Paper Number ICEF

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1 Proceedings of ICEF00 ASME Internal Combustion Engine Division 00 Fall Technical Conference September 11-1, 00, Ottawa, Canada Paper Number ICEF ENHANCEMENT OF COOLANT SIDE HEAT TRANSFER IN WATER COOLED ENGINES BY USING FINNED CYLINDER HEADS Mohamed Y. E. Selim 1 Mech. Eng. Dept., Faculty of Engineering, UAE University, Al-Ain, UAE S.M. S. Elfeky Mechanical Power Engineering Department Faculty of Engineering at Mattaria Helwan University, Cairo - Egypt A. H. B. Helali Mechanical Power Engineering Department Faculty of Engineering at Mattaria Helwan University, Cairo - Egypt ABSTRACT An experimental investigation has been carried out for almost the first time to examine the heat transfer by forced convection and subcooled boiling from a finned water-cooled engine cylinder head using steady state technique. Cast iron and cast steel specimens with and without fins have been used in the present work. The effects of flow velocity, coolant bulk temperature, fin length, fin number and fin material have been examined. It has been found that the use of finned cylinder head surface greatly improves the forced convection heat transfer coefficient and subcooled boiling heat flux as the fin length and number influenced the heat transfer process. The cast iron specimen exhibited better heat transfer characteristics over the cast steel one. The effects of bulk flow velocity and temperature for flat and finned specimens have been evaluated for forced convection and subcooled boiling. A correlation has been developed to relate the Nusselt number with Reynolds number, Prandtl number, viscosity ratio and fin length ratio, for forced convection from the cast iron specimen, which read: Nu = 0.03 Re 0.97 Pr 0.33 µ r 0.1 (1+A) 0.3 KEYWORDS Engine, water-cooling, fins, heat transfer, forced convection, boiling INTRODUCTION It is urgently desired to increase the specific output of internal combustion engines. In diesel engine, this is done by pressure charging the engine, while in petrol engine the engine speed is increased. Such increase in the output consequently increases the heat flux in the combustion chamber components. Heat flux increase will result in an increase in the metal temperatures. If the cooling system design is not effective, metal cracks will occur due to high thermal stresses [1-]. Heat transfer in the combustion chamber components occurs either by means of forced convection or, at high heat flux, by sub-cooled boiling, in which case the bulk temperature of the coolant is below its boiling point, local boiling occurs in the boundary layers adjacent to the heated metal surface []. The heat flux varies substantially with location in the combustion chamber of the engine. Regions of the combustion chamber that are contacted by rapidly moving hot gases generally experience the highest fluxes [-]. This is particularly critical in regions where water cooling is limited, such as in the narrow bridge between valves, or around the exhaust valve seat [7-]. In the new trend of using highly rated water cooled spark ignition engines, or diesel engines, the heat flux is expected to be very high as well as the coolant side wall temperature. The optimum solution to this problem would be by constructing fins in the cylinder head cooling passages especially in the critical areas e.g. in the valves bridge, near the injector and the prechamber. Many attempts have been done to improve the heat transfer from the coolant side of the engine, e.g. by using aluminum finned surface [9], by using coolant additives [] or by using coolant ducts with T-shaped cross section [11]. Therefore, the objective of the present work is to investigate the possibility of utilizing fins (will act as 1 Corresponding Author: Tel. (9713) Office, Fax (9713) Office, Mohamed.Selim@uaeu.ac.ae 1 Copyright #### by ASME

2 supporting webs too) in the liquid cooled cylinder head cooling passages to increase the heat transfer surface area and hence reduces greatly the wall metal temperatures and enables the cylinder head to work under high heat flux or high metal temperature resulted from high power rating. The use of fins in the cooling passages of cylinder head also increases its mechanical strength and enables the use of thinner lower deck of cylinder head. The fins will transfer the mechanical stresses to the upper deck of the cylinder head and this would make the overall engine weight even less. In the present work a steady state technique has been used to examine the heat flux transferred through cast iron and cast steel finned specimens. Seven specimens have been used, one with flat surface (without fins) facing the coolant side, and the other six specimens have fins with different lengths, numbers, and materials. Steady state heat flux crossing the specimens has been measured and the coolant side metal temperature has been calculated. The effects of flow velocity, coolant bulk temperature, fin length, fin number and fin material have been studied in the present work. The complete matrix of experimental data has been used to develop a correlation relating the dimensionless groups concerned, e.g. Nusselt number, Reynolds number, Prandtl number, coolant relative viscosity and fin length. EXPERIMENTAL TEST RIG The test rig used in the present work is shown in Fig. 1. It mainly consists of a main water tank () equipped with a copper cooling coil () and a kw electric immersion heater () for water cooling and heating as well as for fine bulk temperature control. The electric motor-driven circulating pump () withdraws the water from the main tank where the flow rate was controlled via the valve (). A bypass valve (19) was provided as shown for accurate flow control. The flow then passes to a inch pipe leading the flow to an orifice plate flow meter (13); to measure the flow rates. The flow at exit from the orifice plate was led through inch piping to the test duct (17) which are of rectangular cross-section. To reduce the effect of the flow disturbances due to change of flow area from circular to rectangular, more than twenty hydraulic diameters of rectangular duct are provided before the test section for flow straightening purposes and thus provide a hydrodynamically fully-developed flow. The water pressure at the test section is measured by a burdon-type pressure gauge (), while the bulk temperatures of the inlet and exit from the test section are measured by insulated 0. mm diameter type K thermocouples (9). At the test section a copper heater bar is provided, at the tip of which the test specimen (1) is brazed. A powerful gas-burner (1) is used to heat up the specimen and vary the heat flux. The water leaving the test section returns back to the main water tank which is connected to an expansion tank (1) via ½ inch piping, which serves as a deaeration and filling-up vessel. In addition, the expansion tank was equipped with a 3kW immersion heater (3) for system pressurization if required. All pipes, test ducts and tanks are thermally lagged by a inch thick fiber-glass insulation to minimize heat losses. Test Section In order to study the effect of the fins of the liquid cooled cylinder head on heat transfer (as compared to nonfinned passages), rectangular duct was manufactured to accommodate the finned specimens with different fins length. Figure shows the test section details with one of the specimen mounted. The duct was manufactured giving aspect ratio (height of channel normal to the heating surface to the duct breadth ratio) of 0. (0x0 mm). Cast iron and cast steel specimens are cut from real engine cylinder heads with the dimensions shown in Fig. 3 and Table 1. Six cast iron specimens and one cast steel specimen have been designed and manufactured. The cast iron specimens with different fin heights and numbers were used to study the effect of fins height (0,, 0, 30 and 0 mm). One cast steel specimen was used (n=, L f =0 mm) for the purpose of comparing different materials of the cylinder head; see Table 1. The overall width of all specimens is the same as the duct breadth (0 mm). In order to estimate the heat flux, the temperature difference across the specimen has to be measured. Also, it was imperative to ensure uniform heat flux if meaningful data are to be obtained. Thus, two rows of 1. mm diameter square bottomed holes are drilled which stop at the center line of the specimen, see Fig. 3. The distance between the two rows is mm. In such holes, fiber glass insulated micro thermocouples (0. mm wire diameter) are installed and the wires are led outside the test section. The wires are then connected to a selector switch and a self-compensated digital thermometer, accurate to within 0.1 o C. High temperature Teflon coat is applied on the heater bar surface to prevent water leakage. The specimen is mounted flush with the inner bottom surface of the duct to avoid flow separation at the test section in the flat specimen case. In case of finned specimens, the fins base is mounted flush with the inner bottom surface of the duct. Care is paid to locate the top row of thermocouple holes at a distance of more than one hole diameter from the metal-cooling interface. An electrolytic analogous experiment [1] has revealed that this practice avoids heat flow pattern disturbance at the metal-coolant interface. During experimentation, all thermocouples in each row read merely the same temperature, indicating the uniformity of heat flux. The maximum difference in reading in each row at the highest heat flux applied did not exceed 1 o C. Thus, to evaluate the temperature difference used to calculate the heat flux, the average readings of the two thermocouple rows are taken. In order to evaluate the thermal conductivity data for the specimen at different temperatures, special test specimen was machined from the cylinder head blocks and used in a thermal conductivity apparatus. Two thermocouples of type K are installed before and after the test section to evaluate the bulk water temperature. The bulk water temperature,, is taken as the average of the two thermocouple readings. EXPERIMENTAL PROCEDURE The experiment is started by fitting the required specimen (with or without fins) in the duct. The test rig is flushed with hot water to remove any contaminants. Since all highly rated engines must run with distilled water as a coolant [], distilled water is used for experimentation after flushing. The circulating pump is started and the heaters ( and 3) in main water tank and the expansion tank, Fig. 1, are switched on. After the water reaches the saturation temperature, the rig is left running for one hour at such temperature since this was Copyright #### by ASME

3 found sufficient to degas the liquid [13]. The separated dissolved gasses escape from the deaeration tank. That was necessary, since dissolved gasses can separate at the heating surface in the form of gas bubbles; and additional convection, probably by thermo-capillarity effect can modify the heattransfer characteristics under forced convection conditions. At the same time the gas burner is used to run the specimen at a high heat flux up to surface boiling. The head differential across the orifice plate that results in a predetermined flow velocity in the duct was calculated and chosen from the orifice equation. The water bulk temperature,, is adjusted at a predetermined value using the electric heater () and cooling coil () in the main water tank, Fig. 1. The heat flux q is calculated from Fourier s equation of heat-conduction in metals viz.: q = k (T 1 T ) / x 1 Where T 1 and T are the average temperatures in the two thermocouple rows, x 1 is the distance between the thermocouple rows ( mm), see Fig. 3. k is the metal thermal conductivity obtained at the average temperature (T 1 +T )/. The metal coolant interface temperature, T w, is obtained by mathematical extrapolation of the temperature gradient line for the distance x. Thus, (T w ) is evaluated. The heat flux is varied in steps by the gas burner; and the above measurements are recorded when temperatures reach steady state. It ought to be stated that the heat flux is varied from very low values of about 0 kw/m to above 300 kw/m. The heat transfer coefficients, h, and Nusselt numbers may then be calculated. In this work all experimental data are collected at atmospheric pressure. In fact, it has long been known that system pressure affects heat-transfer particularly in nucleate boiling region. However, coolant pressure in the engine usually ranges from 1 to bar, and it was found [1-1] that in this pressure range, the effect on wall temperature is very small (less than 1. o C) The experiments have been carried out at the following conditions: a- Average flow velocity in the test section, upstream the fins, of 1, and. m/s b- Coolant bulk temperature of 0 o C, 70 o C and 90 o C c- Fin length of 0 (no fins),, 0, 30 and 0 mm which gives the aspect ratio of fins to duct height of 0, 0., 0., 0.7 and 1 (the duct has 0 mm height and 0 mm width) d- Fin number of and e- Specimen material of cast iron and cast steel The experimental error in measuring thermal conductivity, the distance between thermocouple rows, metal temperature difference, metal coolant interface temperature, and bulk liquid temperature, are as the following: 3%, 0.%, 1.31%,.37%, and 0.%, respectively. The error involved in determining T w -, heat flux, heat transfer coefficient, and flow velocity are.7%,.1%, 7.0%, and.3%, respectively. RESULTS AND DISCUSSION The experiments presented here examine the effect of using finned cast iron and cast steel water cooled cylinder head on the heat transfer under forced convection and subcooled boiling conditions. The experiments have been carried out under steady state conditions in the test rig described above. All experimental data are obtained at atmospheric pressure with the heat flux varied in steps from about 0 to 300 kw/m. The forced convection results are presented as heat transfer coefficient against the wall to bulk temperature difference, whereas the boiling results are presented as heat flux versus wall to saturation temperature difference, for different fins and flow conditions. However, the effects of flow velocity, bulk temperature and fin parameters have been discussed. The complete matrix of experimental data has been used to correlate Nusselt number with Reynolds number, Prandtl number, relative viscosity, and fin length. EFFECT OF FLOW VELOCITY Forced convection Figures -a and -b show the effect of upstream (before fins) flow velocity on the convective heat transfer coefficient for flat specimen (no fin) and for 0 mm height finned specimens respectively. The average flow velocity has been varied from 1 to. m/s while the flow bulk temperature was kept constant at 70 o C. It may be seen that the heat transfer coefficient increases generally with increasing the T w, at all flow velocities and for the fins and no-fins cases. This may be due the decrease in fluid viscosity near the duct wall (as T w increases). This increases both the viscosity ratio and the heat transfer coefficient. At a constant wall temperature, (T w ), of 0 o C, for fluid velocity of 1,, and. m/s, the heat transfer coefficient increases from 0.7 to 1. and 3.3 kw/m K respectively, for no fin specimen, while it increases from. to. and 7. kw/m K for finned specimen. The increase in convection heat transfer coefficient with flow velocity may be attributed to the highly turbulent flow associated with high velocities, which reduce the boundary layer thickness and improve the heat transfer. The increase in flow velocity can also improve the heat transfer by removing the accumulated corrosion contaminants on the surface. The increase in flow velocity from 1 to. m/s increased the heat transfer coefficient by about 0% for no-fins case, whereas it is increased by about 10% for finned case. It may emphasized here that although the effect of flow velocity is more profound in the case of no-fins than the finned case, however the heat transfer coefficient itself is much higher for finned case than for no-fins case. This means that when fins are used much less coolant flow velocities may be used which in turn can reduce the coolant pump size and power. Subcooled boiling The effect of flow velocity on the subcooled flow boiling curve for 70 o C is shown in Figs. -a and -b for no-fin and finned specimen respectively. It may be noticed that increasing the heat flux generally increases the wall superheat, (T w T sat ). For the same heat flux, increasing the flow velocity decreases the wall superheat (T w T sat ) which means the wall becomes cooler and less susceptible to crack. Similarly, for constant wall to saturation temperature (T w T sat ) of o C, as the flow velocity increases from 1 to. m/s, the heat flux increases by about 00% for no-fins case, and by about 10% for finned case. This may be postulated to the fact that increasing the flow velocity results in an increase in Reynolds 3 Copyright #### by ASME

4 number (Re). This increase in Re produces more turbulent flow and reduces the boundary sublayer, which improves the heat transfer coefficient and hence the heat flux as well. In the finned specimen case, a similar trend is also noticed but for the same wall temperature, the heat flux in the case of finned specimen is higher than that for the no fin specimen. This is due to the increase in flow velocity in the fins passage (multi-channel flow) as well as the surface area, which leads to an increase in heat flux. This increase in surface area of fins leads the heat flux to increase. The heat flux in flow boiling is composed of the boiling component superimposed on the forced convection component. Thus, the improvement in the heat flux in the forced convection region, due to the increase in flow velocity, will contribute to the boiling heat transfer. Therefore, for highly output engines with high heat flux and expected high wall temperature, a high flow velocities may be used in the critical areas of cylinder head (e.g. in the vicinity of inlet/exhaust valve bridge) unless finned cylinder heads are used then the flow velocities may be reduced. EFFECT OF COOLANT BULK TEMPERATURE Forced convection The effect of coolant bulk temperature on the convection heat transfer coefficient at average flow velocity of. m/s from the flat and finned specimens is illustrated in Figs -a and -b, respectively. It may be seen that increasing (T w ) results in an increase in the heat transfer coefficient for all bulk temperature and for both no-fin and finned specimens. At any value of (T w ) increasing the bulk temperature from 70 to 90 o C increases the heat transfer coefficient. This increase may be postulated to the variations in the thermophysical properties of the coolant with the bulk temperature. In addition, as the bulk temperature increases from 70 to 90 o C, the increase in Reynolds' number (due to reduction in bulk viscosity) dominates the reduction in Prandtl number and viscosity ratio. For the specimen with fin length of 0 mm, the heat transfer coefficient at any corresponding bulk temperature is more than double the value for the no-fin specimen. This indicates the major improvement in the heat transfer coefficient due to the use of finned surface in the forced convection region. Subcooled boiling Figures 7-a and 7-b depict the effect of coolant bulk temperature on the subcooled boiling curves at average flow velocity of. m/s for the flat and finned specimens, respectively. It may be seen that at the same heat flux applied to the specimen, increasing the coolant bulk temperature has resulted in an increase in the wall temperature (the curve is shifted to the right). Alternatively, although the heat transfer coefficient increases with increasing the bulk temperature the heat flux is decreased. This is so, because for the same wall temperature, as the bulk temperature increases, the reduction in the temperature difference between the wall and bulk temperature (driving force) overwhelms the slight increase in the heat transfer coefficient. However, the wall temperature would be much lower if the finned cylinder head geometry is used as might be noticed by comparing Fig. 7-a to Fig. 7-b. At the same heat flux of kw/m, using 0 mm fins causes the wall temperature to drop from 11 o C to 1 o C for the bulk temperature of 90 o C and the same trend is repeated at the other bulk temperature too. The increase in wall temperature seems unavoidable as the coolant temperature increases especially in the highly rated engines. Thus it is concluded that the higher bulk temperature in the engine will lead to lower heat flux for the flat specimen compared to that case of a finned cylinder head which would much reduce the wall temperature due to the increased surface area of the fins and increase in heat transfer coefficient. As indicated earlier, the heat flux for the finned specimen is greater than that for flat specimen. As a result any increase in the wall temperature due to the increase in coolant bulk temperature would be totally recovered by using the fins in cylinder head and thus increasing the heat transfer coefficient and surface area. EFFECT OF FIN LENGTH The effect of fin length of the cast iron specimens on the convective heat transfer coefficient and subcooled boiling heat flux is illustrated in Figs.-a and -b, respectively. The h versus (T w ) and q versus (T w T sat ) relationships in all cases show almost the same trend with much higher values of heat transfer coefficient and heat flux for finned specimens at the same wall temperature. At (T w ) of 0 o C, increasing the fin length from 0 to, 0, 30 and 0 mm has increased the heat transfer coefficient by 0%, 9%, 17%, and 00%, respectively; Fig. -a. Similar increase has resulted in the subcooled boiling heat flux; Fig. -b, i.e. increasing the fin length from 0 to, 0, 30 and 0 mm increased the heat flux subjected to the wall by 0%, 90%, % and 170%, respectively. This means that the watercooled engine with finned cylinder head can run at higher loads and outputs while having the cylinder head surface temperature kept lower and the engine can tolerate this high output without metal cracking. When the 0 mm height fin is used, the heat flux increased dramatically due to the increase in surface area and heat transfer coefficient. Alternatively, for the same heat flux applied, the wall temperature (T w ) will be much lower for the finned cases, see Fig.. This means that even if we use short fins ( or 0 mm length) the heat transfer would improve much as compared to no fins or flat specimen case. The use of fins, even with shorter length (or narrower ducts) will help in increasing the heat transfer and in transferring the mechanical stresses from the cylinder head lower deck to the upper deck of it, i.e. the fins will act as webs to support the cylinder head decks. The engine weight may be reduced further by reducing the thickness of the cylinder head lower deck in the case of using fins (or webs) in the cylinder head. EFFECT OF FIN NUMBER The effect of number of fins on the convective heat transfer coefficient and boiling heat flux may be found in Figs.9-a and 9-b, respectively. The experiments have been carried out for average flow velocity, V = m/s, bulk flow temperature, of 70 o C and fin length, L f, of 30 mm. The fin number has increased from to so that the surface area of the Copyright #### by ASME

5 fins is increased by about 17%. In the forced convection region, for (T w ) of 0 o C increasing the fin number from to has increased the convective heat transfer coefficient by about %. Also for the same wall superheat (T w T sat ) of o C, the subcooled boiling heat flux has increased by about 33%. Alternatively, for the same heat flux applied of 0 kw/m, increasing the fins number from to reduced the wall temperature from 9 to 1 o C. The improvement in convective heat transfer coefficient and heat flux (or less wall temperature for the same heat flux) may be attributed to the increased surface area of the fin when the fin number increased from to. The practical limit to increasing the fin number or having more fins would be the manufacturing or casting of the surface of cylinder heads or cylinder liners. EFFECT OF FIN MATERIAL Figures-a and -b show the effect of specimen material on the convective heat transfer coefficient and subcooled boiling heat flux, respectively. The results are compared at the same coolant bulk temperature of 70 o C, fin length of 0 mm and coolant upstream average velocity of m/s. The cast iron and cast steel specimen were manufactured with the same dimensions as listed in Table 1 (sample number 3 and 7). It has been shown earlier [1] that for flat surface (with no fins) cast iron exhibited a better heat transfer performance as compared to cast steel, due to its higher thermal conductivity. For a given (T w ) of 0 o C the convective heat transfer coefficient is about 3. kw/m K for cast steel specimen and about. kw/m K for cast iron one. Also for the same wall superheat (T w T sat ) of o C the heat flux for cast steel is about 1 kw/m while in the case of cast iron it is about 13 kw/m. Alternatively, for the same subcooled boiling heat flux of about 1 kw/m, the cast steel wall temperature is 11 o C, while it is about o C for cast iron specimen. The improved heat transfer for cast iron specimen over the cast steel is mainly due to its higher thermal conductivity. This has the implications that cast iron cylinder head are used when thermal load is dominant while cast steel cylinder head are used when mechanical loads are dominant. CORRELATION OF DATA The complete matrix of experimental data has been used here to develop a correlation for the heat transfer by forced convection for the cast iron specimen (n=). The correlation relates the Nusselt number, Nu, (heat transfer coefficient) with Reynolds number, Re (based on upstream velocity in test section, i.e. before the fins and hydraulic diameter), Prandtl number, Pr, viscosity ratio, µ r, (bulk to wall viscosity) and the aspect ratio, L f /H, (the length of fins to height of duct). The dimensionless groups used are: Nu = h D h / k b Re = ρ v b D h / µ b Pr = µ b C p / k b µ r = µ b / µ w A = L f / H The above dimensionless groups are calculated from the experimental results and fed to the Data fit software to produce the correlation: Nu = 0.03 Re 0.97 Pr 0.33 µ r 0.1 (1+A) 0.3 The above correlation is valid for Reynolds' numbers from about 0000 to 3000, Prandtl numbers from 1.9 to 3., viscosity ratios from 1 to 1., and L f /H from 0 to 1. This applies to forced convection heat transfer for cast iron fins with n=. The exponent of the fin to duct height ratio indicated the significant effect of the fins on the convection heat transfer coefficient. The correlation fitted the experimental data with coefficient of multiple determination (R ) of 0.009, and the correlated versus the measured Nusselt number is shown in Fig.11, which shows reasonable correlation between them. CONCLUSIONS From the results discussed in the previous section, the following conclusions may be drawn: 1- The use of finned cylinder head for a water-cooled engine has great favorable effect of reducing the wall temperature of the cylinder head as compared to no-fins cylinder heads. Also, the use of fins enables the engine designer to reduce the thickness of lower cylinder head deck, and hence reduces the overall engine weight more, since the fins (webs) increases the strength of cylinder heads. - The convective heat transfer coefficient and subcooled boiling heat flux have improved when the finned specimens were used. As a result any increase in the wall temperature due to the increase in coolant bulk temperature would be totally recovered by using the fins in cylinder head and thus increasing the heat transfer coefficient 3- Increasing the fin length from 0 to 0 mm improved the convection heat transfer coefficient by about 00% and sub-cooled boiling heat flux by about 170% - Increasing the number of fins generally increases the convective heat transfer coefficient and the sub-cooled boiling heat flux - The use of cast iron cylinder head specimen, with high thermal conductivity, causes the wall temperature to decrease compared to cast steel which can carry higher mechanical loads - A correlation has been developed to correlate the Nusselt number, Nu, with Reynolds number, Re, Prandtl number, Pr, viscosity ratio, µ r, and the fin length aspect ratio, L f /H, for the finned specimens 7- Increasing the flow velocity over the flat and finned specimens results in a reduction in the wall temperature. - The heat transfer coefficient is much higher for finned case than for no-fins case. When fins are used much less coolant flow velocities may be used which in turn can reduce the coolant pump size and power 9- Increasing the coolant bulk temperature causes an increase in wall temperature of both flat and finned specimens for the same heat flux although it improves the forced convection heat transfer coefficient - Higher bulk temperature in the engine will lead to lower heat flux for the flat specimen unless a finned cylinder head is used which would reduce the wall temperature due to the increased surface area of the fins and increased heat transfer coefficient Copyright #### by ASME

6 NOMENCLATURE A Aspect ratio of fins =L f /H, -- C p coolant specific heat, kj/kg.k D h hydraulic diameter = area / perimeter, m h heat transfer coefficient in forced convection region, kw/m o K H Duct height, m k thermal conductivity, kw/m o C k b coolant thermal conductivity at bulk temperature, kw/m o C L f fin length, mm n fin number, -- Nu Nusselt number -- p fin spacing mm Pr Prandtl number -- q heat flux kw/m Re Reynolds number -- t fin thickness mm o C o C coolant bulk temperature T w coolant side wall temperature V coolant average velocity in test section, m/s µ b coolant dynamic viscosity at bulk temperature,n.s/m µ r coolant viscosity ratio, µ b / µ w -- µ w coolant dynamic viscosity at wall temperature, N.s/m ρ coolant density at bulk temperature, kg/m 3 REFERENCES (1) Lee, K.S., Assanis, D.N., Lee, J. and Chun, K.M., 1999, Measurements and Predictions of Steady State and Transient Stress Distribution in a Diesel Engines Cylinder Head, SAE paper () French, C.C.J., 199, Taking the Heat Off the Highly Boosted Diesel, SAE Transaction paper 903, vol. 7. (3) Danieision, D.T., Elwart, J. and Bryzik, W., 1993, Thermochemical Stress Analysis of Novel Low Heat Rejection Cylinder Head Design, SAE Trans. paper () Huang, J.C. and Borman, C.L., 197, Measurements of Instantaneous Heat Flux to Metal and Ceramic Surface in a Diesel Engine, SAE Trans. paper 701. () Heywood, J.B., 19, ICE Fundamentals, MacGraw- Hill. () Assanis, D.N., and Heywood, J.B., 19, Development and Use of a Computer Simulation of the Turbocompounded Diesel Systems for Engine Performance and Component Heat Transfer Studies, SAE paper 039. (7) Shalev, M., Zvirin, Y. and Scotter, A., 193, Experimental and Analytical Investigation of the Heat Transfer and Thermal Stress in a Cylinder Head of a Diesel Engine, Int. J. Mech. Society, Vol., No. 7, pp () Bing, L., Yong, Z. and Meilin, Z., 1999, A Study on the Structural Design and Reliability of Cylinder Head for Vehicle Engine, SAE paper 991. (9) Elfeky, S.M.S. and Selim, M. Y. E., 000, On the Possibility of Using Aluminum Alloy Water Cooled Cylinder Head in I. C. Engines by Using Finned Surfaces, Engineering Research Journal, Helwan University, Egypt, October 000. () Selim, M.Y.E. and Helali, A.H.B., 001, Effect of Coolant Additives on Thermal Loading of Diesel Engine, Journal of Automobile Engineering, Vol. 1, pp , Proceedings of the Institution of Mechanical Engineers, Part D. (11) Abou-Ziyan, H. Z., 003, Forced convection and subcooled flow boiling heat transfer in asymmetrically heated ducts of T-section, Journal of Energy Conversion and Management, In Press, Corrected Proof, Available online Sept (1) Alcock, J.F., 19, Thermal Loading of Diesel Engines, Trans. of the Inst. of Eng., Vol. 77, No.1, Oct.19. (13) Cheong, S.K.A., 19, The Measurements of Low Concentration of Dissolved Gas in Water, M.Sc. Thesis, University of Toronto. (1) Addoms, J.N., 19, Heat Transfer at High Rates to Water Boiling Outside Cylinders, Dept. of Chem. Eng., MIT, Cambridge Mass. (1) Helali, A.B., 00, Evaluation of propylene glycol and ethylene glycol engine coolant additives under forced convection and boiling conditions, Res Eng J, Helwan Univ. (1) Helali, A.H.B., 199, Some Aspects of Heat Transfer in Water Cooled Cylinder Heads, Ph.D. Thesis, Helwan University, Egypt. Copyright #### by ASME

7 Table 1 Finned specimen dimensions Sample number Fin length, L f (mm) Fin number, n Fin thickness,, t, mm Fin spacing,, p, mm Surface area, mm Fin material Cast Iron 0 Cast Iron Cast Iron Cast Iron Cast Iron Cast Iron Cast Steel (1) Expansion Tank () Pressure Gauge (3) Small Electric Heater () Main tank () Cooling Coil () Immersion Heater (7) Feed Water Cooling Valve () Circulating Pump (9) Thermocouples () Control valve (11) Stop Valve (1) Manometer (13) Orifice Plate (1) Drain Valve (1) Test Specimen (1) Gas Burner (17) Test Duct (1) Discharge Valve (19) ByPass Valve Figure 1 Schematic diagram of the test rig 7 Copyright #### by AS

8 A 10 B DUCT SPECIMEN COPPER ROD 90 0 A B SEC. ELEVATION AT B - B SEC. SIDE VIEW AT A - A Figure Test section details t p L f φ x 1 = Figure 3 Finned specimen details Copyright #### by AS

9 9 9 h, (kw/m K) Lf = 0 mm, Tb = 70 oc, V =. m/s V = m/s V = 1 m/s Tw - Tb, (K) h, (kw/m K) Lf = 0 mm, Tb = 70 o C, V =. m/s V = m/s V = 1 m/s Tw - Tb, (K) (a) No fins, forced convection (b) With fins, forced convection Figure Effect of flow velocity for forced convection, =70 o C Heat Flux, (kw/m ) 0 Lf = 0 mm, Tb = 70 0 C, C.I V =. m/s V = m/s V = 1 m/s Tw-Tsat, (K) Heat Flux, (kw/m ) 0 Lf = 0 mm, Tb = 70 o C, V =. m/s V = m/s V = 1 m/s Tw-Tsat, (K) (a) No fins, subcooled boiling (b) With fins, subcooled boiling Figure Effect of flow velocity for subcooled boiling, =70 o C 9 Copyright #### by ASME

10 L f = 0 mm, V =. m/s, = 90 o C = 70 o C h, (kw/m K) h, (kw/m K) Tw - Tb, (K) Lf = 0 mm, V =. m/s, = 90 o C = 70 o C Tw - Tb, (K) (a) No fins, forced convection Figure Effect of bulk temperature for forced convection, V=. m/s b) With fins, forced convection 0 L f = 0 mm, V =. m/s, = 70 o C = 90 o C 0 Heat Flux, (kw/m ) 1 T w -T sat, (K) Heat Flux, (kw/m) Lf = 0mm, V =. m/s, = 70 o C = 90 o C 1 T w - T sat, (K) (a) No fins, subcooled boiling Figure 7 Effect of bulk temperature for subcooled boiling, V=. m/s (b) With fins, subcooled boiling Copyright #### by ASME

11 h, (kw/mk) V = m/s, = 70 o C, Lf = 0 mm Lf = 30 mm Lf = 0 mm Lf = mm Lf = 0 mm Tw - Tb, (K) Heat Flux, (kw/m ) V= m/s, =70 0 C C.I Lf=0 mm Lf=30 mm Lf=0 mm Lf= mm Lf=0 mm Tw - Tsat, (K) (a) Forced convection Figure Effect of fin length on forced convection and subcooled boiling for specimen, V = m/s, = 70 o C (b) Subcooled boiling h, (kw/m K) L f =30 mm, V=m/s, =70 o C n = fins n = fins Heat Flux, (kw/m ) 00 L f =30 mm, V=m/s, =70 o C n = fins n = fins Tw - Tb, (K) 1 Tw - Tsat, (K) (a) Forced convection Figure 9 Effect of fin number on forced convection and subcooled boiling for specimen, L f =30 mm, V = m/s, = 70 o C (b) Subcooled boiling 11 Copyright #### by ASME

12 7 L f =0 mm, V= m/s, =70 o C, n= fins Cast Iron Cast Steel 300 L f =0 mm, V= m/s, =70 o C, n= fins Cast Iron Cast Steel h, (kw/m) Heat Flux, (kw/m ) Tw - Tb, (K) (a) Forced convection Figure Effect of fin material on forced convection and subcooled boiling, at L f = 0 mm, V = m/s, = 70 o C, and n = 1 Tw - Tsat, (K) (b) Subcooled boiling Nu d Figure 11 Correlated Nusselt number against measured Nusselt number 1 Copyright #### by ASME

13 13 Copyright #### by ASME