CN110059386B - Calibration calculation method for outlet parameters of shell-and-tube heat exchanger - Google Patents
Calibration calculation method for outlet parameters of shell-and-tube heat exchanger Download PDFInfo
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Abstract
The invention discloses a calibration calculation method for outlet parameters of a shell-and-tube heat exchanger, which comprises the steps of firstly obtaining inlet parameters of hot molten salt and steam water and structural parameters of the heat exchanger, then assuming outlet temperature and dryness of the steam water, then determining a heat exchange process of the steam water in a heat exchange tube, then calculating an actual heat transfer coefficient and a theoretical heat transfer coefficient of each heat exchange section, then comparing whether a difference value between the actual heat transfer coefficient and the theoretical heat transfer coefficient is less than or equal to an allowable difference value, if so, terminating the calculation, and if so, assuming new outlet temperature and dryness of the steam water, and calculating again; the method of the invention calculates the outlet parameter of the shell-and-tube type hot molten salt-steam-water heat exchanger with given structural parameters under the condition of only knowing the inlet thermodynamic parameters of steam-water in the heat exchange tube and hot molten salt outside the heat exchange tube, so as to check whether the heat exchanger can achieve the required heat exchange effect.
Description
Technical Field
The invention belongs to the field of tower type solar hot molten salt photo-thermal power generation, and particularly relates to a calculation method for verifying outlet parameters of a shell-and-tube heat exchanger with steam-water flowing inside a tube and hot molten salt flowing outside the tube.
Background
The molten salt gradually becomes a mainstream heat collection working medium in the tower type solar photo-thermal power generation system due to superior thermal physical properties such as low working pressure, high working temperature and the like, and at the power generation side, high-temperature steam is still used as the working medium at present to push a steam turbine to generate power. Therefore, research on a molten salt-steam water heat exchanger is necessary. A set of complete calculation method is provided, which can be used for outlet parameter calibration of a shell-and-tube heat exchanger aiming at the steam water flowing in the tube and the hot molten salt flowing out of the tube, and can calculate the outlet parameters of the working medium inside and outside the tube under the condition of knowing the inlet parameters of the working medium inside and outside the tube and the structural parameters of the heat exchanger so as to judge whether the heat exchange performance of the heat exchanger can meet the required requirements under the operation parameters, thereby providing reference for the design of the molten salt-steam water heat exchanger.
Disclosure of Invention
The invention provides a calibration calculation method for outlet parameters of a shell-and-tube heat exchanger, which is used for calculating the outlet parameters of the shell-and-tube heat molten salt-steam water heat exchanger with given structural parameters under the condition of only knowing inlet thermodynamic parameters of steam water in a heat exchange tube and heat molten salt outside the heat exchange tube so as to check whether the heat exchanger can achieve the required heat exchange effect.
In order to achieve the above purpose, the invention adopts the following technical scheme
A calibration calculation method for outlet parameters of a shell-and-tube heat exchanger is characterized in that steam water flows in a tube of the shell-and-tube heat exchanger, and hot molten salt flows out of the tube, and the method is hereinafter referred to as a heat exchanger; the method comprises the following specific steps:
step 1, obtaining the temperature t of steam water in a heat exchange pipe in a heat exchanger at an inlet1Pressure PwAnd flow rate qwObtaining the temperature T of the hot melt salt outside the heat exchange tube at the inlet in the heat exchanger1Pressure PsAnd flow rate qsObtaining structural parameters of the heat exchanger, and setting the temperature cycle step length to be H1The dryness cycle step length is H2The allowable error value is;
step 2, judging the phase state of the steam-water in the heat exchange tube at the inlet of the heat exchange tube;
step 3, assuming that the initial temperature of the steam-water in the pipe at the outlet of the heat exchange pipe is t2＝T1When t is2When the steam-water separator is in a superheated zone or a saturated zone of water, the initial dryness of the steam-water at the outlet of the heat exchange tube is assumed to be x2When t is equal to 12In the supercooling region of water, the initial dryness of the steam-water at the outlet of the heat exchange tube is assumed as x2＝0；
Step 4, judging the phase state change possibly experienced by the steam-water in the heat exchange tube:
when the steam-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in an overheating zone, the steam-water in the heat exchanger tube is considered to sequentially experience an overcooling state, a gas-liquid two-phase state and an overheating state in the heat exchanger tube, which is the first condition;
when the steam-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in a gas-liquid two-phase region, the vapor and water in the heat exchanger tube are considered to be in a super-cooled state and a gas-liquid two-phase state in turn, which is the second case;
when the vapor-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and at the outlet of the heat exchange tubeThe initial temperature at t is assumed2When the heat exchanger is in the supercooling zone, the steam-water in the heat exchanger only passes through the supercooling zone, which is the third case;
when steam-water in the tube is in a two-phase region at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in an overheating zone, the steam-water in the heat exchanger tube is considered to be in a gas-liquid two-phase state and an overheating state in turn, and the situation is four;
when steam-water in the pipe is in a gas-liquid two-phase region at the inlet of the heat exchange pipe and the initial temperature t at the outlet of the heat exchange pipe is assumed2When the heat exchanger is in a gas-liquid two-phase region, the steam-water in the heat exchanger only passes through the gas-liquid two-phase region, which is the fifth case;
when steam-water in the tube is in the superheat zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in the overheating zone, the steam-water in the heat exchanger only passes through the overheating zone, which is the sixth case;
step 5, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the outlet of the heat exchange tube2Wherein a is1Is the enthalpy value of vapor and water in the heat exchange tube at the inlet of the heat exchange tube, a2Is the enthalpy value of the vapor-water in the tube at the outlet of the heat exchange tube, cp，sIs the specific heat capacity of the hot molten salt;
step 6, for the first condition in the step 4, the process of the vapor-water in the pipe is from a supercooled state to a gas-liquid two-phase state to a superheated state, and the following specific steps are carried out at this time:
step 6-1, according to a heat balance formula
Calculating the temperature T of the hot-melt salt at the end of the supercooling regionl，1Wherein a'sThe liquid phase enthalpy value of the steam water in the pipe at the saturation point is obtained;
step 6-2, calculating the local average heat exchange coefficient h of the hot molten salt in the supercooling zones，1Calculating the local average heat exchange coefficient h of the steam-water in the super-cooling areaw，1；
Step 6-3, according to
Calculating the actual local average heat transfer coefficient k of the supercooling region1The thickness of the heat exchange tube is the wall thickness, and lambda is the heat conductivity coefficient of the heat exchange tube;
step 6-4, according to
Calculating the heat exchange area A of the supercooling region1Wherein Q isw，1、Qs，1The local heat exchange quantity delta t of water and hot molten salt in the supercooling heat exchange area respectively1Is the local mean logarithmic temperature difference of the supercooling region;
step 6-5, according to A1＝2πl1(di+do) And/4, calculating the length l of the supercooling heat exchange segment1Wherein d isiIs the inner diameter of the heat exchange tube, doIs the outer diameter of the heat exchange tube;
step 6-6, comparison l1L is equal to the total length L of the heat exchange tube1If less than L, go to step 6-7, otherwise, get t2Minus H1The result obtained is taken as a new t2The value returns to the step 4 until the calculated l1Satisfy inequality l1If the value is less than L, entering the step 6-7;
6-7, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the termination point of the two-phase regionl，2Wherein a ″)sThe vapor phase enthalpy value of vapor-water in the pipe at a saturation point is obtained;
6-8, calculating the local average heat exchange coefficient h of the hot molten salt in the two-phase regions，2Calculating the local average heat exchange coefficient h of the steam-water in the tube in the two-phase regionw，2；
Step 6-9, according to
Determining the actual local average heat transfer coefficient k of the two-phase region2；
Step 6-10, according to
Calculating the heat exchange area A of the two-phase region2Wherein Q isw，2、Qs，2Respectively the local heat exchange quantity delta t of water and hot molten salt in the two-phase heat exchange area2Is the local average logarithmic temperature difference of the two-phase region;
step 6-11, according to A2＝2πl2(di+do) And/4, calculating the length l of the heat exchange segment of the two-phase region2；
Step 6-12, comparison (l)1+l2) The total length L of the heat exchange tube is equal to (L)1+l2) If less than L, go to step 7, otherwise, get t2Minus H1The result obtained is taken as a new t2Value is returned to step 4 until the calculated (l)1+l2) Satisfy the inequality (l)1+l2) If the value is less than L, entering a step 7;
for the second case in the step 4, the process of the steam-water in the pipe is from the supercooled state to the gas-liquid two-phase state, the steps 6-1 to 6-5 are the same as the first case, but the specific contents of the step 6-6 are as follows:
step 6-6, comparison l1L is equal to the total length L of the heat exchange tube1If less than L, go to step 7, otherwise, let x2Minus H2The result obtained is new x2The value returns to the step 4 until the calculated l1Satisfy inequality l1If the value is less than L, entering a step 7;
for the case three in step 4, directly entering step 7;
for the fourth case of step 4, the steam-water in the pipe is in a state from a gas-liquid two-phase state to an overheated state, and the specific content of step 6 is as follows:
step 6-1, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the termination point of the two-phase regionl，2；
Step 6-2, calculating the local average heat exchange coefficient h of the hot molten salt side in the two-phase regions，2Calculating the local average heat exchange coefficient h of the steam-water side in the tube in the two-phase regionw，2；
Step 6-3, according to
Determining the actual local average heat transfer coefficient k of the two-phase region2；
Step 6-4, according to
Calculating the heat exchange area A of the two-phase region2；
Step 6-5, according to A2＝2πl2(di+do) And/4, calculating the length l of the two-phase heat exchange segment2；
Step 6-6, comparison l2L is equal to the total length L of the heat exchange tube2If less than L, go to step 7, otherwise, get t2Minus H1The result obtained is taken as a new t2The value returns to the step 4 until the calculated l2Satisfy inequality l2If the value is less than L, entering a step 7;
directly entering the step 7 for the fifth case and the sixth case in the step 4;
step 7, calculating the local average heat exchange coefficient h of the hot melt salt side of the final section heat exchange areas，3Calculating the local average heat exchange coefficient h of the steam-water side of the final section heat exchange areaw，3：
For the case one, the case four and the case six in the step 4, the final section heat exchange area is the overheating heat exchange area;
for the second case and the fifth case, the final section heat exchange area is a two-phase heat exchange area;
for the third case, the final heat exchange area is an overcooling heat exchange area;
step 8, according to
Calculating the actual local average heat transfer coefficient k of the final-stage heat exchange area3；
Step 9, according to A3＝2πl3(di+do) And/4, calculating the area A of the heat exchange section at the final section3Wherein l is3The length of the final heat exchange zone;
step 10, according to
Calculating the final stage actual heat transfer coefficient k'3Wherein Q iss，3And Qw，3The heat exchange quantity of the hot melt salt in the final section heat exchange area and the heat exchange quantity of the steam-water in the pipe in the final section heat exchange area are respectively, and delta t is the logarithmic mean temperature difference of the final section heat exchange area;
step 11, comparison
And an allowable error value when
If the larger one of the values is smaller than the smaller one, the calculation is terminated, and the steam-water outlet temperature t in the pipe is considered to be at the moment2Steam-water outlet dryness x in pipe2Temperature T of hot molten salt outlet outside pipe2The actual outlet parameters of the working medium inside and outside the pipe are obtained, otherwise:
when t is2In the superheated or supercooled region of water, let t2Minus H1The obtained value is new t2The value returns to the step 4 until the value is obtained by calculation
The larger one, the size of which is also smaller than the other;
when t is2In the two-phase region of water, let x2Minus H2The obtained value is new x2The value returns to the step 4 until the value is obtained by calculation
The larger one, the smaller one.
In summary, the invention adopts the traversal algorithm based on the heat balance equation, the fused salt-steam/water heat exchange correlation and the convection heat exchange equation, fully considers the heat exchange condition possibly existing in the heat exchanger, can accurately calculate the outlet temperature and the state of the working medium inside and outside the pipe, and verifies the heat exchange performance of the heat exchanger.
Detailed Description
The technical solution of the present invention is further described in detail by the following examples.
The invention is further described by carrying out actual calculation according to specific structural parameters of a certain shell-and-tube type hot molten salt-steam/water heat exchanger and the working conditions inside and outside the tube.
TABLE 1 Heat exchanger parameters and design conditions inside and outside the tubes
The temperature of the steam-water in the heat exchange tube at the inlet of the heat exchange tube is 320 ℃, and the pressure is 13.82 MPa. The saturation temperature of water corresponding to 13.82MPa is 335.64 ℃, so that the steam-water in the heat exchange tube is in a supercooled state at the inlet of the heat exchange tube. Setting the initial parameter of the vapor-water in the tube at the outlet of the heat exchange tube as t2＝T1The temperature is in the region of the superheat of the water, so that the initial dryness x2＝1。
And judging to know that the heat exchange condition belongs to the condition I.
According to the formula of heat balance
Calculating the temperature T of the hot molten salt at the outlet of the heat exchange tube2＝331.88℃。
According to the formula of heat balance
Calculating the temperature T of the hot melt salt at the termination point of the supercooling zonel，1＝341.99℃
According to the genistein formula (gnilinski formula):
and formula
Calculating the local average heat exchange coefficient h of the steam-water in the super-cooling areaw，1. Wherein, Re1Is the local average Reynolds number, Pr, of the supercooling region on the vapor-water sidef，1Is the local average Plantt number, lambda, of the supercooled region on the vapor-water sidewThermal conductivity coefficient l of water1The length of the supercooling heat exchange segment, f is the Darcy resistance coefficient of turbulent flow in the tube, ctTake 1.
According to the heat exchange correlation formula of the hot molten salt and the supercooled water:
and formula
Calculating the local average heat exchange coefficient h of the hot molten salt in the supercooling regions，1＝1.7785×103W/(m2C.g. to be prepared into a preparation. Wherein Res，1Local average Reynolds number, Pr, of supercooled region on the hot melt salt sides，1Local average prandtl number, lambda, of supercooled region on the hot melt salt sidesIs the thermal conductivity of the hot molten salt, s1Is the tube spacing, s, perpendicular to the incoming flow direction2The tube spacing being parallel to the direction of incoming flow, a1、b1、c1、d1Is an experimental coefficient of a hot melt salt-supercooled water heat exchange correlation formula,nis a correction factor.
According to
Calculating the local average heat transfer coefficient k of the supercooling region1According to
And A1＝2πl1(di+do) And/4, solving an equation, and calculating the length l of the supercooling heat exchange section18.2308 meters.
Comparison l1The total length L of the heat exchange tube is compared to obtain L1If L, the calculation of the length of the two-phase region is continued.
According to the Dengler formula:
calculating the local average heat exchange coefficient h of the steam-water in the tube in the two-phase regionw，2＝4.6265×103W/(m2C.g. to be prepared into a preparation. Wherein h isLoIs the heat exchange coefficient when the vapor-liquid two phases are all liquid phases, and X is the Martherley number.
According to a heat fused salt-steam-water two-phase heat exchange formula:
and formula
Calculating the local average heat exchange coefficient h of the hot molten salt in the two-phase regions，2＝3.778×103W/(m2C.g. to be prepared into a preparation. Wherein Res，2Is the local average Reynolds number, Pr, of the two-phase region on the hot-melt salt sides，2Local average prandtl number, a, in the two-phase region on the hot-melt salt side2、b2、c2、d2Is an experimental coefficient of a hot-melt salt-gas-liquid two-phase water heat exchange correlation formula.
According to
Calculating the actual local average heat transfer coefficient k of the two-phase region2＝1.65×103W/(m2In DEG C) according to
And A2＝2πl2(di+do) And/4, calculating the length l of the heat exchange section of the two-phase region252.2 meters.
At this time, (l)1+l2) > L, thus will t2Minus H1The result obtained is taken as a new t2And (4) returning to the step 4.
……
Calculate to t2＝335.64℃，x2When the heat exchange rate is 0.42, the heat exchange condition is judged to belong to the second condition.
By the formula of heat balance
Calculating the temperature T of the hot molten salt at the outlet of the heat exchange tube2＝390.67℃。
According to the formula of heat balance
Calculating the temperature T of the hot melt salt at the termination point of the supercooling zonel，1＝400℃。
According to the genistein formula (gnilinski formula):
and formula
Calculating the local average heat exchange coefficient h of the steam-water in the super-cooling areaw，1。
According to the heat exchange correlation formula of the hot molten salt and the supercooled water:
and formula
Calculating the local average heat exchange coefficient h of the hot molten salt in the supercooling regions，1＝2.6679×103W/(m2·℃)。
According to
Calculating the actual local average heat transfer coefficient k of the supercooling region1According to
And A1＝2πl1(di+do) And/4, solving an equation, and calculating the length l of the supercooling heat exchange section1＝4.39m。
Because l1L, therefore, the calculation result indicates that the vapor-water in the pipe is in a two-phase region at the outlet of the heat exchange pipe, and the assumed t2The value is also in the two-phase region of water, therefore, the calculation result is consistent with the hypothesis, and the actual outlet parameter of the heat exchange tube entering the terminal heat exchange region, namely the two-phase region, is calculated.
Calculating the convective heat transfer coefficient of the water side and the convective heat transfer coefficient of the salt side in the two-phase region according to the Dengler formula (Dengler formula):
calculating the local average heat exchange coefficient h of the steam-water side of the final section heat exchange areaw，3＝6.5582×103W/(m2·℃)。
According to a heat fused salt-steam-water two-phase heat exchange formula:
and formula
Calculating the local average heat exchange coefficient h of the hot melt salt side of the final section heat exchange zones，3＝5.5763×103W/(m2C.g. to be prepared into a preparation. Wherein Res，3Is the local average Reynolds number, Pr, of the two-phase region at the steam-heat molten salt sides，3Local average prandtl number, a, in the two-phase region on the hot-melt salt side3、b3、c3、d3Is an experimental coefficient of a hot-melt salt-gas-liquid two-phase water heat exchange correlation formula.
According to
Calculating the actual local average heat transfer coefficient k of the final section heat exchange area3＝2.189×103W/(m2C.) according to
And A3＝2πl3(di+do) And/4, calculating the final stage actual heat transfer coefficient k'3＝2.3818×103W/(m2·℃)。
The calculation results in that,
at the moment, the calculation is terminated, the steam-water in the pipe is calculated to be in a two-phase region at the outlet of the heat exchange pipe, and the outlet temperature is t2335.64 ℃, outlet dryness x 0.42, temperature T of hot molten salt at outlet2＝390.67℃。
Claims (1)
1. A calibration calculation method for outlet parameters of a shell-and-tube heat exchanger is characterized in that steam water flows in a tube of the shell-and-tube heat exchanger, and hot molten salt flows out of the tube, and the method is hereinafter referred to as a heat exchanger; the method comprises the following specific steps:
step 1, obtaining the temperature t of steam water in a heat exchange pipe in a heat exchanger at an inlet1Pressure PwAnd flow rate qwObtaining the temperature T of the hot melt salt outside the heat exchange tube at the inlet in the heat exchanger1Pressure PsAnd flow rate qsObtaining structural parameters of the heat exchanger, and setting the temperature cycle step length to be H1The dryness cycle step length is H2The allowable error value is;
step 2, judging the phase state of the steam-water in the heat exchange tube at the inlet of the heat exchange tube;
step 3, assuming that the initial temperature of the steam-water in the pipe at the outlet of the heat exchange pipe is t2＝T1When t is2When the steam-water separator is in a superheated zone or a saturated zone of water, the initial dryness of the steam-water at the outlet of the heat exchange tube is assumed to be x2When t is equal to 12In the supercooling region of water, the initial dryness of the steam-water at the outlet of the heat exchange tube is assumed as x2＝0；
Step 4, judging the phase state change possibly experienced by the steam-water in the heat exchange tube:
when the steam-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in an overheating zone, the steam-water in the heat exchanger tube is considered to sequentially experience an overcooling state, a gas-liquid two-phase state and an overheating state in the heat exchanger tube, which is the first condition;
when the steam-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in a gas-liquid two-phase region, the vapor and water in the heat exchanger tube are considered to be in a super-cooled state and a gas-liquid two-phase state in turn, which is the second case;
when the steam-water in the tube is in the supercooling zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in the supercooling zone, the steam-water in the heat exchanger only passes through the supercooling zone, which is the third case;
when steam-water in the pipe is in a gas-liquid two-phase region at the inlet of the heat exchange pipe and the initial temperature t at the outlet of the heat exchange pipe is assumed2When the heat exchanger is in an overheating zone, the steam-water in the heat exchanger tube is considered to be in a gas-liquid two-phase state and an overheating state in turn, and the situation is four;
when steam-water in the pipe is in a gas-liquid two-phase region at the inlet of the heat exchange pipe and the initial temperature t at the outlet of the heat exchange pipe is assumed2When the heat exchanger is in a gas-liquid two-phase region, the steam-water in the heat exchanger only passes through the gas-liquid two-phase region, which is the fifth case;
when steam-water in the tube is in the superheat zone at the inlet of the heat exchange tube and the initial temperature t at the outlet of the heat exchange tube is assumed2When the heat exchanger is in the overheating zone, the steam-water in the heat exchanger only passes through the overheating zone, which is the sixth case;
step 5, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the outlet of the heat exchange tube2Wherein a is1The enthalpy value of the steam-water in the tube at the inlet of the heat exchange tube, a2Is the enthalpy value of the vapor-water in the tube at the outlet of the heat exchange tube, cp，sIs the specific heat capacity of the hot molten salt;
step 6, for the first condition in the step 4, the process of the vapor-water in the pipe is from a supercooled state to a gas-liquid two-phase state to a superheated state, and the following specific steps are carried out at this time:
step 6-1, according to a heat balance formula
Calculating the temperature T of the hot-melt salt at the end of the supercooling regionl，1Wherein a'sThe liquid phase enthalpy value of the steam water in the pipe at the saturation point is obtained;
step 6-2, calculating the local average heat exchange coefficient h of the hot molten salt in the supercooling zones，1Calculating the local average heat exchange coefficient h of the steam-water in the super-cooling areaw，1；
Step 6-3, according toCalculating the actual local average heat transfer coefficient k of the supercooling region1The thickness of the heat exchange tube is the wall thickness, and lambda is the heat conductivity coefficient of the heat exchange tube;
step 6-4, according to
Calculating the heat exchange area A of the supercooling region1Wherein Q isw，1、Qs，1Sub-cooling exchange of water and hot molten salt respectivelyLocal heat exchange, Δ t, in the hot zone1Is the local mean logarithmic temperature difference of the supercooling region;
step 6-5, according to A1＝2πl1(di+do) And/4, calculating the length l of the supercooling heat exchange segment1Wherein d isiIs the inner diameter of the heat exchange tube, doIs the outer diameter of the heat exchange tube;
step 6-6, comparison l1L is equal to the total length L of the heat exchange tube1If less than L, go to step 6-7, otherwise, get t2Minus H1The result obtained is taken as a new t2The value returns to the step 4 until the calculated l1Satisfy inequality l1If the value is less than L, entering the step 6-7;
6-7, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the termination point of the gas-liquid two-phase regionl，2Wherein a ″)sThe vapor phase enthalpy value of vapor-water in the pipe at a saturation point is obtained;
6-8, calculating the local average heat exchange coefficient h of the hot molten salt in a gas-liquid two-phase regions，2Calculating the local average heat exchange coefficient h of the vapor-water in the gas-liquid two-phase regionw，2；
Step 6-9, according to
Calculating the actual local average heat transfer coefficient k of the gas-liquid two-phase region2；
Step 6-10, according to
Calculating the heat exchange area A of the gas-liquid two-phase region2Wherein Q isw，2、Qs，2Respectively the local heat exchange quantity delta t of water and hot molten salt in a gas-liquid two-phase heat exchange area2The local average logarithmic temperature difference of the gas-liquid two-phase region;
step 6-11, according to A2＝2πl2(di+do) (4) calculating the heat exchange of the gas-liquid two-phase regionLength l of segment2；
Step 6-12, comparison (l)1+l2) The total length L of the heat exchange tube is equal to (L)1+l2) If less than L, go to step 7, otherwise, get t2Minus H1The result obtained is taken as a new t2Value is returned to step 4 until the calculated (l)1+l2) Satisfy the inequality (l)1+l2) If the value is less than L, entering a step 7;
for the second case in the step 4, the process of the steam-water in the pipe is from the supercooled state to the gas-liquid two-phase state, the steps 6-1 to 6-5 are the same as the first case, but the specific contents of the step 6-6 are as follows:
step 6-6, comparison l1L is equal to the total length L of the heat exchange tube1If less than L, go to step 7, otherwise, let x2Minus H2The result obtained is new x2The value returns to the step 4 until the calculated l1Satisfy inequality l1If the value is less than L, entering a step 7;
for the case three in step 4, directly entering step 7;
in the fourth case in step 4, the steam-water in the pipe is in a state from a gas-liquid two-phase state to an overheated state, and the specific content in step 6 is as follows:
step 6-1, according to a heat balance formula
Calculating the temperature T of the hot molten salt at the termination point of the gas-liquid two-phase regionl，2；
Step 6-2, calculating the local average heat exchange coefficient h of the hot molten salt side in a gas-liquid two-phase regions，2Calculating the local average heat exchange coefficient h of the vapor-water side in the tube in the gas-liquid two-phase regionw，2；
Step 6-3, according to
Calculating the actual local average heat transfer coefficient k of the gas-liquid two-phase region2；
Step 6-4, according to
Calculating the heat exchange area A of the gas-liquid two-phase region2；
Step 6-5, according to A2＝2πl2(di+do) And/4, calculating the length l of the gas-liquid two-phase heat exchange segment2；
Step 6-6, comparison l2L is equal to the total length L of the heat exchange tube2If less than L, go to step 7, otherwise, get t2Minus H1The result obtained is taken as a new t2The value returns to the step 4 until the calculated l2Satisfy inequality l2If the value is less than L, entering a step 7;
directly entering the step 7 for the fifth case and the sixth case in the step 4;
step 7, calculating the local average heat exchange coefficient h of the hot melt salt side of the final section heat exchange areas，3Calculating the local average heat exchange coefficient h of the steam-water side of the final section heat exchange areaw，3：
For the case one, the case four and the case six in the step 4, the final section heat exchange area is the overheating heat exchange area;
for the second case and the fifth case, the final-stage heat exchange area is a gas-liquid two-phase heat exchange area;
for the third case, the final heat exchange area is an overcooling heat exchange area;
step 8, according to
Calculating the actual local average heat transfer coefficient k of the final-stage heat exchange area3；
Step 9, according to A3＝2πl3(di+do) And/4, calculating the area A of the heat exchange section at the final section3Wherein l is3The length of the final heat exchange zone;
step 10, according to
Calculating the final stage actual heat transfer coefficient k'3Wherein Q iss，3And Qw，3Respectively the heat exchange quantity of the hot melt salt in the final section heat exchange area and the heat exchange quantity of the steam water in the pipe in the final section heat exchange area, delta t3The logarithmic mean temperature difference of the final heat exchange zone is obtained;
step 11, comparison
And an allowable error value when
If the larger one of the values is smaller than the smaller one, the calculation is terminated, and the steam-water outlet temperature t in the pipe is considered to be at the moment2Steam-water outlet dryness x in pipe2Temperature T of hot molten salt outlet outside pipe2The actual outlet parameters of the working medium inside and outside the pipe are obtained, otherwise:
when t is2In the superheated or supercooled region of water, let t2Minus H1The obtained value is new t2The value returns to the step 4 until the value is obtained by calculation
And the larger, which is also smaller in size than the former;
when t is2When the gas-liquid two-phase region of water exists, x is enabled to be2Minus H2The obtained value is new x2The value returns to the step 4 until the value is obtained by calculation
The larger one, the smaller one.
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| CN108170998A (en) * | 2018-02-13 | 2018-06-15 | 上海市特种设备监督检验技术研究院 | A kind of shell-and-tube exchanger efficiency evaluation method |
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| CN108170998A (en) * | 2018-02-13 | 2018-06-15 | 上海市特种设备监督检验技术研究院 | A kind of shell-and-tube exchanger efficiency evaluation method |
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