Spectrally selective solar absorbers in different non-black colours

Silicon paints were prepared from yellow, ochre, dark ochre, green and blue pigments. To improve the solar absorptance, a_s, of these coatings, an existing black paint was admixed in different ratios. The optical properties of the mixed paints thus formed are expressed in terms of the Kubelka–Munk absorption and scattering coefficients in the spectral region 400–17000 nm. The scattering coefficient obtained for all paints was essentially equal. In the visible region the absorption coefficient follows the spectral characteristics of each respective colour. In the infrared absorption at 9000 nm and above 12000 nm are seen in all cases which result in a thickness-dependent increase of the thermal emittance, e_T, of the coating. The metric chroma (C_ab^*) and lightness (L^*) in CIELAB colour space were calculated for wide-angle observer in average daylight conditions. A range of non-black spectrally selective solar absorber surfaces with a_s>0.8 and e_T<0.3 have been prepared with L^*<45 and C_ab^*<10.     

Calculation of the photocurrent-potential characteristic for regenerative, sensitized semiconductor electrodes

The steady state anodic photocurrent for sensitized semiconductor electrodes, where the sensitizer is regenerated by a redox electrolyte, has been modeled taking into account the rate of light absorption by the sensitizer S, the rate of electron injection from the excited state S^* of the sensitizer to the conduction band of the semiconductor, the rate of decay of S^* (radiative and non-radiative) and the rate of reductive regeneration of the sensitizer by the redox electrolyte. In this model the rate of recombination between the conduction band electron and the oxidized sensitizer, S⁺, and the reactions between S^* and the redox couple have been assumed to be negligible. The rate constant for injection, k_inj, the injection efficiency, φ_inj, the photocurrent density, J_P, and the steady state concentrations of S^* and S⁺, have been calculated as a function of light intensity, Helmholtz potential, λ_max and halfwidth, ΔE_0.5, of the sensitizer absorption spectrum, and the semiconductor band gap and electron affinity both for monochromatic light and for AM1.5 sunlight simulated by radiation from a 5600K black body. For the calculation of k_inj as a function of Helmholtz potential, the Gurney -Gerischer-Marcus (GGM) model has been used. Allowance for the distribution of electrode potential between the semiconductor and the electrolyte has been introduced in principle. The steady state concentrations of S^* and S⁺ were used in the Nernst equation to calculate the S^*/S⁺ quasi-reversible potential. It is shown that the short-circuit current density of the cell is a maximum for a sensitizer with a λ_max of about 1550 nm. Inter-relationships between variables involving the sensitizer have been used to show that only four sensitizer parameters are needed when considering the effects of changing the sensitizer. These parameters are the reorganization energies and the standard reduction potentials for the couples S⁺/S^* and S⁺/S. For a related series of sensitizers, such as obtained by changing a substituent group, only the two standard reduction potentials are required to predict the effects of changing the sensitizer.     

Performance study of an evaporator tube working under high heat fluxes

The performance of an evaporator tube operating under high fluxes with water is studied analytically for possible thermal conditions in the pre- and post-burnout regions. A correlation is proposed for predicting the critical heat flux under slow burnout conditions making use of the concept proposed by Mozharov that the dry-out conditions in the tube arise due to tearing of the liquid film on the periphery due to shearing action of the lighter phase flowing in the core. The correlation is found to reasonably satisfy experimental data in the Russian literature.Besides a computational procedure is employed to describe the nature of variation of both heat transfer coefficient and thermal potential (T_W − T_S) all along the length of the evaporator tube.     

Parametric study on the thermoelectric conversion performance of a concentrated solar‐driven thermionic‐thermoelectric hybrid generator

A concentrated solar‐driven thermionic‐thermoelectric hybrid generator composed of solar heat collector, thermionic generator (TIG), thermoelectric generator (TEG), and radiator is introduced in this paper. A theoretical model of thermoelectric conversion performance for the hybrid generator is built up based on the heat source of the concentrated solar radiation rather than isothermal heat source. Based on the model, the impacts of related parameters on the internal temperature distributions, output power, and efficiency have been discussed. Moreover, the optimal operating conditions of the TIG‐TEG hybrid device at its maximum output power and efficiency have been determined. Results show that when cascading the TEG with the TIG, there is very little change of the TIG cathode temperature in most conditions, namely, T_C ≈ T_C′. Meanwhile, the anode temperature becomes higher, and the TEG cold end temperature T₂ is close to the anode temperature T_A′ for the single TIG system, ie, T_A > T_A′ ≈ T₂. In theory, the optimal concentrated solar radiation I₀ for the maximum output power P_max and the maximum efficiency η_max differs, which are I_0,P = 2.5 × 10⁶ W/m² and I_0,η = 2 × 10⁶ W/m², respectively, whereas the output power and efficiency of the TIG‐TEG hybrid system simultaneously reach their maximum values when the optimal TIG anode temperature T_A,opt = 1025 K, the optimal TIG output voltage V_opt = 2 V, and the optimal ratio of load resistance to internal resistance (R₂/R)_opt = 2. However, in practice, the parameter values of I₀, Φ_A, and T_A should be strictly controlled under 1.8 × 10⁶ W/m², 1.4 eV, and 660 K, respectively. Generally, the maximum output power and efficiency of the hybrid TIG‐TEG system are, respectively, 35% and 4% higher than that of the single TIG.     

Natural convective heat transfer in uniformly heated vertical pipe annuli

Natural convective heat transfer in vertical concentric pipe annuli is investigated both numerically and experimentally for a fluid having a Prandtl number of 0.7. Numerical calculations for three cases of different heating conditions for pipes (heated inner pipe, heated outer pipe, both pipes heated) are made of laminar flows for different inner‐to‐outer‐pipe diameter ratios d_i/d_o from 0.2 to 0.8. For each case, the thermal entrance length x/b at the modified Grashof numbers Gr^*=10² to 5 × 10⁵ is well correlated with Grashof number Gr^* and annulus length to clearance ratio L/b. Local Nusselt numbers Nu_i and Nu_o in the thermally fully developed region have certain constant values dependent on the diameter ratio d_i/d_o, regardless of Gr^* and L/b. Average Nusselt numbers Nu_i and Nu_o in the thermal entrance region are also independent of Gr^* and L/b. © 2001 Scripta Technica, Heat Trans Asian Res, 30(8): 676–688, 2001     

Thermodynamic characterization of the (H2 + C3H8) system significant for the hydrogen economy: Experimental (p, ρ, T) determination and equation-of-state modelling

For the gradual introduction of hydrogen in the energy market, the study of the properties of mixtures of hydrogen with typical components of natural gas (NG) and liquefied petroleum gas (LPG) is of great importance. This work aims to provide accurate experimental (p, ρ, T) data for three hydrogen-propane mixtures with nominal compositions (amount of substance, mol/mol) of (0.95H₂ + 0.05C₃H₈), (0.90H₂ + 0.10C₃H₈), and (0.83H₂ + 0.17C₃H₈), at temperatures of 250, 275, 300, 325, 350, and 375 K, and pressures up to 20 MPa. A single-sinker densimeter was used to determine the density of the mixtures. Experimental density data were compared to the densities calculated from two reference equations of state: the GERG-2008 and the AGA8-DC92. Relative deviations from the GERG-2008 EoS are systematically larger than those from the AGA8-DC92. They are within the ±0.5% band for the mixture with 5% of propane, but deviations are higher than 0.5% for the mixtures with 10% and 17% of propane, especially at low temperatures and high pressures. Finally, the sets of new experimental data have been processed by the application of two different statistical equations of state: the virial equation of state, through the second and third virial coefficients, B(T, x) and C(T, x), and the PC-SAFT equation of state.     

The Second Law of Thermodynamics for a Two-Temperature Model of Heat Transport in Metal Films

ABSTRACT

The second law of thermodynamics asserts that heat will always flow “downhill”, i.e., from an object having a higher temperature to one having a lower temperature. For a parabolic rigid heat conductor with a single temperature T and a single heat-flux q this amounts to the statement that the inner product of q and ?T must be non-positive for every point x of the conductor and for every non-negative time t. For a homogeneous and isotropic body in which classical Fourier law with a heat conductivity coefficient k is postulated, the second law is satisfied if k is a positive parameter. For ultra-fast pulse-laser heating on metal films, a parabolic two-temperature model coupling an electron temperature T_e with a metal lattice temperature T_l has been proposed by several authors. For such a model, at a given point of space x and a given time t there are two different temperatures T_e and T_l as well as two different heat-fluxes q _e and q _l related to the gradients of T_e and T_l, respectively, through classical Fourier law. As a result, for a homogeneous and isotropic model the positive definiteness of the heat conductivity coefficients k_e and k_l corresponding to T_e and T_l, respectively, implies that the second law of thermodynamics is satisfied for each of the pairs (T_e, q _e) and (T_l, q _l), separately. Also, the positive definiteness of k_e and k_l, and of the corresponding heat capacities c_e and c_l as well as of a coupling factor G imply that a temperature initial-boundary value problem for the two-temperature model has unique solution. In the present paper, an alternative form of the second law of thermodynamics for the two-temperature model with k_l = 0 and q _l =  0 is obtained from which it follows that in a one-dimensional case the electron heat-flux q_e(x, t) has direction that is opposite not only to that of ?T_e(x, t)/?x but also to that of ?T_l(x, t + τ_T)/?x, where τ_T is an intrinsic small time of the model. Also, for a general two-temperature rigid heat conductor in which k_e, k_l, c_e, c_l, and G are positive, an inequality of the second law of thermodynamics type involving a pair (T_e ? T_l, q _e ?  q _l) is postulated to prove that a two-heat-flux initial-boundary value problem of the two-temperature model has a unique solution. For a one-dimensional case, the semi-infinite sectors of the plane ( q _l, q _e) over which uniqueness does not hold true are also revealed.     

Chemical kinetics modeling of n-nonane oxidation in oxygen/argon using excited-state species time histories

Chemical reactions of ground-state species strongly govern the formation of excited-state species, including OH^* and CH^*, which are commonly used to determine ignition delay times of fuels. With well-characterized chemiluminescence rates embedded in chemical kinetics mechanisms, time histories of excited-state species can aid in identifying influential ground-state reactions which are important to processes such as ignition delay time. Placing emphasis on the high-temperature regime, improvements were made to a detailed chemical kinetics mechanism of n-nonane oxidation developed previously by the authors. Using characteristic features of OH^* time histories measured in shock-tube experiments as a metric, detailed model analyses were performed over a broad range of conditions: T > 1100 K, 1.5 < P (atm) < 10.5, ? = 0.5, 1.0, 2.0. OH^* time history measurements, particularly under fuel-rich conditions (? = 2.0), displayed a two-peak behavior, with the first peak occurring within the first 5–10 μs after reflected-shock passage, and the second, wider peak corresponding to main oxidation and ignition. In the initial version of the kinetics mechanism, the two peaks at rich conditions were predicted to merge, blurring the main ignition process prior to the second peak. The work herein presents modifications to the initial chemical kinetics mechanism which led to improved agreement between measurements and model-based predictions, with emphasis on the fuel-rich condition. To this end, the predicted shapes of the OH^* time histories were crucial to matching the two-peak behavior detected in the experiments. A first-order resistance–capacitance (RC) model of the experimental time response of the optical setup was developed and shown to reproduce the measured time dependence and peak behavior that are vital for matching the OH^* behavior near time-zero. The RC model processes the kinetics predictions in a way that allows the kinetics model predictions to directly correspond to the true conditions in the experiment. In moving towards improved agreement in OH^*-profile predictions for all conditions, improvements in the kinetics mechanism were also realized at the two leaner equivalence ratios (? = 1.0 and 0.5), both in terms of OH^* profile shape and ignition delay times. Model calculations of oxidation processes indicate that reactions leading to the first OH^* peak originate from fuel homolysis. The resulting (alkyl) radicals lead to the formation of methyl which then, through a series of H-abstraction reactions, leads to the production of the methylidyne radical (CH) that reacts with molecular oxygen to form OH^*. The oxidation processes near time-zero terminate, in part, due to methyl depletion by methylene forming C₂H₄ + H₂. In addition to the insight gained on n-nonane ignition and oxidation chemistry, the present study highlights the utility of correctly interpreted OH^* measurements for inference of kinetic information other than ignition delay times.     

Vanadium based zinc spinel oxides: Potential materials as photoanode for water oxidation and optoelectronic devices

In the recent past, layered zinc-based vanadium spinel oxides (ZnVOs) have shown an intriguing way to accomplish the challenges of energy conversion, storage, and utilization issues. Here, through first-principles calculations, a comprehensive study has been carried out to investigate the AV₂M (where A = Zn, Zn₂, Zn₃, Zn_4, and M = O₄, O₆, O₇, O₈, O₉ respectively) electronic, photocatalytic, and optical properties. Formation energies with a negative sign express that the final compounds from the pure elements are possible and cohesive energies revealed that compounds are energetically stable. Spin-polarized calculations are also taken into account for better approximation of the electronic properties (band structure and density of states). All layered structures show indirect bandgap for spin-up calculations in range 0.3 eV–2.4 eV, while spin-down calculations show mix trends in range 2.3 eV–3.50 eV. An appropriate band edge with large enough kinetic over-potentials of the oxygen evolution reaction (ΔE_V ≥ 1.244 eV) makes them potential candidates as photoanode for water splitting. ZnV₂O₄ is more suitable for OER as it has small kinetic overpotential as compared to the oxidation potential of water. Interestingly, all ZnVOs display a dramatically large coefficient (~10⁵ cm⁻¹) for optical absorption. Photogenerated electrons and holes on the layered zinc-based vanadium spinel oxide surfaces could make these spinel oxides promising materials for photocatalytic water splitting and solar energy conversion.     

Effect of proton irradiation on electrical properties of CuInSe2 thin films

High-energy proton irradiation (380 keV and 1 MeV) on the electrical properties of CuInSe₂ (CIS) thin films has been investigated. The samples were epitaxially grown on GaAs (0 0 1) substrates by Radio Frequency sputtering. As the proton fluence exceeded 1×10¹³ cm⁻², the carrier concentration and mobility of the CIS thin films were decreased. The carrier removal rate with proton fluence was estimated to be about 1000 cm⁻¹. The electrical properties of CIS thin films before and after irradiation were studied between 80 and 300 K. From the temperature dependence of the carrier concentration in CIS thin films, we found N_D=9.5×10¹⁶ cm⁻³, N_A=3.7×10¹⁶ cm⁻³ and E_D=21 meV from the fitting to the experimental data on the basis of the charge balance equation. After irradiation, a defect level was created, and N_T=1×10¹⁷ cm⁻³ for a fluence of 3×10¹³ cm⁻², N_T=5.7×10¹⁷ cm⁻³ for a fluence of 1×10¹⁴ cm⁻² and E_T=95 meV were also obtained from the same fitting. The new defect, which acted as an electron trap, was due to proton irradiation, and the defect density was increased with proton fluence.     

Evaporation of an oil‐in‐water type emulsion droplet on a hot surface

Evaporation characteristics of an Oil‐in‐Water (O/W) emulsion droplet were examined experimentally. The evaporation time per unit of initial surface area of a droplet τ^* was used to estimate the evaporation characteristics of droplets with different diameters and to compare a water droplet and an emulsion droplet. Results show that τ^* of an O/W emulsion droplet is shorter than a water droplet in the Leidenfrost film boiling regime. The four evaporation modes of O/W type emulsion droplets were observed. These depended on the mixing ratio of water and oil, G_S, and hot surface temperature, T_W. Increasing G_S increases the emulsion droplet's Leidenfrost temperature when the droplet is used as a die‐cast releasing agent. Microexplosions were observed during Leidenfrost film boiling when T_W was greater than 250^°C. © 2005 Wiley Periodicals, Inc. Heat Trans Asian Res, 34(7): 527–537, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20081     

Comparison of entropy minimization principles in heat exchange and a short-cut principle: EoTD

In this paper the principles called ‘equipartition of forces, EoF’ and ‘equipartition of entropy production, EoEP’ are compared in minimizing the entropy production in heat exchange. Entropy production rates for various cases are calculated according to both principles. The calculations show that entropy productions calculated with EoEP principle are always smaller than those calculated with EoF principle although the differences are considerably small. It is also shown that the heat exchange with EoEP principle implied T_H/T_C=const. Additionally, a new approach, equipartition of temperature difference, EoTD, has been tested comparatively. Although the entropy production rates calculated by this approach are slightly larger than those of two other principles, it can be used as a new principle for quick determination. Copyright © 2003 John Wiley & Sons, Ltd.     

Fluid flow and heat transfer of opposing mixed convection adjacent to upward‐facing,inclined heated plates

Opposing mixed convective flows of air induced over uniformly heated, upward‐facing, inclined plates were investigated experimentally. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers, Re_L=7.2×10² to 1×10⁴ and Ra_L^*=5×10⁶ to 8×10⁸, and the inclination angles from θ=15 to 75^° from horizontal. The flow fields over plates were visualized with smoke. The results showed that a separation of forced boundary layer flow occurs first at the trailing edge, and then the separation point shifts toward upstream with increasing the wall heat flux, and finally, reaches to the leading edge of the plates. It was also found that the separations at the trailing and leading edges are correlated well with the non‐dimensional parameter as (Gr_θ^*/Re_L^2.5)=0.35 and 1.0, respectively. The local heat transfer coefficients of the inclined plates were also measured and the results showed that the above separation retards the heat transfer significantly from that of the forced convection. It was also revealed that the heat transfer by forced, natural, and combined convections can be classified with the above parameter as (Gr_θ^*/Re_L^2.5)<0.2,(Gr_θ^*)/Re_L^2.5)>3, and 0.2<(Gr_θ^*/Re_L^2.5)<3, respectively. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(3): 127– 142, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20151     

Screening of novel water/ionic liquid working fluids for absorption thermal energy storage in cooling systems

Absorption thermal energy storage (ATES) is significant for renewable/waste energy utilization in buildings. The ATES systems using ionic liquids (ILs) are explored to avoid crystallization and enhance the performance. Property model and cycle model have been established with verified accuracies. Based on the preliminary screening, seven ILs are found feasible to be ATES working fluids, while four ILs ([DMIM][DMP], [EMIM][Ac], [EMIM][DEP], and [EMIM][EtSO₄]) have been selected for detailed comparisons. The coefficient of performance (COP) and energy storage density (ESD) of the ATES using different H₂O/ILs are compared with H₂O/LiBr. Results show that the operating temperatures of LiBr are constrained by crystallization, limiting the COPs and ESDs under higher generation temperatures and lower condensation temperatures. With varying T_g, [DMIM][DMP] yields higher COPs with T_g above 100°C and [EMIM][Ac] yields comparable ESDs (67.7 vs 67.1 kWh/m³) with T_g around 120°C, as compared with LiBr. The maximum COP is 0.745 for [DMIM][DMP]. With varying T_c, [DMIM][DMP] yields higher COPs with T_c below 38°C and [EMIM][Ac] yields higher ESDs with T_c below 33°C, as compared with LiBr. The maximum ESD is 87.5 kWh/m³ for [EMIM][Ac]. With varying T_e, [DMIM][DMP] yields higher COPs with T_e above 8°C, as compared with LiBr. The maximum ESD of ILs is 104.0 kWh/m³ for [EMIM][EtSO₄]. Comparing with the volume-based ESDs, the differences between ILs and LiBr are smaller for the mass-based ESDs. This work can provide suggestions for the selection of novel working fluids for ATES for performance and reliability enhancement.     

A thermal nonequilibrium model to natural convection inside non-Darcy porous layer surrounded by horizontal heated plates with periodic boundary temperatures

This article displays a numerical investigation on natural convection within non-Darcy porous layer surrounded by two horizontal surfaces having sinusoidal temperature profiles with difference in phase and wave number. The Darcy–Brinkman–Forchheimer model and local thermal nonequilibrium condition have been employed. Simulations have been performed for wide ranges of inertia coefficient (10^–4 ≤ Fs/Pr* ≤ 10^–2), thermal conductivity ratio (0.1 ≤ K _r ≤ 100), phase difference (0 ≤ β ≤ π), modified Rayleigh number (200 ≤ Ra* ≤ 1000), wavelength (3 ≤ k ≤ 12), and nondimensional heat transfer coefficient (0.1 ≤ H ≤ 100). Results demonstrate that Nusselt number highly relies on Fs/Pr*, K _r, β, Ra*, and k as compared to H. A considerable enhancement in fluid, solid, and overall Nusselt numbers has been observed with diminishing Fs/Pr* and β and increasing k, K _r, and H. The raising in β has a significant impact on Nu for smaller k and this effect is almost ignored when k > 12. The increase in Ra*, K _r, β, and H and decrease in Fs/Pr* and k acts to reduce the severity of nonequilibrium zone and increase the size of thermal equilibrium zone. The influence of H on nonequilibrium area is more evident than K _r.     

Burnout of soot particles in a two-stage burner with a JP-8 surrogate fuel

This work focuses on the understanding of the oxidation of soot particles which were the result of using a JP-8 surrogate fuel in a two-stage burner. The two-stage system consists of an initial premixed burner where soot was generated with an air/fuel mixture, specifically a JP-8 surrogate (m-xylene and n-dodecane), under a variety of conditions. Downstream, the soot-laden combustion gases were passed through a second, flat-flame burner where soot was burned out under fuel-lean or slightly fuel-rich conditions. Soot oxidation in the secondary burner was determined by investigating particle size distribution (PSD), flame temperature, gas-phase composition, soot surface area, and soot morphology and nanostructure as a function of the height above the second burner (HAB). Measurements of soot size distribution and number concentration as a function of the HAB under fuel lean (Φoverall = 0.8) and slightly rich (Φoverall = 1.14) conditions showed a decrease in particle mean diameter and a significant increase in number concentration in the region where O₂ concentration decreased. In this region, the effectiveness factor for O₂ was found to be 1, indicating the potential for internal oxygen diffusion and burning. This caused both the breakup of the bridges cementing primary particles and the rupture of the primary particles. Higher in the burner, where modeling suggested the presence of OH^*, soot oxidation was attributed to OH^* mechanisms which are faster as compared to O₂ oxidation.     

Low-temperature deposition of amorphous silicon solar cells

We develop amorphous silicon (a-Si:H)-based solar cells by plasma-enhanced chemical vapor deposition (PECVD) at deposition temperatures of T_s=75°C and 100°C, compatible with low-cost plastic substrates. The structural and electronic properties of low-temperature standard PECVD a-Si:H, both doped and undoped, prevent the photovoltaic application of this material. In this paper, we demonstrate how to achieve device-quality a-Si:H even at low deposition temperatures. In the first part, we show the dependence of structural and carrier transport properties on the deposition temperature. The sub-band gap absorption coefficient and the Urbach energy increase when the deposition temperature declines from T_s=150°C to 50°C, the conductivity of doped layers and mobility-lifetime product of intrinsic a-Si:H drop drastically. Therefore, in the second part we investigate the impact of increasing hydrogen dilution of the feedstock gases on the properties of low-temperature a-Si:H. We restore n-type a-Si : H device-quality conductivity while the p-type a-Si:H conductivity is still inferior. For undoped layers, we depict the hole diffusion length, the mobility-lifetime product for electrons, the Urbach energy, and sub-band gap absorption coefficient as a function of the hydrogen dilution ratio. We incorporate these optimized materials in solar cell structures of single and multilayer design and record initial efficiencies of η=6.0% at a deposition temperature of T_s=100°C, and η=3.8% at T_s=75°C. For prospective opaque polymer substrates we develop, in addition to our conventional pin cells, devices in nip design with similar performance.     

Theoretical storage capacity for solar air pretreatment liquid collector/regenerator

A new liquid regeneration equipment—solar air pretreatment collector/regenerator for liquid desiccant cooling system is put forward in this paper, which is preferable to solution regeneration in hot and moist climate in South China. The equipment can achieve liquid regeneration in lower temperature. When the solution and the air are in “match” state in collector/regenerator, a match air to salt mass ratio ASMR^* is found by theoretical study in which there is the largest theoretical storage capacity SC_max. At T_r = 60 °C and X_in = 2.33 kg/kg, theoretical calculation discovers when Y_in drops from 29 to 14 g/kg, the SC_max increase 50% compared with ASMR^* being around 26–27. After two new concepts of the effective solution proportion (EPS) and the effective storage capacity (ESC) are defined, it is found by theoretical calculation that when ESP drops from 100% to 67%, ESC raises lowly, not drops and liquid outlet concentration C_str.sol increases from 40% to 49% in which its increment totals to 90%. All these data explain fully that air pretreatment liquid regeneration equipment enables to improve the performance of liquid desiccant cooling system.     

Experimental and theoretical investigation of a solar heating system with heat pump

In this study, the performance of a solar heating system with a heat pump was investigated both experimentally and theoretically. The experimental results were obtained from November to April during the heating season. The experimentally obtained results are used to calculate the heat pump coefficient of performance (COP), seasonal heating performance, the fraction of annual load met by free energy, storage and collector efficiencies and total energy consumption of the systems during the heating season. The average seasonal heating performance values are 4.0 and 3.0 for series and parallel heat pump systems, respectively. A mathematical model was also developed for the analysis of the solar heating system. The model consists of dynamic and heat transfer relations concerning the fundamental components in the system such as solar collector, latent heat thermal energy storage tank, compressor, condenser, evaporator and meteorological data. Some model parameters of the system such as COP, theoretical collector numbers (N_c), collector efficiency, heating capacity, compressor power, and temperatures (T₁, T₂, T₃, T_T) in the storage tank were calculated by using the experimental results. It is concluded that the theoretical model agreed well with the experimental results.     

A hybrid solar-assisted adsorption cooling unit for vaccine storage

A concept of a hybrid adsorption cooling unit for vaccine storage utilizing solar energy as a main power supply and a gas burner as an alternative power supply has been developed. The components of the cooling unit have been designed to work under the weathering conditions of Burkina Faso, West coast of Africa according to the requirements of the World Health Organization. For the first adsorber, which is driven by a gas burner, zeolite-13X has been selected. For the second adsorber to be driven by solar energy selective water sorbent SWS-2L has been applied. Water is selected as a refrigerant for both adsorbents. Theoretical investigations of the expected performance of the designed cooling unit have shown a coefficient of performance (COP) of 0.28 for the solar-operated system based on the heat input to the adsorption unit, at the design conditions of T_evap=−5 °C, T_con=55 °C, T_ads=38 °C, T_des(max)=122 °C. For the gas-heated system, also a COP of 0.28 has been estimated at the design conditions of T_evap=−5 °C, T_con=55 °C, T_ads=38 °C, T_des(max)=280 °C. The variations of COP, cooling capacity and the heating power required to operate both systems have been estimated for a broad range of desorption temperatures. It turns out that the SWS-2L/water system is much more sensitive to the operating conditions than the zeolite-13X/water system. The obtained results should serve in designing both control and heating components of the cooling unit.