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Increasing the hydraulic and thermal efficiency of transport heat exchangers

Name
Igor
Surname
Popov
Scientific organization
Kazan National Research Technical University n.a.A.N.Tupolev - KAI
Academic degree
Doctor of Science (Technical)
Position
Professor
Scientific discipline
Machinery & Energy
Topic
Increasing the hydraulic and thermal efficiency of transport heat exchangers
Abstract
We present a review on heat transfer equipment of modern heavy vehicles. Heat exchanger characteristics can be improved through the use of heat transfer insifiers - vortex generators, swirling devices, microsctructurized surfaces. We show efficiency of heat transfer enhancement methods on the basis of numerical and experimental studies. We present recommendations on their use. We show their influence on the performance of the engines on the example of EGR cooler.
Keywords
Heat transfer, hydraulic resistance, intensification, heat exchangers
Summary

Block 1 - Numerical studies:

1.1. We proposed and substantiated the concept of composite grids constructed by intersecting multiscale structured mesh topology with a simple substitution of unstructured overlay inserts zones. We have developed a generator of 2-2.5 D composite meshes.

1.2. We spent improving the accuracy and computational efficiency is developing a package of hydrodynamic and thermal profile of VP2/3 and sigma-Flow through the introduction and adaptation Demidov library for algebraic accelerator convergence of the iterative process.

1.3. We performed verification modified 2003 Rodi-Leshtsiner-Isaev model shear stress transfer in compared with the forecasts on models of different levels and the experimental data, in particular obtained by the project at the Institute of Mechanics, Moscow State University.

Block 2 - Heat transfer enhancement - numerical and experimental studies:

2.1. We have proposed and numerically substantiated the new form of the surface vortex generator - elongated oval dimple, which is thermal and thermal-hydraulic efficiency significantly superior to traditional spherical and cylindrical wells at an intensification of turbulent heat transfer in a narrow channel. We studied the properties of an elongated oval dimple in the wall of the narrow channel. We found a tendency to increase the maximum in modulus of the transverse flow velocity in a channel with oval dimple elongating fixed spot area and the depth values ​​of the order to the weight average speed in the channel. With the broadening of the oval dimple we found a tendency to laminar vortex flow in the channel. Size separation zone in the upper wells sharply reduced with a decrease in the width of the oval dimple and virtually the entire hole gets filled with swirling flow.

2.2. Based on the results of experimental research and analysis of the literature on the flow resistance and heat transfer medium pipes and channels with the systems of spherical projections:
- We have identified the mechanisms of intensification of heat transfer and the border of the laminar-turbulent transition;

- We found that the intensification of heat transfer in these pipes is up to 1.89 in the range of small numbers Re = 200-2200 with an increase in the hydraulic resistance to 1.97. In the transition range of Reynolds numbers Re = 800-2100 intensification of heat transfer in these pipes is up to 6.98 with an increase in the hydraulic resistance to 6.82 times. When Reynolds number Re = 5000-100000 intensification of heat transfer in these pipes is up to 2.89 with an increase in the hydraulic resistance to 6.7;

- We have identified the impact of the major operating and geometrical parameters in the coefficient of hydraulic resistance and heat transfer coefficient. We got generalizing dependences for calculation of hydraulic resistance and heat transfer for turbulent flow regime.

2.3. On the basis of the pilot study, we have formed a data bank on the coefficients of hydraulic resistance and heat transfer medium flat channels with one-sided arrangement of cylindrical dimples. On the basis of an integrated experimental and numerical studies, we have developed guidelines for the calculation of hydraulic resistance and heat-transfer channels with cylindrical dimples. We have established the effect of regime parameters of the flow and design parameters intensifiers on hydraulic resistance and heat transfer channels with cylindrical dimples. We got generalizing dependences for calculation of hydraulic resistance coefficients and heat transfer medium, describing the experimental data in the laminar and turbulent regimes with a tolerance of ± 10% at a confidence level of 0.95. We performed a numerical study of flow and heat transfer in channels with cylindrical dimples with package VP2/3. We showed a satisfactory agreement on the thermal-hydraulic efficiency of the results of numerical and experimental studies. We have shown that patterns of behavior of thermal and hydraulic performance as a whole do not differ from those of channel characteristics and bears the spherical dimples.

2.4. We continued the study of heat transfer and hydrodynamics in the flow of spherical dimples. On the basis of the restructuring jet-wave structure with increasing depth of the spherical dimples in the wall of a narrow plane-parallel channel with a fully developed turbulent flow of an incompressible fluid is proposed map mode it separated flow for a fixed Reynolds number 40000. Special attention was paid to the intensification of mono tornado-like swirling flow in the dimple, which is formed when transition from symmetric to asymmetric flow.

2.5. We have received the influence of dimensionless geometrical and operational parameters on the hydraulic resistance of bundles with different layout on the surface of the spherical dimples.

2.6. We have singled out the cork, wave, ring, dispersed and threadlike flow regimes with visual study of the structure of air-water flow in the tubes with inserted tape. Visualization of the flow of boiling freon confirmed the existence of threadlike streams on the tape and heat conditions. We have found that a discrete placing on the tape edges at an angle to the axis of the belt shifts the belt to the liquid surface of the heat exchange tube, which favorably affects the characteristics of the boiling process.

We experimentally investigated the heat transfer and hydraulic resistance of tubes with a variety of twisted tapes at boiling Freon. On the basis of experimental studies found that when calculating the coefficient of heat transfer in channels with embedded smooth and ribbed twisted tapes with forced convection R134a can be used Manglik-Bergles relation and Giniyatullins relation obtained for water. We studied the effect of regime parameters on heat transfer during boiling of refrigerant R134a in channels with twisted tape. We noted that a greater impact on the change of heat transfer provides the heat load delivered to the work site. We found no effect of the Reynolds number in the range of 31000 ÷ 83000. The increase in heat transfer coefficient occurs with a decrease in the relative step twist, due to the growing influence of mass forces. Intensification of heat transfer in channels with twisted tape relatively straight channel without inserts on average for y = 3 to 1.61; y = 4 to 1.51; 6 and y = 1.42. We got a generalization relationship to calculate the heat loss at boiling refrigerant R134a in channels with embedded smooth twisted tapes.

Block 3 - Studies of heat exchangers:

3.1. We conducted tests of laboratory samples of shell and tube heat exchangers with surface heat transfer intensifiers in the form of spherical and annular projections for various combinations of pairs of working fluids in a wide range of regime parameters for fixed overall weight and size characteristics:

- We got an increase in power of heat exchangers with intensifiers heat in the form of spherical or annular projections at a turbulent flow regime  (Re = 4000-20000) in the tubes to 1.25-1.37 times during the growth of the hydraulic resistance in the heat exchange system of tubes up to 1.1 -1.6 times;

- We found an increase of heat power of heat exchangers with intensifiers in the form of spherical and annular projections in the transition Reynolds number (Re = 1000-4000) to 1,45-2,85 times during the growth of the hydraulic resistance in the heat exchange system of tubes up to 2.5 times;

- We found an increase of heat power of heat exchangers with intensifiers in the form of spherical or annular projections for a range of numbers Reynolds Re = 1200-3300 to 2.3-3 times in the flow of viscous fluids in tubes during the growth of the hydraulic resistance in the heat exchange tube system to 2,1-3,6 times.

3.2. The results are used to create a heat exchanger with heat power 65 kW and 26 kW for the cooling system EGR of gas engine KamAZ.

3.3. We have identified the impact of recirculation gases on emissions of harmful substances to exhaust gases and relative cost-effectiveness of the diesel engine fuel. The use of EGR system to reduce NOx emissions allowed by 28%.

3.4. We have proposed and numerically substantiated technical solution of significantly (1.5-time) increasing of  the thermal efficiency of the condenser at the  laminar heat transfer enhancement by elongated dimples.

Block 4 - Study of systems including heat exchangers and heat transfer processes:

4.1. On the basis of numerical simulations of air flow distribution inside the vehicle turbocharger, we analyzed the velocity and pressure distribution pattern in unsteady and steady air flow in the flow of the compressor. Based on these results we carried out  impeller design optimization, the flow of the compressor, the cochlea. Due to this increased strength and stability of the dies

4.2. We have created a functional and mathematical models to calculate the temperature regimes and thermal processes occurring in the cooling elements and parts of piston engines, in which we have carried out numerical studies in the engine warming up. We have identified rational speed of water pump in the engine cooling system, allow you to reduce the engine warm-up and to provide its high technical and economic indicators. We proposed schematic and constructive solution of high-performance adaptive cooling piston diesel engine with controllable electrical drives the water pump. We have identified the optimal characteristics of the impeller of water pump. We have designed and manufactured high-efficiency impeller provide increased pressure by 30%, productivity by 15% and an efficiency of 20% at rated speed of the engine at speed of 3500 1/min.

4.3. To create a functional and mathematical models to calculate the temperature regimes and thermal processes occurring in the cooling system and the details of piston aircraft engines, which carried out numerical studies in the engine warm-up mode. The rational speed water pump in the engine cooling system, allow you to reduce the engine warm-up and to provide its high technical and economic indicators. Proposed schematic and design solution highly adaptive system cooling piston aircraft V-type diesel engine with regulated electric drive water pump, ensuring optimum thermal state of the internal combustion engine corresponding to the highest technical and economic, environmental and resource engine performance. The optimal characteristics of the impeller of water pump, designed and manufactured high-efficiency impeller provide increased pressure by 30%, supplying 15% and increase efficiency by 20% in nominal engine operation at 3500 1 / min.

4.4. We numerically investigated the heavy vehicle cabin ventilation and heating system. We conducted a study of heating and air conditioning control system. We upgraded elements of the cabin ventilation and heating system depending on the operating mode (shutter opening angle) by calculation results. We performed tests of the new system of ventilation and heating systems.