Cooled Heat Exchanger Research Articles

Performance Improvement of Biomass Cogeneration Plant by Dual Loop Organic Rankine Cycle

Biomass cogeneration plants in wood industry are usually designed to cover large share of site heat demand. However, plant capability to cover peak load in winter could lead to low utilisation of installed capacities at sites whit high seasonal heat demand fluctuations. At some sites, where income of sold electricity is essential for plant investment payback, non-cogeneration operation mode is applied and evacuation of surplus heat through air cooled heat exchangers is usual practice. Price increase of wood chips, as a consequence of increased demand, accompanied by implementation of sustainability criteria for biomass utilisation forced plant owners to reconsider existing business model and to find more efficient ways of biomass utilisation. Based on analysis of operational pattern of existing 1 MW organic Rankine cycle plant in wood pellets processing industry in Croatia, configuration and parameters of an additional low temperature organic Rankine cycle have been investigated in order to find technically and economically optimal configuration. Taking into account time dependant variation of surplus heat of the high temperature cycle in the range of 1 to 3 MW and variation of ambient temperature, net output power of the low temperature cycle has been optimised. Off-design and part-load operating conditions have been also considered and results of analyses have been presented.

Finite Element Analysis of Split Type Header in Air Cooled Heat Exchanger

Split type header is a part of tube bundle of an Air-cooled heat exchanger, used in refinery and oil & gas production. Typically, header can be considered as a pressure vessel subjected to uniform internal pressure. Hence the header and nozzle in various design and operating conditions needs to be checked and verified for soundness of participating components. Top plate due to uniform internal pressure in the nozzle & header plate can produce high-localized stress and deformation. If the components are not designed for these conditions, safety of the equipment is at stake. Hence check for the stress and displacement of the header during operating condition is carried out using finite element analysis software and observed that header nozzle is free from collapse and serviceability failure. I. Introduction (1) Heat exchangers are systems that transfer heat between fluid mediums. The fluids or gases in a heat exchanger can be mixed or the energy transference can go through a conductive wall that keeps them separate. Air-cooled heat exchangers typically have rectangular bundles containing several rows of tubes. The hot fluid enters at the top of the bundle through nozzle pipe. While air is blown by fans vertically upwards across the tube bank, i.e. counter current flow. Structural integrity of the header box can be checked by using (12) Appendix 13 of ASME Sec VIII Div I and other parts of the exchanger header box with the respective clauses of ASME code. For installing the nozzle on the header box opening is made on it, this opening of the vessel must be reinforced with an equal amount of metal which has been cut out for the opening. The reinforcement may be an integral part of the vessel and nozzle or may be an additional reinforcing pad. In addition the compensation must account for the bending strength as well as the membrane strength. The reinforcement calculations for nozzle openings according to UG-39 are in addition to bending & membrane strength. However, the calculation of Area required, according to UG-39, requires that the required thickness(tr) be substituted for in the formula, and it has not been calculated, since the method used in Appendix 13 is by assuming a and calculating stresses then comparing with allowable stresses and yield stress. This means that required thickness (tr) cannot be directly calculated. Accordingly, the area A cannot be directly calculated however in this case nozzle opening is larger than ½ of the header opening hence is beyond the scope of UG-39 of ASME Sec VIII Div-I and therefore the calculation has to done by finite element method.

A Novel Design of Heat Exchanger for Epsom Salt Cooling Crystallization

We introduced a design of a novel cooling heat exchanger for crystallization process of MgSO4.7H2O, and described the concepts of primary nucleation and secondary nucleation. To avoid the primary nucleation during crystallization process, the super-cooling degree limit of the salt lake brine was measured to define the supersaturation limit to MgSO4.7H2O, and the result is 1.32°C at-1°C. In this design, a primary circulation of solution is employed with a large enough flow rate to control the super-cooling degree of solution not to exceed 0.7 °C. A secondary circulation of cooling media is designed to add to this system, instead of the coldest cooling media being fed to shell directly, it is fed to the circulation pipe of the shell. It will help to prevent the supersaturation of solution exceeding the metastable zone width, thus to gurantee no primary nucleation during the Epsom salt crysatllization process.

Finite Element Analysis of Split Type Header in Air Cooled Heat Exchanger

Finite Element Analysis of Split Type Header in Air Cooled Heat Exchanger

500Ps급 상용차량 디젤엔진을 이용한 선박용 디젤엔진 개발 연구

This study was carried out to develop a diesel engine for marine propulsion. This marine diesel engine was developed based on a 500Ps vehicle diesel engine. Many main parts, such as the intercooler, radiator, and engine controller were designed for the marine diesel engine. The intercooler was designed to be of sea water cooling type; inlet air is cooled by sea water. Engine coolant is cooled by sea water in the radiator too. The water cooling heat exchanger has high cooling performance. In the cooling system, consists of the intercooler and the radiator, the sea water passes through the intercooler and then the radiator, in sequence. This process is very effective compared to the reverse method in which sea water passes through the radiator and then the intercooler, in sequence. The control performance of the engine controller and the fuel injection rate were improved using an engine speed controller. This system was tested on an engine dynamometer and an exhaust gas analyzer using the marine diesel engine test method. Test results show that the 500Ps marine diesel engine satisfied the IMO NOx regulations; Tier II.

Optimization mathematical model for the detailed design of air cooled heat exchangers

This paper presents a disjunctive mathematical model for the optimal design of air cooled heat exchangers. The model involves seven discrete decisions which are related to the selection of the type of the finned tube, number of tube rows, number of tube per row, number of passes, fins per unit length, mean fin thickness and the type of the flow regime. Each discrete decision is modeled using disjunctions, boolean variables and logical propositions. The main continuous decisions are: fan diameter, bundle width, tube length, pressure drops and velocities in both sides of the ACHE, heat transfer area, fan power consumption. Then, the resulting generalized disjunctive programming model is reformulated as a mixed integer non-linear programming, implemented in GAMS (general algebraic modeling system) and solved using a branch-and-bound method. The proposed model was successfully verified by comparing the obtained output results with different designs taken from the literature. Then, the model is solved to obtain the optimal designs corresponding to the following optimization criteria: a) minimization the total annual cost which includes investment (heat transfer area) and operating cost (fan power consumption), b) minimization the heat transfer area and c) minimization the fan power consumption. Obtained optimal and sub-optimal designs are compared in detail.

Experimental study on the evaporative cooling of an air-cooled condenser with humidifying air

Using six different materials to construct a water curtain, this study aims to determine the most effective spray cooling of an air cooled heat exchanger under wet conditions. The experiments were carried out at a mass flow rate of 0.005–0.01 kg/s (spraying water), an airspeed of 0.6–2.4 m/s and a run time of 0–72 h for the material degradation tests. The experimental results indicate that the cooling efficiency, the heat rejection, and the sprinkling density increase as the amount of spraying water increases, but, the air-flow of the condenser is reduced at the same time. In addition, the cooling efficiency of the pads decreases with an increase of the inlet air velocity. In terms of experimental range, the natural wood pulp fiberscan can reach 42.7–66 % for cooling efficiency and 17.17–24.48 % for increases of heat rejection. This means that the natural wood pulp fiberscan pad most effectively enhances cooling performance, followed in terms of cooling effectiveness by the special non-woven rayon pad, the woollen blanket, biochemistry cotton and kapok, non-woven cloth of rayon cotton and kapok, and white cotton pad, respectively. However, the natural wood pulp fiberscan and special non-woven rayon display a relatively greater degradation of the cooling efficiency than the other test pads used in the material degradation tests.

Parametric System Identification of Thermoelectric Cooler for Single Photon Avalanche Diode Application

The purpose of this study is to model the Thermoelectric Coolers (TEC) by means of computational intelligence system identification. Thermoelectric coolers are widely used in cooling, maintaining and stabilizing the temperature of the Single Photon Avalanche Diode (SPAD). SPAD is a temperature sensitive optoelectronic device, where even a slight variation in temperature can cause unstable performance in quantum efficiency, responsibility and dark counts. However, it is not a simple task to derive a mathematical model for TEC since it varies with the operating condition. In this study, Particle Swarm Optimization (PSO) was used to identify the mathematical model of the multistage TEC (1639733 from Element 14), which encapsulates dynamics of the SPAD, heat sink and components of the cooling heat exchanger. The model was validated by correlation tests, percentage accuracy and also by comparing its time and frequency responses against that of the TEC. It was found that the obtained model has a good representation of the actual system.

Experimental study on the flow and heat transfer characteristics of thermoacoustic core

In this study, the interaction between thermal convection and acoustic oscillation with different driving powers was investigated. The temperature and velocity distributions of thermoacoustic core between the hot and cooling heat exchangers were measured by Thermal Infrared Imager and Particle Image Velocimetry (PIV) at 205Hz, which is the resonance frequency of this thermoacoustic engine. The results indicate that acoustic oscillation has a significant effect on the thermal convection and the heat transfer is enhanced with the perturbation of acoustic streaming.

Direct fluorination of carbon monoxide in microreactors

Many attempts to obtain a clean stream of COF2 have been carried out in the past by means of the direct fluorination of carbon monoxide with elemental fluorine or by electrochemical fluorination. The reaction is highly exothermic, therefore difficult to control. It can easily develop into a thermal runaway with a poor selectivity. We have successfully circumvented these critical issues by using a stainless steel parallel channel microreactor (surface/volume ratio≈1×104m−1, residence time τ≈0.1s) for the direct fluorination of carbon monoxide. Its performance in terms of operability and selectivity is compared to that of a standard reactor assembly, namely a fluorine burner reactor coupled with a water cooled heat exchanger. While the microreactor assembly succeeded to control the exothermic reaction, in the same experimental conditions the standard assembly reactor underwent serious corrosion issues that lead to nozzle meltdown lack of selectivity and consequent plant shutdowns.

De-nickelification of 70/30 Cupronickel Tubing in a Cooling Heat Exchanger

A cupronickel heat exchanger failed after 10 years of service. The cooling heat exchanger was in service in a marine environment, with water flowing along shellside and natural gas along tubeside. Many tubes showed leakages during a regular maintenance test. A comprehensive failure analysis of the heat exchanger revealed the de-nickelification process on the external side of the damaged tubes (shellside). The de-nickelification originated from a large deposit of sea water scale, over tube lengths, which completely covered the area just outside the internal portion of the tubesheet, and occurred because of a failure of the regular cleaning operation. Stagnant water and possible hot spot formations on the tubes probably caused the phenomenon.

The Potential of Earth-air Heat Exchangers for Low Energy Cooling of Buildings in South Algeria

A one-dimensional steady numerical model is proposed to estimate the performance of earth-to-air heat exchangers, installed at different depth, used for building cooling/heating. Two parameters are considered to evaluate the performance of the system (Reynolds number and the form factor). With appropriate simplifications; Numerical simulation treatment is proposed to predict the temperature fields of the fluids in the pipe and the soil in the proximity of the buried pipe, taking into account meteorological data of south Algeria. Moreover, the agreement with some experimental data available in the literature is very satisfactory.

Prediction of the Heat Transfer in an Air Cooler Equipped with Classic Twisted Tape Inserts using Artificial Neural Network (ANN)

The present study is conducted in order to demonstrate the capability of the artificial neural network (ANN) in predicting the heat transfer in an air cooled heat exchanger equipped with classic twisted tape inserts. The effects of the twist ratio of classic inserts (Y) and Reynolds number (Re) variation on average heat transfer in the air cooler are considered via this prediction. The training data for optimizing the ANN structure is based on available experimental data. The Levenberg-Marquardt back propagation algorithm is used for ANN training. The proposed ANN is developed using MATLAB functions. For the best ANN structure obtained in this investigation, the mean relative errors of 0.457% and 0.478% were reached for the training and test data respectively. The results show that predicted values are very close to experimental values. Index Terms—Air cooled heat exchanger; classic twisted tape inserts; twist ratio; modeling; artificial neural network (ANN)

자연에너지를 이용한 생활공간 냉난방용 열펌프의 성능향상을 위한 과냉 촉진 신개념 열교환기(HESC) 개발

자연에너지를 이용한 생활공간 냉난방용 열펌프의 성능향상을 위한 과냉 촉진 신개념 열교환기(HESC) 개발

Optimization of heat transfer in an air cooler equipped with classic twisted tape inserts using imperialist competitive algorithm

In this paper a novel optimization algorithm based on Imperialist Competitive Algorithm (ICA) is used to optimize the heat transfer in an air cooled heat exchanger equipped with the classic twisted tape inserts. This algorithm has some advantages such as simplicity, accuracy, and time saving. Experiments included the twist ratio ranging from 1.76 to 3.53. Also, the Reynolds number varied from 4021 to 16,118. After data reduction, the regression equation of average Nusselt number was obtained as a function of Reynolds number and the twist ratio. Then the cost function was optimized by the use of ICA. One can be sure that the Nusselt number will be optimized due to the optimization of the cost function. Computational results indicate that the proposed optimization algorithm is quite effective and powerful in optimizing the cost function. According to the results, in order to obtain maximum heat transfer, the twist ratio must be at the lowest level.

Vacuum Paddle Fast Pyrolysis Reactor Design and Internal Heat Transfer Investigation

Fast pyrolysis is cracking process in which macromolecule of biomass is broken into small molecular under moderate temperature and at high heating speed. Bio-oil produced by the process can be used as potential alternatives of diesel oil and other chemicals. By investigate different kinds of reactor, a new type reactor called vacuum paddle fast pryoysis reactor is developed with low manufacture cost and operating fee and more stable performance. Two stage condensing system composed of 1st quench stage and 2nd cooling heat exchanger is designed, which is proven effective in avoiding secondary cracking of biomass oil and eliminating block of equipment by tar. At same time, a model describing heat transfer in new reactor is established and solved by unsteady heat conduction equation, which give conclusion on minimum agitating speed and therefore, provide basic theoretical foundation. Keywords: fast pyrolysis, vacuum paddle reactor, condenser, heat transfer

Fuzzy logic to predict the heat transfer in an air cooler equipped with different tube inserts

This paper highlights the application of fuzzy logic to predict the heat transfer in an air cooled heat exchanger equipped with three types of tube inserts including; butterfly, classic and jagged twisted tape. In the study which was carried out in the range of Reynolds number, the maximum heat transfer was obtained by the butterfly insert with an inclined angle of 90°. The results have also revealed that the heat transfer rates obtained by employing the classic and jagged inserts, reduced by increasing twist ratio. Moreover, it has been also shown that, fuzzy logic is a powerful technique used for predicting the heat transfer due to its low error rate. The average error of fuzzy technique as compared with experimental data was found to be 0.68% for this study.

Test of a 10 kA HTS Current Lead for ITER

The ITER Organization (IO) and the Institute of Plasma Physics at the Chinese Academy of Sciences (ASIPP) are jointly developing the design of the 10 kA Current Leads (CL) using High Temperature Superconductors (HTS) for the Correction Coil (CC) Magnet System of the International Thermonuclear Experimental Reactor, ITER. The proposed design combines a conventional helium cooled heat exchanger operating between 65 K and 300 K with a HTS module covering the low temperature end using Bi-2223 tapes. The details of the design and test results obtained on a first prototype lead will be discussed in this paper.

Experimental Analysis of the Effects of Particulate Fouling on Heat Exchanger Heat Transfer and Air-Side Pressure Drop for a Hybrid Dry Cooler

It is well known that significant fouling by particulate matter can have a deleterious effect on the performance of enhanced surface heat exchangers, and the same is true for hybrid heat exchangers. Hybrid heat exchangers are heat exchangers that are typically run in dry mode to reject heat. When the ambient conditions require more heat rejection than can be provided by sensible heat transfer, a water pump is turned on and water flows over the fins, and the evaporation of water provides a further cooling effect. Fouling in dry-mode operation is physically similar to that of air-cooled heat exchangers, but in evaporative mode the flow of the water over the coil eliminates the impact of fouling. A hybrid dry cooler heat exchanger of 60 cm × 60 cm frontal area has been installed in a well-instrumented wind tunnel to measure the heat exchanger's performance. Hot water flows through the coil to provide the load, and air flows over the coil to provide cooling. During evaporative mode operation another stream of water flows over the outside face of the coil, adhering mainly to the louvered fins. The louvered fins are specially designed for optimized water flow during wetting mode. The fins are made of aluminum, the tubes are copper, and protection against corrosion is realized by a special E-coating. This coil has been tested clean and fouled with ASHRAE standard dust, for both dry and wet operation. Results are presented for the air-side pressure drop and overall heat transfer conductance of the coil under all conditions for which 50% increases in air-side pressure drop are found under heavy fouling. The influence of fouling on heat transfer is small. Also, using the wetting water to wash the fouling off the coil is investigated and is found to be of some limited utility.

Effect of Fatty Acid Composition of Monoglycerides and Shear on the Polymorph Behavior in Water‐in‐Palm Oil‐Based Blend

AbstractEffect of the fatty acid composition of monoglycerides and shear on the polymorphic behavior in a water‐in‐oil (W/O) emulsion semi‐solid fats blend was investigated. The bulk fat blend and the W/O emulsion fat blend with added either unsaturated or saturated monoglycerides were prepared using a rapid cooling heat exchanger, and the polymorphic transitions from β′ to β‐form during storage were compared by X‐ray diffraction. The peak intensity of the β‐polymorph of the samples with added saturated monoglycerides was stronger than that of unsaturated monoglycerides, and the peak intensity of the β‐polymorph of the W/O fat blend emulsions was stronger than that of the bulk fat blends. The polymorphic transition to the β‐form during storage of the W/O emulsion fat blend was promoted by the applied shear. In contrast, that of the bulk fat blend was retarded by shear. These results suggested that fatty acids, which combined to monoglycerides on the surface of water droplets, influenced the polymorph transformation of the fat crystal network in a continuous semi‐solid fat phase because of the acyl–acyl interactions between the fatty acid residues of the monoglycerides and triacylglycerols in the fat crystal network.