RU178100U1 - Freezer for determining frost resistance - Google Patents

Abstract

The utility model relates to the field of testing. The freezer for determining frost resistance contains a heat-insulated casing, in the upper part of which there is a machine room with refrigerating machines, and a processor control unit, configured to implement the functions of measuring and regulating temperature, in the lower part there is a working freezer with shelves to be closed by the door for placing test samples, and in the central part of the cavity of which temperature sensors are fixed, and in the upper part of this chamber there is a monoblock air cooler in the form two fans speed 2600 rev / min for mixing air in the cavity of the freezing chamber evaporator surface and cleaning snow from lamellas coats have broken chiller. The processor control unit is configured to implement the additional control function of both chillers for their joint operation in the initial cooling mode of the freezer to a temperature of minus 15 ° C and their alternate operation with long-term cooling at a temperature in the range of minus (15-20) ° C in replaceable the operation mode of one chiller while the other chiller is idle. The air cooler is made in the form of two fans. 2 ill.

Description

The utility model relates to the field of testing equipment used to determine the frost resistance of samples of various materials (concrete, brick, mortar, cement, asbestos cement, asphalt concrete, crushed stone, etc.). In the framework of this utility model, the design of a freezer in the form of a refrigerator is considered, designed to determine the frost resistance of concrete samples by the first basic method according to GOST 10060-2012 “Concretes. Methods for determining frost resistance ", brick samples in accordance with GOST 7025-91" Brick and ceramic and silicate stones. Methods for determining water absorption, density and frost resistance control "and mortar samples according to GOST 5802-86" Building solutions. Test Methods. "

Concrete frost resistance - the ability of concrete to maintain physical and mechanical properties during repeated alternate freezing and thawing. Concrete frost resistance is characterized by the frost resistance brand, which means the maximum number of freezing and thawing cycles of concrete samples established by the standards, carried out according to the basic methods, in which the initial physical and mechanical properties are maintained within the limits approved by the standard. The method for determining the frost resistance of concrete is regulated by the GOST 10060-2012 standard, according to which all samples, including control ones, are saturated with water at a temperature of (20 ± 2) ° C before testing. To do this, they are first immersed in water (or saline) at 1/3 of their height and held for 24 hours, then the liquid level is brought up to 2/3 of the height of the samples and also held for 24 hours. After that, the samples are completely immersed in the liquid so that she surrounded them on all sides with a layer of at least 20 mm, and in this state they stand for another 48 hours.

Control samples are tested for compression after 2 ... 4 hours after extraction from the bath, where they were saturated. The concrete samples to be tested, after being saturated with water for 96 hours, are loaded into containers in the freezer or placed on the mesh racks of the freezer so that the distance between them, the walls of the containers and the overlying racks is at least 50 mm. If after loading the chamber the temperature in it rises above -16 ° C, then the start of freezing is considered to be the moment the temperature in the freezer is set to -16 ° C. During the entire freezing cycle, the temperature in the chamber is maintained in the range of -16 ... -20 ° C, measuring it in the center of the volume of the freezer in the immediate vicinity of the samples. Thawing is carried out in a bath with water at a temperature of (20 ± 2) ° C; in this case, the samples should be surrounded by a layer of water with a thickness of at least 50 mm.

The number of freezing and thawing cycles of basic concrete samples should be at least one per day. In case of forced (technically justified) interruptions in the frost test, the samples must be in a frozen state.

2 ... 4 hours after the appropriate number of freezing and thawing cycles, the main samples removed from the bath are inspected and weighed, and then tested for compression.

Concrete samples are frozen in freezers.

Thus, a freezer in the form of a refrigerator is known, consisting of a thermally insulated casing assembled from the outer and inner boxes and in the upper part of the casing there is a machine room with a single-stage refrigerating machine containing an SC-15CM compressor that provides a temperature of minus 18 ± in the cooled working chamber volume 2 ° C, which is necessary for frost resistance tests by the first basic method according to the requirements of GOST 10060-2012, and a control unit with a microprocessor meter-temperature controller, and in the lower part STI is a working body freezer with shelves for placement of the test specimens, the door is closed. An air cooler and a heating element are located in the upper part of the cooled chamber of the working chamber, and temperature sensors are fixed in the center of the working chamber (RU 77403, F25D 13/00, published on October 20, 2008).

In a known solution, water-saturated test specimens for frost resistance are wiped with a cloth and placed in a working chamber at a temperature of minus 18 ° C. The start of the freezing cycle is considered to include the ninth step of the test program after the temperature in the working chamber is minus 16 ÷ 20 ° C. Temperature control in the cooled volume of the working chamber is carried out according to the indications on the display of the microprocessor meter-controller of the temperature of the control unit. The end of the freezing cycle is considered to include the tenth step of the program. During reaching the temperature of minus 16 ÷ 20 ° C in the working chamber and at the tenth step, the defrosting of the heat exchange surface of the evaporator is programmed to clean it from the snow coat during and after freezing by means of a heater. After freezing, the samples are removed from the working chamber.

A disadvantage of the known solution lies in the long time it takes to reach the required temperature in the chamber after loading the samples and in sufficient energy consumption due to the constant operation of one refrigeration machine and its frequent switching from the compressor operation mode to off mode. In addition, the operation of the heating element for thawing the evaporator (cleaning the surface of the evaporator lamellae from the snow coat of an idle refrigeration machine) affects the energy consumption. Constant long-term operation of the chiller and the use of heating elements also affect the operational life of the freezer.

This utility model is aimed at achieving a technical result consisting in the maximum possible increase in the productivity of the freezer in order to reduce the cycle time for freezing samples, in the operational life of the freezer due to the use of two refrigeration machines and the elimination of heating elements for defrosting evaporators due to the experimentally selected increased heat exchange surface of evaporators and with partial transfer of the function of the heating elements to the fans for blowing evaporators power.

The specified technical result is achieved in that a freezer for determining frost resistance, comprising a thermally insulated body, in the upper part of which there is a machine room with a refrigerating machine, and a processor control unit, configured to implement the functions of measuring and regulating the temperature, in the bottom - a working freezer closed by a door a chamber with shelves for placement of test samples and in the central part of the cavity of which temperature sensors are fixed, and in the upper part of this measures, an air cooler is located, equipped with an additional refrigerating machine located in the engine room and not hydraulically connected to the first refrigerating machine, the processor control unit is configured to implement an additional control function for both refrigerating machines for their joint operation in the initial cooling mode of the freezer to a temperature of minus 15 ° C and their alternate operation with prolonged cooling at a temperature in the range of minus (15-20) ° C in a shift mode of operation of one refrigerating machine s when broken another refrigerating machine and an air cooler is designed as a fan with a rotation speed 2600 rev / min for effective heat exchange, mixing air into the freezer cavity and partial purification of the evaporator lamellas from snow coats have broken chiller.

These features are significant and are interconnected with the formation of a stable set of essential features sufficient to obtain the desired technical result.

The present utility model is illustrated by a specific example of execution, which, however, is not the only possible one, but clearly demonstrates the possibility of achieving the required technical result.

In FIG. 1 shows a general view of a freezer with an open door;

FIG. 2 is a diagram of the operation of two refrigeration machines using the example of a program for determining the frost resistance of brick samples by volumetric freezing according to GOST 7025-91 “Brick and ceramic and silicate stones. Methods for determining water absorption, density and frost resistance control. "

According to this utility model, an improved design of a freezer used to determine the frost resistance of concrete samples according to the first basic method described in GOST 10060-2012 mortar samples according to GOST 5802-86 and in accordance with the requirements of GOST 7025-91, which are within the requirements in time intervals and temperature conditions are shown in figure 2 on the diagram of the program for determining the frost resistance of brick samples.

These tests should be carried out in a freezer compartment with forced ventilation and automatically controlled temperature from minus 5 to minus 20 ° C.

To solve this problem, a freezer (Fig. 1) is used consisting of a thermally insulated casing 1, for example, assembled from two boxes - an external 2 and an internal 3. In the upper part of the casing 1 there is an engine room 4 with two single-stage refrigerating machines 5, which are hydraulically between microprocessor control unit 6 with a temperature meter-controller 7, configured to implement the functions of measuring and regulating the temperature in the freezer 8. In the lower part of the case and the freezer 8 with shelves 9 for placing the test samples, this freezer is closed by the door 10. In the upper part of the cooled volume of the freezer 8 there is a monoblock air cooler 11, made in the form of two evaporative batteries, blown by two powerful fans with a speed of 2600 rpm for heat transfer and air mixing in the cavity of the freezer. Both fans blowing evaporators are active when the active state of any of the compressors of refrigeration machines in order to create a powerful flow of air mass with a given speed of its movement. This allows not only to efficiently exchange heat and mix air in the cavity of the freezer, but also to use the energy of the air flow to partially clean the surface of the evaporator lamellas from the snow coat of the refrigeration machine that is currently not working.

The accumulation of snow coat or frost on the lamellas of evaporators is a completely natural process, which lasts from a good refrigerator for 3 months to six months, unless of course you have installed the No Frost system (a system for forcing the evaporator to clear the snow coat by defrosting with a heating element controlled by a timer ) The physical component of the freezing process is quite simple. During evaporation, the refrigerant takes heat from the refrigerator and gives off heat to the environment when it is forced to condense. This happens in cycles:

- cooling to the set temperature

- rest, during which the temperature rises to a predetermined value.

And this cycle is constantly repeating. Moisture condensed from the air begins to freeze on the surface of the evaporators, since the temperature on the surface of the evaporator tubes ranges from -10 ° C during the start of cooling to -30 ° C when the required temperature in the freezer is reached.

In this regard, the rate of involvement of moisture vapor in the air flow from the surface of the frozen samples is directly related to the speed of movement of the air mass. This is based on the physical ability of air to retain a large amount of water vapor and the greater the higher the temperature.

In the center of the freezer, temperature sensors 12 are fixed.

The presence of two (instead of one) hydraulically independent chillers allows you to organize a new algorithm for the operation of the freezer to reduce the time required to reach a given temperature. This algorithm is shown in FIG. 2 (provided by the control program in the processor control unit): in the 1st, 2nd and 3rd test steps, both chillers operate simultaneously. At the 4th, 5th and 6th steps, the chillers operate alternately one at a time: one chiller is working, the other is in the off state. Such an operation algorithm makes it possible to achieve the minimum possible time to reach the required temperature in the chamber after loading the samples, uniform use of the technical resource of both chillers, and minimal energy consumption.

For this, the processor control unit is configured to implement an additional control function for both chillers for their joint operation in the initial cooling mode of the freezer to a temperature of minus 15 ° C and their alternate operation with prolonged cooling at a temperature in the range of minus (15-20) ° C in a shift mode of operation of one refrigerating machine while another refrigerating machine is idle.

The necessary algorithm for the operation of chillers with the maintenance of the necessary parameters of air temperature and time intervals regulated by GOSTs is provided by the control program for all elements of the freezer. The original control program is embedded in the non-volatile memory of the microprocessor of the camera control controller.

The purpose of equipping the freezer compartment with two refrigerators is to achieve the minimum possible time to reach the required temperature before and after loading the samples, to achieve uniform use of the technical life of both refrigerators, to achieve the optimal operation of both refrigerators according to the criterion for the permissible on / off frequency of the compressor of the refrigeration machine and minimization of the consumption of technical resources of refrigeration machines and energy consumption. Achieving the minimum possible time to reach the required temperature regime before and after loading the samples allows to achieve the maximum productivity of the freezer in the number of freezing cycles per day.

It is impossible to achieve the same camera performance in the prototype (with one refrigeration machine) compared to a freezer equipped with a duplicated refrigeration system. So, a simple increase in the compressor chamber power of the prototype chamber allows achieving a similar time interval at the 1st, 2nd and 3rd steps of program execution, but does not allow the compressor to work in normal cyclic mode on the 4th, 5th and 6th steps. The overestimated power of the chiller will lead to unnecessarily frequent on-off of the compressor and its failure. The normal number of compressor starts should not exceed 7 ÷ 10 cycles in one hour. The lower this indicator, the easier the compressor operates and the higher the safety of its technical resource. For a camera equipped with a duplicated refrigeration system, this figure is 3 cycles per hour.

The operation of the freezer is as follows. Samples for frost resistance tests saturated with water, wiped with a cloth and placed in the freezer 8 at a temperature of minus 18 ° C. The start of the freezing cycle is considered to be the execution of the test program after the temperature in this chamber is set to 8 minus 15 ÷ 20 ° C. Temperature control in the cooled volume of the freezer 8 is carried out according to the indications on the display of the microprocessor meter-temperature controller 7 of the control unit 6. The end of the freezing cycle is considered to include the last step of the program. After freezing, the samples are removed from the working chamber.

The use of heating elements for defrosting evaporators in the prototype is due to the need to clean the surface of the evaporator lamellas from the resulting snow coat during reaching the required temperature regime after loading the samples, since the samples are placed for freezing in the freezer after the next thawing procedure in water and have high moisture saturation. Without the use of defrosting the evaporators of the prototype, it is impossible to achieve the necessary negative temperature in the chamber due to the deterioration of heat transfer due to the formation of a snow coat or the likelihood of non-compliance with the required standardized temperature conditions during freezing of samples at the 4th, 5th and 6th steps of the program.

The possibility of excluding from the structure of the design of chillers TENs for thawing evaporators of the chiller is achieved due to the experimentally selected more developed surface of the lamellas of the evaporators of each chiller and the presence of two independent chillers. The presence of two alternately working refrigerators while maintaining the required standardized temperature conditions at the 4th, 5th and 6th steps of the program execution allows partial self-cleaning of the surface of the evaporator lamellas from the snow coat of an idle refrigeration machine while another refrigeration machine is operating. The exclusion from the design of chillers of heating elements of thawing of evaporators of refrigerating machines increases the productivity of the freezer by the number of freezing cycles per day, reduces the likelihood of failure of the freezer due to failure of the heating elements, eliminates fire hazard and reduces energy consumption.

Self-cleaning the surface of the evaporator lamellas from the snow coat of an idle chiller is enhanced by the use of constantly working fans with a rotation frequency of 2600 rpm against 1300 rpm, as in the prototype. The use of high-speed fans with a rotation frequency of 2600 rpm increases the mixing of air in the freezer and improves the indicator of temperature unevenness at different points of the chamber.

This utility model is industrially applicable and can be manufactured industrially using the technologies used in the manufacture of refrigeration units for various purposes.

Claims (1)

A freezer for determining frost resistance, comprising a thermally insulated casing, in the upper part of which there is a machine room with refrigerating machines, and a processor control unit configured to implement temperature measurement and control functions, and in the lower part, a working freezer with shelves to be closed by a door for placing test samples and in the central part of the cavity of which temperature sensors are fixed, and in the upper part of this chamber there is a monoblock air cooler, from characterized in that it is equipped with an additional refrigerating machine located in the engine room and is not hydraulically connected to the first refrigerating machine, the processor control unit is configured to implement an additional control function for both refrigerating machines for their joint operation in the initial cooling mode of the freezer to a temperature of minus 15 ° C and their alternate operation during prolonged cooling at a temperature in the range of minus (15-20) ° C in a shift mode of operation of one chiller when not working another refrigerating machine, and the air cooler is made in the form of two evaporative batteries, blown by two fans with a speed of 2600 rpm to mix the air in the cavity of the freezer and clean the surface of the evaporator lamellas from the snow coat of an idle refrigeration machine.

Images