A light-gravity fluidized bed analysis and testing system and analysis and testing method

Abstract

The present invention discloses an analysis and testing system and analysis and testing method of a photogravimetric fluidized bed, including: a weight in-situ measurement subsystem, a solar simulator subsystem, a fluidized bed heat absorber subsystem, an infrared temperature measurement subsystem, an integrated control subsystem and an air supply subsystem. The in-situ test platform for heat storage and release of fluidized modified particles under direct solar irradiation of the present invention reveals the coupling mechanism of heat transfer, mass transfer and chemical reaction at the macroscopic system level according to the influence of parameters such as airflow organization form, heat transfer characteristics and solar radiation flux on temperature field, flow field and spatial distribution of chemical reaction rate; compared with the traditional weight fluidized bed, the present invention uses high-efficiency modified calcium carbonate to conduct research under direct solar irradiation, which is an important step in achieving low-carbon and high-efficiency energy utilization; compared with the traditional calcium carbonate material performance research, this discovery uses a laboratory-grade fluidized bed reactor with a multi-parameter in-situ measurement system, which can more realistically simulate industrial application scenarios.

Description

Technical Field

[0001] The present invention relates to the field of solar chemical heat storage technology, in particular to an analysis and testing system and an analysis and testing method for a light-gravity fluidized bed Background Art

[0002] As an inexhaustible clean energy, solar energy is widely distributed and has abundant reserves. It is undoubtedly one of the most effective ways to solve energy and environmental problems. Concentrated solar power generation with a heat storage system is an environmentally friendly way of power generation. It can store solar energy during sunshine hours for use during non-sunshine hours, thereby realizing on-demand power supply. Compared with sensible heat and latent heat storage, thermochemical energy storage systems have the advantages of high energy storage density, suitable reaction temperature (which can meet the higher operating temperature requirements of the next generation of high-efficiency solar thermal power generation), and long-term storage at room temperature. Among them, the calcium carbonate / calcium oxide heat storage system is one of the most promising high-density and low-loss heat storage methods. Calcium carbonate heat storage is closely related to solar energy capture, thermal decomposition heat storage, acidification heat release, and reactant-working fluid heat exchange characteristics. As far as the current research status is concerned, related work is mostly focused on the cyclic stability of calcium oxide adsorption activity. The heat storage and release characteristics of thermochemical heat storage systems have not been comprehensively analyzed from various factors of energy transfer and conversion, and the key factors affecting the volatility of thermal energy storage and release are still unclear. In addition, the current research on heat storage materials mainly uses commercial thermogravimetric analysis methods and electrically heated fluidized bed thermogravimetric analysis methods. The electrically heated commercial thermogravimetric analysis method mainly uses an electrically heated furnace to indirectly transfer heat to the heat storage material. Commercial thermogravimetric analysis samples react in a small crucible in the form of a pile, which has defects such as insufficient gas-solid contact and a small amount of analyzable samples. Electrically heated fluidized bed thermogravimetry requires a lot of energy, which does not comply with the carbon neutrality policy, and the fluidized bed under solar irradiation is usually unevenly distributed. However, the heating mode of electrically heated fluidized bed thermogravimetry makes the entire furnace evenly heated, so electrically heated fluidized bed thermogravimetry cannot simulate the actual reaction conditions of power generation relying on green solar energy storage. Therefore, the study of fluidized bed particles under direct solar irradiation has important academic significance and application prospects for improving the efficiency of solar thermal storage and developing the next generation of high-temperature and high-efficiency solar thermal power generation technology. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an analysis and testing system and an analysis and testing method for a photogravimetric fluidized bed, which can more realistically simulate industrial application scenarios.

[0004] In order to solve the above technical problems, the present invention provides an analysis and testing system for a photogravimetric fluidized bed, comprising: an in-situ weight measurement subsystem, a solar simulator subsystem, a fluidized bed heat absorber subsystem, an infrared temperature measurement subsystem, an integrated control subsystem and an air supply subsystem; an in-situ weight measurement subsystem, a solar simulator subsystem, a fluidized bed heat absorber subsystem, an infrared temperature measurement subsystem, an integrated control subsystem and an air supply subsystem; the in-situ weight measurement subsystem is arranged in the fluidized bed heat absorber subsystem under direct solar energy radiation, so as to obtain the dynamic changes of in-situ parameters of temperature, weight and inlet pressure of fluidized particles under direct solar energy radiation; the infrared temperature measurement subsystem is located directly above the fluidized bed heat absorber subsystem, so as to measure the upper surface temperature and fluidization state of the fluidized bed; the air supply subsystem is connected to the fluidized bed heat absorber subsystem through an air path; and each subsystem is connected to the integrated control subsystem.

[0005] Preferably, the weight in-situ measurement subsystem includes a weight sensor 5, an auxiliary gas pipeline 7, a cooling unit 9 and a circulating cooling water tank 10; the auxiliary gas pipeline 7 is connected to the weight sensor 5 and is discharged from the double-layer reactor 12; the circulating cooling water tank 10 transports water to the cooling unit 9 through an air pump, and the auxiliary gas pipeline 7, the cooling unit 9 and the circulating cooling water tank 10 are used to protect the weight sensor 5 so that it meets the accuracy requirements at a suitable temperature; the weight sensor 5 is placed at the bottom of the reactor 12 to obtain the weight change during the fluidized particle reaction under solar radiation.

[0006] Preferably, the solar simulator subsystem includes 13 10 kW xenon short arc lamps and reflectors, which are coupled to provide highly concentrated solar radiation energy for directly irradiating and heating the fluidized particles.

[0007] Preferably, the fluidized bed heat absorber subsystem includes a pressure sensor 6, a fluidizing gas pipeline 8, an air distribution plate 11, a reactor 12, a reflective cavity 13, a focusing device 14 and a thermocouple 16; the pressure sensor 6 is located at the inlet of the fluidizing gas pipeline 8; the air distribution plate 11 is located in the double-layer reactor 12 and is used to fluidize the particles; the thermocouple 16 is located in the double-layer reactor 12; the double-layer reactor 12 is located in the center of the reflective cavity 13; the radiation energy of the focusing device 14 enters the reflective cavity 13 through the light entrance; the fluidized bed heat absorber subsystem directly absorbs solar radiation to heat the bed particles.

[0008] Preferably, the air distribution plate 11 is 4 mm thick and has a mesh size of 60-80, which produces uniform air distribution and causes disordered collision of particles; the fluidized bed absorber subsystem is a quartz tube fluidized bed with an outer diameter of 30 mm, and the fluidized particles are modified calcium carbonate particles with high absorption rate, and the weight of the modified calcium carbonate particles is 5-30 g, which has the advantages of high solar full spectrum absorption rate, good cycle stability, and fast reaction rate; the thermocouple 16 is arranged at 1.5 mm, 3 mm, and 4.5 mm above the middle of the air distribution plate 11, and is used to measure the temperature at different heights of the bed; the pressure sensor 6 is arranged at the gas inlet to measure the pressure at the bottom of the reactor; the focusing device 14 has an inlet diameter of 150 cm and an outlet of 50 cm, which is used to collect the radiation light from the solar simulator and focus it into the quartz tube fluidized bed and the reflection cavity. The interior of the reflection cavity 13 is spherical with a diameter of 100 cm, which is used to reflect the energy not absorbed by the particles back into the fluidized bed.

[0009] Preferably, the infrared temperature measurement subsystem includes a one-dimensional slide 17, a two-dimensional slide 18 and an infrared thermal imager 19; the infrared thermal imager 19 is connected to the one-dimensional slide 17 and the two-dimensional slide 18, and can move in two dimensions; the infrared temperature measurement subsystem tests the flow state and particle temperature in the fluidized bed just above the bed layer.

[0010] Preferably, the integrated control subsystem transmits the signals of the mass flow meter 2, the flow control panel 3, the weight sensor 5, the pressure sensor 6, the solar simulator 15, the thermocouple 16, the one-dimensional slide 17 and the two-dimensional slide 18 to the computer 4, thereby performing in-situ analysis and control of the entire solar thermochemical heat storage system.

[0011] Preferably, the gas supply subsystem includes a gas cylinder 1, a mass flow meter 2, an auxiliary gas pipeline 7 and a fluidizing gas pipeline 8; the gas from the gas cylinder 1 is output to the mass flow meter 2 for flow control, and is divided into two paths and flows through the auxiliary gas pipeline 7 and the fluidizing gas pipeline 8; it is used to provide cooling gas for the weight sensor 5 and reaction gas and fluidizing gas for the fluidized bed.

[0012] Accordingly, a light-gravity fluidized bed analysis and testing method comprises the following steps:

[0013] Step 1. Before the reaction, connect the gas cylinder, mass flow meter, computer, auxiliary gas pipeline, fluidizing gas pipeline and pressure sensor in sequence, place the quartz reactor on the mass sensor, connect the reflection cavity and focusing device to the one-dimensional slide, adjust the one-dimensional slide, place the reflection cavity and focusing device in the center of the solar irradiation spot, place three thermocouples at different heights in the fluidized bed, install the infrared thermal imager vertically downward on the two-dimensional slide, move the two-dimensional slide so that the center of the infrared thermal imager is consistent with the center of the reactor, connect the power supply line of the solar simulator, set the temperature control program of the solar simulator, connect each data acquisition line to the computer, and wait for data collection;

[0014] Step 2: Add an appropriate amount of modified calcium carbonate particles to the fluidized bed, turn on the infrared thermal imager, focus it so that the particles in the fluidized bed are clearly visible; open the gas cylinder valve to introduce fluidizing gas, and wait for the weight signal to stabilize; remotely turn on the solar simulator light source to ensure that its temperature reaches the set temperature, observe and record various parameters on the computer, switch the gas to an inert gas, and allow it to decompose completely; use remote control to switch the reaction gas so that it adsorbs carbon dioxide to become calcium carbonate.

[0015] Preferably, the in situ parameters include temperature, weight, inlet pressure in the fluidized bed and movement and temperature of particles on the upper surface of the bed.

[0016] The beneficial effects of the present invention are as follows: the in-situ test platform for heat storage and release of fluidized modified particles under direct solar radiation of the present invention reveals the coupling mechanism of heat transfer, mass transfer and chemical reaction at the macroscopic system level according to the influence of parameters such as airflow organization form, heat transfer characteristics and solar radiation flux on temperature field, flow field and spatial distribution of chemical reaction rate; compared with the traditional weight fluidized bed, the present invention uses high-efficiency modified calcium carbonate to conduct research under direct solar radiation, which is an important step to achieve low-carbon and efficient energy utilization; compared with the traditional calcium carbonate material performance research, this discovery adopts a laboratory-grade fluidized bed reactor with a multi-parameter in-situ measurement system, which can more realistically simulate industrial application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of the analysis and testing system of the present invention.

[0018] Figure 2 The figure is a graph showing the weight change of the modified fluidized particles under direct irradiation of concentrated solar energy over time.

[0019] Figure 3 This is a trend chart of temperature change over time in a fluidized bed (located 1.5 cm above the air distribution plate) under direct irradiation of concentrated solar energy of the present invention.

[0020] Figure 4 This is a graph showing the change trend of the fluidized bed inlet pressure over time under direct irradiation of concentrated solar energy according to the present invention.

[0021] Among them, 1-gas cylinder; 2-mass flow meter; 3-flow control panel; 4-computer; 5-weight sensor; 6-pressure sensor; 7-auxiliary gas pipeline; 8-fluidizing gas pipeline; 9-cooling unit; 10-circulating cooling water tank; 11-air distribution plate; 12-reactor; 13-reflection cavity; 14-focusing device; 15-solar simulator; 16-thermocouple; 17-one-dimensional slide; 18-two-dimensional slide; 19-infrared thermal imager. DETAILED DESCRIPTION

[0022] like Figure 1 As shown, an analysis and testing system for a photogravimetric fluidized bed comprises: a weight in-situ measurement subsystem, a solar simulator subsystem, a fluidized bed absorber subsystem, an infrared temperature measurement subsystem, an integrated control subsystem and an air supply subsystem; a weight in-situ measurement subsystem, a solar simulator subsystem, a fluidized bed absorber subsystem, an infrared temperature measurement subsystem, an integrated control subsystem and an air supply subsystem; the weight in-situ measurement subsystem is arranged in the fluidized bed absorber subsystem under direct solar energy radiation, so as to obtain the dynamic changes of the in-situ parameters of the temperature, weight and inlet pressure of the fluidized particles under direct solar energy radiation; the infrared temperature measurement subsystem is located directly above the fluidized bed absorber subsystem, so as to measure the upper surface temperature and the fluidization state of the fluidized bed; the air supply subsystem is connected to the fluidized bed absorber subsystem through an air path; and each subsystem is connected to the integrated control subsystem.

[0023] The weight in-situ measurement subsystem includes a weight sensor 5, an auxiliary gas pipeline 7, a cooling unit 9 and a circulating cooling water tank 10; the auxiliary gas pipeline 7 is connected to the weight sensor 5 and is discharged from the double-layer reactor 12; the circulating cooling water tank 10 transports water to the cooling unit 9 through an air pump, and the auxiliary gas pipeline 7, the cooling unit 9 and the circulating cooling water tank 10 are used to protect the weight sensor 5 so that it meets the accuracy requirements at a suitable temperature; the weight sensor 5 is placed at the bottom of the reactor 12 to obtain the weight change during the fluidized particle reaction under solar radiation.

[0024] The solar simulator subsystem includes 13 10 kW xenon short arc lamps and reflectors, which are coupled to provide highly concentrated solar radiation energy to directly irradiate and heat the fluidized particles.

[0025] The fluidized bed heat absorber subsystem includes a pressure sensor 6, a fluidizing gas pipeline 8, an air distribution plate 11, a reactor 12, a reflective cavity 13, a focusing device 14 and a thermocouple 16; the pressure sensor 6 is located at the inlet of the fluidizing gas pipeline 8; the air distribution plate 11 is located in the double-layer reactor 12 and is used to fluidize the particles; the thermocouple 16 is located in the double-layer reactor 12; the double-layer reactor 12 is located in the center of the reflective cavity 13; the radiation energy of the focusing device 14 enters the reflective cavity 13 through the light entrance; the fluidized bed heat absorber subsystem directly absorbs solar radiation and heats the bed particles.

[0026] The air distribution plate 11 is 4mm thick and has a mesh size of 60-80, which produces uniform air distribution and causes disordered collision of particles. The fluidized bed absorber subsystem is a quartz tube fluidized bed with an outer diameter of 30mm. The fluidized particles are modified calcium carbonate particles with high absorption rate. The modified calcium carbonate particles weigh 5-30g and have the advantages of high solar full spectrum absorption rate, good cycle stability and fast reaction rate. The thermocouple 16 is arranged at 1.5mm, 3mm and 4.5mm above the middle of the air distribution plate 11 to measure the temperature at different heights of the bed. The pressure sensor 6 is arranged at the gas inlet to measure the pressure at the bottom of the reactor. The concentrator 14 has an inlet diameter of 150 cm and an outlet of 50 cm. It is used to collect radiation from the solar simulator and focus it into the quartz tube fluidized bed and the reflection cavity. The interior of the reflection cavity 13 is spherical with a diameter of 100 cm, which is used to reflect the energy not absorbed by the particles back into the fluidized bed.

[0027] The infrared temperature measurement subsystem includes a one-dimensional slide 17, a two-dimensional slide 18 and an infrared thermal imager 19; the infrared thermal imager 19 is connected to the one-dimensional slide 17 and the two-dimensional slide 18, and can move in two dimensions; the infrared temperature measurement subsystem tests the flow state and particle temperature in the fluidized bed just above the bed layer.

[0028] The integrated control subsystem transmits the signals of the mass flow meter 2, the flow control panel 3, the weight sensor 5, the pressure sensor 6, the solar simulator 15, the thermocouple 16, the one-dimensional slide 17 and the two-dimensional slide 18 to the computer 4, thereby performing in-situ analysis and control of the entire solar thermochemical heat storage system.

[0029] The gas supply subsystem includes a gas cylinder 1, a mass flow meter 2, an auxiliary gas pipeline 7 and a fluidizing gas pipeline 8; the gas from the gas cylinder 1 is output to the mass flow meter 2 for flow control, and is divided into two paths to flow through the auxiliary gas pipeline 7 and the fluidizing gas pipeline 8; it is used to provide cooling gas for the weight sensor 5 and to provide reaction gas and fluidizing gas for the fluidized bed.

[0030] Accordingly, a light-gravity fluidized bed analysis and testing method comprises the following steps:

[0031] Step 1. Before the reaction, connect the gas cylinder, mass flow meter, computer, auxiliary gas pipeline, fluidizing gas pipeline and pressure sensor in sequence, place the quartz reactor on the mass sensor, connect the reflection cavity and focusing device to the one-dimensional slide, adjust the one-dimensional slide, place the reflection cavity and focusing device in the center of the solar irradiation spot, place three thermocouples at different heights in the fluidized bed, install the infrared thermal imager vertically downward on the two-dimensional slide, move the two-dimensional slide so that the center of the infrared thermal imager is consistent with the center of the reactor, connect the power supply line of the solar simulator, set the temperature control program of the solar simulator, connect each data acquisition line to the computer, and wait for data collection;

[0032] Step 2: Add an appropriate amount of modified calcium carbonate particles to the fluidized bed, turn on the infrared thermal imager, focus it, and make the particles in the fluidized bed clearly visible; open the valve of the gas cylinder to introduce fluidizing gas, and wait for the weight signal to stabilize; remotely turn on the light source of the solar simulator to determine that its temperature reaches the set temperature, observe and record various parameters on the computer, switch the gas to an inert gas, and allow it to decompose completely; use remote control to switch the reaction gas to adsorb carbon dioxide to become calcium carbonate. The in-situ parameters include the temperature, weight, inlet pressure in the fluidized bed, and the movement and temperature of the particles on the surface of the bed.

[0033] Figure 2 In order to measure the weight change of modified calcium carbonate when switching the reaction gas, the decomposition time of modified calcium carbonate was set to 20 minutes and the adsorption time was set to 10 minutes. Figure 3 The temperature of particles in the fluidized bed (1.5 cm away from the air distribution plate) changes with time. It can be seen from the figure that the bed temperature is about 750 degrees. Figure 4 This is a graph of the pressure at the gas inlet changing with time. Since the weight in the bed changes during the cycle, the fluidization state changes.

[0034] The present invention is applicable to the testing of various fluidized particle parameters under direct solar radiation, including but not limited to methane dry reforming, particle thermochemical energy storage, cement calcination, dry desulfurization and other reaction processes under direct solar radiation.

Claims

1. An analytical testing system for a photogravimetric fluidized bed, characterized in that: include: The weight in-situ measurement subsystem, solar simulator subsystem, fluidized bed heat absorber subsystem, infrared temperature measurement subsystem, integrated control subsystem and air supply subsystem are provided; the weight in-situ measurement subsystem is arranged in the fluidized bed heat absorber subsystem under direct solar radiation, and is used to obtain the dynamic changes of the in-situ parameters of the temperature, weight and inlet pressure of the fluidized particles under direct solar radiation; the infrared temperature measurement subsystem is located directly above the fluidized bed heat absorber subsystem, and measures the upper surface temperature and fluidization state of the fluidized bed; the air supply subsystem is connected to the fluidized bed heat absorber subsystem through an air path; each subsystem is connected to the integrated control subsystem; The weight in-situ measurement subsystem comprises a weight sensor (5), an auxiliary gas pipeline (7), a cooling unit (9) and a circulating cooling water tank (10); the auxiliary gas pipeline (7) is connected to the weight sensor (5) and is discharged from the double-layer reactor (12); the circulating cooling water tank (10) transports water to the cooling unit (9) through an air pump, and the auxiliary gas pipeline (7), the cooling unit (9) and the circulating cooling water tank (10) are used to protect the weight sensor (5) so that it meets the accuracy requirements at a suitable temperature; the weight sensor (5) is placed at the bottom of the reactor (12) and is used to obtain the weight change during the reaction of fluidized particles under solar radiation; The solar simulator subsystem includes 13 10 kW xenon short arc lamps and reflectors, which are coupled to provide highly concentrated solar radiation energy to directly irradiate and heat the fluidized particles. The fluidized bed heat absorber subsystem comprises a pressure sensor (6), a fluidizing gas pipeline (8), an air distribution plate (11), a reactor (12), a reflective cavity (13), a focusing device (14) and a thermocouple (16); the pressure sensor (6) is located at the inlet of the fluidizing gas pipeline (8); the air distribution plate (11) is located in the double-layer reactor (12) for fluidizing particles; the thermocouple (16) is located in the double-layer reactor (12); the double-layer reactor (12) is located in the center of the reflective cavity (13); the radiation energy of the focusing device (14) enters the reflective cavity (13) through the light inlet; the fluidized bed heat absorber subsystem directly absorbs solar radiation to heat the bed particles.

2. The photogravimetric fluidized bed analysis and testing system according to claim 1, characterized in that: The air distribution plate (11) is 4 mm thick and has a mesh size of 60-80; the fluidized bed absorber subsystem is a quartz tube fluidized bed with an outer diameter of 30 mm, and the fluidized particles are modified calcium carbonate particles with high absorption rate, and the weight of the modified calcium carbonate particles is 5-30 g; the thermocouples (16) are arranged at 1.5 mm, 3 mm, and 4.5 mm above the center of the air distribution plate (11) to measure the temperature at different heights of the bed; the pressure sensor (6) is arranged at the gas inlet to measure the pressure at the bottom of the reactor; the focusing device (14) has an inlet diameter of 150 cm and an outlet of 50 cm, which is used to collect the radiation light from the solar simulator and focus it into the quartz tube fluidized bed and the reflection cavity; the interior of the reflection cavity (13) is spherical with a diameter of 100 cm, which is used to reflect the energy not absorbed by the particles back into the fluidized bed.

3. The photogravimetric fluidized bed analysis and testing system according to claim 1, characterized in that: The infrared temperature measurement subsystem includes a one-dimensional slide (17), a two-dimensional slide (18) and an infrared thermal imager (19); the infrared thermal imager (19) is connected to the one-dimensional slide (17) and the two-dimensional slide (18) and can move in two dimensions; the infrared temperature measurement subsystem tests the flow state and particle temperature in the fluidized bed just above the bed layer.

4. The photogravimetric fluidized bed analysis and testing system according to claim 1, characterized in that: The integrated control subsystem transmits the signals of the mass flow meter (2), the flow control panel (3), the weight sensor (5), the pressure sensor (6), the solar simulator (15), the thermocouple (16), the one-dimensional slide table (17) and the two-dimensional slide table (18) to the computer (4), thereby performing in-situ analysis and control of the entire solar thermochemical heat storage system.

5. The photogravimetric fluidized bed analysis and testing system according to claim 1, characterized in that: The gas supply subsystem comprises a gas cylinder (1), a mass flow meter (2), an auxiliary gas pipeline (7) and a fluidizing gas pipeline (8); the gas in the gas cylinder (1) is output to the mass flow meter (2) for flow control and is divided into two paths to flow through the auxiliary gas pipeline (7) and the fluidizing gas pipeline (8); and is used to provide cooling gas for the weight sensor (5) and to provide reaction gas and fluidizing gas for the fluidized bed.

6. An analytical testing method using the analytical testing system of the photogravimetric fluidized bed as claimed in claim 1, characterized in that: The steps include: Step 1. Before the reaction, connect the gas cylinder, mass flow meter, computer, auxiliary gas pipeline, fluidizing gas pipeline and pressure sensor in sequence, place the quartz reactor on the mass sensor, connect the reflection cavity and focusing device to the one-dimensional slide, adjust the one-dimensional slide, place the reflection cavity and focusing device in the center of the solar irradiation spot, place three thermocouples at different heights in the fluidized bed, install the infrared thermal imager vertically downward on the two-dimensional slide, move the two-dimensional slide so that the center of the infrared thermal imager is consistent with the center of the reactor, connect the power supply line of the solar simulator, set the temperature control program of the solar simulator, connect each data acquisition line to the computer, and wait for data collection; Step 2: Add an appropriate amount of modified calcium carbonate particles to the fluidized bed, turn on the infrared thermal imager, focus it so that the particles in the fluidized bed are clearly visible; open the gas cylinder valve to introduce fluidizing gas, and wait for the weight signal to stabilize; remotely turn on the solar simulator light source to ensure that its temperature reaches the set temperature, observe and record various parameters on the computer, switch the gas to an inert gas, and allow it to decompose completely; use remote control to switch the reaction gas so that it adsorbs carbon dioxide to become calcium carbonate.

7. The photogravimetric fluidized bed analysis and testing method according to claim 6, characterized in that: In-situ parameters include temperature, weight, inlet pressure in the fluidized bed, and movement and temperature of particles on the upper surface of the bed.

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