混合制冷剂J-T循环热力学性能研究毕业论文

2020-02-19 09:02

摘要

J-T循环简单而紧凑，能够低温制冷。使用混合工质/制冷剂（MR）具有较强的制冷能力。本文建立了MR热力学理想循环模型，以研究其参数工作特性，确定最佳MR组成。本文主要内容如下：

（1）以图形方式将参数研究的结果呈现在等高线图上，其中参数空间是换热器中干度的极限（即，换热器中各地方的最低和最高干度）。

（2）以图像轮廓显示标准化制冷功率的恒定值。通过图像显示MR组成对循环性能的影响用于选择高冷却负荷的MR，同时将回热器限制在增强的传热区域中。

（3）以循环图显示在增强的传热区域中最大可能减少的冷却负荷。指定了一条设计线，用于识别给定干度约束条件下具有最高热力学冷却负荷的所有混合物。沿着这条线识别的MR可以用作实验测试的初始起点。使用不同的模型输入参数测试模型和绘图技术，以确保它对所有周期都有效。

另外，本文描述了用于确定最佳组分数量的方法。改进绘图技术以为具有最大COP的循环提供最佳混合。最后，修改模型以考虑换热器中的压降，并且绘图方法也用于确定该情况下的最佳混合物。

关键词：混合制冷剂；J-T循环；热力学；理想循环；最佳混合物

Abstract

A J-T cycle is simple and compact to provide a low temperature cooling load, where mixedworking fluids/refrigerants (MR) may be utilized to significantly improve its cooling capacity. For determination of the optimal MR composition, a thermodynamically ideal model was established to perform the parametric study. The primary contents are listed as follows:

1).The results of the parametric study are graphically presented on a contour plot with the parameter space being the limits of quality in the recuperator (i.e., lowest and highest quality anywhere in the recuperator).

2).The contours show constant values of the normalized refrigeration power. This ‘map’ shows the effect of MR composition on the cycle performance and it can be used to select the MR that provides a high cooling load while also constraining the recuperator to be in the enhanced heat transfer region.

3).The cycle map shows that the cost of operating in the enhanced heat transfer region is a reduction in the maximum possible cooling load. A design line is specified that identifies all mixtures that have the highest thermodynamic cooling load for a given quality constraint. The MRs identified along this line can be used as the initial starting point for experimental testing. The model and plotting technique is tested with different model input parameters to ensure it is valid for all cycles.

Additionally, a method for determining the optimal number of components is described. The plotting technique is modified to provide the optimal mixture for a cycle operating with the maximum COP. Finally, the model is modified to consider the pressure drop in the recuperator, and the plotting method is used to determine the optimal mixture in that case as well.

Keywords:Mixed refrigerant; J-T cycle; thermodynamically ideal cycle; optimal mixture

符号对照表

符号	描述	单位
a₁	J-T效应曲线拟合参数
a₂	J-T效应曲线拟合参数
A_HP	换热器高压侧对流面积	m²
A_LP	换热器低压侧的对流区域	m²
A_CS	换热器传导的横截面积	m²
C	间隙体积分数
C_P	恒压比热容	kJ/(kgK)
C_V	恒定体积比热容	kJ/(kgK)
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\2_~G7FT)`$705D]EBP6E2]L.png$	在恒定焓下相对于压力的温度变化	k/kPa
h_C,i	节点i处冷流的焓	kJ/kg
h_f	饱和液焓	kJ/kg
h_g	饱和蒸气焓	kJ/kg
h_H,i	节点i处热流的焓	kJ/kg
h̅_HP	高压流的对流换热系数	W/(m²K)
h_i	节点i处的焓	kJ/kg
h̅_LP	低压流的对流传热系数	W/(m²K)
htc	对流换热系数	W/(m²K)
k	比热比
k_h	换热器导电率	W/(mK)
L_c	传导长度	m
ṁ	质量流量	kg/s
P_discharge	排气压力	kPa
P_high	回热器高压	kPa
P_i	节点i处的压力	kPa
P_suction	吸入压力	kPa
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _aftercool	后冷器传热率	kW
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _load	冷负荷	kW
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _load,morn	冷却负荷按位移率归一化	kW/(m³/s)
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _{load,morn,frac}	由位移速率和最大冷负荷归一化的冷负荷
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _rec	回热器的传热率	kW
Q_rec	换热器中的比热传递	kJ/kg
$C:\Users\Administrator\AppData\Roaming\Tencent\Users\337212683\QQ\WinTemp\RichOle\0MGV[[V%1]PI9J6K3R8XJU3.png$ _reheat	再热器的传热率	kW
RPM	压缩机转速	rpm
ΔT_app	趋近温差	K
T_C,i	节点i处的冷流温度	K
T_H,i	节点i（K）处的热流温度
T_i	节点i处的温度	K
UA	电导率	W/K
V_clear	压缩机间隙容积	m³
V_dis	压缩机排量	m³
_displace	压缩机排量率	m³/s
v_suc	压缩机吸气比容	m³/kg
V_swep	压缩机扫气量	m³
_comp	压缩机功	kW
x_avg	平均干度
x_cs	过冷MR的干度
x_sh	过热MR的干度
ΔP	压差	kPa
_ovl	容积效率