 14 effects is calculated using the ESD model. Compared with the experimental data, the relative error of the accumulated vapor mass flow rate in each effect ranged between 1% and 8%, that of the evaporator area is about 7%. The ESD model is accurate and convenient in engineering design.

The sloshing effects on distribution characteristics of gas–liquid mixture in spiral-wound heat exchanger

Spiral-wound heat exchanger (SWHE) is important equipment for industry, and it is suitable for floating production storage off-loading (FPSO). However, two-phase mixture maldistribution always restricts the heat transfer capacity of SWHE in FPSO. Few studies have focused on the maldistribution of SWHE. According to this, an experimental device was fabricated to evaluate the maldistribution of a novel distributor on the sloshing platform. The effects of vapor qualities and mass flow rates were analyzed at the range of 0.106–0.702 and 608.5–1491.6 kg h−1, respectively. The following conclusions are drawn: With the augmentation of vapor quality, the gas–liquid uniformity deteriorates after optimizing under steady and sloshing conditions. Heave condition improves gas and liquid flow uniformity by 2.9–11.0% and 1.7–3.7% separately, and pitch condition improves the gas flow uniformity by 0.5–3.7%, and roll condition lowers the liquid flow uniformity by 2.0–7.2% in the variation of vapor quality. It is also proved that the flow uniformity achieves better performance with the increasing mass flow rate under steady, heave and pitch conditions. Heave condition improves the distribution characteristic by 4.4–8.7% for the gas phase and 2.0–9.5% for the liquid phase, and pitch condition elevates the gas flow uniformity by 3.1–7.7%. Under the roll condition, the distribution performance of the experimental model changes worse after better and obtains the best performance at the mass flow rate of 1183.8 kg/h. At large mass flow rates, gas entering into liquid space under roll condition can bring the structural problem. Increasing the tube diameter and making the upper baffle tilt from shell to center barrel are beneficial to keep the distributor structure safe.

Experimental investigations of the influence factors for the boiling heat transfer characteristics of R134a coolant in a loop thermosiphon system

This study focuses on the heat transfer and flow characteristics of the evaporator of a loop thermosiphon system. The loop thermosiphon is a type of heat pipe that is driven by gravity rather than a pump. Thus, the flow and heat transfer characteristics may be different from those for pump driven forced convection boiling. It is important to investigate the heat transfer and flow conditions of the loop thermosiphon. This study is focused on the working conditions at different filling ratios, particularly the relationship between the mass flow and boiling heat transfer inside the evaporator. In the experiment, the heat transfer capacity varies in the range of approximately 200–1000 W and the filling ratio is approximately 60%-130%. Three major results are obtained: (1) when the filling ratio is greater than 100%, the real mass flow rate is much higher than the pure vapor mass flow rate, and the higher the filling ratio, the larger the mass flow rate will be; (2) the filling ratio will influence the mass flow rate of the coolant and the mass flow rate will then influence the vapor quality of the evaporator; and (3) the boiling heat transfer coefficient does not vary with the filling ratio, even though the mass flow rate at different filling ratios changes significantly

Experimental Investigation on Airflow and Water Production in the Integrated Rooftop Solar Thermal System

Abstract Solar chimney is a passive renewable technology, adopted and followed widely for the application of room ventilation and power production. It requires a wide space for operation. Hence, an effective heat transfer mechanism is required within the available space to improve the performance. The solar chimney is integrated with a solar still using an external condenser to effectively utilize the energy released during the condensation of water vapor in the external condenser. The external condenser acts as an additional heat source besides the solar collector in the solar chimney. The experiments were conducted with the solar chimney of heights 1 m and 2 m, by considering the effects of an external condenser in both summer and winter. Heat transfer studies on the external condenser are also made to determine the effectiveness and the number of transfer units. The temperature and mass flow rate of vapor in the still are the influential parameters on the effectiveness of the external condenser. The condensation energy released from the external condenser increased the daily average air velocity by 14.9% and 22.4% in summer and winter, respectively. However, the overall solar chimney efficiency was improved by 37.1% in summer and 14.5% in winter for the integrated system with the chimney of height 2 m.

Power output, thermal efficiency and exergy-based ecological performance optimizations of an irreversible KCS-34 coupled to variable temperature heat reservoirs

An irreversible Kalina cycle system 34 (KCS-34) model with variable temperature heat reservoirs is studied by using finite-time thermodynamics. The power output, thermal efficiency and exergy-based ecological function of the KCS-34 are derived, and the effects of evaporator outlet dryness and mass flow rate of the working fluid on these performances are analyzed. With constant total heat transfer area, the heat transfer area distributions are optimized, and the optimal performances of the KCS-34 are obtained. The results show that the power output, thermal efficiency and ecological function have their triple maximum by optimizing the heat transfer area distributions, and the optimal distributions are different from each other. The ecological function shows a trade-off between power output and thermal efficiency to some extent. Compared with the initial designs, the power output, thermal efficiency and ecological function after triple optimizations of the heat transfer area distributions are increased by 17.27%, 5.79% and 1.05%, respectively. It shows that parameter optimization is important to improve the performances of the KCS-34, and the corresponding optimization work is significant.

Comparison of the Trilateral Flash Cycle and Rankine Cycle with Organic Fluid Using the Pinch Point Temperature

Low-temperature heat utilization can be applied to waste heat from industrial processes or renewable energy sources such as geothermal and ocean energy. The most common low-temperature waste-heat recovery technology is the organic Rankine cycle (ORC). However, the phase change of ORC working fluid for the heat extraction process causes a pinch-point problem, and the heat recovery cannot be efficiently used. To improve heat extraction and power generation, this study explored the cycle characteristics of the trilateral flash cycle (TFC) in a low-temperature heat source. A pinch-point-based methodology was developed for studying the optimal design point and operating conditions and for optimizing working fluid evaporation temperature and mass flow rate. According to the simulation results, the TFC system can recover more waste heat than ORC under the same operating conditions. The net power output of the TFC was approximately 30% higher than ORC but at a cost of higher pump power consumption. Additionally, the TFC was superior to ORC with an extremely low-temperature heat source (<80 °C), and the ideal efficiency was approximately 3% at the highest work output condition. The TFC system is economically beneficial for waste-heat recovery for low-temperature heat sources.

Modeling and analysis of the influence of the protective garment movement on the skin temperature and burn degree

A numerical thermal model of the multi-layer protective clothing which accounts for the clothing movement is presented. The model includes heat conduction and thermal radiation in non-grey fabrics and air gaps, diffusive transfer of water vapour through fabrics and air gaps, sorption and desorption of water in fabric fibers, non-equilibrium bio-heat transfer in the skin and perspiration on the skin surface. Moreover, the model contains infiltration of fresh air into the widest air gap between the clothing and skin due to the clothing movement. In the simulations the clothing was for a short time exposed to the radiative heat flux emitted from the external source and cooled down in the surroundings with its movement accounted for. The results obtained are used to assess the influence of frequency and amplitude of variation of the thickness of the widest air gap on the skin temperature and burn degree, heat fluxes and vapour mass flow rate on the skin surface as well as relative humidity close to the skin. Numerical simulations reveal that an increase in the movement frequency and amplitude results in a decrease of average values of the majority of monitored quantities on the skin surface or close to it. The most visible decreases are observed for the average skin surface temperature and values of the Henriques-Moritz integral.

Condensation Heat Transfer and Flow Properties of R134a Refrigerant in Rectangular Minichannel: A Numerical Study

Abstract This study numerically investigated the condensation heat transfer and flow characteristics of refrigerant R134a in a rectangular minichannel. Three-dimensional simulations were carried out at different mass fluxes, vapor qualities, and gravity conditions using the volume-of-fluid (VOF) model, a turbulence model, and a phase transition model. The effects of various parameters on the surface heat transfer coefficient and the frictional pressure gradient are investigated. The condensation process was found to be enhanced due to the increase of vapor quality and mass flow rate, while the frictional pressure gradient was found to decrease with the decrease of vapor quality and mass flow rate. Simulation results revealed that the liquid film tends to accumulate along the corner of the cross section of the minichannel. Furthermore, the thickness of the liquid film was found to increase with the decrease of mass flux and vapor quality.

Numerical investigation of an evaporating meniscus in a heated capillary slot

This paper numerically studies heat transfer and fluid flow from an evaporating meniscus of a wetting fluid within a heated capillary. A simplified steady state mathematical model is developed for predicting the wicking height of the meniscus and the evaporation mass flow rate which includes: (1) one-dimensional flow and energy equations for the liquid and vapor regions, (2) one-dimensional model for the evaporating meniscus region, and (3) two-dimensional energy equation for the capillary wall. Three parameters, namely, apparent contact angle, cumulative heat transfer, and evaporating meniscus height characterize the evaporating meniscus region. In this paper, the apparent contact angle in the evaporating meniscus is uniquely deduced from the meniscus curvature at the centre of the capillary using the thickness profile obtained from standard extended meniscus theory (which includes the evaporating thin film and bulk meniscus regions). Correlations are obtained for the cumulative heat transfer, apparent contact angle and evaporating meniscus height as a function of the difference between the wall and saturation temperatures from the evaporating thin film theory for the meniscus region, which is called as micromodel. The macroscopic model accounts for wall heat conduction and heat transfer with fluid flow in the liquid and vapor regions. The micromodel deals with heat transfer and fluid flow in the evaporating meniscus region. In this paper, a novel scheme to link the “macroscopic” momentum and energy equations in the capillary slot and the evaporating meniscus through the correlations developed above is proposed. Using this numerical model, the wicking height and the evaporation mass flow rate are estimated and the results are compared with previously conducted experiments. The trends in the numerical results of the mathematical model correlate reasonably well with the experimental data.

Studi Kemungkinan Pemakaian Sekam dan Jerami Padi sebagai Bahan Bakar Briket untuk Ketel Uap di RSUP dr. Wahidin Sudirohusodo Makassar

This study aims to: (1) make briquettes from rice husk and straw with some mixture proportions, (2) determine the heating value (HHV) and the compressive strength of the produced briquettes (3) determine the physical properties of the produced briquettes through the proximate analysis and determine the best briquettes mixture, and (4) know the possibility of using rice husk and straw as briquette fuel for steam boilers. The produced briquettes contained 85% of rice husk charcoal and straw, and adhesive subtance consisting of clay (10%) and strach (5%). The briquettes were made with five mixture proportions with an average mass ratio of 260 gramsduce briquettes briquette type E as the best. The examination of heating value reveals that the higher the percentage of staw in the mixture, the lower the briquette heating value will be; while the testing of compressive strength reveals that the higher the percentage of straw in the mixture, the higher the briquette compressive strength will be. Based on the proximate analysis, it is found that generally the produced briquettes have fulfilled the briquette standard quality. The results of calculations analysis reveal that there is a possibility to use briquettes made of rice husks and straw as steam boilers the ratio between the fuel mass flow rate and vapor mass flow rate is 0.231.

Optimization design of falling film type plate-fin condenser/reboilers by minimizing specific entropy generation rate

This paper presents an optimization model for falling film type plate-fin condenser/reboilers based on the entropy generation minimization method, which considers the irreversibilities owing to both irreversible heat transfer and pressure drop. The specific entropy generation rate, i.e. the entropy generation rate per unit total heat transfer area, is proposed as an optimization objective function. Main geometrical parameters (i.e. fin height and fin pitch) of the evaporation channel of a falling film type plate-fin condenser/reboiler are optimized. The analytical results show that under certain fin pitch, there exist different optimal fin heights corresponding to the minimum entropy generation rate and the minimum specific entropy generation rate, respectively. In addition, the value of minimum specific entropy generation rate decreases with the increase of the fin pitch, and the optimal value of the fin height varies little with the fin pitch. Effects of the heat transfer temperature difference, inlet mass flow rate of liquid to be evaporated and inlet mass flow rate of vapor to be condensed on both the minimum specific entropy generation rate and optimum values of fin parameters are also analyzed in detail.

Nucleate pool boiling enhancement by ultrafast water permeation in graphene-nanostructure

Nucleate boiling efficiency can be significantly enhanced using the nanostructured graphene surface. The wettability of the graphene nanoplatelets (GNPs) coated surface is tunable using thermal curing process. The uncured GNPs surface is hydrophobic in nature while the cured GNPs surface manifests a hydrophilic characteristic and the latter performs better than the former in the nucleate boiling regime. Ultimately the ultrafast water permeation property of the cured GNPs enhances the efficiency of nucleate pool boiling, leading to a maximum enhancement of 151% in the boiling heat transfer coefficient and 154% in the vapor mass flow rate. The boiling performance of the uncured GNPs surface is also enhanced despite its hydrophobicity. Hence, the enhancement in boiling is not solely attributed to the surface wettability. The enhancement is attributed to the fascinating ultrafast water permeation property of graphene on top of its nanoporous structure. The unimpeded fast water transport within the nanochannel-network of GNPs facilitates the fast absorption of latent heat of vaporization by the water molecules, leading to a substantial increase in the nucleation, growth and departure of vapor bubbles. We propose a new explanation on the role of graphene coating on nucleate pool boiling enhancement. This study provides important insights into the effects of ultrafast water permeation property of graphene on the nucleate boiling heat transfer.

Heat transfer characteristics in super-low finned-tube bundles of moisture separator reheaters

Abstract Experimental investigation on the heat transfer characteristics of superheat vapor through a new designed moisture separator reheater with “super-low” finned-tube bundles for Generation III+ nuclear power plant, was carried out based on a 5*30 tube bundle test section. Impacts of the vapor mass flow rates are analyzed on the heat transfer characteristics of superheat vapor through the finned-tube bundle. A group of experiments are reviewed on single-phase fluid flowing across the triangular super-low finned-tube bundles whose fin heights are less than 2.75 mm and ratios of fin height to fin diameter are from 0.05 to 0.15. Combining the presented experimental data with the other open published data for single-phase turbulent gases flowing across triangular super-low finned-tube, a new heat transfer correlation is proposed for the MSRs super-low finned-tube bundles, which shows better accuracy and has wider Reynolds number range in application.

Optimization of a vapor injection refrigeration cycle using hydrocarbon mixed refrigerants

Refrigeration systems are major consumers of electrical energy in many process industries. Hydrocarbons have regained interest as refrigerants because of the increasing restrictions applied to halogenated fluids. In this work, the use of hydrocarbons mixed refrigerants and an alternative flash tank with vapor injection (FTVI) refrigeration cycle were combined. Five different binary mixed refrigerants involving R170 (ethane), R290 (propane), R600 (n-butane) and R600a (isobutane) were studied. Using different refrigerant compositions, the cycle was simulated and optimized for maximum COP, considering a fixed refrigeration capacity in the evaporator to reduce the temperature of a secondary thermal fluid from 281.55 K to 269.15 K. Parameters analyzed were: coefficient of performance, temperature glide in the evaporator and refrigerant mass flow rate. The use of a FTVI led to a COP improvement from 4% to 36% when compared to the traditional vapor compression cycle (VCC). The pair R290/R600 with 60/40 wt% presented the maximum COP of 4.88.

Distribution characteristics of gas-liquid mixture in plate-fin heat exchangers under sloshing conditions

Gas-liquid two-phase maldistribution is an important problem for plate-fin heat exchangers (PFHEs), which has hampered the application of PFHEs in offshore natural gas liquefaction. In order to efficiently use PFHEs in the field of offshore natural gas exploration, it is necessary to study the two-phase distribution performance of PFHEs under sloshing conditions. In this paper, the experimental bench of gas-liquid distribution was built and the distribution characteristics of distributor in PFHEs referred to as liquid-injected seal was investigated under sloshing conditions using air and water as mediums. The effects of vapor quality (0.2–0.4) and mass flow rate (647–1310 kg/h) under sloshing conditions were analyzed. The results showed that by increasing vapor quality, the gas distribution performance in the distributor changed more significantly than the liquid one and the liquid distribution performance at low vapor qualities cases strongly depended on sloshing conditions. It was also proved that the gas-liquid distribution performance of liquid-injected seal enhanced with the increase of mass flow rate, and its sloshing resistance was increased as well.

Optimal Performance Characteristics of Subcritical Simple Irreversible Organic Rankine Cycle

Based on the theory of finite time thermodynamics, a subcritical simple irreversible organic Rankine cycle (SSIORC) model considering heat transfer loss and internal irreversible losses is established in this paper. The total heat transfer surface area is taken as a constraint, and R245fa is adopted as working fluid of the cycle in the performance optimization. The evaporator heat transfer surface area and mass flow rate of the working fluid are optimized to obtain the maximum power output and thermal efficiency of the SSIORC, respectively. In addition, the influences of the internal irreversibilities on the optimal performances are also investigated. The results show that when the evaporator heat transfer surface area is varied, the relationship between power output and thermal efficiency is a loop-shaped curve, and there exist maximum power output and thermal efficiency points, respectively. However, the two maximum points are very close to each other. When the mass flow rate of the working fluid is varied, the relationship between power output and thermal efficiency is a parabolic-like curve. With the decreases of expander and pump irreversible losses, the performances of the irreversible SSORC are close to those of the endoreversible SSORC with the only loss of heat transfer loss.

Experimental Study of a Bubble Mode Absorption with an Inner Vapor Distributor in a Plate Heat Exchanger-Type Absorber with NH3-LiNO3

Absorption systems are a sustainable solution as solar driven air conditioning devices in places with warm climatic conditions, however, the reliability of these systems must be improved. The absorbing component has a significant effect on the cycle performance, as this process is complex and needs efficient heat exchangers. This paper presents an experimental study of a bubble mode absorption in a plate heat exchanger (PHE)-type absorber with NH3-LiNO3 using a vapor distributor in order to increase the mass transfer at solar cooling operating conditions. The vapor distributor had a diameter of 0.005 m with five perforations distributed uniformly along the tube. Experiments were carried out using a corrugated plate heat exchanger model NB51, with three channels, where the ammonia vapor was injected in a bubble mode into the solution in the central channel. The range of solution concentrations and mass flow rates of the dilute solution were from 35 to 50% weight and 11.69 to 35.46 × 10−3 kg·s−1, respectively. The mass flow rate of ammonia vapor was from 0.79 to 4.92 × 10−3 kg·s−1 and the mass flow rate of cooling water was fixed at 0.31 kg·s−1. The results achieved for the absorbed flux was 0.015 to 0.024 kg m−2·s−1 and the values obtained for the mass transfer coefficient were in the order of 0.036 to 0.059 m·s−1. The solution heat transfer coefficient values were obtained from 0.9 to 1.8 kW·m−2·K−1 under transition conditions and from 0.96 to 3.16 kW·m−2·K−1 at turbulent conditions. Nusselt number correlations were obtained based on experimental data during the absorption process with the NH3-LiNO3 working pair.

Simulation Research of Heat Transfer Characteristics of Carbon Dioxide in Microchannel Evaporator

Abstract In this paper, the simulation model of two-dimensional (2D) distribution parameter of a CO2 microchannel evaporator was developed using the finite element method. The simulation model of the CO2 microchannel evaporator was written using matlab both considering the dry and wet conditions on air side, and different heat transfer characteristics of CO2 in two-phase region and overheated region. The experimental and simulation results in terms of CO2 temperature, wall temperature, inlet and outlet air temperatures, and convective heat transfer coefficient were compared. The simulation results have the same tendency with the experimental correlation results. The convective heat transfer efficient increases with the growth of CO2 inlet dryness, mass flow rate and air speed, while decreases along with the increase of evaporation pressure in two-phase region. The dry-out point appears earlier with larger CO2 inlet dryness, and higher air temperature, humidity and speed; however, it appears later with the increasing evaporation pressure and mass flow rate. The convective heat transfer coefficient at the dry-out point decreases dramatically due to the deteriorated heat transfer at this position, which indicates the necessity to prevent or retard the appearance of dry-out point.

Experimental investigation and theoretical analysis of oil circulation rates in ejector cooling cycles

In this study, the influence of compressor speed, ejector motive nozzle needle position and evaporator inlet metering valve opening on the oil circulation rates (OCRs) of an R744 transcritical standard ejector cycle was experimentally investigated. Significantly higher OCR (∼10%) was observed at the evaporator inlet of the ejector cycle than that at the high pressure side (∼1%) measured in the same cycle under the same conditions. It has been observed that evaporator OCR was increased with increasing compressor speed. When the motive nozzle needle moved towards the nozzle throat, both compressor discharge flow rate and evaporator OCR were observed to be significantly lowered. As the evaporator inlet metering valve opening was adjusted, the compressor mass flow rate did not vary significantly while the evaporator mass flow rate decreased with decreasing metering valve opening. The evaporator OCR decreased from 6.5% to 2.2% as the metering valve opening varied from 86% to 27%. High evaporator OCR results in large evaporator pressure drop and low heat transfer coefficient. In addition to the standard ejector cycle, several alternative ejector cycles were theoretically analyzed to see if there is similar problem of high OCR in the evaporator. In ejector liquid recirculation cycle and multi-stage multi-ejector supermarket refrigeration cycle, similar high OCR problem in the evaporator may exist, while in two evaporator ejector cycle, evaporator OCR is equal to compressor OCR at steady state.

Thermal performance enhancement of vapor chamber by coating mini-channel heat sink with porous sintering media

This paper have been investigated on the thermal performance enhancement of air cooling vapor chamber by coating mini-channel heat sink inside with porous sintering wick sheet. The results obtained from experiments are considered and compared with without porous sintering wick sheet. The effects of power input, amount of filled working fluid into the vapor chamber and mass flow rate of air on the cooling performance and thermal resistance characteristics are considered. It can be found that the porous sintering wick sheet has significant effect on the increment of the capillary force which results in higher heat transfer rate. Therefore, the thermal performance of air cooling vapor chamber with porous sintering wick sheet inside mini-channel shows 20% maximum higher than that without porous sintering wick sheet. In addition, the increasing of power in put and cooling air mass flow rate have significantly increased thermal performance of the vapor chamber. The passive cooling device with vapor chambers is favorable technique that can enhanced thermal performance and reduce heat accumulate on the electronic component.