Water Heat Exchanger Research Articles

Parametric resonance of a fluctuation fluid flow heat exchanger system

The tubes in a component-cooling water heat exchanger are frequently affected by shock waves that occur due to fluid flow in a nuclear power plant. Thus, the tubes often wear out. Such a fluid flow may alter the dynamic characteristics of a water heat exchanger and cause instability in it. In this study, the dynamics and instabilities in a component cooling water heat exchanger are examined. Because of the presence of fluid coupling between tubes, periodic tubes were used to realize a periodic coupling system. It is found that each tube is coupled to the adjacent tube through the fluid, and the system is weakly coupled. The dynamic equations of the heat exchanger system with consideration for the effect of fluid flow were derived using Galerkin method. Numerical results revealed that fluctuations in fluid flow may significantly affect the dynamics and instability of a component cooling water heat exchanger.

Design, evaluation and heat transfer analysis of novel forced draft paddy straw bale combustor using heat sink pipe networks for greenhouse heating

In this study, first of its kind novel design of forced draft paddy straw bale combustor (FDPSBC) coupled with innovative pilot fuel injection system (PFIS) and furnace embedded internal water heat-exchanger for large scale water heating is presented. PFIS is optimized to spray 1.5 ml of diesel after every 3 min interval to achieve complete combustion of the compressed bale by maintaining the flame sustainability. Stainless steel heat-exchanger has 62 L water holding capacity circulating at the rate of 36 L per min using the heat of flue gas and has the capacity to heat 1000 L of water from 30 °C to 65 °C within three hours. Heat of combustion (>90% combustion efficiency) was utilized to generate flue gas at 350 °C and hot water above 65 °C applied to 100 m2 area greenhouse heating located at Punjab Agricultural University, Ludhiana (30.56°N), Punjab, India by designing two heat sink pipe networks; flue gas heat sink pipe network (FGHSPN) fabricated with galvanized iron (GI) and hot water heat sink pipe network (HWHSPN) fabricated with mild steel (MS) respectively laid inside the greenhouse for transfer of heat by radiation and free convection modes. Developed mathematical models showed that FGHSPN was able to transfer 9.6 kW (74%) and where as HWHSPN could transfer 3.38 kW (26%) of heat respectively out of the total heat (12.98 kW) transferred by both the networks to maintain the greenhouse air temperature 10 °C higher than the ambient air temperature after sunset hours as validated by experimental trials conducted in the month of November 2017. Installation cost of FDPSBC technology is Rs 5,00,000 ($8000) and with 24 h continuous operation, it can save about 80 kWh per day and can recover the 50% of installation and operating costs within five years time besides managing about 27% of the total paddy straw available in the state of Punjab (India) through useful heating applications including greenhouse heating.

Thermo-economic evaluation of modifications to a gas power plant with an air bottoming combined cycle

Multigeneration technologies provide a significant potential for efficient, sustainable and economical generation of multiple useful products. A gas turbine with an air bottoming combined cycle is an attractive combined cycle configuration for small scale power generation (less than 50 MW). In this study, eight different hybrid systems are proposed for further heat recovery from a gas turbine with air bottoming combined cycle to generate different useful products including power, fresh water, cooling, hot water, and industrial process heat. For this purpose, an optimized 50 MW gas turbine with air bottoming combined cycle is integrated with several thermodynamic cycles and components such as carbon dioxide transcritical Rankine cycle, water-lithium bromide absorption cooling, ammonia-water absorption refrigeration, thermal vapor compression-multi effect distillation, heat recovery steam generator, and gas (air)-water heat exchanger. The performance of the proposed hybrid configurations is evaluated from both thermodynamic and economic viewpoints. The resulting findings demonstrate that utilization of available waste heats in a gas turbine with air bottoming cycle is beneficial to generate a significant amount of different useful products with a favorable cost. The findings of this study can be useful for development of proposed integrated systems for both residential and industrial applications.

Secure and safe heat supply of residenal buildings during transional climac condions

An elementary arrangement of a heat supply of residential buildings with direct connection to external heating systems is considered, providing reliability of heat supply and comfort required in indoor premises in case of cold snaps after the official closure of the heating season, or before the beginning of the same, by supplying water from the return main of the heating system after the hot water heat exchangers. The basic equations are analyzed relating the heat transfer to the heating system with water temperature in the manifold, the inside air temperature and the characteristics of the heaters, with a review of possible methods of regulating the heat supply near the beginning and the end of the heating period provided taking into account requirements of normative documents of the Russian Federation. Calculations are performed to determine the amount of the main components of the heat balance of a residential building on the example of one of the standard projects used currently in the climatic conditions of Moscow taking into account the constructive structural characteristics of the building and its occupancy level. Analysis of the obtained results and conclusions regarding the appropriateness of the application of this arrangement are provided. It is established that the actual heat output of the heating system when using a chilled water network down-stream the hot water supply heat exchangers as a heat source enables to maintain the safe indoor temperature in the building, with the average daily temperature of outdoor air above +2° C in conditions of moderate amount of heat received with solar radiation. It is shown that the use of this arrangement is virtually not accompanied by additional costs, provides hydraulic resistance of the heating system and gives a system-wide effect in the form of higher electricity generation at thermal consumption when using cogeneration.

Simultaneous Optimization of Non-Isothermal Design of Water Networks with Regeneration and Recycling

Most of the water network design strategies considering regeneration and recycling are using the assumptions that the processes are isothermal and steady state. However, almost all of the available processes have temperature change from the inlets to the outlets of the units. Moreover, to maintain the process units’ temperature under the specified limit, additional heat exchangers are usually required. The traditional approach of designing water network and heat exchanger network are usually made separately. It is reasonable to expect that a simultaneous design procedure of water network and heat exchanger network that considers process temperature change may result in a better design option. In this work, systematic design of non-isothermal water networks with regeneration and recycling is proposed. Superstructure model with non-linear programming (NLP) model is developed accordingly to incorporate all possible networks. Regeneration units and heat exchangers are introduced to achieve the specified contaminant requirements and temperature limits of each process unit. The superstructure model is enhanced with regeneration unit model by considering the removal ratio of contaminants. As opposed to the traditional model, the novel heat exchanger model in this work is constructed separately for the heating side and the cooling side to increase further flexibility to the original model. The overall model is optimized simultaneously to achieve feasible heat exchange network and optimal configuration. The total annual cost (TAC) and global equivalent cost (GEC) are considered as the objective function to represent the economic benefits of the given case study. Several case studies are provided to demonstrate the effectiveness of the proposed design strategy.

Passive water collection with the integument: mechanisms and their biomimetic potential.

Several mechanisms of water acquisition have evolved in animals living in arid habitats to cope with limited water supply. They enable access to water sources such as rain, dew, thermally facilitated condensation on the skin, fog, or moisture from a damp substrate. This Review describes how a significant number of animals - in excess of 39 species from 24 genera - have acquired the ability to passively collect water with their integument. This ability results from chemical and structural properties of the integument, which, in each species, facilitate one or more of six basic mechanisms: increased surface wettability, increased spreading area, transport of water over relatively large distances, accumulation and storage of collected water, condensation, and utilization of gravity. Details are described for each basic mechanism. The potential for bio-inspired improvement of technical applications has been demonstrated in many cases, in particular for several wetting phenomena, fog collection and passive, directional transport of liquids. Also considered here are potential applications in the fields of water supply, lubrication, heat exchangers, microfluidics and hygiene products. These present opportunities for innovations, not only in product functionality, but also for fabrication processes, where resources and environmental impact can be reduced.

Research of multiple refined degree simulating and modeling for high pressure feed water heat exchanger in nuclear power plant

High pressure feed water heat exchangers (HPFWHX) are essential equipments in the nuclear power plant (NPP) secondary loop. Because of the different requirements for the HPFWHX, there are the multiple degrees of refined simulation model developed in this work. The high fidelity simulation model is based on the practical physical structure with the tube bundle and partition plates. Large number of control volumes are divided by partition plates and tube bundles in the steam condensing zone and drain water cooling zone. To test and verify the simulation model, we utilized the main design parameters of No.7 HPFWHX in Qinshan II NPP. The steady state parameters are suitable for limiting model error and increasing its accuracy. Two dynamic conditions are chosen to verify the characteristics of the simulation model. Verification result shows that the dynamic processes are consistent with the theoretical basis used for the analysis. Also, the simulation model provides the parameter distribution and the dynamic state of the major HPFWHX parameters in the normal operation. The simulation model could assist researchers to determine and analyze the thermal features of the HPFWHX with fast calculation speed. The simulation model is also useful for the simulation of similar tube and shell heat exchangers in different conditions.

A surface renewal model for unsteady-state mass transfer using the generalized Danckwerts age distribution function.

The recently derived steady-state generalized Danckwerts age distribution is extended to unsteady-state conditions. For three different wind speeds used by researchers on air–water heat exchange on the Heidelberg Aeolotron, calculations reveal that the distribution has a sharp peak during the initial moments, but flattens out and acquires a bell-shaped character with process time, with the time taken to attain a steady-state profile being a strong and inverse function of wind speed. With increasing wind speed, the age distribution narrows significantly, its skewness decreases and its peak becomes larger. The mean eddy renewal time increases linearly with process time initially but approaches a final steady-state value asymptotically, which decreases dramatically with increased wind speed. Using the distribution to analyse the transient absorption of a gas into a large body of liquid, assuming negligible gas-side mass-transfer resistance, estimates are made of the gas-absorption and dissolved-gas transfer coefficients for oxygen absorption in water at 25°C for the three different wind speeds. Under unsteady-state conditions, these two coefficients show an inverse behaviour, indicating a heightened accumulation of dissolved gas in the surface elements, especially during the initial moments of absorption. However, the two mass-transfer coefficients start merging together as the steady state is approached. Theoretical predictions of the steady-state mass-transfer coefficient or transfer velocity are in fair agreement (average absolute error of prediction = 18.1%) with some experimental measurements of the same for the nitrous oxide–water system at 20°C that were made in the Heidelberg Aeolotron.

Tempering of water storage tank temperature in hot climates regions using earth water heat exchanger

In hot climate regions, outdoor domestic water tank is directly exposed to high solar intensity in addition to hot summer wind stream. The storage water temperature increases above 50 °C. In order to overcome this problem, time dependent analysis of cylindrical domestic storage water tank that exposed to high solar radiation is performed. The analysis includes energy balance for the water tank as well as to an earth water heat exchanger used to reduce the water temperature in summer months. The governing equations are solved numerically using fourth order Runge-Kutta method. It is found that using earth water heat exchanger reduces the water temperature by about 16 °C. A comparison of the numerical results with experimental data showed a good agreement.

Relationship among land surface temperature and LUCC, NDVI in typical karst area

Land surface temperature (LST) can reflect the land surface water-heat exchange process comprehensively, which is considerably significant to the study of environmental change. However, research about LST in karst mountain areas with complex topography is scarce. Therefore, we retrieved the LST in a karst mountain area from Landsat 8 data and explored its relationships with LUCC and NDVI. The results showed that LST of the study area was noticeably affected by altitude and underlying surface type. In summer, abnormal high-temperature zones were observed in the study area, perhaps due to karst rocky desertification. LSTs among different land use types significantly differed with the highest in construction land and the lowest in woodland. The spatial distributions of NDVI and LST exhibited opposite patterns. Under the spatial combination of different land use types, the LST–NDVI feature space showed an obtuse-angled triangle shape and showed a negative linear correlation after removing water body data. In summary, the LST can be retrieved well by the atmospheric correction model from Landsat 8 data. Moreover, the LST of the karst mountain area is controlled by altitude, underlying surface type and aspect. This study provides a reference for land use planning, ecological environment restoration in karst areas.

Energy efficient heat pipe heat exchanger for waste heat recovery in buildings

This study presents a Computational Fluid Dynamics (CFD) Heat Transfer Analysis for an originally designed Energy Efficient Heat Pipe Heat Exchanger for Waste Heat Recovery in Buildings. The research is focused on developing a heat pipe heat exchanger for domestic hot water and thermal agent preparation, preheating / heating the air from ventilation systems in buildings, using as a primary agent the return of the existing heating system. The proposed device has a lot of advantages as high efficiency for heat recovery, low cost of manufacturing, exploitation and maintenance and it is very easy to install and use.

Nicotinamide Inhibition Properties for Copper Corrosion in 3.5% NaCl Solution: Experimental and Theorical Investigations

This work reports the inhibition properties of nicotinamide (NAM) for copper protection during its applications in seawater systems such as water pipelines, shipbuilding, seawater desalination and heat exchange systems. The efficiency of NAM as a copper corrosion inhibitor in simulated seawater (3.5% NaCl solution) was investigated by Tafel extrapolation and linear polarization methods in the temperature range from 20℃ to 50℃. The corrosion parameters and the adsorption isotherms were determined using potentiodynamic polarization techniques. It was found that the inhibition efficiency (η) and the coverage rate (θ) increase up 80% at 25℃ for nicotinamide concentration of 10 mM but decrease as the temperature of the solution increases. Moreover, the obtained thermodynamic parameters using Langmuir model suggested a physical adsorption type. A correlation was found between the corrosion inhibition efficiency and the global theoretical parameters obtained by the functional density method B3LYP/ 6-31 + G (d, p). Local parameters such as condensed Fukui functions [f(r)] and condensed local softness [s(r)] indices have also been determined to obtain a chemical insight into atoms that have a significant tendency toward donation or acceptance of whole or fraction of electrons.

Heat Transfer of Polyolefin Covered STS Corrugated Tube for Surface Water Source Heat Pump

Recently, high density poly ethylene (HDPE) tube has been utilized in surface water source heat pump (SWSHP) as a surface water heat exchanger (SWHE). Stainless steel (STS) corrugated tube has much higher heat transfer coefficient (U value) than HDPE tube in SWHE. However, this material cannot be perfectly protected from corrosion when exposed to aggressive water environments. The goal of this work is to increase U value of SWHE when STS corrugated tube is perfectly protected from corrosion by covering polyolefin material on its corrugated surface. In order to verify the thermal performance of proposed tube, U values and friction factors of the proposed tube were compared with those of the HDPE tube. For the evaluation on possible applicability of proposed tube, the economic evaluation of the proposed tube was also performed based on the result from test bed experiments. The results show that the proposed tube leads to 4.65 times higher U value and 2 times higher friction factor than HDPE smooth tube. Despite with the increased friction loss and installation cost, it was revealed that the proposed tube can achieve COP due to enhanced heat transfer performance.

The economics of flue gas cooling technology for coal-fired power stations with flue gas desulfurisation

Developments in heat exchanger technology, specifically in the use of polymers as tube material, have allowed the use of gas to water heat exchangers under conditions previously not viable. Two applications in the flue gas cleaning circuit of coal-fired power stations are described in this paper. In conventional pulverised coal-fired boilers, cooling of gas prior to the wet flue gas desulfurisation (WFGD) absorber reduces water consumption for evaporative cooling of the flue gas and can recover heat for feed water preheating or for use elsewhere in the plant. In another application, circulating fluidised bed boilers, which are currently proposed for a few independent power producers and may not require wet FGD, heat recovery is still feasible upstream of the bag filter typically used for particulate emission control. The extracted heat can again be recovered for use in other power plant processes, in this case most economically for pre-heating combustion air. This paper presents case studies for each of the above applications, showing that the power station efficiency is typically increased by approximately 1% of its pre-installation value. An economic analysis is provided for each, including additional power sales, reduced water consumption, or reduced fuel use with a reduction in carbon tax. For the larger installations with WFGD, payback time can be in the order of 6 years.

Numerical investigation of subcooled flow boiling in an annulus under the influence of eccentricity

The subcooled flow boiling phenomenon usually occurs in a number of industrial applications, such as Pressurized Heavy Water Reactors (PHWR) and heat exchangers in nuclear power plants. The pressure tube deformation, presence of spacer pads, etc., may result in the eccentricity (e) of the rod bundle which causes coolant flow maldistribution and hence influence the heat transfer characteristics. In the present study, the entire rod bundle is modeled as a single inner rod and Eulerian Eulerian Multiphase Flow (EEMF) and Wall Heat Flux Partition (WHFP) model framework is used to simulate the effect of eccentricity (e). This model is validated against the available experimental data in the literature and found to be in reasonably good agreement. This framework is also compared and contrasted against the subchannel analysis predictions to highlight the importance of detailed CFD simulations. Furthermore, in the present study, the thermal hydraulics of narrow and wide gap regions are numerically investigated in an eccentric annulus. Due to eccentricity, early phase change, higher wall temperature and vapour volume fraction were noticed in the narrow gap region, compared to the concentric case (e=0.0), which is undesirable in the PHWR type reactors.

Life-cycle impacts of shower water waste heat recovery: case study of an installation at a university sport facility in the UK.

Recovering heat from waste water discharged from showers to preheat the incoming cold water has been promoted as a cost-effective, energy-efficient, and low-carbon design option which has been included in the UK's Standard Assessment Procedure (SAP) for demonstrating compliance with the Building Regulation for dwellings. Incentivized by its carbon cost-effectiveness, waste water heat exchangers (WWHX) have been selected and incorporated in a newly constructed Sports Pavilion at the University of Brighton in the UK. This £2-m sports development serving several football fields was completed in August 2015 providing eight water- and energy-efficient shower rooms for students, staff, and external organizations. Six of the shower rooms are located on the ground floor and two on the first floor, each fitted with five or six thermostatically controlled shower units. Inline type of WWHX were installed, each consisted of a copper pipe section wound by an external coil of smaller copper pipe through which the cold water would be warmed before entering the shower mixers. Using the installation at Sport Pavilion as the case study, this research aims to evaluate the environmental and financial sustainability of a vertical waste heat recovery device, over a life cycle of 50years, with comparison to the normal use of a PVC-u pipe. A heat transfer mathematical model representing the system has been developed to inform the development of the methodology for measuring the in-situ thermal performance of individual and multiple use of showers in each changing room. Adopting a system thinking modeling technique, a quasi-dynamic simulation computer model was established enabling the prediction of annual energy consumptions under different shower usage profiles. Data based on the process map and inventory of a functional unit of WWHX were applied to a proprietary assessment software to establish the relevant outputs for the life-cycle environmental impact assessment. Life-cycle cost models were developed and industry price book data were applied. The results indicated that the seasonal thermal effectiveness was over 50% enabling significant energy savings through heat recovery that led to short carbon payback time of less than 2years to compensate for the additional greenhouse gas emissions associated with the WWHX. However, the life-cycle cost of the WWHX is much higher than using the PVC pipe, even with significant heat recovered under heavy usage, highlighting the need to adopt more economic configurations, such as combining waste water through fewer units, in order to maximize the return on investment and improve the financial viability.

Experimental and theoretical analysis of glazed tube-and-sheet photovoltaic/thermal system with earth water heat exchanger cooling

In the present paper, an attempt has been made to investigate the theoretical and practical performances of the photovoltaic/thermal (PV/T) system coupled with earth water heat exchanger (EWHE) cooling system for the conditions of semi-arid region of Pilani, Rajasthan. The experimental studies have been performed for different flow rates of cooling water (0.033 kg/s, 0.025 kg/s and 0.017 kg/s) for a typical day climatic conditions. An electrical efficiency comparison was made for two scenarios when the PV panel was connected or disconnected with the thermal collector and found out that the average electrical efficiency of PV/T panels is higher than the normal PV efficiency. The results of the experimental study showed that the maximum PV panel temperature goes up to 73 °C without any cooling. On the other hand, the PV panel temperature drops in the range of 43.68–49.64 °C with the flow rate of 0.033 kg/s. It has been estimated that the electrical and thermal efficiencies of the PV/T system with cooling are in the range of 8.26–8.52% and 44.06–55.45% respectively for flow rate of 0.033 kg/s. The EWHE pipe length of 38 m found to be sufficient for the proposed system. The experimental results are validated with the theoretical model by using basic energy balance equations and found in good agreement with percentage error of 0.91–12.09%.

Heat-integrated water allocation network synthesis for industrial parks with sequential and simultaneous design

This paper presents a methodology for the synthesis of inter-plant heat-integrated water allocation network (IHIWAN) in industrial parks, to promote the overall level of resource conservation by exploiting the cooperative utilization among multiple plants. Based on superstructure, the proposed method introduces inter-plant integration strategies specific to industrial parks, involving the coupling scheme of water allocation and heat exchange. And a non-linear programming model (NLP) is formulated containing water allocation subsystem and heat integration subsystem. Accordingly, economically optimal IHIWAN is synthesized via two optimization routes respectively: sequential design and simultaneous design. Results of application examples indicate that inter-plant integration of the overall water-heat system in the scale of the park can bring about significant savings compared to the summation of integration within each stand-alone plant. In addition, simultaneous design presents preferable result with regard to overall economic performance, yet sequential design features more targeting flexibility and lower requirement on solution process.

Experimental characterization of an additively manufactured heat exchanger for dry cooling of power plants

Air-cooled heat exchangers for power plant cooling are receiving much attention lately, as they require little or no water for cooling when compared to water-cooled systems. This paper focuses on the design, fabrication, and experimental characterization of a novel additively manufactured air–water heat exchanger for dry cooling of power plants. The heat exchanger consists of manifold-microchannels on the air side and rectangular channels on the water side in a cross-flow configuration. By using additive manufacturing, the manifold-microchannel heat exchanger can be fabricated as a single component, which eliminates the assembly process. Three prototype heat exchangers were fabricated using direct metal laser sintering (DMLS) out of stainless-steel (SS17-4), titanium alloy (Ti64), and aluminum alloy (AlSi10Mg). Air-side heat transfer coefficients in the range of 100–450 W/m2 K at pressure drops of 50–2000 Pa were recorded for the titanium alloy heat exchanger for air flow rate ranging from 1.89 L/s to 18.9 L/s. Based on our analysis and compared to conventional heat exchangers, the performance of this manifold-microchannel heat exchanger was superior. Compared to wavy fin and plain plate fin heat exchangers, up to 30% and 40% improvement, respectively, in gravimetric heat transfer density was recorded for the entire range of experimental data. Compared to state-of-the-art dry cooling, nearly 27% improvement in gravimetric heat transfer density was noted at air-side coefficient of performance (COPair) of 172.

An integrated photovoltaic thermal solar (IPVTS) system with earth water heat exchanger cooling: Energy and exergy analysis

Abstract In the current paper, a new hybrid system is investigated in which integrated photovoltaic thermal solar system (IPVTS) is coupled with earth water heat exchanger (EWHE). The performance of such coupled system is evaluated analytically by developing a theoretical model and validated experimentally on an experimental set-up installed in Pilani, India. Further to identify the grey areas for the improvement and to utilize the maximum energy, second law thermodynamic analysis of coupled system has been carried out in terms of exergy losses and exergy destructions. An electrical efficiency comparison was made between the PV panel connected to the broad water channel cooling and normal PV panel. The results show that with EWHE cooling, there is increase in experimental electrical efficiency of IPVTS by 1.02–1.41% as compared to without cooling. The second law analysis for two different scenarios was carried out. The second law analysis shows that the exergetic efficiency for a first scenario varies from 8.50% to 8.75%; while for the second scenario, it ranges from 8.16% to 8.54%. The analysis provides the feasibility of IPVTS coupled with EWHE system which could be used for the semi-arid regions of North-West India.