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This work evaluates the use of zinc oxide nanorods as intensifiers of a latent heat thermal energy storage system working with adipic acid as the phase change material (PCM). By virtue of not participating directly in the solid–liquid and liquid–solid phase transition, ZnO-adipic acid composites (ZnO-adipic acid) possessed lower specific heat and latent heat. Our results have shown that the overall heat transfer coefficient during the freezing of PCM through heat transfer to a well-mixed liquid bath is amplified by 61%, when adipic acid is replaced with 2 wt.% ZnO-adipic acid. Heterogenous nucleation due to well-dispersed, ZnO nanorods caused this enhancement. The large enhancement in discharge rate of 2 wt.% ZnO-adipic acid during freezing overweighs higher degree of latent heat loss due to its repeated thermal cycling. The enhancement in overall heat transfer coefficient reported here (61%) is the highest reported so far for any latent heat thermal energy system employing adipic acid or its composites.

High-temperature phase change materials (PCMs) with good energy storage density and thermal conductivity are needed to utilize solar thermal energy effectively to meet industrial thermal energy demands. Composite PCMs containing a material of higher thermal conductivity and an inorganic high-temperature PCM can be explored to meet these requirements. Accordingly, a high-temperature, composite inorganic PCM (ZnO-NaNO 3 ) with enhanced thermophysical properties was prepared, and its energy storage potential was investigated experimentally. A maximum thermal conductivity enhancement of 22.7% was achieved at 200 °C for 2 wt% ZnO-NaNO 3 nanocomposite. The increase in thermal conductivity at higher temperatures may be attributed to the formation of ordered sodium nitrate layers on the nanoparticle surfaces. The increase in surface area and surface energy due to the addition of ZnO nanoparticles increased the specific heat of the nanocomposite in both the solid and liquid phases (43.5% in the liquid phase for 2 wt% ZnO-NaNO 3 ). Thus, the addition of ZnO nanoparticles to NaNO 3 increased its energy storage capacity. The addition of ZnO nanoparticles to NaNO 3 did not affect the onset, peak or endset temperature during melting and freezing. Moreover, 2 wt% ZnO-NaNO 3 exhibited cyclic stability even after 500 cycles and thus has potential as an energy storage medium.

In this work, ZnO nanoparticles were used to improve the thermal performance of Therminol 55 oil. The addition of ZnO nanoparticles to Therminol 55 increased the thermal conductivity and viscosity by 6% and 43.9% respectively at room temperature (27 °C) at a nanoparticle concentration of 2 vol.%. The thermal conductivity-temperature relation of ZnO-Therminol 55 nanofluids was biphasic. Thermal conductivity enhancement was observed at lower temperatures (10% enhancement at 10 °C; ϕ = 2 vol. %) as well as at higher temperatures (18.3% enhancement at 100 °C; ϕ = 2 vol. %), which were attributed to the layering of Therminol 55 molecules over ZnO nanoparticles’ surface (at lower temperatures) and Brownian motion of nanoparticles (at higher temperatures) respectively. The relative viscosity of ZnO-Therminol 55 nanofluids also decreased with increasing temperature (μr = 1.44 @ T = 27 °C; μr ~ 1 @ T = 140 °C). The heat transfer performance of ZnO-Therminol 55 nanofluids was tested under constant temperature boundary conditions. About 154% and 203% enhancements in overall heat transfer coefficient and test fluid side heat transfer coefficient were observed for 2 vol. % ZnO-Therminol 55 nanofluid compared to pure Therminol 55 due to the improved thermal conductivity, natural convection currents resulting from Brownian motion and particle migration. ZnO-Therminol 55 nanofluids depicting improved thermal properties at higher temperatures can be potentially used as heat transfer fluids above 100 °C, when the thermal resistance in the heat transfer fluid is rate-controlling.

High-temperature phase change materials (PCMs) with good energy storage density and thermal conductivity are needed to utilize solar thermal energy effectively to meet industrial thermal energy demands. Composite PCMs containing a material of higher thermal conductivity and an inorganic high-temperature PCM can be explored to meet these requirements. Accordingly, a high-temperature, composite inorganic PCM (ZnO-NaNO ) with enhanced thermophysical properties was prepared, and its energy storage potential was investigated experimentally. A maximum thermal conductivity enhancement of 22.7% was achieved at 200 °C for 2 wt% ZnO-NaNO nanocomposite. The increase in thermal conductivity at higher temperatures may be attributed to the formation of ordered sodium nitrate layers on the nanoparticle surfaces. The increase in surface area and surface energy due to the addition of ZnO nanoparticles increased the specific heat of the nanocomposite in both the solid and liquid phases (43.5% in the liquid phase for 2 wt% ZnO-NaNO ). Thus, the addition of ZnO nanoparticles to NaNO increased its energy storage capacity. The addition of ZnO nanoparticles to NaNO did not affect the onset, peak or endset temperature during melting and freezing. Moreover, 2 wt% ZnO-NaNO exhibited cyclic stability even after 500 cycles and thus has potential as an energy storage medium.

Large gains in the rate of cache-aided broadcast communication are obtained using coded caching, but to obtain this most existing centralized coded caching schemes require that the files at the server be divisible into a large number of parts (this number is called subpacketization). In fact, most schemes require the subpacketization to be growing asymptotically as exponential in \\([-11r]K\\) for some positive integer \\(r\\) and \\(K\\) being the number of users. On the other extreme, few schemes having subpacketization linear in \\(K\\) are known; however, they require large number of users to exist, or they offer only little gain in the rate. In this work, we propose two new centralized coded caching schemes with low subpacketization and moderate rate gains utilizing projective geometries over finite fields. Both the schemes achieve the same asymptotic subpacketization, which is exponential in \\(O(( K)^2)\\) (thus improving on the \\([-11r]K\\) exponent). The first scheme has a larger cache requirement but has at most a constant rate (with increasing \\(K\\)), while the second has small cache requirement but has a larger rate. As a special case of our second scheme, we get a new linear subpacketization scheme, which has a more flexible range of parameters than the existing linear subpacketization schemes. Extending our techniques, we also obtain low subpacketization schemes for other multi-receiver settings such as distributed computing and the cache-aided interference channel. We validate the performance of all our schemes via extensive numerical comparisons. For a special class of symmetric caching schemes with a given subpacketization level, we propose two new information theoretic lower bounds on the optimal rate of coded caching.

Consider an interference channel consisting of \\(K_T\\) transmitters and \\(K_R\\) receivers with AWGN noise and complex channel gains, and with \\(N\\) files in the system. The one-shot \\(DoF\\) for this channel is the maximum number of receivers which can be served simultaneously with vanishing probability of error as the \\(SNR\\) grows large, under a class of schemes known as one-shot schemes. Consider that there exists transmitter and receiver side caches which can store fractions \\(M_TN\\) and \\(M_RN\\) of the library respectively. Recent work for this cache-aided interference channel setup shows that, using a carefully designed prefetching(caching) phase, and a one-shot coded delivery scheme combined with a proper choice of beamforming coefficients at the transmitters, we can achieve a \\(DoF\\) of \\(t_T+t_R\\), where \\(t_T=M_T K_TN\\) and \\(t_R=M_R K_RN,\\) which was shown to be almost optimal. The existing scheme involves splitting the file into \\(F\\) subfiles (the parameter \\(F\\) is called the subpacketization), where \\(F\\) can be extremely large (in fact, with constant cache fractions, it becomes exponential in \\(K_R\\), for large \\(K_R\\)). In this work, our first contribution is a scheme which achieves the same \\(DoF\\) of \\(t_T+t_R\\) with a smaller subpacketization than prior schemes. Our second contribution is a new coded caching scheme for the interference channel based on projective geometries over finite fields which achieves a one-shot \\(DoF\\) of \\((log_qK_R+K_T)\\), with a subpacketization \\(F=q^O(K_T+(log_qK_R)^2)\\) (for some prime power \\(q\\)) that is subexponential in \\(K_R\\), for small constant cache fraction at the receivers. To the best of our knowledge, this is the first coded caching scheme with subpacketization subexponential in the number of receivers for this setting.