• Energy Research

In this study, optimum propylene glycol (PG) brine-based nanofluids are being proposed as coolants for a wavy finned automotive radiator. Performance analysis is conducted and compared with conventional Ethylene Glycol (EG) brine and related nanofluids. A 25% PG brine has similar heat transfer characteristics to water at higher operating temperature ranges. The effects on radiator size, weight and cost, engine efficiency and fuel consumtion, and embodied energy saving and environmental impact are discussed as well. Compared to conventional coolant(EG water brine), for the same cooling capacity and radiator size, the coolant requirement and pumping power are reduced significantly by about 25% and 64%, respectively, whereas, for the same cooling capacity and mass flow rate, the radiator size and pumping power is reduced by 4.2% and 25.5%, respectively, with PG brine-based Ag nanofluids.Furthermore, by using optimum PG brine-based nanofluids, 3.5% of the embodied energy may be saved, which may yield reductions in radiator cost, engine fuel consumption and environmental costs.

In this study, optimum propylene glycol (PG) brine-based nanofluids are being proposed as coolants for a wavy finned automotive radiator. Performance analysis is conducted and compared with conventional Ethylene Glycol (EG) brine and related nanofluids. A 25% PG brine has similar heat transfer characteristics to water at higher operating temperature ranges. The effects on radiator size, weight and cost, engine efficiency and fuel consumtion, and embodied energy saving and environmental impact are discussed as well. Compared to conventional coolant(EG water brine), for the same cooling capacity and radiator size, the coolant requirement and pumping power are reduced significantly by about 25% and 64%, respectively, whereas, for the same cooling capacity and mass flow rate, the radiator size and pumping power is reduced by 4.2% and 25.5%, respectively, with PG brine-based Ag nanofluids.Furthermore, by using optimum PG brine-based nanofluids, 3.5% of the embodied energy may be saved, which may yield reductions in radiator cost, engine fuel consumption and environmental costs.

Abstract The convective closed-loop solar-assisted heat pump dryer (batch type) has been designed, fabricated and experimentally investigated for both simple heat pump drying (HPD) and solar-assisted heat pump drying (SAHPD) modes. The banana chips have been dried up to moisture content of 11.5% for both modes. The next-generation environmental-friendly refrigerant R1234yf has been used in the heat pump cycle. Various thermodynamic, exergoeconomic and economic performance parameters have been evaluated and compared for HPD and SAHPD. Both exergy and energy efficiencies are found better in the case of SAHPD. The system coefficient of performance, moisture removal from the product, drying rate and specific moisture extraction rate are found better for the SAHPD than the HPD. The average drying rates of HPD and SAHPD are found 0.205 and 0.342 kg/kg min, respectively. The estimated payback period of the SAHPD instead of HPD is 3.9 years. The exergoeconomic factor is found lowest for the expansion device for both HPD and SAHPD with estimated values of 0.1335 and 0.2003, respectively. The components that need more improvement are evaporator and expansion device based on exergoeconomic factor. On the basis of the present study, it can be concluded that the SAHPD system performs better in all respects.

Abstract The convective closed-loop solar-assisted heat pump dryer (batch type) has been designed, fabricated and experimentally investigated for both simple heat pump drying (HPD) and solar-assisted heat pump drying (SAHPD) modes. The banana chips have been dried up to moisture content of 11.5% for both modes. The next-generation environmental-friendly refrigerant R1234yf has been used in the heat pump cycle. Various thermodynamic, exergoeconomic and economic performance parameters have been evaluated and compared for HPD and SAHPD. Both exergy and energy efficiencies are found better in the case of SAHPD. The system coefficient of performance, moisture removal from the product, drying rate and specific moisture extraction rate are found better for the SAHPD than the HPD. The average drying rates of HPD and SAHPD are found 0.205 and 0.342 kg/kg min, respectively. The estimated payback period of the SAHPD instead of HPD is 3.9 years. The exergoeconomic factor is found lowest for the expansion device for both HPD and SAHPD with estimated values of 0.1335 and 0.2003, respectively. The components that need more improvement are evaporator and expansion device based on exergoeconomic factor. On the basis of the present study, it can be concluded that the SAHPD system performs better in all respects.

Abstract Analyses and operating pressure optimization of the supercritical Rankine cycles with and without regenerator and reheating for low-grade heat conversion have been conducted using N2O as a working fluid and compared with its counterpart CO2 based on various performance indicators. N2O is better in terms of net power output, thermal efficiency and exergetic efficiency and N2O works at much lower pressures at optimum operation; whereas, CO2 is advantageous in terms of turbine size, expansion ratio and heat transfer requirement. The choice of optimum operating conditions will differ depending on the chosen performance indicator. Hence, there is a need of trade-off between various indicators. Component wise irreversibility distribution shows the similar trends for both working fluids. With the increase in cycle temperature lift, both turbine shape parameter and heat transfer requirement decrease, leading to more compactness. Higher pump and turbine isentropic efficiencies yield higher optimum turbine inlet pressure, and lower heat transfer requirement and turbine size. Uses of internal heat exchanger and reheating in the supercritical Rankine cycle not only improve the performances, it also constitutes an excellent compromise between various performance indicators based optimizations. Present study reveals that N2O is a potential option for the supercritical Rankine cycle.

Abstract Analyses and operating pressure optimization of the supercritical Rankine cycles with and without regenerator and reheating for low-grade heat conversion have been conducted using N2O as a working fluid and compared with its counterpart CO2 based on various performance indicators. N2O is better in terms of net power output, thermal efficiency and exergetic efficiency and N2O works at much lower pressures at optimum operation; whereas, CO2 is advantageous in terms of turbine size, expansion ratio and heat transfer requirement. The choice of optimum operating conditions will differ depending on the chosen performance indicator. Hence, there is a need of trade-off between various indicators. Component wise irreversibility distribution shows the similar trends for both working fluids. With the increase in cycle temperature lift, both turbine shape parameter and heat transfer requirement decrease, leading to more compactness. Higher pump and turbine isentropic efficiencies yield higher optimum turbine inlet pressure, and lower heat transfer requirement and turbine size. Uses of internal heat exchanger and reheating in the supercritical Rankine cycle not only improve the performances, it also constitutes an excellent compromise between various performance indicators based optimizations. Present study reveals that N2O is a potential option for the supercritical Rankine cycle.

AbstractTransient and steady‐state characteristics of the natural circulation loop are studied using various water‐based tri‐hybrid (different nature and shaped nanoparticles) nanofluids. Effects of input power, loop inclination and loop aspect ratio on the mass flow rate, effectiveness, and entropy generation rate are studied. Results disclose that tri‐hybrid nanofluids reduce the oscillation and attain steady state faster than water. Effectiveness increases and entropy generation rate decreases by using tri‐hybrid nanofluids. Nanoparticle shape has found a significant impact. Al2O3 + Cu + CNT/water shows the best performance. The mass flow rate increases with input power, loop aspect ratio, whereas, reduces with loop inclination. Effectiveness decreases and then increases with input power, whereas increases with loop inclination and decreases with loop aspect ratio. Entropy generation upsurges with input power and loop inclination, whereas decreases with loop aspect ratio. Loop aspect ratio of 1.5 to 3 is found suitable for better performance.

AbstractTransient and steady‐state characteristics of the natural circulation loop are studied using various water‐based tri‐hybrid (different nature and shaped nanoparticles) nanofluids. Effects of input power, loop inclination and loop aspect ratio on the mass flow rate, effectiveness, and entropy generation rate are studied. Results disclose that tri‐hybrid nanofluids reduce the oscillation and attain steady state faster than water. Effectiveness increases and entropy generation rate decreases by using tri‐hybrid nanofluids. Nanoparticle shape has found a significant impact. Al2O3 + Cu + CNT/water shows the best performance. The mass flow rate increases with input power, loop aspect ratio, whereas, reduces with loop inclination. Effectiveness decreases and then increases with input power, whereas increases with loop inclination and decreases with loop aspect ratio. Entropy generation upsurges with input power and loop inclination, whereas decreases with loop aspect ratio. Loop aspect ratio of 1.5 to 3 is found suitable for better performance.

In the present study, optimization of compressor pressure ratio and intermediate pressure between HP and LP turbines leading to maximum thermal efficiency is implemented for a supercritical CO2 recompression cycle with reheating applicable to next generation nuclear reactors. Effects of various operating conditions and component performances on the optimal values and cycle efficiency are studied as well. Finally, a comparison between supercritical CO2 recompression cycles with and without reheating is presented. The optimization of recompression mass fraction shows that the present cycle configuration yields maximum thermal efficiency for nearly equal heat capacity values of both fluids in LTR. The effect of maximum cycle temperature on the optimum pressure ratio is negligible for lower values of minimum cycle temperature and maximum pressure, and the effect becomes significant with an increase in these parameters. Results show that the thermal efficiency improves with a decrease in minimum cycle temperature and with increase in maximum cycle temperature and pressure. The optimum intermediate pressure is exhibited to be higher than the geometric mean value between minimum and maximum pressure and a simple empirical correlation useful for optimum design is presented. The maximum efficiency improvement using reheating is calculated as 3.5% at optimum conditions.

In the present study, optimization of compressor pressure ratio and intermediate pressure between HP and LP turbines leading to maximum thermal efficiency is implemented for a supercritical CO2 recompression cycle with reheating applicable to next generation nuclear reactors. Effects of various operating conditions and component performances on the optimal values and cycle efficiency are studied as well. Finally, a comparison between supercritical CO2 recompression cycles with and without reheating is presented. The optimization of recompression mass fraction shows that the present cycle configuration yields maximum thermal efficiency for nearly equal heat capacity values of both fluids in LTR. The effect of maximum cycle temperature on the optimum pressure ratio is negligible for lower values of minimum cycle temperature and maximum pressure, and the effect becomes significant with an increase in these parameters. Results show that the thermal efficiency improves with a decrease in minimum cycle temperature and with increase in maximum cycle temperature and pressure. The optimum intermediate pressure is exhibited to be higher than the geometric mean value between minimum and maximum pressure and a simple empirical correlation useful for optimum design is presented. The maximum efficiency improvement using reheating is calculated as 3.5% at optimum conditions.