This research work was sponsored by the National Key Basic Research Program of China (No.2015CB251303), and the National Natural Science Foundation of China (No. 51276005).

1. Experimental Setup
NOTE: The adsorption refrigeration system was composed of the adsorption bed, the evaporator, the condenser, the vacuum pump, and the solar trough collector (Figure 1). An automatic solar tracking device with a parabolic trough was manufactured and applied in the system to improve the efficiency of the solar collector. The automatic solar tracking trough was driven by the worm-gear device as shown in Figure 2. The device consisted of the stepper motor, the worm, the gear, the moving limit block, and the manual wheel. The dimensions of the worm-gear device were 21 x 80 cm2. The trough collector concentrated the solar rays onto the adsorbent bed, which was located along the focus line of the parabolic trough.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/55925/55925fig1v2.jpg" /> 
Figure 1: Experimental system for solar adsorption refrigeration. (Top) Schematic of the system; (bottom) Photograph of the experimental setup. The top panel presents the components of the experimental system, which involves the evaporator, the condenser, the vacuum pump,&#160;etc.&#160;The bottom panel displays the photograph of the assembled adsorption refrigeration system. In the system, the evaporator and the condenser is of the fin-tube structure, a kind of compact heat exchanger. The adsorption bed is reformed from a vacuum solar collector, which can capture solar energy effectively.&#160;<a href="//cloudfront.jove.com/files/ftp_upload/55925/55925fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/55925/55925fig2v2.jpg" /> 
Figure 2: The structure of the worm gear box. The worm gear box is the device that transforms the rotation of the stepper motor into the solar tracking movement of the parabolic trough. In addition to the stepper motor, the worm gear box also involves the reducer, the manual wheel, the worm shaft,&#160;etc.&#160;Pulling the manual/automatic switch handle to the left, gears 5a and 5b are disengaged. Thus, the trough can be manually controlled by rotating the hand wheel. Pulling the manual/automatic switch handle to the right, gears 5a and 5b are engaged together. Thus, it is controlled automatically by the stepper motor.
<ol>
	<li>Connect the tracking solar collector to the worm-wheel shaft by a welding method. Pass the rotation of the stepper motor to the solar collector by matching the gear and the worm. Fix the tubular adsorption bed together with the collector with a pair of pipe collars. 
	NOTE: Driven by the stepper motor, the system rotates daily from the east to the west to follow the solar movement automatically.</li>
	<li>Adjust the tilting angle of the trough to ground level, according to the variation of the solar altitude in different seasons. Determine the tilting angle &#946; of the trough by the local latitude &#934; and the solar declination &#948;, and the formula &#946; = &#934;&#160;- &#948;. Manually rotate the little wheel that is located at the bottom of the angle adjustment lever to regulate the tilting angle of the trough (the part of No. 13, Figure 1). 
	NOTE: In this way, the solar radiation is as normal as possible on the trough. The experimental system was located in the campus of Beijing University of Technology, at the latitude 39.89 &#176;N and longitude 116.38 &#176;E. The adsorption bed took a cylindrical form. It was reformed from a vacuum solar receiver of a tube (Figure 3).</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/55925/55925fig3v2.jpg" /> 
Figure 3: Structure of the adsorption bed and the deployment of the temperature probe. (Top) Schematic of the bed structure; (bottom) The temperature probes and the mass transfer channel in the bed. The top panel shows the basic structure of the bed. The adsorbent material is put into the annular cavity between the solar-absorbing tube and the copper cooling channel. The solar rays penetrate the glass tube and fall onto the surface of the solar-absorbing tube. Then, by heat conduction, the solar energy is transferred to the adsorbent material inside the bed. The bottom panel shows the location of the temperature probes. These probes are used to monitor the temperature change of the bed during the adsorption/desorption process.&#160;<a href="//cloudfront.jove.com/files/ftp_upload/55925/55925fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="3">
	<li>To promote the capture of the solar energy, coat the solar-absorbing tube of the bed, (made of stainless steel with d = 64.5 mm) with a layer of black chrome deposit by the vacuum coating method. Please refer to the previously published literature about selective coating for more information about this technique13. Ensure that the solar absorption rate of the coating layer is 0.95, the infrared emissivity is 0.15, and the thickness of the coating layer is 0.08 mm. 
	NOTE: This coating layer helps to catch the solar radiation effectively but emits very slightly itself. As a result, the solar energy gets into the adsorption bed easily and is transformed to thermal enthalpy of the adsorbent effectively.</li>
	<li>Insert a copper tube (d = 20 mm) along the axis of the adsorption bed. Fix the copper tube to the bed with the flange (see Figure 3, top panel). The copper tube functions as the cooling channel of the bed during the adsorption process.</li>
	<li>Fill the adsorbent material in the annular cavity in the bed that is formed by the bed tube and the copper cooling channel. Use SAPO-34 zeolite as the adsorbent material, and water as the refrigerant. Put 3.171 kg of the SAPO-34 zeolite into the bed. The granular SAPO-34 zeolite is 5.7 mm in diameter.</li>
	<li>Deploy nine temperature probes in three cross-sections of the bed to monitor the temperature change of the bed during the adsorption/desorption process (Figure 3, bottom panel). Fix a probe at each small supporter that is seated on the copper cooling channel.</li>
	<li>Put probes 1 and 2 in section A-A near the inlet of the adsorption bed. Put probes 8 and 9 near the dead end of the bed. Fix the other probes at the middle B-B section (see Figure 3).</li>
	<li>Insert axially a mass-transferring channel of d = 10 mm into the bed. Ensure that the mass channel has the form of reticular tube, and is the same length of the adsorption bed (dbed = 64.5 mm). Extend the channel downwards from the inlet and make it stand in the right position with the extrusion force of the adsorbent material. The reticular tube helps the water vapor to enter the deep region of the bed quickly.</li>
</ol>
2. Experimental Method
NOTE: Adsorption refrigeration is based on the principle that the solid adsorbent material adsorbs the refrigerant vapor strongly at low temperature, while it desorbs the vapor at a higher temperature. Using heat as the driving impetus, the purpose of refrigeration is reached. The refrigeration cycle of the adsorption system involves mainly four steps, i.e., the solar heating-up process, the desorption process, the bed-cooling process, and the adsorption process. The desorption process starts once again after the adsorption process is completed. All the steps of the experiment are equally important because they are interrelated and influence each other interactively.
<ol>
	<li>Regulate the experimental setup by the following procedures to start the solar heating and desorption of the bed.
	<ol>
		<li>Turn the parabolic trough manually until it is facing due east before the experiment, so that the sunlight irradiates the parabolic trough collector normally at noon.</li>
		<li>Shut off all the valves that are connected to the adsorption bed and ensure the pressure of the bed and the pipe is below 800 Pa. Make it ready for solar heating.</li>
		<li>Switch on the controlling rig of the system when the sun light is parallel to the horizon line in the morning. Make the trough automatically rotate to trace the solar movement.</li>
		<li>Allow the adsorption-saturated bed to be heated by solar radiation under closed conditions. As a result, the bed temperature and the bed pressure will increase gradually.</li>
		<li>Monitor the bed pressure with the pressure gauge (Number 6 in Figure 1) until it is higher than the pressure value that corresponds to the condensation temperature of the environment. According to the thermodynamics, the condensation pressure of the water at 30 &#176;C is 4,246 Pa.</li>
	</ol>
	</li>
	<li>Start the desorption process. 
	&#8203;NOTE: In the desorption process, the condensation of water vapor occurs. The condensation temperature is determined by local weather conditions on the test day.
	<ol>
		<li>Open the valve that connects the bed and the condenser. Let water vapor flow into the condenser through the connecting pipe. As water vapor enters the condenser, the temperature of the condenser will rise gradually.</li>
		<li>At the same time, keep the solar heating to the adsorption bed, so that the bed pressure remains high enough to cause the desorption. Do not stop the solar heating until the process is completed.</li>
		<li>End the desorption process when the pressure of the bed is equal to the pressure of the condenser. Turn off the valve when the desorption process is over.</li>
	</ol>
	</li>
	<li>Cool down the bed before the adsorption process, as the bed is still in the state of high temperature after the desorption. The adsorbent material can largely adsorb only at low temperature.
	<ol>
		<li>To start the adsorption process, shield the adsorption bed with an aluminum foil sheet, so that the bed is cut off from the solar radiation.</li>
		<li>Close all the valves that connect the evaporator and the condenser.</li>
		<li>Open the circulating water-loop of the bed and cool down the adsorbent material. With the water continually circulating in the bed, the internal enthalpy is taken out and the bed pressure decreases correspondingly.</li>
		<li>End the cooling process when the bed pressure drops below the saturated vapor pressure at the evaporator&#39;s temperature. 
		NOTE: Be ready for the adsorption refrigeration process after the cooling down of the bed. Now the bed temperature is around the ambient air temperature, and the bed pressure has reached to the minimum level.</li>
		<li>Keep the circulating water-loop in a working state during the adsorption process. The adsorption is an exothermic process, and the generated heat needs to be discharged outside as soon as possible.</li>
		<li>Open the valve between the bed and the evaporator. Let the water vapor rush into the bed from the evaporator. 
		NOTE: The vapor reduction of the evaporator causes more water to vaporize, which results in the drastic decrease of the evaporator temperature. Consequentially, the evaporator absorbs heat from the water tank where the evaporator is seated, and a refrigeration effect is obtained.</li>
		<li>Keep the adsorption process going on, and record the change of the bed temperature and the bed pressure. 
		NOTE: During the adsorption process, the vapor pressure in the evaporator becomes lower and lower, but the bed temperature increases quickly.</li>
		<li>End the adsorption process when the bed pressure is equal to the evaporator pressure. Afterwards, the desorption process will follow again.</li>
	</ol>
	</li>
</ol>
3. Data Reduction Method
<ol>
	<li>Evaluate the performance of the refrigeration system based on the refrigeration capacity and the efficiency of the heat-to-cold transformation. 
	&#8203;NOTE: For the current system, the refrigeration capacity is calculated by the mass amount of the vaporized water and the temperature change of the evaporator itself.
	<ol>
		<li>To determine the total refrigeration capacity (Qref) of the system, calculate the sum of the enthalpy decrement of the chilled water in the tank, the metal evaporator, and the residual water in the evaporator after the adsorption as follows: 
		<img alt="Equation 1" src="/files/ftp_upload/55925/55925eq1.jpg" /> 
		where cp in Eq. (1) is the specific heat at constant pressure, and m denotes the mass. C is a correction factor to the refrigeration capacity of the evaporator considering the heat transfer between the water tank and the ambient environment, and it is assumed C = 1.15 according to the principle of heat transfer. The subscript w and e represents the water and the evaporator, respectively. In the equation mw,tan and mw,eva is the mass of the chilled water in the tank and the mass of the residual water in the evaporator, which corresponds to the temperature drop &#916;Tw and &#916;Te, respectively. 
		NOTE: The solar energy input to the bed is needed to evaluate the efficiency of the heat-to-cold transformation.</li>
		<li>Determine the solar energy input Qs as: 
		<img alt="Equation 2" src="/files/ftp_upload/55925/55925eq2.jpg" /> 
		where, Is,i (t) is the transient solar intensity recorded by the actinometer during the desorption process. The time interval &#916;t of the data acquisition to the Is,i (t) is 10 s. The aperture area of the parabolic trough Ap, the reflective efficiency of the trough surface &#961;, the transmittance of the tube glass &#964;, and the solar absorption coefficient of the coating surface &#945;, together with the parameters in Eq. (1), are all listed in Table 1.</li>
		<li>Based on the Qref and theQs obtained above, determine the COP of the refrigeration system as14: 
		<img alt="Equation 3" src="/files/ftp_upload/55925/55925eq3.jpg" /> 
		&#946;1 and &#946;2 are correction factors to the solar energy input Qs. &#946;1 is the correction factor of the non-parabolic degree of the trough, which takes into account the deformation of the trough because of the limitations of the manufacturing technique, and it is assumed &#946;1 = 0.85. &#946;2 is the correction factor of the real amount of obtained heat of the bed. Due to the smaller size of the metal bed tube than the outer glass tube, the real obtained heat amount is less than that reflected onto the glass tube. &#946;2 is decided by the ratio of the metal bed diameter D2 to the glass tube diameter D1. With D1 = 100 mm and D2 = 64.5 mm, it is calculated that &#946;2 = 0.645.</li>
		<li>Determine the specific cooling power of the bed by the parameters of the experiment as14: 
		<img alt="Equation 4" src="/files/ftp_upload/55925/55925eq4.jpg" /> 
		where ma is the mass of the adsorbent material and tads is the time duration of the adsorption process.</li>
	</ol>
	</li>
</ol>
<img alt="Table 1" src="/files/ftp_upload/55925/55925table1v2.jpg" /> 
Table 1: Values of the parameter in Eq. (1) and Eq. (2). The parameters that are involved in&#160;Eq. (1)&#160;and&#160;Eq. (2)&#160;are listed in this table. The parameters include cp, Ap,&#160;&#945;, etc.

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The authors have nothing to disclose.

As a thermodynamic system, the performance of a solar adsorption refrigeration device depends on the optimum design and the proper operation of the system. Both the heat supply and the cooling method of the bed are important to guarantee the system works well. Water cooling is preferred to air cooling because of the high strength of convection heat transfer of water. The poor conductivity of the adsorbent material has usually determined the limited heat transfer rate of the bed. To improve the heat transfer of the bed, m...

With the ozone-depletion problem of traditional vapor compressed refrigeration growing more serious, substituting traditional refrigeration with green technology has become a hot topic in recent years. Among those green technologies, the solar adsorption refrigeration has attracted much of the attention of researchers. Driven by low-grade thermal energy, the adsorption refrigeration system has the advantages of being environmentally friendly, small, and flexible. This adsorption system can also be driven with non-solar energy, for instance by waste heat discharged from thermal equipment or by engine exhaust gases from vehicles, as mentioned by Hu et al.1
In an adsorption cooling system, the adsorption bed is the key component. Its work directly affects the performance of the whole system. Therefore, the design of the adsorption bed is the most important issue as pointed out by Sutuki.2 A decade ago, the flat bed was mostly used in the adsorption cooling system.3,4,5 Without any solar concentrating device, the flat bed temperature was usually low and hence the COP of the system was unsatisfactory. In contrast, the tubular adsorption bed improved the COP. It was reported that the COP could reach 0.21 in sub-Sahara region by Hadj Ammar et al.6 Furthermore, Wang et al.7 developed a spiral plate adsorber that was distinguished by the characteristic of continuous heat regeneration. The novel design of the adsorption bed shortened the cycle time of the system. Abu-Hamdeh&#160;et al.8 reported their study on the solar adsorption refrigeration system with a parabolic trough collector. Their test results showed the COP of the system varied from 0.18 to 0.20. El Fadar et al.9 studied an adsorption refrigeration system that was coupled with a heat pipe and powered by parabolic trough collector, which showed an optimum COP of 0.18.
To enhance the heat transfer of the tubular bed, some finned tube adsorbers were considered and the effect of the enhancement was examined. An innovative bed that took the form of the shell and tube heat exchanger was presented by Restuccia et al.10. The internal finned tube was coated with a zeolite layer so that the contact transfer resistance of heat/mass between the metal surface and the adsorbent material could be reduced. The system produced an output of 30-60 W/kg of specific cooling power in the cycling time of 15-20 s. Al Mers et al.11demonstrated that the enhanced adsorber with 5-6 fins could significantly reduce the heat loss of the adsorber to ambiance and thereby improving the COP by 45%. The effect of a finned tube adsorber on the performance of the solar driven system was also studied by Louajari et al.12. Using activated carbon-ammonia as the working pair, they showed that the cycling mass transfer in the adsorber with fins was greater than the one without fins.
In the current study, we experimentally studied an improved solar adsorption refrigeration system, in which a solar tracking parabolic trough collector was applied and an internal cooling tunnel was deployed. With the SAPO-34/ZSM-5 zeolite and the water vapor as the working pair, the system showed interesting characteristics in terms of thermodynamics and refrigeration. The experimental methodology as well as the typical test results will be presented and discussed in this report.

<table><tbody><tr><td>evaporator</td><td>home-made</td><td></td><td>finned heat exchange</td></tr><tr><td>condenser</td><td>home-made</td><td></td><td>finned heat exchange</td></tr><tr><td>evaporator water tank</td><td>home-made</td><td></td><td>volume:9L</td></tr><tr><td>condenser water tank</td><td>home-made</td><td></td><td>volume:9L</td></tr><tr><td>vacuum pump</td><td>Beijing Jing Rui Ze Xiang Instrument Co. Ltd.</td><td></td><td>rotation speed:1400 motor pover:370W</td></tr><tr><td>condenser pressure sensor</td><td>Beijing Li Nuo Tian Sheng Instrument Co. Ltd.</td><td>16P2623</td><td>maximum:2200Pa</td></tr><tr><td>bed pressure sensor</td><td>Beijing Li Nuo Tian Sheng Instrument Co. Ltd.</td><td></td><td>maximum:2200Pa</td></tr><tr><td>adsorption bed</td><td>home-made</td><td></td><td>cylundrical glass tube</td></tr><tr><td>parabolic trough</td><td>home-made</td><td></td><td>high reflective aluminum sheet</td></tr><tr><td>water pump</td><td>home-made</td><td></td><td>motor pover:250W, water head:8m</td></tr><tr><td>water tank</td><td>home-made</td><td></td><td>volume:500L</td></tr><tr><td>DRT-2-2 direct solar actinometer</td><td>Beijing Tian Yu De Technology Co. Ltd.</td><td>03140132</td><td>sensitivity:13.257&amp;mu;V/W&amp;bull;m&lt;sup&gt;2&lt;/sup&gt;</td></tr><tr><td>TBQ-2 solar pyranometer</td><td>Jinzhou Sunshine Technology Development Co., Ltd., China</td><td>209079</td><td>sensitivity:12.733&amp;mu;V/W&amp;bull;m&lt;sup&gt;2&lt;/sup&gt;</td></tr><tr><td>SAPO-34 zeolite</td><td>Langfang Peng Cai Co., Ltd., China</td><td></td><td>20mm in length and 2.2mm in diameter</td></tr><tr><td>ZSM-5 zeolite</td><td>Langfang Peng Cai Co., Ltd., China</td><td></td><td>5.7mm in diameter</td></tr></tbody></table>

experimental system of solar adsorption refrigeration with concentrated collector

To improve the performance of solar adsorption refrigeration, an experimental system with a solar concentration collector was set up and investigated. The main components of the system were the adsorbent bed, the condenser, the evaporator, the cooling sub-system, and the solar collector. In the first step of the experiment, the vapor-saturated bed was heated by the solar radiation under closed conditions, which caused the bed temperature and pressure to increase. When the bed pressure became high enough, the bed was switched to connect to the condenser, thus water vapor flowed continually from the bed to the condenser to be liquefied. Next, the bed needed to cool down after the desorption. In the solar-shielded condition, achieved by aluminum foil, the circulating water loop was opened to the bed. With the water continually circulating in the bed, the stored heat in the bed was took out and the bed pressure decreased accordingly. When the bed pressure dropped below the saturation pressure at the evaporation temperature, the valve to the evaporator was opened. A mass of water vapor rushed into the bed and was adsorbed by the zeolite material. With the massive vaporization of the water in the evaporator, the refrigeration effect was generated finally. The experimental result has revealed that both the COP (coefficient of the performance of the system) and the SCP (specific cooling power of the system) of the SAPO-34 zeolite was greater than that of the ZSM-5 zeolite, no matter whether the adsorption time was longer or shorter. The system of the SAPO-34 zeolite generated a maximum COP of 0.169.

Mass transfer characteristic of the bed through the adsorption process 
The adsorption bed is always the most important component in an adsorption refrigeration system, and the heat and mass transfer characteristic are the main factors affecting the performance of the whole system. By analyzing the recorded temperature change in the cross sections as shown in Figure 3(bottom panel),&#160;it is possible to know the heat and mass transfer ...

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Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

With solar energy as the driving force, a novel adsorption refrigeration system has been developed and experimentally investigated. Water vapor and zeolite formed the working pair of the adsorption system. This manuscript describes the setup of the experimental rig, the operation procedure, and the important results.

To improve the performance of solar adsorption refrigeration, an experimental system with a solar concentration collector was set up and investigated. The ...

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14.4K Views.  Beijing University of Technology. With solar energy as the driving force, a novel adsorption refrigeration system has been developed and experimentally investigated. Water vapor and zeolite formed the working pair of the adsorption system. This manuscript describes the setup of the experimental rig, the operation procedure, and the important results.

Video: Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

Engineering

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction of degradation mechanisms and prevention of module field failure can consequently decrease investment risks as well as increase the electricity yield. An improved knowledge level can for these reasons significantly decrease the total costs of PV electricity. 
In order to better understand and minimize the degradation of PV modules, the occurring degradation mechanisms and conditions should be identified. This should preferably happen under combined stresses, since modules in the field are also simultaneously exposed to multiple stress factors. Therefore, two 'Combined Stress test with in situ measurement' setups have been designed and constructed. These setups allow the simultaneous use of humidity, temperature, illumination, and electrical biases as independently controlled stress factors on solar cells and minimodules. The setups also allow real-time monitoring of the electrical properties of these samples. This protocol presents these setups and describes the experimental possibilities. Moreover, results obtained with these setups are also presented: various examples about the influence of both deposition and degradation conditions on the stability of thin film Cu(In,Ga)Se2 (CIGS) as well as Cu2ZnSnSe4 (CZTS) solar cells are described. Results on the temperature dependency of CIGS solar cells are also presented.

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for CuIn,GaSe2 Solar Cells

Two &#39;Combined Stress test with in situ measurement&#39; setups, which allow real-time monitoring of accelerated degradation of solar cells and modules, were designed and constructed. These setups allow the simultaneous use of humidity, temperature, electrical biases, and illumination as independently controlled stress factors. The setups and various experiments executed are presented.

The levelized cost of electricity (LCOE) of photovoltaic (PV) systems is determined by, among other factors, the PV module reliability. Better prediction ...

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is composed of two materials, a plastic and an elastomer, whose dispersion characteristics (refractive index variation with wavelength) are different. We first designed the lens geometry and then used ray-tracing simulation, based on the Monte Carlo method, to analyze its performance from the point of view of both optical efficiency and the maximum attainable concentration. Afterwards, ADG Fresnel lens prototypes were manufactured using a simple and reliable method. It consists of a prior injection of plastic parts and a consecutive lamination, together with the elastomer and a glass substrate to fabricate the parquet of ADG Fresnel lenses. The accuracy of the manufactured lens profile is examined using an optical microscope while its optical performance is evaluated using a solar simulator for concentrator photovoltaic systems. The simulator is composed of a xenon flash lamp whose emitted light is reflected by a parabolic mirror. The collimated light has a spectral distribution and an angular aperture similar to the real Sun. We were able to assess the optical performance of the ADG Fresnel lenses by taking photographs of the irradiance spot cast by the lens using a charge-coupled device (CCD) camera and measuring the photocurrent generated by several types of multi junction (MJ) solar cells, which have been previously characterized at a solar simulator for concentrator solar cells. These measurements have demonstrated the achromatic behavior of ADG Fresnel lenses and, as a consequence, the suitability of the modelling and manufacturing methods.

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass ADG Fresnel Lens for Concentrating Photovoltaics

The achromatic doublet on glass (ADG) Fresnel lens makes use of two materials with differing dispersion to reduce chromatic aberration and increase attainable concentration. In this paper, a protocol for the complete characterization of the ADG Fresnel lens is presented.

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is ...

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea is to use concentration technology to raise the incident solar light intensity. Concentrating a large-area light onto a small area cannot only increase light intensity, but also reduce the catalyst amount, as well as the reactor volume, and increase the surface temperature. The concentration of light can be realized by different devices. In this manuscript, it is realized by a Fresnel lens. The light penetrates the lens and is concentrated on a disc-shaped catalyst. The results show that both the reaction rate and the total yield are efficiently increased. The method can be applied to most CO2 photoreduction catalysts, as well as to similar reactions with a low reaction rate at natural light.

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We present a protocol for improving the performance of CO2 photoreduction to CH4 by heightening the incident light intensity via concentrating solar energy technology.

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea ...

Experimental Methods for Efficient Solar Hydrogen Production in Microgravity Environment

Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the Earth's atmosphere. So-called 'solar fuel' devices, currently developed for terrestrial applications in the quest for realizing a sustainable energy economy on Earth, provide promising alternative systems to existing air-revitalization units employed on the International Space Station (ISS) through photoelectrochemical water-splitting and hydrogen production. One obstacle for water (photo-) electrolysis in reduced gravity environments is the absence of buoyancy and the consequential, hindered gas bubble release from the electrode surface. This causes the formation of gas bubble froth layers in proximity to the electrode surface, leading to an increase in ohmic resistance and cell-efficiency loss due to reduced mass transfer of substrates and products to and from the electrode. Recently, we have demonstrated efficient solar hydrogen production in microgravity environment, using an integrated semiconductor-electrocatalyst system with p-type indium phosphide as the light-absorber and a rhodium electrocatalyst. By nanostructuring the electrocatalyst using shadow nanosphere lithography and thereby creating catalytic 'hot spots' on the photoelectrode surface, we could overcome gas bubble coalescence and mass transfer limitations and demonstrated efficient hydrogen production at high current densities in reduced gravitation. Here, the experimental details are described for the preparations of these nanostructured devices and further on, the procedure for their testing in microgravity environment, realized at the Bremen Drop Tower during 9.3 s of free fall.

Efficient solar-hydrogen production has recently been realized on functionalized semiconductor-electrocatalyst systems in a photoelectrochemical half-cell in microgravity environment at the Bremen Drop Tower. Here, we report the experimental procedures for manufacturing the semiconductor-electrocatalyst device, details of the experimental set-up in the drop capsule and the experimental sequence during free fall.

Long-term space flights and cis-lunar research platforms require a sustainable and light life-support hardware which can be reliably employed outside the ...

Chemistry

Thermocapillary Convection Space Experiment on the SJ-10 Recoverable Satellite

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary convection in an annular liquid pool is one of the 19 scientific experimental projects on the SJ-10 recoverable satellite. Presented is a design for a payload for space experimental study on thermocapillary convection that includes the experimental model, measurement system, and control system. The specifics for the construction of an experimental model of an annular liquid pool with variable volume ratios is provided. The fluid temperatures are recorded by six thermocouples with a high sensitivity of 0.05 &#176;C at different points. The temperature distributions on the liquid free surface are captured by means of an infrared thermal camera. The free surface deformation is detected by a displacement sensor with a high accuracy of 1 &#181;m. The experimental process is fully automated. The research is focused on thermocapillary oscillation phenomena on the liquid-free surface and convective pattern transitions through analyses of experimental data and images. This research will be helpful to understand the mechanism of thermocapillary convection and will offer further insights into the nonlinear characteristics, flow instability, and bifurcation transitions of thermocapillary convection.

A protocol for the space payload design, the space experiment on thermocapillary convection, and analyses of experimental data and images are presented in this paper.

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary ...

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (TH, ~40-90 &#176;C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a TH = 70 &#176;C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We ...

Introduction to Refrigeration

Source: Alexander S Rattner and Christopher J Greer; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
This experiment demonstrates the principles of vapor compression refrigeration. The vapor compression cycle is the dominant refrigeration technology, found in most refrigerators, freezers, air-conditioning systems, and heat pumps. In this cycle, cooling (heat acquisition) is achieved with low-pressure evaporation of refrigerant. Thermal energy absorbed in evaporation is rejected to the surroundings through high-pressure refrigerant condensation. Mechanical work is applied in the compressor to raise the working fluid from low to high pressure. 
While refrigeration technology is ubiquitous, the concealing packaging and autonomous operation of most refrigerators makes it difficult to appreciate the operating principles and function of key components. In this experiment, a rudimentary vapor compression refrigerator is constructed. The compressor is manually actuated with a bicycle pump, allowing intuitive appreciation of cycle operation as the experimenter becomes part of the system. Resulting component pressures and temperatures can be interpreted in terms of the thermodynamic T-s and P-h diagrams, which capture the variation of fluid properties from the liquid-to-vapor states (during evaporation and condensation).

Refrigeration; Vapor Dome; Hand-pump Refrigerator

Source: Alexander S Rattner and Christopher J Greer; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, ...

Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

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