Showing papers by "Shankar Narayanan published in 2016"

Characterization of Adsorption Enthalpy of Novel Water-Stable Zeolites and Metal-Organic Frameworks

Abstract: Water adsorption is becoming increasingly important for many applications including thermal energy storage, desalination, and water harvesting. To develop such applications, it is essential to understand both adsorbent-adsorbate and adsorbate-adsorbate interactions, and also the energy required for adsorption/desorption processes of porous material-adsorbate systems, such as zeolites and metal-organic frameworks (MOFs). In this study, we present a technique to characterize the enthalpy of adsorption/desorption of zeolites and MOF-801 with water as an adsorbate by conducting desorption experiments with conventional differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). With this method, the enthalpies of adsorption of previously uncharacterized adsorbents were estimated as a function of both uptake and temperature. Our characterizations indicate that the adsorption enthalpies of type I zeolites can increase to greater than twice the latent heat whereas adsorption enthalpies of MOF-801 are nearly constant for a wide range of vapor uptakes.

Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

Abstract: We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm2-K, while dissipating a heat flux of 1 kW/cm2. When applied to power electronics, such as GaN high-electron-mobility transistors, this membrane-based evaporative cooling device can lower the near-junction temperature by more than 40 K compared with contemporary single-phase microchannel coolers.

Design and Modeling of Membrane-Based Evaporative Cooling Devices for Thermal Management of High Heat Fluxes

Abstract: We present a high-heat-flux cooling device for advanced thermal management of electronics. The device incorporates nanoporous membranes supported on microchannels to enable thin-film evaporation. The underlying concept takes advantage of the capillary pressure generated by small pores in the membrane, and minimizes the viscous loss by reducing the membrane thickness. The heat transfer and fluid flow in the device were modeled to determine the effect of different geometric parameters. With the optimization of various parameters, the device can achieve a heat transfer coefficient in excess of 0.05 kW/cm2-K, while dissipating a heat flux of 1 kW/cm2. When applied to power electronics, such as GaN high-electron-mobility transistors, this membrane-based evaporative cooling device can lower the near-junction temperature by more than 40 K compared with contemporary single-phase microchannel coolers.

Solar thermal charging properties of graphene oxide embedded myristic acid composites phase change material

Abstract: The present paper reports the heat transfer characteristics of graphene oxide (GO) embedded myristic acid based phase change material (GO-PCM) composites. By varying concentrations of GO (0.1-0.5 wt%), different GO-PCM composites were preapred. Two different experimental setups were used for investigating the heat transfer characteristics of the prepared GO-PCM composites during the melting and solidification processes: (i) conventional heating and (ii) solar illumination. The experimental observations indicated a higher heat transfer rate in the GO-PCM composites as compared to pristine PCM for both experimental setups. From the experimental results of conventional heating setup, it was observed that the melting and solidification rate for GO–PCM composites, at 0.5 wt% of GO, increased by 48% and 70%, respectively in comparison to pristine PCM. The experimental results using solar illumination setup demonstrated an ultrafast heating rate for GO-PCM composites than the conventional heating based approach.