Heat Exchanger Arrangement Research Articles

Effect of feed composition on cryogenic distillation precooling configurations

Precooling the feed of cryogenic distillation columns is achieved by using the cold distillate and bottoms streams. The distillate is typically removed from the top of the reflux drum as a vapor to reduce the condenser refrigeration heat duty. The bottoms stream is typically a liquid at a somewhat higher temperature than the distillate. The colder vapor distillate can only provide sensible heat removal. The warmer bottoms liquid stream can provide more heat removal because of vaporization.The purpose of this paper is to demonstrate that the appropriate arrangement of the precooling heat exchangers depends on the column feed composition. If the feed contains little light key component, the bottoms stream is large and the feed can be easily precooled. If the feed contains little heavy key component, the bottoms stream is small and precooling the feed is more difficult.

An industrial facility layout design method considering energy saving based on surplus rectangle fill algorithm

The facility layout design within a plant is a key step in the process of chemical engineering design. A good layout can save capital cost, energy and natural resource. The aim of this work is to determine the relative location of facilities in a large-scale industrial plant considering multi-floor structure to make the total cost minimum. The objective function consists of piping investment cost, pump power cost, land cost, and floor construction cost. Surplus rectangle fill algorithm is applied in this work, and it is combined with a genetic algorithm to obtain the optimal solution. Constraints of pump area, joint arrangement of heat exchangers, and the cross-floor facilities are also taken into consideration. In the case study, a plant from a real refinery including 217 facilities is designed with different floor number. The comparison of the three different conditions proves the important role of floor number in the trade-off among investment cost, energy consumption, and land resource. The case illustrates that, the proposed method can generate a reasonable layout design for the industrial facilities and save capital and operating cost effectively. A sensitivity analysis is also done to explore the influence of basic data on the optimal construction structure.

Global sensitivity analysis of borehole thermal energy storage efficiency on the heat exchanger arrangement

Global sensitivity analysis of the efficiency of borehole thermal energy storage (BTES) during long-term operation on the borehole heat exchanger (BHE) arrangement was investigated to advance understanding of the system’s thermal performance. Three parameters were assessed to determine the BHE arrangement: the first parameter designate the distance between BHE axis in x direction, the second in y direction and the third an angle between top surface of the rock mass and boreholes axis. Conducting research on the real system is extremely expensive, so it was decided to conduct simulation studies utilising a finite element method. The ANSYS software with a newly implemented heat and mass transport model in BHE was used. Based on conducted numerical simulations, and according to the design of the experiment, a multidimensional response surface was achieved. The global sensitivity was conducted based on a response surface model. It was found that the BHE inclination (SEeffP3=0.97 – FAST algorithm) has a crucial impact for the BTES efficiency. The area on response surface, where the optimal BHE arrangement to maximise BTES efficiency could be reached, is an inclination P3=0° and BHE spacing in the range of P1=P2=(1.5–3m).

Gimazetdinov R.R., Malozemov A.A., Kukis V.S. Diesel-generator plant with the recovery of waste heat of the piston engine

The subject of the investigation was the waste heat recovery system of a small-scale heat electropower station that can be used as stationary and primary, reserve or additional source of electrical and thermal energy. The object of the investigation was the waste heat recovery system of the diesel engine D 180 and the small-scale heat electropower station on the basis of the diesel generator plant DGU-100C produced by JSC «ChTZ». The aim of the investigation was an experimental estimation of the efficient use of the diesel engine’s waste heat recovery system. The recovery system was consisted of an original heat exchanger for the recovery of the waste heat of the diesel engine’s cooling system, the waste heat of the lubricating system, the centers of which is made in a common housing, and the heat exchanger for the recovery of the exhaust gases waste heat from the diesel engine (pre-heater boiler PZD-600). The article presents the small-scale heat electropower station’s arrangement with the waste heat recovery system, the original heat exchanger arrangement and a scheme of the small-scale heat electropower station with the waste heat recovery system. The principle of operation of the proposed system is described. In comparison with the known constructions, in the proposed cogeneration power plant there is no need to separately regulate the temperature of the cooling liquid and the lubricating oil at the inlet to the piston internal combustion engine and the necessity to use an additional liquid-oil heat exchanger or oil cooler in the operation of the cogeneration plant without thermal load. Collectively, it was ensured a reduction of the complexity, material consumption and overall dimensions of the recovery system and the cogeneration power plant in general. The absolute economic effect from the using of the waste heat recovery system is 240…300 thousand rubles for the engine life, specific - 22…28 rubles/h. The payback period of the waste heat recovery system is less than a year. The obtained results convincingly indicate the economic feasibility of implementing the proposed system of waste heat recovery of the diesel engine D 180 of a small-scale heat electropower station based on the DGU-100S.

Multi-dimensional simulation of underground subway spaces coupled with geoenergy systems

Old and deep subway lines suffer from overheating problems, particularly during summer, which is detrimental for passenger comfort and health. Geothermal systems could serve as one of the potential energy efficient cooling solutions, compared to energy intensive conventional cooling. The waste heat of the subway tunnel can be harnessed, to provide heating to residential and commercial blocks above the tunnels. This paper presents a multi-scale co-simulation framework for quantifying the amount of useful heat that can be extracted from overheated underground subway tunnels using geothermal heat exchangers. The co-simulation is applied and tested on a representative section of the London Underground's Central Line. The Central Line is modelled using a 1D heat and mass transfer model. The geothermal system, on the other hand, is represented using a 3D finite element model. The 1D and 3D models are co-simulated, using the subway tunnel's outer wall temperatures as boundary conditions. The model is run parametrically to identify the best arrangement and depth of geothermal heat exchangers for extracting excess heat from subway tunnels. Results show that the depth of 15 m. below the tunnel is sufficient for vertical closed loop heat exchangers to yield temperature drop of 4C in the subway tunnel and platforms. Partially insulated boreholes, alternating between extracting and injecting heat into the soil, are also assessed for their potential to provide heating and cooling demand simultaneously and improve the overall geothermal system efficiency. The heat extracted along a representative section of the tunnels is compared to the heating demand of the buildings above ground.

First operation of the XFEL linac with the 2 K cryogenic system

The RF operation of the about 800 superconducting 1.3 GHz 9-cell cavities of the XFEL linac requires helium II bath cooling at 2 K, corresponding to a vapor pressure of 3100 Pa. After the first cool-down of the XFEL linac to 4 K in December, 27th 2016 the operation of the 2 K cryogenic system was started in January, 2nd 2017. The 2 K cryogenic system consist of a 4-stage set of cold compressors to compress helium vapor at a mass flow of up to 100 g/s from 2400 Pa to about 110 kPa and a full flow bypass with an arrangement of heat exchangers and control valves.This paper describes the XFEL refrigerating plant, especially the 2 K cryogenic system, the tuning of the cold compressor regulation to adapt to the XFEL linac static and dynamic heat loads and experience of about 6 months of operation.

Using duct storage (DST) model for irregular arrangements of borehole heat exchangers

The duct storage (DST) model is one of the most widely used borehole heat exchanger (BHE) models owing to its fast calculation scheme and usability. However, the DST model can simulate only regularly placed BHEs, particularly in cylindrical borefield configurations. As a possibility to describe irregular borefield configurations by adjusting BHE spacing has been reported, we propose optimal values of BHE spacing for typical irregular BHE cases using the GenOpt optimization tool. A regression model based on a set of results obtained from the optimization is proposed to calculate the modified spacing for the DST model directly without optimization simulations. The proposed regression model fits to the datasets of the optimization with an accuracy of 96.5% in predicting the modified BHE spacing. The differences in time-averaged EWTs between the DST model with the proposed modified spacing and a reference model are close to zero, and they are less than 0.5 °C. However, other borefield configurations that have not been used for the model development can result in higher errors.

Thermo-flow performances of natural draft direct dry cooling system at ambient winds

Natural draft direct dry cooling system (NDDDCS) uses the natural draft dry-cooling tower instead of axial flow fans, so can effectively reduce the power consumption, operating costs and also the noise caused by fans. In this work, two types of NDDDCS with horizontally arranged heat exchanger bundles (HAHEBs) and vertically arranged heat exchanger bundles (VAHEBs) are proposed respectively. Furthermore, the cooling delta apex angles from 60° to 180° are further investigated. The air-side velocity, pressure and temperature fields are presented and the heat rejections for various configurations of NDDDCS are calculated and compared. The results show that the cooling performance of NDDDCS with VAHEBs is superior to that with HAHEBs in any case, especially at high wind speeds. The VAHEBs with the apex angle of 150° have the best cooling performance, so can be recommended in the potential practical engineering of natural draft direct dry cooling system in power plants.

土壌熱源ヒートポンプシステム設計・性能予測ツールに関する研究 : 第3報-地中熱交換器の配管仕様に応じた温度計算手法とその応用

土壌熱源ヒートポンプシステム設計・性能予測ツールに関する研究 : 第3報-地中熱交換器の配管仕様に応じた温度計算手法とその応用

Thermo-flow characteristics of indirect dry cooling system with elliptically arranged heat exchanger bundles around a traditional circular cooling tower

In a traditional indirect dry cooling system, the heat exchanger bundles are circularly arranged around the circumference of a cooling tower, which suffers severely from ambient winds. In this paper, an elliptical arrangement of heat exchanger bundles, which surround a traditional circular cooling tower, is proposed to restrain the adverse impacts of ambient winds. Elliptically arranged heat exchanger bundles with four different minor to major axis ratios were investigated on the condition that the total heat transfer area is the same as the traditional indirect dry cooling system. The flow and temperature fields of cooling air in the absence/presence of ambient winds were obtained. The mass flow rate, heat rejection and outlet water temperature of the alternative indirect dry cooling systems were calculated and analyzed. The results show that the elliptically arranged heat exchanger with a small ratio of minor to major axis is superior in thermo-flow performance at high wind speed. It is recommended that indirect dry cooling system incorporating elliptically arranged heat exchanger bundles be applied in regions with strong prevailing winds to achieve better thermo-flow performance.

Novel method for determining optimal heat-exchanger layout for heat recovery steam generators

A new method for determining the optimal heat-exchanger layout in a heat recovery steam generator and its operating parameters are presented in this paper. A robust mathematical model is developed, where arbitrary steam-pressure levels and steam-reheating levels can be set. The method considers all the possible heat-exchanger layouts, in both serial and parallel arrangements of steam pressure levels or steam reheating levels. The maximum thermodynamic efficiency of the steam-turbine cycle is set as the objective function. The results show that the optimal high pressure in heat recovery steam generator without reheating is in the region of subcritical pressures, whereas that for a heat recovery steam generator with reheating is in the region of supercritical pressures. In the case of similar water or steam temperature profiles in the heat exchangers of different steam pressure levels or reheating level, from a thermodynamic viewpoint, it is justified to use a parallel heat-exchanger arrangement.

High efficiency H2O/LiBr double effect absorption cycles with multi-heat sources for tri-generation application

The objective of this study is to develop a high-efficiency double effect absorption cycle using multi-heat sources for tri-generation (trigen) application. The trigen system produces electricity, heating and cooling loads at the same time. The double-effect absorption refrigeration system consists of two generators, condensers, solution heat exchangers, expansion valves, an absorber and an evaporator. The cycle simulation is carried out for the H2O/LiBr double effect absorption cycle with multi-heat sources for parallel, serial, reverse, revised serial and revised reverse flow patterns. The absorption refrigeration system uses the high temperature steam and hot water as the multi-heat sources. A new high-efficiency cycle is selected depending on the arrangements of additional heat exchangers. This study recommends HX 2-2 cycle with two additional heat exchangers (SDHHX and DHX) as the best candidate for trigen application. It is concluded that THotwater has much more significant effect on the COP and Q̇E than Tsteam in the HX 2-2 cycle. It is also found that the most important UA to affect the COP is UALG while that to affect Q̇E is UAA.

Heat transfer characteristics for tube arrangement of heat exchanger

Heat transfer characteristics for tube arrangement of heat exchanger

Triangularly arranged heat exchanger bundles to restrain wind effects on natural draft dry cooling system

It has been commonly recognized that the crosswind may deteriorate the cooling performance of the natural draft dry cooling system with vertically arranged heat exchanger bundles around the circumference of dry-cooling tower. With the purpose for restraining the adverse effects of ambient winds, a novel triangular configuration of heat exchanger bundles is proposed in this work. The air-side flow and heat transfer models coupled with the circulating water heat transfer process are developed for two kinds of natural draft dry cooling systems with the conventional circularly arranged and novel triangularly arranged heat exchanger bundles, by which the flow and temperature fields, mass flow rate of cooling air, outlet water temperature of heat exchanger and turbine back pressure are obtained. Three wind directions of 0°, 90°, and 180° are investigated at various wind speeds for the natural draft dry cooling system with triangularly arranged heat exchanger bundles, which are compared with the conventional system with circularly arranged heat exchanger bundles. The results show that the thermo-flow performances of the natural draft dry cooling system with triangularly arranged heat exchanger get improved significantly at high wind speeds and in the wind direction of 180°, thus a low turbine back pressure can be achieved, which is of benefit to the energy efficiency of the power generating unit. The natural draft dry cooling system with triangularly arranged heat exchanger is recommended to apply to the regions with strong prevailing winds all year around.

Impacts of tower spacing on thermo-flow characteristics of natural draft dry cooling system

Multi-towers are widely introduced to the natural draft dry cooling system in power plants, and the geometrical layout of dry-cooling towers is a key issue to the thermo-flow characteristics of natural draft dry cooling system. Based on a representative two-tower design with vertically arranged heat exchanger bundles around the circumference, the air-side flow and heat transfer models of natural draft dry cooling system at the tower spacing to diameter ratios from 0.1 to 3 are developed and the velocity, pressure and temperature fields of cooling air in the absence and presence of ambient winds are presented. The mass flow rate and heat rejection of the two air-cooled heat exchangers at various wind speeds and in various wind directions are calculated. The correlations between the heat rejection of each tower and the tower spacing, wind speed and angle are obtained. The results show that the impacts of tower spacing on thermo-flow characteristics of natural draft dry cooling system depend on the wind speed and the arrangement of towers. The towers arranged in line are superior to those arranged in other patterns. When the tower spacing to diameter ratio is lower than unity, the conspicuous interaction between two towers will deteriorate the thermo-flow performances of natural draft dry cooling system. The results can contribute to the dry-cooling tower layout of natural draft dry cooling system in power plants.

Heat exchanger network retrofit throughout overall heat transfer coefficient by using genetic algorithm

Heat integration through energy recovery is utilized to reduce energy consumption. Energy or heat recovery can be performed using heat exchanger (HE) in heat exchanger network (HEN). HEN is an arrangement of several interconnected HE, which is used to conduct heat recovery. This arrangement increases complexity of heat integration. In the existing HEN, some of the energy is wasted due to unproper HEN design. HEN retrofit can overcome this problem and increase the heat recovery in existing processes. In this research, HEN retrofit is performed by optimizing the maximum heat recovery (Q) without changing the area of heat transfer or adding new HE and the arrangement of HE in HEN. In order to fid out the maximum Q, genetic algorithm (GA) is used to search the best heat transfer coefficient (U) value. In this paper, three cases of optimization scenarios are performed by some constraints considered on the HEN model. In the first optimization scenario, U is optimized without the given the maximum and minimum limits. While in the second optimization scenario, U has limitation at the minimum value, which is the value of U on the initial design data. And on the third case optimization scenario, U has limits due to availability of existing technology, which is the increase in the maximum of U using internal fins, twisted tape insert, coiled wire insert, and helical baffle. Heat recovery obtained in the first case scenario optimization results was at 13.21%, whereas the second case scenario optimization was at 9.14%, and the third case scenario optimization was at 3.60% with an internal fin technology limitations, 2.77% by limitations of twisted tape inserts technology, 7.69% with coiled wire insert technology, and 4.61% with helical baffles technology.

Numerical Procedure for LMTD Correction Factor Calculation for One Tube and One Shell Pass Shell-and-Tube Heat Exchangers

This paper outlines the application of a numerical procedure to compute the LMTD correction factor for one tube pass and one shell pass, namely 1-1, shell-and-tube heat exchangers. Although the procedure was applied for this specific arrangement, it can easily be applied to different heat exchanger arrangements. The numerical methodology is based on an association of ε-NTU and LMTD approaches introduced by Kays and London (1998). Unlike other shell-and-tube heat exchanger arrangements, such as one tube pass and two shell pass, no available analytical expression in closed form is available in the literature. Hence, the presented numerical procedure is applied to determine the LMTD correction factor for 1-1 shell-and-tube heat exchangers and numerical results were obtained by increasing the number of baffles (1, 3, 7, 9, 19 and 49), in order to analyze the obtained results. Finally, charts for the LMTD correction factor is presented as a function of two dimensionless parameters, namely P and R.

CFD Simulations of one Period of a Louvered Fin where the Airflow is Inclined Relative to the Heat Exchanger

This article presents Computational Fluid Dynamics (CFD) simulations of one period of a louvered fin, for a crossflow compact finned heat exchanger, where the incoming airflow was inclined relative to its core. Four inclinations were investigated: 90°, which was when the air flowed perpendicular to the heat exchanger, 60°, 30° and 10° angles relative to the vertical plane. The study included three heat exchanger designs, where two of them had symmetrical louvered fins and a thickness of 19mm and 52mm. The third had a thickness of 19mm and had the louvers angled in one direction. All heat exchangers have been simulated when the airflow entered both from above and below relative to the horizontal plane. Simulations have also been carried out when the airflow entered from the side, illustrating the heat exchanger to be angled relative to the vertical axis. Two air speeds have been investigated for each configuration, where the results were compared to experimental data. The results showed that the airflow characteristics were strongly dependent on the inclination angle. A more inclined heat exchanger generated larger separated areas at the entrance of the heat exchanger core. After approximately six louvers the airflow was fairly similar for all inclinations. The pressure drop over the core was not affected by the direction of the entered airflow. It was also seen that the heat exchanger with the louvers in only one direction resulted in approximately the same pressure drop as the one with symmetrical louvered fins. For a constant velocity in the longitudinal direction within the core, the pressure drop did not varied between the inclinations. Depending on the definition of the heat exchanger arrangement the heat transfer rate was affected. Simulated pressure drop followed the same trend as experimental data, even though the values were over-predicted.

Influences of height to diameter ratios of dry-cooling tower upon thermo-flow characteristics of indirect dry cooling system

Ambient winds may reduce the cooling efficiency of a nature draft dry-cooling tower, so it is of benefit to the design and operation of indirect dry cooling system to determine the preferred tower shape to restrain the adverse impacts of ambient winds. Based on the dry-cooling tower with vertically arranged heat exchanger bundles around the circumference, air-side flow and heat transfer models are developed for three typical height to diameter ratios of tower. The velocity, pressure and temperature fields of cooling air in the absence and presence of ambient winds are presented, and the mass flow rate, heat rejection and outlet water temperature of each sector and air-cooled heat exchangers are calculated. The results show that the dry-cooling tower with a low height to diameter ratio is superior to that with a high ratio in thermo-flow performances of indirect dry cooling system at high wind speeds on condition that the air-cooled heat exchangers have the same heat transfer surface areas. At low wind speeds, the mass flow rate and heat rejection of air-cooled heat exchanger vary little with height to diameter ratios of tower due to almost the same buoyancy forces. It is recommended to take a low height to diameter ratio of tower, especially at strong ambient winds for better thermo-flow performances of indirect dry cooling system.

Simplified number of transfer unit formulas for the thermal performance calculation of multi-pass fin-tube heat exchangers

The known effectiveness–number of transfer units relationships of multi-pass fin-tube heat exchangers consist of a large number of terms in the series and are not expressed directly in terms of the number of transfer units; as a result, it is difficult to calculate the number of transfer units and the heat transfer coefficient of heat exchangers for a given effectiveness and thermal capacity ratio. To solve this problem, heat transfer models for multi-pass fin-tube heat exchangers based on the heat balance method were established in this article, and simplified number of transfer units formulas for thermal performance calculation were derived according to the flow arrangements of heat exchangers and the flow directions of two fluids. When the number of flow passes in a heat exchanger is greater than four, the relative errors between the calculated number of transfer units by these proposed formulas and those calculated by the effectiveness–number of transfer units relationships of the counter-flow or parallel-flow heat exchangers were all less than 2%. When the number of flow passes in a fin-tube heat exchanger is less than four, a two-pass counter-flow fin-tube heat exchanger was selected as the validation case due to the similar flow characteristics of heat exchangers. The results indicated that the relative errors between the calculated heat transfer coefficients of the heat exchanger according to these proposed number of transfer units formulas and those calculated using the LMTD factor were all less than 5% when the inlet water temperature was in the range of 45°C to 60°C and the water flow rate was in the range of 50 to 170 kg/h. These proposed number of transfer units formulas were determined to be valid and could be beneficial for the design of multi-pass fin-tube heat exchangers.