Thermal Radiation Losses Research Articles

Modeling the external flow of a novel HorseShoe receiver and the evaluation of thermal performance

The linear receiver of a Parabolic Trough Collector is the most critical element in the entire system. The Universal Vacuum Air Collector concept is the most extended type of receiver in both experimental and industrial facilities. Besides their considerable cost, their efficiency usually drops as operation time passes. This is mainly due to a partial loss of vacuum in the evacuated annulus between the absorber and the glass cover. An alternative design called HorseShoe receiver is proposed in this work, whose main goal is to maintain the thermal performance throughout its entire lifespan. This innovative receiver is indicated for low-to-medium temperature ranges, which is particularly suitable for solar heat for industrial processes. It consists of a horseshoe-like cavity absorber having its upper border insulated. In addition, two main advantages can be taken by using two symmetric lenses as glass cover: reconcentrate solar radiation into the cavity (improvement of the intercept factor) and protect stratification conditions (reduction of thermal losses). A transient numerical model with customized boundary conditions has been implemented to evaluate both thermal performance and temperature difference in the absorber domain, which is critical for the thermal stress conditions. For that purpose and as a key contribution, not only the Heat Transfer Fluid (HTF) temperature but also the heat transfer coefficient in the duct are set. In particular, HTF temperature ranges from 80 °C to 220 °C and the inner heat transfer coefficient from 600 W/(m 2 ⋅ K) to 1800 W/(m 2 ⋅ K). Results show that numerical thermal performance is above 96%, which is mainly due to the reduction of thermal radiation losses, where the absorber active surface emittance is ϵ a b s = 0 . 3 . Since no inclination of the receiver has been considered in this initial study, it is shown that the air inside the cavity is stratified, which reduces convective losses. Moreover, temperature difference between the coldest and the hottest spot of the absorber is no higher than 30 K, which is affordable from a technical point of view. A polynomial heat losses correlation is also provided, whose parameters are on the same order of those by conventional receiver correlations available in the literature. • A new concept of solar linear cavity receiver (HorseShoe receiver) is proposed. • Thermal losses have been evaluated numerically. • Thermal performance is above 96% under the selected operation conditions. • The symmetric lenses enhance air stratification. • Most of the thermal losses are due to thermal radiation.

All-Day Freshwater Harvesting by Selective Solar Absorption and Radiative Cooling.

Solar interfacial evaporation for freshwater harvesting has received attention recently due to its high evaporation rate and environmental friendliness. Traditional interfacial evaporation mostly uses black porous polymers to absorb solar radiation and transport water which involve high thermal radiation loss to the environment and heat conduction loss to the bulk water. In addition, the freshwater collection ratio is usually lower than the solar evaporation ratio due to the high temperature of the condensation surface under solar irradiation, and no freshwater can be harvested at night due to the absence of sunlight. Here, we design an all-day freshwater-harvesting device using a solar-selective absorber (SSA) and sky radiative cooling. The prepared SSA with a high solar absorptance of 0.92 and a mid-infrared thermal emittance of 0.11 provides a great solar-thermal conversion performance (87.1% vs 51.4% for the black porous polymer at 25 °C) by minimizing the thermal radiation loss, and a hollow structure is also used to reduce the conductive heat loss, resulting in a high solar evaporation rate (1.23 vs 0.79 kg m-2 h-1 for the black porous polymer). In addition, a transparent radiative cooling polymer after plasma treatment is used for freshwater collection by enhancing the solar transmittance (0.92) and mid-infrared thermal emittance (0.91 at 25 °C). A theoretical freshwater collection rate of 0.044 kg m-2 h-1 is achieved at night-time. Outdoor results show that the all-day water harvesting is 0.87 kg m-2. This strategy to achieve all-day water collection by coupling with the SSA and transparent radiative cooling has potential application in the field of desalination and freshwater harvesting in tropical desert areas.

Construction of coronal hole and active region magnetohydrostatic solutions in two dimensions: Force and energy balance

Coronal holes and active regions are typical magnetic structures found in the solar atmosphere. We propose several magnetohydrostatic equilibrium solutions that are representative of these structures in two dimensions. Our models include the effect of a finite plasma-β and gravity, but the distinctive feature is that we incorporate a thermal structure with properties similar to those reported by observations. We developed a semi-analytical method to compute the equilibrium configuration. Using this method, we obtain cold and under-dense plasma structures in open magnetic fields representing coronal holes, while in closed magnetic configurations, we achieve the characteristic hot and over-dense plasma arrangements of active regions. Although coronal holes and active regions seem to be antagonistic structures, we find that they can be described using a common thermal structure that depends on the flux function. In addition to the force balance, the energy balance is included in the constructed models using an a posteriori approach. From the two-dimensional computation of thermal conduction and radiative losses in our models, we infer the required heating function to achieve energy equilibrium. We find that the temperature dependence on height is an important parameter that may prevent the system from accomplishing thermal balance at certain spatial locations. The implications of these results are discussed in detail.

Solar Selective Absorber for Emerging Sustainable Applications

Solar selective absorbers (SSAs) possess high sunlight absorption (300–2500 nm) and low infrared thermal radiative losses (2.5–25 μm), which are undoubtedly the best choice for photothermal conversion process, and SSAs have been widely used in concentrating solar power, solar water heating, and solar drying. Recently, to promote the realization of “double carbon” goal, SSAs have received widespread attentions, many emerging sustainable applications have been developed. In this review, the recent developments of SSAs and their latest sustainable applications in solar‐driven seawater desalination, multistage solar desalination, atmospheric water harvesting (AWH), wastewater treatment, solar thermophotovoltaics (STPVs), hybrid photovoltaic‐thermal (HPVT), solar‐thermoelectric generators (STEG), personal thermal management (PTM), photothermal catalysis, photothermal deicing, and photothermal sterilization, etc. are systematically summarized. Also, the challenges as well as future opportunities of SSAs are discussion. It is expected that this review will effectively complement the published comments on SSAs and provide more inspirations on sustainable applications of SSAs in the future.

Role of Non-ideal Dissipation with Heating–Cooling Misbalance on the Phase Shifts of Standing Slow Magnetohydrodynamic Waves

We analyse the phase shifts of standing, slow magnetohydrodynamic (MHD) waves in solar coronal loops using a linear MHD model taking into account the role of thermal conductivity, compressive viscosity, radiative losses, and heating-cooling misbalance. We estimate the phase shifts in time and space of density and temperature perturbations with respect to velocity perturbations and also calculate the phase difference between density and temperature perturbations. The overall significance of compressive viscosity is found to be negligible for most of the loops considered in the study. For loops with high background density and/or low background temperature, the role of radiative losses (with heating-cooling misbalance) is found to be more significant. Also the effect of heating-cooling misbalance with a temperature- and density-dependent heating function is found to be more significant in the case of longer loop lengths ($L=500$\, Mm). We derived a general expression for the polytropic index [$\gamma_{\rm eff}$] and found that under linear MHD the effect of compressive viscosity on polytropic index is negligible. The radiative losses with constant heating lead to a monotonic increase of $\gamma_{\rm eff}$ with increasing density whereas the consideration of an assumed heating function [$H(\rho,T) \propto \rho^{a}T^{b}$, where $a=-0.5$ and $b=-3$] makes the $\gamma_{\rm eff}$ peak at a certain loop density. We also explored the role of different heating functions by varying the free parameters $a$ and $b$ for a fixed loop of $\rho_0 = 10^{-11}$\, kg $\text{m}^{-3}$, $T_0 = 6.3$\, MK and loop length $L= 180$\, Mm. We find that the consideration of different heating functions [$H(\rho,T)$] leads to a significant variation in the phase difference between density and temperature perturbations; however, the polytropic index remains close to a value of 1.66.

Conjugate radiation-convection-conduction simulation of cubic lattice solar receiver with high porosity for high-temperature heat absorption

Direct simulation was performed for the solar porous receiver having cubic lattice as elementary structure with high porosity (0.80 - 0.98). The cell size was changed in four steps from 0.49 mm to 2.94 mm at three levels of the power over air mass (POM). Silicon carbide (SiC) was assumed as receiver material, and the absorptivity of the wall surface was assigned 0.9. The numerical data for the porous receiver was compared with the honeycomb receiver with low porosity. Such comparison proved the superiority of the highly porous receiver: the receiver-exit temperature and the receiver efficiency surpass those of honeycomb receiver at the same level of POM. Regarding the size effects, the performance of the porous receiver improves as the cell size reduces. When the cell size is 0.98 mm at POM =1000 kJ/kg, the receiver exit temperature increases beyond 1000 K and the receiver efficiency 0.8. When the cell size is 0.49 mm at POM = 2000 kJ/kg, the receiver exit temperature exceeds 1700 K and the efficiency 0.8. The numerical results thus demonstrated that the smaller cell size maintains the efficiency at the higher levels of POM. The mechanism for superiority of the small cell size was investigated through analysis of the heat transfer loss. This investigation revealed that the convective heat transfer enhancement in the case of small cell size decreases the temperature in the inlet region and attenuates the thermal radiation loss. Therefore, the high performance of the small-cell size receiver is attributed to the cooling effect of the air stream with high heat transfer coefficient.

A fast multi-dimensional magnetohydrodynamic formulation of the transition region adaptive conduction (TRAC) method

We have demonstrated that the transition region adaptive conduction (TRAC) method permits fast and accurate numerical solutions of the field-aligned hydrodynamic equations, successfully removing the influence of numerical resolution on the coronal density response to impulsive heating. This is achieved by adjusting the parallel thermal conductivity, radiative loss, and heating rates to broaden the transition region (TR), below a global cutoff temperature, so that the steep gradients are spatially resolved even when using coarse numerical grids. Implementing the original 1D formulation of TRAC in multi-dimensional magnetohydrodynamic (MHD) models would require tracing a large number of magnetic field lines at every time step in order to prescribe a global cutoff temperature to each field line. In this paper, we present a highly efficient formulation of the TRAC method for use in multi-dimensional MHD simulations, which does not rely on field line tracing. In the TR, adaptive local cutoff temperatures are used instead of global cutoff temperatures to broaden any unresolved parts of the atmosphere. These local cutoff temperatures are calculated using only local grid cell quantities, enabling the MHD extension of TRAC to efficiently account for the magnetic field evolution, without tracing field lines. Consistent with analytical predictions, we show that this approach successfully preserves the properties of the original TRAC method. In particular, the total radiative losses and heating remain conserved under the MHD formulation. Results from 2D MHD simulations of impulsive heating in unsheared and sheared arcades of coronal loops are also presented. These simulations benchmark the MHD TRAC method against a series of 1D models and demonstrate the versatility and robustness of the method in multi-dimensional magnetic fields. We show, for the first time, that pressure differences, generated during the evaporation phase of impulsive heating events, can produce current layers that are significantly narrower than the transverse energy deposition.

When Hot Meets Cold: Post-flare Coronal Rain

Abstract Most solar flares demonstrate a prolonged, hour-long post-flare (or gradual) phase, characterized by arcade-like, post-flare loops (PFLs) visible in many extreme ultraviolet (EUV) passbands. These coronal loops are filled with hot (∼30 MK) and dense plasma that evaporated from the chromosphere during the impulsive phase of the flare, and they very gradually recover to normal coronal density and temperature conditions. During this gradual cooling down to ∼1 MK regimes, much cooler (∼0.01 MK) and denser coronal rain is frequently observed inside PFLs. Understanding PFL dynamics in this long-duration, gradual phase is crucial to the entire corona–chromosphere mass and energy cycle. Here we report a simulation in which a solar flare evolves from pre-flare, over the impulsive phase all the way into its gradual phase, which successfully reproduces post-flare coronal rain. This rain results from catastrophic cooling caused by thermal instability, and we analyze the entire mass and energy budget evolution driving this sudden condensation phenomenon. We find that the runaway cooling and rain formation also induces the appearance of dark post-flare loop systems, as observed in EUV channels. We confirm and augment earlier observational findings, suggesting that thermal conduction and radiative losses alternately dominate the cooling of PFLs.

Manipulation of thermal radiation by using photonic crystals

This paper focuses on manipulating thermal emission and radiation loss of heat energy in a heat waveguide. A One-Dimensional Photonic Crystal is used as a waveguide clad to prohibit the thermal emission from escaping. The model may reduce the radiation loss of heat energy in the waveguide core, and heat energy can be confined to propagate along the waveguide’s longitude axis. The waveguide clad comprises alternative layers of high and low refractive index materials containing sufficient electromagnetic stop bands to trap the thermal emission from escaping out of the waveguide. The numerical simulation of the model shows that the forbidden bandgap of photonic crystal structures with alternative layers of silica and silicon has width enough to make heat energy be confined within the waveguide core so that efficient heat energy transmission can be achieved along the longitude axis of the waveguide.

Conceptual design of porous volumetric solar receiver using molten salt as heat transfer fluid

Thermal radiation loss hinders the high-efficient operation of solar receiver at high temperature. Porous volumetric solar receiver using molten salt instead of air as heat transfer fluid is proposed. A comprehensive literature review is done to investigate the optical and radiative properties of molten in solar and infrared spectra. Direct pore-scale numerical simulation method based on X-ray computed tomography technique is applied to compare the fluid flow and heat transfer performance of molten salt and air porous volumetric solar receiver. The results present that some types of molten salts behave to be transparent in solar spectrum and opaque in infrared spectrum, which allow the penetration of solar radiation while strongly absorb the infrared emission in the receiver. The thermal efficiency of Hitec porous volumetric solar receiver is higher than traditional air porous receiver especially at higher working temperature, and it is improved by 9.6% at receiver’s outlet temperature of 1000 K. Due to its large heat storage capability and efficient convective heat transfer, small mass flow rate is required in the molten salt receiver to absorb solar radiation, which leads to orders-magnitude smaller pressure drop for the Hitec porous receiver. Further research related to this type of porous volumetric solar receiver is outlined with respect to experiment verification and application of high temperature molten salt.

Effect of Thermal Conductivity, Compressive Viscosity and Radiative Cooling on the Phase Shift of Propagating Slow Waves with and Without Heating–Cooling Imbalance

We study phase shifts of the propagating slow waves in coronal loops invoking the effects of thermal conductivity, compressive viscosity, radiative losses and heating-cooling imbalance. We derive a general dispersion relation and solve it to determine phase shifts of density and temperature perturbations relative to the velocity and their dependence on equilibrium parameters ($\rho_0$, $T_0$). We estimate phase difference ($\Delta \phi$) between density and temperature perturbations and its dependence on $\rho_0$ and $T_0$. The effect of viscosity on the phase shifts was found negligible. The role of radiative losses along with h/c imbalance for chosen specific heating function ($H(\rho, T) \propto \rho^{-0.5} T^{-3}$) in determining phase shifts, is found to be significant for the high density and low temperature loops. The h/c imbalance can increase the phase difference ($\Delta \phi \approx 140^\circ$) for low temperature loops compared to the constant heating case ($\Delta \phi \approx 30^\circ$). We derive a general expression for the polytropic index. We find that in the presence of thermal conduction alone, the polytropic index remains close to its classical value for all the considered $\rho_0$ and $T_0$. However, it reduces to a value $1.2$ when loop density is decreased by an order of magnitude compared to its normal coronal value. We find that the inclusion of radiative losses, with or without h/c imbalance, cannot explain the observed polytropic index. The thermal ratio ($d$) needs to be enhanced by an order of magnitude, in order to explain its observed value $1.1 \pm 0.02$ in the solar loops. We also explore the role of different heating functions for typical coronal parameters and found that although the polytropic index remains close to its classical value, the phase difference is highly dependent on the form of heating function (The abstract is restructured for arxiv).

Energy Partition in Four Confined Circular-Ribbon Flares

In this study, we investigated the energy partition of four confined circular-ribbon flares (CRFs) near the solar disk center, which are observed simultaneously by SDO, GOES, and RHESSI. We calculated different energy components, including the radiative outputs in 1$-$8, 1$-$70, and 70$-$370 {\AA}, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accelerated electrons, and magnetic free energy before flares. It is found that the energy components increase systematically with the flare class, indicating that more energies are involved in larger flares. The magnetic free energies are larger than the nonthermal energies and radiative outputs of flares, which is consistent with the magnetic nature of flares. The ratio $\frac{E_{nth}}{E_{mag}}$ of the four flares, being 0.70$-$0.76, is considerably higher than that of eruptive flares. Hence, this ratio may serve as an important factor that discriminates confined and eruptive flares. The nonthermal energies are sufficient to provide the heating requirements including the peak thermal energy and radiative loss. Our findings impose constraint on theoretical models of confined CRFs and have potential implication for the space weather forecast.

Radiative heat loss estimation of building envelopes based on 3D thermographic models utilizing small unmanned aerial systems (sUAS)

The advent of sUAS (small unmanned aerial systems – or surveying drones) technology has made comprehensive thermographic analyses of the built environment feasible. Advantages over traditional thermal survey techniques include a significant increase in ease of three-dimensional (3D) navigation around large structures as well as the ability to perform data-rich measurements. 3D building envelope thermographic models represent the building surface temperatures and can be created using structure-from-motion photogrammetry techniques with the collected high-overlap sUAS thermographic images. This paper introduces an end-to-end workflow for measuring radiative heat loss from building envelopes. This includes the setup and process required for quickly creating accurate 3D thermographic models and their analysis with software developed for this purpose. Three analytical models for building envelope radiative heat loss are applied and tested for viability through controlled experiments. The workflow is then demonstrated by evaluating the thermal radiation losses of two buildings on the campuses of the University of North Georgia. Our findings suggest the workflow can quickly provide good radiative heat loss measurements and may be a valuable addition to more comprehensive thermal analysis techniques.

A metal nanoparticle assembly with broadband absorption and suppressed thermal radiation for enhanced solar steam generation

The efficiency of solar steam generation is boosted by broadband solar absorption and suppressed thermal radiation loss of a nickel-nanoparticle-based spectrally selective absorber.

Using CFD and ray tracing to estimate the heat losses of a tubular cavity dish receiver for different inclination angles

The process of obtaining an accurate estimate of the heat losses of a tubular cavity receiver absorbing concentrated solar energy from a parabolic dish at various inclination angles and wind speeds is described. Computational fluid dynamics (CFD) was used to simulate the conjugate heat transfer of the absorbed solar radiation to the heat transfer fluid while considering thermal radiation as well as forced and natural convective heat losses. Validation is performed against an experimental heating test at full-scale using heated air and measured wind conditions. On-sun conditions were modelled using the ray-tracing software, SolTrace, adapted for complex geometry receivers using ANSYS mesher and user coding. A 200 million ray result was found to be ray and mesh independent for a meshed receiver surface containing 30000 elements. The SolTrace heat flux distribution was implemented as a volumetric source in ANSYS Fluent employing user-defined functions. The losses due to thermal radiation out of the cavity, and due to natural convection (using the buoyancy-driven mechanism afforded by gravity and the ideal gas formulation) and forced convection (due to the atmospheric wind) are presented. For the dish considered, 40–50% of the absorbed solar power was transferred to the heat transfer fluid for dish orientations from −45° to 45°, and wind speeds between 0.5 m/s and 4 m/s. This variation was mainly due to a variation in convective heat losses, with thermal radiative heat losses remaining constant at about 30%. The Nusselt numbers from the CFD simulations are compared against correlations from literature.

DuPont Clean Technologies wins contract to supply Hengyi with alkylation unit

The process of obtaining an accurate estimate of the heat losses of a tubular cavity receiver absorbing concentrated solar energy from a parabolic dish at various inclination angles and wind speeds is described. Computational fluid dynamics (CFD) was used to simulate the conjugate heat transfer of the absorbed solar radiation to the heat transfer fluid while considering thermal radiation as well as forced and natural convective heat losses. Validation is performed against an experimental heating test at full-scale using heated air and measured wind conditions. On-sun conditions were modelled using the ray-tracing software, SolTrace, adapted for complex geometry receivers using ANSYS mesher and user coding. A 200 million ray result was found to be ray and mesh independent for a meshed receiver surface containing 30 000 elements. The SolTrace heat flux distribution was implemented as a volumetric source in ANSYS Fluent employing user-defined functions. The losses due to thermal radiation out of the cavity, and due to natural convection (using the buoyancy-driven mechanism afforded by gravity and the ideal gas formulation) and forced convection (due to the atmospheric wind) are presented. For the dish considered, 40–50% of the absorbed solar power was transferred to the heat transfer fluid for dish orientations from −45° to 45°, and wind speeds between 0.5 m/s and 4 m/s. This variation was mainly due to a variation in convective heat losses, with thermal radiative heat losses remaining constant at about 30%. The Nusselt numbers from the CFD simulations are compared against correlations from literature.

Comparative Study on the Dimethyl Ether Combustion Characteristics in Normal and Inverse Diffusion Spherical Flame Geometries.

This paper makes a comparative study on the normal diffusion flame (NDF) and inverse diffusion flame (IDF) characteristics of dimethyl ether (DME) in microgravitational spherical diffusion flame geometry by simulations with detailed fuel chemistry and a transport model. It is found that there always existed two combustion modes (i.e., hot flame and cool flame) in either NDF or IDF condition. The combustion progress of hot flames was controlled by diffusive mixing, while that of cool flames was controlled by low-temperature competing kinetics. The cool-flame structure dynamics were far away from the chemical equilibrium. The low-temperature branching rate of DME was positively dependent on the oxygen level, while its termination rate was enhanced with the increasing temperature. Being rather distinct from the NDF counterpart, DME IDFs had the oxygen-enriched combustion feature in either hot- or cool-flame condition. Furthermore, DME hot-flame extinction was induced by thermal radiative loss, while the cool-flame extinction was induced especially by the decrease of the low-temperature branching rate. Compared with hot NDFs, it would be of less effectiveness to control the hot IDF combustion process by positive measures. However, combustion in the latter configuration was much more stable than the former. In either NDF or IDF geometry, the cool-flame chemistry could help to extend the fuel flammability range considerably, and the two-reaction-zone structure of cool flame was responsible for cool-flame stability. In addition, the IDFs had much better ignition performance than the NDF counterpart.

Fire behaviors of fuels with different sootiness levels in hot and humid conditions

The behaviors of fires fueled by materials that produce different levels of soot (diesel and alcohol) were studied under hot and humid conditions with natural ventilation. Experimental tests were performed under different initial ambient temperatures (20 °C and 30 °C) and relative humidity levels (50 % and 90 %), and flame temperature, thermal radiation and mass loss rate were measured. A theoretical flame radiation model was established and verified. The fire development index (FDI) was defined as the ratio of the peak flame temperature, Tp, to the duration, tp, during initial fire development stage, and the fire severity index (FSI) was defined as the product of the flame thermal radiation, Rav, and the duration, td, during fully developed stage. The results validated the reasonableness of the established theoretical model. During initial fire development stage, increasing the initial ambient temperature increased the FDI, while increasing the relative humidity decreased it. During fully developed stage, increasing the initial ambient temperature or humidity resulted in a decrease in the FSI under limited-fuel conditions, and the ambient temperature more significantly affected the pool fires fueled by alcohol than those that consumed diesel. Additionally, under conditions of high temperature and high humidity, both the indices were reduced.

Study on lean burn limits and burning characteristics of n-heptane with effects of hydrogen enrichment

Lean combustion can be a more effective method to enhance the thermal efficiency of diesel engine, while also face incomplete-combustion and long-combustion duration issues at ultra-lean conditions. Effects of hydrogen, known with wider flame limits and greater burning velocity, on lean burn limits and burning characteristics of n-heptane were studied fundamentally based on optical experiments and chemical kinetics analysis. The results showed that the laminar flame appeared spherically from λ = 0.8 to λ = 1.5 by spark ignition energy of 37 mJ, whereas leaner mixture, λ ≥ 1.6, could only be ignited by 3000 mJ. However, the low ignition energy failed to burn the ultra-lean mixture, while high ignition energy disturbed the flame morphology. The buoyancy appeared near lean-limits due to lower burning velocity and rapid increase of thermal radiation losses. Lean burn limits of n-heptane increased from λ = 1.9 to λ = 4.2 at 393K, λ = 2.0 to λ = 4.3 at 433K and λ = 2.1 to λ = 4.4 at 473K under H2 addition from 0% to 90%. The increasing impact became more significant at H2 ≥ 70%. Besides, as lifting initial temperature, 393–473K, the lean-limits increased 0.2 λ only. With increase of H2, H increased faster than O and OH because more H2 reacted with both O and OH to produce H. CH2O became prominent among C–H–O species, which reacted with H increased rapidly under H2 addition. Consequently, H and CH2O played a substantial role to improve the lean burn limits and burning velocity of n-heptane under hydrogen addition.

Thermal performance of PCM-to-air heat exchangers in hot desert climate

Utilization of PCM-to-Air Heat Exchangers (PAHXs) in building free cooling applications has been reporting the insufficient cooling charging energy during the PCM solidification, which affects the overall system performance. This study reports the improvements in the cooling potential of the PAHX considering the climatic characteristics of the hot desert climate by taking the advantage of thermal radiation losses to the sky during nighttime. Parametric studies were conducted for the developed PAHX unit with respect to the location, airflow rate, and the PCM type. The improved PAHX unit was integrated into the mechanical ventilation system of an office space under hot desert climatic conditions considering various operational conditions. It was concluded that the PAHX unit outlet air could be directly supplied to the indoor space through a direct free cooling application to satisfy the cooling demand; also, it could be introduced to the mechanical cooling unit to minimize the energy consumption. The results showed that the thermal comfort levels were enhanced by up to 18%, and the cooling system energy consumption was reduced by 18.5% saving an amount of energy up to 10.8 kWh/week.