How to calculate a submersible refrigeration evaporator for water. Selection of heat exchange equipment
Problem 1
The flow of hot product leaving the reactor must be cooled from the initial temperature t 1n = 95 ° C to the final temperature t 1c = 50 ° C, for this it is sent to a refrigerator, where water is fed with an initial temperature t 2n = 20 ° C. It is required to calculate ∆t av in conditions of forward flow and counterflow in the refrigerator.
Solution: 1) The final temperature of the cooling water t 2k in the condition of the direct flow of heat carriers cannot exceed the value of the final temperature of the hot heat carrier (t 1k = 50 ° C), therefore, we take the value of t 2k = 40 ° C.
Let's calculate the average temperatures at the entrance and exit from the refrigerator:
∆t n avg = 95 - 20 = 75;
∆t to cf = 50 - 40 = 10
∆t avg = 75 - 10 / ln (75/10) = 32.3 ° C
2) The final temperature of the water in the countercurrent movement will be the same as in the direct flow of heat carriers t 2k = 40 ° C.
∆t n avg = 95 - 40 = 55;
∆t to cf = 50 - 20 = 30
∆t avg = 55 - 30 / ln (55/30) = 41.3 ° C
Objective 2.
Using the conditions of problem 1, determine the required heat exchange surface (F) and cooling water flow rate (G). The consumption of the hot product is G = 15000 kg / h, its heat capacity is C = 3430 J / kg · deg (0.8 kcal · kg · deg). Cooling water has the following values: heat capacity c = 4080 J / kg deg (1 kcal kg deg), heat transfer coefficient k = 290 W / m2 deg (250 kcal / m2 * deg).
Solution: Using the equation heat balance, we get an expression for determining heat flow when heating a cold heat carrier:
Q = Q rt = Q xt
whence: Q = Q rt = GC (t 1n - t 1k) = (15000/3600) 3430 (95 - 50) = 643125 W
Taking t 2k = 40 ° C, we find the flow rate of the cold heat carrier:
G = Q / s (t 2k - t 2n) = 643125/4080 (40 - 20) = 7.9 kg / sec = 28 500 kg / h
Required heat exchange surface
with forward flow:
F = Q / k ∆t avg = 643125/290 32.3 = 69 m 2
with counterflow:
F = Q / k ∆t avg = 643125/290 41.3 = 54 m 2
Problem 3
At production, gas is transported through a steel pipeline with an outer diameter of d 2 = 1500 mm, wall thickness δ 2 = 15 mm, thermal conductivity λ 2 = 55 W / m · deg. Inside the pipeline is lined fireclay bricks, the thickness of which δ 1 = 85 mm, thermal conductivity λ 1 = 0.91 W / m · deg. The heat transfer coefficient from the gas to the wall α 1 = 12.7 W / m 2 · deg, from the outer surface of the wall to the air α 2 = 17.3 W / m 2 · deg. It is required to find the heat transfer coefficient from gas to air.
Solution: 1) Determine the inner diameter of the pipeline:
d 1 = d 2 - 2 (δ 2 + δ 1) = 1500 - 2 (15 + 85) = 1300 mm = 1.3 m
average lining diameter:
d 1 cf = 1300 + 85 = 1385 mm = 1.385 m
average pipeline wall diameter:
d 2 cf = 1500 - 15 = 1485 mm = 1.485 m
Let's calculate the heat transfer coefficient according to the formula:
k = [(1 / α 1) (1 / d 1) + (δ 1 / λ 1) 1 / α 2)] -1 = [(1 / 12.7) · (1 / 1.3) + (0.085 / 0.91) · (1 / 1.385) + (0.015 / 55) · (1 / 1.485 ) + (1 / 17.3)] -1 = 5.4 W / m2 · deg
Problem 4
In a one-pass shell-and-tube heat exchanger, methyl alcohol is heated with water from an initial temperature of 20 to 45 ° C. The water stream is cooled from 100 to 45 ° C. The tube bundle of the heat exchanger contains 111 tubes, the diameter of one tube is 25x2.5 mm. The flow velocity of methanol through the tubes is 0.8 m / s (w). The heat transfer coefficient is 400 W / m2 · deg. Determine the total length of the tube bundle.
Let us define the average temperature difference of the heat carriers as the mean logarithmic one.
∆t n avg = 95 - 45 = 50;
∆t k avg = 45 - 20 = 25
∆t avg = 45 + 20/2 = 32.5 ° C
Determine the mass consumption of methyl alcohol.
G cn = n · 0.785 · d int 2 · w cn · ρ cn = 111 · 0.785 · 0.02 2 · 0.8 · = 21.8
ρ cn = 785 kg / m 3 - the density of methyl alcohol at 32.5 ° C was found from the reference literature.
Then we define the heat flux.
Q = G cn with cn (t c cn - t n cn) = 21.8 · 2520 (45 - 20) = 1.373 · 10 6 W
c cn = 2520 kg / m 3 - the heat capacity of methyl alcohol at 32.5 ° C was found from the reference literature.
Let us determine the required heat transfer surface.
F = Q / K∆t avg = 1.373 10 6 / (400 37.5) = 91.7 m 3
Let's calculate the total length of the tube bundle by the average diameter of the tubes.
L = F / nπd avg = 91.7 / 111 3.14 0.0225 = 11.7 m.
Problem 5
A plate heat exchanger is used to heat the stream of 10% NaOH solution from 40 ° C to 75 ° C. The sodium hydroxide consumption is 19000 kg / h. Water vapor condensate is used as a heating agent, its consumption is 16000 kg / h, the initial temperature is 95 ° C. Take the heat transfer coefficient equal to 1400 W / m 2 deg. It is necessary to calculate the basic parameters of the plate heat exchanger.
Solution: Find the amount of heat transferred.
Q = G p s p (t k p - t n p) = 19000/3600 3860 (75 - 40) = 713 028 W
From the heat balance equation, we determine the final temperature of the condensate.
t k x = (Q 3600 / G k s k) - 95 = (713028 3600) / (16000 4190) - 95 = 56.7 ° C
с р, к - heat capacity of solution and condensate were found from reference materials.
Determination of average temperatures of heat carriers.
∆t n avg = 95 - 75 = 20;
∆t to cf = 56.7 - 40 = 16.7
∆t avg = 20 + 16.7 / 2 = 18.4 ° C
Let us determine the cross-section of the channels, for the calculation we take the mass velocity of the condensate W к = 1500 kg / m 2 · sec.
S = G / W = 16000/3600 1500 = 0.003 m 2
Taking the channel width b = 6 mm, we find the spiral width.
B = S / b = 0.003 / 0.006 = 0.5 m
We will refine the channel section
S = B b = 0.58 0.006 = 0.0035 m 2
and mass flow rate
W p = G p / S = 19000/3600 0.0035 = 1508 kg / m 3 s
W k = G k / S = 16000/3600 0.0035 = 1270 kg / m 3 s
The determination of the heat exchange surface of a spiral heat exchanger is carried out as follows.
F = Q / K∆t avg = 713028 / (1400 18.4) = 27.7 m 2
Determine the working length of the spiral
L = F / 2B = 27.7 / (2 0.58) = 23.8 m
t = b + δ = 6 + 5 = 11 mm
To calculate the number of turns of each spiral, it is necessary to take the initial spiral diameter based on the recommendations d = 200 mm.
N = (√ (2L / πt) + x 2) - x = (√ (2 23.8 / 3.14 0.011) +8.6 2) - 8.6 = 29.5
where x = 0.5 (d / t - 1) = 0.5 (200/11 - 1) = 8.6
The outer diameter of the spiral is determined as follows.
D = d + 2Nt + δ = 200 + 2 · 29.5 · 11 + 5 = 860 mm.
Problem 6
Determine the hydraulic resistance of heat carriers created in a four-way plate heat exchanger with a channel length of 0.9 m and an equivalent diameter of 7.5 · 10 -3 when cooling butyl alcohol with water. Butyl alcohol has the following characteristics: consumption G = 2.5 kg / s, speed W = 0.240 m / s and density ρ = 776 kg / m 3 (Reynolds criterion Re = 1573> 50). The cooling water has the following characteristics: flow rate G = 5 kg / s, speed of movement W = 0.175 m / s and density ρ = 995 kg / m 3 (Reynolds criterion Re = 3101> 50).
Solution: Determine the coefficient of local hydraulic resistance.
ζ bs = 15 / Re 0.25 = 15/1573 0.25 = 2.38
ζ in = 15 / Re 0.25 = 15/3101 0.25 = 2.01
Let's clarify the speed of movement of alcohol and water in the fittings (for example, d pcs = 0.3m)
W pc = G bs / ρ bs 0.785d pc 2 = 2.5 / 776 · 0.785 · 0.3 2 = 0.05 m / s less than 2 m / s therefore can be ignored.
W pcs = G in / ρ in 0.785d pcs 2 = 5/995 · 0.785 · 0.3 2 = 0.07 m / s less than 2 m / s therefore can be ignored.
Let's determine the value of hydraulic resistance for butyl alcohol and cooling water.
∆Р bs = хζ l/d) (Ρ bs w 2/2) = (4 2.38 0.9 / 0.0075) (776 0.240 2/2) = 25532 Pa
∆Р в = хζ l/d) (Ρ in w 2/2) = (4 2.01 0.9 / 0.0075) (995 0.175 2/2) = 14699 Pa.
Own production of liquid cooling units (chillers) was organized in 2006. The first units had a cooling capacity of 60 kW and were assembled on the basis of plate heat exchangers. If necessary, they were equipped with a hydronic module.
The hydronic module is a heat-insulated tank with a capacity of 500 liters (depending on the capacity, so for an installation with a cooling capacity of 50-60 kW, the tank capacity should be 1.2-1.5 m3), divided by a specially shaped partition into two tanks for "warm" and "cooled" water ... The internal circuit pump, taking water from the "warm" compartment of the tank, delivers it to plate heat exchanger, where it, passing in a countercurrent with freon, is cooled. Chilled water enters the other part of the tank. The capacity of the internal pump must not be less than the capacity of the external circuit pump. The special shape of the baffle allows you to adjust the overflow volume within a wide range with a slight change in the water level.
When using water as a heat carrier, such installations allow it to be cooled down to + 5ºC ÷ + 7ºС. Accordingly, at standard calculation equipment, the temperature of incoming water (coming from the consumer) is assumed to be + 10 ° C ÷ + 12 ° C. The power of the installation is calculated based on the required water consumption.
Our equipment is equipped with multi-stage protection systems. The pressure switches protect the compressor from overload. Limiter low pressure does not allow boiling freon to lower its temperature below minus 2 ° C, protecting the plate heat exchanger from possible freezing of water. Installed relay the duct will turn off refrigeration compressor upon occurrence airlock, with blockage of pipelines, with frosting of the plates. The suction pressure regulator maintains the boiling point of freon + 1 ° C ± 0.2 ° C.
Similar devices were installed by us for cooling the solution of brine baths for salting cheese at cheese factories, for rapid cooling of milk after pasteurization at dairies, for smoothly lowering the temperature of water in pools at factories for the production (breeding and growing) of fish.
If it is necessary to lower the temperature of the heat carrier from + 5ºC ÷ + 7ºC to negative and near zero temperatures, instead of water, a propylene glycol solution is used as a heat carrier. It is also used if the temperature environment drops below -5 ° C, or, if necessary, from time to time turn off the internal circuit pump (circuit: buffer tank - heat exchanger of the refrigeration unit).
When calculating equipment, we must take into account changes in such properties of the coolant as heat capacity and surface heat transfer coefficient. A PLANT DESIGNED FOR WORKING WITH WATER WILL WORK INCORRECTLY WHEN REPLACING THE CARTRIDGE WITH ETHYLENE GLYCOL, PROPYLENE GLYCOL OR BRINE SOLUTIONS. AND VICE VERSA .
The paraffin cooling unit, assembled according to this scheme, works in conjunction with air system coolant cooling in winter time, with automatic shutdown of the refrigeration compressor.
We have experience in the design and manufacture of chillers to solve the problem of cooling in a short period of time, but with a high cooling capacity. For example, a milk receiving shop requires installations with an operating time of 2 hours / day to cool during this time 20 tons of milk from + 25ºC ÷ + 30ºС to + 6ºC ÷ + 8ºС. This is the so-called pulse cooling problem.
When setting the problem of impulse cooling of products, it is economically expedient to manufacture a chiller with a cold accumulator. As a standard, we make such installations as follows:
A) A heat-insulated tank with a volume of 125-150% of the calculated buffer tank filled with water by 90%;
B) An evaporator is placed inside it, made of bent copper pipelines, or metal plates with grooves milled inside;
By supplying freon with a temperature of -17ºC ÷ -25ºС, we ensure the freezing of ice required thickness... The water coming from the consumer is cooled as a result of ice melting. Bubbling is used to increase the rate of melting.
Such a system allows the use of refrigeration units with a capacity of 5 ÷ 10 times less than the value of the impulse power of the refrigeration load. It should be understood that the temperature of the water in the tank may differ significantly from 0 ° C, since the rate of ice melting in water with a temperature of even + 5 ° C is very low. Also, the disadvantages of this system can be attributed to the large weight and size of the tank with the evaporator, which is explained by the need to provide a large heat exchange area at the ice / water interface.
If it is necessary to use water with a near zero temperature (0 ° C ÷ + 1 ° C) as a heat carrier, without the possibility of using propylene glycol, ethylene glycol or brine solutions instead (for example, system leakage or SANPiN requirements), we manufacture chillers using film heat exchangers.
With such a system, the water coming from the consumer, passing through a special system of collectors and nozzles, uniformly washes metal plates of a large area cooled by freon to minus 5 ° C. Flowing down, part of the water freezes on the plates, forming a thin film of ice, the rest of the water, flowing down this film, is cooled to the required temperature and collected in a heat-insulated tank located under the plates, from where it is supplied to the consumer.
Such systems have strict requirements for the level of dustiness of the room where the tank with the evaporator is installed and, for obvious reasons, require more high level ceilings. They are characterized by the largest dimensions and cost.
Our company will solve any problem of liquid cooling set by you. We will assemble (or select a ready-made) installation with an optimal operating principle and minimum cost, both for the installation itself and for its operation.
The area of the heat-transfer surface of the evaporator F, m 2, is determined by the formula:
where is the heat flux in the evaporator, W
k - the heat transfer coefficient of the evaporator, W / (m 2 * K), depends on the type of the evaporator;
Average logarithmic difference between the temperatures of the boiling freon and the cooled medium;
- specific heat flux equal to 4700 W / m 2
The coolant consumption required for the removal of heat fluxes is determined by the formula:
where with - heat capacity of the medium to be cooled: for water 4.187 kJ / (kg * ° C), for brine, the heat capacity is taken according to special tables depending on its freezing temperature, which is taken 5-8 ° C below the boiling point of the refrigerant t 0 for open systems and 8-10 ° C lower t 0 for closed systems;
ρ p is the density of the SCR refrigerant, kg / m 3;
Δ t R - the difference in temperature of the coolant at the inlet to the evaporator and at the outlet from it, ° С.
For air conditioning conditions in the presence of spray irrigation chambers, water flow distribution schemes are used. According to this, Δt p is determined as the temperature difference at the outlet from the sump of the irrigation chamber t w.k and at the outlet of the evaporator t NS :.
8. Selection of the condenser
The calculation of the capacitor is reduced to determining the area of the heat-transfer surface, over which one or more capacitors with a total surface area equal to the calculated one are selected (the margin over the surface is not more than + 15%).
1. The theoretical heat flux in the condenser is determined by the difference in specific enthalpies in the theoretical cycle with or without taking into account the overcooling in the condenser:
a) heat flux, taking into account overcooling in the condenser, is determined by the difference in specific enthalpies in the theoretical cycle:
b) heat flux without taking into account subcooling in the condenser and in the absence of a regenerative heat exchanger
Total heat load taking into account the thermal equivalent of the power expended by the compressor to compress the refrigerant (actual heat flux):
2. The average logarithmic temperature difference θ cf between the condensing refrigerant and the medium cooling the condenser is determined, ° С:
where is the temperature difference at the beginning of the heat transfer surface (large temperature difference), 0 С:
Temperature difference at the end of the heat transfer surface (smaller temperature difference), 0 С:
3. Find the specific heat flux:
where k is the heat transfer coefficient, equal to 700 W / (m 2 * K)
4. The area of the heat transfer surface of the condenser:
5. Consumption of the medium cooling the condenser:
where is the total heat flux in the condenser from all compressor groups, kW;
with - specific heat capacity of the medium cooling the condenser (water, air), kJ / (kg * K);
ρ is the density of the medium cooling the condenser, kg / m 3;
- heating of the medium cooling the condenser, ° С:
1.1 - safety factor (10%), taking into account non-productive losses.
According to the water consumption, taking into account the required pressure, a circulating water supply pump of the required capacity is selected. A backup pump must be provided.
9. Selection of the main refrigeration units
The selection of a refrigeration machine is carried out using one of three methods:
According to the described volume of the compressor included in the machine;
According to the refrigeration capacity graphs of the machine;
According to the tabular values of the cooling capacity of the machine, given in the technical characteristics of the product.
The first method is similar to that used to calculate a single-stage compressor: the required volume described by the pistons of the compressor is determined, and then, according to the tables of technical characteristics, a machine or several machines are selected so that the actual value of the volume described by the pistons is 20-30% more than that obtained by calculation.
When selecting a refrigerating machine by the third method, it is necessary to bring the cooling capacity of the machine, calculated for operating conditions, to the conditions under which it is given in the table of characteristics, that is, to standard conditions.
After selecting the brand of the unit (according to the cooling capacity reduced to standard conditions), it is necessary to check whether the area of the heat transfer surface of the evaporator and condenser is sufficient. If the area of the heat-transferring surface of the devices indicated in the technical specification is equal to the calculated one or slightly more than it, the machine is selected correctly. If, for example, the surface area of the evaporator turned out to be less than the calculated one, it is necessary to set a new value of the temperature head (lower boiling point), and then check whether the compressor capacity is sufficient at the new value of the boiling point.
We accept a York YCWM water-cooled chiller with a cooling capacity of 75 kW.
When calculating the designed evaporator, its heat transfer surface and the volume of circulating brine or water are determined.
The heat transfer surface of the evaporator is found by the formula:
where F is the heat transfer surface of the evaporator, m 2;
Q 0 - cooling capacity of the machine, W;
Dt m - for shell-and-tube evaporators it is the average logarithmic difference between the temperatures of the coolant and the boiling point of the refrigerant, and for panel evaporators it is arithmetic difference between the temperatures of the leaving brine and the boiling point of the refrigerant, 0 С;
- heat flux density, W / m 2.
For approximate calculations of evaporators, the values of the heat transfer coefficients obtained experimentally in W / (m 2 × K) are used:
for ammonia evaporators:
shell-and-tube 450 - 550
panel 550 - 650
for freon shell and tube evaporators with rolling fins 250 - 350.
The average logarithmic difference between the temperatures of the coolant and the boiling point of the refrigerant in the evaporator is calculated by the formula:
(5.2)
where t P1 and t P2 are the temperatures of the coolant at the inlet and outlet of the evaporator, 0 С;
t 0 - boiling point of the refrigerant, 0 С.
For panel evaporators, due to the large volume of the tank and the intensive circulation of the coolant, its average temperature can be taken equal to the temperature at the outlet from the tank t P2. Therefore, for these evaporators 
The volume of the circulating coolant is determined by the formula:
(5.3)
where V P is the volume of the circulating heat carrier, m 3 / s;
с Р - specific heat capacity of brine, J / (kg × 0 С);
r P is the density of the brine, kg / m 3;
t P2 and t P1 are the temperature of the coolant, respectively, when entering and leaving the cooled room, 0 С;
Q 0 - cooling capacity of the machine.
The values with P and r P are found from the reference data for the corresponding coolant, depending on its temperature and concentration.
The temperature of the coolant when it passes through the evaporator decreases by 2 - 3 0 С.
Calculation of evaporators for cooling air in cold rooms
To distribute the evaporators included in the refrigerating machine set, determine the required heat transfer surface according to the formula:
where SQ is the total heat input to the chamber;
K is the heat transfer coefficient of chamber equipment, W / (m 2 × K);
Dt is the calculated temperature difference between the air in the chamber and average temperature coolant with brine cooling, 0 С.
The heat transfer coefficient for the battery is taken as 1.5-2.5 W / (m 2 K), for air coolers - 12-14 W / (m 2 K).
The calculated temperature difference for batteries is 14–16 0 С, for air coolers - 9–11 0 С.
The number of cooling devices for each chamber is determined by the formula:
where n is the required number of cooling devices, pcs;
f - heat transfer surface of one battery or air cooler (taken on the basis of technical characteristics cars).
Capacitors
There are two main types of condensers: water-cooled and air cooled... In refrigeration plants of large capacity, water-air cooled condensers, called evaporative ones, are also used.
In refrigeration units for commercial refrigeration equipment air-cooled condensers are most often used. Compared to a water-cooled condenser, they are economical to operate, easier to install and operate. Chillers with water cooled condensers are more compact than air cooled chillers. In addition, they emit less noise during operation.
Water-cooled condensers are distinguished by the nature of the movement of water: flow-through type and irrigation, and by design - shell-snake, double-pipe and shell-and-tube.
The main type is horizontal shell-and-tube condensers (fig. 5.3). There are some differences in the design of ammonia and freon condensers depending on the type of refrigerant. In terms of the size of the heat transfer surface, ammonia condensers cover the range from about 30 to 1250 m 2, and freon ones - from 5 to 500 m 2. In addition, ammonia vertical shell-and-tube condensers with a heat-transfer surface area from 50 to 250 m 2 are produced.
Shell and tube condensers are used in machines of medium and large capacity. Hot refrigerant vapors enter through branch pipe 3 (Fig. 5.3) into the annular space and condense on the outer surface of the horizontal tube bundle.
Cooling water circulates inside the pipes under the pressure of the pump. The pipes are expanded in tube sheets, closed from the outside with water covers with partitions that create several horizontal passages (2-4-6). Water enters through the branch pipe 8 from below and exits through the branch pipe 7. On the same water cover there is a valve 6 for venting air from the water space and a valve 9 for draining water during revision or repair of the condenser.
Figure 5.3 - Horizontal shell and tube condensers
On top of the device there is safety valve 1, connecting the annular space of the ammonia condenser with a pipeline leading to the outside, above the ridge of the roof of the tallest building within a radius of 50 m.A equalizing line is connected through the branch pipe 2, connecting the condenser with the receiver, where the liquid refrigerant is discharged through the branch pipe 10 from the lower part of the apparatus. An oil sump with a pipe 11 for oil drainage is welded to the bottom of the body. The liquid refrigerant level at the bottom of the casing is monitored with a level gauge 12. During normal operation, all liquid refrigerant should drain into the receiver.
On top of the casing there is a valve 5 for bleeding air, as well as a branch pipe for connecting a pressure gauge 4.
Vertical shell-and-tube condensers are used in ammonia refrigeration machines high performance, they are designed for a thermal load from 225 to 1150 kW and are installed outside the machine room without taking up its usable area.
Recently, capacitors have appeared plate type... The high intensity of heat transfer in plate condensers, in comparison with shell-and-tube condensers, makes it possible, at the same heat load, to approximately halve the metal consumption of the apparatus and increase the compactness by 3-4 times.
Air capacitors are used mainly in small and medium-sized machines. By the nature of air movement, they are divided into two types:
Free air movement; such capacitors are used in machines of very low productivity (up to about 500 W) used in household refrigerators;
With forced air movement, that is, with blowing of the heat transfer surface using axial fans... This type of condenser is most applicable in small and medium-sized machines, however, recently, due to the shortage of water, they are increasingly used in large-capacity machines.
Capacitors air type used in refrigeration units with stuffing box, glandless and hermetic compressors. Condenser designs are of the same type. The condenser consists of two or more sections connected in series by rolls or in parallel by collectors. The sections are straight or U-shaped tubes, assembled into a coil with the help of rolls. Pipes - steel, copper; ribs - steel or aluminum.
Forced air condensers are used in commercial refrigeration units.
Calculation of capacitors
When designing a condenser, the calculation is reduced to determining its heat transfer surface and (if it is water-cooled) the amount of water consumed. First of all, the actual thermal load on the capacitor is calculated
where Q to - the actual thermal load on the capacitor, W;
Q 0 - compressor cooling capacity, W;
N i - indicator power of the compressor, W;
N e - effective power compressor, W;
h m - mechanical efficiency of the compressor.
In units with hermetic or sealless compressors, the thermal load on the condenser should be determined using the formula:
(5.7)
where N e - electric power at the compressor motor terminals, W;
h e - efficiency of the electric motor.
The heat transfer surface of the condenser is determined by the formula:
(5.8)
where F is the area of the heat transfer surface, m 2;
k is the heat transfer coefficient of the condenser, W / (m 2 × K);
Dt m - average logarithmic difference between the condensation temperatures of the refrigerant and cooling water or air, 0 С;
q F - heat flux density, W / m 2.
The average logarithmic difference is determined by the formula:
(5.9)
where t в1 is the temperature of water or air at the inlet to the condenser, 0 С;
t в2 - temperature of water or air at the outlet of the condenser, 0 С;
t to - condensation temperature of the refrigeration unit, 0 С.
Heat transfer coefficients different types capacitors are given in table. 5.1.
Table 5.1 - Heat transfer coefficients of condensers
Irrigation for ammoniaEvaporative for ammonia
Air cooled (at forced circulation air) for freons
The values To defined for a ribbed surface.
Details
Chiller calculation. How to calculate the cooling capacity or power of the chiller and correctly select it.
How to do it right, what should be the first thing to rely on in order to produce a high-quality one among the multitude of proposals?
On this page we will give several recommendations, by listening to which you will get closer to making the right one..
Calculation of the cooling capacity of the chiller. Calculation of the chiller capacity - its cooling capacity.
First of all, according to the formula, in which the volume of the cooled liquid participates; the change in the temperature of the liquid, which must be provided with a coolant; heat capacity of the liquid; and of course the time during which this volume of liquid must be cooled - the cooling capacity is determined:
Cooling formula, i.e. formula for calculating the required cooling capacity:
Q= G * (T1- T2) * C pzh * pzh / 3600
Q- cooling capacity, kW / hour
G- volumetric flow rate of the liquid to be cooled, m 3 / hour
T2- the final temperature of the cooled liquid, о С
T1- initial temperature of the cooled liquid, о С
C rzh -specific heat cooled liquid, kJ / (kg * o C)
pzh- density of the cooled liquid, kg / m 3
* For water C rzh * pzh = 4.2
This formula determines necessary cooling capacity and it is the main choice when choosing a chiller.
- Conversion formulas to calculate cooling capacity of a water cooler:
1 kW = 860 kcal / hour
1 kcal / hour = 4.19 kJ
1 kW = 3.4121 kBTU / hour
Chiller selection
In order to produce chiller selection- it is very important to fulfill correct drafting technical specifications for the calculation of the chiller, in which not only the parameters of the water cooler itself are involved, but also data on its location and its condition working together with the consumer. Based on the calculations performed, you can - select the chiller.
Do not forget about which region you are in. For example, the calculation for the city of Moscow will differ from the calculation for the city of Murmansk, since the maximum temperatures of these two cities are different.
NSon the tables of parameters of water-cooling machines, we make the first choice of a chiller and get acquainted with its characteristics. Further, having on hand the main characteristics of the selected machine, such as:- chiller cooling capacity, the electrical power consumed by it, whether it contains a hydronic module and its - the supply and pressure of the liquid, the volume of air passing through the cooler (which heats up) in cubic meters per second - you can check the possibility of installing a water cooler on a dedicated site. After the proposed water cooler meets the requirements of the technical assignment and is most likely able to work on the site prepared for it, we recommend that you contact the specialists who will check your choice.
Chiller selection - features that must be considered when selecting a chiller.
Basic site requirementsfuture installation of the water cooler and the scheme of its operation with the consumer:
- If the planned place is in the room, then - is it possible to provide a large exchange of air in it, is it possible to add a water cooler to this room, is it possible to serve it in it?
- If the future placement of the water cooler on the street - will there be a need for its operation in winter period, is it possible to use antifreeze liquids, is it possible to protect the water chiller from external influences(anti-vandal, from leaves and tree branches, etc.)?
- If the temperature of the liquid to which it needs cool below +6 o C or higher + 15 O C - most often this temperature range is not included in the quick selection tables. In this case, we recommend that you contact our specialists.
- It is necessary to determine the flow rate of the cooled water and necessary pressure, which must be provided by the hydronic module of the water cooler - the required value may differ from the parameter of the selected machine.
- If the temperature of the liquid needs to be lowered by more than 5 degrees, then the circuit direct cooling water cooler is not used and calculation and completing with additional equipment is required.
- If the cooler will be used around the clock and all year round, and the final temperature of the liquid is high enough - how much expedient would it be to use the unit with?
- In the case of high concentration non-freezing liquids, an additional calculation of the capacity of the water cooler evaporator is required.
Chiller selection program
For your information: gives only an approximate understanding of the required model of the cooler and its compliance with the technical specifications. Next, you need to check the calculations by a specialist. In this case, you can focus on the cost obtained as a result of calculations +/- 30% (in cases with low-temperature models of liquid coolers - the indicated figure is even higher)... Optimal model and cost will be determined only after verification of calculations and comparison of characteristics different models and manufacturers by our specialist.
Chiller selection Online
You can do it by contacting our online consultant, who will quickly and technically provide an answer to your question. Also, the consultant can perform based on the briefly written parameters of the terms of reference chiller calculation online and give an approximately suitable model in terms of parameters.
Calculations made by a non-specialist often lead to the fact that the selected chiller does not fully meet the expected results.
Peter Holod company specializes in integrated solutions for the provision of industrial enterprises equipment that fully meets the requirements of the technical specifications for the supply of a water cooling system. We collect information to fill in the technical task, calculate the cooling capacity of the chiller, determine the optimal water cooler, check with recommendations for its installation on a dedicated site, calculate and complete all additional elements for the operation of the machine in the system with the consumer (calculation of the accumulator tank, hydronic module, additional, if necessary, heat exchangers, pipelines and shut-off and control valves).
Having accumulated many years of experience calculations and subsequent implementations of water cooling systems at various enterprises, we have the knowledge to solve any standard and far from standard tasks associated with the numerous features of installing liquid coolers at the enterprise, combining them with technological lines, setting up specific parameters of equipment operation.
The most optimal and accurate and accordingly, the determination of the model of the water cooler can be done very quickly by calling or sending a request to an engineer of our company.
Additional formulas for calculating the chiller and determining the scheme of its connection to the cold water consumer (calculating the chiller capacity)
- The formula for calculating the temperature, when mixing 2 liquids (formula for mixing liquids):
T mix= (M1 * C1 * T1 + M2 * C2 * T2) / (C1 * M1 + C2 * M2)
T mix- temperature of the mixed liquid, о С
M1- mass of the 1st liquid, kg
C1- specific heat capacity of the 1st liquid, kJ / (kg * о С)
T1- temperature of the 1st liquid, о С
M2- mass of the 2nd liquid, kg
C2- specific heat capacity of the 2nd liquid, kJ / (kg * о С)
T2- temperature of the 2nd liquid, о С
This formula is used if a storage capacity is used in the cooling system, the load is not constant in time and temperature (most often when calculating required power cooling autoclave and reactors)
Chiller cooling capacity.
|