Water-cooled Heat Exchanger Research Articles

Drying performance analysis of a condensing tumbler clothes dryer with a unique water cooled heat exchanger

The experiments are carried out to study the drying performance of a condensing tumbler clothes dryer with a unique water cooled plate-fin heat exchanger under different working conditions. Performance parameters such as Nu, heat transfer coefficient, relative humidity, moisture content and MER are used to indicate the hygrothermal performance of the heat exchanger and drying performance of a condensing clothes dryer. The results show that as the airflow velocity increases, the relative humidity at the air side outlet of the heat exchanger and the final moisture content have a significant decline. The effects of cooling water flow rate on the final moisture content and the relative humidity at the air side outlet of the heat exchanger are not obvious, but as increase the cooling water flow rate, the MER decreases from 1.283 to 1.246, decreased by 3%, so the drying performance of the dryer is improved.

A novel shell-tube water-cooled heat exchanger for high-capacity pulse-tube coolers

Large-capacity pulse-tube coolers are considered promising candidates for applications in high-temperature superconductivity technology, small gas liquefiers, and cryogenic storage tanks. This paper introduces a novel shell-tube heat exchanger particularly designed for such a cooler. In one heat-transfer subunit of this configuration, several small-diameter copper tubes are welded inside a large-diameter tube. This heat exchanger is characterized by small hydraulic diameter, high porosity and uniform gas temperature distribution. To verify its performance, a numerical simulation was first carried out to compare the temperature distributions of the shell-tube and plated-fin configurations. Experiments were then conducted to investigate their cooling performance. According to the experimental results, the shell-tube heat exchanger achieved better heat-transfer performance, especially with large input power. The gas temperature at the inlet of the heat exchanger and the temperature gradient in the regenerator were significantly decreased in the novel shell-tube design, which further demonstrated its better performance.

Study of a thermoelectric generator based on a catalytic premixed meso-scale combustor

The recent advances in miniaturized mechanical devices open exciting new opportunities for combustion, especially in the field of micro power generation, allowing the development of power-supply devices with high specific energy. The development of a device based on a catalytic combustor coupled with thermoelectric modules is particularly appealing for combustion stability and safety. Furthermore, when implemented in micro/meso scale devices, catalytic combustion allows full utilization of hydrocarbon fuel’s high energy densities, but at notably lower operating temperatures than those typical of traditional combustion. These conditions are more suitable for coupling with conventional thermoelectric modules since they prevent the modules’ degradation.In this work a novel catalytic meso-scale combustor fueled with propane/air mixture has been coupled with two conventional thermoelectric modules. The wafer-like combustor is filled with commercially available catalytic pellets of alumina with Platinum (1% weight). Temperature measurements, in terms of point values and 2D distribution across the combustor surfaces, were carried out in different operating conditions. Exhaust gases concentration measurements and pellet aging investigation were performed to determine the combustor efficiency and stability. Starting from these results the combustor has been coupled to bismuth telluride-based thermoelectric modules using a water cooled heat exchanger at the cold side. The system obtained produces 9.86W of electrical power reaching an overall efficiency up to 2.85%: these results represent an improvement in portable-scale electrical power production from hydrocarbon fuels state-of-art. Moreover, the voltage and current characteristics allow using such generator for small portable devices power supplying.

Comparison of measurements and computations of isothermal flow velocity inside HyperVapotrons

HyperVapotrons are two-phase water-cooled heat exchangers able to receive high heat fluxes (HHF) by employing a cyclic phenomenon called the “Vapotron Effect”. HyperVapotrons have been used routinely in HHF nuclear fusion applications. A detailed experimental investigation on the effect giving rise to the ability to sustain steady state heat fluxes in excess of 10MW/m2 has not yet been possible and hence the phenomenon is not yet well understood. The coolant flow structures that promote the effect have been a major point of interest, and many investigations based on computational fluid dynamic (CFD) simulations have been performed in the past. The understanding of the physics of the coolant flow inside the device may hold the key to further optimisation of engineering designs. However, past computational investigations have not been experimentally evaluated. Isothermal flow velocity distribution measurements of the fluid flow in HyperVapotron optical models with high spatial resolution are performed in this paper. The same measurements are subsequently calculated via commercial CFD software. The isothermal CFD calculation is compared to the experimental velocity measurements to deduce the accuracy of the CFD investigations carried out. This unique comparison between computational and experimental results in HyperVapotrons will direct future efforts in analysing similar devices.

A114 JEST型LHPの冷却性能に関する研究(OS-7: 電子機器・デバイスの熱工学的課題と熱流動現象(1))

In recent years, the heat flux of electronic devices has significantly increased due to higher output and downsizing. A JEST type Loop Heat Pipe with a water-cooled heat exchanger has been developed. In the present study, the total thermal resistance was divided to each part of the equipment, and the effect of each thermal resistance on the cooling performance was investigated. As a result, the effect of vapor line inner diameter on the total thermal resistance was clarified. And it was also revealed that the evaporator thermal resistance was 65% of the total thermal resistance. Therefore, an approach to decrease the evaporator thermal resistance is effective for improving the cooling performance.

Fabrication of Wire Mesh Heat Exchangers for Waste Heat Recovery Using Wire-Arc Spraying

Waste heat can be recovered from hot combustion gases using water-cooled heat exchangers. Adding fins to the external surfaces of the water pipes inserted into the hot gases increases their surface area and enhances heat transfer, increasing the efficiency of heat recovery. A method of increasing the heat transfer surface area has been developed using a twin wire-arc thermal spray system to generate a dense, high-strength coating that bonds wire mesh to the outside surfaces of stainless steel pipes through which water passes. At the optimum spray distance of 150 mm, the oxide content, coating porosity, and the adhesion strength of the coating were measured to be 7%, 2%, and 24 MPa, respectively. Experiments were done in which heat exchangers were placed inside a high-temperature oven with temperature varying from 300 to 900 °C. Several different heat exchanger designs were tested to estimate the total heat transfer in each case. The efficiency of heat transfer was found to depend strongly on the quality of the bond between the wire meshes and pipes and the size of openings in the wire mesh.

Potential for improvement in high heat flux HyperVapotron element performance using nanofluids

HyperVapotron (HV) elements have been used extensively as high heat flux beam stopping components in nuclear fusion research facilities. These water-cooled heat exchangers use a boiling heat transfer mechanism and so are inherently limited by their critical heat flux (CHF). The use of a nanofluid as the coolant, instead of water, promises to enhance the heat transfer performance of the HV and increase the CHF by a factor of 2 or 3, which would lead to a step-change improvement in the power handling capability. This paper reports on computational and experimental analyses which have indicated mechanisms for the enhanced thermal performance of nanofluids. A molecular dynamics simulation code has been developed which has identified heat transfer augmentation mechanisms that depart from classical thermodynamics associated with the presence of nanoparticles. In addition, an experiment has been conducted which uses particle image velocimetry to measure the flow field in a full-scale HV. Past studies have yielded qualitative experimental results, but the measurements reported here provide quantitative data to aid the understanding of the initial flow field inside the HV (i.e., before a heat flux is applied). Further, the experiment is conducted using both water and Al2O3–water nanofluid as the flow medium. Thus, these velocity measurements offer a first indication for potentially enhanced heat transfer in HV devices when nanofluids are used as the coolant. The improved understanding of the HV flow regime and the cooling advantage of nanofluids could assist the design of advanced high heat flux components for future fusion machines.

EGR 가스 폐열회수에 의한 디젤엔진의 연비에 미치는 ATF 워밍업의 영향

Cold start driving cycles exhibit an increases in friction losses due to the low temperatures of metal components and media compared to the normal operating engine conditions. These friction losses are adversely affected to fuel economy. Therefore, in recent years, various techniques for the improvement of fuel economy at cold start driving cycles have been introduced. The main techniques are the upward control of coolant temperature and the fast warm-up techniques. In particular, the fast warm-up techniques are implemented with the coolant flow-controlled water pump and the WHRS (waste heat recovery system). This paper deals with an effect of fast ATF (automatic transmission fluid) warm-up on fuel economy using a recovery system of EGR gas waste heat in a diesel engine. On a conventional diesel engine, two ATF coolers have been connected in series, i.e., an air-cooled ATF cooler is placed in front of the condenser of air conditioning system and a water-cooled one is embedded into the radiator header. However, the new system consists of only a water-cooled heat exchanger that has been changed into the integrated structure with an EGR cooler to have the engine coolant directly from the EGR cooler. The ATF cooler becomes the ATF warmer and cooler, i.e., it plays a role of an ATF warmer if the temperature of ATF is lower than that of coolant, and plays a role of an ATF cooler otherwise. Chassis dynamometer experiments demonstrated the fuel economy improvement of over 2.5% with rapid increase in the ATF temperature.

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.

Kilowatt CW Cryogenic 940-nm Diode Lasers

Cryogenically cooled high-power Yb:YAG disk lasers are ideally optically pumped with cryogenically cooled 940-nm diode lasers, but commercially available diode lasers are not optimized for 940-nm cryogenic emission. Special epitaxial designs were used to fabricate diode laser arrays which were mounted on liquid nitrogen impingement heat exchangers. The improved cryogenic thermal characteristics resulted in reduced laser threshold currents and CW operating powers > 1 kW for diode laser arrays with a 1 × 5 cm footprint. The industrial availability of liquid nitrogen makes this mode of operation an excellent candidate for industrial lasers, eliminating large, noisy, expensive and inefficient water-cooled heat exchangers.

Effects of ash fouling on heat transfer during combustion of cattle biomass in a small-scale boiler burner facility under unsteady transition conditions

Combustion of cattle biomass (CB) as a supplementary fuel has been proposed for reducing emissions of NOx, Hg, SO2, and nonrenewable CO2 in large coal-fired power plants; however, its high ash content resulted in fouling and slagging problems when the CB was co-fired with coals during small- and pilot-scale tests. Ash depositions during combustion of the CB as a reburn fuel were investigated using a 30 kWt (100 000 Btu h−1) boiler burner facility with water-cooled heat exchangers (HEXs) under unsteady transition conditions and short-term operations. Two parameters were used to characterize the effects of the ash deposition: (1) Overall heat transfer coefficient (U) and (2) Burnt fraction (BF). A methodology was presented and empirically demonstrated for the effects of ash deposition on heat transfer under unsteady transition conditions. Experiments involving ash deposition during reburning the CB with coals were compared with experiments involving only ash-less natural gas. It was found that the growth of the ash layer during reburning the CB and coals lowered the heat transfer rate to water in the HEXs. In low-temperature regions, the thin layer of the ash deposition promoted radiation effects, while the thick layer of the ash deposition promoted the thermal resistance of the ash layer. A chemical analysis of the heavy ash indicated that the BF increased when a larger fraction of the CB was used in the reburn fuels, indicating better performance compared with coal combustion alone. However, the results of ash fusion temperature indicated the ash deposited during combustion of the CB and coals was more difficult to remove than the ash deposited during coal combustion alone. Copyright © 2010 John Wiley & Sons, Ltd.

Titanium and super stainless steel welded tubing solutions for sea water cooled heat exchangers

Owing to its outstanding resistance to general and localised corrosion, titanium has become established as the preferred material for sea water cooled heat exchanger tubing, be it for power plant surface condensers or heat exchangers in thermal desalination plant or in the chemical and petrochemical processing industry. Periodic increases in the price of titanium have generated interest in cost effective alternatives using so called 'super alloys': highly alloyed stainless steels showing improved corrosion resistance over conventional compositions. Taking sea water cooled power plant condenser tubes as an example, the mechanical and corrosion/erosion properties of titanium are reviewed together with those of three frequently considered alternatives, UNS S31254 super austenitic alloy, and UNS S44735 and S44660 super ferritic alloys. The results of ASTM G48 pitting and crevice corrosion tests and of electrochemical studies in model sea waters are reported. The effect of heat treatment on the corrosion resistance of S44735 has also been examined. It is concluded that while titanium has a superior balance of corrosion and other properties, super alloys can provide excellent performance in service provided certain precautions are observed.

Condensation of pure and near-azeotropic refrigerants in microfin tubes: A new computational procedure

Microfin tubes are widely used in air cooled and water cooled heat exchangers for heat pump and refrigeration applications during condensation or evaporation of refrigerants. In order to design heat exchangers and to optimize heat transfer surfaces, accurate procedures for computing pressure drops and heat transfer coefficients are necessary. This paper presents a new simple model for the prediction of the heat transfer coefficient to be applied to condensation in horizontal microfin tubes of halogenated and natural refrigerants, pure fluids or nearly azeotropic mixtures. The updated model accounts for refrigerant physical properties, two-phase flow patterns in microfin tubes and geometrical characteristics of the tubes. It is validated against a data bank of 3115 experimental heat transfer coefficients measured in different independent laboratories all over the world including diverse inside tube geometries and different condensing refrigerants among which R22, R134a, R123, R410A and CO 2.

Modeling and experimentation of a novel pressurized CHP system with water extraction

A novel cooling and power cycle is proposed, which combines a semi-closed cycle gas turbine called the high-pressure regenerative turbine engine (HPRTE) with a vapor absorption refrigeration system (VARS). This combined HPRTE/VARS cycle is capable of producing power, water and refrigeration effect for external loads. In a previous study, the combined cycle was modeled using zero-dimensional steady-state thermodynamics, with specified values of polytrophic efficiencies and pressure drops for the turbo-machinery and heat exchangers. In this study, a modified version of the combined HPRTE/VARS cycle is experimentally investigated for the demonstration of the combined cycle concept and for the model validation. This modified HPRTE has two water-cooled heat exchangers instead of the absorption refrigeration system. The model of the original combined HPRTE/VARS cycle was modified to simulate the performance of the modified HPRTE cycle. Temperatures, pressure, mass flow rates and other overall cycle parameters obtained from the computer model are compared with the corresponding experimental values of the modified cycle. The agreement between the values is found to be within acceptable limits. In addition, the uncertainty analysis of the experimental data is undertaken to find the uncertainty in the final output variables: thermal efficiency and non-dimensional water extraction parameter. Copyright © 2008 John Wiley & Sons, Ltd.

공기압축기의 인터쿨러 선정을 위한 열교환기의 형상별 성능해석

Intercooling and aftercooling are required in order to operate air compressor, these are conducted through air-cooled or water-cooled heat exchangers. This study aims to find more suitable type of heat exchanger as a water-cooled intercooler of air compressor. Comparative performance evaluation among fin-tube heat exchanger and shell-and-tube (S&T) heat exchanger having various tubes such as circular tube, spiral tube, and internally finned tube was conducted. Thermal-hydraulic performance of each heat exchanger type is evaluated in terms of temperature drop and pressure drop. The comparisons show that shell-and-tube heat exchangers may have similar and larger heat transfer capacity to the fin-tube heat exchanger if tube diameter is reduced and multiple pass is adopted. For these cases, however, compressed air pressure drop in shell-and-tube heat exchanger become much larger than that in fin-tube heat exchanger.

Too Hot for Comfort

Electronics have grown much hotter over the past decade, making cooling a top priority in data centers. APC, better known for backup power supplies, supplies cold air from rack-size towers mounted along each row. It then monitors server temperatures, adjusting each individual air conditioner tower to achieve optimal cooling. Such localized cooling is efficient, such that users can boost server rack power to 18 kW—nearly nine times the average found by Uptime. IBM believes even the largest, most sophisticated data center managers need help with cooling. Like APC, it encloses its racks with a roof, but unlike APC it uses a cold rather than hot center aisle and exhausts the heated air into the data center. IBM also removes heat with a water-cooled heat exchanger attached to the back of a rack. In addition, IBM provides power management software that enables IT managers to adjust power and heat output. This ensures that power managers can power down based on workload, or move workload to environments that are not effectively using the power and cooling capacity that they have.

Mode localization of a component cooling water heat exchanger

In a nuclear power plant, the tubes of a component cooling water heat exchanger are frequently affected by cold and hot fluid shock waves. Thus, tubes are often found to be worn out. This wear may alter the dynamics of the tubes and introduce mode localization in the heat exchanger. This paper examines mode localization in a component cooling water heat exchanger. A heat exchanger, consisting of periodic cooling tubes is used to simulate as a coupled periodic structure system. Each tube is coupled to the adjacent one through the water, and so the system is weakly coupled. The Galerkin method is employed herein to derive the mode localization equations off the mistuned system, with reference to the fluid effect. Numerical results reveal that the wear may introduce mode localization into a mistuned heat exchanger with fluid.

白味噌製造におけるアルコール添加方法について

A new manufacturing process for Sweet White Miso is proposed for keeping the residual alcohol concentration as high as possible. A ratio of 2% alcohol (based on the total weight) was added to Sweet White Miso by three kinds of spraying systems and two kinds of injecting systems. After processing the Sweet White Miso, the residual alcohol concentration and standard deviation were compared with those in conventional systems. The injecting system with the cooling apparatus using a water-cooled scraped-surface heat exchanger was found to have a maximum residual alcohol concentration of 1.78% and standard deviation of 0.02, which was effective for keeping alcohol content with a high concentration and stability.

Experimental measurement of radiative heat transfer in gas‐solid suspension flow system

AbstractAn experimental measurement of the radiative heat flux from a gas‐solid suspension to wall was made in a water cooled heat exchanger. The heat‐transfer test section was 5 cm ID and 90 cm long. Operating temperature ranged from 200 to 600°C and the gas velocity at the inlet of the test section varied from 6 to 11 m/s. The suspension densities covered a range from 3 to 35 kg/m3. Time‐averaged radiative heat flux was directly measured using a radiometer, which allowed to determine suspension emissivity using a measured suspension temperature. Radiative heat flux and suspension emissivity showed strong dependence on the suspension density. The effect of particle size on suspension emissivity was also studied by using two different sizes of particles. Experimentally determined suspension emissivities, which ranged from 0.3 to 0.85, agreed well with the predictable suspension emissivities based on an independent scattering theory. The contribution of radiation to total heat transfer was about 40–50% for the operating condition used in this study.

境膜かき取り式冷却法による白味噌の色調制御

境膜かき取り式冷却法による白味噌の色調制御