Detailed Description
The invention is further described with reference to the following figures and embodiments.
With reference to fig. 1 to 3, the present invention is a phase change thermal storage device based on convective heat transfer, including a phase change thermal storage material 6, a phase change thermal storage unit body 7, and a phase change thermal storage device housing 8;
the phase change heat storage unit body 7 comprises a cooling circulation pipeline 1, a heating circulation pipeline 2, a cover plate 3 and fins 5; a plurality of fins 5 are arranged at equal intervals in the vertical direction; the fins 5 are provided with a plurality of through holes at equal intervals, and the cooling circulation pipeline 1 and the heating circulation pipeline 2 parallelly penetrate through the through holes on the fins 5 and are tightly welded with the fins 5; the upper ends of the cooling circulation pipeline 1 and the heating circulation pipeline 2 are fixed on a cover plate 3, the edge of the cover plate 3 is provided with a counter bore 4 and a fastening screw 9, and the cover plate 3 and a phase change heat storage device shell 8 are tightly connected through the fastening screw 9; the inlet and outlet of the cooling circulation pipeline 1 and the heating circulation pipeline 2 are both positioned at the upper end of the cover plate 3; the cooling circulation pipeline 1 is surrounded by a heating circulation pipeline 2; a plurality of storage cavities are arranged in the phase change heat storage device shell 8; each cavity is internally provided with a heat storage unit body 7 filled with phase change heat storage materials 6, and the edge of each storage cavity is provided with a threaded hole matched with a fastening screw 9 to be connected with the heat storage unit body.
Furthermore, the inlet and outlet of the cooling circulation pipeline 1 and the heating circulation pipeline 2 in the phase change heat storage unit bodies 7 are both provided with threads, and the cooling circulation pipeline 1 and the heating circulation pipeline 2 between different phase change heat storage unit bodies 7 are connected by using the connecting pipes 10, so that the cooling circulation pipeline 1 and the heating circulation pipeline 2 in a split design form a complete circulation.
Furthermore, a filling hole 11 and a sewage draining hole 13 are formed in the phase change heat storage device shell 8. The filling hole 11 is positioned at the top of the phase change heat storage device shell 8 and is arranged in parallel with the cover plate 3, and a top cover 12 with a liquid level scale is arranged on the filling hole 11; the blowdown hole 13 is located at the bottom of the phase change heat storage device case 8 and is provided with a sealing cover 14. Before the phase change heat storage device is used, the phase change heat storage material 6 is injected from the filling hole 11 to the scale position on the liquid level scale 12, the phase change heat storage material 6 is drained from the sewage draining hole 13 when the phase change heat storage device is maintained, the phase change heat storage device is cleaned, and new phase change heat storage material 6 is refilled from the filling hole 11.
Furthermore, the cooling circulation pipeline 1 and the heating circulation pipeline 2 in the phase change heat storage device both adopt red copper heat exchange pipes, the outer diameter of each heat exchange pipe is 3-80 mm, and the space between the heat exchange pipes is 3-50 mm; circulating media of a cooling circulating pipeline 1 in the phase-change heat storage device are various low-temperature refrigerants, and circulating media of a heating circulating pipeline 2 are water added with anti-freezing liquid; the phase change heat storage material 6 is mainly used for enhancing heat transfer through the fins 5, and the volume ratio of the added fins 5 to the filled phase change heat storage material 6 is about 5-30%. The enhanced phase change heat storage material 6 has the heat storage capacity of about 120 kJ/kg-200 kJ/kg and the heat conductivity of about 10W/(mK) -50W/(mK). Referring to fig. 4, the cooling circulation line 1 transfers heat in the phase change heat storage material 6 out of the apparatus and discharges it to the outside; the heating circulating pipeline 2 transfers heat from a heating source into the device and is absorbed by the phase change heat storage material 6; the cooling circulation pipeline 1 has low heat flux density and small heat load; the duration is long; the heating circulating pipeline 2 has high heat flow density, large heat load and short duration. The tube pass numbers of the two circulation pipelines are respectively matched with the heating heat load and the cooling heat load so as to adapt to different requirements of a phase change heating process and a phase change cooling process. The pulse heat load is input from the heating circulation pipeline by taking water added with the anti-freezing liquid as a medium, temporarily stored in the phase change heat storage material in the phase change heat storage device and finally slowly taken away by the cooling circulation pipeline by taking a low-temperature refrigerant as a medium. Through the heat absorption and heat release processes, the phase change heat storage device stabilizes instantaneous heat load into stable heat load, and reduces the requirement on heat dissipation capacity.
A method for determining key parameters of a phase change heat storage device based on convection heat transfer comprises the following steps:
step 1, calculating the phase change point of the phase change heat storage material 6
Determining the phase change point T of the phase change heat storage material 6 according to the following formula0:
Wherein:
T1inputting temperature for the heating circulation pipeline 2;
n 12 pipes of the heating circulating pipeline;
t1is the heating cycle time;
T2inputting temperature for the cooling circulation pipeline 1;
n2the number of the cooling circulation pipeline is 1;
t2is the cooling cycle time;
step 2, calculating the size of the circulating pipeline
The cooling circulation pipeline 1 and the heating circulation pipeline 2 adopt the same red copper heat exchange tubes, the wall thickness t of the heat exchange tubes is selected according to the following formula, and the wall thickness t is less than 0.25mm, namely 0.25 mm:
wherein:
p is the working pressure of the heat exchange tube;
d2the outer diameter of the heat exchange tube;
σaallowable stress for the wall material of the heat exchange tube;
a is the processing and corrosion allowance of the heat exchange tube wall;
inner diameter d of heat exchange tube1Comprises the following steps:
d1=d2-2t
step 3, calculating the volume of the required phase change heat storage material 6
The volume V of the phase change heat storage material 6 to be filled in the phase change heat storage device is calculated according to the following formula:
wherein:
q1inputting power for the heating cycle;
C1the amount of heat stored per unit volume of the phase change heat storage material 6;
step 4, calculating the total heat transfer coefficient h of the heating circulation pipeline 2H
Given the thickness e of the molten layer of the phase change heat storage material 6 and the fins in the phase change heat storage material 6The volume ratio f, the total heat transfer coefficient h of the heating circulation line 2 is calculated according to the following formulaH:
Wherein:
μHis the dynamic viscosity of the fluid in the heating circulation pipeline 2;
cHthe fluid in the circulating pipeline 2 is heated and has constant pressure specific heat capacity;
λHthe heat conductivity coefficient of the fluid in the heating circulation pipeline 2;
vHis the flow rate of the fluid line in the heating circulation pipeline 2;
ρHis the density of the fluid in the heating circulation pipeline 2;
h2is the fouling heat transfer coefficient of the phase change heat storage material 6;
λ1the thermal conductivity of the material used for the tube wall of the heat exchange tube;
λ2the thermal conductivity of the phase change heat storage material 6;
λ3the thermal conductivity of the fins 5;
step 5, calculating the total heat transfer coefficient h of the cooling circulation pipeline 1C
The total heat transfer coefficient h of the cooling circulation line 1 according to the following formulaC:
Wherein:
μCis the dynamic viscosity of the fluid in the cooling circulation pipeline 1;
cCthe constant pressure specific heat capacity of the fluid in the cooling circulation pipeline 1;
λCthe coefficient of heat conductivity of the fluid in the cooling circulation pipeline 1;
vCis the linear flow velocity of the fluid in the cooling circulation pipeline 1;
ρCto be circulated for coolingThe fluid density in the loop pipe 1;
step 6, calculating the total length L of the heating circulating pipeline 2H
The total length L of the heating circulation line 2 is calculated according to the following formulaH:
Step 7, checking and calculating the total length L of the cooling circulation pipeline 1C
The actual total length L of the cooling circulation line 1 in the phase-change heat storage device is calculated according to the following formulaC1
The required total length L of the cooling circulation line 1 in the phase change heat storage device is calculated according to the following formulaC2
If L isC1≥LC2If the phase change heat storage device is calculated to pass, taking LC=LC1. Otherwise, the volume ratio f of the fins 5 in the phase change heat storage material is increased, and the calculation is started from the step 4 again.
Step 8, adjusting the thickness e of the melting layer of the phase change heat storage material 6, repeating the steps 4 to 7, forming various design schemes of the phase change heat storage device, outputting the thickness e of the melting layer of the phase change heat storage material 6, the volume ratio f of the fins 5 and the total length L of the cooling circulation pipeline 1, which are key parameters of the phase change heat storage device in different schemesCAnd the total length L of the heating circulation pipeline 2HThe phase change thermal storage device masses in the different versions are formed and compared, and the lightest of them is selected as the final design result.
Examples
The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
The design conditions were 300kW peak heat load, 6s duration, 100s interval. The input temperature of the heating circulation pipeline is 10 ℃, and the input temperature of the cooling circulation pipeline is-25 ℃.
And calculating parameters of the phase change heat storage device according to the calculating steps.
Step 1, calculating and integrating to obtain a phase change point T of the phase change heat storage material 60Should be-15 deg.C;
step 2, selecting the outer diameter d of the heat exchange tube2The thickness t of the heat exchange tube is calculated to be 0.25mm when the thickness t of the heat exchange tube is 3 mm;
step 3, calculating that the volume V of the phase change heat storage material 6 to be filled is 11.6L;
step 4, selecting the thickness e of the melting layer of the phase change heat storage material 6 as 2.1mm, the volume ratio f of the fins 5 as 6.5%, and calculating to obtain the total heat transfer coefficient h of the heating circulation pipeline 2HIs 1.78 kW/(m)2*K);
Step 5, calculating the total heat transfer coefficient h of the cooling circulation pipeline 1CIs 3.36 kW/(m)2*K);
Step 6, calculating the total length L of the heating circulation pipeline 2HIs 1818 m;
step 7, calculating the actual total length L of the cooling circulation pipelineC1280m, a total length L is requiredC2The total length L of the cooling circuit 1 was calculated to be 259mCIs 280 m;
and 8, adjusting the thickness of the phase change heat storage material melting layer, and calculating the total weight of the phase change heat storage device, wherein the result is shown in fig. 5.
In summary, the optimal thickness of the phase change heat storage material melting layer in the phase change heat storage device is 2.1mm, the volume ratio of the fins 5 is 6.5%, the total length of the heating circulation pipeline 2 is 1818m, the total length of the cooling circulation pipeline 1 is 280m, the total weight of the phase change heat storage device is 70kg, and the volume is 40L;
the device realizes the purpose of converting the pulse heat load of 300kW, lasting 6s and interval 100s into the stable heat load output of 18kW, and reduces the requirement of heat dissipation capacity.