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The subcooled flow boiling occurs when the bulk temperature is less than saturation temperature of the liquid at that pressure while the surface temperature is higher. The most importance of boiling phenomenon is related to the high latent heat of fluid which could removes high heat flux at relatively low temperature difference between liquid and the hot surface. In this study, the impact of velocity and roughness on the subcooled flow boiling were investigated experimentally for pure water. An experimental setup was designed and manufactured. The experimental setup consists of a plexiglass channel with cross section 20×30 mm and the length of 120 cm. A cylindrical heater with diameter 12 mm made of copper is located on the bottom surface of the plexiglass channel. All the experiments were conducted for the surface roughness of 0.65, 2.5 and 4.4 µm at velocities of 0.5, 0.7 and 0.9 m/s. The experimental results show that the surface heat flux increases as the surface roughness and velocity increases. However, this affect of velocity enhancement was only observed for lower boiling surface temperature and opposite trend has taken place for higher boiling surface temperature. This is due to the simultaneous consideration of the convection and boiling terms along with the interaction between them which has not been presented experimentally yet. It appears that this kind of experimental study has not been carried out for copper type surfaces.

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In recent years, many researches have investigated nanofluids pool boiling and reported some contradictory results. In this study, the pool boiling heat transfer of water- alumina and TiO2-water nanofluids at saturated temperature was investigated experimentally. The experiments were conducted to investigate the impact of concentration and type of nanofluid on the pool boiling heat transfer of brass surface. Water- alumina and TiO2-water nanofluids with volumetric concentration of 0.0025-1% and 0.0025, 0.01, 0.25 % was used, respectively. An experimental setup with a cylindrical heated test section made of brass and surface roughness of 0.2µm was designed and fabricated. The experimental results showed that, the heat transfer decreases as the nanoparticles added into the pure water base fluid. At a constant heat flux, the heat transfer coefficient decreases as the alumina volumetric concentration increments from 0.0025 to 0.01% and then increases for further addition from 0.01 to 1%. The TiO2-water nanofluids performance with respect to the water-alumina nanofluids was not very promising. That means, the boiling heat transfer decreases while the boiling surface temperature increase at a constant heat flux.

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A Stirling engine cycle combined with a SI engine cycle to recover the SI engine exhaust gas waste heat. One dimensional combustion simulation code is prepared for Spark Ignition type engine (M355G) simulation. The accuracy of numerical simulated results has been validated with M355G experimentally. The experimental generated power and exhaust gas temperature vary in the range of 84.1- 176.7 kW and 610-710 , respectively. The 1D code estimates the generated power with maximum 5.9% error and average exhaust gas temperature with 3.8% error in the operating range of the engine. The thermal analysis is done, and the results show that about 25% the part of input energy transfers by the exhaust gas as a waste. The results indicate that by installing a Stirling engine heater on the exhaust pipe of the SI engine can recover about 8.4kW of the waste heat at the best condition. The simulation of Alpha-type Stirling engine is done by GT-Suit program and the Solo V161 experimental results is used for the validation. According to 9% error in generated power calculation for validation, the new Stirling engine is suggested for installing in exhaust pipe. The generated power and thermal efficiency is estimated for Stirling engine in various exhaust gas temperature which occurred in various SI engine working condition. The coupled engines heat balance showed that the thermal efficiency is about 2-3% more than the ordinary one.

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The usages of stirling engine in many industry such as aerospace, submarines and combined heat and power systems, requires more and detailed analysis in such engines. This type of engine is an external combustion which may use almost any type of fuel. In this article the Nusselt number and friction coefficient of a Stirling engine heat exchanger is investigated numerically. The geometry of this heat exchanger is an arc shape pipe with reciprocating flow. Various parameters such as angular frequencies, type of fluids, working gas pressures, flow regime and heater geometry impact on the Nusselt number and friction coefficient of the heater were investigated. By increasing the angular frequency and the working gas pressure the Nusselt number increases but the friction coefficient decreases. The influences of different working fluids indicated that the Carbon dioxide has the highest Nusselt number. The results also show that the friction coefficient is highly dependent on the flow regime. The comparison between the two different geometry type heaters show that the arc-type geometry led to higher Nusselt number. The friction coefficients of both geometries are almost similar to each other at high frequencies.

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Vapor compression is an effective method of desalination in a small scale system. Such system has two hot outlet flows. These flows are used to preheat the feedwater. In this research, tube-in-tube heat exchanger with different number of inner tubes was designed and constructed as preheater. This heat exchanger contains many inner tubes where each tube is a separate inner flow line for hot flow. Heat exchanger was tested with one, two and three inner tubes. Volumetric flow rates varried from 30 to 120 lit/hr in annulus and 20 to 90 lit/hr for inner tubes respectively. The results showed that by changing number of inner tubes from 1 to 3, heat transfer increased 29%. However, 38.4% decrease in equivalent hydraulic diameter led to 22% drop in average nusselt number. Afterward, a dimensionless coefficient of performance enhancement, defined as the ratio of heat transfer rate variation and the required pumping power, used to determine number of inner tubes. The results implied that heat exchanger performance improved by increasing the number of inner tubes from 1 to 2. But there is no significant improvement when number of inner tubes changes from 2 to 3. Finally, a semi-emperical equation is presented for determination of Nusselt number in a heat exchanger with two inner tubes. This study indicated that this type of heat exchanger has the best performance for the system within the tested range.

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Oscillating flow is one of the most important characteristics of flow in stirling engine heat exchangers. In this study reciprocating flow in stirling engine cooler is investigated numerically. Numerical solution is based on finite volume and pressure based algorithm by using the commercial CFD code fluent. A Shell and tube type heat exchanger used as cooler. The working fluid, gas flows inside the tubes while the cooling fluid, water flows around the tubes. The heat transfer coefficient, temperature difference between tube walls and working fluid, Nusselt number and friction coefficient are calculated for Helium, Carbon‌ dioxide and Nitrogen at different operating pressure and oscillating frequency. The Nusselt number, heat transfer coefficient and temperature difference between tube walls and working fluid increase with increase of operating pressure or oscillating frequency while Friction coefficient decreases. Helium has the highest heat transfer coefficient and friction coefficient and the lowest temperature difference between tube walls and working fluid. At the highest operating pressure and oscillating frequency, Carbon dioxide has the highest Nusselt number and the lowest Friction coefficient. Finally empirical equations for Nusselt number and friction coefficient are proposed for Helium, Carbon dioxide and Nitrogen, the error of the equations are within 0.23-8.07% when the range of kinetic Reynolds number is 2.96-212.50.